Bug Summary

File:build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
Warning:line 1917, column 47
Called C++ object pointer is null

Annotated Source Code

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clang -cc1 -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name LoopIdiomRecognize.cpp -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -setup-static-analyzer -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -mframe-pointer=none -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -ffunction-sections -fdata-sections -fcoverage-compilation-dir=/build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/build-llvm -resource-dir /usr/lib/llvm-16/lib/clang/16.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/llvm/lib/Transforms/Scalar -I include -I /build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/llvm/include -D _FORTIFY_SOURCE=2 -D NDEBUG -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/x86_64-linux-gnu/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/backward -internal-isystem /usr/lib/llvm-16/lib/clang/16.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fmacro-prefix-map=/build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/build-llvm=build-llvm -fmacro-prefix-map=/build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/= -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/build-llvm=build-llvm -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/= -O3 -Wno-unused-command-line-argument -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wno-comment -Wno-misleading-indentation -std=c++17 -fdeprecated-macro -fdebug-compilation-dir=/build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/build-llvm=build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/= -ferror-limit 19 -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -fcolor-diagnostics -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/scan-build-2022-09-29-125212-15910-1 -x c++ /build/llvm-toolchain-snapshot-16~++20220929111209+ac2e2d659819/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
1//===- LoopIdiomRecognize.cpp - Loop idiom recognition --------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This pass implements an idiom recognizer that transforms simple loops into a
10// non-loop form. In cases that this kicks in, it can be a significant
11// performance win.
12//
13// If compiling for code size we avoid idiom recognition if the resulting
14// code could be larger than the code for the original loop. One way this could
15// happen is if the loop is not removable after idiom recognition due to the
16// presence of non-idiom instructions. The initial implementation of the
17// heuristics applies to idioms in multi-block loops.
18//
19//===----------------------------------------------------------------------===//
20//
21// TODO List:
22//
23// Future loop memory idioms to recognize:
24// memcmp, strlen, etc.
25// Future floating point idioms to recognize in -ffast-math mode:
26// fpowi
27// Future integer operation idioms to recognize:
28// ctpop
29//
30// Beware that isel's default lowering for ctpop is highly inefficient for
31// i64 and larger types when i64 is legal and the value has few bits set. It
32// would be good to enhance isel to emit a loop for ctpop in this case.
33//
34// This could recognize common matrix multiplies and dot product idioms and
35// replace them with calls to BLAS (if linked in??).
36//
37//===----------------------------------------------------------------------===//
38
39#include "llvm/Transforms/Scalar/LoopIdiomRecognize.h"
40#include "llvm/ADT/APInt.h"
41#include "llvm/ADT/ArrayRef.h"
42#include "llvm/ADT/DenseMap.h"
43#include "llvm/ADT/MapVector.h"
44#include "llvm/ADT/SetVector.h"
45#include "llvm/ADT/SmallPtrSet.h"
46#include "llvm/ADT/SmallVector.h"
47#include "llvm/ADT/Statistic.h"
48#include "llvm/ADT/StringRef.h"
49#include "llvm/Analysis/AliasAnalysis.h"
50#include "llvm/Analysis/CmpInstAnalysis.h"
51#include "llvm/Analysis/LoopAccessAnalysis.h"
52#include "llvm/Analysis/LoopInfo.h"
53#include "llvm/Analysis/LoopPass.h"
54#include "llvm/Analysis/MemoryLocation.h"
55#include "llvm/Analysis/MemorySSA.h"
56#include "llvm/Analysis/MemorySSAUpdater.h"
57#include "llvm/Analysis/MustExecute.h"
58#include "llvm/Analysis/OptimizationRemarkEmitter.h"
59#include "llvm/Analysis/ScalarEvolution.h"
60#include "llvm/Analysis/ScalarEvolutionExpressions.h"
61#include "llvm/Analysis/TargetLibraryInfo.h"
62#include "llvm/Analysis/TargetTransformInfo.h"
63#include "llvm/Analysis/ValueTracking.h"
64#include "llvm/IR/BasicBlock.h"
65#include "llvm/IR/Constant.h"
66#include "llvm/IR/Constants.h"
67#include "llvm/IR/DataLayout.h"
68#include "llvm/IR/DebugLoc.h"
69#include "llvm/IR/DerivedTypes.h"
70#include "llvm/IR/Dominators.h"
71#include "llvm/IR/GlobalValue.h"
72#include "llvm/IR/GlobalVariable.h"
73#include "llvm/IR/IRBuilder.h"
74#include "llvm/IR/InstrTypes.h"
75#include "llvm/IR/Instruction.h"
76#include "llvm/IR/Instructions.h"
77#include "llvm/IR/IntrinsicInst.h"
78#include "llvm/IR/Intrinsics.h"
79#include "llvm/IR/LLVMContext.h"
80#include "llvm/IR/Module.h"
81#include "llvm/IR/PassManager.h"
82#include "llvm/IR/PatternMatch.h"
83#include "llvm/IR/Type.h"
84#include "llvm/IR/User.h"
85#include "llvm/IR/Value.h"
86#include "llvm/IR/ValueHandle.h"
87#include "llvm/InitializePasses.h"
88#include "llvm/Pass.h"
89#include "llvm/Support/Casting.h"
90#include "llvm/Support/CommandLine.h"
91#include "llvm/Support/Debug.h"
92#include "llvm/Support/InstructionCost.h"
93#include "llvm/Support/raw_ostream.h"
94#include "llvm/Transforms/Scalar.h"
95#include "llvm/Transforms/Utils/BuildLibCalls.h"
96#include "llvm/Transforms/Utils/Local.h"
97#include "llvm/Transforms/Utils/LoopUtils.h"
98#include "llvm/Transforms/Utils/ScalarEvolutionExpander.h"
99#include <algorithm>
100#include <cassert>
101#include <cstdint>
102#include <utility>
103#include <vector>
104
105using namespace llvm;
106
107#define DEBUG_TYPE"loop-idiom" "loop-idiom"
108
109STATISTIC(NumMemSet, "Number of memset's formed from loop stores")static llvm::Statistic NumMemSet = {"loop-idiom", "NumMemSet"
, "Number of memset's formed from loop stores"}
;
110STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores")static llvm::Statistic NumMemCpy = {"loop-idiom", "NumMemCpy"
, "Number of memcpy's formed from loop load+stores"}
;
111STATISTIC(NumMemMove, "Number of memmove's formed from loop load+stores")static llvm::Statistic NumMemMove = {"loop-idiom", "NumMemMove"
, "Number of memmove's formed from loop load+stores"}
;
112STATISTIC(static llvm::Statistic NumShiftUntilBitTest = {"loop-idiom", "NumShiftUntilBitTest"
, "Number of uncountable loops recognized as 'shift until bitttest' idiom"
}
113 NumShiftUntilBitTest,static llvm::Statistic NumShiftUntilBitTest = {"loop-idiom", "NumShiftUntilBitTest"
, "Number of uncountable loops recognized as 'shift until bitttest' idiom"
}
114 "Number of uncountable loops recognized as 'shift until bitttest' idiom")static llvm::Statistic NumShiftUntilBitTest = {"loop-idiom", "NumShiftUntilBitTest"
, "Number of uncountable loops recognized as 'shift until bitttest' idiom"
}
;
115STATISTIC(NumShiftUntilZero,static llvm::Statistic NumShiftUntilZero = {"loop-idiom", "NumShiftUntilZero"
, "Number of uncountable loops recognized as 'shift until zero' idiom"
}
116 "Number of uncountable loops recognized as 'shift until zero' idiom")static llvm::Statistic NumShiftUntilZero = {"loop-idiom", "NumShiftUntilZero"
, "Number of uncountable loops recognized as 'shift until zero' idiom"
}
;
117
118bool DisableLIRP::All;
119static cl::opt<bool, true>
120 DisableLIRPAll("disable-" DEBUG_TYPE"loop-idiom" "-all",
121 cl::desc("Options to disable Loop Idiom Recognize Pass."),
122 cl::location(DisableLIRP::All), cl::init(false),
123 cl::ReallyHidden);
124
125bool DisableLIRP::Memset;
126static cl::opt<bool, true>
127 DisableLIRPMemset("disable-" DEBUG_TYPE"loop-idiom" "-memset",
128 cl::desc("Proceed with loop idiom recognize pass, but do "
129 "not convert loop(s) to memset."),
130 cl::location(DisableLIRP::Memset), cl::init(false),
131 cl::ReallyHidden);
132
133bool DisableLIRP::Memcpy;
134static cl::opt<bool, true>
135 DisableLIRPMemcpy("disable-" DEBUG_TYPE"loop-idiom" "-memcpy",
136 cl::desc("Proceed with loop idiom recognize pass, but do "
137 "not convert loop(s) to memcpy."),
138 cl::location(DisableLIRP::Memcpy), cl::init(false),
139 cl::ReallyHidden);
140
141static cl::opt<bool> UseLIRCodeSizeHeurs(
142 "use-lir-code-size-heurs",
143 cl::desc("Use loop idiom recognition code size heuristics when compiling"
144 "with -Os/-Oz"),
145 cl::init(true), cl::Hidden);
146
147namespace {
148
149class LoopIdiomRecognize {
150 Loop *CurLoop = nullptr;
151 AliasAnalysis *AA;
152 DominatorTree *DT;
153 LoopInfo *LI;
154 ScalarEvolution *SE;
155 TargetLibraryInfo *TLI;
156 const TargetTransformInfo *TTI;
157 const DataLayout *DL;
158 OptimizationRemarkEmitter &ORE;
159 bool ApplyCodeSizeHeuristics;
160 std::unique_ptr<MemorySSAUpdater> MSSAU;
161
162public:
163 explicit LoopIdiomRecognize(AliasAnalysis *AA, DominatorTree *DT,
164 LoopInfo *LI, ScalarEvolution *SE,
165 TargetLibraryInfo *TLI,
166 const TargetTransformInfo *TTI, MemorySSA *MSSA,
167 const DataLayout *DL,
168 OptimizationRemarkEmitter &ORE)
169 : AA(AA), DT(DT), LI(LI), SE(SE), TLI(TLI), TTI(TTI), DL(DL), ORE(ORE) {
170 if (MSSA)
171 MSSAU = std::make_unique<MemorySSAUpdater>(MSSA);
172 }
173
174 bool runOnLoop(Loop *L);
175
176private:
177 using StoreList = SmallVector<StoreInst *, 8>;
178 using StoreListMap = MapVector<Value *, StoreList>;
179
180 StoreListMap StoreRefsForMemset;
181 StoreListMap StoreRefsForMemsetPattern;
182 StoreList StoreRefsForMemcpy;
183 bool HasMemset;
184 bool HasMemsetPattern;
185 bool HasMemcpy;
186
187 /// Return code for isLegalStore()
188 enum LegalStoreKind {
189 None = 0,
190 Memset,
191 MemsetPattern,
192 Memcpy,
193 UnorderedAtomicMemcpy,
194 DontUse // Dummy retval never to be used. Allows catching errors in retval
195 // handling.
196 };
197
198 /// \name Countable Loop Idiom Handling
199 /// @{
200
201 bool runOnCountableLoop();
202 bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
203 SmallVectorImpl<BasicBlock *> &ExitBlocks);
204
205 void collectStores(BasicBlock *BB);
206 LegalStoreKind isLegalStore(StoreInst *SI);
207 enum class ForMemset { No, Yes };
208 bool processLoopStores(SmallVectorImpl<StoreInst *> &SL, const SCEV *BECount,
209 ForMemset For);
210
211 template <typename MemInst>
212 bool processLoopMemIntrinsic(
213 BasicBlock *BB,
214 bool (LoopIdiomRecognize::*Processor)(MemInst *, const SCEV *),
215 const SCEV *BECount);
216 bool processLoopMemCpy(MemCpyInst *MCI, const SCEV *BECount);
217 bool processLoopMemSet(MemSetInst *MSI, const SCEV *BECount);
218
219 bool processLoopStridedStore(Value *DestPtr, const SCEV *StoreSizeSCEV,
220 MaybeAlign StoreAlignment, Value *StoredVal,
221 Instruction *TheStore,
222 SmallPtrSetImpl<Instruction *> &Stores,
223 const SCEVAddRecExpr *Ev, const SCEV *BECount,
224 bool IsNegStride, bool IsLoopMemset = false);
225 bool processLoopStoreOfLoopLoad(StoreInst *SI, const SCEV *BECount);
226 bool processLoopStoreOfLoopLoad(Value *DestPtr, Value *SourcePtr,
227 const SCEV *StoreSize, MaybeAlign StoreAlign,
228 MaybeAlign LoadAlign, Instruction *TheStore,
229 Instruction *TheLoad,
230 const SCEVAddRecExpr *StoreEv,
231 const SCEVAddRecExpr *LoadEv,
232 const SCEV *BECount);
233 bool avoidLIRForMultiBlockLoop(bool IsMemset = false,
234 bool IsLoopMemset = false);
235
236 /// @}
237 /// \name Noncountable Loop Idiom Handling
238 /// @{
239
240 bool runOnNoncountableLoop();
241
242 bool recognizePopcount();
243 void transformLoopToPopcount(BasicBlock *PreCondBB, Instruction *CntInst,
244 PHINode *CntPhi, Value *Var);
245 bool recognizeAndInsertFFS(); /// Find First Set: ctlz or cttz
246 void transformLoopToCountable(Intrinsic::ID IntrinID, BasicBlock *PreCondBB,
247 Instruction *CntInst, PHINode *CntPhi,
248 Value *Var, Instruction *DefX,
249 const DebugLoc &DL, bool ZeroCheck,
250 bool IsCntPhiUsedOutsideLoop);
251
252 bool recognizeShiftUntilBitTest();
253 bool recognizeShiftUntilZero();
254
255 /// @}
256};
257
258class LoopIdiomRecognizeLegacyPass : public LoopPass {
259public:
260 static char ID;
261
262 explicit LoopIdiomRecognizeLegacyPass() : LoopPass(ID) {
263 initializeLoopIdiomRecognizeLegacyPassPass(
264 *PassRegistry::getPassRegistry());
265 }
266
267 bool runOnLoop(Loop *L, LPPassManager &LPM) override {
268 if (DisableLIRP::All)
269 return false;
270
271 if (skipLoop(L))
272 return false;
273
274 AliasAnalysis *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
275 DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
276 LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
277 ScalarEvolution *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
278 TargetLibraryInfo *TLI =
279 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(
280 *L->getHeader()->getParent());
281 const TargetTransformInfo *TTI =
282 &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
283 *L->getHeader()->getParent());
284 const DataLayout *DL = &L->getHeader()->getModule()->getDataLayout();
285 auto *MSSAAnalysis = getAnalysisIfAvailable<MemorySSAWrapperPass>();
286 MemorySSA *MSSA = nullptr;
287 if (MSSAAnalysis)
288 MSSA = &MSSAAnalysis->getMSSA();
289
290 // For the old PM, we can't use OptimizationRemarkEmitter as an analysis
291 // pass. Function analyses need to be preserved across loop transformations
292 // but ORE cannot be preserved (see comment before the pass definition).
293 OptimizationRemarkEmitter ORE(L->getHeader()->getParent());
294
295 LoopIdiomRecognize LIR(AA, DT, LI, SE, TLI, TTI, MSSA, DL, ORE);
296 return LIR.runOnLoop(L);
297 }
298
299 /// This transformation requires natural loop information & requires that
300 /// loop preheaders be inserted into the CFG.
301 void getAnalysisUsage(AnalysisUsage &AU) const override {
302 AU.addRequired<TargetLibraryInfoWrapperPass>();
303 AU.addRequired<TargetTransformInfoWrapperPass>();
304 AU.addPreserved<MemorySSAWrapperPass>();
305 getLoopAnalysisUsage(AU);
306 }
307};
308
309} // end anonymous namespace
310
311char LoopIdiomRecognizeLegacyPass::ID = 0;
312
313PreservedAnalyses LoopIdiomRecognizePass::run(Loop &L, LoopAnalysisManager &AM,
314 LoopStandardAnalysisResults &AR,
315 LPMUpdater &) {
316 if (DisableLIRP::All)
1
Assuming 'All' is false
2
Taking false branch
317 return PreservedAnalyses::all();
318
319 const auto *DL = &L.getHeader()->getModule()->getDataLayout();
320
321 // For the new PM, we also can't use OptimizationRemarkEmitter as an analysis
322 // pass. Function analyses need to be preserved across loop transformations
323 // but ORE cannot be preserved (see comment before the pass definition).
324 OptimizationRemarkEmitter ORE(L.getHeader()->getParent());
325
326 LoopIdiomRecognize LIR(&AR.AA, &AR.DT, &AR.LI, &AR.SE, &AR.TLI, &AR.TTI,
327 AR.MSSA, DL, ORE);
328 if (!LIR.runOnLoop(&L))
3
Calling 'LoopIdiomRecognize::runOnLoop'
329 return PreservedAnalyses::all();
330
331 auto PA = getLoopPassPreservedAnalyses();
332 if (AR.MSSA)
333 PA.preserve<MemorySSAAnalysis>();
334 return PA;
335}
336
337INITIALIZE_PASS_BEGIN(LoopIdiomRecognizeLegacyPass, "loop-idiom",static void *initializeLoopIdiomRecognizeLegacyPassPassOnce(PassRegistry
&Registry) {
338 "Recognize loop idioms", false, false)static void *initializeLoopIdiomRecognizeLegacyPassPassOnce(PassRegistry
&Registry) {
339INITIALIZE_PASS_DEPENDENCY(LoopPass)initializeLoopPassPass(Registry);
340INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)initializeTargetLibraryInfoWrapperPassPass(Registry);
341INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)initializeTargetTransformInfoWrapperPassPass(Registry);
342INITIALIZE_PASS_END(LoopIdiomRecognizeLegacyPass, "loop-idiom",PassInfo *PI = new PassInfo( "Recognize loop idioms", "loop-idiom"
, &LoopIdiomRecognizeLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<LoopIdiomRecognizeLegacyPass>), false,
false); Registry.registerPass(*PI, true); return PI; } static
llvm::once_flag InitializeLoopIdiomRecognizeLegacyPassPassFlag
; void llvm::initializeLoopIdiomRecognizeLegacyPassPass(PassRegistry
&Registry) { llvm::call_once(InitializeLoopIdiomRecognizeLegacyPassPassFlag
, initializeLoopIdiomRecognizeLegacyPassPassOnce, std::ref(Registry
)); }
343 "Recognize loop idioms", false, false)PassInfo *PI = new PassInfo( "Recognize loop idioms", "loop-idiom"
, &LoopIdiomRecognizeLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<LoopIdiomRecognizeLegacyPass>), false,
false); Registry.registerPass(*PI, true); return PI; } static
llvm::once_flag InitializeLoopIdiomRecognizeLegacyPassPassFlag
; void llvm::initializeLoopIdiomRecognizeLegacyPassPass(PassRegistry
&Registry) { llvm::call_once(InitializeLoopIdiomRecognizeLegacyPassPassFlag
, initializeLoopIdiomRecognizeLegacyPassPassOnce, std::ref(Registry
)); }
344
345Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognizeLegacyPass(); }
346
347static void deleteDeadInstruction(Instruction *I) {
348 I->replaceAllUsesWith(PoisonValue::get(I->getType()));
349 I->eraseFromParent();
350}
351
352//===----------------------------------------------------------------------===//
353//
354// Implementation of LoopIdiomRecognize
355//
356//===----------------------------------------------------------------------===//
357
358bool LoopIdiomRecognize::runOnLoop(Loop *L) {
359 CurLoop = L;
360 // If the loop could not be converted to canonical form, it must have an
361 // indirectbr in it, just give up.
