Bug Summary

File:llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
Warning:line 1905, 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-store=region -analyzer-opt-analyze-nested-blocks -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-14~++20220126111400+9b6c2ea30219/build-llvm -resource-dir /usr/lib/llvm-14/lib/clang/14.0.0 -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-14~++20220126111400+9b6c2ea30219/llvm/lib/Transforms/Scalar -I include -I /build/llvm-toolchain-snapshot-14~++20220126111400+9b6c2ea30219/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-14/lib/clang/14.0.0/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-14~++20220126111400+9b6c2ea30219/build-llvm=build-llvm -fmacro-prefix-map=/build/llvm-toolchain-snapshot-14~++20220126111400+9b6c2ea30219/= -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-14~++20220126111400+9b6c2ea30219/build-llvm=build-llvm -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-14~++20220126111400+9b6c2ea30219/= -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 -std=c++14 -fdeprecated-macro -fdebug-compilation-dir=/build/llvm-toolchain-snapshot-14~++20220126111400+9b6c2ea30219/build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-14~++20220126111400+9b6c2ea30219/build-llvm=build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-14~++20220126111400+9b6c2ea30219/= -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-2022-01-26-130535-15419-1 -x c++ /build/llvm-toolchain-snapshot-14~++20220126111400+9b6c2ea30219/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/Attributes.h"
65#include "llvm/IR/BasicBlock.h"
66#include "llvm/IR/Constant.h"
67#include "llvm/IR/Constants.h"
68#include "llvm/IR/DataLayout.h"
69#include "llvm/IR/DebugLoc.h"
70#include "llvm/IR/DerivedTypes.h"
71#include "llvm/IR/Dominators.h"
72#include "llvm/IR/GlobalValue.h"
73#include "llvm/IR/GlobalVariable.h"
74#include "llvm/IR/IRBuilder.h"
75#include "llvm/IR/InstrTypes.h"
76#include "llvm/IR/Instruction.h"
77#include "llvm/IR/Instructions.h"
78#include "llvm/IR/IntrinsicInst.h"
79#include "llvm/IR/Intrinsics.h"
80#include "llvm/IR/LLVMContext.h"
81#include "llvm/IR/Module.h"
82#include "llvm/IR/PassManager.h"
83#include "llvm/IR/PatternMatch.h"
84#include "llvm/IR/Type.h"
85#include "llvm/IR/User.h"
86#include "llvm/IR/Value.h"
87#include "llvm/IR/ValueHandle.h"
88#include "llvm/InitializePasses.h"
89#include "llvm/Pass.h"
90#include "llvm/Support/Casting.h"
91#include "llvm/Support/CommandLine.h"
92#include "llvm/Support/Debug.h"
93#include "llvm/Support/InstructionCost.h"
94#include "llvm/Support/raw_ostream.h"
95#include "llvm/Transforms/Scalar.h"
96#include "llvm/Transforms/Utils/BuildLibCalls.h"
97#include "llvm/Transforms/Utils/Local.h"
98#include "llvm/Transforms/Utils/LoopUtils.h"
99#include "llvm/Transforms/Utils/ScalarEvolutionExpander.h"
100#include <algorithm>
101#include <cassert>
102#include <cstdint>
103#include <utility>
104#include <vector>
105
106using namespace llvm;
107
108#define DEBUG_TYPE"loop-idiom" "loop-idiom"
109
110STATISTIC(NumMemSet, "Number of memset's formed from loop stores")static llvm::Statistic NumMemSet = {"loop-idiom", "NumMemSet"
, "Number of memset's formed from loop stores"}
;
111STATISTIC(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"}
;
112STATISTIC(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"}
;
113STATISTIC(static llvm::Statistic NumShiftUntilBitTest = {"loop-idiom", "NumShiftUntilBitTest"
, "Number of uncountable loops recognized as 'shift until bitttest' idiom"
}
114 NumShiftUntilBitTest,static llvm::Statistic NumShiftUntilBitTest = {"loop-idiom", "NumShiftUntilBitTest"
, "Number of uncountable loops recognized as 'shift until bitttest' idiom"
}
115 "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"
}
;
116STATISTIC(NumShiftUntilZero,static llvm::Statistic NumShiftUntilZero = {"loop-idiom", "NumShiftUntilZero"
, "Number of uncountable loops recognized as 'shift until zero' idiom"
}
117 "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"
}
;
118
119bool DisableLIRP::All;
120static cl::opt<bool, true>
121 DisableLIRPAll("disable-" DEBUG_TYPE"loop-idiom" "-all",
122 cl::desc("Options to disable Loop Idiom Recognize Pass."),
123 cl::location(DisableLIRP::All), cl::init(false),
124 cl::ReallyHidden);
125
126bool DisableLIRP::Memset;
127static cl::opt<bool, true>
128 DisableLIRPMemset("disable-" DEBUG_TYPE"loop-idiom" "-memset",
129 cl::desc("Proceed with loop idiom recognize pass, but do "
130 "not convert loop(s) to memset."),
131 cl::location(DisableLIRP::Memset), cl::init(false),
132 cl::ReallyHidden);
133
134bool DisableLIRP::Memcpy;
135static cl::opt<bool, true>
136 DisableLIRPMemcpy("disable-" DEBUG_TYPE"loop-idiom" "-memcpy",
137 cl::desc("Proceed with loop idiom recognize pass, but do "
138 "not convert loop(s) to memcpy."),
139 cl::location(DisableLIRP::Memcpy), cl::init(false),
140 cl::ReallyHidden);
141
142static cl::opt<bool> UseLIRCodeSizeHeurs(
143 "use-lir-code-size-heurs",
144 cl::desc("Use loop idiom recognition code size heuristics when compiling"
145 "with -Os/-Oz"),
146 cl::init(true), cl::Hidden);
147
148namespace {
149
150class LoopIdiomRecognize {
151 Loop *CurLoop = nullptr;
152 AliasAnalysis *AA;
153 DominatorTree *DT;
154 LoopInfo *LI;
155 ScalarEvolution *SE;
156 TargetLibraryInfo *TLI;
157 const TargetTransformInfo *TTI;
158 const DataLayout *DL;
159 OptimizationRemarkEmitter &ORE;
160 bool ApplyCodeSizeHeuristics;
161 std::unique_ptr<MemorySSAUpdater> MSSAU;
162
163public:
164 explicit LoopIdiomRecognize(AliasAnalysis *AA, DominatorTree *DT,
165 LoopInfo *LI, ScalarEvolution *SE,
166 TargetLibraryInfo *TLI,
167 const TargetTransformInfo *TTI, MemorySSA *MSSA,
168 const DataLayout *DL,
169 OptimizationRemarkEmitter &ORE)
170 : AA(AA), DT(DT), LI(LI), SE(SE), TLI(TLI), TTI(TTI), DL(DL), ORE(ORE) {
171 if (MSSA)
172 MSSAU = std::make_unique<MemorySSAUpdater>(MSSA);
173 }
174
175 bool runOnLoop(Loop *L);
176
177private:
178 using StoreList = SmallVector<StoreInst *, 8>;
179 using StoreListMap = MapVector<Value *, StoreList>;
180
181 StoreListMap StoreRefsForMemset;
182 StoreListMap StoreRefsForMemsetPattern;
183 StoreList StoreRefsForMemcpy;
184 bool HasMemset;
185 bool HasMemsetPattern;
186 bool HasMemcpy;
187
188 /// Return code for isLegalStore()
189 enum LegalStoreKind {
190 None = 0,
191 Memset,
192 MemsetPattern,
193 Memcpy,
194 UnorderedAtomicMemcpy,
195 DontUse // Dummy retval never to be used. Allows catching errors in retval
196 // handling.
197 };
198
199 /// \name Countable Loop Idiom Handling
200 /// @{
201
202 bool runOnCountableLoop();
203 bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
204 SmallVectorImpl<BasicBlock *> &ExitBlocks);
205
206 void collectStores(BasicBlock *BB);
207 LegalStoreKind isLegalStore(StoreInst *SI);
208 enum class ForMemset { No, Yes };
209 bool processLoopStores(SmallVectorImpl<StoreInst *> &SL, const SCEV *BECount,
210 ForMemset For);
211
212 template <typename MemInst>
213 bool processLoopMemIntrinsic(
214 BasicBlock *BB,
215 bool (LoopIdiomRecognize::*Processor)(MemInst *, const SCEV *),
216 const SCEV *BECount);
217 bool processLoopMemCpy(MemCpyInst *MCI, const SCEV *BECount);
218 bool processLoopMemSet(MemSetInst *MSI, const SCEV *BECount);
219
220 bool processLoopStridedStore(Value *DestPtr, const SCEV *StoreSizeSCEV,
221 MaybeAlign StoreAlignment, Value *StoredVal,
222 Instruction *TheStore,
223 SmallPtrSetImpl<Instruction *> &Stores,
224 const SCEVAddRecExpr *Ev, const SCEV *BECount,
225 bool IsNegStride, bool IsLoopMemset = false);
226 bool processLoopStoreOfLoopLoad(StoreInst *SI, const SCEV *BECount);
227 bool processLoopStoreOfLoopLoad(Value *DestPtr, Value *SourcePtr,
228 const SCEV *StoreSize, MaybeAlign StoreAlign,
229 MaybeAlign LoadAlign, Instruction *TheStore,
230 Instruction *TheLoad,
231 const SCEVAddRecExpr *StoreEv,
232 const SCEVAddRecExpr *LoadEv,
233 const SCEV *BECount);
234 bool avoidLIRForMultiBlockLoop(bool IsMemset = false,
235 bool IsLoopMemset = false);
236
237 /// @}
238 /// \name Noncountable Loop Idiom Handling
239 /// @{
240
241 bool runOnNoncountableLoop();
242
243 bool recognizePopcount();
244 void transformLoopToPopcount(BasicBlock *PreCondBB, Instruction *CntInst,
245 PHINode *CntPhi, Value *Var);
246 bool recognizeAndInsertFFS(); /// Find First Set: ctlz or cttz
247 void transformLoopToCountable(Intrinsic::ID IntrinID, BasicBlock *PreCondBB,
248 Instruction *CntInst, PHINode *CntPhi,
249 Value *Var, Instruction *DefX,
250 const DebugLoc &DL, bool ZeroCheck,
251 bool IsCntPhiUsedOutsideLoop);
252
253 bool recognizeShiftUntilBitTest();
254 bool recognizeShiftUntilZero();
255
256 /// @}
257};
258
259class LoopIdiomRecognizeLegacyPass : public LoopPass {
260public:
261 static char ID;
262
263 explicit LoopIdiomRecognizeLegacyPass() : LoopPass(ID) {
264 initializeLoopIdiomRecognizeLegacyPassPass(
265 *PassRegistry::getPassRegistry());
266 }
267
268 bool runOnLoop(Loop *L, LPPassManager &LPM) override {
269 if (DisableLIRP::All)
270 return false;
271
272 if (skipLoop(L))
273 return false;
274
275 AliasAnalysis *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
276 DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
277 LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
278 ScalarEvolution *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
279 TargetLibraryInfo *TLI =
280 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(
281 *L->getHeader()->getParent());
282 const TargetTransformInfo *TTI =
283 &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
284 *L->getHeader()->getParent());
285 const DataLayout *DL = &L->getHeader()->getModule()->getDataLayout();
286 auto *MSSAAnalysis = getAnalysisIfAvailable<MemorySSAWrapperPass>();
287 MemorySSA *MSSA = nullptr;
288 if (MSSAAnalysis)
289 MSSA = &MSSAAnalysis->getMSSA();
290
291 // For the old PM, we can't use OptimizationRemarkEmitter as an analysis
292 // pass. Function analyses need to be preserved across loop transformations
293 // but ORE cannot be preserved (see comment before the pass definition).
294 OptimizationRemarkEmitter ORE(L->getHeader()->getParent());
295
296 LoopIdiomRecognize LIR(AA, DT, LI, SE, TLI, TTI, MSSA, DL, ORE);
297 return LIR.runOnLoop(L);
298 }
299
300 /// This transformation requires natural loop information & requires that
301 /// loop preheaders be inserted into the CFG.
302 void getAnalysisUsage(AnalysisUsage &AU) const override {
303 AU.addRequired<TargetLibraryInfoWrapperPass>();
304 AU.addRequired<TargetTransformInfoWrapperPass>();
305 AU.addPreserved<MemorySSAWrapperPass>();
306 getLoopAnalysisUsage(AU);
307 }
308};
309
310} // end anonymous namespace
311
312char LoopIdiomRecognizeLegacyPass::ID = 0;
313
314PreservedAnalyses LoopIdiomRecognizePass::run(Loop &L, LoopAnalysisManager &AM,
315 LoopStandardAnalysisResults &AR,
316 LPMUpdater &) {
317 if (DisableLIRP::All)
1
Assuming 'All' is false
2
Taking false branch
318 return PreservedAnalyses::all();
319
320 const auto *DL = &L.getHeader()->getModule()->getDataLayout();
321
322 // For the new PM, we also can't use OptimizationRemarkEmitter as an analysis
323 // pass. Function analyses need to be preserved across loop transformations
324 // but ORE cannot be preserved (see comment before the pass definition).
325 OptimizationRemarkEmitter ORE(L.getHeader()->getParent());
326
327 LoopIdiomRecognize LIR(&AR.AA, &AR.DT, &AR.LI, &AR.SE, &AR.TLI, &AR.TTI,
328 AR.MSSA, DL, ORE);
329 if (!LIR.runOnLoop(&L))
3
Calling 'LoopIdiomRecognize::runOnLoop'
330 return PreservedAnalyses::all();
331
332 auto PA = getLoopPassPreservedAnalyses();
333 if (AR.MSSA)
334 PA.preserve<MemorySSAAnalysis>();
335 return PA;
336}
337
338INITIALIZE_PASS_BEGIN(LoopIdiomRecognizeLegacyPass, "loop-idiom",static void *initializeLoopIdiomRecognizeLegacyPassPassOnce(PassRegistry
&Registry) {
339 "Recognize loop idioms", false, false)static void *initializeLoopIdiomRecognizeLegacyPassPassOnce(PassRegistry
&Registry) {
340INITIALIZE_PASS_DEPENDENCY(LoopPass)initializeLoopPassPass(Registry);
341INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)initializeTargetLibraryInfoWrapperPassPass(Registry);
342INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)initializeTargetTransformInfoWrapperPassPass(Registry);
343INITIALIZE_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
)); }
344 "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
)); }
345
346Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognizeLegacyPass(); }
347
348static void deleteDeadInstruction(Instruction *I) {
349 I->replaceAllUsesWith(UndefValue::get(I->getType()));
350 I->eraseFromParent();
351}
352
353//===----------------------------------------------------------------------===//
354//
355// Implementation of LoopIdiomRecognize
356//
357//===----------------------------------------------------------------------===//
358
359bool LoopIdiomRecognize::runOnLoop(Loop *L) {
360 CurLoop = L;
361 // If the loop could not be converted to canonical form, it must have an
362 // indirectbr in it, just give up.
363 if (!L->getLoopPreheader())
4
Assuming the condition is false
5
Taking false branch
364 return false;
365
366 // Disable loop idiom recognition if the function's name is a common idiom.
367 StringRef Name = L->getHeader()->getParent()->getName();
368 if (Name == "memset" || Name == "memcpy")
6
Assuming the condition is false
7
Assuming the condition is false
369 return false;
370
371 // Determine if code size heuristics need to be applied.
372 ApplyCodeSizeHeuristics =
373 L->getHeader()->getParent()->hasOptSize() && UseLIRCodeSizeHeurs;
8
Assuming the condition is false
374
375 HasMemset = TLI->has(LibFunc_memset);
376 HasMemsetPattern = TLI->has(LibFunc_memset_pattern16);
377 HasMemcpy = TLI->has(LibFunc_memcpy);
378
379 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
380 if (SE->hasLoopInvariantBackedgeTakenCount(L))
381 return runOnCountableLoop();
382
383 return runOnNoncountableLoop();
10
Calling 'LoopIdiomRecognize::runOnNoncountableLoop'
384}
385
386bool LoopIdiomRecognize::runOnCountableLoop() {
387 const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
388 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", 390, __extension__
__PRETTY_FUNCTION__))
389 "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", 390, __extension__
__PRETTY_FUNCTION__))
390 "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", 390, __extension__
__PRETTY_FUNCTION__))
;
391
392 // If this loop executes exactly one time, then it should be peeled, not
393 // optimized by this pass.
394 if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
395 if (BECst->getAPInt() == 0)
396 return false;
397
398 SmallVector<BasicBlock *, 8> ExitBlocks;
399 CurLoop->getUniqueExitBlocks(ExitBlocks);
400
401 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)
402 << 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)
403 << "] 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)
404 << "\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)
;
405
406 // The following transforms hoist stores/memsets into the loop pre-header.
