Bug Summary

File:llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
Warning:line 2638, column 5
Value stored to 'Pred' is never read

Annotated Source Code

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clang -cc1 -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -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 -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -ffunction-sections -fdata-sections -fcoverage-compilation-dir=/build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/build-llvm/lib/Transforms/Scalar -resource-dir /usr/lib/llvm-14/lib/clang/14.0.0 -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/build-llvm/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/llvm/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/build-llvm/include -I /build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/llvm/include -D 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 -O2 -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~++20210903100615+fd66b44ec19e/build-llvm/lib/Transforms/Scalar -fdebug-prefix-map=/build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e=. -ferror-limit 19 -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -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-2021-09-04-040900-46481-1 -x c++ /build/llvm-toolchain-snapshot-14~++20210903100615+fd66b44ec19e/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)
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))
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())
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")
369 return false;
370
371 // Determine if code size heuristics need to be applied.
372 ApplyCodeSizeHeuristics =
373 L->getHeader()->getParent()->hasOptSize() && UseLIRCodeSizeHeurs;
374
375 HasMemset = TLI->has(LibFunc_memset);
376 HasMemsetPattern = TLI->has(LibFunc_memset_pattern16);
377 HasMemcpy = TLI->has(LibFunc_memcpy);
378
379 if (HasMemset || HasMemsetPattern || HasMemcpy)
380 if (SE->hasLoopInvariantBackedgeTakenCount(L))
381 return runOnCountableLoop();
382
383 return runOnNoncountableLoop();
384}
385
386bool LoopIdiomRecognize::runOnCountableLoop() {
387 const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
388 assert(!isa<SCEVCouldNotCompute>(BECount) &&(static_cast<void> (0))
389 "runOnCountableLoop() called on a loop without a predictable"(static_cast<void> (0))
390 "backedge-taken count")(static_cast<void> (0));
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 { } while (false)
402 << CurLoop->getHeader()->getParent()->getName()do { } while (false)
403 << "] Countable Loop %" << CurLoop->getHeader()->getName()do { } while (false)
404 << "\n")do { } 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<void> (0));
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 (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
629 if (!DT->dominates(BB, ExitBlocks[i]))
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<void> (0));
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<void> (0))
692 "Expected either splat value or pattern value.")(static_cast<void> (0));
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<void> (0));
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<void> (0))
725 "Expected either splat value or pattern value.")(static_cast<void> (0));
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 (SetVector<StoreInst *>::iterator it = Heads.begin(), e = Heads.end();
754 it != e; ++it) {
755 if (Tails.count(*it))
756 continue;
757
758 // We found a store instr that starts a chain. Now follow the chain and try
759 // to transform it.
760 SmallPtrSet<Instruction *, 8> AdjacentStores;
761 StoreInst *I = *it;
762
763 StoreInst *HeadStore = I;
764 unsigned StoreSize = 0;
765
766 // Collect the chain into a list.
767 while (Tails.count(I) || Heads.count(I)) {
768 if (TransformedStores.count(I))
769 break;
770 AdjacentStores.insert(I);
771
772 StoreSize += DL->getTypeStoreSize(I->getValueOperand()->getType());
773 // Move to the next value in the chain.
774 I = ConsecutiveChain[I];
775 }
776
777 Value *StoredVal = HeadStore->getValueOperand();
778 Value *StorePtr = HeadStore->getPointerOperand();
779 const SCEVAddRecExpr *StoreEv = cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
780 APInt Stride = getStoreStride(StoreEv);
781
782 // Check to see if the stride matches the size of the stores. If so, then
783 // we know that every byte is touched in the loop.
784 if (StoreSize != Stride && StoreSize != -Stride)
785 continue;
786
787 bool IsNegStride = StoreSize == -Stride;
788
789 const SCEV *StoreSizeSCEV = SE->getConstant(BECount->getType(), StoreSize);
790 if (processLoopStridedStore(StorePtr, StoreSizeSCEV,
791 MaybeAlign(HeadStore->getAlignment()),
792 StoredVal, HeadStore, AdjacentStores, StoreEv,
793 BECount, IsNegStride)) {
794 TransformedStores.insert(AdjacentStores.begin(), AdjacentStores.end());
795 Changed = true;
796 }
797 }
798
799 return Changed;
800}
801
802/// processLoopMemIntrinsic - Template function for calling different processor
803/// functions based on mem instrinsic type.
804template <typename MemInst>
805bool LoopIdiomRecognize::processLoopMemIntrinsic(
806 BasicBlock *BB,
807 bool (LoopIdiomRecognize::*Processor)(MemInst *, const SCEV *),
808 const SCEV *BECount) {
809 bool MadeChange = false;
810 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
811 Instruction *Inst = &*I++;
812 // Look for memory instructions, which may be optimized to a larger one.
813 if (MemInst *MI = dyn_cast<MemInst>(Inst)) {
814 WeakTrackingVH InstPtr(&*I);
815 if (!(this->*Processor)(MI, BECount))
816 continue;
817 MadeChange = true;
818
819 // If processing the instruction invalidated our iterator, start over from
820 // the top of the block.
821 if (!InstPtr)
822 I = BB->begin();
823 }
824 }
825 return MadeChange;
826}
827
828/// processLoopMemCpy - See if this memcpy can be promoted to a large memcpy
829bool LoopIdiomRecognize::processLoopMemCpy(MemCpyInst *MCI,
830 const SCEV *BECount) {
831 // We can only handle non-volatile memcpys with a constant size.
832 if (MCI->isVolatile() || !isa<ConstantInt>(MCI->getLength()))
833 return false;
834
835 // If we're not allowed to hack on memcpy, we fail.
836 if ((!HasMemcpy && !isa<MemCpyInlineInst>(MCI)) || DisableLIRP::Memcpy)
837 return false;
838
839 Value *Dest = MCI->getDest();
840 Value *Source = MCI->getSource();
841 if (!Dest || !Source)
842 return false;
843
844 // See if the load and store pointer expressions are AddRec like {base,+,1} on
845 // the current loop, which indicates a strided load and store. If we have
846 // something else, it's a random load or store we can't handle.
847 const SCEVAddRecExpr *StoreEv = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Dest));
848 if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
849 return false;
850 const SCEVAddRecExpr *LoadEv = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Source));
851 if (!LoadEv || LoadEv->getLoop() != CurLoop || !LoadEv->isAffine())
852 return false;
853
854 // Reject memcpys that are so large that they overflow an unsigned.
855 uint64_t SizeInBytes = cast<ConstantInt>(MCI->getLength())->getZExtValue();
856 if ((SizeInBytes >> 32) != 0)
857 return false;
858
859 // Check if the stride matches the size of the memcpy. If so, then we know
860 // that every byte is touched in the loop.
861 const SCEVConstant *ConstStoreStride =
862 dyn_cast<SCEVConstant>(StoreEv->getOperand(1));
863 const SCEVConstant *ConstLoadStride =
864 dyn_cast<SCEVConstant>(LoadEv->getOperand(1));
865 if (!ConstStoreStride || !ConstLoadStride)
866 return false;
867
868 APInt StoreStrideValue = ConstStoreStride->getAPInt();
869 APInt LoadStrideValue = ConstLoadStride->getAPInt();
870 // Huge stride value - give up
871 if (StoreStrideValue.getBitWidth() > 64 || LoadStrideValue.getBitWidth() > 64)
872 return false;
873
874 if (SizeInBytes != StoreStrideValue && SizeInBytes != -StoreStrideValue) {
875 ORE.emit([&]() {
876 return OptimizationRemarkMissed(DEBUG_TYPE"loop-idiom", "SizeStrideUnequal", MCI)
877 << ore::NV("Inst", "memcpy") << " in "
878 << ore::NV("Function", MCI->getFunction())
879 << " function will not be hoisted: "
880 << ore::NV("Reason", "memcpy size is not equal to stride");
881 });
882 return false;
883 }
884
885 int64_t StoreStrideInt = StoreStrideValue.getSExtValue();
886 int64_t LoadStrideInt = LoadStrideValue.getSExtValue();
887 // Check if the load stride matches the store stride.
888 if (StoreStrideInt != LoadStrideInt)
889 return false;
890
891 return processLoopStoreOfLoopLoad(
892 Dest, Source, SE->getConstant(Dest->getType(), SizeInBytes),
893 MCI->getDestAlign(), MCI->getSourceAlign(), MCI, MCI, StoreEv, LoadEv,
894 BECount);
895}
896
897/// processLoopMemSet - See if this memset can be promoted to a large memset.
898bool LoopIdiomRecognize::processLoopMemSet(MemSetInst *MSI,
899 const SCEV *BECount) {
900 // We can only handle non-volatile memsets.
901 if (MSI->isVolatile())
902 return false;
903
904 // If we're not allowed to hack on memset, we fail.
905 if (!HasMemset || DisableLIRP::Memset)
906 return false;
907
908 Value *Pointer = MSI->getDest();
909
910 // See if the pointer expression is an AddRec like {base,+,1} on the current
911 // loop, which indicates a strided store. If we have something else, it's a
912 // random store we can't handle.
913 const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
914 if (!Ev || Ev->getLoop() != CurLoop)
915 return false;
916 if (!Ev->isAffine()) {
917 LLVM_DEBUG(dbgs() << " Pointer is not affine, abort\n")do { } while (false);
918 return false;
919 }
920
921 const SCEV *PointerStrideSCEV = Ev->getOperand(1);
922 const SCEV *MemsetSizeSCEV = SE->getSCEV(MSI->getLength());
923 if (!PointerStrideSCEV || !MemsetSizeSCEV)
924 return false;
925
926 bool IsNegStride = false;
927 const bool IsConstantSize = isa<ConstantInt>(MSI->getLength());
928
929 if (IsConstantSize) {
930 // Memset size is constant.
931 // Check if the pointer stride matches the memset size. If so, then
932 // we know that every byte is touched in the loop.
933 LLVM_DEBUG(dbgs() << " memset size is constant\n")do { } while (false);
934 uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
935 const SCEVConstant *ConstStride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
936 if (!ConstStride)
937 return false;
938
939 APInt Stride = ConstStride->getAPInt();
940 if (SizeInBytes != Stride && SizeInBytes != -Stride)
941 return false;
942
943 IsNegStride = SizeInBytes == -Stride;
944 } else {
945 // Memset size is non-constant.
946 // Check if the pointer stride matches the memset size.
947 // To be conservative, the pass would not promote pointers that aren't in
948 // address space zero. Also, the pass only handles memset length and stride
949 // that are invariant for the top level loop.
950 LLVM_DEBUG(dbgs() << " memset size is non-constant\n")do { } while (false);
951 if (Pointer->getType()->getPointerAddressSpace() != 0) {
952 LLVM_DEBUG(dbgs() << " pointer is not in address space zero, "do { } while (false)
953 << "abort\n")do { } while (false);
954 return false;
955 }
956 if (!SE->isLoopInvariant(MemsetSizeSCEV, CurLoop)) {
957 LLVM_DEBUG(dbgs() << " memset size is not a loop-invariant, "do { } while (false)
958 << "abort\n")do { } while (false);
959 return false;
960 }
961
962 // Compare positive direction PointerStrideSCEV with MemsetSizeSCEV
963 IsNegStride = PointerStrideSCEV->isNonConstantNegative();
964 const SCEV *PositiveStrideSCEV =
965 IsNegStride ? SE->getNegativeSCEV(PointerStrideSCEV)
966 : PointerStrideSCEV;
967 LLVM_DEBUG(dbgs() << " MemsetSizeSCEV: " << *MemsetSizeSCEV << "\n"do { } while (false)
968 << " PositiveStrideSCEV: " << *PositiveStrideSCEVdo { } while (false)
969 << "\n")do { } while (false);
970
971 if (PositiveStrideSCEV != MemsetSizeSCEV) {
972 // TODO: folding can be done to the SCEVs
973 // The folding is to fold expressions that is covered by the loop guard
974 // at loop entry. After the folding, compare again and proceed
975 // optimization if equal.
976 LLVM_DEBUG(dbgs() << " SCEV don't match, abort\n")do { } while (false);
977 return false;
978 }
979 }
980
981 // Verify that the memset value is loop invariant. If not, we can't promote
982 // the memset.
983 Value *SplatValue = MSI->getValue();
984 if (!SplatValue || !CurLoop->isLoopInvariant(SplatValue))
985 return false;
986
987 SmallPtrSet<Instruction *, 1> MSIs;
988 MSIs.insert(MSI);
989 return processLoopStridedStore(Pointer, SE->getSCEV(MSI->getLength()),
990 MaybeAlign(MSI->getDestAlignment()),
991 SplatValue, MSI, MSIs, Ev, BECount,
992 IsNegStride, /*IsLoopMemset=*/true);
993}
994
995/// mayLoopAccessLocation - Return true if the specified loop might access the
996/// specified pointer location, which is a loop-strided access. The 'Access'
997/// argument specifies what the verboten forms of access are (read or write).
