1 //===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===//
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 performs loop invariant code motion, attempting to remove as much
10 // code from the body of a loop as possible. It does this by either hoisting
11 // code into the preheader block, or by sinking code to the exit blocks if it is
12 // safe. This pass also promotes must-aliased memory locations in the loop to
13 // live in registers, thus hoisting and sinking "invariant" loads and stores.
14 //
15 // Hoisting operations out of loops is a canonicalization transform. It
16 // enables and simplifies subsequent optimizations in the middle-end.
17 // Rematerialization of hoisted instructions to reduce register pressure is the
18 // responsibility of the back-end, which has more accurate information about
19 // register pressure and also handles other optimizations than LICM that
20 // increase live-ranges.
21 //
22 // This pass uses alias analysis for two purposes:
23 //
24 // 1. Moving loop invariant loads and calls out of loops. If we can determine
25 // that a load or call inside of a loop never aliases anything stored to,
26 // we can hoist it or sink it like any other instruction.
27 // 2. Scalar Promotion of Memory - If there is a store instruction inside of
28 // the loop, we try to move the store to happen AFTER the loop instead of
29 // inside of the loop. This can only happen if a few conditions are true:
30 // A. The pointer stored through is loop invariant
31 // B. There are no stores or loads in the loop which _may_ alias the
32 // pointer. There are no calls in the loop which mod/ref the pointer.
33 // If these conditions are true, we can promote the loads and stores in the
34 // loop of the pointer to use a temporary alloca'd variable. We then use
35 // the SSAUpdater to construct the appropriate SSA form for the value.
36 //
37 //===----------------------------------------------------------------------===//
38
39 #include "llvm/Transforms/Scalar/LICM.h"
40 #include "llvm/ADT/SetOperations.h"
41 #include "llvm/ADT/Statistic.h"
42 #include "llvm/Analysis/AliasAnalysis.h"
43 #include "llvm/Analysis/AliasSetTracker.h"
44 #include "llvm/Analysis/BasicAliasAnalysis.h"
45 #include "llvm/Analysis/BlockFrequencyInfo.h"
46 #include "llvm/Analysis/CaptureTracking.h"
47 #include "llvm/Analysis/ConstantFolding.h"
48 #include "llvm/Analysis/GlobalsModRef.h"
49 #include "llvm/Analysis/GuardUtils.h"
50 #include "llvm/Analysis/LazyBlockFrequencyInfo.h"
51 #include "llvm/Analysis/Loads.h"
52 #include "llvm/Analysis/LoopInfo.h"
53 #include "llvm/Analysis/LoopIterator.h"
54 #include "llvm/Analysis/LoopPass.h"
55 #include "llvm/Analysis/MemoryBuiltins.h"
56 #include "llvm/Analysis/MemorySSA.h"
57 #include "llvm/Analysis/MemorySSAUpdater.h"
58 #include "llvm/Analysis/MustExecute.h"
59 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
60 #include "llvm/Analysis/ScalarEvolution.h"
61 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
62 #include "llvm/Analysis/TargetLibraryInfo.h"
63 #include "llvm/Analysis/ValueTracking.h"
64 #include "llvm/IR/CFG.h"
65 #include "llvm/IR/Constants.h"
66 #include "llvm/IR/DataLayout.h"
67 #include "llvm/IR/DebugInfoMetadata.h"
68 #include "llvm/IR/DerivedTypes.h"
69 #include "llvm/IR/Dominators.h"
70 #include "llvm/IR/Instructions.h"
71 #include "llvm/IR/IntrinsicInst.h"
72 #include "llvm/IR/LLVMContext.h"
73 #include "llvm/IR/Metadata.h"
74 #include "llvm/IR/PatternMatch.h"
75 #include "llvm/IR/PredIteratorCache.h"
76 #include "llvm/InitializePasses.h"
77 #include "llvm/Support/CommandLine.h"
78 #include "llvm/Support/Debug.h"
79 #include "llvm/Support/raw_ostream.h"
80 #include "llvm/Transforms/Scalar.h"
81 #include "llvm/Transforms/Scalar/LoopPassManager.h"
82 #include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
83 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
84 #include "llvm/Transforms/Utils/Local.h"
85 #include "llvm/Transforms/Utils/LoopUtils.h"
86 #include "llvm/Transforms/Utils/SSAUpdater.h"
87 #include <algorithm>
88 #include <utility>
89 using namespace llvm;
90
91 #define DEBUG_TYPE "licm"
92
93 STATISTIC(NumCreatedBlocks, "Number of blocks created");
94 STATISTIC(NumClonedBranches, "Number of branches cloned");
95 STATISTIC(NumSunk, "Number of instructions sunk out of loop");
96 STATISTIC(NumHoisted, "Number of instructions hoisted out of loop");
97 STATISTIC(NumMovedLoads, "Number of load insts hoisted or sunk");
98 STATISTIC(NumMovedCalls, "Number of call insts hoisted or sunk");
99 STATISTIC(NumPromoted, "Number of memory locations promoted to registers");
100
101 /// Memory promotion is enabled by default.