407 // Give up if the loop has instructions that may throw.
408 SimpleLoopSafetyInfo SafetyInfo;
409 SafetyInfo.computeLoopSafetyInfo(CurLoop);
410 if (SafetyInfo.anyBlockMayThrow())
411 return false;
412
413 bool MadeChange = false;
414
415 // Scan all the blocks in the loop that are not in subloops.
416 for (auto *BB : CurLoop->getBlocks()) {
417 // Ignore blocks in subloops.
418 if (LI->getLoopFor(BB) != CurLoop)
419 continue;
420
421 MadeChange |= runOnLoopBlock(BB, BECount, ExitBlocks);
422 }
423 return MadeChange;
424}
425
426static APInt getStoreStride(const SCEVAddRecExpr *StoreEv) {
427 const SCEVConstant *ConstStride = cast<SCEVConstant>(StoreEv->getOperand(1));
428 return ConstStride->getAPInt();
429}
430
431/// getMemSetPatternValue - If a strided store of the specified value is safe to
432/// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
433/// be passed in. Otherwise, return null.
434///
435/// Note that we don't ever attempt to use memset_pattern8 or 4, because these
436/// just replicate their input array and then pass on to memset_pattern16.
437static Constant *getMemSetPatternValue(Value *V, const DataLayout *DL) {
438 // FIXME: This could check for UndefValue because it can be merged into any
439 // other valid pattern.
440
441 // If the value isn't a constant, we can't promote it to being in a constant
442 // array. We could theoretically do a store to an alloca or something, but
443 // that doesn't seem worthwhile.
444 Constant *C = dyn_cast<Constant>(V);
445 if (!C)
446 return nullptr;
447
448 // Only handle simple values that are a power of two bytes in size.
449 uint64_t Size = DL->getTypeSizeInBits(V->getType());
450 if (Size == 0 || (Size & 7) || (Size & (Size - 1)))
451 return nullptr;
452
453 // Don't care enough about darwin/ppc to implement this.
454 if (DL->isBigEndian())
455 return nullptr;
456
457 // Convert to size in bytes.
458 Size /= 8;
459
460 // TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
461 // if the top and bottom are the same (e.g. for vectors and large integers).
462 if (Size > 16)
463 return nullptr;
464
465 // If the constant is exactly 16 bytes, just use it.
466 if (Size == 16)
467 return C;
468
469 // Otherwise, we'll use an array of the constants.
470 unsigned ArraySize = 16 / Size;
471 ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
472 return ConstantArray::get(AT, std::vector<Constant *>(ArraySize, C));
473}
474
475LoopIdiomRecognize::LegalStoreKind
476LoopIdiomRecognize::isLegalStore(StoreInst *SI) {
477 // Don't touch volatile stores.
478 if (SI->isVolatile())
479 return LegalStoreKind::None;
480 // We only want simple or unordered-atomic stores.
481 if (!SI->isUnordered())
482 return LegalStoreKind::None;
483
484 // Avoid merging nontemporal stores.
485 if (SI->getMetadata(LLVMContext::MD_nontemporal))
486 return LegalStoreKind::None;
487
488 Value *StoredVal = SI->getValueOperand();
489 Value *StorePtr = SI->getPointerOperand();
490
491 // Don't convert stores of non-integral pointer types to memsets (which stores
492 // integers).
493 if (DL->isNonIntegralPointerType(StoredVal->getType()->getScalarType()))
494 return LegalStoreKind::None;
495
496 // Reject stores that are so large that they overflow an unsigned.
497 // When storing out scalable vectors we bail out for now, since the code
498 // below currently only works for constant strides.
499 TypeSize SizeInBits = DL->getTypeSizeInBits(StoredVal->getType());
500 if (SizeInBits.isScalable() || (SizeInBits.getFixedSize() & 7) ||
501 (SizeInBits.getFixedSize() >> 32) != 0)
502 return LegalStoreKind::None;
503
504 // See if the pointer expression is an AddRec like {base,+,1} on the current
505 // loop, which indicates a strided store. If we have something else, it's a
506 // random store we can't handle.
507 const SCEVAddRecExpr *StoreEv =
508 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
509 if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
510 return LegalStoreKind::None;
511
512 // Check to see if we have a constant stride.
513 if (!isa<SCEVConstant>(StoreEv->getOperand(1)))
514 return LegalStoreKind::None;
515
516 // See if the store can be turned into a memset.
517
518 // If the stored value is a byte-wise value (like i32 -1), then it may be
519 // turned into a memset of i8 -1, assuming that all the consecutive bytes
520 // are stored. A store of i32 0x01020304 can never be turned into a memset,
521 // but it can be turned into memset_pattern if the target supports it.
522 Value *SplatValue = isBytewiseValue(StoredVal, *DL);
523
524 // Note: memset and memset_pattern on unordered-atomic is yet not supported
525 bool UnorderedAtomic = SI->isUnordered() && !SI->isSimple();
526
527 // If we're allowed to form a memset, and the stored value would be
528 // acceptable for memset, use it.
529 if (!UnorderedAtomic && HasMemset && SplatValue && !DisableLIRP::Memset &&
530 // Verify that the stored value is loop invariant. If not, we can't
531 // promote the memset.
532 CurLoop->isLoopInvariant(SplatValue)) {
533 // It looks like we can use SplatValue.
534 return LegalStoreKind::Memset;
535 }
536 if (!UnorderedAtomic && HasMemsetPattern && !DisableLIRP::Memset &&
537 // Don't create memset_pattern16s with address spaces.
538 StorePtr->getType()->getPointerAddressSpace() == 0 &&
539 getMemSetPatternValue(StoredVal, DL)) {
540 // It looks like we can use PatternValue!
541 return LegalStoreKind::MemsetPattern;
542 }
543
544 // Otherwise, see if the store can be turned into a memcpy.
545 if (HasMemcpy && !DisableLIRP::Memcpy) {
546 // Check to see if the stride matches the size of the store. If so, then we
547 // know that every byte is touched in the loop.
548 APInt Stride = getStoreStride(StoreEv);
549 unsigned StoreSize = DL->getTypeStoreSize(SI->getValueOperand()->getType());
550 if (StoreSize != Stride && StoreSize != -Stride)
551 return LegalStoreKind::None;
552
553 // The store must be feeding a non-volatile load.
554 LoadInst *LI = dyn_cast<LoadInst>(SI->getValueOperand());
555
556 // Only allow non-volatile loads
557 if (!LI || LI->isVolatile())
558 return LegalStoreKind::None;
559 // Only allow simple or unordered-atomic loads
560 if (!LI->isUnordered())
561 return LegalStoreKind::None;
562
563 // See if the pointer expression is an AddRec like {base,+,1} on the current
564 // loop, which indicates a strided load. If we have something else, it's a
565 // random load we can't handle.
566 const SCEVAddRecExpr *LoadEv =
567 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getPointerOperand()));
568 if (!LoadEv || LoadEv->getLoop() != CurLoop || !LoadEv->isAffine())
569 return LegalStoreKind::None;
570
571 // The store and load must share the same stride.
572 if (StoreEv->getOperand(1) != LoadEv->getOperand(1))
573 return LegalStoreKind::None;
574
575 // Success. This store can be converted into a memcpy.
576 UnorderedAtomic = UnorderedAtomic || LI->isAtomic();
577 return UnorderedAtomic ? LegalStoreKind::UnorderedAtomicMemcpy
578 : LegalStoreKind::Memcpy;
579 }
580 // This store can't be transformed into a memset/memcpy.
581 return LegalStoreKind::None;
582}
583
584void LoopIdiomRecognize::collectStores(BasicBlock *BB) {
585 StoreRefsForMemset.clear();
586 StoreRefsForMemsetPattern.clear();
587 StoreRefsForMemcpy.clear();
588 for (Instruction &I : *BB) {
589 StoreInst *SI = dyn_cast<StoreInst>(&I);
590 if (!SI)
591 continue;
592
593 // Make sure this is a strided store with a constant stride.
594 switch (isLegalStore(SI)) {
595 case LegalStoreKind::None:
596 // Nothing to do
597 break;
598 case LegalStoreKind::Memset: {
599 // Find the base pointer.
600 Value *Ptr = getUnderlyingObject(SI->getPointerOperand());
601 StoreRefsForMemset[Ptr].push_back(SI);
602 } break;
603 case LegalStoreKind::MemsetPattern: {
604 // Find the base pointer.
605 Value *Ptr = getUnderlyingObject(SI->getPointerOperand());
606 StoreRefsForMemsetPattern[Ptr].push_back(SI);
607 } break;
608 case LegalStoreKind::Memcpy:
609 case LegalStoreKind::UnorderedAtomicMemcpy:
610 StoreRefsForMemcpy.push_back(SI);
611 break;
612 default:
613 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", 613, __extension__
__PRETTY_FUNCTION__))
;
614 break;
615 }
616 }
617}
618
619/// runOnLoopBlock - Process the specified block, which lives in a counted loop
620/// with the specified backedge count. This block is known to be in the current
621/// loop and not in any subloops.
622bool LoopIdiomRecognize::runOnLoopBlock(
623 BasicBlock *BB, const SCEV *BECount,
624 SmallVectorImpl<BasicBlock *> &ExitBlocks) {
625 // We can only promote stores in this block if they are unconditionally
626 // executed in the loop. For a block to be unconditionally executed, it has
627 // to dominate all the exit blocks of the loop. Verify this now.
628 for (BasicBlock *ExitBlock : ExitBlocks)
629 if (!DT->dominates(BB, ExitBlock))
630 return false;
631
632 bool MadeChange = false;
633 // Look for store instructions, which may be optimized to memset/memcpy.
634 collectStores(BB);
635
636 // Look for a single store or sets of stores with a common base, which can be
637 // optimized into a memset (memset_pattern). The latter most commonly happens
638 // with structs and handunrolled loops.
639 for (auto &SL : StoreRefsForMemset)
640 MadeChange |= processLoopStores(SL.second, BECount, ForMemset::Yes);
641
642 for (auto &SL : StoreRefsForMemsetPattern)
643 MadeChange |= processLoopStores(SL.second, BECount, ForMemset::No);
644
645 // Optimize the store into a memcpy, if it feeds an similarly strided load.
646 for (auto &SI : StoreRefsForMemcpy)
647 MadeChange |= processLoopStoreOfLoopLoad(SI, BECount);
648
649 MadeChange |= processLoopMemIntrinsic<MemCpyInst>(
650 BB, &LoopIdiomRecognize::processLoopMemCpy, BECount);
651 MadeChange |= processLoopMemIntrinsic<MemSetInst>(
652 BB, &LoopIdiomRecognize::processLoopMemSet, BECount);
653
654 return MadeChange;
655}
656
657/// See if this store(s) can be promoted to a memset.
658bool LoopIdiomRecognize::processLoopStores(SmallVectorImpl<StoreInst *> &SL,
659 const SCEV *BECount, ForMemset For) {
660 // Try to find consecutive stores that can be transformed into memsets.
661 SetVector<StoreInst *> Heads, Tails;
662 SmallDenseMap<StoreInst *, StoreInst *> ConsecutiveChain;
663
664 // Do a quadratic search on all of the given stores and find
665 // all of the pairs of stores that follow each other.
666 SmallVector<unsigned, 16> IndexQueue;
667 for (unsigned i = 0, e = SL.size(); i < e; ++i) {
668 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", 668, __extension__
__PRETTY_FUNCTION__))
;
669
670 Value *FirstStoredVal = SL[i]->getValueOperand();
671 Value *FirstStorePtr = SL[i]->getPointerOperand();
672 const SCEVAddRecExpr *FirstStoreEv =
673 cast<SCEVAddRecExpr>(SE->getSCEV(FirstStorePtr));
674 APInt FirstStride = getStoreStride(FirstStoreEv);
675 unsigned FirstStoreSize = DL->getTypeStoreSize(SL[i]->getValueOperand()->getType());
676
677 // See if we can optimize just this store in isolation.
678 if (FirstStride == FirstStoreSize || -FirstStride == FirstStoreSize) {
679 Heads.insert(SL[i]);
680 continue;
681 }
682
683 Value *FirstSplatValue = nullptr;
684 Constant *FirstPatternValue = nullptr;
685
686 if (For == ForMemset::Yes)
687 FirstSplatValue = isBytewiseValue(FirstStoredVal, *DL);
688 else
689 FirstPatternValue = getMemSetPatternValue(FirstStoredVal, DL);
690
691 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", 692, __extension__
__PRETTY_FUNCTION__))
692 "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", 692, __extension__
__PRETTY_FUNCTION__))
;
693
694 IndexQueue.clear();
695 // If a store has multiple consecutive store candidates, search Stores
696 // array according to the sequence: from i+1 to e, then from i-1 to 0.
697 // This is because usually pairing with immediate succeeding or preceding
698 // candidate create the best chance to find memset opportunity.
699 unsigned j = 0;
700 for (j = i + 1; j < e; ++j)
701 IndexQueue.push_back(j);
702 for (j = i; j > 0; --j)
703 IndexQueue.push_back(j - 1);
704
705 for (auto &k : IndexQueue) {
706 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", 706, __extension__
__PRETTY_FUNCTION__))
;
707 Value *SecondStorePtr = SL[k]->getPointerOperand();
708 const SCEVAddRecExpr *SecondStoreEv =
709 cast<SCEVAddRecExpr>(SE->getSCEV(SecondStorePtr));
710 APInt SecondStride = getStoreStride(SecondStoreEv);
711
712 if (FirstStride != SecondStride)
713 continue;
714
715 Value *SecondStoredVal = SL[k]->getValueOperand();
716 Value *SecondSplatValue = nullptr;
717 Constant *SecondPatternValue = nullptr;
718
719 if (For == ForMemset::Yes)
720 SecondSplatValue = isBytewiseValue(SecondStoredVal, *DL);
721 else
722 SecondPatternValue = getMemSetPatternValue(SecondStoredVal, DL);
723
724 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", 725, __extension__
__PRETTY_FUNCTION__))
725 "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", 725, __extension__
__PRETTY_FUNCTION__))
;
726
727 if (isConsecutiveAccess(SL[i], SL[k], *DL, *SE, false)) {
728 if (For == ForMemset::Yes) {
729 if (isa<UndefValue>(FirstSplatValue))
730 FirstSplatValue = SecondSplatValue;
731 if (FirstSplatValue != SecondSplatValue)
732 continue;
733 } else {
734 if (isa<UndefValue>(FirstPatternValue))
735 FirstPatternValue = SecondPatternValue;
736 if (FirstPatternValue != SecondPatternValue)
737 continue;
738 }
739 Tails.insert(SL[k]);
740 Heads.insert(SL[i]);
741 ConsecutiveChain[SL[i]] = SL[k];
742 break;
743 }
744 }
745 }
746
747 // We may run into multiple chains that merge into a single chain. We mark the
748 // stores that we transformed so that we don't visit the same store twice.
749 SmallPtrSet<Value *, 16> TransformedStores;
750 bool Changed = false;
751
752 // For stores that start but don't end a link in the chain:
753 for (StoreInst *I : Heads) {
754 if (Tails.count(I))
755 continue;
756
757 // We found a store instr that starts a chain. Now follow the chain and try
758 // to transform it.
759 SmallPtrSet<Instruction *, 8> AdjacentStores;
760 StoreInst *HeadStore = I;
761 unsigned StoreSize = 0;
762
763 // Collect the chain into a list.
764 while (Tails.count(I) || Heads.count(I)) {
765 if (TransformedStores.count(I))
766 break;
767 AdjacentStores.insert(I);
768
769 StoreSize += DL->getTypeStoreSize(I->getValueOperand()->getType());
770 // Move to the next value in the chain.
771 I = ConsecutiveChain[I];
772 }
773
774 Value *StoredVal = HeadStore->getValueOperand();
775 Value *StorePtr = HeadStore->getPointerOperand();
776 const SCEVAddRecExpr *StoreEv = cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
777 APInt Stride = getStoreStride(StoreEv);
778
779 // Check to see if the stride matches the size of the stores. If so, then
780 // we know that every byte is touched in the loop.
781 if (StoreSize != Stride && StoreSize != -Stride)
782 continue;
783
784 bool IsNegStride = StoreSize == -Stride;
785
786 Type *IntIdxTy = DL->getIndexType(StorePtr->getType());
787 const SCEV *StoreSizeSCEV = SE->getConstant(IntIdxTy, StoreSize);
788 if (processLoopStridedStore(StorePtr, StoreSizeSCEV,
789 MaybeAlign(HeadStore->getAlign()), StoredVal,
790 HeadStore, AdjacentStores, StoreEv, BECount,
791 IsNegStride)) {
792 TransformedStores.insert(AdjacentStores.begin(), AdjacentStores.end());
793 Changed = true;
794 }
795 }
796
797 return Changed;
798}
799
800/// processLoopMemIntrinsic - Template function for calling different processor
801/// functions based on mem instrinsic type.