998static bool
999mayLoopAccessLocation(Value *Ptr, ModRefInfo Access, Loop *L,
1000 const SCEV *BECount, const SCEV *StoreSizeSCEV,
1001 AliasAnalysis &AA,
1002 SmallPtrSetImpl<Instruction *> &IgnoredInsts) {
1003 // Get the location that may be stored across the loop. Since the access is
1004 // strided positively through memory, we say that the modified location starts
1005 // at the pointer and has infinite size.
1006 LocationSize AccessSize = LocationSize::afterPointer();
1007
1008 // If the loop iterates a fixed number of times, we can refine the access size
1009 // to be exactly the size of the memset, which is (BECount+1)*StoreSize
1010 const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount);
1011 const SCEVConstant *ConstSize = dyn_cast<SCEVConstant>(StoreSizeSCEV);
1012 if (BECst && ConstSize)
1013 AccessSize = LocationSize::precise((BECst->getValue()->getZExtValue() + 1) *
1014 ConstSize->getValue()->getZExtValue());
1015
1016 // TODO: For this to be really effective, we have to dive into the pointer
1017 // operand in the store. Store to &A[i] of 100 will always return may alias
1018 // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
1019 // which will then no-alias a store to &A[100].
1020 MemoryLocation StoreLoc(Ptr, AccessSize);
1021
1022 for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
1023 ++BI)
1024 for (Instruction &I : **BI)
1025 if (IgnoredInsts.count(&I) == 0 &&
1026 isModOrRefSet(
1027 intersectModRef(AA.getModRefInfo(&I, StoreLoc), Access)))
1028 return true;
1029 return false;
1030}
1031
1032// If we have a negative stride, Start refers to the end of the memory location
1033// we're trying to memset. Therefore, we need to recompute the base pointer,
1034// which is just Start - BECount*Size.
1035static const SCEV *getStartForNegStride(const SCEV *Start, const SCEV *BECount,
1036 Type *IntPtr, const SCEV *StoreSizeSCEV,
1037 ScalarEvolution *SE) {
1038 const SCEV *Index = SE->getTruncateOrZeroExtend(BECount, IntPtr);
1039 if (!StoreSizeSCEV->isOne()) {
1040 // index = back edge count * store size
1041 Index = SE->getMulExpr(Index,
1042 SE->getTruncateOrZeroExtend(StoreSizeSCEV, IntPtr),
1043 SCEV::FlagNUW);
1044 }
1045 // base pointer = start - index * store size
1046 return SE->getMinusSCEV(Start, Index);
1047}
1048
1049/// Compute trip count from the backedge taken count.
1050static const SCEV *getTripCount(const SCEV *BECount, Type *IntPtr,
1051 Loop *CurLoop, const DataLayout *DL,
1052 ScalarEvolution *SE) {
1053 const SCEV *TripCountS = nullptr;
1054 // The # stored bytes is (BECount+1). Expand the trip count out to
1055 // pointer size if it isn't already.
1056 //
1057 // If we're going to need to zero extend the BE count, check if we can add
1058 // one to it prior to zero extending without overflow. Provided this is safe,
1059 // it allows better simplification of the +1.
1060 if (DL->getTypeSizeInBits(BECount->getType()) <
1061 DL->getTypeSizeInBits(IntPtr) &&
1062 SE->isLoopEntryGuardedByCond(
1063 CurLoop, ICmpInst::ICMP_NE, BECount,
1064 SE->getNegativeSCEV(SE->getOne(BECount->getType())))) {
1065 TripCountS = SE->getZeroExtendExpr(
1066 SE->getAddExpr(BECount, SE->getOne(BECount->getType()), SCEV::FlagNUW),
1067 IntPtr);
1068 } else {
1069 TripCountS = SE->getAddExpr(SE->getTruncateOrZeroExtend(BECount, IntPtr),
1070 SE->getOne(IntPtr), SCEV::FlagNUW);
1071 }
1072
1073 return TripCountS;
1074}
1075
1076/// Compute the number of bytes as a SCEV from the backedge taken count.
1077///
1078/// This also maps the SCEV into the provided type and tries to handle the
1079/// computation in a way that will fold cleanly.
1080static const SCEV *getNumBytes(const SCEV *BECount, Type *IntPtr,
1081 const SCEV *StoreSizeSCEV, Loop *CurLoop,
1082 const DataLayout *DL, ScalarEvolution *SE) {
1083 const SCEV *TripCountSCEV = getTripCount(BECount, IntPtr, CurLoop, DL, SE);
1084
1085 return SE->getMulExpr(TripCountSCEV,
1086 SE->getTruncateOrZeroExtend(StoreSizeSCEV, IntPtr),
1087 SCEV::FlagNUW);
1088}
1089
1090/// processLoopStridedStore - We see a strided store of some value. If we can
1091/// transform this into a memset or memset_pattern in the loop preheader, do so.
1092bool LoopIdiomRecognize::processLoopStridedStore(
1093 Value *DestPtr, const SCEV *StoreSizeSCEV, MaybeAlign StoreAlignment,
1094 Value *StoredVal, Instruction *TheStore,
1095 SmallPtrSetImpl<Instruction *> &Stores, const SCEVAddRecExpr *Ev,
1096 const SCEV *BECount, bool IsNegStride, bool IsLoopMemset) {
1097 Value *SplatValue = isBytewiseValue(StoredVal, *DL);
1098 Constant *PatternValue = nullptr;
1099
1100 if (!SplatValue)
1101 PatternValue = getMemSetPatternValue(StoredVal, DL);
1102
1103 assert((SplatValue || PatternValue) &&(static_cast<void> (0))
1104 "Expected either splat value or pattern value.")(static_cast<void> (0));
1105
1106 // The trip count of the loop and the base pointer of the addrec SCEV is
1107 // guaranteed to be loop invariant, which means that it should dominate the
1108 // header. This allows us to insert code for it in the preheader.
1109 unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();
1110 BasicBlock *Preheader = CurLoop->getLoopPreheader();
1111 IRBuilder<> Builder(Preheader->getTerminator());
1112 SCEVExpander Expander(*SE, *DL, "loop-idiom");
1113 SCEVExpanderCleaner ExpCleaner(Expander, *DT);
1114
1115 Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
1116 Type *IntIdxTy = DL->getIndexType(DestPtr->getType());
1117
1118 bool Changed = false;
1119 const SCEV *Start = Ev->getStart();
1120 // Handle negative strided loops.
1121 if (IsNegStride)
1122 Start = getStartForNegStride(Start, BECount, IntIdxTy, StoreSizeSCEV, SE);
1123
1124 // TODO: ideally we should still be able to generate memset if SCEV expander
1125 // is taught to generate the dependencies at the latest point.
1126 if (!isSafeToExpand(Start, *SE))
1127 return Changed;
1128
1129 // Okay, we have a strided store "p[i]" of a splattable value. We can turn
1130 // this into a memset in the loop preheader now if we want. However, this
1131 // would be unsafe to do if there is anything else in the loop that may read
1132 // or write to the aliased location. Check for any overlap by generating the
1133 // base pointer and checking the region.
1134 Value *BasePtr =
1135 Expander.expandCodeFor(Start, DestInt8PtrTy, Preheader->getTerminator());
1136
1137 // From here on out, conservatively report to the pass manager that we've
1138 // changed the IR, even if we later clean up these added instructions. There
1139 // may be structural differences e.g. in the order of use lists not accounted
1140 // for in just a textual dump of the IR. This is written as a variable, even
1141 // though statically all the places this dominates could be replaced with
1142 // 'true', with the hope that anyone trying to be clever / "more precise" with
1143 // the return value will read this comment, and leave them alone.
1144 Changed = true;
1145
1146 if (mayLoopAccessLocation(BasePtr, ModRefInfo::ModRef, CurLoop, BECount,
1147 StoreSizeSCEV, *AA, Stores))
1148 return Changed;
1149
1150 if (avoidLIRForMultiBlockLoop(/*IsMemset=*/true, IsLoopMemset))
1151 return Changed;
1152
1153 // Okay, everything looks good, insert the memset.
1154
1155 const SCEV *NumBytesS =
1156 getNumBytes(BECount, IntIdxTy, StoreSizeSCEV, CurLoop, DL, SE);
1157
1158 // TODO: ideally we should still be able to generate memset if SCEV expander
1159 // is taught to generate the dependencies at the latest point.
1160 if (!isSafeToExpand(NumBytesS, *SE))
1161 return Changed;
1162
1163 Value *NumBytes =
1164 Expander.expandCodeFor(NumBytesS, IntIdxTy, Preheader->getTerminator());
1165
1166 CallInst *NewCall;
1167 if (SplatValue) {
1168 NewCall = Builder.CreateMemSet(BasePtr, SplatValue, NumBytes,
1169 MaybeAlign(StoreAlignment));
1170 } else {
1171 // Everything is emitted in default address space
1172 Type *Int8PtrTy = DestInt8PtrTy;
1173
1174 Module *M = TheStore->getModule();
1175 StringRef FuncName = "memset_pattern16";
1176 FunctionCallee MSP = M->getOrInsertFunction(FuncName, Builder.getVoidTy(),
1177 Int8PtrTy, Int8PtrTy, IntIdxTy);
1178 inferLibFuncAttributes(M, FuncName, *TLI);
1179
1180 // Otherwise we should form a memset_pattern16. PatternValue is known to be
1181 // an constant array of 16-bytes. Plop the value into a mergable global.
1182 GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
1183 GlobalValue::PrivateLinkage,
1184 PatternValue, ".memset_pattern");
1185 GV->setUnnamedAddr(GlobalValue::UnnamedAddr::Global); // Ok to merge these.
1186 GV->setAlignment(Align(16));
1187 Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
1188 NewCall = Builder.CreateCall(MSP, {BasePtr, PatternPtr, NumBytes});
1189 }
1190 NewCall->setDebugLoc(TheStore->getDebugLoc());
1191
1192 if (MSSAU) {
1193 MemoryAccess *NewMemAcc = MSSAU->createMemoryAccessInBB(
1194 NewCall, nullptr, NewCall->getParent(), MemorySSA::BeforeTerminator);
1195 MSSAU->insertDef(cast<MemoryDef>(NewMemAcc), true);
1196 }
1197
1198 LLVM_DEBUG(dbgs() << " Formed memset: " << *NewCall << "\n"do { } while (false)
1199 << " from store to: " << *Ev << " at: " << *TheStoredo { } while (false)
1200 << "\n")do { } while (false);
1201
1202 ORE.emit([&]() {
1203 return OptimizationRemark(DEBUG_TYPE"loop-idiom", "ProcessLoopStridedStore",
1204 NewCall->getDebugLoc(), Preheader)
1205 << "Transformed loop-strided store in "
1206 << ore::NV("Function", TheStore->getFunction())
1207 << " function into a call to "
1208 << ore::NV("NewFunction", NewCall->getCalledFunction())
1209 << "() intrinsic";
1210 });
1211
1212 // Okay, the memset has been formed. Zap the original store and anything that
1213 // feeds into it.
1214 for (auto *I : Stores) {
1215 if (MSSAU)
1216 MSSAU->removeMemoryAccess(I, true);
1217 deleteDeadInstruction(I);
1218 }
1219 if (MSSAU && VerifyMemorySSA)
1220 MSSAU->getMemorySSA()->verifyMemorySSA();
1221 ++NumMemSet;
1222 ExpCleaner.markResultUsed();
1223 return true;
1224}
1225
1226/// If the stored value is a strided load in the same loop with the same stride
1227/// this may be transformable into a memcpy. This kicks in for stuff like
1228/// for (i) A[i] = B[i];
1229bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(StoreInst *SI,
1230 const SCEV *BECount) {
1231 assert(SI->isUnordered() && "Expected only non-volatile non-ordered stores.")(static_cast<void> (0));
1232
1233 Value *StorePtr = SI->getPointerOperand();
1234 const SCEVAddRecExpr *StoreEv = cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
1235 unsigned StoreSize = DL->getTypeStoreSize(SI->getValueOperand()->getType());
1236
1237 // The store must be feeding a non-volatile load.
1238 LoadInst *LI = cast<LoadInst>(SI->getValueOperand());
1239 assert(LI->isUnordered() && "Expected only non-volatile non-ordered loads.")(static_cast<void> (0));
1240
1241 // See if the pointer expression is an AddRec like {base,+,1} on the current
1242 // loop, which indicates a strided load. If we have something else, it's a
1243 // random load we can't handle.