102 static cl::opt<bool>
103 DisablePromotion("disable-licm-promotion", cl::Hidden, cl::init(false),
104 cl::desc("Disable memory promotion in LICM pass"));
105
106 static cl::opt<bool> ControlFlowHoisting(
107 "licm-control-flow-hoisting", cl::Hidden, cl::init(false),
108 cl::desc("Enable control flow (and PHI) hoisting in LICM"));
109
110 static cl::opt<unsigned> HoistSinkColdnessThreshold(
111 "licm-coldness-threshold", cl::Hidden, cl::init(4),
112 cl::desc("Relative coldness Threshold of hoisting/sinking destination "
113 "block for LICM to be considered beneficial"));
114
115 static cl::opt<uint32_t> MaxNumUsesTraversed(
116 "licm-max-num-uses-traversed", cl::Hidden, cl::init(8),
117 cl::desc("Max num uses visited for identifying load "
118 "invariance in loop using invariant start (default = 8)"));
119
120 // Experimental option to allow imprecision in LICM in pathological cases, in
121 // exchange for faster compile. This is to be removed if MemorySSA starts to
122 // address the same issue. This flag applies only when LICM uses MemorySSA
123 // instead on AliasSetTracker. LICM calls MemorySSAWalker's
124 // getClobberingMemoryAccess, up to the value of the Cap, getting perfect
125 // accuracy. Afterwards, LICM will call into MemorySSA's getDefiningAccess,
126 // which may not be precise, since optimizeUses is capped. The result is
127 // correct, but we may not get as "far up" as possible to get which access is
128 // clobbering the one queried.
129 cl::opt<unsigned> llvm::SetLicmMssaOptCap(
130 "licm-mssa-optimization-cap", cl::init(100), cl::Hidden,
131 cl::desc("Enable imprecision in LICM in pathological cases, in exchange "
132 "for faster compile. Caps the MemorySSA clobbering calls."));
133
134 // Experimentally, memory promotion carries less importance than sinking and
135 // hoisting. Limit when we do promotion when using MemorySSA, in order to save
136 // compile time.
137 cl::opt<unsigned> llvm::SetLicmMssaNoAccForPromotionCap(
138 "licm-mssa-max-acc-promotion", cl::init(250), cl::Hidden,
139 cl::desc("[LICM & MemorySSA] When MSSA in LICM is disabled, this has no "
140 "effect. When MSSA in LICM is enabled, then this is the maximum "
141 "number of accesses allowed to be present in a loop in order to "
142 "enable memory promotion."));
143
144 static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI);
145 static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop,
146 const LoopSafetyInfo *SafetyInfo,
147 TargetTransformInfo *TTI, bool &FreeInLoop,
148 bool LoopNestMode);
149 static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
150 BasicBlock *Dest, ICFLoopSafetyInfo *SafetyInfo,
151 MemorySSAUpdater *MSSAU, ScalarEvolution *SE,
152 OptimizationRemarkEmitter *ORE);
153 static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
154 BlockFrequencyInfo *BFI, const Loop *CurLoop,
155 ICFLoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU,
156 OptimizationRemarkEmitter *ORE);
157 static bool isSafeToExecuteUnconditionally(Instruction &Inst,
158 const DominatorTree *DT,
159 const TargetLibraryInfo *TLI,
160 const Loop *CurLoop,
161 const LoopSafetyInfo *SafetyInfo,
162 OptimizationRemarkEmitter *ORE,
163 const Instruction *CtxI = nullptr);
164 static bool pointerInvalidatedByLoop(MemoryLocation MemLoc,
165 AliasSetTracker *CurAST, Loop *CurLoop,
166 AAResults *AA);
167 static bool pointerInvalidatedByLoopWithMSSA(MemorySSA *MSSA, MemoryUse *MU,
168 Loop *CurLoop, Instruction &I,
169 SinkAndHoistLICMFlags &Flags);
170 static bool pointerInvalidatedByBlockWithMSSA(BasicBlock &BB, MemorySSA &MSSA,
171 MemoryUse &MU);
172 static Instruction *cloneInstructionInExitBlock(
173 Instruction &I, BasicBlock &ExitBlock, PHINode &PN, const LoopInfo *LI,
174 const LoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU);
175
176 static void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo,
177 MemorySSAUpdater *MSSAU);
178
179 static void moveInstructionBefore(Instruction &I, Instruction &Dest,
180 ICFLoopSafetyInfo &SafetyInfo,
181 MemorySSAUpdater *MSSAU, ScalarEvolution *SE);
182