802template <typename MemInst>
803bool LoopIdiomRecognize::processLoopMemIntrinsic(
804 BasicBlock *BB,
805 bool (LoopIdiomRecognize::*Processor)(MemInst *, const SCEV *),
806 const SCEV *BECount) {
807 bool MadeChange = false;
808 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
809 Instruction *Inst = &*I++;
810 // Look for memory instructions, which may be optimized to a larger one.
811 if (MemInst *MI = dyn_cast<MemInst>(Inst)) {
812 WeakTrackingVH InstPtr(&*I);
813 if (!(this->*Processor)(MI, BECount))
814 continue;
815 MadeChange = true;
816
817 // If processing the instruction invalidated our iterator, start over from
818 // the top of the block.
819 if (!InstPtr)
820 I = BB->begin();
821 }
822 }
823 return MadeChange;
824}
825
826/// processLoopMemCpy - See if this memcpy can be promoted to a large memcpy
827bool LoopIdiomRecognize::processLoopMemCpy(MemCpyInst *MCI,
828 const SCEV *BECount) {
829 // We can only handle non-volatile memcpys with a constant size.
830 if (MCI->isVolatile() || !isa<ConstantInt>(MCI->getLength()))
831 return false;
832
833 // If we're not allowed to hack on memcpy, we fail.
834 if ((!HasMemcpy && !isa<MemCpyInlineInst>(MCI)) || DisableLIRP::Memcpy)
835 return false;
836
837 Value *Dest = MCI->getDest();
838 Value *Source = MCI->getSource();
839 if (!Dest || !Source)
840 return false;
841
842 // See if the load and store pointer expressions are AddRec like {base,+,1} on
843 // the current loop, which indicates a strided load and store. If we have
844 // something else, it's a random load or store we can't handle.
845 const SCEVAddRecExpr *StoreEv = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Dest));
846 if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
847 return false;
848 const SCEVAddRecExpr *LoadEv = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Source));
849 if (!LoadEv || LoadEv->getLoop() != CurLoop || !LoadEv->isAffine())
850 return false;
851
852 // Reject memcpys that are so large that they overflow an unsigned.
853 uint64_t SizeInBytes = cast<ConstantInt>(MCI->getLength())->getZExtValue();
854 if ((SizeInBytes >> 32) != 0)
855 return false;
856
857 // Check if the stride matches the size of the memcpy. If so, then we know
858 // that every byte is touched in the loop.
859 const SCEVConstant *ConstStoreStride =
860 dyn_cast<SCEVConstant>(StoreEv->getOperand(1));
861 const SCEVConstant *ConstLoadStride =
862 dyn_cast<SCEVConstant>(LoadEv->getOperand(1));
863 if (!ConstStoreStride || !ConstLoadStride)
864 return false;
865
866 APInt StoreStrideValue = ConstStoreStride->getAPInt();
867 APInt LoadStrideValue = ConstLoadStride->getAPInt();
868 // Huge stride value - give up
869 if (StoreStrideValue.getBitWidth() > 64 || LoadStrideValue.getBitWidth() > 64)
870 return false;
871
872 if (SizeInBytes != StoreStrideValue && SizeInBytes != -StoreStrideValue) {
873 ORE.emit([&]() {
874 return OptimizationRemarkMissed(DEBUG_TYPE"loop-idiom", "SizeStrideUnequal", MCI)
875 << ore::NV("Inst", "memcpy") << " in "
876 << ore::NV("Function", MCI->getFunction())
877 << " function will not be hoisted: "
878 << ore::NV("Reason", "memcpy size is not equal to stride");
879 });
880 return false;
881 }
882
883 int64_t StoreStrideInt = StoreStrideValue.getSExtValue();
884 int64_t LoadStrideInt = LoadStrideValue.getSExtValue();
885 // Check if the load stride matches the store stride.
886 if (StoreStrideInt != LoadStrideInt)
887 return false;
888
889 return processLoopStoreOfLoopLoad(
890 Dest, Source, SE->getConstant(Dest->getType(), SizeInBytes),
891 MCI->getDestAlign(), MCI->getSourceAlign(), MCI, MCI, StoreEv, LoadEv,
892 BECount);
893}
894
895/// processLoopMemSet - See if this memset can be promoted to a large memset.
896bool LoopIdiomRecognize::processLoopMemSet(MemSetInst *MSI,
897 const SCEV *BECount) {
898 // We can only handle non-volatile memsets.
899 if (MSI->isVolatile())
900 return false;
901
902 // If we're not allowed to hack on memset, we fail.
903 if (!HasMemset || DisableLIRP::Memset)
904 return false;
905
906 Value *Pointer = MSI->getDest();
907
908 // See if the pointer expression is an AddRec like {base,+,1} on the current
909 // loop, which indicates a strided store. If we have something else, it's a
910 // random store we can't handle.
911 const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
912 if (!Ev || Ev->getLoop() != CurLoop)
913 return false;
914 if (!Ev->isAffine()) {
915 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)
;
916 return false;
917 }
918
919 const SCEV *PointerStrideSCEV = Ev->getOperand(1);
920 const SCEV *MemsetSizeSCEV = SE->getSCEV(MSI->getLength());
921 if (!PointerStrideSCEV || !MemsetSizeSCEV)
922 return false;
923
924 bool IsNegStride = false;
925 const bool IsConstantSize = isa<ConstantInt>(MSI->getLength());
926
927 if (IsConstantSize) {
928 // Memset size is constant.
929 // Check if the pointer stride matches the memset size. If so, then
930 // we know that every byte is touched in the loop.
931 LLVM_DEBUG(dbgs() << " memset size is constant\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " memset size is constant\n"
; } } while (false)
;
932 uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
933 const SCEVConstant *ConstStride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
934 if (!ConstStride)
935 return false;
936
937 APInt Stride = ConstStride->getAPInt();
938 if (SizeInBytes != Stride && SizeInBytes != -Stride)
939 return false;
940
941 IsNegStride = SizeInBytes == -Stride;
942 } else {
943 // Memset size is non-constant.
944 // Check if the pointer stride matches the memset size.
945 // To be conservative, the pass would not promote pointers that aren't in
946 // address space zero. Also, the pass only handles memset length and stride
947 // that are invariant for the top level loop.
948 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)
;
949 if (Pointer->getType()->getPointerAddressSpace() != 0) {
950 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)
951 << "abort\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " pointer is not in address space zero, "
<< "abort\n"; } } while (false)
;
952 return false;
953 }
954 if (!SE->isLoopInvariant(MemsetSizeSCEV, CurLoop)) {
955 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)
956 << "abort\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " memset size is not a loop-invariant, "
<< "abort\n"; } } while (false)
;
957 return false;
958 }
959
960 // Compare positive direction PointerStrideSCEV with MemsetSizeSCEV
961 IsNegStride = PointerStrideSCEV->isNonConstantNegative();
962 const SCEV *PositiveStrideSCEV =
963 IsNegStride ? SE->getNegativeSCEV(PointerStrideSCEV)
964 : PointerStrideSCEV;
965 LLVM_DEBUG(dbgs() << " MemsetSizeSCEV: " << *MemsetSizeSCEV << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " MemsetSizeSCEV: " <<
*MemsetSizeSCEV << "\n" << " PositiveStrideSCEV: "
<< *PositiveStrideSCEV << "\n"; } } while (false
)
966 << " PositiveStrideSCEV: " << *PositiveStrideSCEVdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " MemsetSizeSCEV: " <<
*MemsetSizeSCEV << "\n" << " PositiveStrideSCEV: "
<< *PositiveStrideSCEV << "\n"; } } while (false
)
967 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " MemsetSizeSCEV: " <<
*MemsetSizeSCEV << "\n" << " PositiveStrideSCEV: "
<< *PositiveStrideSCEV << "\n"; } } while (false
)
;
968
969 if (PositiveStrideSCEV != MemsetSizeSCEV) {
970 // If an expression is covered by the loop guard, compare again and
971 // proceed with optimization if equal.
972 const SCEV *FoldedPositiveStride =
973 SE->applyLoopGuards(PositiveStrideSCEV, CurLoop);
974 const SCEV *FoldedMemsetSize =
975 SE->applyLoopGuards(MemsetSizeSCEV, CurLoop);
976
977 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)
978 << " 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)
979 << " 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)
980 << "\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)
;
981
982 if (FoldedPositiveStride != FoldedMemsetSize) {
983 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)
;
984 return false;
985 }
986 }
987 }
988
989 // Verify that the memset value is loop invariant. If not, we can't promote
990 // the memset.
991 Value *SplatValue = MSI->getValue();
992 if (!SplatValue || !CurLoop->isLoopInvariant(SplatValue))
993 return false;
994
995 SmallPtrSet<Instruction *, 1> MSIs;
996 MSIs.insert(MSI);
997 return processLoopStridedStore(Pointer, SE->getSCEV(MSI->getLength()),
998 MaybeAlign(MSI->getDestAlignment()),
999 SplatValue, MSI, MSIs, Ev, BECount,
1000 IsNegStride, /*IsLoopMemset=*/true);
1001}
1002
1003/// mayLoopAccessLocation - Return true if the specified loop might access the
1004/// specified pointer location, which is a loop-strided access. The 'Access'
1005/// argument specifies what the verboten forms of access are (read or write).
1006static bool
1007mayLoopAccessLocation(Value *Ptr, ModRefInfo Access, Loop *L,
1008 const SCEV *BECount, const SCEV *StoreSizeSCEV,
1009 AliasAnalysis &AA,
1010 SmallPtrSetImpl<Instruction *> &IgnoredInsts) {
1011 // Get the location that may be stored across the loop. Since the access is
1012 // strided positively through memory, we say that the modified location starts
1013 // at the pointer and has infinite size.
1014 LocationSize AccessSize = LocationSize::afterPointer();
1015
1016 // If the loop iterates a fixed number of times, we can refine the access size
1017 // to be exactly the size of the memset, which is (BECount+1)*StoreSize
1018 const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount);
1019 const SCEVConstant *ConstSize = dyn_cast<SCEVConstant>(StoreSizeSCEV);
1020 if (BECst && ConstSize)
1021 AccessSize = LocationSize::precise((BECst->getValue()->getZExtValue() + 1) *
1022 ConstSize->getValue()->getZExtValue());
1023
1024 // TODO: For this to be really effective, we have to dive into the pointer
1025 // operand in the store. Store to &A[i] of 100 will always return may alias
1026 // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
1027 // which will then no-alias a store to &A[100].
1028 MemoryLocation StoreLoc(Ptr, AccessSize);
1029
1030 for (BasicBlock *B : L->blocks())
1031 for (Instruction &I : *B)
1032 if (!IgnoredInsts.contains(&I) &&
1033 isModOrRefSet(
1034 intersectModRef(AA.getModRefInfo(&I, StoreLoc), Access)))
1035 return true;
1036 return false;
1037}
1038
1039// If we have a negative stride, Start refers to the end of the memory location
1040// we're trying to memset. Therefore, we need to recompute the base pointer,
1041// which is just Start - BECount*Size.
1042static const SCEV *getStartForNegStride(const SCEV *Start, const SCEV *BECount,
1043 Type *IntPtr, const SCEV *StoreSizeSCEV,
1044 ScalarEvolution *SE) {
1045 const SCEV *Index = SE->getTruncateOrZeroExtend(BECount, IntPtr);
1046 if (!StoreSizeSCEV->isOne()) {
1047 // index = back edge count * store size
1048 Index = SE->getMulExpr(Index,
1049 SE->getTruncateOrZeroExtend(StoreSizeSCEV, IntPtr),
1050 SCEV::FlagNUW);
1051 }
1052 // base pointer = start - index * store size
1053 return SE->getMinusSCEV(Start, Index);
1054}
1055
1056/// Compute trip count from the backedge taken count.
1057static const SCEV *getTripCount(const SCEV *BECount, Type *IntPtr,
1058 Loop *CurLoop, const DataLayout *DL,
1059 ScalarEvolution *SE) {
1060 const SCEV *TripCountS = nullptr;
1061 // The # stored bytes is (BECount+1). Expand the trip count out to
1062 // pointer size if it isn't already.
1063 //
1064 // If we're going to need to zero extend the BE count, check if we can add
1065 // one to it prior to zero extending without overflow. Provided this is safe,
1066 // it allows better simplification of the +1.
1067 if (DL->getTypeSizeInBits(BECount->getType()) <
1068 DL->getTypeSizeInBits(IntPtr) &&
1069 SE->isLoopEntryGuardedByCond(
1070 CurLoop, ICmpInst::ICMP_NE, BECount,
1071 SE->getNegativeSCEV(SE->getOne(BECount->getType())))) {
1072 TripCountS = SE->getZeroExtendExpr(
1073 SE->getAddExpr(BECount, SE->getOne(BECount->getType()), SCEV::FlagNUW),
1074 IntPtr);
1075 } else {
1076 TripCountS = SE->getAddExpr(SE->getTruncateOrZeroExtend(BECount, IntPtr),
1077 SE->getOne(IntPtr), SCEV::FlagNUW);
1078 }
1079
1080 return TripCountS;
1081}
1082
1083/// Compute the number of bytes as a SCEV from the backedge taken count.
1084///
1085/// This also maps the SCEV into the provided type and tries to handle the
1086/// computation in a way that will fold cleanly.
1087static const SCEV *getNumBytes(const SCEV *BECount, Type *IntPtr,
1088 const SCEV *StoreSizeSCEV, Loop *CurLoop,
1089 const DataLayout *DL, ScalarEvolution *SE) {
1090 const SCEV *TripCountSCEV = getTripCount(BECount, IntPtr, CurLoop, DL, SE);
1091
1092 return SE->getMulExpr(TripCountSCEV,
1093 SE->getTruncateOrZeroExtend(StoreSizeSCEV, IntPtr),
1094 SCEV::FlagNUW);
1095}
1096
1097/// processLoopStridedStore - We see a strided store of some value. If we can
1098/// transform this into a memset or memset_pattern in the loop preheader, do so.
1099bool LoopIdiomRecognize::processLoopStridedStore(
1100 Value *DestPtr, const SCEV *StoreSizeSCEV, MaybeAlign StoreAlignment,
1101 Value *StoredVal, Instruction *TheStore,
1102 SmallPtrSetImpl<Instruction *> &Stores, const SCEVAddRecExpr *Ev,
1103 const SCEV *BECount, bool IsNegStride, bool IsLoopMemset) {
1104 Value *SplatValue = isBytewiseValue(StoredVal, *DL);
1105 Constant *PatternValue = nullptr;
1106
1107 if (!SplatValue)
1108 PatternValue = getMemSetPatternValue(StoredVal, DL);
1109
1110 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", 1111, __extension__
__PRETTY_FUNCTION__))
1111 "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", 1111, __extension__
__PRETTY_FUNCTION__))
;
1112
1113 // The trip count of the loop and the base pointer of the addrec SCEV is
1114 // guaranteed to be loop invariant, which means that it should dominate the
1115 // header. This allows us to insert code for it in the preheader.
1116 unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();
1117 BasicBlock *Preheader = CurLoop->getLoopPreheader();
1118 IRBuilder<> Builder(Preheader->getTerminator());
1119 SCEVExpander Expander(*SE, *DL, "loop-idiom");
1120 SCEVExpanderCleaner ExpCleaner(Expander);
1121
1122 Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
1123 Type *IntIdxTy = DL->getIndexType(DestPtr->getType());
1124
1125 bool Changed = false;
1126 const SCEV *Start = Ev->getStart();
1127 // Handle negative strided loops.
1128 if (IsNegStride)
1129 Start = getStartForNegStride(Start, BECount, IntIdxTy, StoreSizeSCEV, SE);
1130
1131 // TODO: ideally we should still be able to generate memset if SCEV expander
1132 // is taught to generate the dependencies at the latest point.
1133 if (!isSafeToExpand(Start, *SE))
1134 return Changed;
1135
1136 // Okay, we have a strided store "p[i]" of a splattable value. We can turn
1137 // this into a memset in the loop preheader now if we want. However, this
1138 // would be unsafe to do if there is anything else in the loop that may read
1139 // or write to the aliased location. Check for any overlap by generating the
1140 // base pointer and checking the region.