1244 Value *LoadPtr = LI->getPointerOperand();
1245 const SCEVAddRecExpr *LoadEv = cast<SCEVAddRecExpr>(SE->getSCEV(LoadPtr));
1246
1247 const SCEV *StoreSizeSCEV = SE->getConstant(StorePtr->getType(), StoreSize);
1248 return processLoopStoreOfLoopLoad(StorePtr, LoadPtr, StoreSizeSCEV,
1249 SI->getAlign(), LI->getAlign(), SI, LI,
1250 StoreEv, LoadEv, BECount);
1251}
1252
1253bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(
1254 Value *DestPtr, Value *SourcePtr, const SCEV *StoreSizeSCEV,
1255 MaybeAlign StoreAlign, MaybeAlign LoadAlign, Instruction *TheStore,
1256 Instruction *TheLoad, const SCEVAddRecExpr *StoreEv,
1257 const SCEVAddRecExpr *LoadEv, const SCEV *BECount) {
1258
1259 // FIXME: until llvm.memcpy.inline supports dynamic sizes, we need to
1260 // conservatively bail here, since otherwise we may have to transform
1261 // llvm.memcpy.inline into llvm.memcpy which is illegal.
1262 if (isa<MemCpyInlineInst>(TheStore))
1263 return false;
1264
1265 // The trip count of the loop and the base pointer of the addrec SCEV is
1266 // guaranteed to be loop invariant, which means that it should dominate the
1267 // header. This allows us to insert code for it in the preheader.
1268 BasicBlock *Preheader = CurLoop->getLoopPreheader();
1269 IRBuilder<> Builder(Preheader->getTerminator());
1270 SCEVExpander Expander(*SE, *DL, "loop-idiom");
1271
1272 SCEVExpanderCleaner ExpCleaner(Expander, *DT);
1273
1274 bool Changed = false;
1275 const SCEV *StrStart = StoreEv->getStart();
1276 unsigned StrAS = DestPtr->getType()->getPointerAddressSpace();
1277 Type *IntIdxTy = Builder.getIntNTy(DL->getIndexSizeInBits(StrAS));
1278
1279 APInt Stride = getStoreStride(StoreEv);
1280 const SCEVConstant *ConstStoreSize = dyn_cast<SCEVConstant>(StoreSizeSCEV);
1281
1282 // TODO: Deal with non-constant size; Currently expect constant store size
1283 assert(ConstStoreSize && "store size is expected to be a constant")(static_cast<void> (0));
1284
1285 int64_t StoreSize = ConstStoreSize->getValue()->getZExtValue();
1286 bool IsNegStride = StoreSize == -Stride;
1287
1288 // Handle negative strided loops.
1289 if (IsNegStride)
1290 StrStart =
1291 getStartForNegStride(StrStart, BECount, IntIdxTy, StoreSizeSCEV, SE);
1292
1293 // Okay, we have a strided store "p[i]" of a loaded value. We can turn
1294 // this into a memcpy in the loop preheader now if we want. However, this
1295 // would be unsafe to do if there is anything else in the loop that may read
1296 // or write the memory region we're storing to. This includes the load that
1297 // feeds the stores. Check for an alias by generating the base address and
1298 // checking everything.
1299 Value *StoreBasePtr = Expander.expandCodeFor(
1300 StrStart, Builder.getInt8PtrTy(StrAS), Preheader->getTerminator());
1301
1302 // From here on out, conservatively report to the pass manager that we've
1303 // changed the IR, even if we later clean up these added instructions. There
1304 // may be structural differences e.g. in the order of use lists not accounted
1305 // for in just a textual dump of the IR. This is written as a variable, even
1306 // though statically all the places this dominates could be replaced with
1307 // 'true', with the hope that anyone trying to be clever / "more precise" with
1308 // the return value will read this comment, and leave them alone.
1309 Changed = true;
1310
1311 SmallPtrSet<Instruction *, 2> IgnoredInsts;
1312 IgnoredInsts.insert(TheStore);
1313
1314 bool IsMemCpy = isa<MemCpyInst>(TheStore);
1315 const StringRef InstRemark = IsMemCpy ? "memcpy" : "load and store";
1316
1317 bool UseMemMove =
1318 mayLoopAccessLocation(StoreBasePtr, ModRefInfo::ModRef, CurLoop, BECount,
1319 StoreSizeSCEV, *AA, IgnoredInsts);
1320 if (UseMemMove) {
1321 // For memmove case it's not enough to guarantee that loop doesn't access
1322 // TheStore and TheLoad. Additionally we need to make sure that TheStore is
1323 // the only user of TheLoad.
1324 if (!TheLoad->hasOneUse())
1325 return Changed;
1326 IgnoredInsts.insert(TheLoad);
1327 if (mayLoopAccessLocation(StoreBasePtr, ModRefInfo::ModRef, CurLoop,
1328 BECount, StoreSizeSCEV, *AA, IgnoredInsts)) {
1329 ORE.emit([&]() {
1330 return OptimizationRemarkMissed(DEBUG_TYPE"loop-idiom", "LoopMayAccessStore",
1331 TheStore)
1332 << ore::NV("Inst", InstRemark) << " in "
1333 << ore::NV("Function", TheStore->getFunction())
1334 << " function will not be hoisted: "
1335 << ore::NV("Reason", "The loop may access store location");
1336 });
1337 return Changed;
1338 }
1339 IgnoredInsts.erase(TheLoad);
1340 }
1341
1342 const SCEV *LdStart = LoadEv->getStart();
1343 unsigned LdAS = SourcePtr->getType()->getPointerAddressSpace();
1344
1345 // Handle negative strided loops.
1346 if (IsNegStride)
1347 LdStart =
1348 getStartForNegStride(LdStart, BECount, IntIdxTy, StoreSizeSCEV, SE);
1349
1350 // For a memcpy, we have to make sure that the input array is not being
1351 // mutated by the loop.
1352 Value *LoadBasePtr = Expander.expandCodeFor(
1353 LdStart, Builder.getInt8PtrTy(LdAS), Preheader->getTerminator());
1354
1355 // If the store is a memcpy instruction, we must check if it will write to
1356 // the load memory locations. So remove it from the ignored stores.
1357 if (IsMemCpy)
1358 IgnoredInsts.erase(TheStore);
1359 if (mayLoopAccessLocation(LoadBasePtr, ModRefInfo::Mod, CurLoop, BECount,
1360 StoreSizeSCEV, *AA, IgnoredInsts)) {
1361 ORE.emit([&]() {
1362 return OptimizationRemarkMissed(DEBUG_TYPE"loop-idiom", "LoopMayAccessLoad", TheLoad)
1363 << ore::NV("Inst", InstRemark) << " in "
1364 << ore::NV("Function", TheStore->getFunction())
1365 << " function will not be hoisted: "
1366 << ore::NV("Reason", "The loop may access load location");
1367 });
1368 return Changed;
1369 }
1370 if (UseMemMove) {
1371 // Ensure that LoadBasePtr is after StoreBasePtr or before StoreBasePtr for
1372 // negative stride. LoadBasePtr shouldn't overlap with StoreBasePtr.
1373 int64_t LoadOff = 0, StoreOff = 0;
1374 const Value *BP1 = llvm::GetPointerBaseWithConstantOffset(
1375 LoadBasePtr->stripPointerCasts(), LoadOff, *DL);
1376 const Value *BP2 = llvm::GetPointerBaseWithConstantOffset(
1377 StoreBasePtr->stripPointerCasts(), StoreOff, *DL);
1378 int64_t LoadSize =
1379 DL->getTypeSizeInBits(TheLoad->getType()).getFixedSize() / 8;
1380 if (BP1 != BP2 || LoadSize != int64_t(StoreSize))
1381 return Changed;
1382 if ((!IsNegStride && LoadOff < StoreOff + int64_t(StoreSize)) ||
1383 (IsNegStride && LoadOff + LoadSize > StoreOff))
1384 return Changed;
1385 }
1386
1387 if (avoidLIRForMultiBlockLoop())
1388 return Changed;
1389
1390 // Okay, everything is safe, we can transform this!
1391
1392 const SCEV *NumBytesS =
1393 getNumBytes(BECount, IntIdxTy, StoreSizeSCEV, CurLoop, DL, SE);
1394
1395 Value *NumBytes =
1396 Expander.expandCodeFor(NumBytesS, IntIdxTy, Preheader->getTerminator());
1397
1398 CallInst *NewCall = nullptr;
1399 // Check whether to generate an unordered atomic memcpy:
1400 // If the load or store are atomic, then they must necessarily be unordered
1401 // by previous checks.
1402 if (!TheStore->isAtomic() && !TheLoad->isAtomic()) {
1403 if (UseMemMove)
1404 NewCall = Builder.CreateMemMove(StoreBasePtr, StoreAlign, LoadBasePtr,
1405 LoadAlign, NumBytes);
1406 else
1407 NewCall = Builder.CreateMemCpy(StoreBasePtr, StoreAlign, LoadBasePtr,
1408 LoadAlign, NumBytes);
1409 } else {
1410 // For now don't support unordered atomic memmove.
1411 if (UseMemMove)
1412 return Changed;
1413 // We cannot allow unaligned ops for unordered load/store, so reject
1414 // anything where the alignment isn't at least the element size.
1415 assert((StoreAlign.hasValue() && LoadAlign.hasValue()) &&(static_cast<void> (0))
1416 "Expect unordered load/store to have align.")(static_cast<void> (0));
1417 if (StoreAlign.getValue() < StoreSize || LoadAlign.getValue() < StoreSize)
1418 return Changed;
1419
1420 // If the element.atomic memcpy is not lowered into explicit
1421 // loads/stores later, then it will be lowered into an element-size
1422 // specific lib call. If the lib call doesn't exist for our store size, then
1423 // we shouldn't generate the memcpy.
1424 if (StoreSize > TTI->getAtomicMemIntrinsicMaxElementSize())
1425 return Changed;
1426
1427 // Create the call.
1428 // Note that unordered atomic loads/stores are *required* by the spec to
1429 // have an alignment but non-atomic loads/stores may not.
1430 NewCall = Builder.CreateElementUnorderedAtomicMemCpy(
1431 StoreBasePtr, StoreAlign.getValue(), LoadBasePtr, LoadAlign.getValue(),
1432 NumBytes, StoreSize);
1433 }
1434 NewCall->setDebugLoc(TheStore->getDebugLoc());
1435
1436 if (MSSAU) {
1437 MemoryAccess *NewMemAcc = MSSAU->createMemoryAccessInBB(
1438 NewCall, nullptr, NewCall->getParent(), MemorySSA::BeforeTerminator);
1439 MSSAU->insertDef(cast<MemoryDef>(NewMemAcc), true);
1440 }
1441
1442 LLVM_DEBUG(dbgs() << " Formed new call: " << *NewCall << "\n"do { } while (false)
1443 << " from load ptr=" << *LoadEv << " at: " << *TheLoaddo { } while (false)
1444 << "\n"do { } while (false)
1445 << " from store ptr=" << *StoreEv << " at: " << *TheStoredo { } while (false)
1446 << "\n")do { } while (false);
1447
1448 ORE.emit([&]() {
1449 return OptimizationRemark(DEBUG_TYPE"loop-idiom", "ProcessLoopStoreOfLoopLoad",
1450 NewCall->getDebugLoc(), Preheader)
1451 << "Formed a call to "
1452 << ore::NV("NewFunction", NewCall->getCalledFunction())
1453 << "() intrinsic from " << ore::NV("Inst", InstRemark)
1454 << " instruction in " << ore::NV("Function", TheStore->getFunction())
1455 << " function";
1456 });
1457
1458 // Okay, a new call to memcpy/memmove has been formed. Zap the original store
1459 // and anything that feeds into it.
1460 if (MSSAU)
1461 MSSAU->removeMemoryAccess(TheStore, true);
1462 deleteDeadInstruction(TheStore);
1463 if (MSSAU && VerifyMemorySSA)
1464 MSSAU->getMemorySSA()->verifyMemorySSA();
1465 if (UseMemMove)
1466 ++NumMemMove;
1467 else
1468 ++NumMemCpy;
1469 ExpCleaner.markResultUsed();
1470 return true;
1471}
1472
1473// When compiling for codesize we avoid idiom recognition for a multi-block loop
1474// unless it is a loop_memset idiom or a memset/memcpy idiom in a nested loop.