183 static void foreachMemoryAccess(MemorySSA *MSSA, Loop *L,
184 function_ref<void(Instruction *)> Fn);
185 static SmallVector<SmallSetVector<Value *, 8>, 0>
186 collectPromotionCandidates(MemorySSA *MSSA, AliasAnalysis *AA, Loop *L);
187
188 namespace {
189 struct LoopInvariantCodeMotion {
190 bool runOnLoop(Loop *L, AAResults *AA, LoopInfo *LI, DominatorTree *DT,
191 BlockFrequencyInfo *BFI, TargetLibraryInfo *TLI,
192 TargetTransformInfo *TTI, ScalarEvolution *SE, MemorySSA *MSSA,
193 OptimizationRemarkEmitter *ORE, bool LoopNestMode = false);
194
LoopInvariantCodeMotion__anonb92366510111::LoopInvariantCodeMotion195 LoopInvariantCodeMotion(unsigned LicmMssaOptCap,
196 unsigned LicmMssaNoAccForPromotionCap)
197 : LicmMssaOptCap(LicmMssaOptCap),
198 LicmMssaNoAccForPromotionCap(LicmMssaNoAccForPromotionCap) {}
199
200 private:
201 unsigned LicmMssaOptCap;
202 unsigned LicmMssaNoAccForPromotionCap;
203 };
204
205 struct LegacyLICMPass : public LoopPass {
206 static char ID; // Pass identification, replacement for typeid
LegacyLICMPass__anonb92366510111::LegacyLICMPass207 LegacyLICMPass(
208 unsigned LicmMssaOptCap = SetLicmMssaOptCap,
209 unsigned LicmMssaNoAccForPromotionCap = SetLicmMssaNoAccForPromotionCap)
210 : LoopPass(ID), LICM(LicmMssaOptCap, LicmMssaNoAccForPromotionCap) {
211 initializeLegacyLICMPassPass(*PassRegistry::getPassRegistry());
212 }
213
runOnLoop__anonb92366510111::LegacyLICMPass214 bool runOnLoop(Loop *L, LPPassManager &LPM) override {
215 if (skipLoop(L))
216 return false;
217
218 LLVM_DEBUG(dbgs() << "Perform LICM on Loop with header at block "
219 << L->getHeader()->getNameOrAsOperand() << "\n");
220
221 auto *SE = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
222 MemorySSA *MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
223 bool hasProfileData = L->getHeader()->getParent()->hasProfileData();
224 BlockFrequencyInfo *BFI =
225 hasProfileData ? &getAnalysis<LazyBlockFrequencyInfoPass>().getBFI()
226 : nullptr;
227 // For the old PM, we can't use OptimizationRemarkEmitter as an analysis
228 // pass. Function analyses need to be preserved across loop transformations
229 // but ORE cannot be preserved (see comment before the pass definition).
230 OptimizationRemarkEmitter ORE(L->getHeader()->getParent());
231 return LICM.runOnLoop(
232 L, &getAnalysis<AAResultsWrapperPass>().getAAResults(),
233 &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(),
234 &getAnalysis<DominatorTreeWrapperPass>().getDomTree(), BFI,
235 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(
236 *L->getHeader()->getParent()),
237 &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
238 *L->getHeader()->getParent()),
239 SE ? &SE->getSE() : nullptr, MSSA, &ORE);
240 }
241
242 /// This transformation requires natural loop information & requires that
243 /// loop preheaders be inserted into the CFG...
244 ///
getAnalysisUsage__anonb92366510111::LegacyLICMPass245 void getAnalysisUsage(AnalysisUsage &AU) const override {
246 AU.addPreserved<DominatorTreeWrapperPass>();
247 AU.addPreserved<LoopInfoWrapperPass>();
248 AU.addRequired<TargetLibraryInfoWrapperPass>();
249 AU.addRequired<MemorySSAWrapperPass>();
250 AU.addPreserved<MemorySSAWrapperPass>();
251 AU.addRequired<TargetTransformInfoWrapperPass>();
252 getLoopAnalysisUsage(AU);
253 LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU);
254 AU.addPreserved<LazyBlockFrequencyInfoPass>();
255 AU.addPreserved<LazyBranchProbabilityInfoPass>();
256 }
257
258 private:
259 LoopInvariantCodeMotion LICM;
260 };
261 } // namespace
262
run(Loop & L,LoopAnalysisManager & AM,LoopStandardAnalysisResults & AR,LPMUpdater &)263 PreservedAnalyses LICMPass::run(Loop &L, LoopAnalysisManager &AM,
264 LoopStandardAnalysisResults &AR, LPMUpdater &) {
265 if (!AR.MSSA)
266 report_fatal_error("LICM requires MemorySSA (loop-mssa)");
267
268 // For the new PM, we also can't use OptimizationRemarkEmitter as an analysis
269 // pass. Function analyses need to be preserved across loop transformations
270 // but ORE cannot be preserved (see comment before the pass definition).