362 if (!L->getLoopPreheader())
4
Assuming the condition is false
5
Taking false branch
363 return false;
364
365 // Disable loop idiom recognition if the function's name is a common idiom.
366 StringRef Name = L->getHeader()->getParent()->getName();
367 if (Name == "memset" || Name == "memcpy")
6
Assuming the condition is false
7
Assuming the condition is false
368 return false;
369
370 // Determine if code size heuristics need to be applied.
371 ApplyCodeSizeHeuristics =
372 L->getHeader()->getParent()->hasOptSize() && UseLIRCodeSizeHeurs;
8
Assuming the condition is false
373
374 HasMemset = TLI->has(LibFunc_memset);
375 HasMemsetPattern = TLI->has(LibFunc_memset_pattern16);
376 HasMemcpy = TLI->has(LibFunc_memcpy);
377
378 if (HasMemset
8.1
Field 'HasMemset' is false
|| HasMemsetPattern
8.2
Field 'HasMemsetPattern' is false
|| HasMemcpy
8.3
Field 'HasMemcpy' is false
)
9
Taking false branch
379 if (SE->hasLoopInvariantBackedgeTakenCount(L))
380 return runOnCountableLoop();
381
382 return runOnNoncountableLoop();
10
Calling 'LoopIdiomRecognize::runOnNoncountableLoop'
383}
384
385bool LoopIdiomRecognize::runOnCountableLoop() {
386 const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
387 assert(!isa<SCEVCouldNotCompute>(BECount) &&(static_cast <bool> (!isa<SCEVCouldNotCompute>(BECount
) && "runOnCountableLoop() called on a loop without a predictable"
"backedge-taken count") ? void (0) : __assert_fail ("!isa<SCEVCouldNotCompute>(BECount) && \"runOnCountableLoop() called on a loop without a predictable\" \"backedge-taken count\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 389, __extension__
__PRETTY_FUNCTION__))
388 "runOnCountableLoop() called on a loop without a predictable"(static_cast <bool> (!isa<SCEVCouldNotCompute>(BECount
) && "runOnCountableLoop() called on a loop without a predictable"
"backedge-taken count") ? void (0) : __assert_fail ("!isa<SCEVCouldNotCompute>(BECount) && \"runOnCountableLoop() called on a loop without a predictable\" \"backedge-taken count\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 389, __extension__
__PRETTY_FUNCTION__))
389 "backedge-taken count")(static_cast <bool> (!isa<SCEVCouldNotCompute>(BECount
) && "runOnCountableLoop() called on a loop without a predictable"
"backedge-taken count") ? void (0) : __assert_fail ("!isa<SCEVCouldNotCompute>(BECount) && \"runOnCountableLoop() called on a loop without a predictable\" \"backedge-taken count\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 389, __extension__
__PRETTY_FUNCTION__))
;
390
391 // If this loop executes exactly one time, then it should be peeled, not
392 // optimized by this pass.
393 if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
394 if (BECst->getAPInt() == 0)
395 return false;
396
397 SmallVector<BasicBlock *, 8> ExitBlocks;
398 CurLoop->getUniqueExitBlocks(ExitBlocks);
399
400 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Scanning: F["do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Scanning: F["
<< CurLoop->getHeader()->getParent()->getName
() << "] Countable Loop %" << CurLoop->getHeader
()->getName() << "\n"; } } while (false)
401 << CurLoop->getHeader()->getParent()->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Scanning: F["
<< CurLoop->getHeader()->getParent()->getName
() << "] Countable Loop %" << CurLoop->getHeader
()->getName() << "\n"; } } while (false)
402 << "] Countable Loop %" << CurLoop->getHeader()->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Scanning: F["
<< CurLoop->getHeader()->getParent()->getName
() << "] Countable Loop %" << CurLoop->getHeader
()->getName() << "\n"; } } while (false)
403 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Scanning: F["
<< CurLoop->getHeader()->getParent()->getName
() << "] Countable Loop %" << CurLoop->getHeader
()->getName() << "\n"; } } while (false)
;
404
405 // The following transforms hoist stores/memsets into the loop pre-header.
406 // Give up if the loop has instructions that may throw.
407 SimpleLoopSafetyInfo SafetyInfo;
408 SafetyInfo.computeLoopSafetyInfo(CurLoop);
409 if (SafetyInfo.anyBlockMayThrow())
410 return false;
411
412 bool MadeChange = false;
413
414 // Scan all the blocks in the loop that are not in subloops.
415 for (auto *BB : CurLoop->getBlocks()) {
416 // Ignore blocks in subloops.
417 if (LI->getLoopFor(BB) != CurLoop)
418 continue;
419
420 MadeChange |= runOnLoopBlock(BB, BECount, ExitBlocks);
421 }
422 return MadeChange;
423}
424
425static APInt getStoreStride(const SCEVAddRecExpr *StoreEv) {
426 const SCEVConstant *ConstStride = cast<SCEVConstant>(StoreEv->getOperand(1));
427 return ConstStride->getAPInt();
428}
429
430/// getMemSetPatternValue - If a strided store of the specified value is safe to
431/// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
432/// be passed in. Otherwise, return null.
433///
434/// Note that we don't ever attempt to use memset_pattern8 or 4, because these
435/// just replicate their input array and then pass on to memset_pattern16.
436static Constant *getMemSetPatternValue(Value *V, const DataLayout *DL) {
437 // FIXME: This could check for UndefValue because it can be merged into any
438 // other valid pattern.
439
440 // If the value isn't a constant, we can't promote it to being in a constant
441 // array. We could theoretically do a store to an alloca or something, but
442 // that doesn't seem worthwhile.
443 Constant *C = dyn_cast<Constant>(V);
444 if (!C)
445 return nullptr;
446
447 // Only handle simple values that are a power of two bytes in size.
448 uint64_t Size = DL->getTypeSizeInBits(V->getType());
449 if (Size == 0 || (Size & 7) || (Size & (Size - 1)))
450 return nullptr;
451
452 // Don't care enough about darwin/ppc to implement this.
453 if (DL->isBigEndian())
454 return nullptr;
455
456 // Convert to size in bytes.
457 Size /= 8;
458
459 // TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
460 // if the top and bottom are the same (e.g. for vectors and large integers).
461 if (Size > 16)
462 return nullptr;
463
464 // If the constant is exactly 16 bytes, just use it.
465 if (Size == 16)
466 return C;
467
468 // Otherwise, we'll use an array of the constants.
469 unsigned ArraySize = 16 / Size;
470 ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
471 return ConstantArray::get(AT, std::vector<Constant *>(ArraySize, C));
472}
473
474LoopIdiomRecognize::LegalStoreKind
475LoopIdiomRecognize::isLegalStore(StoreInst *SI) {
476 // Don't touch volatile stores.
477 if (SI->isVolatile())
478 return LegalStoreKind::None;
479 // We only want simple or unordered-atomic stores.
480 if (!SI->isUnordered())
481 return LegalStoreKind::None;
482
483 // Avoid merging nontemporal stores.
484 if (SI->getMetadata(LLVMContext::MD_nontemporal))
485 return LegalStoreKind::None;
486
487 Value *StoredVal = SI->getValueOperand();
488 Value *StorePtr = SI->getPointerOperand();
489
490 // Don't convert stores of non-integral pointer types to memsets (which stores
491 // integers).
492 if (DL->isNonIntegralPointerType(StoredVal->getType()->getScalarType()))
493 return LegalStoreKind::None;
494
495 // Reject stores that are so large that they overflow an unsigned.
496 // When storing out scalable vectors we bail out for now, since the code
497 // below currently only works for constant strides.
498 TypeSize SizeInBits = DL->getTypeSizeInBits(StoredVal->getType());
499 if (SizeInBits.isScalable() || (SizeInBits.getFixedSize() & 7) ||
500 (SizeInBits.getFixedSize() >> 32) != 0)
501 return LegalStoreKind::None;
502
503 // See if the pointer expression is an AddRec like {base,+,1} on the current
504 // loop, which indicates a strided store. If we have something else, it's a
505 // random store we can't handle.
506 const SCEVAddRecExpr *StoreEv =
507 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
508 if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
509 return LegalStoreKind::None;
510
511 // Check to see if we have a constant stride.
512 if (!isa<SCEVConstant>(StoreEv->getOperand(1)))
513 return LegalStoreKind::None;
514
515 // See if the store can be turned into a memset.
516
517 // If the stored value is a byte-wise value (like i32 -1), then it may be
518 // turned into a memset of i8 -1, assuming that all the consecutive bytes
519 // are stored. A store of i32 0x01020304 can never be turned into a memset,
520 // but it can be turned into memset_pattern if the target supports it.
521 Value *SplatValue = isBytewiseValue(StoredVal, *DL);
522
523 // Note: memset and memset_pattern on unordered-atomic is yet not supported
524 bool UnorderedAtomic = SI->isUnordered() && !SI->isSimple();
525
526 // If we're allowed to form a memset, and the stored value would be
527 // acceptable for memset, use it.
528 if (!UnorderedAtomic && HasMemset && SplatValue && !DisableLIRP::Memset &&
529 // Verify that the stored value is loop invariant. If not, we can't
530 // promote the memset.
531 CurLoop->isLoopInvariant(SplatValue)) {
532 // It looks like we can use SplatValue.
533 return LegalStoreKind::Memset;
534 }
535 if (!UnorderedAtomic && HasMemsetPattern && !DisableLIRP::Memset &&
536 // Don't create memset_pattern16s with address spaces.
537 StorePtr->getType()->getPointerAddressSpace() == 0 &&
538 getMemSetPatternValue(StoredVal, DL)) {
539 // It looks like we can use PatternValue!
540 return LegalStoreKind::MemsetPattern;
541 }
542
543 // Otherwise, see if the store can be turned into a memcpy.
544 if (HasMemcpy && !DisableLIRP::Memcpy) {
545 // Check to see if the stride matches the size of the store. If so, then we
546 // know that every byte is touched in the loop.
547 APInt Stride = getStoreStride(StoreEv);
548 unsigned StoreSize = DL->getTypeStoreSize(SI->getValueOperand()->getType());
549 if (StoreSize != Stride && StoreSize != -Stride)
550 return LegalStoreKind::None;
551
552 // The store must be feeding a non-volatile load.
553 LoadInst *LI = dyn_cast<LoadInst>(SI->getValueOperand());
554
555 // Only allow non-volatile loads
556 if (!LI || LI->isVolatile())
557 return LegalStoreKind::None;
558 // Only allow simple or unordered-atomic loads
559 if (!LI->isUnordered())
560 return LegalStoreKind::None;
561
562 // See if the pointer expression is an AddRec like {base,+,1} on the current
563 // loop, which indicates a strided load. If we have something else, it's a
564 // random load we can't handle.
565 const SCEVAddRecExpr *LoadEv =
566 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getPointerOperand()));
567 if (!LoadEv || LoadEv->getLoop() != CurLoop || !LoadEv->isAffine())
568 return LegalStoreKind::None;
569
570 // The store and load must share the same stride.
571 if (StoreEv->getOperand(1) != LoadEv->getOperand(1))
572 return LegalStoreKind::None;
573
574 // Success. This store can be converted into a memcpy.
575 UnorderedAtomic = UnorderedAtomic || LI->isAtomic();
576 return UnorderedAtomic ? LegalStoreKind::UnorderedAtomicMemcpy
577 : LegalStoreKind::Memcpy;
578 }
579 // This store can't be transformed into a memset/memcpy.
580 return LegalStoreKind::None;
581}
582
583void LoopIdiomRecognize::collectStores(BasicBlock *BB) {
584 StoreRefsForMemset.clear();
585 StoreRefsForMemsetPattern.clear();
586 StoreRefsForMemcpy.clear();
587 for (Instruction &I : *BB) {
588 StoreInst *SI = dyn_cast<StoreInst>(&I);
589 if (!SI)
590 continue;
591
592 // Make sure this is a strided store with a constant stride.
593 switch (isLegalStore(SI)) {
594 case LegalStoreKind::None:
595 // Nothing to do
596 break;
597 case LegalStoreKind::Memset: {
598 // Find the base pointer.
599 Value *Ptr = getUnderlyingObject(SI->getPointerOperand());
600 StoreRefsForMemset[Ptr].push_back(SI);
601 } break;
602 case LegalStoreKind::MemsetPattern: {
603 // Find the base pointer.
604 Value *Ptr = getUnderlyingObject(SI->getPointerOperand());
605 StoreRefsForMemsetPattern[Ptr].push_back(SI);
606 } break;
607 case LegalStoreKind::Memcpy:
608 case LegalStoreKind::UnorderedAtomicMemcpy:
609 StoreRefsForMemcpy.push_back(SI);
610 break;
611 default:
612 assert(false && "unhandled return value")(static_cast <bool> (false && "unhandled return value"
) ? void (0) : __assert_fail ("false && \"unhandled return value\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 612, __extension__
__PRETTY_FUNCTION__))
;
613 break;
614 }
615 }
616}
617
618/// runOnLoopBlock - Process the specified block, which lives in a counted loop
619/// with the specified backedge count. This block is known to be in the current
620/// loop and not in any subloops.
621bool LoopIdiomRecognize::runOnLoopBlock(
622 BasicBlock *BB, const SCEV *BECount,
623 SmallVectorImpl<BasicBlock *> &ExitBlocks) {
624 // We can only promote stores in this block if they are unconditionally
625 // executed in the loop. For a block to be unconditionally executed, it has
626 // to dominate all the exit blocks of the loop. Verify this now.
627 for (BasicBlock *ExitBlock : ExitBlocks)
628 if (!DT->dominates(BB, ExitBlock))
629 return false;
630
631 bool MadeChange = false;
632 // Look for store instructions, which may be optimized to memset/memcpy.
633 collectStores(BB);
634
635 // Look for a single store or sets of stores with a common base, which can be
636 // optimized into a memset (memset_pattern). The latter most commonly happens
637 // with structs and handunrolled loops.
638 for (auto &SL : StoreRefsForMemset)
639 MadeChange |= processLoopStores(SL.second, BECount, ForMemset::Yes);
640
641 for (auto &SL : StoreRefsForMemsetPattern)
642 MadeChange |= processLoopStores(SL.second, BECount, ForMemset::No);
643
644 // Optimize the store into a memcpy, if it feeds an similarly strided load.
645 for (auto &SI : StoreRefsForMemcpy)
646 MadeChange |= processLoopStoreOfLoopLoad(SI, BECount);
647
648 MadeChange |= processLoopMemIntrinsic<MemCpyInst>(
649 BB, &LoopIdiomRecognize::processLoopMemCpy, BECount);
650 MadeChange |= processLoopMemIntrinsic<MemSetInst>(
651 BB, &LoopIdiomRecognize::processLoopMemSet, BECount);
652
653 return MadeChange;
654}
655
656/// See if this store(s) can be promoted to a memset.
657bool LoopIdiomRecognize::processLoopStores(SmallVectorImpl<StoreInst *> &SL,
658 const SCEV *BECount, ForMemset For) {
659 // Try to find consecutive stores that can be transformed into memsets.
660 SetVector<StoreInst *> Heads, Tails;
661 SmallDenseMap<StoreInst *, StoreInst *> ConsecutiveChain;
662
663 // Do a quadratic search on all of the given stores and find
664 // all of the pairs of stores that follow each other.
665 SmallVector<unsigned, 16> IndexQueue;
666 for (unsigned i = 0, e = SL.size(); i < e; ++i) {
667 assert(SL[i]->isSimple() && "Expected only non-volatile stores.")(static_cast <bool> (SL[i]->isSimple() && "Expected only non-volatile stores."
) ? void (0) : __assert_fail ("SL[i]->isSimple() && \"Expected only non-volatile stores.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 667, __extension__
__PRETTY_FUNCTION__))
;
668
669 Value *FirstStoredVal = SL[i]->getValueOperand();
670 Value *FirstStorePtr = SL[i]->getPointerOperand();
671 const SCEVAddRecExpr *FirstStoreEv =
672 cast<SCEVAddRecExpr>(SE->getSCEV(FirstStorePtr));
673 APInt FirstStride = getStoreStride(FirstStoreEv);
674 unsigned FirstStoreSize = DL->getTypeStoreSize(SL[i]->getValueOperand()->getType());
675
676 // See if we can optimize just this store in isolation.
677 if (FirstStride == FirstStoreSize || -FirstStride == FirstStoreSize) {
678 Heads.insert(SL[i]);
679 continue;
680 }
681
682 Value *FirstSplatValue = nullptr;
683 Constant *FirstPatternValue = nullptr;
684
685 if (For == ForMemset::Yes)
686 FirstSplatValue = isBytewiseValue(FirstStoredVal, *DL);
687 else
688 FirstPatternValue = getMemSetPatternValue(FirstStoredVal, DL);
689
690 assert((FirstSplatValue || FirstPatternValue) &&(static_cast <bool> ((FirstSplatValue || FirstPatternValue
) && "Expected either splat value or pattern value.")
? void (0) : __assert_fail ("(FirstSplatValue || FirstPatternValue) && \"Expected either splat value or pattern value.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 691, __extension__
__PRETTY_FUNCTION__))
691 "Expected either splat value or pattern value.")(static_cast <bool> ((FirstSplatValue || FirstPatternValue
) && "Expected either splat value or pattern value.")
? void (0) : __assert_fail ("(FirstSplatValue || FirstPatternValue) && \"Expected either splat value or pattern value.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 691, __extension__
__PRETTY_FUNCTION__))
;
692
693 IndexQueue.clear();
694 // If a store has multiple consecutive store candidates, search Stores
695 // array according to the sequence: from i+1 to e, then from i-1 to 0.
696 // This is because usually pairing with immediate succeeding or preceding
697 // candidate create the best chance to find memset opportunity.
698 unsigned j = 0;
699 for (j = i + 1; j < e; ++j)
700 IndexQueue.push_back(j);
701 for (j = i; j > 0; --j)
702 IndexQueue.push_back(j - 1);
703
704 for (auto &k : IndexQueue) {
705 assert(SL[k]->isSimple() && "Expected only non-volatile stores.")(static_cast <bool> (SL[k]->isSimple() && "Expected only non-volatile stores."
) ? void (0) : __assert_fail ("SL[k]->isSimple() && \"Expected only non-volatile stores.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 705, __extension__
__PRETTY_FUNCTION__))
;
706 Value *SecondStorePtr = SL[k]->getPointerOperand();
707 const SCEVAddRecExpr *SecondStoreEv =
708 cast<SCEVAddRecExpr>(SE->getSCEV(SecondStorePtr));
709 APInt SecondStride = getStoreStride(SecondStoreEv);
710
711 if (FirstStride != SecondStride)
712 continue;
713
714 Value *SecondStoredVal = SL[k]->getValueOperand();
715 Value *SecondSplatValue = nullptr;
716 Constant *SecondPatternValue = nullptr;
717
718 if (For == ForMemset::Yes)
719 SecondSplatValue = isBytewiseValue(SecondStoredVal, *DL);
720 else
721 SecondPatternValue = getMemSetPatternValue(SecondStoredVal, DL);
722
723 assert((SecondSplatValue || SecondPatternValue) &&(static_cast <bool> ((SecondSplatValue || SecondPatternValue
) && "Expected either splat value or pattern value.")