1475//
1476bool LoopIdiomRecognize::avoidLIRForMultiBlockLoop(bool IsMemset,
1477 bool IsLoopMemset) {
1478 if (ApplyCodeSizeHeuristics && CurLoop->getNumBlocks() > 1) {
1479 if (CurLoop->isOutermost() && (!IsMemset || !IsLoopMemset)) {
1480 LLVM_DEBUG(dbgs() << " " << CurLoop->getHeader()->getParent()->getName()do { } while (false)
1481 << " : LIR " << (IsMemset ? "Memset" : "Memcpy")do { } while (false)
1482 << " avoided: multi-block top-level loop\n")do { } while (false);
1483 return true;
1484 }
1485 }
1486
1487 return false;
1488}
1489
1490bool LoopIdiomRecognize::runOnNoncountableLoop() {
1491 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Scanning: F["do { } while (false)
1492 << CurLoop->getHeader()->getParent()->getName()do { } while (false)
1493 << "] Noncountable Loop %"do { } while (false)
1494 << CurLoop->getHeader()->getName() << "\n")do { } while (false);
1495
1496 return recognizePopcount() || recognizeAndInsertFFS() ||
1497 recognizeShiftUntilBitTest() || recognizeShiftUntilZero();
1498}
1499
1500/// Check if the given conditional branch is based on the comparison between
1501/// a variable and zero, and if the variable is non-zero or zero (JmpOnZero is
1502/// true), the control yields to the loop entry. If the branch matches the
1503/// behavior, the variable involved in the comparison is returned. This function
1504/// will be called to see if the precondition and postcondition of the loop are
1505/// in desirable form.
1506static Value *matchCondition(BranchInst *BI, BasicBlock *LoopEntry,
1507 bool JmpOnZero = false) {
1508 if (!BI || !BI->isConditional())
1509 return nullptr;
1510
1511 ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
1512 if (!Cond)
1513 return nullptr;
1514
1515 ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
1516 if (!CmpZero || !CmpZero->isZero())
1517 return nullptr;
1518
1519 BasicBlock *TrueSucc = BI->getSuccessor(0);
1520 BasicBlock *FalseSucc = BI->getSuccessor(1);
1521 if (JmpOnZero)
1522 std::swap(TrueSucc, FalseSucc);
1523
1524 ICmpInst::Predicate Pred = Cond->getPredicate();
1525 if ((Pred == ICmpInst::ICMP_NE && TrueSucc == LoopEntry) ||
1526 (Pred == ICmpInst::ICMP_EQ && FalseSucc == LoopEntry))
1527 return Cond->getOperand(0);
1528
1529 return nullptr;
1530}
1531
1532// Check if the recurrence variable `VarX` is in the right form to create
1533// the idiom. Returns the value coerced to a PHINode if so.
1534static PHINode *getRecurrenceVar(Value *VarX, Instruction *DefX,
1535 BasicBlock *LoopEntry) {
1536 auto *PhiX = dyn_cast<PHINode>(VarX);
1537 if (PhiX && PhiX->getParent() == LoopEntry &&
1538 (PhiX->getOperand(0) == DefX || PhiX->getOperand(1) == DefX))
1539 return PhiX;
1540 return nullptr;
1541}
1542
1543/// Return true iff the idiom is detected in the loop.
1544///
1545/// Additionally:
1546/// 1) \p CntInst is set to the instruction counting the population bit.
1547/// 2) \p CntPhi is set to the corresponding phi node.
1548/// 3) \p Var is set to the value whose population bits are being counted.
1549///
1550/// The core idiom we are trying to detect is:
1551/// \code
1552/// if (x0 != 0)
1553/// goto loop-exit // the precondition of the loop
1554/// cnt0 = init-val;
1555/// do {
1556/// x1 = phi (x0, x2);
1557/// cnt1 = phi(cnt0, cnt2);
1558///
1559/// cnt2 = cnt1 + 1;
1560/// ...
1561/// x2 = x1 & (x1 - 1);
1562/// ...
1563/// } while(x != 0);
1564///
1565/// loop-exit:
1566/// \endcode
1567static bool detectPopcountIdiom(Loop *CurLoop, BasicBlock *PreCondBB,
1568 Instruction *&CntInst, PHINode *&CntPhi,
1569 Value *&Var) {
1570 // step 1: Check to see if the look-back branch match this pattern:
1571 // "if (a!=0) goto loop-entry".
1572 BasicBlock *LoopEntry;
1573 Instruction *DefX2, *CountInst;
1574 Value *VarX1, *VarX0;
1575 PHINode *PhiX, *CountPhi;
1576
1577 DefX2 = CountInst = nullptr;
1578 VarX1 = VarX0 = nullptr;
1579 PhiX = CountPhi = nullptr;
1580 LoopEntry = *(CurLoop->block_begin());
1581
1582 // step 1: Check if the loop-back branch is in desirable form.
1583 {
1584 if (Value *T = matchCondition(
1585 dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
1586 DefX2 = dyn_cast<Instruction>(T);
1587 else
1588 return false;
1589 }
1590
1591 // step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
1592 {
1593 if (!DefX2 || DefX2->getOpcode() != Instruction::And)
1594 return false;
1595
1596 BinaryOperator *SubOneOp;
1597
1598 if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
1599 VarX1 = DefX2->getOperand(1);
1600 else {
1601 VarX1 = DefX2->getOperand(0);
1602 SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
1603 }
1604 if (!SubOneOp || SubOneOp->getOperand(0) != VarX1)
1605 return false;
1606
1607 ConstantInt *Dec = dyn_cast<ConstantInt>(SubOneOp->getOperand(1));
1608 if (!Dec ||
1609 !((SubOneOp->getOpcode() == Instruction::Sub && Dec->isOne()) ||
1610 (SubOneOp->getOpcode() == Instruction::Add &&
1611 Dec->isMinusOne()))) {
1612 return false;
1613 }
1614 }
1615
1616 // step 3: Check the recurrence of variable X
1617 PhiX = getRecurrenceVar(VarX1, DefX2, LoopEntry);
1618 if (!PhiX)
1619 return false;
1620
1621 // step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
1622 {
1623 CountInst = nullptr;
1624 for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI()->getIterator(),
1625 IterE = LoopEntry->end();
1626 Iter != IterE; Iter++) {
1627 Instruction *Inst = &*Iter;
1628 if (Inst->getOpcode() != Instruction::Add)
1629 continue;
1630
1631 ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
1632 if (!Inc || !Inc->isOne())
1633 continue;
1634
1635 PHINode *Phi = getRecurrenceVar(Inst->getOperand(0), Inst, LoopEntry);
1636 if (!Phi)
1637 continue;
1638
1639 // Check if the result of the instruction is live of the loop.
1640 bool LiveOutLoop = false;
1641 for (User *U : Inst->users()) {
1642 if ((cast<Instruction>(U))->getParent() != LoopEntry) {
1643 LiveOutLoop = true;
1644 break;
1645 }
1646 }
1647
1648 if (LiveOutLoop) {
1649 CountInst = Inst;
1650 CountPhi = Phi;
1651 break;
1652 }
1653 }
1654
1655 if (!CountInst)
1656 return false;
1657 }
1658
1659 // step 5: check if the precondition is in this form:
1660 // "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
1661 {
1662 auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
1663 Value *T = matchCondition(PreCondBr, CurLoop->getLoopPreheader());
1664 if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
1665 return false;
1666
1667 CntInst = CountInst;
1668 CntPhi = CountPhi;
1669 Var = T;
1670 }
1671
1672 return true;
1673}
1674
1675/// Return true if the idiom is detected in the loop.
1676///
1677/// Additionally:
1678/// 1) \p CntInst is set to the instruction Counting Leading Zeros (CTLZ)
1679/// or nullptr if there is no such.
1680/// 2) \p CntPhi is set to the corresponding phi node
1681/// or nullptr if there is no such.
1682/// 3) \p Var is set to the value whose CTLZ could be used.
1683/// 4) \p DefX is set to the instruction calculating Loop exit condition.
1684///
1685/// The core idiom we are trying to detect is:
1686/// \code
1687/// if (x0 == 0)
1688/// goto loop-exit // the precondition of the loop
1689/// cnt0 = init-val;
1690/// do {
1691/// x = phi (x0, x.next); //PhiX
1692/// cnt = phi(cnt0, cnt.next);
1693///
1694/// cnt.next = cnt + 1;
1695/// ...
1696/// x.next = x >> 1; // DefX
1697/// ...
1698/// } while(x.next != 0);
1699///
1700/// loop-exit:
1701/// \endcode
1702static bool detectShiftUntilZeroIdiom(Loop *CurLoop, const DataLayout &DL,
1703 Intrinsic::ID &IntrinID, Value *&InitX,
1704 Instruction *&CntInst, PHINode *&CntPhi,
1705 Instruction *&DefX) {
1706 BasicBlock *LoopEntry;
1707 Value *VarX = nullptr;
1708
1709 DefX = nullptr;
1710 CntInst = nullptr;
1711 CntPhi = nullptr;
1712 LoopEntry = *(CurLoop->block_begin());
1713
1714 // step 1: Check if the loop-back branch is in desirable form.
1715 if (Value *T = matchCondition(
1716 dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
1717 DefX = dyn_cast<Instruction>(T);
1718 else
1719 return false;
1720
1721 // step 2: detect instructions corresponding to "x.next = x >> 1 or x << 1"
1722 if (!DefX || !DefX->isShift())
1723 return false;
1724 IntrinID = DefX->getOpcode() == Instruction::Shl ? Intrinsic::cttz :
1725 Intrinsic::ctlz;
1726 ConstantInt *Shft = dyn_cast<ConstantInt>(DefX->getOperand(1));
1727 if (!Shft || !Shft->isOne())
1728 return false;
1729 VarX = DefX->getOperand(0);
1730
1731 // step 3: Check the recurrence of variable X
1732 PHINode *PhiX = getRecurrenceVar(VarX, DefX, LoopEntry);
1733 if (!PhiX)
1734 return false;
1735
1736 InitX = PhiX->getIncomingValueForBlock(CurLoop->getLoopPreheader());
1737
1738 // Make sure the initial value can't be negative otherwise the ashr in the
1739 // loop might never reach zero which would make the loop infinite.
1740 if (DefX->getOpcode() == Instruction::AShr && !isKnownNonNegative(InitX, DL))
1741 return false;
1742
1743 // step 4: Find the instruction which count the CTLZ: cnt.next = cnt + 1
1744 // or cnt.next = cnt + -1.
1745 // TODO: We can skip the step. If loop trip count is known (CTLZ),
1746 // then all uses of "cnt.next" could be optimized to the trip count
1747 // plus "cnt0". Currently it is not optimized.
1748 // This step could be used to detect POPCNT instruction:
1749 // cnt.next = cnt + (x.next & 1)
1750 for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI()->getIterator(),
1751 IterE = LoopEntry->end();
1752 Iter != IterE; Iter++) {
1753 Instruction *Inst = &*Iter;
1754 if (Inst->getOpcode() != Instruction::Add)
1755 continue;
1756
1757 ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
1758 if (!Inc || (!Inc->isOne() && !Inc->isMinusOne()))
1759 continue;
1760
1761 PHINode *Phi = getRecurrenceVar(Inst->getOperand(0), Inst, LoopEntry);
1762 if (!Phi)
1763 continue;
1764
1765 CntInst = Inst;
1766 CntPhi = Phi;
1767 break;
1768 }
1769 if (!CntInst)
1770 return false;
1771
1772 return true;
1773}
1774
1775/// Recognize CTLZ or CTTZ idiom in a non-countable loop and convert the loop
1776/// to countable (with CTLZ / CTTZ trip count). If CTLZ / CTTZ inserted as a new
1777/// trip count returns true; otherwise, returns false.
1778bool LoopIdiomRecognize::recognizeAndInsertFFS() {
1779 // Give up if the loop has multiple blocks or multiple backedges.
1780 if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
1781 return false;
1782
1783 Intrinsic::ID IntrinID;
1784 Value *InitX;
1785 Instruction *DefX = nullptr;
1786 PHINode *CntPhi = nullptr;
1787 Instruction *CntInst = nullptr;
1788 // Help decide if transformation is profitable. For ShiftUntilZero idiom,
1789 // this is always 6.
1790 size_t IdiomCanonicalSize = 6;
1791
1792 if (!detectShiftUntilZeroIdiom(CurLoop, *DL, IntrinID, InitX,
1793 CntInst, CntPhi, DefX))
1794 return false;
1795
1796 bool IsCntPhiUsedOutsideLoop = false;
1797 for (User *U : CntPhi->users())
1798 if (!CurLoop->contains(cast<Instruction>(U))) {
1799 IsCntPhiUsedOutsideLoop = true;
1800 break;
1801 }
1802 bool IsCntInstUsedOutsideLoop = false;
1803 for (User *U : CntInst->users())
1804 if (!CurLoop->contains(cast<Instruction>(U))) {
1805 IsCntInstUsedOutsideLoop = true;
1806 break;
1807 }
1808 // If both CntInst and CntPhi are used outside the loop the profitability
1809 // is questionable.
1810 if (IsCntInstUsedOutsideLoop && IsCntPhiUsedOutsideLoop)
1811 return false;
1812
1813 // For some CPUs result of CTLZ(X) intrinsic is undefined
1814 // when X is 0. If we can not guarantee X != 0, we need to check this
1815 // when expand.