271 OptimizationRemarkEmitter ORE(L.getHeader()->getParent());
272
273 LoopInvariantCodeMotion LICM(LicmMssaOptCap, LicmMssaNoAccForPromotionCap);
274 if (!LICM.runOnLoop(&L, &AR.AA, &AR.LI, &AR.DT, AR.BFI, &AR.TLI, &AR.TTI,
275 &AR.SE, AR.MSSA, &ORE))
276 return PreservedAnalyses::all();
277
278 auto PA = getLoopPassPreservedAnalyses();
279
280 PA.preserve<DominatorTreeAnalysis>();
281 PA.preserve<LoopAnalysis>();
282 PA.preserve<MemorySSAAnalysis>();
283
284 return PA;
285 }
286
run(LoopNest & LN,LoopAnalysisManager & AM,LoopStandardAnalysisResults & AR,LPMUpdater &)287 PreservedAnalyses LNICMPass::run(LoopNest &LN, LoopAnalysisManager &AM,
288 LoopStandardAnalysisResults &AR,
289 LPMUpdater &) {
290 if (!AR.MSSA)
291 report_fatal_error("LNICM requires MemorySSA (loop-mssa)");
292
293 // For the new PM, we also can't use OptimizationRemarkEmitter as an analysis
294 // pass. Function analyses need to be preserved across loop transformations
295 // but ORE cannot be preserved (see comment before the pass definition).
296 OptimizationRemarkEmitter ORE(LN.getParent());
297
298 LoopInvariantCodeMotion LICM(LicmMssaOptCap, LicmMssaNoAccForPromotionCap);
299
300 Loop &OutermostLoop = LN.getOutermostLoop();
301 bool Changed = LICM.runOnLoop(&OutermostLoop, &AR.AA, &AR.LI, &AR.DT, AR.BFI,
302 &AR.TLI, &AR.TTI, &AR.SE, AR.MSSA, &ORE, true);
303
304 if (!Changed)
305 return PreservedAnalyses::all();
306
307 auto PA = getLoopPassPreservedAnalyses();
308
309 PA.preserve<DominatorTreeAnalysis>();
310 PA.preserve<LoopAnalysis>();
311 PA.preserve<MemorySSAAnalysis>();
312
313 return PA;
314 }
315
316 char LegacyLICMPass::ID = 0;
317 INITIALIZE_PASS_BEGIN(LegacyLICMPass, "licm", "Loop Invariant Code Motion",
318 false, false)
INITIALIZE_PASS_DEPENDENCY(LoopPass)319 INITIALIZE_PASS_DEPENDENCY(LoopPass)
320 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
321 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
322 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
323 INITIALIZE_PASS_DEPENDENCY(LazyBFIPass)
324 INITIALIZE_PASS_END(LegacyLICMPass, "licm", "Loop Invariant Code Motion", false,
325 false)
326
327 Pass *llvm::createLICMPass() { return new LegacyLICMPass(); }
createLICMPass(unsigned LicmMssaOptCap,unsigned LicmMssaNoAccForPromotionCap)328 Pass *llvm::createLICMPass(unsigned LicmMssaOptCap,
329 unsigned LicmMssaNoAccForPromotionCap) {
330 return new LegacyLICMPass(LicmMssaOptCap, LicmMssaNoAccForPromotionCap);
331 }
332
SinkAndHoistLICMFlags(bool IsSink,Loop * L,MemorySSA * MSSA)333 llvm::SinkAndHoistLICMFlags::SinkAndHoistLICMFlags(bool IsSink, Loop *L,
334 MemorySSA *MSSA)
335 : SinkAndHoistLICMFlags(SetLicmMssaOptCap, SetLicmMssaNoAccForPromotionCap,
336 IsSink, L, MSSA) {}
337
SinkAndHoistLICMFlags(unsigned LicmMssaOptCap,unsigned LicmMssaNoAccForPromotionCap,bool IsSink,Loop * L,MemorySSA * MSSA)338 llvm::SinkAndHoistLICMFlags::SinkAndHoistLICMFlags(
339 unsigned LicmMssaOptCap, unsigned LicmMssaNoAccForPromotionCap, bool IsSink,
340 Loop *L, MemorySSA *MSSA)
341 : LicmMssaOptCap(LicmMssaOptCap),
342 LicmMssaNoAccForPromotionCap(LicmMssaNoAccForPromotionCap),
343 IsSink(IsSink) {
344 assert(((L != nullptr) == (MSSA != nullptr)) &&
345 "Unexpected values for SinkAndHoistLICMFlags");
346 if (!MSSA)
347 return;
348
349 unsigned AccessCapCount = 0;
350 for (auto *BB : L->getBlocks())
351 if (const auto *Accesses = MSSA->getBlockAccesses(BB))
352 for (const auto &MA : *Accesses) {
353 (void)MA;
354 ++AccessCapCount;
355 if (AccessCapCount > LicmMssaNoAccForPromotionCap) {
356 NoOfMemAccTooLarge = true;
357 return;
358 }
359 }
360 }
361
362 /// Hoist expressions out of the specified loop. Note, alias info for inner
363 /// loop is not preserved so it is not a good idea to run LICM multiple
364 /// times on one loop.