? void (0) : __assert_fail ("(SecondSplatValue || SecondPatternValue) && \"Expected either splat value or pattern value.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 724, __extension__
__PRETTY_FUNCTION__))
724 "Expected either splat value or pattern value.")(static_cast <bool> ((SecondSplatValue || SecondPatternValue
) && "Expected either splat value or pattern value.")
? void (0) : __assert_fail ("(SecondSplatValue || SecondPatternValue) && \"Expected either splat value or pattern value.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 724, __extension__
__PRETTY_FUNCTION__))
;
725
726 if (isConsecutiveAccess(SL[i], SL[k], *DL, *SE, false)) {
727 if (For == ForMemset::Yes) {
728 if (isa<UndefValue>(FirstSplatValue))
729 FirstSplatValue = SecondSplatValue;
730 if (FirstSplatValue != SecondSplatValue)
731 continue;
732 } else {
733 if (isa<UndefValue>(FirstPatternValue))
734 FirstPatternValue = SecondPatternValue;
735 if (FirstPatternValue != SecondPatternValue)
736 continue;
737 }
738 Tails.insert(SL[k]);
739 Heads.insert(SL[i]);
740 ConsecutiveChain[SL[i]] = SL[k];
741 break;
742 }
743 }
744 }
745
746 // We may run into multiple chains that merge into a single chain. We mark the
747 // stores that we transformed so that we don't visit the same store twice.
748 SmallPtrSet<Value *, 16> TransformedStores;
749 bool Changed = false;
750
751 // For stores that start but don't end a link in the chain:
752 for (StoreInst *I : Heads) {
753 if (Tails.count(I))
754 continue;
755
756 // We found a store instr that starts a chain. Now follow the chain and try
757 // to transform it.
758 SmallPtrSet<Instruction *, 8> AdjacentStores;
759 StoreInst *HeadStore = I;
760 unsigned StoreSize = 0;
761
762 // Collect the chain into a list.
763 while (Tails.count(I) || Heads.count(I)) {
764 if (TransformedStores.count(I))
765 break;
766 AdjacentStores.insert(I);
767
768 StoreSize += DL->getTypeStoreSize(I->getValueOperand()->getType());
769 // Move to the next value in the chain.
770 I = ConsecutiveChain[I];
771 }
772
773 Value *StoredVal = HeadStore->getValueOperand();
774 Value *StorePtr = HeadStore->getPointerOperand();
775 const SCEVAddRecExpr *StoreEv = cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
776 APInt Stride = getStoreStride(StoreEv);
777
778 // Check to see if the stride matches the size of the stores. If so, then
779 // we know that every byte is touched in the loop.
780 if (StoreSize != Stride && StoreSize != -Stride)
781 continue;
782
783 bool IsNegStride = StoreSize == -Stride;
784
785 Type *IntIdxTy = DL->getIndexType(StorePtr->getType());
786 const SCEV *StoreSizeSCEV = SE->getConstant(IntIdxTy, StoreSize);
787 if (processLoopStridedStore(StorePtr, StoreSizeSCEV,
788 MaybeAlign(HeadStore->getAlign()), StoredVal,
789 HeadStore, AdjacentStores, StoreEv, BECount,
790 IsNegStride)) {
791 TransformedStores.insert(AdjacentStores.begin(), AdjacentStores.end());
792 Changed = true;
793 }
794 }
795
796 return Changed;
797}
798
799/// processLoopMemIntrinsic - Template function for calling different processor
800/// functions based on mem intrinsic type.
801template <typename MemInst>
802bool LoopIdiomRecognize::processLoopMemIntrinsic(
803 BasicBlock *BB,
804 bool (LoopIdiomRecognize::*Processor)(MemInst *, const SCEV *),
805 const SCEV *BECount) {
806 bool MadeChange = false;
807 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
808 Instruction *Inst = &*I++;
809 // Look for memory instructions, which may be optimized to a larger one.
810 if (MemInst *MI = dyn_cast<MemInst>(Inst)) {
811 WeakTrackingVH InstPtr(&*I);
812 if (!(this->*Processor)(MI, BECount))
813 continue;
814 MadeChange = true;
815
816 // If processing the instruction invalidated our iterator, start over from
817 // the top of the block.
818 if (!InstPtr)
819 I = BB->begin();
820 }
821 }
822 return MadeChange;
823}
824
825/// processLoopMemCpy - See if this memcpy can be promoted to a large memcpy
826bool LoopIdiomRecognize::processLoopMemCpy(MemCpyInst *MCI,
827 const SCEV *BECount) {
828 // We can only handle non-volatile memcpys with a constant size.
829 if (MCI->isVolatile() || !isa<ConstantInt>(MCI->getLength()))
830 return false;
831
832 // If we're not allowed to hack on memcpy, we fail.
833 if ((!HasMemcpy && !isa<MemCpyInlineInst>(MCI)) || DisableLIRP::Memcpy)
834 return false;
835
836 Value *Dest = MCI->getDest();
837 Value *Source = MCI->getSource();
838 if (!Dest || !Source)
839 return false;
840
841 // See if the load and store pointer expressions are AddRec like {base,+,1} on
842 // the current loop, which indicates a strided load and store. If we have
843 // something else, it's a random load or store we can't handle.
844 const SCEVAddRecExpr *StoreEv = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Dest));
845 if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
846 return false;
847 const SCEVAddRecExpr *LoadEv = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Source));
848 if (!LoadEv || LoadEv->getLoop() != CurLoop || !LoadEv->isAffine())
849 return false;
850
851 // Reject memcpys that are so large that they overflow an unsigned.
852 uint64_t SizeInBytes = cast<ConstantInt>(MCI->getLength())->getZExtValue();
853 if ((SizeInBytes >> 32) != 0)
854 return false;
855
856 // Check if the stride matches the size of the memcpy. If so, then we know
857 // that every byte is touched in the loop.
858 const SCEVConstant *ConstStoreStride =
859 dyn_cast<SCEVConstant>(StoreEv->getOperand(1));
860 const SCEVConstant *ConstLoadStride =
861 dyn_cast<SCEVConstant>(LoadEv->getOperand(1));
862 if (!ConstStoreStride || !ConstLoadStride)
863 return false;
864
865 APInt StoreStrideValue = ConstStoreStride->getAPInt();
866 APInt LoadStrideValue = ConstLoadStride->getAPInt();
867 // Huge stride value - give up
868 if (StoreStrideValue.getBitWidth() > 64 || LoadStrideValue.getBitWidth() > 64)
869 return false;
870
871 if (SizeInBytes != StoreStrideValue && SizeInBytes != -StoreStrideValue) {
872 ORE.emit([&]() {
873 return OptimizationRemarkMissed(DEBUG_TYPE"loop-idiom", "SizeStrideUnequal", MCI)
874 << ore::NV("Inst", "memcpy") << " in "
875 << ore::NV("Function", MCI->getFunction())
876 << " function will not be hoisted: "
877 << ore::NV("Reason", "memcpy size is not equal to stride");
878 });
879 return false;
880 }
881
882 int64_t StoreStrideInt = StoreStrideValue.getSExtValue();
883 int64_t LoadStrideInt = LoadStrideValue.getSExtValue();
884 // Check if the load stride matches the store stride.
885 if (StoreStrideInt != LoadStrideInt)
886 return false;
887
888 return processLoopStoreOfLoopLoad(
889 Dest, Source, SE->getConstant(Dest->getType(), SizeInBytes),
890 MCI->getDestAlign(), MCI->getSourceAlign(), MCI, MCI, StoreEv, LoadEv,
891 BECount);
892}
893
894/// processLoopMemSet - See if this memset can be promoted to a large memset.
895bool LoopIdiomRecognize::processLoopMemSet(MemSetInst *MSI,
896 const SCEV *BECount) {
897 // We can only handle non-volatile memsets.
898 if (MSI->isVolatile())
899 return false;
900
901 // If we're not allowed to hack on memset, we fail.
902 if (!HasMemset || DisableLIRP::Memset)
903 return false;
904
905 Value *Pointer = MSI->getDest();
906
907 // See if the pointer expression is an AddRec like {base,+,1} on the current
908 // loop, which indicates a strided store. If we have something else, it's a
909 // random store we can't handle.
910 const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
911 if (!Ev || Ev->getLoop() != CurLoop)
912 return false;
913 if (!Ev->isAffine()) {
914 LLVM_DEBUG(dbgs() << " Pointer is not affine, abort\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Pointer is not affine, abort\n"
; } } while (false)
;
915 return false;
916 }
917
918 const SCEV *PointerStrideSCEV = Ev->getOperand(1);
919 const SCEV *MemsetSizeSCEV = SE->getSCEV(MSI->getLength());
920 if (!PointerStrideSCEV || !MemsetSizeSCEV)
921 return false;
922
923 bool IsNegStride = false;
924 const bool IsConstantSize = isa<ConstantInt>(MSI->getLength());
925
926 if (IsConstantSize) {
927 // Memset size is constant.
928 // Check if the pointer stride matches the memset size. If so, then
929 // we know that every byte is touched in the loop.
930 LLVM_DEBUG(dbgs() << " memset size is constant\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " memset size is constant\n"
; } } while (false)
;
931 uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
932 const SCEVConstant *ConstStride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
933 if (!ConstStride)
934 return false;
935
936 APInt Stride = ConstStride->getAPInt();
937 if (SizeInBytes != Stride && SizeInBytes != -Stride)
938 return false;
939
940 IsNegStride = SizeInBytes == -Stride;
941 } else {
942 // Memset size is non-constant.
943 // Check if the pointer stride matches the memset size.
944 // To be conservative, the pass would not promote pointers that aren't in
945 // address space zero. Also, the pass only handles memset length and stride
946 // that are invariant for the top level loop.
947 LLVM_DEBUG(dbgs() << " memset size is non-constant\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " memset size is non-constant\n"
; } } while (false)
;
948 if (Pointer->getType()->getPointerAddressSpace() != 0) {
949 LLVM_DEBUG(dbgs() << " pointer is not in address space zero, "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " pointer is not in address space zero, "
<< "abort\n"; } } while (false)
950 << "abort\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " pointer is not in address space zero, "
<< "abort\n"; } } while (false)
;
951 return false;
952 }
953 if (!SE->isLoopInvariant(MemsetSizeSCEV, CurLoop)) {
954 LLVM_DEBUG(dbgs() << " memset size is not a loop-invariant, "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " memset size is not a loop-invariant, "
<< "abort\n"; } } while (false)
955 << "abort\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " memset size is not a loop-invariant, "
<< "abort\n"; } } while (false)
;
956 return false;
957 }
958
959 // Compare positive direction PointerStrideSCEV with MemsetSizeSCEV
960 IsNegStride = PointerStrideSCEV->isNonConstantNegative();
961 const SCEV *PositiveStrideSCEV =
962 IsNegStride ? SE->getNegativeSCEV(PointerStrideSCEV)
963 : PointerStrideSCEV;
964 LLVM_DEBUG(dbgs() << " MemsetSizeSCEV: " << *MemsetSizeSCEV << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " MemsetSizeSCEV: " <<
*MemsetSizeSCEV << "\n" << " PositiveStrideSCEV: "
<< *PositiveStrideSCEV << "\n"; } } while (false
)
965 << " PositiveStrideSCEV: " << *PositiveStrideSCEVdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " MemsetSizeSCEV: " <<
*MemsetSizeSCEV << "\n" << " PositiveStrideSCEV: "
<< *PositiveStrideSCEV << "\n"; } } while (false
)
966 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " MemsetSizeSCEV: " <<
*MemsetSizeSCEV << "\n" << " PositiveStrideSCEV: "
<< *PositiveStrideSCEV << "\n"; } } while (false
)
;
967
968 if (PositiveStrideSCEV != MemsetSizeSCEV) {
969 // If an expression is covered by the loop guard, compare again and
970 // proceed with optimization if equal.
971 const SCEV *FoldedPositiveStride =
972 SE->applyLoopGuards(PositiveStrideSCEV, CurLoop);
973 const SCEV *FoldedMemsetSize =
974 SE->applyLoopGuards(MemsetSizeSCEV, CurLoop);
975
976 LLVM_DEBUG(dbgs() << " Try to fold SCEV based on loop guard\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Try to fold SCEV based on loop guard\n"
<< " FoldedMemsetSize: " << *FoldedMemsetSize
<< "\n" << " FoldedPositiveStride: " <<
*FoldedPositiveStride << "\n"; } } while (false)
977 << " FoldedMemsetSize: " << *FoldedMemsetSize << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Try to fold SCEV based on loop guard\n"
<< " FoldedMemsetSize: " << *FoldedMemsetSize
<< "\n" << " FoldedPositiveStride: " <<
*FoldedPositiveStride << "\n"; } } while (false)
978 << " FoldedPositiveStride: " << *FoldedPositiveStridedo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Try to fold SCEV based on loop guard\n"
<< " FoldedMemsetSize: " << *FoldedMemsetSize
<< "\n" << " FoldedPositiveStride: " <<
*FoldedPositiveStride << "\n"; } } while (false)
979 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Try to fold SCEV based on loop guard\n"
<< " FoldedMemsetSize: " << *FoldedMemsetSize
<< "\n" << " FoldedPositiveStride: " <<
*FoldedPositiveStride << "\n"; } } while (false)
;
980
981 if (FoldedPositiveStride != FoldedMemsetSize) {
982 LLVM_DEBUG(dbgs() << " SCEV don't match, abort\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " SCEV don't match, abort\n"
; } } while (false)
;
983 return false;
984 }
985 }
986 }
987
988 // Verify that the memset value is loop invariant. If not, we can't promote
989 // the memset.
990 Value *SplatValue = MSI->getValue();
991 if (!SplatValue || !CurLoop->isLoopInvariant(SplatValue))
992 return false;
993
994 SmallPtrSet<Instruction *, 1> MSIs;
995 MSIs.insert(MSI);
996 return processLoopStridedStore(Pointer, SE->getSCEV(MSI->getLength()),
997 MSI->getDestAlign(), SplatValue, MSI, MSIs, Ev,
998 BECount, IsNegStride, /*IsLoopMemset=*/true);
999}
1000
1001/// mayLoopAccessLocation - Return true if the specified loop might access the
1002/// specified pointer location, which is a loop-strided access. The 'Access'
1003/// argument specifies what the verboten forms of access are (read or write).
1004static bool
1005mayLoopAccessLocation(Value *Ptr, ModRefInfo Access, Loop *L,
1006 const SCEV *BECount, const SCEV *StoreSizeSCEV,
1007 AliasAnalysis &AA,
1008 SmallPtrSetImpl<Instruction *> &IgnoredInsts) {
1009 // Get the location that may be stored across the loop. Since the access is
1010 // strided positively through memory, we say that the modified location starts
1011 // at the pointer and has infinite size.
1012 LocationSize AccessSize = LocationSize::afterPointer();
1013
1014 // If the loop iterates a fixed number of times, we can refine the access size
1015 // to be exactly the size of the memset, which is (BECount+1)*StoreSize
1016 const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount);
1017 const SCEVConstant *ConstSize = dyn_cast<SCEVConstant>(StoreSizeSCEV);
1018 if (BECst && ConstSize)
1019 AccessSize = LocationSize::precise((BECst->getValue()->getZExtValue() + 1) *
1020 ConstSize->getValue()->getZExtValue());
1021
1022 // TODO: For this to be really effective, we have to dive into the pointer
1023 // operand in the store. Store to &A[i] of 100 will always return may alias
1024 // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
1025 // which will then no-alias a store to &A[100].
1026 MemoryLocation StoreLoc(Ptr, AccessSize);
1027
1028 for (BasicBlock *B : L->blocks())
1029 for (Instruction &I : *B)
1030 if (!IgnoredInsts.contains(&I) &&
1031 isModOrRefSet(AA.getModRefInfo(&I, StoreLoc) & Access))
1032 return true;
1033 return false;
1034}
1035
1036// If we have a negative stride, Start refers to the end of the memory location
1037// we're trying to memset. Therefore, we need to recompute the base pointer,
1038// which is just Start - BECount*Size.
1039static const SCEV *getStartForNegStride(const SCEV *Start, const SCEV *BECount,
1040 Type *IntPtr, const SCEV *StoreSizeSCEV,
1041 ScalarEvolution *SE) {
1042 const SCEV *Index = SE->getTruncateOrZeroExtend(BECount, IntPtr);
1043 if (!StoreSizeSCEV->isOne()) {
1044 // index = back edge count * store size
1045 Index = SE->getMulExpr(Index,
1046 SE->getTruncateOrZeroExtend(StoreSizeSCEV, IntPtr),
1047 SCEV::FlagNUW);
1048 }
1049 // base pointer = start - index * store size
1050 return SE->getMinusSCEV(Start, Index);
1051}
1052
1053/// Compute trip count from the backedge taken count.
1054static const SCEV *getTripCount(const SCEV *BECount, Type *IntPtr,
1055 Loop *CurLoop, const DataLayout *DL,
1056 ScalarEvolution *SE) {
1057 const SCEV *TripCountS = nullptr;
1058 // The # stored bytes is (BECount+1). Expand the trip count out to
1059 // pointer size if it isn't already.
1060 //
1061 // If we're going to need to zero extend the BE count, check if we can add
1062 // one to it prior to zero extending without overflow. Provided this is safe,
1063 // it allows better simplification of the +1.
1064 if (DL->getTypeSizeInBits(BECount->getType()) <
1065 DL->getTypeSizeInBits(IntPtr) &&
1066 SE->isLoopEntryGuardedByCond(
1067 CurLoop, ICmpInst::ICMP_NE, BECount,
1068 SE->getNegativeSCEV(SE->getOne(BECount->getType())))) {
1069 TripCountS = SE->getZeroExtendExpr(
1070 SE->getAddExpr(BECount, SE->getOne(BECount->getType()), SCEV::FlagNUW),
1071 IntPtr);
1072 } else {
1073 TripCountS = SE->getAddExpr(SE->getTruncateOrZeroExtend(BECount, IntPtr),
1074 SE->getOne(IntPtr), SCEV::FlagNUW);
1075 }
1076
1077 return TripCountS;
1078}
1079
1080/// Compute the number of bytes as a SCEV from the backedge taken count.
1081///
1082/// This also maps the SCEV into the provided type and tries to handle the
1083/// computation in a way that will fold cleanly.
1084static const SCEV *getNumBytes(const SCEV *BECount, Type *IntPtr,
1085 const SCEV *StoreSizeSCEV, Loop *CurLoop,
1086 const DataLayout *DL, ScalarEvolution *SE) {
1087 const SCEV *TripCountSCEV = getTripCount(BECount, IntPtr, CurLoop, DL, SE);
1088
1089 return SE->getMulExpr(TripCountSCEV,
1090 SE->getTruncateOrZeroExtend(StoreSizeSCEV, IntPtr),
1091 SCEV::FlagNUW);
1092}
1093
1094/// processLoopStridedStore - We see a strided store of some value. If we can
1095/// transform this into a memset or memset_pattern in the loop preheader, do so.