1141 Value *BasePtr =
1142 Expander.expandCodeFor(Start, DestInt8PtrTy, Preheader->getTerminator());
1143
1144 // From here on out, conservatively report to the pass manager that we've
1145 // changed the IR, even if we later clean up these added instructions. There
1146 // may be structural differences e.g. in the order of use lists not accounted
1147 // for in just a textual dump of the IR. This is written as a variable, even
1148 // though statically all the places this dominates could be replaced with
1149 // 'true', with the hope that anyone trying to be clever / "more precise" with
1150 // the return value will read this comment, and leave them alone.
1151 Changed = true;
1152
1153 if (mayLoopAccessLocation(BasePtr, ModRefInfo::ModRef, CurLoop, BECount,
1154 StoreSizeSCEV, *AA, Stores))
1155 return Changed;
1156
1157 if (avoidLIRForMultiBlockLoop(/*IsMemset=*/true, IsLoopMemset))
1158 return Changed;
1159
1160 // Okay, everything looks good, insert the memset.
1161
1162 const SCEV *NumBytesS =
1163 getNumBytes(BECount, IntIdxTy, StoreSizeSCEV, CurLoop, DL, SE);
1164
1165 // TODO: ideally we should still be able to generate memset if SCEV expander
1166 // is taught to generate the dependencies at the latest point.
1167 if (!isSafeToExpand(NumBytesS, *SE))
1168 return Changed;
1169
1170 Value *NumBytes =
1171 Expander.expandCodeFor(NumBytesS, IntIdxTy, Preheader->getTerminator());
1172
1173 CallInst *NewCall;
1174 if (SplatValue) {
1175 NewCall = Builder.CreateMemSet(BasePtr, SplatValue, NumBytes,
1176 MaybeAlign(StoreAlignment));
1177 } else {
1178 // Everything is emitted in default address space
1179 Type *Int8PtrTy = DestInt8PtrTy;
1180
1181 Module *M = TheStore->getModule();
1182 StringRef FuncName = "memset_pattern16";
1183 FunctionCallee MSP = M->getOrInsertFunction(FuncName, Builder.getVoidTy(),
1184 Int8PtrTy, Int8PtrTy, IntIdxTy);
1185 inferLibFuncAttributes(M, FuncName, *TLI);
1186
1187 // Otherwise we should form a memset_pattern16. PatternValue is known to be
1188 // an constant array of 16-bytes. Plop the value into a mergable global.
1189 GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
1190 GlobalValue::PrivateLinkage,
1191 PatternValue, ".memset_pattern");
1192 GV->setUnnamedAddr(GlobalValue::UnnamedAddr::Global); // Ok to merge these.
1193 GV->setAlignment(Align(16));
1194 Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
1195 NewCall = Builder.CreateCall(MSP, {BasePtr, PatternPtr, NumBytes});
1196 }
1197 NewCall->setDebugLoc(TheStore->getDebugLoc());
1198
1199 if (MSSAU) {
1200 MemoryAccess *NewMemAcc = MSSAU->createMemoryAccessInBB(
1201 NewCall, nullptr, NewCall->getParent(), MemorySSA::BeforeTerminator);
1202 MSSAU->insertDef(cast<MemoryDef>(NewMemAcc), true);
1203 }
1204
1205 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)
1206 << " 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)
1207 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << " Formed memset: " <<
*NewCall << "\n" << " from store to: " <<
*Ev << " at: " << *TheStore << "\n"; } } while
(false)
;
1208
1209 ORE.emit([&]() {
1210 OptimizationRemark R(DEBUG_TYPE"loop-idiom", "ProcessLoopStridedStore",
1211 NewCall->getDebugLoc(), Preheader);
1212 R << "Transformed loop-strided store in "
1213 << ore::NV("Function", TheStore->getFunction())
1214 << " function into a call to "
1215 << ore::NV("NewFunction", NewCall->getCalledFunction())
1216 << "() intrinsic";
1217 if (!Stores.empty())
1218 R << ore::setExtraArgs();
1219 for (auto *I : Stores) {
1220 R << ore::NV("FromBlock", I->getParent()->getName())
1221 << ore::NV("ToBlock", Preheader->getName());
1222 }
1223 return R;
1224 });
1225
1226 // Okay, the memset has been formed. Zap the original store and anything that
1227 // feeds into it.
1228 for (auto *I : Stores) {
1229 if (MSSAU)
1230 MSSAU->removeMemoryAccess(I, true);
1231 deleteDeadInstruction(I);
1232 }
1233 if (MSSAU && VerifyMemorySSA)
1234 MSSAU->getMemorySSA()->verifyMemorySSA();
1235 ++NumMemSet;
1236 ExpCleaner.markResultUsed();
1237 return true;
1238}
1239
1240/// If the stored value is a strided load in the same loop with the same stride
1241/// this may be transformable into a memcpy. This kicks in for stuff like
1242/// for (i) A[i] = B[i];
1243bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(StoreInst *SI,
1244 const SCEV *BECount) {
1245 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", 1245, __extension__
__PRETTY_FUNCTION__))
;
1246
1247 Value *StorePtr = SI->getPointerOperand();
1248 const SCEVAddRecExpr *StoreEv = cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
1249 unsigned StoreSize = DL->getTypeStoreSize(SI->getValueOperand()->getType());
1250
1251 // The store must be feeding a non-volatile load.
1252 LoadInst *LI = cast<LoadInst>(SI->getValueOperand());
1253 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", 1253, __extension__
__PRETTY_FUNCTION__))
;
1254
1255 // See if the pointer expression is an AddRec like {base,+,1} on the current
1256 // loop, which indicates a strided load. If we have something else, it's a
1257 // random load we can't handle.
1258 Value *LoadPtr = LI->getPointerOperand();
1259 const SCEVAddRecExpr *LoadEv = cast<SCEVAddRecExpr>(SE->getSCEV(LoadPtr));
1260
1261 const SCEV *StoreSizeSCEV = SE->getConstant(StorePtr->getType(), StoreSize);
1262 return processLoopStoreOfLoopLoad(StorePtr, LoadPtr, StoreSizeSCEV,
1263 SI->getAlign(), LI->getAlign(), SI, LI,
1264 StoreEv, LoadEv, BECount);
1265}
1266
1267class MemmoveVerifier {
1268public:
1269 explicit MemmoveVerifier(const Value &LoadBasePtr, const Value &StoreBasePtr,
1270 const DataLayout &DL)
1271 : DL(DL), LoadOff(0), StoreOff(0),
1272 BP1(llvm::GetPointerBaseWithConstantOffset(
1273 LoadBasePtr.stripPointerCasts(), LoadOff, DL)),
1274 BP2(llvm::GetPointerBaseWithConstantOffset(
1275 StoreBasePtr.stripPointerCasts(), StoreOff, DL)),
1276 IsSameObject(BP1 == BP2) {}
1277
1278 bool loadAndStoreMayFormMemmove(unsigned StoreSize, bool IsNegStride,
1279 const Instruction &TheLoad,
1280 bool IsMemCpy) const {
1281 if (IsMemCpy) {
1282 // Ensure that LoadBasePtr is after StoreBasePtr or before StoreBasePtr
1283 // for negative stride.
1284 if ((!IsNegStride && LoadOff <= StoreOff) ||
1285 (IsNegStride && LoadOff >= StoreOff))
1286 return false;
1287 } else {
1288 // Ensure that LoadBasePtr is after StoreBasePtr or before StoreBasePtr
1289 // for negative stride. LoadBasePtr shouldn't overlap with StoreBasePtr.
1290 int64_t LoadSize =
1291 DL.getTypeSizeInBits(TheLoad.getType()).getFixedSize() / 8;
1292 if (BP1 != BP2 || LoadSize != int64_t(StoreSize))
1293 return false;
1294 if ((!IsNegStride && LoadOff < StoreOff + int64_t(StoreSize)) ||
1295 (IsNegStride && LoadOff + LoadSize > StoreOff))
1296 return false;
1297 }
1298 return true;
1299 }
1300
1301private:
1302 const DataLayout &DL;
1303 int64_t LoadOff;
1304 int64_t StoreOff;
1305 const Value *BP1;
1306 const Value *BP2;
1307
1308public:
1309 const bool IsSameObject;
1310};
1311
1312bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(
1313 Value *DestPtr, Value *SourcePtr, const SCEV *StoreSizeSCEV,
1314 MaybeAlign StoreAlign, MaybeAlign LoadAlign, Instruction *TheStore,
1315 Instruction *TheLoad, const SCEVAddRecExpr *StoreEv,
1316 const SCEVAddRecExpr *LoadEv, const SCEV *BECount) {
1317
1318 // FIXME: until llvm.memcpy.inline supports dynamic sizes, we need to
1319 // conservatively bail here, since otherwise we may have to transform
1320 // llvm.memcpy.inline into llvm.memcpy which is illegal.
1321 if (isa<MemCpyInlineInst>(TheStore))
1322 return false;
1323
1324 // The trip count of the loop and the base pointer of the addrec SCEV is
1325 // guaranteed to be loop invariant, which means that it should dominate the
1326 // header. This allows us to insert code for it in the preheader.
1327 BasicBlock *Preheader = CurLoop->getLoopPreheader();
1328 IRBuilder<> Builder(Preheader->getTerminator());
1329 SCEVExpander Expander(*SE, *DL, "loop-idiom");
1330
1331 SCEVExpanderCleaner ExpCleaner(Expander);
1332
1333 bool Changed = false;
1334 const SCEV *StrStart = StoreEv->getStart();
1335 unsigned StrAS = DestPtr->getType()->getPointerAddressSpace();
1336 Type *IntIdxTy = Builder.getIntNTy(DL->getIndexSizeInBits(StrAS));
1337
1338 APInt Stride = getStoreStride(StoreEv);
1339 const SCEVConstant *ConstStoreSize = dyn_cast<SCEVConstant>(StoreSizeSCEV);
1340
1341 // TODO: Deal with non-constant size; Currently expect constant store size
1342 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", 1342, __extension__
__PRETTY_FUNCTION__))
;
1343
1344 int64_t StoreSize = ConstStoreSize->getValue()->getZExtValue();
1345 bool IsNegStride = StoreSize == -Stride;
1346
1347 // Handle negative strided loops.
1348 if (IsNegStride)
1349 StrStart =
1350 getStartForNegStride(StrStart, BECount, IntIdxTy, StoreSizeSCEV, SE);
1351
1352 // Okay, we have a strided store "p[i]" of a loaded value. We can turn
1353 // this into a memcpy in the loop preheader now if we want. However, this
1354 // would be unsafe to do if there is anything else in the loop that may read
1355 // or write the memory region we're storing to. This includes the load that
1356 // feeds the stores. Check for an alias by generating the base address and
1357 // checking everything.
1358 Value *StoreBasePtr = Expander.expandCodeFor(
1359 StrStart, Builder.getInt8PtrTy(StrAS), Preheader->getTerminator());
1360
1361 // From here on out, conservatively report to the pass manager that we've
1362 // changed the IR, even if we later clean up these added instructions. There
1363 // may be structural differences e.g. in the order of use lists not accounted
1364 // for in just a textual dump of the IR. This is written as a variable, even
1365 // though statically all the places this dominates could be replaced with
1366 // 'true', with the hope that anyone trying to be clever / "more precise" with
1367 // the return value will read this comment, and leave them alone.
1368 Changed = true;
1369
1370 SmallPtrSet<Instruction *, 2> IgnoredInsts;
1371 IgnoredInsts.insert(TheStore);
1372
1373 bool IsMemCpy = isa<MemCpyInst>(TheStore);
1374 const StringRef InstRemark = IsMemCpy ? "memcpy" : "load and store";
1375
1376 bool LoopAccessStore =
1377 mayLoopAccessLocation(StoreBasePtr, ModRefInfo::ModRef, CurLoop, BECount,
1378 StoreSizeSCEV, *AA, IgnoredInsts);
1379 if (LoopAccessStore) {
1380 // For memmove case it's not enough to guarantee that loop doesn't access
1381 // TheStore and TheLoad. Additionally we need to make sure that TheStore is
1382 // the only user of TheLoad.
1383 if (!TheLoad->hasOneUse())
1384 return Changed;
1385 IgnoredInsts.insert(TheLoad);
1386 if (mayLoopAccessLocation(StoreBasePtr, ModRefInfo::ModRef, CurLoop,
1387 BECount, StoreSizeSCEV, *AA, IgnoredInsts)) {
1388 ORE.emit([&]() {
1389 return OptimizationRemarkMissed(DEBUG_TYPE"loop-idiom", "LoopMayAccessStore",
1390 TheStore)
1391 << ore::NV("Inst", InstRemark) << " in "
1392 << ore::NV("Function", TheStore->getFunction())
1393 << " function will not be hoisted: "
1394 << ore::NV("Reason", "The loop may access store location");
1395 });
1396 return Changed;
1397 }
1398 IgnoredInsts.erase(TheLoad);
1399 }
1400
1401 const SCEV *LdStart = LoadEv->getStart();
1402 unsigned LdAS = SourcePtr->getType()->getPointerAddressSpace();
1403
1404 // Handle negative strided loops.
1405 if (IsNegStride)
1406 LdStart =
1407 getStartForNegStride(LdStart, BECount, IntIdxTy, StoreSizeSCEV, SE);
1408
1409 // For a memcpy, we have to make sure that the input array is not being
1410 // mutated by the loop.
1411 Value *LoadBasePtr = Expander.expandCodeFor(
1412 LdStart, Builder.getInt8PtrTy(LdAS), Preheader->getTerminator());
1413
1414 // If the store is a memcpy instruction, we must check if it will write to
1415 // the load memory locations. So remove it from the ignored stores.
1416 if (IsMemCpy)
1417 IgnoredInsts.erase(TheStore);
1418 MemmoveVerifier Verifier(*LoadBasePtr, *StoreBasePtr, *DL);
1419 if (mayLoopAccessLocation(LoadBasePtr, ModRefInfo::Mod, CurLoop, BECount,
1420 StoreSizeSCEV, *AA, IgnoredInsts)) {
1421 if (!IsMemCpy) {
1422 ORE.emit([&]() {
1423 return OptimizationRemarkMissed(DEBUG_TYPE"loop-idiom", "LoopMayAccessLoad",
1424 TheLoad)
1425 << ore::NV("Inst", InstRemark) << " in "
1426 << ore::NV("Function", TheStore->getFunction())
1427 << " function will not be hoisted: "
1428 << ore::NV("Reason", "The loop may access load location");
1429 });
1430 return Changed;
1431 }
1432 // At this point loop may access load only for memcpy in same underlying
1433 // object. If that's not the case bail out.
1434 if (!Verifier.IsSameObject)
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 CallInst *NewCall = nullptr;
1456 // Check whether to generate an unordered atomic memcpy:
1457 // If the load or store are atomic, then they must necessarily be unordered
1458 // by previous checks.
1459 if (!TheStore->isAtomic() && !TheLoad->isAtomic()) {
1460 if (UseMemMove)
1461 NewCall = Builder.CreateMemMove(StoreBasePtr, StoreAlign, LoadBasePtr,
1462 LoadAlign, NumBytes);
1463 else
1464 NewCall = Builder.CreateMemCpy(StoreBasePtr, StoreAlign, LoadBasePtr,
1465 LoadAlign, NumBytes);
1466 } else {
1467 // For now don't support unordered atomic memmove.
1468 if (UseMemMove)
1469 return Changed;
1470 // We cannot allow unaligned ops for unordered load/store, so reject
1471 // anything where the alignment isn't at least the element size.
1472 assert((StoreAlign.hasValue() && LoadAlign.hasValue()) &&(static_cast <bool> ((StoreAlign.hasValue() && LoadAlign
.hasValue()) && "Expect unordered load/store to have align."
) ? void (0) : __assert_fail ("(StoreAlign.hasValue() && LoadAlign.hasValue()) && \"Expect unordered load/store to have align.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 1473, __extension__
__PRETTY_FUNCTION__))
1473 "Expect unordered load/store to have align.")(static_cast <bool> ((StoreAlign.hasValue() && LoadAlign
.hasValue()) && "Expect unordered load/store to have align."
) ? void (0) : __assert_fail ("(StoreAlign.hasValue() && LoadAlign.hasValue()) && \"Expect unordered load/store to have align.\""
, "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp", 1473, __extension__
__PRETTY_FUNCTION__))
;
1474 if (StoreAlign.getValue() < StoreSize || LoadAlign.getValue() < StoreSize)
1475 return Changed;
1476
1477 // If the element.atomic memcpy is not lowered into explicit
1478 // loads/stores later, then it will be lowered into an element-size
1479 // specific lib call. If the lib call doesn't exist for our store size, then
1480 // we shouldn't generate the memcpy.
1481 if (StoreSize > TTI->getAtomicMemIntrinsicMaxElementSize())
1482 return Changed;
1483
1484 // Create the call.