runOnLoop(Loop * L,AAResults * AA,LoopInfo * LI,DominatorTree * DT,BlockFrequencyInfo * BFI,TargetLibraryInfo * TLI,TargetTransformInfo * TTI,ScalarEvolution * SE,MemorySSA * MSSA,OptimizationRemarkEmitter * ORE,bool LoopNestMode)365 bool LoopInvariantCodeMotion::runOnLoop(
366 Loop *L, AAResults *AA, LoopInfo *LI, DominatorTree *DT,
367 BlockFrequencyInfo *BFI, TargetLibraryInfo *TLI, TargetTransformInfo *TTI,
368 ScalarEvolution *SE, MemorySSA *MSSA, OptimizationRemarkEmitter *ORE,
369 bool LoopNestMode) {
370 bool Changed = false;
371
372 assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form.");
373
374 // If this loop has metadata indicating that LICM is not to be performed then
375 // just exit.
376 if (hasDisableLICMTransformsHint(L)) {
377 return false;
378 }
379
380 // Don't sink stores from loops with coroutine suspend instructions.
381 // LICM would sink instructions into the default destination of
382 // the coroutine switch. The default destination of the switch is to
383 // handle the case where the coroutine is suspended, by which point the
384 // coroutine frame may have been destroyed. No instruction can be sunk there.
385 // FIXME: This would unfortunately hurt the performance of coroutines, however
386 // there is currently no general solution for this. Similar issues could also
387 // potentially happen in other passes where instructions are being moved
388 // across that edge.
389 bool HasCoroSuspendInst = llvm::any_of(L->getBlocks(), [](BasicBlock *BB) {
390 return llvm::any_of(*BB, [](Instruction &I) {
391 IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I);
392 return II && II->getIntrinsicID() == Intrinsic::coro_suspend;
393 });
394 });
395
396 MemorySSAUpdater MSSAU(MSSA);
397 SinkAndHoistLICMFlags Flags(LicmMssaOptCap, LicmMssaNoAccForPromotionCap,
398 /*IsSink=*/true, L, MSSA);
399
400 // Get the preheader block to move instructions into...
401 BasicBlock *Preheader = L->getLoopPreheader();
402
403 // Compute loop safety information.
404 ICFLoopSafetyInfo SafetyInfo;
405 SafetyInfo.computeLoopSafetyInfo(L);
406
407 // We want to visit all of the instructions in this loop... that are not parts
408 // of our subloops (they have already had their invariants hoisted out of
409 // their loop, into this loop, so there is no need to process the BODIES of
410 // the subloops).
411 //
412 // Traverse the body of the loop in depth first order on the dominator tree so
413 // that we are guaranteed to see definitions before we see uses. This allows
414 // us to sink instructions in one pass, without iteration. After sinking
415 // instructions, we perform another pass to hoist them out of the loop.
416 if (L->hasDedicatedExits())
417 Changed |= LoopNestMode
418 ? sinkRegionForLoopNest(DT->getNode(L->getHeader()), AA, LI,
419 DT, BFI, TLI, TTI, L, &MSSAU,
420 &SafetyInfo, Flags, ORE)
421 : sinkRegion(DT->getNode(L->getHeader()), AA, LI, DT, BFI,
422 TLI, TTI, L, &MSSAU, &SafetyInfo, Flags, ORE);
423 Flags.setIsSink(false);
424 if (Preheader)
425 Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, BFI, TLI, L,
426 &MSSAU, SE, &SafetyInfo, Flags, ORE, LoopNestMode);
427
428 // Now that all loop invariants have been removed from the loop, promote any
429 // memory references to scalars that we can.
430 // Don't sink stores from loops without dedicated block exits. Exits
431 // containing indirect branches are not transformed by loop simplify,
432 // make sure we catch that. An additional load may be generated in the
433 // preheader for SSA updater, so also avoid sinking when no preheader
434 // is available.