1096bool LoopIdiomRecognize::processLoopStridedStore(
1097 Value *DestPtr, const SCEV *StoreSizeSCEV, MaybeAlign StoreAlignment,
1098 Value *StoredVal, Instruction *TheStore,
1099 SmallPtrSetImpl<Instruction *> &Stores, const SCEVAddRecExpr *Ev,
1100 const SCEV *BECount, bool IsNegStride, bool IsLoopMemset) {
1101 Module *M = TheStore->getModule();
1102 Value *SplatValue = isBytewiseValue(StoredVal, *DL);
1103 Constant *PatternValue = nullptr;
1104
1105 if (!SplatValue)
1106 PatternValue = getMemSetPatternValue(StoredVal, DL);
1107
1108 assert((SplatValue || PatternValue) &&(static_cast <bool> ((SplatValue || PatternValue) &&
"Expected either splat value or pattern value.") ? void (0) :
__assert_fail ("(SplatValue || PatternValue) && \"Expected either splat value or pattern value.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 1109, __extension__
__PRETTY_FUNCTION__))
1109 "Expected either splat value or pattern value.")(static_cast <bool> ((SplatValue || PatternValue) &&
"Expected either splat value or pattern value.") ? void (0) :
__assert_fail ("(SplatValue || PatternValue) && \"Expected either splat value or pattern value.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 1109, __extension__
__PRETTY_FUNCTION__))
;
1110
1111 // The trip count of the loop and the base pointer of the addrec SCEV is
1112 // guaranteed to be loop invariant, which means that it should dominate the
1113 // header. This allows us to insert code for it in the preheader.
1114 unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();
1115 BasicBlock *Preheader = CurLoop->getLoopPreheader();
1116 IRBuilder<> Builder(Preheader->getTerminator());
1117 SCEVExpander Expander(*SE, *DL, "loop-idiom");
1118 SCEVExpanderCleaner ExpCleaner(Expander);
1119
1120 Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
1121 Type *IntIdxTy = DL->getIndexType(DestPtr->getType());
1122
1123 bool Changed = false;
1124 const SCEV *Start = Ev->getStart();
1125 // Handle negative strided loops.
1126 if (IsNegStride)
1127 Start = getStartForNegStride(Start, BECount, IntIdxTy, StoreSizeSCEV, SE);
1128
1129 // TODO: ideally we should still be able to generate memset if SCEV expander
1130 // is taught to generate the dependencies at the latest point.
1131 if (!Expander.isSafeToExpand(Start))
1132 return Changed;
1133
1134 // Okay, we have a strided store "p[i]" of a splattable value. We can turn
1135 // this into a memset in the loop preheader now if we want. However, this
1136 // would be unsafe to do if there is anything else in the loop that may read
1137 // or write to the aliased location. Check for any overlap by generating the
1138 // base pointer and checking the region.
1139 Value *BasePtr =
1140 Expander.expandCodeFor(Start, DestInt8PtrTy, Preheader->getTerminator());
1141
1142 // From here on out, conservatively report to the pass manager that we've
1143 // changed the IR, even if we later clean up these added instructions. There
1144 // may be structural differences e.g. in the order of use lists not accounted
1145 // for in just a textual dump of the IR. This is written as a variable, even
1146 // though statically all the places this dominates could be replaced with
1147 // 'true', with the hope that anyone trying to be clever / "more precise" with
1148 // the return value will read this comment, and leave them alone.
1149 Changed = true;
1150
1151 if (mayLoopAccessLocation(BasePtr, ModRefInfo::ModRef, CurLoop, BECount,
1152 StoreSizeSCEV, *AA, Stores))
1153 return Changed;
1154
1155 if (avoidLIRForMultiBlockLoop(/*IsMemset=*/true, IsLoopMemset))
1156 return Changed;
1157
1158 // Okay, everything looks good, insert the memset.
1159
1160 const SCEV *NumBytesS =
1161 getNumBytes(BECount, IntIdxTy, StoreSizeSCEV, CurLoop, DL, SE);
1162
1163 // TODO: ideally we should still be able to generate memset if SCEV expander
1164 // is taught to generate the dependencies at the latest point.
1165 if (!Expander.isSafeToExpand(NumBytesS))
1166 return Changed;
1167
1168 Value *NumBytes =
1169 Expander.expandCodeFor(NumBytesS, IntIdxTy, Preheader->getTerminator());
1170
1171 CallInst *NewCall;
1172 if (SplatValue) {
1173 AAMDNodes AATags = TheStore->getAAMetadata();
1174 for (Instruction *Store : Stores)
1175 AATags = AATags.merge(Store->getAAMetadata());
1176 if (auto CI = dyn_cast<ConstantInt>(NumBytes))
1177 AATags = AATags.extendTo(CI->getZExtValue());
1178 else
1179 AATags = AATags.extendTo(-1);
1180
1181 NewCall = Builder.CreateMemSet(
1182 BasePtr, SplatValue, NumBytes, MaybeAlign(StoreAlignment),
1183 /*isVolatile=*/false, AATags.TBAA, AATags.Scope, AATags.NoAlias);
1184 } else if (isLibFuncEmittable(M, TLI, LibFunc_memset_pattern16)) {
1185 // Everything is emitted in default address space
1186 Type *Int8PtrTy = DestInt8PtrTy;
1187
1188 StringRef FuncName = "memset_pattern16";
1189 FunctionCallee MSP = getOrInsertLibFunc(M, *TLI, LibFunc_memset_pattern16,
1190 Builder.getVoidTy(), Int8PtrTy, Int8PtrTy, IntIdxTy);
1191 inferNonMandatoryLibFuncAttrs(M, FuncName, *TLI);
1192
1193 // Otherwise we should form a memset_pattern16. PatternValue is known to be
1194 // an constant array of 16-bytes. Plop the value into a mergable global.
1195 GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
1196 GlobalValue::PrivateLinkage,
1197 PatternValue, ".memset_pattern");
1198 GV->setUnnamedAddr(GlobalValue::UnnamedAddr::Global); // Ok to merge these.
1199 GV->setAlignment(Align(16));
1200 Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
1201 NewCall = Builder.CreateCall(MSP, {BasePtr, PatternPtr, NumBytes});
1202 } else
1203 return Changed;
1204
1205 NewCall->setDebugLoc(TheStore->getDebugLoc());
1206
1207 if (MSSAU) {
1208 MemoryAccess *NewMemAcc = MSSAU->createMemoryAccessInBB(
1209 NewCall, nullptr, NewCall->getParent(), MemorySSA::BeforeTerminator);
1210 MSSAU->insertDef(cast<MemoryDef>(NewMemAcc), true);
1211 }
1212
1213 LLVM_DEBUG(dbgs() << " Formed memset: " << *NewCall << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Formed memset: " <<
*NewCall << "\n" << " from store to: " <<
*Ev << " at: " << *TheStore << "\n"; } } while
(false)
1214 << " from store to: " << *Ev << " at: " << *TheStoredo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Formed memset: " <<
*NewCall << "\n" << " from store to: " <<
*Ev << " at: " << *TheStore << "\n"; } } while
(false)
1215 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Formed memset: " <<
*NewCall << "\n" << " from store to: " <<
*Ev << " at: " << *TheStore << "\n"; } } while
(false)
;
1216
1217 ORE.emit([&]() {
1218 OptimizationRemark R(DEBUG_TYPE"loop-idiom", "ProcessLoopStridedStore",
1219 NewCall->getDebugLoc(), Preheader);
1220 R << "Transformed loop-strided store in "
1221 << ore::NV("Function", TheStore->getFunction())
1222 << " function into a call to "
1223 << ore::NV("NewFunction", NewCall->getCalledFunction())
1224 << "() intrinsic";
1225 if (!Stores.empty())
1226 R << ore::setExtraArgs();
1227 for (auto *I : Stores) {
1228 R << ore::NV("FromBlock", I->getParent()->getName())
1229 << ore::NV("ToBlock", Preheader->getName());
1230 }
1231 return R;
1232 });
1233
1234 // Okay, the memset has been formed. Zap the original store and anything that
1235 // feeds into it.
1236 for (auto *I : Stores) {
1237 if (MSSAU)
1238 MSSAU->removeMemoryAccess(I, true);
1239 deleteDeadInstruction(I);
1240 }
1241 if (MSSAU && VerifyMemorySSA)
1242 MSSAU->getMemorySSA()->verifyMemorySSA();
1243 ++NumMemSet;
1244 ExpCleaner.markResultUsed();
1245 return true;
1246}
1247
1248/// If the stored value is a strided load in the same loop with the same stride
1249/// this may be transformable into a memcpy. This kicks in for stuff like
1250/// for (i) A[i] = B[i];
1251bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(StoreInst *SI,
1252 const SCEV *BECount) {
1253 assert(SI->isUnordered() && "Expected only non-volatile non-ordered stores.")(static_cast <bool> (SI->isUnordered() && "Expected only non-volatile non-ordered stores."
) ? void (0) : __assert_fail ("SI->isUnordered() && \"Expected only non-volatile non-ordered stores.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 1253, __extension__
__PRETTY_FUNCTION__))
;
1254
1255 Value *StorePtr = SI->getPointerOperand();
1256 const SCEVAddRecExpr *StoreEv = cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
1257 unsigned StoreSize = DL->getTypeStoreSize(SI->getValueOperand()->getType());
1258
1259 // The store must be feeding a non-volatile load.
1260 LoadInst *LI = cast<LoadInst>(SI->getValueOperand());
1261 assert(LI->isUnordered() && "Expected only non-volatile non-ordered loads.")(static_cast <bool> (LI->isUnordered() && "Expected only non-volatile non-ordered loads."
) ? void (0) : __assert_fail ("LI->isUnordered() && \"Expected only non-volatile non-ordered loads.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 1261, __extension__
__PRETTY_FUNCTION__))
;
1262
1263 // See if the pointer expression is an AddRec like {base,+,1} on the current
1264 // loop, which indicates a strided load. If we have something else, it's a
1265 // random load we can't handle.
1266 Value *LoadPtr = LI->getPointerOperand();
1267 const SCEVAddRecExpr *LoadEv = cast<SCEVAddRecExpr>(SE->getSCEV(LoadPtr));
1268
1269 const SCEV *StoreSizeSCEV = SE->getConstant(StorePtr->getType(), StoreSize);
1270 return processLoopStoreOfLoopLoad(StorePtr, LoadPtr, StoreSizeSCEV,
1271 SI->getAlign(), LI->getAlign(), SI, LI,
1272 StoreEv, LoadEv, BECount);
1273}
1274
1275class MemmoveVerifier {
1276public:
1277 explicit MemmoveVerifier(const Value &LoadBasePtr, const Value &StoreBasePtr,
1278 const DataLayout &DL)
1279 : DL(DL), BP1(llvm::GetPointerBaseWithConstantOffset(
1280 LoadBasePtr.stripPointerCasts(), LoadOff, DL)),
1281 BP2(llvm::GetPointerBaseWithConstantOffset(
1282 StoreBasePtr.stripPointerCasts(), StoreOff, DL)),
1283 IsSameObject(BP1 == BP2) {}
1284
1285 bool loadAndStoreMayFormMemmove(unsigned StoreSize, bool IsNegStride,
1286 const Instruction &TheLoad,
1287 bool IsMemCpy) const {
1288 if (IsMemCpy) {
1289 // Ensure that LoadBasePtr is after StoreBasePtr or before StoreBasePtr
1290 // for negative stride.
1291 if ((!IsNegStride && LoadOff <= StoreOff) ||
1292 (IsNegStride && LoadOff >= StoreOff))
1293 return false;
1294 } else {
1295 // Ensure that LoadBasePtr is after StoreBasePtr or before StoreBasePtr
1296 // for negative stride. LoadBasePtr shouldn't overlap with StoreBasePtr.
1297 int64_t LoadSize =
1298 DL.getTypeSizeInBits(TheLoad.getType()).getFixedSize() / 8;
1299 if (BP1 != BP2 || LoadSize != int64_t(StoreSize))
1300 return false;
1301 if ((!IsNegStride && LoadOff < StoreOff + int64_t(StoreSize)) ||
1302 (IsNegStride && LoadOff + LoadSize > StoreOff))
1303 return false;
1304 }
1305 return true;
1306 }
1307
1308private:
1309 const DataLayout &DL;
1310 int64_t LoadOff = 0;
1311 int64_t StoreOff = 0;
1312 const Value *BP1;
1313 const Value *BP2;
1314
1315public:
1316 const bool IsSameObject;
1317};
1318
1319bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(
1320 Value *DestPtr, Value *SourcePtr, const SCEV *StoreSizeSCEV,
1321 MaybeAlign StoreAlign, MaybeAlign LoadAlign, Instruction *TheStore,
1322 Instruction *TheLoad, const SCEVAddRecExpr *StoreEv,
1323 const SCEVAddRecExpr *LoadEv, const SCEV *BECount) {
1324
1325 // FIXME: until llvm.memcpy.inline supports dynamic sizes, we need to
1326 // conservatively bail here, since otherwise we may have to transform
1327 // llvm.memcpy.inline into llvm.memcpy which is illegal.
1328 if (isa<MemCpyInlineInst>(TheStore))
1329 return false;
1330
1331 // The trip count of the loop and the base pointer of the addrec SCEV is
1332 // guaranteed to be loop invariant, which means that it should dominate the
1333 // header. This allows us to insert code for it in the preheader.
1334 BasicBlock *Preheader = CurLoop->getLoopPreheader();
1335 IRBuilder<> Builder(Preheader->getTerminator());
1336 SCEVExpander Expander(*SE, *DL, "loop-idiom");
1337
1338 SCEVExpanderCleaner ExpCleaner(Expander);
1339
1340 bool Changed = false;
1341 const SCEV *StrStart = StoreEv->getStart();
1342 unsigned StrAS = DestPtr->getType()->getPointerAddressSpace();
1343 Type *IntIdxTy = Builder.getIntNTy(DL->getIndexSizeInBits(StrAS));
1344
1345 APInt Stride = getStoreStride(StoreEv);
1346 const SCEVConstant *ConstStoreSize = dyn_cast<SCEVConstant>(StoreSizeSCEV);
1347
1348 // TODO: Deal with non-constant size; Currently expect constant store size
1349 assert(ConstStoreSize && "store size is expected to be a constant")(static_cast <bool> (ConstStoreSize && "store size is expected to be a constant"
) ? void (0) : __assert_fail ("ConstStoreSize && \"store size is expected to be a constant\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 1349, __extension__
__PRETTY_FUNCTION__))
;
1350
1351 int64_t StoreSize = ConstStoreSize->getValue()->getZExtValue();
1352 bool IsNegStride = StoreSize == -Stride;
1353
1354 // Handle negative strided loops.
1355 if (IsNegStride)
1356 StrStart =
1357 getStartForNegStride(StrStart, BECount, IntIdxTy, StoreSizeSCEV, SE);
1358
1359 // Okay, we have a strided store "p[i]" of a loaded value. We can turn
1360 // this into a memcpy in the loop preheader now if we want. However, this
1361 // would be unsafe to do if there is anything else in the loop that may read
1362 // or write the memory region we're storing to. This includes the load that
1363 // feeds the stores. Check for an alias by generating the base address and
1364 // checking everything.
1365 Value *StoreBasePtr = Expander.expandCodeFor(
1366 StrStart, Builder.getInt8PtrTy(StrAS), Preheader->getTerminator());
1367
1368 // From here on out, conservatively report to the pass manager that we've
1369 // changed the IR, even if we later clean up these added instructions. There
1370 // may be structural differences e.g. in the order of use lists not accounted
1371 // for in just a textual dump of the IR. This is written as a variable, even
1372 // though statically all the places this dominates could be replaced with
1373 // 'true', with the hope that anyone trying to be clever / "more precise" with
1374 // the return value will read this comment, and leave them alone.
1375 Changed = true;
1376
1377 SmallPtrSet<Instruction *, 2> IgnoredInsts;
1378 IgnoredInsts.insert(TheStore);
1379
1380 bool IsMemCpy = isa<MemCpyInst>(TheStore);
1381 const StringRef InstRemark = IsMemCpy ? "memcpy" : "load and store";
1382
1383 bool LoopAccessStore =
1384 mayLoopAccessLocation(StoreBasePtr, ModRefInfo::ModRef, CurLoop, BECount,
1385 StoreSizeSCEV, *AA, IgnoredInsts);
1386 if (LoopAccessStore) {
1387 // For memmove case it's not enough to guarantee that loop doesn't access
1388 // TheStore and TheLoad. Additionally we need to make sure that TheStore is
1389 // the only user of TheLoad.
1390 if (!TheLoad->hasOneUse())
1391 return Changed;
1392 IgnoredInsts.insert(TheLoad);
1393 if (mayLoopAccessLocation(StoreBasePtr, ModRefInfo::ModRef, CurLoop,
1394 BECount, StoreSizeSCEV, *AA, IgnoredInsts)) {
1395 ORE.emit([&]() {
1396 return OptimizationRemarkMissed(DEBUG_TYPE"loop-idiom", "LoopMayAccessStore",
1397 TheStore)
1398 << ore::NV("Inst", InstRemark) << " in "
1399 << ore::NV("Function", TheStore->getFunction())
1400 << " function will not be hoisted: "
1401 << ore::NV("Reason", "The loop may access store location");
1402 });
1403 return Changed;
1404 }
1405 IgnoredInsts.erase(TheLoad);
1406 }
1407
1408 const SCEV *LdStart = LoadEv->getStart();
1409 unsigned LdAS = SourcePtr->getType()->getPointerAddressSpace();
1410
1411 // Handle negative strided loops.
1412 if (IsNegStride)
1413 LdStart =
1414 getStartForNegStride(LdStart, BECount, IntIdxTy, StoreSizeSCEV, SE);
1415
1416 // For a memcpy, we have to make sure that the input array is not being
1417 // mutated by the loop.
1418 Value *LoadBasePtr = Expander.expandCodeFor(
1419 LdStart, Builder.getInt8PtrTy(LdAS), Preheader->getTerminator());
1420
1421 // If the store is a memcpy instruction, we must check if it will write to
1422 // the load memory locations. So remove it from the ignored stores.
1423 MemmoveVerifier Verifier(*LoadBasePtr, *StoreBasePtr, *DL);
1424 if (IsMemCpy && !Verifier.IsSameObject)
1425 IgnoredInsts.erase(TheStore);
1426 if (mayLoopAccessLocation(LoadBasePtr, ModRefInfo::Mod, CurLoop, BECount,
1427 StoreSizeSCEV, *AA, IgnoredInsts)) {
1428 ORE.emit([&]() {
1429 return OptimizationRemarkMissed(DEBUG_TYPE"loop-idiom", "LoopMayAccessLoad", TheLoad)
1430 << ore::NV("Inst", InstRemark) << " in "
1431 << ore::NV("Function", TheStore->getFunction())
1432 << " function will not be hoisted: "
1433 << ore::NV("Reason", "The loop may access load location");
1434 });
1435 return Changed;
1436 }
1437
1438 bool UseMemMove = IsMemCpy ? Verifier.IsSameObject : LoopAccessStore;
1439 if (UseMemMove)
1440 if (!Verifier.loadAndStoreMayFormMemmove(StoreSize, IsNegStride, *TheLoad,
1441 IsMemCpy))
1442 return Changed;
1443
1444 if (avoidLIRForMultiBlockLoop())
1445 return Changed;
1446
1447 // Okay, everything is safe, we can transform this!