1816 bool ZeroCheck = false;
1817 // It is safe to assume Preheader exist as it was checked in
1818 // parent function RunOnLoop.
1819 BasicBlock *PH = CurLoop->getLoopPreheader();
1820
1821 // If we are using the count instruction outside the loop, make sure we
1822 // have a zero check as a precondition. Without the check the loop would run
1823 // one iteration for before any check of the input value. This means 0 and 1
1824 // would have identical behavior in the original loop and thus
1825 if (!IsCntPhiUsedOutsideLoop) {
1826 auto *PreCondBB = PH->getSinglePredecessor();
1827 if (!PreCondBB)
1828 return false;
1829 auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
1830 if (!PreCondBI)
1831 return false;
1832 if (matchCondition(PreCondBI, PH) != InitX)
1833 return false;
1834 ZeroCheck = true;
1835 }
1836
1837 // Check if CTLZ / CTTZ intrinsic is profitable. Assume it is always
1838 // profitable if we delete the loop.
1839
1840 // the loop has only 6 instructions:
1841 // %n.addr.0 = phi [ %n, %entry ], [ %shr, %while.cond ]
1842 // %i.0 = phi [ %i0, %entry ], [ %inc, %while.cond ]
1843 // %shr = ashr %n.addr.0, 1
1844 // %tobool = icmp eq %shr, 0
1845 // %inc = add nsw %i.0, 1
1846 // br i1 %tobool
1847
1848 const Value *Args[] = {InitX,
1849 ConstantInt::getBool(InitX->getContext(), ZeroCheck)};
1850
1851 // @llvm.dbg doesn't count as they have no semantic effect.
1852 auto InstWithoutDebugIt = CurLoop->getHeader()->instructionsWithoutDebug();
1853 uint32_t HeaderSize =
1854 std::distance(InstWithoutDebugIt.begin(), InstWithoutDebugIt.end());
1855
1856 IntrinsicCostAttributes Attrs(IntrinID, InitX->getType(), Args);
1857 InstructionCost Cost =
1858 TTI->getIntrinsicInstrCost(Attrs, TargetTransformInfo::TCK_SizeAndLatency);
1859 if (HeaderSize != IdiomCanonicalSize &&
1860 Cost > TargetTransformInfo::TCC_Basic)
1861 return false;
1862
1863 transformLoopToCountable(IntrinID, PH, CntInst, CntPhi, InitX, DefX,
1864 DefX->getDebugLoc(), ZeroCheck,
1865 IsCntPhiUsedOutsideLoop);
1866 return true;
1867}
1868
1869/// Recognizes a population count idiom in a non-countable loop.
1870///
1871/// If detected, transforms the relevant code to issue the popcount intrinsic
1872/// function call, and returns true; otherwise, returns false.
1873bool LoopIdiomRecognize::recognizePopcount() {
1874 if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
1875 return false;
1876
1877 // Counting population are usually conducted by few arithmetic instructions.
1878 // Such instructions can be easily "absorbed" by vacant slots in a
1879 // non-compact loop. Therefore, recognizing popcount idiom only makes sense
1880 // in a compact loop.
1881
1882 // Give up if the loop has multiple blocks or multiple backedges.
1883 if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
1884 return false;
1885
1886 BasicBlock *LoopBody = *(CurLoop->block_begin());
1887 if (LoopBody->size() >= 20) {
1888 // The loop is too big, bail out.
1889 return false;
1890 }
1891
1892 // It should have a preheader containing nothing but an unconditional branch.
1893 BasicBlock *PH = CurLoop->getLoopPreheader();
1894 if (!PH || &PH->front() != PH->getTerminator())
1895 return false;
1896 auto *EntryBI = dyn_cast<BranchInst>(PH->getTerminator());
1897 if (!EntryBI || EntryBI->isConditional())
1898 return false;
1899
1900 // It should have a precondition block where the generated popcount intrinsic
1901 // function can be inserted.
1902 auto *PreCondBB = PH->getSinglePredecessor();
1903 if (!PreCondBB)
1904 return false;
1905 auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
1906 if (!PreCondBI || PreCondBI->isUnconditional())
1907 return false;
1908
1909 Instruction *CntInst;
1910 PHINode *CntPhi;
1911 Value *Val;
1912 if (!detectPopcountIdiom(CurLoop, PreCondBB, CntInst, CntPhi, Val))
1913 return false;
1914
1915 transformLoopToPopcount(PreCondBB, CntInst, CntPhi, Val);
1916 return true;
1917}
1918
1919static CallInst *createPopcntIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
1920 const DebugLoc &DL) {
1921 Value *Ops[] = {Val};
1922 Type *Tys[] = {Val->getType()};
1923
1924 Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
1925 Function *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
1926 CallInst *CI = IRBuilder.CreateCall(Func, Ops);
1927 CI->setDebugLoc(DL);
1928
1929 return CI;
1930}
1931
1932static CallInst *createFFSIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
1933 const DebugLoc &DL, bool ZeroCheck,
1934 Intrinsic::ID IID) {
1935 Value *Ops[] = {Val, IRBuilder.getInt1(ZeroCheck)};
1936 Type *Tys[] = {Val->getType()};
1937
1938 Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
1939 Function *Func = Intrinsic::getDeclaration(M, IID, Tys);
1940 CallInst *CI = IRBuilder.CreateCall(Func, Ops);
1941 CI->setDebugLoc(DL);
1942
1943 return CI;
1944}
1945
1946/// Transform the following loop (Using CTLZ, CTTZ is similar):
1947/// loop:
1948/// CntPhi = PHI [Cnt0, CntInst]
1949/// PhiX = PHI [InitX, DefX]
1950/// CntInst = CntPhi + 1
1951/// DefX = PhiX >> 1
1952/// LOOP_BODY
1953/// Br: loop if (DefX != 0)
1954/// Use(CntPhi) or Use(CntInst)
1955///
1956/// Into:
1957/// If CntPhi used outside the loop:
1958/// CountPrev = BitWidth(InitX) - CTLZ(InitX >> 1)
1959/// Count = CountPrev + 1
1960/// else
1961/// Count = BitWidth(InitX) - CTLZ(InitX)
1962/// loop:
1963/// CntPhi = PHI [Cnt0, CntInst]
1964/// PhiX = PHI [InitX, DefX]
1965/// PhiCount = PHI [Count, Dec]
1966/// CntInst = CntPhi + 1
1967/// DefX = PhiX >> 1
1968/// Dec = PhiCount - 1
1969/// LOOP_BODY
1970/// Br: loop if (Dec != 0)
1971/// Use(CountPrev + Cnt0) // Use(CntPhi)
1972/// or
1973/// Use(Count + Cnt0) // Use(CntInst)
1974///
1975/// If LOOP_BODY is empty the loop will be deleted.
1976/// If CntInst and DefX are not used in LOOP_BODY they will be removed.
1977void LoopIdiomRecognize::transformLoopToCountable(
1978 Intrinsic::ID IntrinID, BasicBlock *Preheader, Instruction *CntInst,
1979 PHINode *CntPhi, Value *InitX, Instruction *DefX, const DebugLoc &DL,
1980 bool ZeroCheck, bool IsCntPhiUsedOutsideLoop) {
1981 BranchInst *PreheaderBr = cast<BranchInst>(Preheader->getTerminator());
1982
1983 // Step 1: Insert the CTLZ/CTTZ instruction at the end of the preheader block
1984 IRBuilder<> Builder(PreheaderBr);
1985 Builder.SetCurrentDebugLocation(DL);
1986
1987 // If there are no uses of CntPhi crate:
1988 // Count = BitWidth - CTLZ(InitX);
1989 // NewCount = Count;
1990 // If there are uses of CntPhi create:
1991 // NewCount = BitWidth - CTLZ(InitX >> 1);
1992 // Count = NewCount + 1;
1993 Value *InitXNext;
1994 if (IsCntPhiUsedOutsideLoop) {
1995 if (DefX->getOpcode() == Instruction::AShr)
1996 InitXNext = Builder.CreateAShr(InitX, 1);
1997 else if (DefX->getOpcode() == Instruction::LShr)
1998 InitXNext = Builder.CreateLShr(InitX, 1);
1999 else if (DefX->getOpcode() == Instruction::Shl) // cttz
2000 InitXNext = Builder.CreateShl(InitX, 1);
2001 else
2002 llvm_unreachable("Unexpected opcode!")__builtin_unreachable();
2003 } else
2004 InitXNext = InitX;
2005 Value *Count =
2006 createFFSIntrinsic(Builder, InitXNext, DL, ZeroCheck, IntrinID);
2007 Type *CountTy = Count->getType();
2008 Count = Builder.CreateSub(
2009 ConstantInt::get(CountTy, CountTy->getIntegerBitWidth()), Count);
2010 Value *NewCount = Count;
2011 if (IsCntPhiUsedOutsideLoop)
2012 Count = Builder.CreateAdd(Count, ConstantInt::get(CountTy, 1));
2013
2014 NewCount = Builder.CreateZExtOrTrunc(NewCount, CntInst->getType());
2015
2016 Value *CntInitVal = CntPhi->getIncomingValueForBlock(Preheader);
2017 if (cast<ConstantInt>(CntInst->getOperand(1))->isOne()) {
2018 // If the counter was being incremented in the loop, add NewCount to the
2019 // counter's initial value, but only if the initial value is not zero.
2020 ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
2021 if (!InitConst || !InitConst->isZero())
2022 NewCount = Builder.CreateAdd(NewCount, CntInitVal);
2023 } else {
2024 // If the count was being decremented in the loop, subtract NewCount from
2025 // the counter's initial value.
2026 NewCount = Builder.CreateSub(CntInitVal, NewCount);
2027 }
2028
2029 // Step 2: Insert new IV and loop condition:
2030 // loop:
2031 // ...
2032 // PhiCount = PHI [Count, Dec]
2033 // ...
2034 // Dec = PhiCount - 1
2035 // ...
2036 // Br: loop if (Dec != 0)
2037 BasicBlock *Body = *(CurLoop->block_begin());
2038 auto *LbBr = cast<BranchInst>(Body->getTerminator());
2039 ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
2040
2041 PHINode *TcPhi = PHINode::Create(CountTy, 2, "tcphi", &Body->front());
2042
2043 Builder.SetInsertPoint(LbCond);
2044 Instruction *TcDec = cast<Instruction>(Builder.CreateSub(
2045 TcPhi, ConstantInt::get(CountTy, 1), "tcdec", false, true));
2046
2047 TcPhi->addIncoming(Count, Preheader);
2048 TcPhi->addIncoming(TcDec, Body);
2049
2050 CmpInst::Predicate Pred =
2051 (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_NE : CmpInst::ICMP_EQ;
2052 LbCond->setPredicate(Pred);
2053 LbCond->setOperand(0, TcDec);
2054 LbCond->setOperand(1, ConstantInt::get(CountTy, 0));
2055
2056 // Step 3: All the references to the original counter outside
2057 // the loop are replaced with the NewCount
2058 if (IsCntPhiUsedOutsideLoop)
2059 CntPhi->replaceUsesOutsideBlock(NewCount, Body);
2060 else
2061 CntInst->replaceUsesOutsideBlock(NewCount, Body);
2062
2063 // step 4: Forget the "non-computable" trip-count SCEV associated with the
2064 // loop. The loop would otherwise not be deleted even if it becomes empty.
2065 SE->forgetLoop(CurLoop);
2066}
2067
2068void LoopIdiomRecognize::transformLoopToPopcount(BasicBlock *PreCondBB,
2069 Instruction *CntInst,
2070 PHINode *CntPhi, Value *Var) {
2071 BasicBlock *PreHead = CurLoop->getLoopPreheader();
2072 auto *PreCondBr = cast<BranchInst>(PreCondBB->getTerminator());
2073 const DebugLoc &DL = CntInst->getDebugLoc();
2074
2075 // Assuming before transformation, the loop is following:
2076 // if (x) // the precondition
2077 // do { cnt++; x &= x - 1; } while(x);
2078
2079 // Step 1: Insert the ctpop instruction at the end of the precondition block
2080 IRBuilder<> Builder(PreCondBr);
2081 Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
2082 {
2083 PopCnt = createPopcntIntrinsic(Builder, Var, DL);
2084 NewCount = PopCntZext =
2085 Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));
2086
2087 if (NewCount != PopCnt)
2088 (cast<Instruction>(NewCount))->setDebugLoc(DL);
2089
2090 // TripCnt is exactly the number of iterations the loop has
2091 TripCnt = NewCount;
2092
2093 // If the population counter's initial value is not zero, insert Add Inst.