435 if (!DisablePromotion && Preheader && L->hasDedicatedExits() &&
436 !Flags.tooManyMemoryAccesses() && !HasCoroSuspendInst) {
437 // Figure out the loop exits and their insertion points
438 SmallVector<BasicBlock *, 8> ExitBlocks;
439 L->getUniqueExitBlocks(ExitBlocks);
440
441 // We can't insert into a catchswitch.
442 bool HasCatchSwitch = llvm::any_of(ExitBlocks, [](BasicBlock *Exit) {
443 return isa<CatchSwitchInst>(Exit->getTerminator());
444 });
445
446 if (!HasCatchSwitch) {
447 SmallVector<Instruction *, 8> InsertPts;
448 SmallVector<MemoryAccess *, 8> MSSAInsertPts;
449 InsertPts.reserve(ExitBlocks.size());
450 MSSAInsertPts.reserve(ExitBlocks.size());
451 for (BasicBlock *ExitBlock : ExitBlocks) {
452 InsertPts.push_back(&*ExitBlock->getFirstInsertionPt());
453 MSSAInsertPts.push_back(nullptr);
454 }
455
456 PredIteratorCache PIC;
457
458 // Promoting one set of accesses may make the pointers for another set
459 // loop invariant, so run this in a loop (with the MaybePromotable set
460 // decreasing in size over time).
461 bool Promoted = false;
462 bool LocalPromoted;
463 do {
464 LocalPromoted = false;
465 for (const SmallSetVector<Value *, 8> &PointerMustAliases :
466 collectPromotionCandidates(MSSA, AA, L)) {
467 LocalPromoted |= promoteLoopAccessesToScalars(
468 PointerMustAliases, ExitBlocks, InsertPts, MSSAInsertPts, PIC,
469 LI, DT, TLI, L, &MSSAU, &SafetyInfo, ORE);
470 }
471 Promoted |= LocalPromoted;
472 } while (LocalPromoted);
473
474 // Once we have promoted values across the loop body we have to
475 // recursively reform LCSSA as any nested loop may now have values defined
476 // within the loop used in the outer loop.
477 // FIXME: This is really heavy handed. It would be a bit better to use an
478 // SSAUpdater strategy during promotion that was LCSSA aware and reformed
479 // it as it went.
480 if (Promoted)
481 formLCSSARecursively(*L, *DT, LI, SE);
482
483 Changed |= Promoted;
484 }
485 }
486
487 // Check that neither this loop nor its parent have had LCSSA broken. LICM is
488 // specifically moving instructions across the loop boundary and so it is
489 // especially in need of sanity checking here.
490 assert(L->isLCSSAForm(*DT) && "Loop not left in LCSSA form after LICM!");
491 assert((L->isOutermost() || L->getParentLoop()->isLCSSAForm(*DT)) &&
492 "Parent loop not left in LCSSA form after LICM!");
493
494 if (VerifyMemorySSA)
495 MSSA->verifyMemorySSA();
496
497 if (Changed && SE)
498 SE->forgetLoopDispositions(L);
499 return Changed;
500 }
501
502 /// Walk the specified region of the CFG (defined by all blocks dominated by
503 /// the specified block, and that are in the current loop) in reverse depth
504 /// first order w.r.t the DominatorTree. This allows us to visit uses before
505 /// definitions, allowing us to sink a loop body in one pass without iteration.
506 ///
sinkRegion(DomTreeNode * N,AAResults * AA,LoopInfo * LI,DominatorTree * DT,BlockFrequencyInfo * BFI,TargetLibraryInfo * TLI,TargetTransformInfo * TTI,Loop * CurLoop,MemorySSAUpdater * MSSAU,ICFLoopSafetyInfo * SafetyInfo,SinkAndHoistLICMFlags & Flags,OptimizationRemarkEmitter * ORE,Loop * OutermostLoop)507 bool llvm::sinkRegion(DomTreeNode *N, AAResults *AA, LoopInfo *LI,
508 DominatorTree *DT, BlockFrequencyInfo *BFI,
509 TargetLibraryInfo *TLI, TargetTransformInfo *TTI,
510 Loop *CurLoop, MemorySSAUpdater *MSSAU,
511 ICFLoopSafetyInfo *SafetyInfo,
512 SinkAndHoistLICMFlags &Flags,
513 OptimizationRemarkEmitter *ORE, Loop *OutermostLoop) {
514
515 // Verify inputs.
516 assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
517 CurLoop != nullptr && MSSAU != nullptr && SafetyInfo != nullptr &&
518 "Unexpected input to sinkRegion.");
519
520 // We want to visit children before parents. We will enque all the parents
521 // before their children in the worklist and process the worklist in reverse
522 // order.