1485 // Note that unordered atomic loads/stores are *required* by the spec to
1486 // have an alignment but non-atomic loads/stores may not.
1487 NewCall = Builder.CreateElementUnorderedAtomicMemCpy(
1488 StoreBasePtr, StoreAlign.getValue(), LoadBasePtr, LoadAlign.getValue(),
1489 NumBytes, StoreSize);
1490 }
1491 NewCall->setDebugLoc(TheStore->getDebugLoc());
1492
1493 if (MSSAU) {
1494 MemoryAccess *NewMemAcc = MSSAU->createMemoryAccessInBB(
1495 NewCall, nullptr, NewCall->getParent(), MemorySSA::BeforeTerminator);
1496 MSSAU->insertDef(cast<MemoryDef>(NewMemAcc), true);
1497 }
1498
1499 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)
1500 << " 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)
1501 << "\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)
1502 << " 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)
1503 << "\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)
;
1504
1505 ORE.emit([&]() {
1506 return OptimizationRemark(DEBUG_TYPE"loop-idiom", "ProcessLoopStoreOfLoopLoad",
1507 NewCall->getDebugLoc(), Preheader)
1508 << "Formed a call to "
1509 << ore::NV("NewFunction", NewCall->getCalledFunction())
1510 << "() intrinsic from " << ore::NV("Inst", InstRemark)
1511 << " instruction in " << ore::NV("Function", TheStore->getFunction())
1512 << " function"
1513 << ore::setExtraArgs()
1514 << ore::NV("FromBlock", TheStore->getParent()->getName())
1515 << ore::NV("ToBlock", Preheader->getName());
1516 });
1517
1518 // Okay, a new call to memcpy/memmove has been formed. Zap the original store
1519 // and anything that feeds into it.
1520 if (MSSAU)
1521 MSSAU->removeMemoryAccess(TheStore, true);
1522 deleteDeadInstruction(TheStore);
1523 if (MSSAU && VerifyMemorySSA)
1524 MSSAU->getMemorySSA()->verifyMemorySSA();
1525 if (UseMemMove)
1526 ++NumMemMove;
1527 else
1528 ++NumMemCpy;
1529 ExpCleaner.markResultUsed();
1530 return true;
1531}
1532
1533// When compiling for codesize we avoid idiom recognition for a multi-block loop
1534// unless it is a loop_memset idiom or a memset/memcpy idiom in a nested loop.
1535//
1536bool LoopIdiomRecognize::avoidLIRForMultiBlockLoop(bool IsMemset,
1537 bool IsLoopMemset) {
1538 if (ApplyCodeSizeHeuristics && CurLoop->getNumBlocks() > 1) {
1539 if (CurLoop->isOutermost() && (!IsMemset || !IsLoopMemset)) {
1540 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)
1541 << " : 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)
1542 << " 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)
;
1543 return true;
1544 }
1545 }
1546
1547 return false;
1548}
1549
1550bool LoopIdiomRecognize::runOnNoncountableLoop() {
1551 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
1552 << 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)
1553 << "] 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)
1554 << 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)
;
1555
1556 return recognizePopcount() || recognizeAndInsertFFS() ||
12
Calling 'LoopIdiomRecognize::recognizeAndInsertFFS'
1557 recognizeShiftUntilBitTest() || recognizeShiftUntilZero();
1558}
1559
1560/// Check if the given conditional branch is based on the comparison between
1561/// a variable and zero, and if the variable is non-zero or zero (JmpOnZero is
1562/// true), the control yields to the loop entry. If the branch matches the
1563/// behavior, the variable involved in the comparison is returned. This function
1564/// will be called to see if the precondition and postcondition of the loop are
1565/// in desirable form.
1566static Value *matchCondition(BranchInst *BI, BasicBlock *LoopEntry,
1567 bool JmpOnZero = false) {
1568 if (!BI || !BI->isConditional())
1569 return nullptr;
1570
1571 ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
1572 if (!Cond)
1573 return nullptr;
1574
1575 ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
1576 if (!CmpZero || !CmpZero->isZero())
1577 return nullptr;
1578
1579 BasicBlock *TrueSucc = BI->getSuccessor(0);
1580 BasicBlock *FalseSucc = BI->getSuccessor(1);
1581 if (JmpOnZero)
1582 std::swap(TrueSucc, FalseSucc);
1583
1584 ICmpInst::Predicate Pred = Cond->getPredicate();
1585 if ((Pred == ICmpInst::ICMP_NE && TrueSucc == LoopEntry) ||
1586 (Pred == ICmpInst::ICMP_EQ && FalseSucc == LoopEntry))
1587 return Cond->getOperand(0);
1588
1589 return nullptr;
1590}
1591
1592// Check if the recurrence variable `VarX` is in the right form to create
1593// the idiom. Returns the value coerced to a PHINode if so.
1594static PHINode *getRecurrenceVar(Value *VarX, Instruction *DefX,
1595 BasicBlock *LoopEntry) {
1596 auto *PhiX = dyn_cast<PHINode>(VarX);
1597 if (PhiX && PhiX->getParent() == LoopEntry &&
1598 (PhiX->getOperand(0) == DefX || PhiX->getOperand(1) == DefX))
1599 return PhiX;
1600 return nullptr;
1601}
1602
1603/// Return true iff the idiom is detected in the loop.
1604///
1605/// Additionally:
1606/// 1) \p CntInst is set to the instruction counting the population bit.
1607/// 2) \p CntPhi is set to the corresponding phi node.
1608/// 3) \p Var is set to the value whose population bits are being counted.
1609///
1610/// The core idiom we are trying to detect is:
1611/// \code
1612/// if (x0 != 0)
1613/// goto loop-exit // the precondition of the loop
1614/// cnt0 = init-val;
1615/// do {
1616/// x1 = phi (x0, x2);
1617/// cnt1 = phi(cnt0, cnt2);
1618///
1619/// cnt2 = cnt1 + 1;
1620/// ...
1621/// x2 = x1 & (x1 - 1);
1622/// ...
1623/// } while(x != 0);
1624///
1625/// loop-exit:
1626/// \endcode
1627static bool detectPopcountIdiom(Loop *CurLoop, BasicBlock *PreCondBB,
1628 Instruction *&CntInst, PHINode *&CntPhi,
1629 Value *&Var) {
1630 // step 1: Check to see if the look-back branch match this pattern:
1631 // "if (a!=0) goto loop-entry".
1632 BasicBlock *LoopEntry;
1633 Instruction *DefX2, *CountInst;
1634 Value *VarX1, *VarX0;
1635 PHINode *PhiX, *CountPhi;
1636
1637 DefX2 = CountInst = nullptr;
1638 VarX1 = VarX0 = nullptr;
1639 PhiX = CountPhi = nullptr;
1640 LoopEntry = *(CurLoop->block_begin());
1641
1642 // step 1: Check if the loop-back branch is in desirable form.
1643 {
1644 if (Value *T = matchCondition(
1645 dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
1646 DefX2 = dyn_cast<Instruction>(T);
1647 else
1648 return false;
1649 }
1650
1651 // step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
1652 {
1653 if (!DefX2 || DefX2->getOpcode() != Instruction::And)
1654 return false;
1655
1656 BinaryOperator *SubOneOp;
1657
1658 if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
1659 VarX1 = DefX2->getOperand(1);
1660 else {
1661 VarX1 = DefX2->getOperand(0);
1662 SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
1663 }
1664 if (!SubOneOp || SubOneOp->getOperand(0) != VarX1)
1665 return false;
1666
1667 ConstantInt *Dec = dyn_cast<ConstantInt>(SubOneOp->getOperand(1));
1668 if (!Dec ||
1669 !((SubOneOp->getOpcode() == Instruction::Sub && Dec->isOne()) ||
1670 (SubOneOp->getOpcode() == Instruction::Add &&
1671 Dec->isMinusOne()))) {
1672 return false;
1673 }
1674 }
1675
1676 // step 3: Check the recurrence of variable X
1677 PhiX = getRecurrenceVar(VarX1, DefX2, LoopEntry);
1678 if (!PhiX)
1679 return false;
1680
1681 // step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
1682 {
1683 CountInst = nullptr;
1684 for (Instruction &Inst : llvm::make_range(
1685 LoopEntry->getFirstNonPHI()->getIterator(), LoopEntry->end())) {
1686 if (Inst.getOpcode() != Instruction::Add)
1687 continue;
1688
1689 ConstantInt *Inc = dyn_cast<ConstantInt>(Inst.getOperand(1));
1690 if (!Inc || !Inc->isOne())
1691 continue;
1692
1693 PHINode *Phi = getRecurrenceVar(Inst.getOperand(0), &Inst, LoopEntry);
1694 if (!Phi)
1695 continue;
1696
1697 // Check if the result of the instruction is live of the loop.
1698 bool LiveOutLoop = false;
1699 for (User *U : Inst.users()) {
1700 if ((cast<Instruction>(U))->getParent() != LoopEntry) {
1701 LiveOutLoop = true;
1702 break;
1703 }
1704 }
1705
1706 if (LiveOutLoop) {
1707 CountInst = &Inst;
1708 CountPhi = Phi;
1709 break;
1710 }
1711 }
1712
1713 if (!CountInst)
1714 return false;
1715 }
1716
1717 // step 5: check if the precondition is in this form:
1718 // "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
1719 {
1720 auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
1721 Value *T = matchCondition(PreCondBr, CurLoop->getLoopPreheader());
1722 if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
1723 return false;
1724
1725 CntInst = CountInst;
1726 CntPhi = CountPhi;
1727 Var = T;
1728 }
1729
1730 return true;
1731}
1732
1733/// Return true if the idiom is detected in the loop.
1734///
1735/// Additionally:
1736/// 1) \p CntInst is set to the instruction Counting Leading Zeros (CTLZ)
1737/// or nullptr if there is no such.
1738/// 2) \p CntPhi is set to the corresponding phi node
1739/// or nullptr if there is no such.
1740/// 3) \p Var is set to the value whose CTLZ could be used.
1741/// 4) \p DefX is set to the instruction calculating Loop exit condition.
1742///
1743/// The core idiom we are trying to detect is:
1744/// \code
1745/// if (x0 == 0)
1746/// goto loop-exit // the precondition of the loop
1747/// cnt0 = init-val;
1748/// do {
1749/// x = phi (x0, x.next); //PhiX
1750/// cnt = phi(cnt0, cnt.next);
1751///
1752/// cnt.next = cnt + 1;
1753/// ...
1754/// x.next = x >> 1; // DefX
1755/// ...
1756/// } while(x.next != 0);
1757///
1758/// loop-exit:
1759/// \endcode
1760static bool detectShiftUntilZeroIdiom(Loop *CurLoop, const DataLayout &DL,
1761 Intrinsic::ID &IntrinID, Value *&InitX,
1762 Instruction *&CntInst, PHINode *&CntPhi,
1763 Instruction *&DefX) {
1764 BasicBlock *LoopEntry;
1765 Value *VarX = nullptr;
1766
1767 DefX = nullptr;
1768 CntInst = nullptr;
1769 CntPhi = nullptr;
1770 LoopEntry = *(CurLoop->block_begin());
1771
1772 // step 1: Check if the loop-back branch is in desirable form.
1773 if (Value *T = matchCondition(
18
Assuming 'T' is non-null, which participates in a condition later
19
Taking true branch
1774 dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
17
Assuming the object is not a 'BranchInst'
1775 DefX = dyn_cast<Instruction>(T);
20
Assuming 'T' is a 'Instruction'
1776 else
1777 return false;
1778
1779 // step 2: detect instructions corresponding to "x.next = x >> 1 or x << 1"
1780 if (!DefX
20.1
'DefX' is non-null
|| !DefX->isShift())
21
Assuming the condition is false
1781 return false;
1782 IntrinID = DefX->getOpcode() == Instruction::Shl ? Intrinsic::cttz :
22
Taking false branch
23
Assuming the condition is false
24
'?' condition is false
1783 Intrinsic::ctlz;
1784 ConstantInt *Shft = dyn_cast<ConstantInt>(DefX->getOperand(1));
25
Assuming the object is a 'ConstantInt'
1785 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
1786 return false;
1787 VarX = DefX->getOperand(0);
1788
1789 // step 3: Check the recurrence of variable X
1790 PHINode *PhiX = getRecurrenceVar(VarX, DefX, LoopEntry);
1791 if (!PhiX)
28
Assuming 'PhiX' is non-null, which participates in a condition later
29
Taking false branch
1792 return false;
1793
1794 InitX = PhiX->getIncomingValueForBlock(CurLoop->getLoopPreheader());
30
Value assigned to 'InitX'
1795
1796 // Make sure the initial value can't be negative otherwise the ashr in the
1797 // loop might never reach zero which would make the loop infinite.
1798 if (DefX->getOpcode() == Instruction::AShr && !isKnownNonNegative(InitX, DL))
31
Assuming the condition is false
1799 return false;
1800
1801 // step 4: Find the instruction which count the CTLZ: cnt.next = cnt + 1
1802 // or cnt.next = cnt + -1.
1803 // TODO: We can skip the step. If loop trip count is known (CTLZ),
1804 // then all uses of "cnt.next" could be optimized to the trip count
1805 // plus "cnt0". Currently it is not optimized.
1806 // This step could be used to detect POPCNT instruction:
1807 // cnt.next = cnt + (x.next & 1)
1808 for (Instruction &Inst : llvm::make_range(
1809 LoopEntry->getFirstNonPHI()->getIterator(), LoopEntry->end())) {
1810 if (Inst.getOpcode() != Instruction::Add)
32
Assuming the condition is false
33
Taking false branch
1811 continue;
1812
1813 ConstantInt *Inc = dyn_cast<ConstantInt>(Inst.getOperand(1));
34
Assuming the object is a 'ConstantInt'
1814 if (!Inc
34.1
'Inc' is non-null, which participates in a condition later
|| (!Inc->isOne() && !Inc->isMinusOne()))
35
Assuming the condition is false
1815 continue;
1816
1817 PHINode *Phi = getRecurrenceVar(Inst.getOperand(0), &Inst, LoopEntry);
1818 if (!Phi)
36
Assuming 'Phi' is non-null, which participates in a condition later
37
Taking false branch
1819 continue;
1820
1821 CntInst = &Inst;
1822 CntPhi = Phi;
1823 break;
1824 }
1825 if (!CntInst
38.1
'CntInst' is non-null
)
38
Execution continues on line 1825
39
Taking false branch
1826 return false;
1827
1828 return true;
40
Returning the value 1, which participates in a condition later
1829}
1830
1831/// Recognize CTLZ or CTTZ idiom in a non-countable loop and convert the loop
1832/// to countable (with CTLZ / CTTZ trip count). If CTLZ / CTTZ inserted as a new
1833/// trip count returns true; otherwise, returns false.
1834bool LoopIdiomRecognize::recognizeAndInsertFFS() {
1835 // Give up if the loop has multiple blocks or multiple backedges.
1836 if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
13
Assuming the condition is false
14
Assuming the condition is false
15
Taking false branch
1837 return false;
1838
1839 Intrinsic::ID IntrinID;
1840 Value *InitX;
1841 Instruction *DefX = nullptr;
1842 PHINode *CntPhi = nullptr;
1843 Instruction *CntInst = nullptr;
1844 // Help decide if transformation is profitable. For ShiftUntilZero idiom,
1845 // this is always 6.
1846 size_t IdiomCanonicalSize = 6;
1847
1848 if (!detectShiftUntilZeroIdiom(CurLoop, *DL, IntrinID, InitX,
16
Calling 'detectShiftUntilZeroIdiom'
41
Returning from 'detectShiftUntilZeroIdiom'
42
Taking false branch
1849 CntInst, CntPhi, DefX))
1850 return false;
1851
1852 bool IsCntPhiUsedOutsideLoop = false;
1853 for (User *U : CntPhi->users())
1854 if (!CurLoop->contains(cast<Instruction>(U))) {
1855 IsCntPhiUsedOutsideLoop = true;
1856 break;
1857 }
1858 bool IsCntInstUsedOutsideLoop = false;
1859 for (User *U : CntInst->users())
1860 if (!CurLoop->contains(cast<Instruction>(U))) {
1861 IsCntInstUsedOutsideLoop = true;
1862 break;
1863 }
1864 // If both CntInst and CntPhi are used outside the loop the profitability
1865 // is questionable.
1866 if (IsCntInstUsedOutsideLoop
42.1
'IsCntInstUsedOutsideLoop' is false
&& IsCntPhiUsedOutsideLoop)
1867 return false;
1868
1869 // For some CPUs result of CTLZ(X) intrinsic is undefined
1870 // when X is 0. If we can not guarantee X != 0, we need to check this
1871 // when expand.