2094 Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
2095 ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
2096 if (!InitConst || !InitConst->isZero()) {
2097 NewCount = Builder.CreateAdd(NewCount, CntInitVal);
2098 (cast<Instruction>(NewCount))->setDebugLoc(DL);
2099 }
2100 }
2101
2102 // Step 2: Replace the precondition from "if (x == 0) goto loop-exit" to
2103 // "if (NewCount == 0) loop-exit". Without this change, the intrinsic
2104 // function would be partial dead code, and downstream passes will drag
2105 // it back from the precondition block to the preheader.
2106 {
2107 ICmpInst *PreCond = cast<ICmpInst>(PreCondBr->getCondition());
2108
2109 Value *Opnd0 = PopCntZext;
2110 Value *Opnd1 = ConstantInt::get(PopCntZext->getType(), 0);
2111 if (PreCond->getOperand(0) != Var)
2112 std::swap(Opnd0, Opnd1);
2113
2114 ICmpInst *NewPreCond = cast<ICmpInst>(
2115 Builder.CreateICmp(PreCond->getPredicate(), Opnd0, Opnd1));
2116 PreCondBr->setCondition(NewPreCond);
2117
2118 RecursivelyDeleteTriviallyDeadInstructions(PreCond, TLI);
2119 }
2120
2121 // Step 3: Note that the population count is exactly the trip count of the
2122 // loop in question, which enable us to convert the loop from noncountable
2123 // loop into a countable one. The benefit is twofold:
2124 //
2125 // - If the loop only counts population, the entire loop becomes dead after
2126 // the transformation. It is a lot easier to prove a countable loop dead
2127 // than to prove a noncountable one. (In some C dialects, an infinite loop
2128 // isn't dead even if it computes nothing useful. In general, DCE needs
2129 // to prove a noncountable loop finite before safely delete it.)
2130 //
2131 // - If the loop also performs something else, it remains alive.
2132 // Since it is transformed to countable form, it can be aggressively
2133 // optimized by some optimizations which are in general not applicable
2134 // to a noncountable loop.
2135 //
2136 // After this step, this loop (conceptually) would look like following:
2137 // newcnt = __builtin_ctpop(x);
2138 // t = newcnt;
2139 // if (x)
2140 // do { cnt++; x &= x-1; t--) } while (t > 0);
2141 BasicBlock *Body = *(CurLoop->block_begin());
2142 {
2143 auto *LbBr = cast<BranchInst>(Body->getTerminator());
2144 ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
2145 Type *Ty = TripCnt->getType();
2146
2147 PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", &Body->front());
2148
2149 Builder.SetInsertPoint(LbCond);
2150 Instruction *TcDec = cast<Instruction>(
2151 Builder.CreateSub(TcPhi, ConstantInt::get(Ty, 1),
2152 "tcdec", false, true));
2153
2154 TcPhi->addIncoming(TripCnt, PreHead);
2155 TcPhi->addIncoming(TcDec, Body);
2156
2157 CmpInst::Predicate Pred =
2158 (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_UGT : CmpInst::ICMP_SLE;
2159 LbCond->setPredicate(Pred);
2160 LbCond->setOperand(0, TcDec);
2161 LbCond->setOperand(1, ConstantInt::get(Ty, 0));
2162 }
2163
2164 // Step 4: All the references to the original population counter outside
2165 // the loop are replaced with the NewCount -- the value returned from
2166 // __builtin_ctpop().
2167 CntInst->replaceUsesOutsideBlock(NewCount, Body);
2168
2169 // step 5: Forget the "non-computable" trip-count SCEV associated with the
2170 // loop. The loop would otherwise not be deleted even if it becomes empty.
2171 SE->forgetLoop(CurLoop);
2172}
2173
2174/// Match loop-invariant value.
2175template <typename SubPattern_t> struct match_LoopInvariant {
2176 SubPattern_t SubPattern;
2177 const Loop *L;
2178
2179 match_LoopInvariant(const SubPattern_t &SP, const Loop *L)
2180 : SubPattern(SP), L(L) {}
2181
2182 template <typename ITy> bool match(ITy *V) {
2183 return L->isLoopInvariant(V) && SubPattern.match(V);
2184 }
2185};
2186
2187/// Matches if the value is loop-invariant.
2188template <typename Ty>
2189inline match_LoopInvariant<Ty> m_LoopInvariant(const Ty &M, const Loop *L) {
2190 return match_LoopInvariant<Ty>(M, L);
2191}
2192
2193/// Return true if the idiom is detected in the loop.
2194///
2195/// The core idiom we are trying to detect is:
2196/// \code
2197/// entry:
2198/// <...>
2199/// %bitmask = shl i32 1, %bitpos
2200/// br label %loop
2201///
2202/// loop:
2203/// %x.curr = phi i32 [ %x, %entry ], [ %x.next, %loop ]
2204/// %x.curr.bitmasked = and i32 %x.curr, %bitmask
2205/// %x.curr.isbitunset = icmp eq i32 %x.curr.bitmasked, 0
2206/// %x.next = shl i32 %x.curr, 1
2207/// <...>
2208/// br i1 %x.curr.isbitunset, label %loop, label %end
2209///
2210/// end:
2211/// %x.curr.res = phi i32 [ %x.curr, %loop ] <...>
2212/// %x.next.res = phi i32 [ %x.next, %loop ] <...>
2213/// <...>
2214/// \endcode
2215static bool detectShiftUntilBitTestIdiom(Loop *CurLoop, Value *&BaseX,
2216 Value *&BitMask, Value *&BitPos,
2217 Value *&CurrX, Instruction *&NextX) {
2218 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { } while (false)
2219 " Performing shift-until-bittest idiom detection.\n")do { } while (false);
2220
2221 // Give up if the loop has multiple blocks or multiple backedges.
2222 if (CurLoop->getNumBlocks() != 1 || CurLoop->getNumBackEdges() != 1) {
2223 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad block/backedge count.\n")do { } while (false);
2224 return false;
2225 }
2226
2227 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2228 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2229 assert(LoopPreheaderBB && "There is always a loop preheader.")(static_cast<void> (0));
2230
2231 using namespace PatternMatch;
2232
2233 // Step 1: Check if the loop backedge is in desirable form.
2234
2235 ICmpInst::Predicate Pred;
2236 Value *CmpLHS, *CmpRHS;
2237 BasicBlock *TrueBB, *FalseBB;
2238 if (!match(LoopHeaderBB->getTerminator(),
2239 m_Br(m_ICmp(Pred, m_Value(CmpLHS), m_Value(CmpRHS)),
2240 m_BasicBlock(TrueBB), m_BasicBlock(FalseBB)))) {
2241 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad backedge structure.\n")do { } while (false);
2242 return false;
2243 }
2244
2245 // Step 2: Check if the backedge's condition is in desirable form.
2246
2247 auto MatchVariableBitMask = [&]() {
2248 return ICmpInst::isEquality(Pred) && match(CmpRHS, m_Zero()) &&
2249 match(CmpLHS,
2250 m_c_And(m_Value(CurrX),
2251 m_CombineAnd(
2252 m_Value(BitMask),
2253 m_LoopInvariant(m_Shl(m_One(), m_Value(BitPos)),
2254 CurLoop))));
2255 };
2256 auto MatchConstantBitMask = [&]() {
2257 return ICmpInst::isEquality(Pred) && match(CmpRHS, m_Zero()) &&
2258 match(CmpLHS, m_And(m_Value(CurrX),
2259 m_CombineAnd(m_Value(BitMask), m_Power2()))) &&
2260 (BitPos = ConstantExpr::getExactLogBase2(cast<Constant>(BitMask)));
2261 };
2262 auto MatchDecomposableConstantBitMask = [&]() {
2263 APInt Mask;
2264 return llvm::decomposeBitTestICmp(CmpLHS, CmpRHS, Pred, CurrX, Mask) &&
2265 ICmpInst::isEquality(Pred) && Mask.isPowerOf2() &&
2266 (BitMask = ConstantInt::get(CurrX->getType(), Mask)) &&
2267 (BitPos = ConstantInt::get(CurrX->getType(), Mask.logBase2()));
2268 };
2269
2270 if (!MatchVariableBitMask() && !MatchConstantBitMask() &&
2271 !MatchDecomposableConstantBitMask()) {
2272 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad backedge comparison.\n")do { } while (false);
2273 return false;
2274 }
2275
2276 // Step 3: Check if the recurrence is in desirable form.
2277 auto *CurrXPN = dyn_cast<PHINode>(CurrX);
2278 if (!CurrXPN || CurrXPN->getParent() != LoopHeaderBB) {
2279 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Not an expected PHI node.\n")do { } while (false);
2280 return false;
2281 }
2282
2283 BaseX = CurrXPN->getIncomingValueForBlock(LoopPreheaderBB);
2284 NextX =
2285 dyn_cast<Instruction>(CurrXPN->getIncomingValueForBlock(LoopHeaderBB));
2286
2287 assert(CurLoop->isLoopInvariant(BaseX) &&(static_cast<void> (0))
2288 "Expected BaseX to be avaliable in the preheader!")(static_cast<void> (0));
2289
2290 if (!NextX || !match(NextX, m_Shl(m_Specific(CurrX), m_One()))) {
2291 // FIXME: support right-shift?
2292 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad recurrence.\n")do { } while (false);
2293 return false;
2294 }
2295
2296 // Step 4: Check if the backedge's destinations are in desirable form.
2297
2298 assert(ICmpInst::isEquality(Pred) &&(static_cast<void> (0))
2299 "Should only get equality predicates here.")(static_cast<void> (0));
2300
2301 // cmp-br is commutative, so canonicalize to a single variant.
2302 if (Pred != ICmpInst::Predicate::ICMP_EQ) {
2303 Pred = ICmpInst::getInversePredicate(Pred);
2304 std::swap(TrueBB, FalseBB);
2305 }
2306
2307 // We expect to exit loop when comparison yields false,
2308 // so when it yields true we should branch back to loop header.
2309 if (TrueBB != LoopHeaderBB) {
2310 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad backedge flow.\n")do { } while (false);
2311 return false;
2312 }
2313
2314 // Okay, idiom checks out.
2315 return true;
2316}
2317
2318/// Look for the following loop:
2319/// \code
2320/// entry:
2321/// <...>
2322/// %bitmask = shl i32 1, %bitpos
2323/// br label %loop
2324///
2325/// loop:
2326/// %x.curr = phi i32 [ %x, %entry ], [ %x.next, %loop ]
2327/// %x.curr.bitmasked = and i32 %x.curr, %bitmask
2328/// %x.curr.isbitunset = icmp eq i32 %x.curr.bitmasked, 0
2329/// %x.next = shl i32 %x.curr, 1
2330/// <...>
2331/// br i1 %x.curr.isbitunset, label %loop, label %end
2332///
2333/// end:
2334/// %x.curr.res = phi i32 [ %x.curr, %loop ] <...>
2335/// %x.next.res = phi i32 [ %x.next, %loop ] <...>
2336/// <...>
2337/// \endcode
2338///
2339/// And transform it into:
2340/// \code
2341/// entry:
2342/// %bitmask = shl i32 1, %bitpos
2343/// %lowbitmask = add i32 %bitmask, -1
2344/// %mask = or i32 %lowbitmask, %bitmask
2345/// %x.masked = and i32 %x, %mask
2346/// %x.masked.numleadingzeros = call i32 @llvm.ctlz.i32(i32 %x.masked,
2347/// i1 true)
2348/// %x.masked.numactivebits = sub i32 32, %x.masked.numleadingzeros
2349/// %x.masked.leadingonepos = add i32 %x.masked.numactivebits, -1
2350/// %backedgetakencount = sub i32 %bitpos, %x.masked.leadingonepos
2351/// %tripcount = add i32 %backedgetakencount, 1
2352/// %x.curr = shl i32 %x, %backedgetakencount
2353/// %x.next = shl i32 %x, %tripcount
2354/// br label %loop
2355///
2356/// loop:
2357/// %loop.iv = phi i32 [ 0, %entry ], [ %loop.iv.next, %loop ]
2358/// %loop.iv.next = add nuw i32 %loop.iv, 1
2359/// %loop.ivcheck = icmp eq i32 %loop.iv.next, %tripcount
2360/// <...>
2361/// br i1 %loop.ivcheck, label %end, label %loop
2362///
2363/// end:
2364/// %x.curr.res = phi i32 [ %x.curr, %loop ] <...>
2365/// %x.next.res = phi i32 [ %x.next, %loop ] <...>
2366/// <...>
2367/// \endcode
2368bool LoopIdiomRecognize::recognizeShiftUntilBitTest() {
2369 bool MadeChange = false;
2370
2371 Value *X, *BitMask, *BitPos, *XCurr;
2372 Instruction *XNext;
2373 if (!detectShiftUntilBitTestIdiom(CurLoop, X, BitMask, BitPos, XCurr,
2374 XNext)) {
2375 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { } while (false)
2376 " shift-until-bittest idiom detection failed.\n")do { } while (false);
2377 return MadeChange;
2378 }
2379 LLVM_DEBUG(dbgs() << DEBUG_TYPE " shift-until-bittest idiom detected!\n")do { } while (false);
2380
2381 // Ok, it is the idiom we were looking for, we *could* transform this loop,
2382 // but is it profitable to transform?