1448
1449 const SCEV *NumBytesS =
1450 getNumBytes(BECount, IntIdxTy, StoreSizeSCEV, CurLoop, DL, SE);
1451
1452 Value *NumBytes =
1453 Expander.expandCodeFor(NumBytesS, IntIdxTy, Preheader->getTerminator());
1454
1455 AAMDNodes AATags = TheLoad->getAAMetadata();
1456 AAMDNodes StoreAATags = TheStore->getAAMetadata();
1457 AATags = AATags.merge(StoreAATags);
1458 if (auto CI = dyn_cast<ConstantInt>(NumBytes))
1459 AATags = AATags.extendTo(CI->getZExtValue());
1460 else
1461 AATags = AATags.extendTo(-1);
1462
1463 CallInst *NewCall = nullptr;
1464 // Check whether to generate an unordered atomic memcpy:
1465 // If the load or store are atomic, then they must necessarily be unordered
1466 // by previous checks.
1467 if (!TheStore->isAtomic() && !TheLoad->isAtomic()) {
1468 if (UseMemMove)
1469 NewCall = Builder.CreateMemMove(
1470 StoreBasePtr, StoreAlign, LoadBasePtr, LoadAlign, NumBytes,
1471 /*isVolatile=*/false, AATags.TBAA, AATags.Scope, AATags.NoAlias);
1472 else
1473 NewCall =
1474 Builder.CreateMemCpy(StoreBasePtr, StoreAlign, LoadBasePtr, LoadAlign,
1475 NumBytes, /*isVolatile=*/false, AATags.TBAA,
1476 AATags.TBAAStruct, AATags.Scope, AATags.NoAlias);
1477 } else {
1478 // For now don't support unordered atomic memmove.
1479 if (UseMemMove)
1480 return Changed;
1481 // We cannot allow unaligned ops for unordered load/store, so reject
1482 // anything where the alignment isn't at least the element size.
1483 assert((StoreAlign && LoadAlign) &&(static_cast <bool> ((StoreAlign && LoadAlign) &&
"Expect unordered load/store to have align.") ? void (0) : __assert_fail
("(StoreAlign && LoadAlign) && \"Expect unordered load/store to have align.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 1484, __extension__
__PRETTY_FUNCTION__))
1484 "Expect unordered load/store to have align.")(static_cast <bool> ((StoreAlign && LoadAlign) &&
"Expect unordered load/store to have align.") ? void (0) : __assert_fail
("(StoreAlign && LoadAlign) && \"Expect unordered load/store to have align.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 1484, __extension__
__PRETTY_FUNCTION__))
;
1485 if (StoreAlign.value() < StoreSize || LoadAlign.value() < StoreSize)
1486 return Changed;
1487
1488 // If the element.atomic memcpy is not lowered into explicit
1489 // loads/stores later, then it will be lowered into an element-size
1490 // specific lib call. If the lib call doesn't exist for our store size, then
1491 // we shouldn't generate the memcpy.
1492 if (StoreSize > TTI->getAtomicMemIntrinsicMaxElementSize())
1493 return Changed;
1494
1495 // Create the call.
1496 // Note that unordered atomic loads/stores are *required* by the spec to
1497 // have an alignment but non-atomic loads/stores may not.
1498 NewCall = Builder.CreateElementUnorderedAtomicMemCpy(
1499 StoreBasePtr, StoreAlign.value(), LoadBasePtr, LoadAlign.value(),
1500 NumBytes, StoreSize, AATags.TBAA, AATags.TBAAStruct, AATags.Scope,
1501 AATags.NoAlias);
1502 }
1503 NewCall->setDebugLoc(TheStore->getDebugLoc());
1504
1505 if (MSSAU) {
1506 MemoryAccess *NewMemAcc = MSSAU->createMemoryAccessInBB(
1507 NewCall, nullptr, NewCall->getParent(), MemorySSA::BeforeTerminator);
1508 MSSAU->insertDef(cast<MemoryDef>(NewMemAcc), true);
1509 }
1510
1511 LLVM_DEBUG(dbgs() << " Formed new call: " << *NewCall << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Formed new call: " <<
*NewCall << "\n" << " from load ptr=" <<
*LoadEv << " at: " << *TheLoad << "\n" <<
" from store ptr=" << *StoreEv << " at: " <<
*TheStore << "\n"; } } while (false)
1512 << " from load ptr=" << *LoadEv << " at: " << *TheLoaddo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Formed new call: " <<
*NewCall << "\n" << " from load ptr=" <<
*LoadEv << " at: " << *TheLoad << "\n" <<
" from store ptr=" << *StoreEv << " at: " <<
*TheStore << "\n"; } } while (false)
1513 << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Formed new call: " <<
*NewCall << "\n" << " from load ptr=" <<
*LoadEv << " at: " << *TheLoad << "\n" <<
" from store ptr=" << *StoreEv << " at: " <<
*TheStore << "\n"; } } while (false)
1514 << " from store ptr=" << *StoreEv << " at: " << *TheStoredo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Formed new call: " <<
*NewCall << "\n" << " from load ptr=" <<
*LoadEv << " at: " << *TheLoad << "\n" <<
" from store ptr=" << *StoreEv << " at: " <<
*TheStore << "\n"; } } while (false)
1515 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Formed new call: " <<
*NewCall << "\n" << " from load ptr=" <<
*LoadEv << " at: " << *TheLoad << "\n" <<
" from store ptr=" << *StoreEv << " at: " <<
*TheStore << "\n"; } } while (false)
;
1516
1517 ORE.emit([&]() {
1518 return OptimizationRemark(DEBUG_TYPE"loop-idiom", "ProcessLoopStoreOfLoopLoad",
1519 NewCall->getDebugLoc(), Preheader)
1520 << "Formed a call to "
1521 << ore::NV("NewFunction", NewCall->getCalledFunction())
1522 << "() intrinsic from " << ore::NV("Inst", InstRemark)
1523 << " instruction in " << ore::NV("Function", TheStore->getFunction())
1524 << " function"
1525 << ore::setExtraArgs()
1526 << ore::NV("FromBlock", TheStore->getParent()->getName())
1527 << ore::NV("ToBlock", Preheader->getName());
1528 });
1529
1530 // Okay, a new call to memcpy/memmove has been formed. Zap the original store
1531 // and anything that feeds into it.
1532 if (MSSAU)
1533 MSSAU->removeMemoryAccess(TheStore, true);
1534 deleteDeadInstruction(TheStore);
1535 if (MSSAU && VerifyMemorySSA)
1536 MSSAU->getMemorySSA()->verifyMemorySSA();
1537 if (UseMemMove)
1538 ++NumMemMove;
1539 else
1540 ++NumMemCpy;
1541 ExpCleaner.markResultUsed();
1542 return true;
1543}
1544
1545// When compiling for codesize we avoid idiom recognition for a multi-block loop
1546// unless it is a loop_memset idiom or a memset/memcpy idiom in a nested loop.
1547//
1548bool LoopIdiomRecognize::avoidLIRForMultiBlockLoop(bool IsMemset,
1549 bool IsLoopMemset) {
1550 if (ApplyCodeSizeHeuristics && CurLoop->getNumBlocks() > 1) {
1551 if (CurLoop->isOutermost() && (!IsMemset || !IsLoopMemset)) {
1552 LLVM_DEBUG(dbgs() << " " << CurLoop->getHeader()->getParent()->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " " << CurLoop->getHeader
()->getParent()->getName() << " : LIR " << (
IsMemset ? "Memset" : "Memcpy") << " avoided: multi-block top-level loop\n"
; } } while (false)
1553 << " : LIR " << (IsMemset ? "Memset" : "Memcpy")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " " << CurLoop->getHeader
()->getParent()->getName() << " : LIR " << (
IsMemset ? "Memset" : "Memcpy") << " avoided: multi-block top-level loop\n"
; } } while (false)
1554 << " avoided: multi-block top-level loop\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " " << CurLoop->getHeader
()->getParent()->getName() << " : LIR " << (
IsMemset ? "Memset" : "Memcpy") << " avoided: multi-block top-level loop\n"
; } } while (false)
;
1555 return true;
1556 }
1557 }
1558
1559 return false;
1560}
1561
1562bool LoopIdiomRecognize::runOnNoncountableLoop() {
1563 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Scanning: F["do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Scanning: F["
<< CurLoop->getHeader()->getParent()->getName
() << "] Noncountable Loop %" << CurLoop->getHeader
()->getName() << "\n"; } } while (false)
11
Assuming 'DebugFlag' is false
1564 << CurLoop->getHeader()->getParent()->getName()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Scanning: F["
<< CurLoop->getHeader()->getParent()->getName
() << "] Noncountable Loop %" << CurLoop->getHeader
()->getName() << "\n"; } } while (false)
1565 << "] Noncountable Loop %"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Scanning: F["
<< CurLoop->getHeader()->getParent()->getName
() << "] Noncountable Loop %" << CurLoop->getHeader
()->getName() << "\n"; } } while (false)
1566 << CurLoop->getHeader()->getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Scanning: F["
<< CurLoop->getHeader()->getParent()->getName
() << "] Noncountable Loop %" << CurLoop->getHeader
()->getName() << "\n"; } } while (false)
;
1567
1568 return recognizePopcount() || recognizeAndInsertFFS() ||
12
Calling 'LoopIdiomRecognize::recognizeAndInsertFFS'
1569 recognizeShiftUntilBitTest() || recognizeShiftUntilZero();
1570}
1571
1572/// Check if the given conditional branch is based on the comparison between
1573/// a variable and zero, and if the variable is non-zero or zero (JmpOnZero is
1574/// true), the control yields to the loop entry. If the branch matches the
1575/// behavior, the variable involved in the comparison is returned. This function
1576/// will be called to see if the precondition and postcondition of the loop are
1577/// in desirable form.
1578static Value *matchCondition(BranchInst *BI, BasicBlock *LoopEntry,
1579 bool JmpOnZero = false) {
1580 if (!BI || !BI->isConditional())
1581 return nullptr;
1582
1583 ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
1584 if (!Cond)
1585 return nullptr;
1586
1587 ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
1588 if (!CmpZero || !CmpZero->isZero())
1589 return nullptr;
1590
1591 BasicBlock *TrueSucc = BI->getSuccessor(0);
1592 BasicBlock *FalseSucc = BI->getSuccessor(1);
1593 if (JmpOnZero)
1594 std::swap(TrueSucc, FalseSucc);
1595
1596 ICmpInst::Predicate Pred = Cond->getPredicate();
1597 if ((Pred == ICmpInst::ICMP_NE && TrueSucc == LoopEntry) ||
1598 (Pred == ICmpInst::ICMP_EQ && FalseSucc == LoopEntry))
1599 return Cond->getOperand(0);
1600
1601 return nullptr;
1602}
1603
1604// Check if the recurrence variable `VarX` is in the right form to create
1605// the idiom. Returns the value coerced to a PHINode if so.
1606static PHINode *getRecurrenceVar(Value *VarX, Instruction *DefX,
1607 BasicBlock *LoopEntry) {
1608 auto *PhiX = dyn_cast<PHINode>(VarX);
1609 if (PhiX && PhiX->getParent() == LoopEntry &&
1610 (PhiX->getOperand(0) == DefX || PhiX->getOperand(1) == DefX))
1611 return PhiX;
1612 return nullptr;
1613}
1614
1615/// Return true iff the idiom is detected in the loop.
1616///
1617/// Additionally:
1618/// 1) \p CntInst is set to the instruction counting the population bit.
1619/// 2) \p CntPhi is set to the corresponding phi node.
1620/// 3) \p Var is set to the value whose population bits are being counted.
1621///
1622/// The core idiom we are trying to detect is:
1623/// \code
1624/// if (x0 != 0)
1625/// goto loop-exit // the precondition of the loop
1626/// cnt0 = init-val;
1627/// do {
1628/// x1 = phi (x0, x2);
1629/// cnt1 = phi(cnt0, cnt2);
1630///
1631/// cnt2 = cnt1 + 1;
1632/// ...
1633/// x2 = x1 & (x1 - 1);
1634/// ...
1635/// } while(x != 0);
1636///
1637/// loop-exit:
1638/// \endcode
1639static bool detectPopcountIdiom(Loop *CurLoop, BasicBlock *PreCondBB,
1640 Instruction *&CntInst, PHINode *&CntPhi,
1641 Value *&Var) {
1642 // step 1: Check to see if the look-back branch match this pattern:
1643 // "if (a!=0) goto loop-entry".
1644 BasicBlock *LoopEntry;
1645 Instruction *DefX2, *CountInst;
1646 Value *VarX1, *VarX0;
1647 PHINode *PhiX, *CountPhi;
1648
1649 DefX2 = CountInst = nullptr;
1650 VarX1 = VarX0 = nullptr;
1651 PhiX = CountPhi = nullptr;
1652 LoopEntry = *(CurLoop->block_begin());
1653
1654 // step 1: Check if the loop-back branch is in desirable form.
1655 {
1656 if (Value *T = matchCondition(
1657 dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
1658 DefX2 = dyn_cast<Instruction>(T);
1659 else
1660 return false;
1661 }
1662
1663 // step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
1664 {
1665 if (!DefX2 || DefX2->getOpcode() != Instruction::And)
1666 return false;
1667
1668 BinaryOperator *SubOneOp;
1669
1670 if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
1671 VarX1 = DefX2->getOperand(1);
1672 else {
1673 VarX1 = DefX2->getOperand(0);
1674 SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
1675 }
1676 if (!SubOneOp || SubOneOp->getOperand(0) != VarX1)
1677 return false;
1678
1679 ConstantInt *Dec = dyn_cast<ConstantInt>(SubOneOp->getOperand(1));
1680 if (!Dec ||
1681 !((SubOneOp->getOpcode() == Instruction::Sub && Dec->isOne()) ||
1682 (SubOneOp->getOpcode() == Instruction::Add &&
1683 Dec->isMinusOne()))) {
1684 return false;
1685 }
1686 }
1687
1688 // step 3: Check the recurrence of variable X
1689 PhiX = getRecurrenceVar(VarX1, DefX2, LoopEntry);
1690 if (!PhiX)
1691 return false;
1692
1693 // step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
1694 {
1695 CountInst = nullptr;
1696 for (Instruction &Inst : llvm::make_range(
1697 LoopEntry->getFirstNonPHI()->getIterator(), LoopEntry->end())) {
1698 if (Inst.getOpcode() != Instruction::Add)
1699 continue;
1700
1701 ConstantInt *Inc = dyn_cast<ConstantInt>(Inst.getOperand(1));
1702 if (!Inc || !Inc->isOne())
1703 continue;
1704
1705 PHINode *Phi = getRecurrenceVar(Inst.getOperand(0), &Inst, LoopEntry);
1706 if (!Phi)
1707 continue;
1708
1709 // Check if the result of the instruction is live of the loop.
1710 bool LiveOutLoop = false;
1711 for (User *U : Inst.users()) {
1712 if ((cast<Instruction>(U))->getParent() != LoopEntry) {
1713 LiveOutLoop = true;
1714 break;
1715 }
1716 }
1717
1718 if (LiveOutLoop) {
1719 CountInst = &Inst;
1720 CountPhi = Phi;
1721 break;
1722 }
1723 }
1724
1725 if (!CountInst)
1726 return false;
1727 }
1728
1729 // step 5: check if the precondition is in this form:
1730 // "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
1731 {
1732 auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
1733 Value *T = matchCondition(PreCondBr, CurLoop->getLoopPreheader());
1734 if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
1735 return false;
1736
1737 CntInst = CountInst;
1738 CntPhi = CountPhi;
1739 Var = T;
1740 }
1741
1742 return true;
1743}
1744
1745/// Return true if the idiom is detected in the loop.
1746///
1747/// Additionally:
1748/// 1) \p CntInst is set to the instruction Counting Leading Zeros (CTLZ)
1749/// or nullptr if there is no such.
1750/// 2) \p CntPhi is set to the corresponding phi node
1751/// or nullptr if there is no such.
1752/// 3) \p Var is set to the value whose CTLZ could be used.
1753/// 4) \p DefX is set to the instruction calculating Loop exit condition.
1754///
1755/// The core idiom we are trying to detect is:
1756/// \code
1757/// if (x0 == 0)
1758/// goto loop-exit // the precondition of the loop
1759/// cnt0 = init-val;
1760/// do {
1761/// x = phi (x0, x.next); //PhiX
1762/// cnt = phi(cnt0, cnt.next);
1763///
1764/// cnt.next = cnt + 1;
1765/// ...
1766/// x.next = x >> 1; // DefX
1767/// ...
1768/// } while(x.next != 0);
1769///
1770/// loop-exit:
1771/// \endcode
1772static bool detectShiftUntilZeroIdiom(Loop *CurLoop, const DataLayout &DL,
1773 Intrinsic::ID &IntrinID, Value *&InitX,
1774 Instruction *&CntInst, PHINode *&CntPhi,
1775 Instruction *&DefX) {
1776 BasicBlock *LoopEntry;
1777 Value *VarX = nullptr;
1778
1779 DefX = nullptr;
1780 CntInst = nullptr;
1781 CntPhi = nullptr;
1782 LoopEntry = *(CurLoop->block_begin());
1783
1784 // step 1: Check if the loop-back branch is in desirable form.
1785 if (Value *T = matchCondition(
18
Assuming 'T' is non-null, which participates in a condition later
19
Taking true branch
1786 dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
17
Assuming the object is not a 'CastReturnType'
1787 DefX = dyn_cast<Instruction>(T);
20
Assuming 'T' is a 'CastReturnType'
1788 else
1789 return false;
1790
1791 // step 2: detect instructions corresponding to "x.next = x >> 1 or x << 1"
1792 if (!DefX
20.1
'DefX' is non-null
|| !DefX->isShift())
21
Assuming the condition is false
1793 return false;
1794 IntrinID = DefX->getOpcode() == Instruction::Shl ? Intrinsic::cttz :
22
Taking false branch
23
Assuming the condition is false
24
'?' condition is false
1795 Intrinsic::ctlz;
1796 ConstantInt *Shft = dyn_cast<ConstantInt>(DefX->getOperand(1));
25
Assuming the object is a 'CastReturnType'
1797 if (!Shft
25.1
'Shft' is non-null, which participates in a condition later
|| !Shft->isOne())
26
Assuming the condition is false
27
Taking false branch
1798 return false;
1799 VarX = DefX->getOperand(0);
1800
1801 // step 3: Check the recurrence of variable X
1802 PHINode *PhiX = getRecurrenceVar(VarX, DefX, LoopEntry);
1803 if (!PhiX)
28
Assuming 'PhiX' is non-null, which participates in a condition later
29
Taking false branch
1804 return false;
1805
1806 InitX = PhiX->getIncomingValueForBlock(CurLoop->getLoopPreheader());
30
Value assigned to 'InitX'
1807
1808 // Make sure the initial value can't be negative otherwise the ashr in the
1809 // loop might never reach zero which would make the loop infinite.
1810 if (DefX->getOpcode() == Instruction::AShr && !isKnownNonNegative(InitX, DL))
31
Assuming the condition is false
1811 return false;
1812
1813 // step 4: Find the instruction which count the CTLZ: cnt.next = cnt + 1
1814 // or cnt.next = cnt + -1.
1815 // TODO: We can skip the step. If loop trip count is known (CTLZ),
1816 // then all uses of "cnt.next" could be optimized to the trip count
1817 // plus "cnt0". Currently it is not optimized.