1872 bool ZeroCheck = false;
1873 // It is safe to assume Preheader exist as it was checked in
1874 // parent function RunOnLoop.
1875 BasicBlock *PH = CurLoop->getLoopPreheader();
1876
1877 // If we are using the count instruction outside the loop, make sure we
1878 // have a zero check as a precondition. Without the check the loop would run
1879 // one iteration for before any check of the input value. This means 0 and 1
1880 // would have identical behavior in the original loop and thus
1881 if (!IsCntPhiUsedOutsideLoop
42.2
'IsCntPhiUsedOutsideLoop' is false
) {
43
Taking true branch
1882 auto *PreCondBB = PH->getSinglePredecessor();
1883 if (!PreCondBB)
44
Assuming 'PreCondBB' is non-null
45
Taking false branch
1884 return false;
1885 auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
46
Assuming the object is a 'BranchInst'
1886 if (!PreCondBI
46.1
'PreCondBI' is non-null
)
47
Taking false branch
1887 return false;
1888 if (matchCondition(PreCondBI, PH) != InitX)
48
Assuming pointer value is null
49
Taking false branch
1889 return false;
1890 ZeroCheck = true;
1891 }
1892
1893 // Check if CTLZ / CTTZ intrinsic is profitable. Assume it is always
1894 // profitable if we delete the loop.
1895
1896 // the loop has only 6 instructions:
1897 // %n.addr.0 = phi [ %n, %entry ], [ %shr, %while.cond ]
1898 // %i.0 = phi [ %i0, %entry ], [ %inc, %while.cond ]
1899 // %shr = ashr %n.addr.0, 1
1900 // %tobool = icmp eq %shr, 0
1901 // %inc = add nsw %i.0, 1
1902 // br i1 %tobool
1903
1904 const Value *Args[] = {InitX,
1905 ConstantInt::getBool(InitX->getContext(), ZeroCheck)};
50
Called C++ object pointer is null
1906
1907 // @llvm.dbg doesn't count as they have no semantic effect.
1908 auto InstWithoutDebugIt = CurLoop->getHeader()->instructionsWithoutDebug();
1909 uint32_t HeaderSize =
1910 std::distance(InstWithoutDebugIt.begin(), InstWithoutDebugIt.end());
1911
1912 IntrinsicCostAttributes Attrs(IntrinID, InitX->getType(), Args);
1913 InstructionCost Cost =
1914 TTI->getIntrinsicInstrCost(Attrs, TargetTransformInfo::TCK_SizeAndLatency);
1915 if (HeaderSize != IdiomCanonicalSize &&
1916 Cost > TargetTransformInfo::TCC_Basic)
1917 return false;
1918
1919 transformLoopToCountable(IntrinID, PH, CntInst, CntPhi, InitX, DefX,
1920 DefX->getDebugLoc(), ZeroCheck,
1921 IsCntPhiUsedOutsideLoop);
1922 return true;
1923}
1924
1925/// Recognizes a population count idiom in a non-countable loop.
1926///
1927/// If detected, transforms the relevant code to issue the popcount intrinsic
1928/// function call, and returns true; otherwise, returns false.
1929bool LoopIdiomRecognize::recognizePopcount() {
1930 if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
1931 return false;
1932
1933 // Counting population are usually conducted by few arithmetic instructions.
1934 // Such instructions can be easily "absorbed" by vacant slots in a
1935 // non-compact loop. Therefore, recognizing popcount idiom only makes sense
1936 // in a compact loop.
1937
1938 // Give up if the loop has multiple blocks or multiple backedges.
1939 if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
1940 return false;
1941
1942 BasicBlock *LoopBody = *(CurLoop->block_begin());
1943 if (LoopBody->size() >= 20) {
1944 // The loop is too big, bail out.
1945 return false;
1946 }
1947
1948 // It should have a preheader containing nothing but an unconditional branch.
1949 BasicBlock *PH = CurLoop->getLoopPreheader();
1950 if (!PH || &PH->front() != PH->getTerminator())
1951 return false;
1952 auto *EntryBI = dyn_cast<BranchInst>(PH->getTerminator());
1953 if (!EntryBI || EntryBI->isConditional())
1954 return false;
1955
1956 // It should have a precondition block where the generated popcount intrinsic
1957 // function can be inserted.
1958 auto *PreCondBB = PH->getSinglePredecessor();
1959 if (!PreCondBB)
1960 return false;
1961 auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
1962 if (!PreCondBI || PreCondBI->isUnconditional())
1963 return false;
1964
1965 Instruction *CntInst;
1966 PHINode *CntPhi;
1967 Value *Val;
1968 if (!detectPopcountIdiom(CurLoop, PreCondBB, CntInst, CntPhi, Val))
1969 return false;
1970
1971 transformLoopToPopcount(PreCondBB, CntInst, CntPhi, Val);
1972 return true;
1973}
1974
1975static CallInst *createPopcntIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
1976 const DebugLoc &DL) {
1977 Value *Ops[] = {Val};
1978 Type *Tys[] = {Val->getType()};
1979
1980 Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
1981 Function *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
1982 CallInst *CI = IRBuilder.CreateCall(Func, Ops);
1983 CI->setDebugLoc(DL);
1984
1985 return CI;
1986}
1987
1988static CallInst *createFFSIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
1989 const DebugLoc &DL, bool ZeroCheck,
1990 Intrinsic::ID IID) {
1991 Value *Ops[] = {Val, IRBuilder.getInt1(ZeroCheck)};
1992 Type *Tys[] = {Val->getType()};
1993
1994 Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
1995 Function *Func = Intrinsic::getDeclaration(M, IID, Tys);
1996 CallInst *CI = IRBuilder.CreateCall(Func, Ops);
1997 CI->setDebugLoc(DL);
1998
1999 return CI;
2000}
2001
2002/// Transform the following loop (Using CTLZ, CTTZ is similar):
2003/// loop:
2004/// CntPhi = PHI [Cnt0, CntInst]
2005/// PhiX = PHI [InitX, DefX]
2006/// CntInst = CntPhi + 1
2007/// DefX = PhiX >> 1
2008/// LOOP_BODY
2009/// Br: loop if (DefX != 0)
2010/// Use(CntPhi) or Use(CntInst)
2011///
2012/// Into:
2013/// If CntPhi used outside the loop:
2014/// CountPrev = BitWidth(InitX) - CTLZ(InitX >> 1)
2015/// Count = CountPrev + 1
2016/// else
2017/// Count = BitWidth(InitX) - CTLZ(InitX)
2018/// loop:
2019/// CntPhi = PHI [Cnt0, CntInst]
2020/// PhiX = PHI [InitX, DefX]
2021/// PhiCount = PHI [Count, Dec]
2022/// CntInst = CntPhi + 1
2023/// DefX = PhiX >> 1
2024/// Dec = PhiCount - 1
2025/// LOOP_BODY
2026/// Br: loop if (Dec != 0)
2027/// Use(CountPrev + Cnt0) // Use(CntPhi)
2028/// or
2029/// Use(Count + Cnt0) // Use(CntInst)
2030///
2031/// If LOOP_BODY is empty the loop will be deleted.
2032/// If CntInst and DefX are not used in LOOP_BODY they will be removed.
2033void LoopIdiomRecognize::transformLoopToCountable(
2034 Intrinsic::ID IntrinID, BasicBlock *Preheader, Instruction *CntInst,
2035 PHINode *CntPhi, Value *InitX, Instruction *DefX, const DebugLoc &DL,
2036 bool ZeroCheck, bool IsCntPhiUsedOutsideLoop) {
2037 BranchInst *PreheaderBr = cast<BranchInst>(Preheader->getTerminator());
2038
2039 // Step 1: Insert the CTLZ/CTTZ instruction at the end of the preheader block
2040 IRBuilder<> Builder(PreheaderBr);
2041 Builder.SetCurrentDebugLocation(DL);
2042
2043 // If there are no uses of CntPhi crate:
2044 // Count = BitWidth - CTLZ(InitX);
2045 // NewCount = Count;
2046 // If there are uses of CntPhi create:
2047 // NewCount = BitWidth - CTLZ(InitX >> 1);
2048 // Count = NewCount + 1;
2049 Value *InitXNext;
2050 if (IsCntPhiUsedOutsideLoop) {
2051 if (DefX->getOpcode() == Instruction::AShr)
2052 InitXNext = Builder.CreateAShr(InitX, 1);
2053 else if (DefX->getOpcode() == Instruction::LShr)
2054 InitXNext = Builder.CreateLShr(InitX, 1);
2055 else if (DefX->getOpcode() == Instruction::Shl) // cttz
2056 InitXNext = Builder.CreateShl(InitX, 1);
2057 else
2058 llvm_unreachable("Unexpected opcode!")::llvm::llvm_unreachable_internal("Unexpected opcode!", "llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp"
, 2058)
;
2059 } else
2060 InitXNext = InitX;
2061 Value *Count =
2062 createFFSIntrinsic(Builder, InitXNext, DL, ZeroCheck, IntrinID);
2063 Type *CountTy = Count->getType();
2064 Count = Builder.CreateSub(
2065 ConstantInt::get(CountTy, CountTy->getIntegerBitWidth()), Count);
2066 Value *NewCount = Count;
2067 if (IsCntPhiUsedOutsideLoop)
2068 Count = Builder.CreateAdd(Count, ConstantInt::get(CountTy, 1));
2069
2070 NewCount = Builder.CreateZExtOrTrunc(NewCount, CntInst->getType());
2071
2072 Value *CntInitVal = CntPhi->getIncomingValueForBlock(Preheader);
2073 if (cast<ConstantInt>(CntInst->getOperand(1))->isOne()) {
2074 // If the counter was being incremented in the loop, add NewCount to the
2075 // counter's initial value, but only if the initial value is not zero.
2076 ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
2077 if (!InitConst || !InitConst->isZero())
2078 NewCount = Builder.CreateAdd(NewCount, CntInitVal);
2079 } else {
2080 // If the count was being decremented in the loop, subtract NewCount from
2081 // the counter's initial value.
2082 NewCount = Builder.CreateSub(CntInitVal, NewCount);
2083 }
2084
2085 // Step 2: Insert new IV and loop condition:
2086 // loop:
2087 // ...
2088 // PhiCount = PHI [Count, Dec]
2089 // ...
2090 // Dec = PhiCount - 1
2091 // ...
2092 // Br: loop if (Dec != 0)
2093 BasicBlock *Body = *(CurLoop->block_begin());
2094 auto *LbBr = cast<BranchInst>(Body->getTerminator());
2095 ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
2096
2097 PHINode *TcPhi = PHINode::Create(CountTy, 2, "tcphi", &Body->front());
2098
2099 Builder.SetInsertPoint(LbCond);
2100 Instruction *TcDec = cast<Instruction>(Builder.CreateSub(
2101 TcPhi, ConstantInt::get(CountTy, 1), "tcdec", false, true));
2102
2103 TcPhi->addIncoming(Count, Preheader);
2104 TcPhi->addIncoming(TcDec, Body);
2105
2106 CmpInst::Predicate Pred =
2107 (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_NE : CmpInst::ICMP_EQ;
2108 LbCond->setPredicate(Pred);
2109 LbCond->setOperand(0, TcDec);
2110 LbCond->setOperand(1, ConstantInt::get(CountTy, 0));
2111
2112 // Step 3: All the references to the original counter outside
2113 // the loop are replaced with the NewCount
2114 if (IsCntPhiUsedOutsideLoop)
2115 CntPhi->replaceUsesOutsideBlock(NewCount, Body);
2116 else
2117 CntInst->replaceUsesOutsideBlock(NewCount, Body);
2118
2119 // step 4: Forget the "non-computable" trip-count SCEV associated with the
2120 // loop. The loop would otherwise not be deleted even if it becomes empty.
2121 SE->forgetLoop(CurLoop);
2122}
2123
2124void LoopIdiomRecognize::transformLoopToPopcount(BasicBlock *PreCondBB,
2125 Instruction *CntInst,
2126 PHINode *CntPhi, Value *Var) {
2127 BasicBlock *PreHead = CurLoop->getLoopPreheader();
2128 auto *PreCondBr = cast<BranchInst>(PreCondBB->getTerminator());
2129 const DebugLoc &DL = CntInst->getDebugLoc();
2130
2131 // Assuming before transformation, the loop is following:
2132 // if (x) // the precondition
2133 // do { cnt++; x &= x - 1; } while(x);
2134
2135 // Step 1: Insert the ctpop instruction at the end of the precondition block
2136 IRBuilder<> Builder(PreCondBr);
2137 Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
2138 {
2139 PopCnt = createPopcntIntrinsic(Builder, Var, DL);
2140 NewCount = PopCntZext =
2141 Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));
2142
2143 if (NewCount != PopCnt)
2144 (cast<Instruction>(NewCount))->setDebugLoc(DL);
2145
2146 // TripCnt is exactly the number of iterations the loop has
2147 TripCnt = NewCount;
2148
2149 // If the population counter's initial value is not zero, insert Add Inst.
2150 Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
2151 ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
2152 if (!InitConst || !InitConst->isZero()) {
2153 NewCount = Builder.CreateAdd(NewCount, CntInitVal);
2154 (cast<Instruction>(NewCount))->setDebugLoc(DL);
2155 }
2156 }
2157
2158 // Step 2: Replace the precondition from "if (x == 0) goto loop-exit" to
2159 // "if (NewCount == 0) loop-exit". Without this change, the intrinsic
2160 // function would be partial dead code, and downstream passes will drag
2161 // it back from the precondition block to the preheader.
2162 {
2163 ICmpInst *PreCond = cast<ICmpInst>(PreCondBr->getCondition());
2164
2165 Value *Opnd0 = PopCntZext;
2166 Value *Opnd1 = ConstantInt::get(PopCntZext->getType(), 0);
2167 if (PreCond->getOperand(0) != Var)
2168 std::swap(Opnd0, Opnd1);
2169
2170 ICmpInst *NewPreCond = cast<ICmpInst>(
2171 Builder.CreateICmp(PreCond->getPredicate(), Opnd0, Opnd1));
2172 PreCondBr->setCondition(NewPreCond);
2173
2174 RecursivelyDeleteTriviallyDeadInstructions(PreCond, TLI);
2175 }
2176
2177 // Step 3: Note that the population count is exactly the trip count of the
2178 // loop in question, which enable us to convert the loop from noncountable
2179 // loop into a countable one. The benefit is twofold:
2180 //
2181 // - If the loop only counts population, the entire loop becomes dead after
2182 // the transformation. It is a lot easier to prove a countable loop dead
2183 // than to prove a noncountable one. (In some C dialects, an infinite loop
2184 // isn't dead even if it computes nothing useful. In general, DCE needs
2185 // to prove a noncountable loop finite before safely delete it.)
2186 //
2187 // - If the loop also performs something else, it remains alive.
2188 // Since it is transformed to countable form, it can be aggressively
2189 // optimized by some optimizations which are in general not applicable
2190 // to a noncountable loop.
2191 //
2192 // After this step, this loop (conceptually) would look like following:
2193 // newcnt = __builtin_ctpop(x);
2194 // t = newcnt;
2195 // if (x)
2196 // do { cnt++; x &= x-1; t--) } while (t > 0);
2197 BasicBlock *Body = *(CurLoop->block_begin());
2198 {
2199 auto *LbBr = cast<BranchInst>(Body->getTerminator());
2200 ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
2201 Type *Ty = TripCnt->getType();
2202
2203 PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", &Body->front());
2204
2205 Builder.SetInsertPoint(LbCond);
2206 Instruction *TcDec = cast<Instruction>(
2207 Builder.CreateSub(TcPhi, ConstantInt::get(Ty, 1),
2208 "tcdec", false, true));
2209
2210 TcPhi->addIncoming(TripCnt, PreHead);
2211 TcPhi->addIncoming(TcDec, Body);
2212
2213 CmpInst::Predicate Pred =
2214 (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_UGT : CmpInst::ICMP_SLE;
2215 LbCond->setPredicate(Pred);
2216 LbCond->setOperand(0, TcDec);
2217 LbCond->setOperand(1, ConstantInt::get(Ty, 0));
2218 }
2219
2220 // Step 4: All the references to the original population counter outside
2221 // the loop are replaced with the NewCount -- the value returned from
2222 // __builtin_ctpop().
2223 CntInst->replaceUsesOutsideBlock(NewCount, Body);
2224
2225 // step 5: Forget the "non-computable" trip-count SCEV associated with the
2226 // loop. The loop would otherwise not be deleted even if it becomes empty.
2227 SE->forgetLoop(CurLoop);
2228}
2229
2230/// Match loop-invariant value.