2383
2384 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2385 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2386 assert(LoopPreheaderBB && "There is always a loop preheader.")(static_cast<void> (0));
2387
2388 BasicBlock *SuccessorBB = CurLoop->getExitBlock();
2389 assert(SuccessorBB && "There is only a single successor.")(static_cast<void> (0));
2390
2391 IRBuilder<> Builder(LoopPreheaderBB->getTerminator());
2392 Builder.SetCurrentDebugLocation(cast<Instruction>(XCurr)->getDebugLoc());
2393
2394 Intrinsic::ID IntrID = Intrinsic::ctlz;
2395 Type *Ty = X->getType();
2396 unsigned Bitwidth = Ty->getScalarSizeInBits();
2397
2398 TargetTransformInfo::TargetCostKind CostKind =
2399 TargetTransformInfo::TCK_SizeAndLatency;
2400
2401 // The rewrite is considered to be unprofitable iff and only iff the
2402 // intrinsic/shift we'll use are not cheap. Note that we are okay with *just*
2403 // making the loop countable, even if nothing else changes.
2404 IntrinsicCostAttributes Attrs(
2405 IntrID, Ty, {UndefValue::get(Ty), /*is_zero_undef=*/Builder.getTrue()});
2406 InstructionCost Cost = TTI->getIntrinsicInstrCost(Attrs, CostKind);
2407 if (Cost > TargetTransformInfo::TCC_Basic) {
2408 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { } while (false)
2409 " Intrinsic is too costly, not beneficial\n")do { } while (false);
2410 return MadeChange;
2411 }
2412 if (TTI->getArithmeticInstrCost(Instruction::Shl, Ty, CostKind) >
2413 TargetTransformInfo::TCC_Basic) {
2414 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Shift is too costly, not beneficial\n")do { } while (false);
2415 return MadeChange;
2416 }
2417
2418 // Ok, transform appears worthwhile.
2419 MadeChange = true;
2420
2421 // Step 1: Compute the loop trip count.
2422
2423 Value *LowBitMask = Builder.CreateAdd(BitMask, Constant::getAllOnesValue(Ty),
2424 BitPos->getName() + ".lowbitmask");
2425 Value *Mask =
2426 Builder.CreateOr(LowBitMask, BitMask, BitPos->getName() + ".mask");
2427 Value *XMasked = Builder.CreateAnd(X, Mask, X->getName() + ".masked");
2428 CallInst *XMaskedNumLeadingZeros = Builder.CreateIntrinsic(
2429 IntrID, Ty, {XMasked, /*is_zero_undef=*/Builder.getTrue()},
2430 /*FMFSource=*/nullptr, XMasked->getName() + ".numleadingzeros");
2431 Value *XMaskedNumActiveBits = Builder.CreateSub(
2432 ConstantInt::get(Ty, Ty->getScalarSizeInBits()), XMaskedNumLeadingZeros,
2433 XMasked->getName() + ".numactivebits", /*HasNUW=*/true,
2434 /*HasNSW=*/Bitwidth != 2);
2435 Value *XMaskedLeadingOnePos =
2436 Builder.CreateAdd(XMaskedNumActiveBits, Constant::getAllOnesValue(Ty),
2437 XMasked->getName() + ".leadingonepos", /*HasNUW=*/false,
2438 /*HasNSW=*/Bitwidth > 2);
2439
2440 Value *LoopBackedgeTakenCount = Builder.CreateSub(
2441 BitPos, XMaskedLeadingOnePos, CurLoop->getName() + ".backedgetakencount",
2442 /*HasNUW=*/true, /*HasNSW=*/true);
2443 // We know loop's backedge-taken count, but what's loop's trip count?
2444 // Note that while NUW is always safe, while NSW is only for bitwidths != 2.
2445 Value *LoopTripCount =
2446 Builder.CreateAdd(LoopBackedgeTakenCount, ConstantInt::get(Ty, 1),
2447 CurLoop->getName() + ".tripcount", /*HasNUW=*/true,
2448 /*HasNSW=*/Bitwidth != 2);
2449
2450 // Step 2: Compute the recurrence's final value without a loop.
2451
2452 // NewX is always safe to compute, because `LoopBackedgeTakenCount`
2453 // will always be smaller than `bitwidth(X)`, i.e. we never get poison.
2454 Value *NewX = Builder.CreateShl(X, LoopBackedgeTakenCount);
2455 NewX->takeName(XCurr);
2456 if (auto *I = dyn_cast<Instruction>(NewX))
2457 I->copyIRFlags(XNext, /*IncludeWrapFlags=*/true);
2458
2459 Value *NewXNext;
2460 // Rewriting XNext is more complicated, however, because `X << LoopTripCount`
2461 // will be poison iff `LoopTripCount == bitwidth(X)` (which will happen
2462 // iff `BitPos` is `bitwidth(x) - 1` and `X` is `1`). So unless we know
2463 // that isn't the case, we'll need to emit an alternative, safe IR.
2464 if (XNext->hasNoSignedWrap() || XNext->hasNoUnsignedWrap() ||
2465 PatternMatch::match(
2466 BitPos, PatternMatch::m_SpecificInt_ICMP(
2467 ICmpInst::ICMP_NE, APInt(Ty->getScalarSizeInBits(),
2468 Ty->getScalarSizeInBits() - 1))))
2469 NewXNext = Builder.CreateShl(X, LoopTripCount);
2470 else {
2471 // Otherwise, just additionally shift by one. It's the smallest solution,
2472 // alternatively, we could check that NewX is INT_MIN (or BitPos is )
2473 // and select 0 instead.
2474 NewXNext = Builder.CreateShl(NewX, ConstantInt::get(Ty, 1));
2475 }
2476
2477 NewXNext->takeName(XNext);
2478 if (auto *I = dyn_cast<Instruction>(NewXNext))
2479 I->copyIRFlags(XNext, /*IncludeWrapFlags=*/true);
2480
2481 // Step 3: Adjust the successor basic block to recieve the computed
2482 // recurrence's final value instead of the recurrence itself.
2483
2484 XCurr->replaceUsesOutsideBlock(NewX, LoopHeaderBB);
2485 XNext->replaceUsesOutsideBlock(NewXNext, LoopHeaderBB);
2486
2487 // Step 4: Rewrite the loop into a countable form, with canonical IV.
2488
2489 // The new canonical induction variable.
2490 Builder.SetInsertPoint(&LoopHeaderBB->front());
2491 auto *IV = Builder.CreatePHI(Ty, 2, CurLoop->getName() + ".iv");
2492
2493 // The induction itself.
2494 // Note that while NUW is always safe, while NSW is only for bitwidths != 2.
2495 Builder.SetInsertPoint(LoopHeaderBB->getTerminator());
2496 auto *IVNext =
2497 Builder.CreateAdd(IV, ConstantInt::get(Ty, 1), IV->getName() + ".next",
2498 /*HasNUW=*/true, /*HasNSW=*/Bitwidth != 2);
2499
2500 // The loop trip count check.
2501 auto *IVCheck = Builder.CreateICmpEQ(IVNext, LoopTripCount,
2502 CurLoop->getName() + ".ivcheck");
2503 Builder.CreateCondBr(IVCheck, SuccessorBB, LoopHeaderBB);
2504 LoopHeaderBB->getTerminator()->eraseFromParent();
2505
2506 // Populate the IV PHI.
2507 IV->addIncoming(ConstantInt::get(Ty, 0), LoopPreheaderBB);
2508 IV->addIncoming(IVNext, LoopHeaderBB);
2509
2510 // Step 5: Forget the "non-computable" trip-count SCEV associated with the
2511 // loop. The loop would otherwise not be deleted even if it becomes empty.
2512
2513 SE->forgetLoop(CurLoop);
2514
2515 // Other passes will take care of actually deleting the loop if possible.
2516
2517 LLVM_DEBUG(dbgs() << DEBUG_TYPE " shift-until-bittest idiom optimized!\n")do { } while (false);
2518
2519 ++NumShiftUntilBitTest;
2520 return MadeChange;
2521}
2522
2523/// Return true if the idiom is detected in the loop.
2524///
2525/// The core idiom we are trying to detect is:
2526/// \code
2527/// entry:
2528/// <...>
2529/// %start = <...>
2530/// %extraoffset = <...>
2531/// <...>
2532/// br label %for.cond
2533///
2534/// loop:
2535/// %iv = phi i8 [ %start, %entry ], [ %iv.next, %for.cond ]
2536/// %nbits = add nsw i8 %iv, %extraoffset
2537/// %val.shifted = {{l,a}shr,shl} i8 %val, %nbits
2538/// %val.shifted.iszero = icmp eq i8 %val.shifted, 0
2539/// %iv.next = add i8 %iv, 1
2540/// <...>
2541/// br i1 %val.shifted.iszero, label %end, label %loop
2542///
2543/// end:
2544/// %iv.res = phi i8 [ %iv, %loop ] <...>
2545/// %nbits.res = phi i8 [ %nbits, %loop ] <...>
2546/// %val.shifted.res = phi i8 [ %val.shifted, %loop ] <...>
2547/// %val.shifted.iszero.res = phi i1 [ %val.shifted.iszero, %loop ] <...>
2548/// %iv.next.res = phi i8 [ %iv.next, %loop ] <...>
2549/// <...>
2550/// \endcode
2551static bool detectShiftUntilZeroIdiom(Loop *CurLoop, ScalarEvolution *SE,
2552 Instruction *&ValShiftedIsZero,
2553 Intrinsic::ID &IntrinID, Instruction *&IV,
2554 Value *&Start, Value *&Val,
2555 const SCEV *&ExtraOffsetExpr,
2556 bool &InvertedCond) {
2557 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { } while (false)
2558 " Performing shift-until-zero idiom detection.\n")do { } while (false);
2559
2560 // Give up if the loop has multiple blocks or multiple backedges.
2561 if (CurLoop->getNumBlocks() != 1 || CurLoop->getNumBackEdges() != 1) {
2562 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad block/backedge count.\n")do { } while (false);
2563 return false;
2564 }
2565
2566 Instruction *ValShifted, *NBits, *IVNext;
2567 Value *ExtraOffset;
2568
2569 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2570 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2571 assert(LoopPreheaderBB && "There is always a loop preheader.")(static_cast<void> (0));
2572
2573 using namespace PatternMatch;
2574
2575 // Step 1: Check if the loop backedge, condition is in desirable form.
2576
2577 ICmpInst::Predicate Pred;
2578 BasicBlock *TrueBB, *FalseBB;
2579 if (!match(LoopHeaderBB->getTerminator(),
2580 m_Br(m_Instruction(ValShiftedIsZero), m_BasicBlock(TrueBB),
2581 m_BasicBlock(FalseBB))) ||
2582 !match(ValShiftedIsZero,
2583 m_ICmp(Pred, m_Instruction(ValShifted), m_Zero())) ||
2584 !ICmpInst::isEquality(Pred)) {
2585 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad backedge structure.\n")do { } while (false);
2586 return false;
2587 }
2588
2589 // Step 2: Check if the comparison's operand is in desirable form.
2590 // FIXME: Val could be a one-input PHI node, which we should look past.
2591 if (!match(ValShifted, m_Shift(m_LoopInvariant(m_Value(Val), CurLoop),
2592 m_Instruction(NBits)))) {
2593 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad comparisons value computation.\n")do { } while (false);
2594 return false;
2595 }
2596 IntrinID = ValShifted->getOpcode() == Instruction::Shl ? Intrinsic::cttz
2597 : Intrinsic::ctlz;
2598
2599 // Step 3: Check if the shift amount is in desirable form.
2600
2601 if (match(NBits, m_c_Add(m_Instruction(IV),
2602 m_LoopInvariant(m_Value(ExtraOffset), CurLoop))) &&
2603 (NBits->hasNoSignedWrap() || NBits->hasNoUnsignedWrap()))
2604 ExtraOffsetExpr = SE->getNegativeSCEV(SE->getSCEV(ExtraOffset));
2605 else if (match(NBits,
2606 m_Sub(m_Instruction(IV),
2607 m_LoopInvariant(m_Value(ExtraOffset), CurLoop))) &&
2608 NBits->hasNoSignedWrap())
2609 ExtraOffsetExpr = SE->getSCEV(ExtraOffset);
2610 else {
2611 IV = NBits;
2612 ExtraOffsetExpr = SE->getZero(NBits->getType());
2613 }
2614
2615 // Step 4: Check if the recurrence is in desirable form.