1818 // This step could be used to detect POPCNT instruction:
1819 // cnt.next = cnt + (x.next & 1)
1820 for (Instruction &Inst : llvm::make_range(
1821 LoopEntry->getFirstNonPHI()->getIterator(), LoopEntry->end())) {
1822 if (Inst.getOpcode() != Instruction::Add)
32
Assuming the condition is false
33
Taking false branch
1823 continue;
1824
1825 ConstantInt *Inc = dyn_cast<ConstantInt>(Inst.getOperand(1));
34
Assuming the object is a 'CastReturnType'
1826 if (!Inc
34.1
'Inc' is non-null
|| (!Inc->isOne() && !Inc->isMinusOne()))
35
Assuming the condition is false
1827 continue;
1828
1829 PHINode *Phi = getRecurrenceVar(Inst.getOperand(0), &Inst, LoopEntry);
1830 if (!Phi)
36
Assuming 'Phi' is non-null
37
Taking false branch
1831 continue;
1832
1833 CntInst = &Inst;
1834 CntPhi = Phi;
1835 break;
1836 }
1837 if (!CntInst
38.1
'CntInst' is non-null
)
38
Execution continues on line 1837
39
Taking false branch
1838 return false;
1839
1840 return true;
1841}
1842
1843/// Recognize CTLZ or CTTZ idiom in a non-countable loop and convert the loop
1844/// to countable (with CTLZ / CTTZ trip count). If CTLZ / CTTZ inserted as a new
1845/// trip count returns true; otherwise, returns false.
1846bool LoopIdiomRecognize::recognizeAndInsertFFS() {
1847 // Give up if the loop has multiple blocks or multiple backedges.
1848 if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
13
Assuming the condition is false
14
Assuming the condition is false
15
Taking false branch
1849 return false;
1850
1851 Intrinsic::ID IntrinID;
1852 Value *InitX;
1853 Instruction *DefX = nullptr;
1854 PHINode *CntPhi = nullptr;
1855 Instruction *CntInst = nullptr;
1856 // Help decide if transformation is profitable. For ShiftUntilZero idiom,
1857 // this is always 6.
1858 size_t IdiomCanonicalSize = 6;
1859
1860 if (!detectShiftUntilZeroIdiom(CurLoop, *DL, IntrinID, InitX,
16
Calling 'detectShiftUntilZeroIdiom'
40
Returning from 'detectShiftUntilZeroIdiom'
41
Taking false branch
1861 CntInst, CntPhi, DefX))
1862 return false;
1863
1864 bool IsCntPhiUsedOutsideLoop = false;
1865 for (User *U : CntPhi->users())
1866 if (!CurLoop->contains(cast<Instruction>(U))) {
1867 IsCntPhiUsedOutsideLoop = true;
1868 break;
1869 }
1870 bool IsCntInstUsedOutsideLoop = false;
1871 for (User *U : CntInst->users())
1872 if (!CurLoop->contains(cast<Instruction>(U))) {
1873 IsCntInstUsedOutsideLoop = true;
1874 break;
1875 }
1876 // If both CntInst and CntPhi are used outside the loop the profitability
1877 // is questionable.
1878 if (IsCntInstUsedOutsideLoop
41.1
'IsCntInstUsedOutsideLoop' is false
&& IsCntPhiUsedOutsideLoop)
1879 return false;
1880
1881 // For some CPUs result of CTLZ(X) intrinsic is undefined
1882 // when X is 0. If we can not guarantee X != 0, we need to check this
1883 // when expand.
1884 bool ZeroCheck = false;
1885 // It is safe to assume Preheader exist as it was checked in
1886 // parent function RunOnLoop.
1887 BasicBlock *PH = CurLoop->getLoopPreheader();
1888
1889 // If we are using the count instruction outside the loop, make sure we
1890 // have a zero check as a precondition. Without the check the loop would run
1891 // one iteration for before any check of the input value. This means 0 and 1
1892 // would have identical behavior in the original loop and thus
1893 if (!IsCntPhiUsedOutsideLoop
41.2
'IsCntPhiUsedOutsideLoop' is false
) {
42
Taking true branch
1894 auto *PreCondBB = PH->getSinglePredecessor();
1895 if (!PreCondBB)
43
Assuming 'PreCondBB' is non-null
44
Taking false branch
1896 return false;
1897 auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
45
Assuming the object is a 'CastReturnType'
1898 if (!PreCondBI
45.1
'PreCondBI' is non-null
)
46
Taking false branch
1899 return false;
1900 if (matchCondition(PreCondBI, PH) != InitX)
47
Assuming pointer value is null
48
Taking false branch
1901 return false;
1902 ZeroCheck = true;
1903 }
1904
1905 // Check if CTLZ / CTTZ intrinsic is profitable. Assume it is always
1906 // profitable if we delete the loop.
1907
1908 // the loop has only 6 instructions:
1909 // %n.addr.0 = phi [ %n, %entry ], [ %shr, %while.cond ]
1910 // %i.0 = phi [ %i0, %entry ], [ %inc, %while.cond ]
1911 // %shr = ashr %n.addr.0, 1
1912 // %tobool = icmp eq %shr, 0
1913 // %inc = add nsw %i.0, 1
1914 // br i1 %tobool
1915
1916 const Value *Args[] = {InitX,
1917 ConstantInt::getBool(InitX->getContext(), ZeroCheck)};
49
Called C++ object pointer is null
1918
1919 // @llvm.dbg doesn't count as they have no semantic effect.
1920 auto InstWithoutDebugIt = CurLoop->getHeader()->instructionsWithoutDebug();
1921 uint32_t HeaderSize =
1922 std::distance(InstWithoutDebugIt.begin(), InstWithoutDebugIt.end());
1923
1924 IntrinsicCostAttributes Attrs(IntrinID, InitX->getType(), Args);
1925 InstructionCost Cost =
1926 TTI->getIntrinsicInstrCost(Attrs, TargetTransformInfo::TCK_SizeAndLatency);
1927 if (HeaderSize != IdiomCanonicalSize &&
1928 Cost > TargetTransformInfo::TCC_Basic)
1929 return false;
1930
1931 transformLoopToCountable(IntrinID, PH, CntInst, CntPhi, InitX, DefX,
1932 DefX->getDebugLoc(), ZeroCheck,
1933 IsCntPhiUsedOutsideLoop);
1934 return true;
1935}
1936
1937/// Recognizes a population count idiom in a non-countable loop.
1938///
1939/// If detected, transforms the relevant code to issue the popcount intrinsic
1940/// function call, and returns true; otherwise, returns false.
1941bool LoopIdiomRecognize::recognizePopcount() {
1942 if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
1943 return false;
1944
1945 // Counting population are usually conducted by few arithmetic instructions.
1946 // Such instructions can be easily "absorbed" by vacant slots in a
1947 // non-compact loop. Therefore, recognizing popcount idiom only makes sense
1948 // in a compact loop.
1949
1950 // Give up if the loop has multiple blocks or multiple backedges.
1951 if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
1952 return false;
1953
1954 BasicBlock *LoopBody = *(CurLoop->block_begin());
1955 if (LoopBody->size() >= 20) {
1956 // The loop is too big, bail out.
1957 return false;
1958 }
1959
1960 // It should have a preheader containing nothing but an unconditional branch.
1961 BasicBlock *PH = CurLoop->getLoopPreheader();
1962 if (!PH || &PH->front() != PH->getTerminator())
1963 return false;
1964 auto *EntryBI = dyn_cast<BranchInst>(PH->getTerminator());
1965 if (!EntryBI || EntryBI->isConditional())
1966 return false;
1967
1968 // It should have a precondition block where the generated popcount intrinsic
1969 // function can be inserted.
1970 auto *PreCondBB = PH->getSinglePredecessor();
1971 if (!PreCondBB)
1972 return false;
1973 auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
1974 if (!PreCondBI || PreCondBI->isUnconditional())
1975 return false;
1976
1977 Instruction *CntInst;
1978 PHINode *CntPhi;
1979 Value *Val;
1980 if (!detectPopcountIdiom(CurLoop, PreCondBB, CntInst, CntPhi, Val))
1981 return false;
1982
1983 transformLoopToPopcount(PreCondBB, CntInst, CntPhi, Val);
1984 return true;
1985}
1986
1987static CallInst *createPopcntIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
1988 const DebugLoc &DL) {
1989 Value *Ops[] = {Val};
1990 Type *Tys[] = {Val->getType()};
1991
1992 Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
1993 Function *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
1994 CallInst *CI = IRBuilder.CreateCall(Func, Ops);
1995 CI->setDebugLoc(DL);
1996
1997 return CI;
1998}
1999
2000static CallInst *createFFSIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
2001 const DebugLoc &DL, bool ZeroCheck,
2002 Intrinsic::ID IID) {
2003 Value *Ops[] = {Val, IRBuilder.getInt1(ZeroCheck)};
2004 Type *Tys[] = {Val->getType()};
2005
2006 Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
2007 Function *Func = Intrinsic::getDeclaration(M, IID, Tys);
2008 CallInst *CI = IRBuilder.CreateCall(Func, Ops);
2009 CI->setDebugLoc(DL);
2010
2011 return CI;
2012}
2013
2014/// Transform the following loop (Using CTLZ, CTTZ is similar):
2015/// loop:
2016/// CntPhi = PHI [Cnt0, CntInst]
2017/// PhiX = PHI [InitX, DefX]
2018/// CntInst = CntPhi + 1
2019/// DefX = PhiX >> 1
2020/// LOOP_BODY
2021/// Br: loop if (DefX != 0)
2022/// Use(CntPhi) or Use(CntInst)
2023///
2024/// Into:
2025/// If CntPhi used outside the loop:
2026/// CountPrev = BitWidth(InitX) - CTLZ(InitX >> 1)
2027/// Count = CountPrev + 1
2028/// else
2029/// Count = BitWidth(InitX) - CTLZ(InitX)
2030/// loop:
2031/// CntPhi = PHI [Cnt0, CntInst]
2032/// PhiX = PHI [InitX, DefX]
2033/// PhiCount = PHI [Count, Dec]
2034/// CntInst = CntPhi + 1
2035/// DefX = PhiX >> 1
2036/// Dec = PhiCount - 1
2037/// LOOP_BODY
2038/// Br: loop if (Dec != 0)
2039/// Use(CountPrev + Cnt0) // Use(CntPhi)
2040/// or
2041/// Use(Count + Cnt0) // Use(CntInst)
2042///
2043/// If LOOP_BODY is empty the loop will be deleted.
2044/// If CntInst and DefX are not used in LOOP_BODY they will be removed.
2045void LoopIdiomRecognize::transformLoopToCountable(
2046 Intrinsic::ID IntrinID, BasicBlock *Preheader, Instruction *CntInst,
2047 PHINode *CntPhi, Value *InitX, Instruction *DefX, const DebugLoc &DL,
2048 bool ZeroCheck, bool IsCntPhiUsedOutsideLoop) {
2049 BranchInst *PreheaderBr = cast<BranchInst>(Preheader->getTerminator());
2050
2051 // Step 1: Insert the CTLZ/CTTZ instruction at the end of the preheader block
2052 IRBuilder<> Builder(PreheaderBr);
2053 Builder.SetCurrentDebugLocation(DL);
2054
2055 // If there are no uses of CntPhi crate:
2056 // Count = BitWidth - CTLZ(InitX);
2057 // NewCount = Count;
2058 // If there are uses of CntPhi create:
2059 // NewCount = BitWidth - CTLZ(InitX >> 1);
2060 // Count = NewCount + 1;
2061 Value *InitXNext;
2062 if (IsCntPhiUsedOutsideLoop) {
2063 if (DefX->getOpcode() == Instruction::AShr)
2064 InitXNext = Builder.CreateAShr(InitX, 1);
2065 else if (DefX->getOpcode() == Instruction::LShr)
2066 InitXNext = Builder.CreateLShr(InitX, 1);
2067 else if (DefX->getOpcode() == Instruction::Shl) // cttz
2068 InitXNext = Builder.CreateShl(InitX, 1);
2069 else
2070 llvm_unreachable("Unexpected opcode!")::llvm::llvm_unreachable_internal("Unexpected opcode!", "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp"
, 2070)
;
2071 } else
2072 InitXNext = InitX;
2073 Value *Count =
2074 createFFSIntrinsic(Builder, InitXNext, DL, ZeroCheck, IntrinID);
2075 Type *CountTy = Count->getType();
2076 Count = Builder.CreateSub(
2077 ConstantInt::get(CountTy, CountTy->getIntegerBitWidth()), Count);
2078 Value *NewCount = Count;
2079 if (IsCntPhiUsedOutsideLoop)
2080 Count = Builder.CreateAdd(Count, ConstantInt::get(CountTy, 1));
2081
2082 NewCount = Builder.CreateZExtOrTrunc(NewCount, CntInst->getType());
2083
2084 Value *CntInitVal = CntPhi->getIncomingValueForBlock(Preheader);
2085 if (cast<ConstantInt>(CntInst->getOperand(1))->isOne()) {
2086 // If the counter was being incremented in the loop, add NewCount to the
2087 // counter's initial value, but only if the initial value is not zero.
2088 ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
2089 if (!InitConst || !InitConst->isZero())
2090 NewCount = Builder.CreateAdd(NewCount, CntInitVal);
2091 } else {
2092 // If the count was being decremented in the loop, subtract NewCount from
2093 // the counter's initial value.
2094 NewCount = Builder.CreateSub(CntInitVal, NewCount);
2095 }
2096
2097 // Step 2: Insert new IV and loop condition:
2098 // loop:
2099 // ...
2100 // PhiCount = PHI [Count, Dec]
2101 // ...
2102 // Dec = PhiCount - 1
2103 // ...
2104 // Br: loop if (Dec != 0)
2105 BasicBlock *Body = *(CurLoop->block_begin());
2106 auto *LbBr = cast<BranchInst>(Body->getTerminator());
2107 ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
2108
2109 PHINode *TcPhi = PHINode::Create(CountTy, 2, "tcphi", &Body->front());
2110
2111 Builder.SetInsertPoint(LbCond);
2112 Instruction *TcDec = cast<Instruction>(Builder.CreateSub(
2113 TcPhi, ConstantInt::get(CountTy, 1), "tcdec", false, true));
2114
2115 TcPhi->addIncoming(Count, Preheader);
2116 TcPhi->addIncoming(TcDec, Body);
2117
2118 CmpInst::Predicate Pred =
2119 (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_NE : CmpInst::ICMP_EQ;
2120 LbCond->setPredicate(Pred);
2121 LbCond->setOperand(0, TcDec);
2122 LbCond->setOperand(1, ConstantInt::get(CountTy, 0));
2123
2124 // Step 3: All the references to the original counter outside
2125 // the loop are replaced with the NewCount
2126 if (IsCntPhiUsedOutsideLoop)
2127 CntPhi->replaceUsesOutsideBlock(NewCount, Body);
2128 else
2129 CntInst->replaceUsesOutsideBlock(NewCount, Body);
2130
2131 // step 4: Forget the "non-computable" trip-count SCEV associated with the
2132 // loop. The loop would otherwise not be deleted even if it becomes empty.
2133 SE->forgetLoop(CurLoop);
2134}
2135
2136void LoopIdiomRecognize::transformLoopToPopcount(BasicBlock *PreCondBB,
2137 Instruction *CntInst,
2138 PHINode *CntPhi, Value *Var) {
2139 BasicBlock *PreHead = CurLoop->getLoopPreheader();
2140 auto *PreCondBr = cast<BranchInst>(PreCondBB->getTerminator());
2141 const DebugLoc &DL = CntInst->getDebugLoc();
2142
2143 // Assuming before transformation, the loop is following:
2144 // if (x) // the precondition
2145 // do { cnt++; x &= x - 1; } while(x);
2146
2147 // Step 1: Insert the ctpop instruction at the end of the precondition block
2148 IRBuilder<> Builder(PreCondBr);
2149 Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
2150 {
2151 PopCnt = createPopcntIntrinsic(Builder, Var, DL);
2152 NewCount = PopCntZext =
2153 Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));
2154
2155 if (NewCount != PopCnt)
2156 (cast<Instruction>(NewCount))->setDebugLoc(DL);
2157
2158 // TripCnt is exactly the number of iterations the loop has
2159 TripCnt = NewCount;
2160
2161 // If the population counter's initial value is not zero, insert Add Inst.
2162 Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
2163 ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
2164 if (!InitConst || !InitConst->isZero()) {
2165 NewCount = Builder.CreateAdd(NewCount, CntInitVal);
2166 (cast<Instruction>(NewCount))->setDebugLoc(DL);
2167 }
2168 }
2169
2170 // Step 2: Replace the precondition from "if (x == 0) goto loop-exit" to
2171 // "if (NewCount == 0) loop-exit". Without this change, the intrinsic
2172 // function would be partial dead code, and downstream passes will drag
2173 // it back from the precondition block to the preheader.
2174 {
2175 ICmpInst *PreCond = cast<ICmpInst>(PreCondBr->getCondition());
2176
2177 Value *Opnd0 = PopCntZext;
2178 Value *Opnd1 = ConstantInt::get(PopCntZext->getType(), 0);
2179 if (PreCond->getOperand(0) != Var)
2180 std::swap(Opnd0, Opnd1);
2181
2182 ICmpInst *NewPreCond = cast<ICmpInst>(
2183 Builder.CreateICmp(PreCond->getPredicate(), Opnd0, Opnd1));
2184 PreCondBr->setCondition(NewPreCond);
2185
2186 RecursivelyDeleteTriviallyDeadInstructions(PreCond, TLI);
2187 }
2188
2189 // Step 3: Note that the population count is exactly the trip count of the
2190 // loop in question, which enable us to convert the loop from noncountable
2191 // loop into a countable one. The benefit is twofold:
2192 //
2193 // - If the loop only counts population, the entire loop becomes dead after
2194 // the transformation. It is a lot easier to prove a countable loop dead
2195 // than to prove a noncountable one. (In some C dialects, an infinite loop
2196 // isn't dead even if it computes nothing useful. In general, DCE needs
2197 // to prove a noncountable loop finite before safely delete it.)
2198 //
2199 // - If the loop also performs something else, it remains alive.
2200 // Since it is transformed to countable form, it can be aggressively
2201 // optimized by some optimizations which are in general not applicable
2202 // to a noncountable loop.
2203 //
2204 // After this step, this loop (conceptually) would look like following:
2205 // newcnt = __builtin_ctpop(x);
2206 // t = newcnt;
2207 // if (x)
2208 // do { cnt++; x &= x-1; t--) } while (t > 0);
2209 BasicBlock *Body = *(CurLoop->block_begin());
2210 {
2211 auto *LbBr = cast<BranchInst>(Body->getTerminator());
2212 ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
2213 Type *Ty = TripCnt->getType();
2214
2215 PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", &Body->front());
2216
2217 Builder.SetInsertPoint(LbCond);
2218 Instruction *TcDec = cast<Instruction>(
2219 Builder.CreateSub(TcPhi, ConstantInt::get(Ty, 1),
2220 "tcdec", false, true));
2221
2222 TcPhi->addIncoming(TripCnt, PreHead);
2223 TcPhi->addIncoming(TcDec, Body);
2224
2225 CmpInst::Predicate Pred =
2226 (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_UGT : CmpInst::ICMP_SLE;
2227 LbCond->setPredicate(Pred);
2228 LbCond->setOperand(0, TcDec);
2229 LbCond->setOperand(1, ConstantInt::get(Ty, 0));
2230 }
2231
2232 // Step 4: All the references to the original population counter outside
2233 // the loop are replaced with the NewCount -- the value returned from
2234 // __builtin_ctpop().