2231template <typename SubPattern_t> struct match_LoopInvariant {
2232 SubPattern_t SubPattern;
2233 const Loop *L;
2234
2235 match_LoopInvariant(const SubPattern_t &SP, const Loop *L)
2236 : SubPattern(SP), L(L) {}
2237
2238 template <typename ITy> bool match(ITy *V) {
2239 return L->isLoopInvariant(V) && SubPattern.match(V);
2240 }
2241};
2242
2243/// Matches if the value is loop-invariant.
2244template <typename Ty>
2245inline match_LoopInvariant<Ty> m_LoopInvariant(const Ty &M, const Loop *L) {
2246 return match_LoopInvariant<Ty>(M, L);
2247}
2248
2249/// Return true if the idiom is detected in the loop.
2250///
2251/// The core idiom we are trying to detect is:
2252/// \code
2253/// entry:
2254/// <...>
2255/// %bitmask = shl i32 1, %bitpos
2256/// br label %loop
2257///
2258/// loop:
2259/// %x.curr = phi i32 [ %x, %entry ], [ %x.next, %loop ]
2260/// %x.curr.bitmasked = and i32 %x.curr, %bitmask
2261/// %x.curr.isbitunset = icmp eq i32 %x.curr.bitmasked, 0
2262/// %x.next = shl i32 %x.curr, 1
2263/// <...>
2264/// br i1 %x.curr.isbitunset, label %loop, label %end
2265///
2266/// end:
2267/// %x.curr.res = phi i32 [ %x.curr, %loop ] <...>
2268/// %x.next.res = phi i32 [ %x.next, %loop ] <...>
2269/// <...>
2270/// \endcode
2271static bool detectShiftUntilBitTestIdiom(Loop *CurLoop, Value *&BaseX,
2272 Value *&BitMask, Value *&BitPos,
2273 Value *&CurrX, Instruction *&NextX) {
2274 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Performing shift-until-bittest idiom detection.\n"
; } } while (false)
2275 " 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)
;
2276
2277 // Give up if the loop has multiple blocks or multiple backedges.
2278 if (CurLoop->getNumBlocks() != 1 || CurLoop->getNumBackEdges() != 1) {
2279 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)
;
2280 return false;
2281 }
2282
2283 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2284 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2285 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", 2285, __extension__
__PRETTY_FUNCTION__))
;
2286
2287 using namespace PatternMatch;
2288
2289 // Step 1: Check if the loop backedge is in desirable form.
2290
2291 ICmpInst::Predicate Pred;
2292 Value *CmpLHS, *CmpRHS;
2293 BasicBlock *TrueBB, *FalseBB;
2294 if (!match(LoopHeaderBB->getTerminator(),
2295 m_Br(m_ICmp(Pred, m_Value(CmpLHS), m_Value(CmpRHS)),
2296 m_BasicBlock(TrueBB), m_BasicBlock(FalseBB)))) {
2297 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)
;
2298 return false;
2299 }
2300
2301 // Step 2: Check if the backedge's condition is in desirable form.
2302
2303 auto MatchVariableBitMask = [&]() {
2304 return ICmpInst::isEquality(Pred) && match(CmpRHS, m_Zero()) &&
2305 match(CmpLHS,
2306 m_c_And(m_Value(CurrX),
2307 m_CombineAnd(
2308 m_Value(BitMask),
2309 m_LoopInvariant(m_Shl(m_One(), m_Value(BitPos)),
2310 CurLoop))));
2311 };
2312 auto MatchConstantBitMask = [&]() {
2313 return ICmpInst::isEquality(Pred) && match(CmpRHS, m_Zero()) &&
2314 match(CmpLHS, m_And(m_Value(CurrX),
2315 m_CombineAnd(m_Value(BitMask), m_Power2()))) &&
2316 (BitPos = ConstantExpr::getExactLogBase2(cast<Constant>(BitMask)));
2317 };
2318 auto MatchDecomposableConstantBitMask = [&]() {
2319 APInt Mask;
2320 return llvm::decomposeBitTestICmp(CmpLHS, CmpRHS, Pred, CurrX, Mask) &&
2321 ICmpInst::isEquality(Pred) && Mask.isPowerOf2() &&
2322 (BitMask = ConstantInt::get(CurrX->getType(), Mask)) &&
2323 (BitPos = ConstantInt::get(CurrX->getType(), Mask.logBase2()));
2324 };
2325
2326 if (!MatchVariableBitMask() && !MatchConstantBitMask() &&
2327 !MatchDecomposableConstantBitMask()) {
2328 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)
;
2329 return false;
2330 }
2331
2332 // Step 3: Check if the recurrence is in desirable form.
2333 auto *CurrXPN = dyn_cast<PHINode>(CurrX);
2334 if (!CurrXPN || CurrXPN->getParent() != LoopHeaderBB) {
2335 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)
;
2336 return false;
2337 }
2338
2339 BaseX = CurrXPN->getIncomingValueForBlock(LoopPreheaderBB);
2340 NextX =
2341 dyn_cast<Instruction>(CurrXPN->getIncomingValueForBlock(LoopHeaderBB));
2342
2343 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", 2344, __extension__
__PRETTY_FUNCTION__))
2344 "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", 2344, __extension__
__PRETTY_FUNCTION__))
;
2345
2346 if (!NextX || !match(NextX, m_Shl(m_Specific(CurrX), m_One()))) {
2347 // FIXME: support right-shift?
2348 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad recurrence.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad recurrence.\n"
; } } while (false)
;
2349 return false;
2350 }
2351
2352 // Step 4: Check if the backedge's destinations are in desirable form.
2353
2354 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", 2355, __extension__
__PRETTY_FUNCTION__))
2355 "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", 2355, __extension__
__PRETTY_FUNCTION__))
;
2356
2357 // cmp-br is commutative, so canonicalize to a single variant.
2358 if (Pred != ICmpInst::Predicate::ICMP_EQ) {
2359 Pred = ICmpInst::getInversePredicate(Pred);
2360 std::swap(TrueBB, FalseBB);
2361 }
2362
2363 // We expect to exit loop when comparison yields false,
2364 // so when it yields true we should branch back to loop header.
2365 if (TrueBB != LoopHeaderBB) {
2366 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)
;
2367 return false;
2368 }
2369
2370 // Okay, idiom checks out.
2371 return true;
2372}
2373
2374/// Look for the following loop:
2375/// \code
2376/// entry:
2377/// <...>
2378/// %bitmask = shl i32 1, %bitpos
2379/// br label %loop
2380///
2381/// loop:
2382/// %x.curr = phi i32 [ %x, %entry ], [ %x.next, %loop ]
2383/// %x.curr.bitmasked = and i32 %x.curr, %bitmask
2384/// %x.curr.isbitunset = icmp eq i32 %x.curr.bitmasked, 0
2385/// %x.next = shl i32 %x.curr, 1
2386/// <...>
2387/// br i1 %x.curr.isbitunset, label %loop, label %end
2388///
2389/// end:
2390/// %x.curr.res = phi i32 [ %x.curr, %loop ] <...>
2391/// %x.next.res = phi i32 [ %x.next, %loop ] <...>
2392/// <...>
2393/// \endcode
2394///
2395/// And transform it into:
2396/// \code
2397/// entry:
2398/// %bitmask = shl i32 1, %bitpos
2399/// %lowbitmask = add i32 %bitmask, -1
2400/// %mask = or i32 %lowbitmask, %bitmask
2401/// %x.masked = and i32 %x, %mask
2402/// %x.masked.numleadingzeros = call i32 @llvm.ctlz.i32(i32 %x.masked,
2403/// i1 true)
2404/// %x.masked.numactivebits = sub i32 32, %x.masked.numleadingzeros
2405/// %x.masked.leadingonepos = add i32 %x.masked.numactivebits, -1
2406/// %backedgetakencount = sub i32 %bitpos, %x.masked.leadingonepos
2407/// %tripcount = add i32 %backedgetakencount, 1
2408/// %x.curr = shl i32 %x, %backedgetakencount
2409/// %x.next = shl i32 %x, %tripcount
2410/// br label %loop
2411///
2412/// loop:
2413/// %loop.iv = phi i32 [ 0, %entry ], [ %loop.iv.next, %loop ]
2414/// %loop.iv.next = add nuw i32 %loop.iv, 1
2415/// %loop.ivcheck = icmp eq i32 %loop.iv.next, %tripcount
2416/// <...>
2417/// br i1 %loop.ivcheck, label %end, label %loop
2418///
2419/// end:
2420/// %x.curr.res = phi i32 [ %x.curr, %loop ] <...>
2421/// %x.next.res = phi i32 [ %x.next, %loop ] <...>
2422/// <...>
2423/// \endcode
2424bool LoopIdiomRecognize::recognizeShiftUntilBitTest() {
2425 bool MadeChange = false;
2426
2427 Value *X, *BitMask, *BitPos, *XCurr;
2428 Instruction *XNext;
2429 if (!detectShiftUntilBitTestIdiom(CurLoop, X, BitMask, BitPos, XCurr,
2430 XNext)) {
2431 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " shift-until-bittest idiom detection failed.\n"
; } } while (false)
2432 " 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)
;
2433 return MadeChange;
2434 }
2435 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)
;
2436
2437 // Ok, it is the idiom we were looking for, we *could* transform this loop,
2438 // but is it profitable to transform?
2439
2440 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2441 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2442 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", 2442, __extension__
__PRETTY_FUNCTION__))
;
2443
2444 BasicBlock *SuccessorBB = CurLoop->getExitBlock();
2445 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", 2445, __extension__
__PRETTY_FUNCTION__))
;
2446
2447 IRBuilder<> Builder(LoopPreheaderBB->getTerminator());
2448 Builder.SetCurrentDebugLocation(cast<Instruction>(XCurr)->getDebugLoc());
2449
2450 Intrinsic::ID IntrID = Intrinsic::ctlz;
2451 Type *Ty = X->getType();
2452 unsigned Bitwidth = Ty->getScalarSizeInBits();
2453
2454 TargetTransformInfo::TargetCostKind CostKind =
2455 TargetTransformInfo::TCK_SizeAndLatency;
2456
2457 // The rewrite is considered to be unprofitable iff and only iff the
2458 // intrinsic/shift we'll use are not cheap. Note that we are okay with *just*
2459 // making the loop countable, even if nothing else changes.
2460 IntrinsicCostAttributes Attrs(
2461 IntrID, Ty, {UndefValue::get(Ty), /*is_zero_undef=*/Builder.getTrue()});
2462 InstructionCost Cost = TTI->getIntrinsicInstrCost(Attrs, CostKind);
2463 if (Cost > TargetTransformInfo::TCC_Basic) {
2464 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Intrinsic is too costly, not beneficial\n"
; } } while (false)
2465 " 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)
;
2466 return MadeChange;
2467 }
2468 if (TTI->getArithmeticInstrCost(Instruction::Shl, Ty, CostKind) >
2469 TargetTransformInfo::TCC_Basic) {
2470 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)
;
2471 return MadeChange;
2472 }
2473
2474 // Ok, transform appears worthwhile.
2475 MadeChange = true;
2476
2477 // Step 1: Compute the loop trip count.
2478
2479 Value *LowBitMask = Builder.CreateAdd(BitMask, Constant::getAllOnesValue(Ty),
2480 BitPos->getName() + ".lowbitmask");
2481 Value *Mask =
2482 Builder.CreateOr(LowBitMask, BitMask, BitPos->getName() + ".mask");
2483 Value *XMasked = Builder.CreateAnd(X, Mask, X->getName() + ".masked");
2484 CallInst *XMaskedNumLeadingZeros = Builder.CreateIntrinsic(
2485 IntrID, Ty, {XMasked, /*is_zero_undef=*/Builder.getTrue()},
2486 /*FMFSource=*/nullptr, XMasked->getName() + ".numleadingzeros");
2487 Value *XMaskedNumActiveBits = Builder.CreateSub(
2488 ConstantInt::get(Ty, Ty->getScalarSizeInBits()), XMaskedNumLeadingZeros,
2489 XMasked->getName() + ".numactivebits", /*HasNUW=*/true,
2490 /*HasNSW=*/Bitwidth != 2);
2491 Value *XMaskedLeadingOnePos =
2492 Builder.CreateAdd(XMaskedNumActiveBits, Constant::getAllOnesValue(Ty),
2493 XMasked->getName() + ".leadingonepos", /*HasNUW=*/false,
2494 /*HasNSW=*/Bitwidth > 2);
2495
2496 Value *LoopBackedgeTakenCount = Builder.CreateSub(
2497 BitPos, XMaskedLeadingOnePos, CurLoop->getName() + ".backedgetakencount",
2498 /*HasNUW=*/true, /*HasNSW=*/true);
2499 // We know loop's backedge-taken count, but what's loop's trip count?
2500 // Note that while NUW is always safe, while NSW is only for bitwidths != 2.
2501 Value *LoopTripCount =
2502 Builder.CreateAdd(LoopBackedgeTakenCount, ConstantInt::get(Ty, 1),
2503 CurLoop->getName() + ".tripcount", /*HasNUW=*/true,
2504 /*HasNSW=*/Bitwidth != 2);
2505
2506 // Step 2: Compute the recurrence's final value without a loop.
2507
2508 // NewX is always safe to compute, because `LoopBackedgeTakenCount`
2509 // will always be smaller than `bitwidth(X)`, i.e. we never get poison.
2510 Value *NewX = Builder.CreateShl(X, LoopBackedgeTakenCount);
2511 NewX->takeName(XCurr);
2512 if (auto *I = dyn_cast<Instruction>(NewX))
2513 I->copyIRFlags(XNext, /*IncludeWrapFlags=*/true);
2514
2515 Value *NewXNext;
2516 // Rewriting XNext is more complicated, however, because `X << LoopTripCount`
2517 // will be poison iff `LoopTripCount == bitwidth(X)` (which will happen
2518 // iff `BitPos` is `bitwidth(x) - 1` and `X` is `1`). So unless we know
2519 // that isn't the case, we'll need to emit an alternative, safe IR.
2520 if (XNext->hasNoSignedWrap() || XNext->hasNoUnsignedWrap() ||
2521 PatternMatch::match(
2522 BitPos, PatternMatch::m_SpecificInt_ICMP(
2523 ICmpInst::ICMP_NE, APInt(Ty->getScalarSizeInBits(),
2524 Ty->getScalarSizeInBits() - 1))))
2525 NewXNext = Builder.CreateShl(X, LoopTripCount);
2526 else {
2527 // Otherwise, just additionally shift by one. It's the smallest solution,
2528 // alternatively, we could check that NewX is INT_MIN (or BitPos is )
2529 // and select 0 instead.
2530 NewXNext = Builder.CreateShl(NewX, ConstantInt::get(Ty, 1));
2531 }
2532
2533 NewXNext->takeName(XNext);
2534 if (auto *I = dyn_cast<Instruction>(NewXNext))
2535 I->copyIRFlags(XNext, /*IncludeWrapFlags=*/true);
2536
2537 // Step 3: Adjust the successor basic block to recieve the computed
2538 // recurrence's final value instead of the recurrence itself.
2539
2540 XCurr->replaceUsesOutsideBlock(NewX, LoopHeaderBB);
2541 XNext->replaceUsesOutsideBlock(NewXNext, LoopHeaderBB);
2542
2543 // Step 4: Rewrite the loop into a countable form, with canonical IV.
2544
2545 // The new canonical induction variable.
2546 Builder.SetInsertPoint(&LoopHeaderBB->front());
2547 auto *IV = Builder.CreatePHI(Ty, 2, CurLoop->getName() + ".iv");
2548
2549 // The induction itself.
2550 // Note that while NUW is always safe, while NSW is only for bitwidths != 2.
2551 Builder.SetInsertPoint(LoopHeaderBB->getTerminator());
2552 auto *IVNext =
2553 Builder.CreateAdd(IV, ConstantInt::get(Ty, 1), IV->getName() + ".next",
2554 /*HasNUW=*/true, /*HasNSW=*/Bitwidth != 2);
2555
2556 // The loop trip count check.
2557 auto *IVCheck = Builder.CreateICmpEQ(IVNext, LoopTripCount,
2558 CurLoop->getName() + ".ivcheck");
2559 Builder.CreateCondBr(IVCheck, SuccessorBB, LoopHeaderBB);
2560 LoopHeaderBB->getTerminator()->eraseFromParent();
2561
2562 // Populate the IV PHI.
2563 IV->addIncoming(ConstantInt::get(Ty, 0), LoopPreheaderBB);
2564 IV->addIncoming(IVNext, LoopHeaderBB);
2565
2566 // Step 5: Forget the "non-computable" trip-count SCEV associated with the
2567 // loop. The loop would otherwise not be deleted even if it becomes empty.