523 SmallVector<DomTreeNode *, 16> Worklist = collectChildrenInLoop(N, CurLoop);
524
525 bool Changed = false;
526 for (DomTreeNode *DTN : reverse(Worklist)) {
527 BasicBlock *BB = DTN->getBlock();
528 // Only need to process the contents of this block if it is not part of a
529 // subloop (which would already have been processed).
530 if (inSubLoop(BB, CurLoop, LI))
531 continue;
532
533 for (BasicBlock::iterator II = BB->end(); II != BB->begin();) {
534 Instruction &I = *--II;
535
536 // The instruction is not used in the loop if it is dead. In this case,
537 // we just delete it instead of sinking it.
538 if (isInstructionTriviallyDead(&I, TLI)) {
539 LLVM_DEBUG(dbgs() << "LICM deleting dead inst: " << I << '\n');
540 salvageKnowledge(&I);
541 salvageDebugInfo(I);
542 ++II;
543 eraseInstruction(I, *SafetyInfo, MSSAU);
544 Changed = true;
545 continue;
546 }
547
548 // Check to see if we can sink this instruction to the exit blocks
549 // of the loop. We can do this if the all users of the instruction are
550 // outside of the loop. In this case, it doesn't even matter if the
551 // operands of the instruction are loop invariant.
552 //
553 bool FreeInLoop = false;
554 bool LoopNestMode = OutermostLoop != nullptr;
555 if (!I.mayHaveSideEffects() &&
556 isNotUsedOrFreeInLoop(I, LoopNestMode ? OutermostLoop : CurLoop,
557 SafetyInfo, TTI, FreeInLoop, LoopNestMode) &&
558 canSinkOrHoistInst(I, AA, DT, CurLoop, /*CurAST*/nullptr, MSSAU, true,
559 &Flags, ORE)) {
560 if (sink(I, LI, DT, BFI, CurLoop, SafetyInfo, MSSAU, ORE)) {
561 if (!FreeInLoop) {
562 ++II;
563 salvageDebugInfo(I);
564 eraseInstruction(I, *SafetyInfo, MSSAU);
565 }
566 Changed = true;
567 }
568 }
569 }
570 }
571 if (VerifyMemorySSA)
572 MSSAU->getMemorySSA()->verifyMemorySSA();
573 return Changed;
574 }
575
sinkRegionForLoopNest(DomTreeNode * N,AAResults * AA,LoopInfo * LI,DominatorTree * DT,BlockFrequencyInfo * BFI,TargetLibraryInfo * TLI,TargetTransformInfo * TTI,Loop * CurLoop,MemorySSAUpdater * MSSAU,ICFLoopSafetyInfo * SafetyInfo,SinkAndHoistLICMFlags & Flags,OptimizationRemarkEmitter * ORE)576 bool llvm::sinkRegionForLoopNest(
577 DomTreeNode *N, AAResults *AA, LoopInfo *LI, DominatorTree *DT,
578 BlockFrequencyInfo *BFI, TargetLibraryInfo *TLI, TargetTransformInfo *TTI,
579 Loop *CurLoop, MemorySSAUpdater *MSSAU, ICFLoopSafetyInfo *SafetyInfo,
580 SinkAndHoistLICMFlags &Flags, OptimizationRemarkEmitter *ORE) {
581
582 bool Changed = false;
583 SmallPriorityWorklist<Loop *, 4> Worklist;
584 Worklist.insert(CurLoop);
585 appendLoopsToWorklist(*CurLoop, Worklist);
586 while (!Worklist.empty()) {
587 Loop *L = Worklist.pop_back_val();
588 Changed |= sinkRegion(DT->getNode(L->getHeader()), AA, LI, DT, BFI, TLI,
589 TTI, L, MSSAU, SafetyInfo, Flags, ORE, CurLoop);
590 }
591 return Changed;
592 }
593
594 namespace {
595 // This is a helper class for hoistRegion to make it able to hoist control flow
596 // in order to be able to hoist phis. The way this works is that we initially
597 // start hoisting to the loop preheader, and when we see a loop invariant branch
598 // we make note of this. When we then come to hoist an instruction that's
599 // conditional on such a branch we duplicate the branch and the relevant control
600 // flow, then hoist the instruction into the block corresponding to its original
601 // block in the duplicated control flow.
602 class ControlFlowHoister {
603 private:
604 // Information about the loop we are hoisting from
605 LoopInfo *LI;
606 DominatorTree *DT;
607 Loop *CurLoop;
608 MemorySSAUpdater *MSSAU;
609
610 // A map of blocks in the loop to the block their instructions will be hoisted
611 // to.
612 DenseMap<BasicBlock *, BasicBlock *> HoistDestinationMap;
613
614 // The branches that we can hoist, mapped to the block that marks a
615 // convergence point of their control flow.