2235 CntInst->replaceUsesOutsideBlock(NewCount, Body);
2236
2237 // step 5: Forget the "non-computable" trip-count SCEV associated with the
2238 // loop. The loop would otherwise not be deleted even if it becomes empty.
2239 SE->forgetLoop(CurLoop);
2240}
2241
2242/// Match loop-invariant value.
2243template <typename SubPattern_t> struct match_LoopInvariant {
2244 SubPattern_t SubPattern;
2245 const Loop *L;
2246
2247 match_LoopInvariant(const SubPattern_t &SP, const Loop *L)
2248 : SubPattern(SP), L(L) {}
2249
2250 template <typename ITy> bool match(ITy *V) {
2251 return L->isLoopInvariant(V) && SubPattern.match(V);
2252 }
2253};
2254
2255/// Matches if the value is loop-invariant.
2256template <typename Ty>
2257inline match_LoopInvariant<Ty> m_LoopInvariant(const Ty &M, const Loop *L) {
2258 return match_LoopInvariant<Ty>(M, L);
2259}
2260
2261/// Return true if the idiom is detected in the loop.
2262///
2263/// The core idiom we are trying to detect is:
2264/// \code
2265/// entry:
2266/// <...>
2267/// %bitmask = shl i32 1, %bitpos
2268/// br label %loop
2269///
2270/// loop:
2271/// %x.curr = phi i32 [ %x, %entry ], [ %x.next, %loop ]
2272/// %x.curr.bitmasked = and i32 %x.curr, %bitmask
2273/// %x.curr.isbitunset = icmp eq i32 %x.curr.bitmasked, 0
2274/// %x.next = shl i32 %x.curr, 1
2275/// <...>
2276/// br i1 %x.curr.isbitunset, label %loop, label %end
2277///
2278/// end:
2279/// %x.curr.res = phi i32 [ %x.curr, %loop ] <...>
2280/// %x.next.res = phi i32 [ %x.next, %loop ] <...>
2281/// <...>
2282/// \endcode
2283static bool detectShiftUntilBitTestIdiom(Loop *CurLoop, Value *&BaseX,
2284 Value *&BitMask, Value *&BitPos,
2285 Value *&CurrX, Instruction *&NextX) {
2286 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Performing shift-until-bittest idiom detection.\n"
; } } while (false)
2287 " Performing shift-until-bittest idiom detection.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Performing shift-until-bittest idiom detection.\n"
; } } while (false)
;
2288
2289 // Give up if the loop has multiple blocks or multiple backedges.
2290 if (CurLoop->getNumBlocks() != 1 || CurLoop->getNumBackEdges() != 1) {
2291 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad block/backedge count.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad block/backedge count.\n"
; } } while (false)
;
2292 return false;
2293 }
2294
2295 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2296 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2297 assert(LoopPreheaderBB && "There is always a loop preheader.")(static_cast <bool> (LoopPreheaderBB && "There is always a loop preheader."
) ? void (0) : __assert_fail ("LoopPreheaderBB && \"There is always a loop preheader.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2297, __extension__
__PRETTY_FUNCTION__))
;
2298
2299 using namespace PatternMatch;
2300
2301 // Step 1: Check if the loop backedge is in desirable form.
2302
2303 ICmpInst::Predicate Pred;
2304 Value *CmpLHS, *CmpRHS;
2305 BasicBlock *TrueBB, *FalseBB;
2306 if (!match(LoopHeaderBB->getTerminator(),
2307 m_Br(m_ICmp(Pred, m_Value(CmpLHS), m_Value(CmpRHS)),
2308 m_BasicBlock(TrueBB), m_BasicBlock(FalseBB)))) {
2309 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad backedge structure.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad backedge structure.\n"
; } } while (false)
;
2310 return false;
2311 }
2312
2313 // Step 2: Check if the backedge's condition is in desirable form.
2314
2315 auto MatchVariableBitMask = [&]() {
2316 return ICmpInst::isEquality(Pred) && match(CmpRHS, m_Zero()) &&
2317 match(CmpLHS,
2318 m_c_And(m_Value(CurrX),
2319 m_CombineAnd(
2320 m_Value(BitMask),
2321 m_LoopInvariant(m_Shl(m_One(), m_Value(BitPos)),
2322 CurLoop))));
2323 };
2324 auto MatchConstantBitMask = [&]() {
2325 return ICmpInst::isEquality(Pred) && match(CmpRHS, m_Zero()) &&
2326 match(CmpLHS, m_And(m_Value(CurrX),
2327 m_CombineAnd(m_Value(BitMask), m_Power2()))) &&
2328 (BitPos = ConstantExpr::getExactLogBase2(cast<Constant>(BitMask)));
2329 };
2330 auto MatchDecomposableConstantBitMask = [&]() {
2331 APInt Mask;
2332 return llvm::decomposeBitTestICmp(CmpLHS, CmpRHS, Pred, CurrX, Mask) &&
2333 ICmpInst::isEquality(Pred) && Mask.isPowerOf2() &&
2334 (BitMask = ConstantInt::get(CurrX->getType(), Mask)) &&
2335 (BitPos = ConstantInt::get(CurrX->getType(), Mask.logBase2()));
2336 };
2337
2338 if (!MatchVariableBitMask() && !MatchConstantBitMask() &&
2339 !MatchDecomposableConstantBitMask()) {
2340 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad backedge comparison.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad backedge comparison.\n"
; } } while (false)
;
2341 return false;
2342 }
2343
2344 // Step 3: Check if the recurrence is in desirable form.
2345 auto *CurrXPN = dyn_cast<PHINode>(CurrX);
2346 if (!CurrXPN || CurrXPN->getParent() != LoopHeaderBB) {
2347 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Not an expected PHI node.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Not an expected PHI node.\n"
; } } while (false)
;
2348 return false;
2349 }
2350
2351 BaseX = CurrXPN->getIncomingValueForBlock(LoopPreheaderBB);
2352 NextX =
2353 dyn_cast<Instruction>(CurrXPN->getIncomingValueForBlock(LoopHeaderBB));
2354
2355 assert(CurLoop->isLoopInvariant(BaseX) &&(static_cast <bool> (CurLoop->isLoopInvariant(BaseX)
&& "Expected BaseX to be avaliable in the preheader!"
) ? void (0) : __assert_fail ("CurLoop->isLoopInvariant(BaseX) && \"Expected BaseX to be avaliable in the preheader!\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2356, __extension__
__PRETTY_FUNCTION__))
2356 "Expected BaseX to be avaliable in the preheader!")(static_cast <bool> (CurLoop->isLoopInvariant(BaseX)
&& "Expected BaseX to be avaliable in the preheader!"
) ? void (0) : __assert_fail ("CurLoop->isLoopInvariant(BaseX) && \"Expected BaseX to be avaliable in the preheader!\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2356, __extension__
__PRETTY_FUNCTION__))
;
2357
2358 if (!NextX || !match(NextX, m_Shl(m_Specific(CurrX), m_One()))) {
2359 // FIXME: support right-shift?
2360 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad recurrence.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad recurrence.\n"
; } } while (false)
;
2361 return false;
2362 }
2363
2364 // Step 4: Check if the backedge's destinations are in desirable form.
2365
2366 assert(ICmpInst::isEquality(Pred) &&(static_cast <bool> (ICmpInst::isEquality(Pred) &&
"Should only get equality predicates here.") ? void (0) : __assert_fail
("ICmpInst::isEquality(Pred) && \"Should only get equality predicates here.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2367, __extension__
__PRETTY_FUNCTION__))
2367 "Should only get equality predicates here.")(static_cast <bool> (ICmpInst::isEquality(Pred) &&
"Should only get equality predicates here.") ? void (0) : __assert_fail
("ICmpInst::isEquality(Pred) && \"Should only get equality predicates here.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2367, __extension__
__PRETTY_FUNCTION__))
;
2368
2369 // cmp-br is commutative, so canonicalize to a single variant.
2370 if (Pred != ICmpInst::Predicate::ICMP_EQ) {
2371 Pred = ICmpInst::getInversePredicate(Pred);
2372 std::swap(TrueBB, FalseBB);
2373 }
2374
2375 // We expect to exit loop when comparison yields false,
2376 // so when it yields true we should branch back to loop header.
2377 if (TrueBB != LoopHeaderBB) {
2378 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad backedge flow.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad backedge flow.\n"
; } } while (false)
;
2379 return false;
2380 }
2381
2382 // Okay, idiom checks out.
2383 return true;
2384}
2385
2386/// Look for the following loop:
2387/// \code
2388/// entry:
2389/// <...>
2390/// %bitmask = shl i32 1, %bitpos
2391/// br label %loop
2392///
2393/// loop:
2394/// %x.curr = phi i32 [ %x, %entry ], [ %x.next, %loop ]
2395/// %x.curr.bitmasked = and i32 %x.curr, %bitmask
2396/// %x.curr.isbitunset = icmp eq i32 %x.curr.bitmasked, 0
2397/// %x.next = shl i32 %x.curr, 1
2398/// <...>
2399/// br i1 %x.curr.isbitunset, label %loop, label %end
2400///
2401/// end:
2402/// %x.curr.res = phi i32 [ %x.curr, %loop ] <...>
2403/// %x.next.res = phi i32 [ %x.next, %loop ] <...>
2404/// <...>
2405/// \endcode
2406///
2407/// And transform it into:
2408/// \code
2409/// entry:
2410/// %bitmask = shl i32 1, %bitpos
2411/// %lowbitmask = add i32 %bitmask, -1
2412/// %mask = or i32 %lowbitmask, %bitmask
2413/// %x.masked = and i32 %x, %mask
2414/// %x.masked.numleadingzeros = call i32 @llvm.ctlz.i32(i32 %x.masked,
2415/// i1 true)
2416/// %x.masked.numactivebits = sub i32 32, %x.masked.numleadingzeros
2417/// %x.masked.leadingonepos = add i32 %x.masked.numactivebits, -1
2418/// %backedgetakencount = sub i32 %bitpos, %x.masked.leadingonepos
2419/// %tripcount = add i32 %backedgetakencount, 1
2420/// %x.curr = shl i32 %x, %backedgetakencount
2421/// %x.next = shl i32 %x, %tripcount
2422/// br label %loop
2423///
2424/// loop:
2425/// %loop.iv = phi i32 [ 0, %entry ], [ %loop.iv.next, %loop ]
2426/// %loop.iv.next = add nuw i32 %loop.iv, 1
2427/// %loop.ivcheck = icmp eq i32 %loop.iv.next, %tripcount
2428/// <...>
2429/// br i1 %loop.ivcheck, label %end, label %loop
2430///
2431/// end:
2432/// %x.curr.res = phi i32 [ %x.curr, %loop ] <...>
2433/// %x.next.res = phi i32 [ %x.next, %loop ] <...>
2434/// <...>
2435/// \endcode
2436bool LoopIdiomRecognize::recognizeShiftUntilBitTest() {
2437 bool MadeChange = false;
2438
2439 Value *X, *BitMask, *BitPos, *XCurr;
2440 Instruction *XNext;
2441 if (!detectShiftUntilBitTestIdiom(CurLoop, X, BitMask, BitPos, XCurr,
2442 XNext)) {
2443 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " shift-until-bittest idiom detection failed.\n"
; } } while (false)
2444 " shift-until-bittest idiom detection failed.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " shift-until-bittest idiom detection failed.\n"
; } } while (false)
;
2445 return MadeChange;
2446 }
2447 LLVM_DEBUG(dbgs() << DEBUG_TYPE " shift-until-bittest idiom detected!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " shift-until-bittest idiom detected!\n"
; } } while (false)
;
2448
2449 // Ok, it is the idiom we were looking for, we *could* transform this loop,
2450 // but is it profitable to transform?
2451
2452 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2453 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2454 assert(LoopPreheaderBB && "There is always a loop preheader.")(static_cast <bool> (LoopPreheaderBB && "There is always a loop preheader."
) ? void (0) : __assert_fail ("LoopPreheaderBB && \"There is always a loop preheader.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2454, __extension__
__PRETTY_FUNCTION__))
;
2455
2456 BasicBlock *SuccessorBB = CurLoop->getExitBlock();
2457 assert(SuccessorBB && "There is only a single successor.")(static_cast <bool> (SuccessorBB && "There is only a single successor."
) ? void (0) : __assert_fail ("SuccessorBB && \"There is only a single successor.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2457, __extension__
__PRETTY_FUNCTION__))
;
2458
2459 IRBuilder<> Builder(LoopPreheaderBB->getTerminator());
2460 Builder.SetCurrentDebugLocation(cast<Instruction>(XCurr)->getDebugLoc());
2461
2462 Intrinsic::ID IntrID = Intrinsic::ctlz;
2463 Type *Ty = X->getType();
2464 unsigned Bitwidth = Ty->getScalarSizeInBits();
2465
2466 TargetTransformInfo::TargetCostKind CostKind =
2467 TargetTransformInfo::TCK_SizeAndLatency;
2468
2469 // The rewrite is considered to be unprofitable iff and only iff the
2470 // intrinsic/shift we'll use are not cheap. Note that we are okay with *just*
2471 // making the loop countable, even if nothing else changes.
2472 IntrinsicCostAttributes Attrs(
2473 IntrID, Ty, {UndefValue::get(Ty), /*is_zero_undef=*/Builder.getTrue()});
2474 InstructionCost Cost = TTI->getIntrinsicInstrCost(Attrs, CostKind);
2475 if (Cost > TargetTransformInfo::TCC_Basic) {
2476 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Intrinsic is too costly, not beneficial\n"
; } } while (false)
2477 " Intrinsic is too costly, not beneficial\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Intrinsic is too costly, not beneficial\n"
; } } while (false)
;
2478 return MadeChange;
2479 }
2480 if (TTI->getArithmeticInstrCost(Instruction::Shl, Ty, CostKind) >
2481 TargetTransformInfo::TCC_Basic) {
2482 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Shift is too costly, not beneficial\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Shift is too costly, not beneficial\n"
; } } while (false)
;
2483 return MadeChange;
2484 }
2485
2486 // Ok, transform appears worthwhile.
2487 MadeChange = true;
2488
2489 // Step 1: Compute the loop trip count.
2490
2491 Value *LowBitMask = Builder.CreateAdd(BitMask, Constant::getAllOnesValue(Ty),
2492 BitPos->getName() + ".lowbitmask");
2493 Value *Mask =
2494 Builder.CreateOr(LowBitMask, BitMask, BitPos->getName() + ".mask");
2495 Value *XMasked = Builder.CreateAnd(X, Mask, X->getName() + ".masked");
2496 CallInst *XMaskedNumLeadingZeros = Builder.CreateIntrinsic(
2497 IntrID, Ty, {XMasked, /*is_zero_undef=*/Builder.getTrue()},
2498 /*FMFSource=*/nullptr, XMasked->getName() + ".numleadingzeros");
2499 Value *XMaskedNumActiveBits = Builder.CreateSub(
2500 ConstantInt::get(Ty, Ty->getScalarSizeInBits()), XMaskedNumLeadingZeros,
2501 XMasked->getName() + ".numactivebits", /*HasNUW=*/true,
2502 /*HasNSW=*/Bitwidth != 2);
2503 Value *XMaskedLeadingOnePos =
2504 Builder.CreateAdd(XMaskedNumActiveBits, Constant::getAllOnesValue(Ty),
2505 XMasked->getName() + ".leadingonepos", /*HasNUW=*/false,
2506 /*HasNSW=*/Bitwidth > 2);
2507
2508 Value *LoopBackedgeTakenCount = Builder.CreateSub(
2509 BitPos, XMaskedLeadingOnePos, CurLoop->getName() + ".backedgetakencount",
2510 /*HasNUW=*/true, /*HasNSW=*/true);
2511 // We know loop's backedge-taken count, but what's loop's trip count?
2512 // Note that while NUW is always safe, while NSW is only for bitwidths != 2.
2513 Value *LoopTripCount =
2514 Builder.CreateAdd(LoopBackedgeTakenCount, ConstantInt::get(Ty, 1),
2515 CurLoop->getName() + ".tripcount", /*HasNUW=*/true,
2516 /*HasNSW=*/Bitwidth != 2);
2517
2518 // Step 2: Compute the recurrence's final value without a loop.
2519
2520 // NewX is always safe to compute, because `LoopBackedgeTakenCount`
2521 // will always be smaller than `bitwidth(X)`, i.e. we never get poison.
2522 Value *NewX = Builder.CreateShl(X, LoopBackedgeTakenCount);
2523 NewX->takeName(XCurr);
2524 if (auto *I = dyn_cast<Instruction>(NewX))
2525 I->copyIRFlags(XNext, /*IncludeWrapFlags=*/true);
2526
2527 Value *NewXNext;
2528 // Rewriting XNext is more complicated, however, because `X << LoopTripCount`
2529 // will be poison iff `LoopTripCount == bitwidth(X)` (which will happen
2530 // iff `BitPos` is `bitwidth(x) - 1` and `X` is `1`). So unless we know
2531 // that isn't the case, we'll need to emit an alternative, safe IR.
2532 if (XNext->hasNoSignedWrap() || XNext->hasNoUnsignedWrap() ||
2533 PatternMatch::match(
2534 BitPos, PatternMatch::m_SpecificInt_ICMP(
2535 ICmpInst::ICMP_NE, APInt(Ty->getScalarSizeInBits(),
2536 Ty->getScalarSizeInBits() - 1))))
2537 NewXNext = Builder.CreateShl(X, LoopTripCount);
2538 else {
2539 // Otherwise, just additionally shift by one. It's the smallest solution,
2540 // alternatively, we could check that NewX is INT_MIN (or BitPos is )
2541 // and select 0 instead.
2542 NewXNext = Builder.CreateShl(NewX, ConstantInt::get(Ty, 1));
2543 }
2544
2545 NewXNext->takeName(XNext);
2546 if (auto *I = dyn_cast<Instruction>(NewXNext))
2547 I->copyIRFlags(XNext, /*IncludeWrapFlags=*/true);
2548
2549 // Step 3: Adjust the successor basic block to recieve the computed
2550 // recurrence's final value instead of the recurrence itself.
2551
2552 XCurr->replaceUsesOutsideBlock(NewX, LoopHeaderBB);
2553 XNext->replaceUsesOutsideBlock(NewXNext, LoopHeaderBB);
2554
2555 // Step 4: Rewrite the loop into a countable form, with canonical IV.
2556
2557 // The new canonical induction variable.
2558 Builder.SetInsertPoint(&LoopHeaderBB->front());
2559 auto *IV = Builder.CreatePHI(Ty, 2, CurLoop->getName() + ".iv");
2560
2561 // The induction itself.
2562 // Note that while NUW is always safe, while NSW is only for bitwidths != 2.
2563 Builder.SetInsertPoint(LoopHeaderBB->getTerminator());
2564 auto *IVNext =
2565 Builder.CreateAdd(IV, ConstantInt::get(Ty, 1), IV->getName() + ".next",
2566 /*HasNUW=*/true, /*HasNSW=*/Bitwidth != 2);
2567
2568 // The loop trip count check.
2569 auto *IVCheck = Builder.CreateICmpEQ(IVNext, LoopTripCount,
2570 CurLoop->getName() + ".ivcheck");
2571 Builder.CreateCondBr(IVCheck, SuccessorBB, LoopHeaderBB);
2572 LoopHeaderBB->getTerminator()->eraseFromParent();
2573
2574 // Populate the IV PHI.