2568
2569 SE->forgetLoop(CurLoop);
2570
2571 // Other passes will take care of actually deleting the loop if possible.
2572
2573 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)
;
2574
2575 ++NumShiftUntilBitTest;
2576 return MadeChange;
2577}
2578
2579/// Return true if the idiom is detected in the loop.
2580///
2581/// The core idiom we are trying to detect is:
2582/// \code
2583/// entry:
2584/// <...>
2585/// %start = <...>
2586/// %extraoffset = <...>
2587/// <...>
2588/// br label %for.cond
2589///
2590/// loop:
2591/// %iv = phi i8 [ %start, %entry ], [ %iv.next, %for.cond ]
2592/// %nbits = add nsw i8 %iv, %extraoffset
2593/// %val.shifted = {{l,a}shr,shl} i8 %val, %nbits
2594/// %val.shifted.iszero = icmp eq i8 %val.shifted, 0
2595/// %iv.next = add i8 %iv, 1
2596/// <...>
2597/// br i1 %val.shifted.iszero, label %end, label %loop
2598///
2599/// end:
2600/// %iv.res = phi i8 [ %iv, %loop ] <...>
2601/// %nbits.res = phi i8 [ %nbits, %loop ] <...>
2602/// %val.shifted.res = phi i8 [ %val.shifted, %loop ] <...>
2603/// %val.shifted.iszero.res = phi i1 [ %val.shifted.iszero, %loop ] <...>
2604/// %iv.next.res = phi i8 [ %iv.next, %loop ] <...>
2605/// <...>
2606/// \endcode
2607static bool detectShiftUntilZeroIdiom(Loop *CurLoop, ScalarEvolution *SE,
2608 Instruction *&ValShiftedIsZero,
2609 Intrinsic::ID &IntrinID, Instruction *&IV,
2610 Value *&Start, Value *&Val,
2611 const SCEV *&ExtraOffsetExpr,
2612 bool &InvertedCond) {
2613 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Performing shift-until-zero idiom detection.\n"
; } } while (false)
2614 " 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)
;
2615
2616 // Give up if the loop has multiple blocks or multiple backedges.
2617 if (CurLoop->getNumBlocks() != 1 || CurLoop->getNumBackEdges() != 1) {
2618 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)
;
2619 return false;
2620 }
2621
2622 Instruction *ValShifted, *NBits, *IVNext;
2623 Value *ExtraOffset;
2624
2625 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2626 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2627 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", 2627, __extension__
__PRETTY_FUNCTION__))
;
2628
2629 using namespace PatternMatch;
2630
2631 // Step 1: Check if the loop backedge, condition is in desirable form.
2632
2633 ICmpInst::Predicate Pred;
2634 BasicBlock *TrueBB, *FalseBB;
2635 if (!match(LoopHeaderBB->getTerminator(),
2636 m_Br(m_Instruction(ValShiftedIsZero), m_BasicBlock(TrueBB),
2637 m_BasicBlock(FalseBB))) ||
2638 !match(ValShiftedIsZero,
2639 m_ICmp(Pred, m_Instruction(ValShifted), m_Zero())) ||
2640 !ICmpInst::isEquality(Pred)) {
2641 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)
;
2642 return false;
2643 }
2644
2645 // Step 2: Check if the comparison's operand is in desirable form.
2646 // FIXME: Val could be a one-input PHI node, which we should look past.
2647 if (!match(ValShifted, m_Shift(m_LoopInvariant(m_Value(Val), CurLoop),
2648 m_Instruction(NBits)))) {
2649 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)
;
2650 return false;
2651 }
2652 IntrinID = ValShifted->getOpcode() == Instruction::Shl ? Intrinsic::cttz
2653 : Intrinsic::ctlz;
2654
2655 // Step 3: Check if the shift amount is in desirable form.
2656
2657 if (match(NBits, m_c_Add(m_Instruction(IV),
2658 m_LoopInvariant(m_Value(ExtraOffset), CurLoop))) &&
2659 (NBits->hasNoSignedWrap() || NBits->hasNoUnsignedWrap()))
2660 ExtraOffsetExpr = SE->getNegativeSCEV(SE->getSCEV(ExtraOffset));
2661 else if (match(NBits,
2662 m_Sub(m_Instruction(IV),
2663 m_LoopInvariant(m_Value(ExtraOffset), CurLoop))) &&
2664 NBits->hasNoSignedWrap())
2665 ExtraOffsetExpr = SE->getSCEV(ExtraOffset);
2666 else {
2667 IV = NBits;
2668 ExtraOffsetExpr = SE->getZero(NBits->getType());
2669 }
2670
2671 // Step 4: Check if the recurrence is in desirable form.
2672 auto *IVPN = dyn_cast<PHINode>(IV);
2673 if (!IVPN || IVPN->getParent() != LoopHeaderBB) {
2674 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)
;
2675 return false;
2676 }
2677
2678 Start = IVPN->getIncomingValueForBlock(LoopPreheaderBB);
2679 IVNext = dyn_cast<Instruction>(IVPN->getIncomingValueForBlock(LoopHeaderBB));
2680
2681 if (!IVNext || !match(IVNext, m_Add(m_Specific(IVPN), m_One()))) {
2682 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad recurrence.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Bad recurrence.\n"
; } } while (false)
;
2683 return false;
2684 }
2685
2686 // Step 4: Check if the backedge's destinations are in desirable form.
2687
2688 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", 2689, __extension__
__PRETTY_FUNCTION__))
2689 "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", 2689, __extension__
__PRETTY_FUNCTION__))
;
2690
2691 // cmp-br is commutative, so canonicalize to a single variant.
2692 InvertedCond = Pred != ICmpInst::Predicate::ICMP_EQ;
2693 if (InvertedCond) {
2694 Pred = ICmpInst::getInversePredicate(Pred);
2695 std::swap(TrueBB, FalseBB);
2696 }
2697
2698 // We expect to exit loop when comparison yields true,
2699 // so when it yields false we should branch back to loop header.
2700 if (FalseBB != LoopHeaderBB) {
2701 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)
;
2702 return false;
2703 }
2704
2705 // The new, countable, loop will certainly only run a known number of
2706 // iterations, It won't be infinite. But the old loop might be infinite
2707 // under certain conditions. For logical shifts, the value will become zero
2708 // after at most bitwidth(%Val) loop iterations. However, for arithmetic
2709 // right-shift, iff the sign bit was set, the value will never become zero,
2710 // and the loop may never finish.
2711 if (ValShifted->getOpcode() == Instruction::AShr &&
2712 !isMustProgress(CurLoop) && !SE->isKnownNonNegative(SE->getSCEV(Val))) {
2713 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)
;
2714 return false;
2715 }
2716
2717 // Okay, idiom checks out.
2718 return true;
2719}
2720
2721/// Look for the following loop:
2722/// \code
2723/// entry:
2724/// <...>
2725/// %start = <...>
2726/// %extraoffset = <...>
2727/// <...>
2728/// br label %for.cond
2729///
2730/// loop:
2731/// %iv = phi i8 [ %start, %entry ], [ %iv.next, %for.cond ]
2732/// %nbits = add nsw i8 %iv, %extraoffset
2733/// %val.shifted = {{l,a}shr,shl} i8 %val, %nbits
2734/// %val.shifted.iszero = icmp eq i8 %val.shifted, 0
2735/// %iv.next = add i8 %iv, 1
2736/// <...>
2737/// br i1 %val.shifted.iszero, label %end, label %loop
2738///
2739/// end:
2740/// %iv.res = phi i8 [ %iv, %loop ] <...>
2741/// %nbits.res = phi i8 [ %nbits, %loop ] <...>
2742/// %val.shifted.res = phi i8 [ %val.shifted, %loop ] <...>
2743/// %val.shifted.iszero.res = phi i1 [ %val.shifted.iszero, %loop ] <...>
2744/// %iv.next.res = phi i8 [ %iv.next, %loop ] <...>
2745/// <...>
2746/// \endcode
2747///
2748/// And transform it into:
2749/// \code
2750/// entry:
2751/// <...>
2752/// %start = <...>
2753/// %extraoffset = <...>
2754/// <...>
2755/// %val.numleadingzeros = call i8 @llvm.ct{l,t}z.i8(i8 %val, i1 0)
2756/// %val.numactivebits = sub i8 8, %val.numleadingzeros
2757/// %extraoffset.neg = sub i8 0, %extraoffset
2758/// %tmp = add i8 %val.numactivebits, %extraoffset.neg
2759/// %iv.final = call i8 @llvm.smax.i8(i8 %tmp, i8 %start)
2760/// %loop.tripcount = sub i8 %iv.final, %start
2761/// br label %loop
2762///
2763/// loop:
2764/// %loop.iv = phi i8 [ 0, %entry ], [ %loop.iv.next, %loop ]
2765/// %loop.iv.next = add i8 %loop.iv, 1
2766/// %loop.ivcheck = icmp eq i8 %loop.iv.next, %loop.tripcount
2767/// %iv = add i8 %loop.iv, %start
2768/// <...>
2769/// br i1 %loop.ivcheck, label %end, label %loop
2770///
2771/// end:
2772/// %iv.res = phi i8 [ %iv.final, %loop ] <...>
2773/// <...>
2774/// \endcode
2775bool LoopIdiomRecognize::recognizeShiftUntilZero() {
2776 bool MadeChange = false;
2777
2778 Instruction *ValShiftedIsZero;
2779 Intrinsic::ID IntrID;
2780 Instruction *IV;
2781 Value *Start, *Val;
2782 const SCEV *ExtraOffsetExpr;
2783 bool InvertedCond;
2784 if (!detectShiftUntilZeroIdiom(CurLoop, SE, ValShiftedIsZero, IntrID, IV,
2785 Start, Val, ExtraOffsetExpr, InvertedCond)) {
2786 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " shift-until-zero idiom detection failed.\n"
; } } while (false)
2787 " 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)
;
2788 return MadeChange;
2789 }
2790 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)
;
2791
2792 // Ok, it is the idiom we were looking for, we *could* transform this loop,
2793 // but is it profitable to transform?
2794
2795 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2796 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2797 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", 2797, __extension__
__PRETTY_FUNCTION__))
;
2798
2799 BasicBlock *SuccessorBB = CurLoop->getExitBlock();
2800 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", 2800, __extension__
__PRETTY_FUNCTION__))
;
2801
2802 IRBuilder<> Builder(LoopPreheaderBB->getTerminator());
2803 Builder.SetCurrentDebugLocation(IV->getDebugLoc());
2804
2805 Type *Ty = Val->getType();
2806 unsigned Bitwidth = Ty->getScalarSizeInBits();
2807
2808 TargetTransformInfo::TargetCostKind CostKind =
2809 TargetTransformInfo::TCK_SizeAndLatency;
2810
2811 // The rewrite is considered to be unprofitable iff and only iff the
2812 // intrinsic we'll use are not cheap. Note that we are okay with *just*
2813 // making the loop countable, even if nothing else changes.
2814 IntrinsicCostAttributes Attrs(
2815 IntrID, Ty, {UndefValue::get(Ty), /*is_zero_undef=*/Builder.getFalse()});
2816 InstructionCost Cost = TTI->getIntrinsicInstrCost(Attrs, CostKind);
2817 if (Cost > TargetTransformInfo::TCC_Basic) {
2818 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-idiom")) { dbgs() << "loop-idiom" " Intrinsic is too costly, not beneficial\n"
; } } while (false)
2819 " 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)
;
2820 return MadeChange;
2821 }
2822
2823 // Ok, transform appears worthwhile.
2824 MadeChange = true;
2825
2826 bool OffsetIsZero = false;
2827 if (auto *ExtraOffsetExprC = dyn_cast<SCEVConstant>(ExtraOffsetExpr))
2828 OffsetIsZero = ExtraOffsetExprC->isZero();
2829
2830 // Step 1: Compute the loop's final IV value / trip count.
2831
2832 CallInst *ValNumLeadingZeros = Builder.CreateIntrinsic(
2833 IntrID, Ty, {Val, /*is_zero_undef=*/Builder.getFalse()},
2834 /*FMFSource=*/nullptr, Val->getName() + ".numleadingzeros");
2835 Value *ValNumActiveBits = Builder.CreateSub(
2836 ConstantInt::get(Ty, Ty->getScalarSizeInBits()), ValNumLeadingZeros,
2837 Val->getName() + ".numactivebits", /*HasNUW=*/true,
2838 /*HasNSW=*/Bitwidth != 2);
2839
2840 SCEVExpander Expander(*SE, *DL, "loop-idiom");
2841 Expander.setInsertPoint(&*Builder.GetInsertPoint());
2842 Value *ExtraOffset = Expander.expandCodeFor(ExtraOffsetExpr);
2843
2844 Value *ValNumActiveBitsOffset = Builder.CreateAdd(
2845 ValNumActiveBits, ExtraOffset, ValNumActiveBits->getName() + ".offset",
2846 /*HasNUW=*/OffsetIsZero, /*HasNSW=*/true);
2847 Value *IVFinal = Builder.CreateIntrinsic(Intrinsic::smax, {Ty},
2848 {ValNumActiveBitsOffset, Start},
2849 /*FMFSource=*/nullptr, "iv.final");
2850
2851 auto *LoopBackedgeTakenCount = cast<Instruction>(Builder.CreateSub(
2852 IVFinal, Start, CurLoop->getName() + ".backedgetakencount",
2853 /*HasNUW=*/OffsetIsZero, /*HasNSW=*/true));
2854 // FIXME: or when the offset was `add nuw`
2855
2856 // We know loop's backedge-taken count, but what's loop's trip count?
2857 Value *LoopTripCount =
2858 Builder.CreateAdd(LoopBackedgeTakenCount, ConstantInt::get(Ty, 1),
2859 CurLoop->getName() + ".tripcount", /*HasNUW=*/true,
2860 /*HasNSW=*/Bitwidth != 2);
2861
2862 // Step 2: Adjust the successor basic block to recieve the original
2863 // induction variable's final value instead of the orig. IV itself.
2864
2865 IV->replaceUsesOutsideBlock(IVFinal, LoopHeaderBB);
2866
2867 // Step 3: Rewrite the loop into a countable form, with canonical IV.
2868
2869 // The new canonical induction variable.
2870 Builder.SetInsertPoint(&LoopHeaderBB->front());
2871 auto *CIV = Builder.CreatePHI(Ty, 2, CurLoop->getName() + ".iv");
2872
2873 // The induction itself.
2874 Builder.SetInsertPoint(LoopHeaderBB->getFirstNonPHI());
2875 auto *CIVNext =
2876 Builder.CreateAdd(CIV, ConstantInt::get(Ty, 1), CIV->getName() + ".next",
2877 /*HasNUW=*/true, /*HasNSW=*/Bitwidth != 2);
2878
2879 // The loop trip count check.
2880 auto *CIVCheck = Builder.CreateICmpEQ(CIVNext, LoopTripCount,
2881 CurLoop->getName() + ".ivcheck");
2882 auto *NewIVCheck = CIVCheck;
2883 if (InvertedCond) {
2884 NewIVCheck = Builder.CreateNot(CIVCheck);
2885 NewIVCheck->takeName(ValShiftedIsZero);
2886 }
2887
2888 // The original IV, but rebased to be an offset to the CIV.
2889 auto *IVDePHId = Builder.CreateAdd(CIV, Start, "", /*HasNUW=*/false,
2890 /*HasNSW=*/true); // FIXME: what about NUW?
2891 IVDePHId->takeName(IV);
2892
2893 // The loop terminator.
2894 Builder.SetInsertPoint(LoopHeaderBB->getTerminator());
2895 Builder.CreateCondBr(CIVCheck, SuccessorBB, LoopHeaderBB);
2896 LoopHeaderBB->getTerminator()->eraseFromParent();
2897
2898 // Populate the IV PHI.
2899 CIV->addIncoming(ConstantInt::get(Ty, 0), LoopPreheaderBB);
2900 CIV->addIncoming(CIVNext, LoopHeaderBB);
2901
2902 // Step 4: Forget the "non-computable" trip-count SCEV associated with the
2903 // loop. The loop would otherwise not be deleted even if it becomes empty.
2904
2905 SE->forgetLoop(CurLoop);
2906
2907 // Step 5: Try to cleanup the loop's body somewhat.
2908 IV->replaceAllUsesWith(IVDePHId);
2909 IV->eraseFromParent();
2910
2911 ValShiftedIsZero->replaceAllUsesWith(NewIVCheck);
2912 ValShiftedIsZero->eraseFromParent();
2913
2914 // Other passes will take care of actually deleting the loop if possible.
2915
2916 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)
;
2917
2918 ++NumShiftUntilZero;
2919 return MadeChange;
2920}