2616 auto *IVPN = dyn_cast<PHINode>(IV);
2617 if (!IVPN || IVPN->getParent() != LoopHeaderBB) {
2618 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Not an expected PHI node.\n")do { } while (false);
2619 return false;
2620 }
2621
2622 Start = IVPN->getIncomingValueForBlock(LoopPreheaderBB);
2623 IVNext = dyn_cast<Instruction>(IVPN->getIncomingValueForBlock(LoopHeaderBB));
2624
2625 if (!IVNext || !match(IVNext, m_Add(m_Specific(IVPN), m_One()))) {
2626 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad recurrence.\n")do { } while (false);
2627 return false;
2628 }
2629
2630 // Step 4: Check if the backedge's destinations are in desirable form.
2631
2632 assert(ICmpInst::isEquality(Pred) &&(static_cast<void> (0))
2633 "Should only get equality predicates here.")(static_cast<void> (0));
2634
2635 // cmp-br is commutative, so canonicalize to a single variant.
2636 InvertedCond = Pred != ICmpInst::Predicate::ICMP_EQ;
2637 if (InvertedCond) {
2638 Pred = ICmpInst::getInversePredicate(Pred);
Value stored to 'Pred' is never read
2639 std::swap(TrueBB, FalseBB);
2640 }
2641
2642 // We expect to exit loop when comparison yields true,
2643 // so when it yields false we should branch back to loop header.
2644 if (FalseBB != LoopHeaderBB) {
2645 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Bad backedge flow.\n")do { } while (false);
2646 return false;
2647 }
2648
2649 // The new, countable, loop will certainly only run a known number of
2650 // iterations, It won't be infinite. But the old loop might be infinite
2651 // under certain conditions. For logical shifts, the value will become zero
2652 // after at most bitwidth(%Val) loop iterations. However, for arithmetic
2653 // right-shift, iff the sign bit was set, the value will never become zero,
2654 // and the loop may never finish.
2655 if (ValShifted->getOpcode() == Instruction::AShr &&
2656 !isMustProgress(CurLoop) && !SE->isKnownNonNegative(SE->getSCEV(Val))) {
2657 LLVM_DEBUG(dbgs() << DEBUG_TYPE " Can not prove the loop is finite.\n")do { } while (false);
2658 return false;
2659 }
2660
2661 // Okay, idiom checks out.
2662 return true;
2663}
2664
2665/// Look for the following loop:
2666/// \code
2667/// entry:
2668/// <...>
2669/// %start = <...>
2670/// %extraoffset = <...>
2671/// <...>
2672/// br label %for.cond
2673///
2674/// loop:
2675/// %iv = phi i8 [ %start, %entry ], [ %iv.next, %for.cond ]
2676/// %nbits = add nsw i8 %iv, %extraoffset
2677/// %val.shifted = {{l,a}shr,shl} i8 %val, %nbits
2678/// %val.shifted.iszero = icmp eq i8 %val.shifted, 0
2679/// %iv.next = add i8 %iv, 1
2680/// <...>
2681/// br i1 %val.shifted.iszero, label %end, label %loop
2682///
2683/// end:
2684/// %iv.res = phi i8 [ %iv, %loop ] <...>
2685/// %nbits.res = phi i8 [ %nbits, %loop ] <...>
2686/// %val.shifted.res = phi i8 [ %val.shifted, %loop ] <...>
2687/// %val.shifted.iszero.res = phi i1 [ %val.shifted.iszero, %loop ] <...>
2688/// %iv.next.res = phi i8 [ %iv.next, %loop ] <...>
2689/// <...>
2690/// \endcode
2691///
2692/// And transform it into:
2693/// \code
2694/// entry:
2695/// <...>
2696/// %start = <...>
2697/// %extraoffset = <...>
2698/// <...>
2699/// %val.numleadingzeros = call i8 @llvm.ct{l,t}z.i8(i8 %val, i1 0)
2700/// %val.numactivebits = sub i8 8, %val.numleadingzeros
2701/// %extraoffset.neg = sub i8 0, %extraoffset
2702/// %tmp = add i8 %val.numactivebits, %extraoffset.neg
2703/// %iv.final = call i8 @llvm.smax.i8(i8 %tmp, i8 %start)
2704/// %loop.tripcount = sub i8 %iv.final, %start
2705/// br label %loop
2706///
2707/// loop:
2708/// %loop.iv = phi i8 [ 0, %entry ], [ %loop.iv.next, %loop ]
2709/// %loop.iv.next = add i8 %loop.iv, 1
2710/// %loop.ivcheck = icmp eq i8 %loop.iv.next, %loop.tripcount
2711/// %iv = add i8 %loop.iv, %start
2712/// <...>
2713/// br i1 %loop.ivcheck, label %end, label %loop
2714///
2715/// end:
2716/// %iv.res = phi i8 [ %iv.final, %loop ] <...>
2717/// <...>
2718/// \endcode
2719bool LoopIdiomRecognize::recognizeShiftUntilZero() {
2720 bool MadeChange = false;
2721
2722 Instruction *ValShiftedIsZero;
2723 Intrinsic::ID IntrID;
2724 Instruction *IV;
2725 Value *Start, *Val;
2726 const SCEV *ExtraOffsetExpr;
2727 bool InvertedCond;
2728 if (!detectShiftUntilZeroIdiom(CurLoop, SE, ValShiftedIsZero, IntrID, IV,
2729 Start, Val, ExtraOffsetExpr, InvertedCond)) {
2730 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { } while (false)
2731 " shift-until-zero idiom detection failed.\n")do { } while (false);
2732 return MadeChange;
2733 }
2734 LLVM_DEBUG(dbgs() << DEBUG_TYPE " shift-until-zero idiom detected!\n")do { } while (false);
2735
2736 // Ok, it is the idiom we were looking for, we *could* transform this loop,
2737 // but is it profitable to transform?
2738
2739 BasicBlock *LoopHeaderBB = CurLoop->getHeader();
2740 BasicBlock *LoopPreheaderBB = CurLoop->getLoopPreheader();
2741 assert(LoopPreheaderBB && "There is always a loop preheader.")(static_cast<void> (0));
2742
2743 BasicBlock *SuccessorBB = CurLoop->getExitBlock();
2744 assert(SuccessorBB && "There is only a single successor.")(static_cast<void> (0));
2745
2746 IRBuilder<> Builder(LoopPreheaderBB->getTerminator());
2747 Builder.SetCurrentDebugLocation(IV->getDebugLoc());
2748
2749 Type *Ty = Val->getType();
2750 unsigned Bitwidth = Ty->getScalarSizeInBits();
2751
2752 TargetTransformInfo::TargetCostKind CostKind =
2753 TargetTransformInfo::TCK_SizeAndLatency;
2754
2755 // The rewrite is considered to be unprofitable iff and only iff the
2756 // intrinsic we'll use are not cheap. Note that we are okay with *just*
2757 // making the loop countable, even if nothing else changes.
2758 IntrinsicCostAttributes Attrs(
2759 IntrID, Ty, {UndefValue::get(Ty), /*is_zero_undef=*/Builder.getFalse()});
2760 InstructionCost Cost = TTI->getIntrinsicInstrCost(Attrs, CostKind);
2761 if (Cost > TargetTransformInfo::TCC_Basic) {
2762 LLVM_DEBUG(dbgs() << DEBUG_TYPEdo { } while (false)
2763 " Intrinsic is too costly, not beneficial\n")do { } while (false);
2764 return MadeChange;
2765 }
2766
2767 // Ok, transform appears worthwhile.
2768 MadeChange = true;
2769
2770 bool OffsetIsZero = false;
2771 if (auto *ExtraOffsetExprC = dyn_cast<SCEVConstant>(ExtraOffsetExpr))
2772 OffsetIsZero = ExtraOffsetExprC->isZero();
2773
2774 // Step 1: Compute the loop's final IV value / trip count.
2775
2776 CallInst *ValNumLeadingZeros = Builder.CreateIntrinsic(
2777 IntrID, Ty, {Val, /*is_zero_undef=*/Builder.getFalse()},
2778 /*FMFSource=*/nullptr, Val->getName() + ".numleadingzeros");
2779 Value *ValNumActiveBits = Builder.CreateSub(
2780 ConstantInt::get(Ty, Ty->getScalarSizeInBits()), ValNumLeadingZeros,
2781 Val->getName() + ".numactivebits", /*HasNUW=*/true,
2782 /*HasNSW=*/Bitwidth != 2);
2783
2784 SCEVExpander Expander(*SE, *DL, "loop-idiom");
2785 Expander.setInsertPoint(&*Builder.GetInsertPoint());
2786 Value *ExtraOffset = Expander.expandCodeFor(ExtraOffsetExpr);
2787
2788 Value *ValNumActiveBitsOffset = Builder.CreateAdd(
2789 ValNumActiveBits, ExtraOffset, ValNumActiveBits->getName() + ".offset",
2790 /*HasNUW=*/OffsetIsZero, /*HasNSW=*/true);
2791 Value *IVFinal = Builder.CreateIntrinsic(Intrinsic::smax, {Ty},
2792 {ValNumActiveBitsOffset, Start},
2793 /*FMFSource=*/nullptr, "iv.final");
2794
2795 auto *LoopBackedgeTakenCount = cast<Instruction>(Builder.CreateSub(
2796 IVFinal, Start, CurLoop->getName() + ".backedgetakencount",
2797 /*HasNUW=*/OffsetIsZero, /*HasNSW=*/true));
2798 // FIXME: or when the offset was `add nuw`
2799
2800 // We know loop's backedge-taken count, but what's loop's trip count?
2801 Value *LoopTripCount =
2802 Builder.CreateAdd(LoopBackedgeTakenCount, ConstantInt::get(Ty, 1),
2803 CurLoop->getName() + ".tripcount", /*HasNUW=*/true,
2804 /*HasNSW=*/Bitwidth != 2);
2805
2806 // Step 2: Adjust the successor basic block to recieve the original
2807 // induction variable's final value instead of the orig. IV itself.
2808
2809 IV->replaceUsesOutsideBlock(IVFinal, LoopHeaderBB);
2810
2811 // Step 3: Rewrite the loop into a countable form, with canonical IV.
2812
2813 // The new canonical induction variable.
2814 Builder.SetInsertPoint(&LoopHeaderBB->front());
2815 auto *CIV = Builder.CreatePHI(Ty, 2, CurLoop->getName() + ".iv");
2816
2817 // The induction itself.
2818 Builder.SetInsertPoint(LoopHeaderBB->getFirstNonPHI());
2819 auto *CIVNext =
2820 Builder.CreateAdd(CIV, ConstantInt::get(Ty, 1), CIV->getName() + ".next",
2821 /*HasNUW=*/true, /*HasNSW=*/Bitwidth != 2);
2822
2823 // The loop trip count check.
2824 auto *CIVCheck = Builder.CreateICmpEQ(CIVNext, LoopTripCount,
2825 CurLoop->getName() + ".ivcheck");
2826 auto *NewIVCheck = CIVCheck;
2827 if (InvertedCond) {
2828 NewIVCheck = Builder.CreateNot(CIVCheck);
2829 NewIVCheck->takeName(ValShiftedIsZero);
2830 }
2831
2832 // The original IV, but rebased to be an offset to the CIV.
2833 auto *IVDePHId = Builder.CreateAdd(CIV, Start, "", /*HasNUW=*/false,
2834 /*HasNSW=*/true); // FIXME: what about NUW?
2835 IVDePHId->takeName(IV);
2836
2837 // The loop terminator.
2838 Builder.SetInsertPoint(LoopHeaderBB->getTerminator());
2839 Builder.CreateCondBr(CIVCheck, SuccessorBB, LoopHeaderBB);
2840 LoopHeaderBB->getTerminator()->eraseFromParent();
2841
2842 // Populate the IV PHI.
2843 CIV->addIncoming(ConstantInt::get(Ty, 0), LoopPreheaderBB);
2844 CIV->addIncoming(CIVNext, LoopHeaderBB);
2845
2846 // Step 4: Forget the "non-computable" trip-count SCEV associated with the
2847 // loop. The loop would otherwise not be deleted even if it becomes empty.
2848
2849 SE->forgetLoop(CurLoop);
2850
2851 // Step 5: Try to cleanup the loop's body somewhat.
2852 IV->replaceAllUsesWith(IVDePHId);
2853 IV->eraseFromParent();
2854
2855 ValShiftedIsZero->replaceAllUsesWith(NewIVCheck);
2856 ValShiftedIsZero->eraseFromParent();
2857
2858 // Other passes will take care of actually deleting the loop if possible.
2859
2860 LLVM_DEBUG(dbgs() << DEBUG_TYPE " shift-until-zero idiom optimized!\n")do { } while (false);
2861
2862 ++NumShiftUntilZero;
2863 return MadeChange;
2864}