2575 IV->addIncoming(ConstantInt::get(Ty, 0), LoopPreheaderBB);
2576 IV->addIncoming(IVNext, LoopHeaderBB);
2577
2578 // Step 5: Forget the "non-computable" trip-count SCEV associated with the
2579 // loop. The loop would otherwise not be deleted even if it becomes empty.
2580
2581 SE->forgetLoop(CurLoop);
2582
2583 // Other passes will take care of actually deleting the loop if possible.
2584
2585 LLVM_DEBUG(dbgs() << DEBUG_TYPE " shift-until-bittest idiom optimized!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " shift-until-bittest idiom optimized!\n"
; } } while (false)
;
2586
2587 ++NumShiftUntilBitTest;
2588 return MadeChange;
2589}
2590
2591/// Return true if the idiom is detected in the loop.
2592///
2593/// The core idiom we are trying to detect is:
2594/// \code
2595/// entry:
2596/// <...>
2597/// %start = <...>
2598/// %extraoffset = <...>
2599/// <...>
2600/// br label %for.cond
2601///
2602/// loop:
2603/// %iv = phi i8 [ %start, %entry ], [ %iv.next, %for.cond ]
2604/// %nbits = add nsw i8 %iv, %extraoffset
2605/// %val.shifted = {{l,a}shr,shl} i8 %val, %nbits
2606/// %val.shifted.iszero = icmp eq i8 %val.shifted, 0
2607/// %iv.next = add i8 %iv, 1
2608/// <...>
2609/// br i1 %val.shifted.iszero, label %end, label %loop
2610///
2611/// end:
2612/// %iv.res = phi i8 [ %iv, %loop ] <...>
2613/// %nbits.res = phi i8 [ %nbits, %loop ] <...>
2614/// %val.shifted.res = phi i8 [ %val.shifted, %loop ] <...>
2615/// %val.shifted.iszero.res = phi i1 [ %val.shifted.iszero, %loop ] <...>
2616/// %iv.next.res = phi i8 [ %iv.next, %loop ] <...>
2617/// <...>
2618/// \endcode
2619static bool detectShiftUntilZeroIdiom(Loop *CurLoop, ScalarEvolution *SE,
2620 Instruction *&ValShiftedIsZero,
2621 Intrinsic::ID &IntrinID, Instruction *&IV,
2622 Value *&Start, Value *&Val,
2623 const SCEV *&ExtraOffsetExpr,
2624 bool &InvertedCond) {
2625 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Performing shift-until-zero idiom detection.\n"
; } } while (false)
2626 " Performing shift-until-zero idiom detection.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Performing shift-until-zero idiom detection.\n"
; } } while (false)
;
2627
2628 // Give up if the loop has multiple blocks or multiple backedges.
2629 if (CurLoop->getNumBlocks() != 1 || CurLoop->getNumBackEdges() != 1) {
2630 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad block/backedge count.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad block/backedge count.\n"
; } } while (false)
;
2631 return false;
2632 }
2633
2634 Instruction *ValShifted, *NBits, *IVNext;
2635 Value *ExtraOffset;
2636
2637 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2638 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2639 assert(LoopPreheaderBB && "There is always a loop preheader.")(static_cast <bool> (LoopPreheaderBB && "There is always a loop preheader."
) ? void (0) : __assert_fail ("LoopPreheaderBB && \"There is always a loop preheader.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2639, __extension__
__PRETTY_FUNCTION__))
;
2640
2641 using namespace PatternMatch;
2642
2643 // Step 1: Check if the loop backedge, condition is in desirable form.
2644
2645 ICmpInst::Predicate Pred;
2646 BasicBlock *TrueBB, *FalseBB;
2647 if (!match(LoopHeaderBB->getTerminator(),
2648 m_Br(m_Instruction(ValShiftedIsZero), m_BasicBlock(TrueBB),
2649 m_BasicBlock(FalseBB))) ||
2650 !match(ValShiftedIsZero,
2651 m_ICmp(Pred, m_Instruction(ValShifted), m_Zero())) ||
2652 !ICmpInst::isEquality(Pred)) {
2653 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad backedge structure.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad backedge structure.\n"
; } } while (false)
;
2654 return false;
2655 }
2656
2657 // Step 2: Check if the comparison's operand is in desirable form.
2658 // FIXME: Val could be a one-input PHI node, which we should look past.
2659 if (!match(ValShifted, m_Shift(m_LoopInvariant(m_Value(Val), CurLoop),
2660 m_Instruction(NBits)))) {
2661 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad comparisons value computation.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad comparisons value computation.\n"
; } } while (false)
;
2662 return false;
2663 }
2664 IntrinID = ValShifted->getOpcode() == Instruction::Shl ? Intrinsic::cttz
2665 : Intrinsic::ctlz;
2666
2667 // Step 3: Check if the shift amount is in desirable form.
2668
2669 if (match(NBits, m_c_Add(m_Instruction(IV),
2670 m_LoopInvariant(m_Value(ExtraOffset), CurLoop))) &&
2671 (NBits->hasNoSignedWrap() || NBits->hasNoUnsignedWrap()))
2672 ExtraOffsetExpr = SE->getNegativeSCEV(SE->getSCEV(ExtraOffset));
2673 else if (match(NBits,
2674 m_Sub(m_Instruction(IV),
2675 m_LoopInvariant(m_Value(ExtraOffset), CurLoop))) &&
2676 NBits->hasNoSignedWrap())
2677 ExtraOffsetExpr = SE->getSCEV(ExtraOffset);
2678 else {
2679 IV = NBits;
2680 ExtraOffsetExpr = SE->getZero(NBits->getType());
2681 }
2682
2683 // Step 4: Check if the recurrence is in desirable form.
2684 auto *IVPN = dyn_cast<PHINode>(IV);
2685 if (!IVPN || IVPN->getParent() != LoopHeaderBB) {
2686 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Not an expected PHI node.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Not an expected PHI node.\n"
; } } while (false)
;
2687 return false;
2688 }
2689
2690 Start = IVPN->getIncomingValueForBlock(LoopPreheaderBB);
2691 IVNext = dyn_cast<Instruction>(IVPN->getIncomingValueForBlock(LoopHeaderBB));
2692
2693 if (!IVNext || !match(IVNext, m_Add(m_Specific(IVPN), m_One()))) {
2694 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad recurrence.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad recurrence.\n"
; } } while (false)
;
2695 return false;
2696 }
2697
2698 // Step 4: Check if the backedge's destinations are in desirable form.
2699
2700 assert(ICmpInst::isEquality(Pred) &&(static_cast <bool> (ICmpInst::isEquality(Pred) &&
"Should only get equality predicates here.") ? void (0) : __assert_fail
("ICmpInst::isEquality(Pred) && \"Should only get equality predicates here.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2701, __extension__
__PRETTY_FUNCTION__))
2701 "Should only get equality predicates here.")(static_cast <bool> (ICmpInst::isEquality(Pred) &&
"Should only get equality predicates here.") ? void (0) : __assert_fail
("ICmpInst::isEquality(Pred) && \"Should only get equality predicates here.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2701, __extension__
__PRETTY_FUNCTION__))
;
2702
2703 // cmp-br is commutative, so canonicalize to a single variant.
2704 InvertedCond = Pred != ICmpInst::Predicate::ICMP_EQ;
2705 if (InvertedCond) {
2706 Pred = ICmpInst::getInversePredicate(Pred);
2707 std::swap(TrueBB, FalseBB);
2708 }
2709
2710 // We expect to exit loop when comparison yields true,
2711 // so when it yields false we should branch back to loop header.
2712 if (FalseBB != LoopHeaderBB) {
2713 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad backedge flow.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad backedge flow.\n"
; } } while (false)
;
2714 return false;
2715 }
2716
2717 // The new, countable, loop will certainly only run a known number of
2718 // iterations, It won't be infinite. But the old loop might be infinite
2719 // under certain conditions. For logical shifts, the value will become zero
2720 // after at most bitwidth(%Val) loop iterations. However, for arithmetic
2721 // right-shift, iff the sign bit was set, the value will never become zero,
2722 // and the loop may never finish.
2723 if (ValShifted->getOpcode() == Instruction::AShr &&
2724 !isMustProgress(CurLoop) && !SE->isKnownNonNegative(SE->getSCEV(Val))) {
2725 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Can not prove the loop is finite.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Can not prove the loop is finite.\n"
; } } while (false)
;
2726 return false;
2727 }
2728
2729 // Okay, idiom checks out.
2730 return true;
2731}
2732
2733/// Look for the following loop:
2734/// \code
2735/// entry:
2736/// <...>
2737/// %start = <...>
2738/// %extraoffset = <...>
2739/// <...>
2740/// br label %for.cond
2741///
2742/// loop:
2743/// %iv = phi i8 [ %start, %entry ], [ %iv.next, %for.cond ]
2744/// %nbits = add nsw i8 %iv, %extraoffset
2745/// %val.shifted = {{l,a}shr,shl} i8 %val, %nbits
2746/// %val.shifted.iszero = icmp eq i8 %val.shifted, 0
2747/// %iv.next = add i8 %iv, 1
2748/// <...>
2749/// br i1 %val.shifted.iszero, label %end, label %loop
2750///
2751/// end:
2752/// %iv.res = phi i8 [ %iv, %loop ] <...>
2753/// %nbits.res = phi i8 [ %nbits, %loop ] <...>
2754/// %val.shifted.res = phi i8 [ %val.shifted, %loop ] <...>
2755/// %val.shifted.iszero.res = phi i1 [ %val.shifted.iszero, %loop ] <...>
2756/// %iv.next.res = phi i8 [ %iv.next, %loop ] <...>
2757/// <...>
2758/// \endcode
2759///
2760/// And transform it into:
2761/// \code
2762/// entry:
2763/// <...>
2764/// %start = <...>
2765/// %extraoffset = <...>
2766/// <...>
2767/// %val.numleadingzeros = call i8 @llvm.ct{l,t}z.i8(i8 %val, i1 0)
2768/// %val.numactivebits = sub i8 8, %val.numleadingzeros
2769/// %extraoffset.neg = sub i8 0, %extraoffset
2770/// %tmp = add i8 %val.numactivebits, %extraoffset.neg
2771/// %iv.final = call i8 @llvm.smax.i8(i8 %tmp, i8 %start)
2772/// %loop.tripcount = sub i8 %iv.final, %start
2773/// br label %loop
2774///
2775/// loop:
2776/// %loop.iv = phi i8 [ 0, %entry ], [ %loop.iv.next, %loop ]
2777/// %loop.iv.next = add i8 %loop.iv, 1
2778/// %loop.ivcheck = icmp eq i8 %loop.iv.next, %loop.tripcount
2779/// %iv = add i8 %loop.iv, %start
2780/// <...>
2781/// br i1 %loop.ivcheck, label %end, label %loop
2782///
2783/// end:
2784/// %iv.res = phi i8 [ %iv.final, %loop ] <...>
2785/// <...>
2786/// \endcode
2787bool LoopIdiomRecognize::recognizeShiftUntilZero() {
2788 bool MadeChange = false;
2789
2790 Instruction *ValShiftedIsZero;
2791 Intrinsic::ID IntrID;
2792 Instruction *IV;
2793 Value *Start, *Val;
2794 const SCEV *ExtraOffsetExpr;
2795 bool InvertedCond;
2796 if (!detectShiftUntilZeroIdiom(CurLoop, SE, ValShiftedIsZero, IntrID, IV,
2797 Start, Val, ExtraOffsetExpr, InvertedCond)) {
2798 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " shift-until-zero idiom detection failed.\n"
; } } while (false)
2799 " shift-until-zero idiom detection failed.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " shift-until-zero idiom detection failed.\n"
; } } while (false)
;
2800 return MadeChange;
2801 }
2802 LLVM_DEBUG(dbgs() << DEBUG_TYPE " shift-until-zero idiom detected!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " shift-until-zero idiom detected!\n"
; } } while (false)
;
2803
2804 // Ok, it is the idiom we were looking for, we *could* transform this loop,
2805 // but is it profitable to transform?
2806
2807 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2808 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2809 assert(LoopPreheaderBB && "There is always a loop preheader.")(static_cast <bool> (LoopPreheaderBB && "There is always a loop preheader."
) ? void (0) : __assert_fail ("LoopPreheaderBB && \"There is always a loop preheader.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2809, __extension__
__PRETTY_FUNCTION__))
;
2810
2811 BasicBlock *SuccessorBB = CurLoop->getExitBlock();
2812 assert(SuccessorBB && "There is only a single successor.")(static_cast <bool> (SuccessorBB && "There is only a single successor."
) ? void (0) : __assert_fail ("SuccessorBB && \"There is only a single successor.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 2812, __extension__
__PRETTY_FUNCTION__))
;
2813
2814 IRBuilder<> Builder(LoopPreheaderBB->getTerminator());
2815 Builder.SetCurrentDebugLocation(IV->getDebugLoc());
2816
2817 Type *Ty = Val->getType();
2818 unsigned Bitwidth = Ty->getScalarSizeInBits();
2819
2820 TargetTransformInfo::TargetCostKind CostKind =
2821 TargetTransformInfo::TCK_SizeAndLatency;
2822
2823 // The rewrite is considered to be unprofitable iff and only iff the
2824 // intrinsic we'll use are not cheap. Note that we are okay with *just*
2825 // making the loop countable, even if nothing else changes.
2826 IntrinsicCostAttributes Attrs(
2827 IntrID, Ty, {UndefValue::get(Ty), /*is_zero_undef=*/Builder.getFalse()});
2828 InstructionCost Cost = TTI->getIntrinsicInstrCost(Attrs, CostKind);
2829 if (Cost > TargetTransformInfo::TCC_Basic) {
2830 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Intrinsic is too costly, not beneficial\n"
; } } while (false)
2831 " Intrinsic is too costly, not beneficial\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Intrinsic is too costly, not beneficial\n"
; } } while (false)
;
2832 return MadeChange;
2833 }
2834
2835 // Ok, transform appears worthwhile.
2836 MadeChange = true;
2837
2838 bool OffsetIsZero = false;
2839 if (auto *ExtraOffsetExprC = dyn_cast<SCEVConstant>(ExtraOffsetExpr))
2840 OffsetIsZero = ExtraOffsetExprC->isZero();
2841
2842 // Step 1: Compute the loop's final IV value / trip count.
2843
2844 CallInst *ValNumLeadingZeros = Builder.CreateIntrinsic(
2845 IntrID, Ty, {Val, /*is_zero_undef=*/Builder.getFalse()},
2846 /*FMFSource=*/nullptr, Val->getName() + ".numleadingzeros");
2847 Value *ValNumActiveBits = Builder.CreateSub(
2848 ConstantInt::get(Ty, Ty->getScalarSizeInBits()), ValNumLeadingZeros,
2849 Val->getName() + ".numactivebits", /*HasNUW=*/true,
2850 /*HasNSW=*/Bitwidth != 2);
2851
2852 SCEVExpander Expander(*SE, *DL, "loop-idiom");
2853 Expander.setInsertPoint(&*Builder.GetInsertPoint());
2854 Value *ExtraOffset = Expander.expandCodeFor(ExtraOffsetExpr);
2855
2856 Value *ValNumActiveBitsOffset = Builder.CreateAdd(
2857 ValNumActiveBits, ExtraOffset, ValNumActiveBits->getName() + ".offset",
2858 /*HasNUW=*/OffsetIsZero, /*HasNSW=*/true);
2859 Value *IVFinal = Builder.CreateIntrinsic(Intrinsic::smax, {Ty},
2860 {ValNumActiveBitsOffset, Start},
2861 /*FMFSource=*/nullptr, "iv.final");
2862
2863 auto *LoopBackedgeTakenCount = cast<Instruction>(Builder.CreateSub(
2864 IVFinal, Start, CurLoop->getName() + ".backedgetakencount",
2865 /*HasNUW=*/OffsetIsZero, /*HasNSW=*/true));
2866 // FIXME: or when the offset was `add nuw`
2867
2868 // We know loop's backedge-taken count, but what's loop's trip count?
2869 Value *LoopTripCount =
2870 Builder.CreateAdd(LoopBackedgeTakenCount, ConstantInt::get(Ty, 1),
2871 CurLoop->getName() + ".tripcount", /*HasNUW=*/true,
2872 /*HasNSW=*/Bitwidth != 2);
2873
2874 // Step 2: Adjust the successor basic block to recieve the original
2875 // induction variable's final value instead of the orig. IV itself.
2876
2877 IV->replaceUsesOutsideBlock(IVFinal, LoopHeaderBB);
2878
2879 // Step 3: Rewrite the loop into a countable form, with canonical IV.
2880
2881 // The new canonical induction variable.
2882 Builder.SetInsertPoint(&LoopHeaderBB->front());
2883 auto *CIV = Builder.CreatePHI(Ty, 2, CurLoop->getName() + ".iv");
2884
2885 // The induction itself.
2886 Builder.SetInsertPoint(LoopHeaderBB->getFirstNonPHI());
2887 auto *CIVNext =
2888 Builder.CreateAdd(CIV, ConstantInt::get(Ty, 1), CIV->getName() + ".next",
2889 /*HasNUW=*/true, /*HasNSW=*/Bitwidth != 2);
2890
2891 // The loop trip count check.
2892 auto *CIVCheck = Builder.CreateICmpEQ(CIVNext, LoopTripCount,
2893 CurLoop->getName() + ".ivcheck");
2894 auto *NewIVCheck = CIVCheck;
2895 if (InvertedCond) {
2896 NewIVCheck = Builder.CreateNot(CIVCheck);
2897 NewIVCheck->takeName(ValShiftedIsZero);
2898 }
2899
2900 // The original IV, but rebased to be an offset to the CIV.
2901 auto *IVDePHId = Builder.CreateAdd(CIV, Start, "", /*HasNUW=*/false,
2902 /*HasNSW=*/true); // FIXME: what about NUW?
2903 IVDePHId->takeName(IV);
2904
2905 // The loop terminator.
2906 Builder.SetInsertPoint(LoopHeaderBB->getTerminator());
2907 Builder.CreateCondBr(CIVCheck, SuccessorBB, LoopHeaderBB);
2908 LoopHeaderBB->getTerminator()->eraseFromParent();
2909
2910 // Populate the IV PHI.
2911 CIV->addIncoming(ConstantInt::get(Ty, 0), LoopPreheaderBB);
2912 CIV->addIncoming(CIVNext, LoopHeaderBB);
2913
2914 // Step 4: Forget the "non-computable" trip-count SCEV associated with the
2915 // loop. The loop would otherwise not be deleted even if it becomes empty.
2916
2917 SE->forgetLoop(CurLoop);
2918
2919 // Step 5: Try to cleanup the loop's body somewhat.
2920 IV->replaceAllUsesWith(IVDePHId);
2921 IV->eraseFromParent();
2922
2923 ValShiftedIsZero->replaceAllUsesWith(NewIVCheck);
2924 ValShiftedIsZero->eraseFromParent();
2925
2926 // Other passes will take care of actually deleting the loop if possible.
2927
2928 LLVM_DEBUG(dbgs() << DEBUG_TYPE " shift-until-zero idiom optimized!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " shift-until-zero idiom optimized!\n"
; } } while (false)
;
2929
2930 ++NumShiftUntilZero;
2931 return MadeChange;
2932}