616 DenseMap<BranchInst *, BasicBlock *> HoistableBranches;
617
618 public:
ControlFlowHoister(LoopInfo * LI,DominatorTree * DT,Loop * CurLoop,MemorySSAUpdater * MSSAU)619 ControlFlowHoister(LoopInfo *LI, DominatorTree *DT, Loop *CurLoop,
620 MemorySSAUpdater *MSSAU)
621 : LI(LI), DT(DT), CurLoop(CurLoop), MSSAU(MSSAU) {}
622
registerPossiblyHoistableBranch(BranchInst * BI)623 void registerPossiblyHoistableBranch(BranchInst *BI) {
624 // We can only hoist conditional branches with loop invariant operands.
625 if (!ControlFlowHoisting || !BI->isConditional() ||
626 !CurLoop->hasLoopInvariantOperands(BI))
627 return;
628
629 // The branch destinations need to be in the loop, and we don't gain
630 // anything by duplicating conditional branches with duplicate successors,
631 // as it's essentially the same as an unconditional branch.
632 BasicBlock *TrueDest = BI->getSuccessor(0);
633 BasicBlock *FalseDest = BI->getSuccessor(1);
634 if (!CurLoop->contains(TrueDest) || !CurLoop->contains(FalseDest) ||
635 TrueDest == FalseDest)
636 return;
637
638 // We can hoist BI if one branch destination is the successor of the other,
639 // or both have common successor which we check by seeing if the
640 // intersection of their successors is non-empty.
641 // TODO: This could be expanded to allowing branches where both ends
642 // eventually converge to a single block.
643 SmallPtrSet<BasicBlock *, 4> TrueDestSucc, FalseDestSucc;
644 TrueDestSucc.insert(succ_begin(TrueDest), succ_end(TrueDest));
645 FalseDestSucc.insert(succ_begin(FalseDest), succ_end(FalseDest));
646 BasicBlock *CommonSucc = nullptr;
647 if (TrueDestSucc.count(FalseDest)) {
648 CommonSucc = FalseDest;
649 } else if (FalseDestSucc.count(TrueDest)) {
650 CommonSucc = TrueDest;
651 } else {
652 set_intersect(TrueDestSucc, FalseDestSucc);
653 // If there's one common successor use that.
654 if (TrueDestSucc.size() == 1)
655 CommonSucc = *TrueDestSucc.begin();
656 // If there's more than one pick whichever appears first in the block list
657 // (we can't use the value returned by TrueDestSucc.begin() as it's
658 // unpredicatable which element gets returned).
659 else if (!TrueDestSucc.empty()) {
660 Function *F = TrueDest->getParent();
661 auto IsSucc = [&](BasicBlock &BB) { return TrueDestSucc.count(&BB); };
662 auto It = llvm::find_if(*F, IsSucc);
663 assert(It != F->end() && "Could not find successor in function");
664 CommonSucc = &*It;
665 }
666 }
667 // The common successor has to be dominated by the branch, as otherwise
668 // there will be some other path to the successor that will not be
669 // controlled by this branch so any phi we hoist would be controlled by the
670 // wrong condition. This also takes care of avoiding hoisting of loop back
671 // edges.
672 // TODO: In some cases this could be relaxed if the successor is dominated
673 // by another block that's been hoisted and we can guarantee that the
674 // control flow has been replicated exactly.
675 if (CommonSucc && DT->dominates(BI, CommonSucc))
676 HoistableBranches[BI] = CommonSucc;
677 }
678
canHoistPHI(PHINode * PN)679 bool canHoistPHI(PHINode *PN) {
680 // The phi must have loop invariant operands.
681 if (!ControlFlowHoisting || !CurLoop->hasLoopInvariantOperands(PN))
682 return false;
683 // We can hoist phis if the block they are in is the target of hoistable
684 // branches which cover all of the predecessors of the block.
685 SmallPtrSet<BasicBlock *, 8> PredecessorBlocks;
686 BasicBlock *BB = PN->getParent();
687 for (BasicBlock *PredBB : predecessors(BB))
688 PredecessorBlocks.insert(PredBB);
689 // If we have less predecessor blocks than predecessors then the phi will
690 // have more than one incoming value for the same block which we can't
691 // handle.
692 // TODO: This could be handled be erasing some of the duplicate incoming
693 // values.
694 if (PredecessorBlocks.size() != pred_size(BB))
695 return false;
696 for (auto &Pair : HoistableBranches) {
697 if (Pair.second == BB) {
698 // Which blocks are predecessors via this branch depends on if the
699 // branch is triangle-like or diamond-like.
700 if (Pair.first->getSuccessor(0) == BB) {
701 PredecessorBlocks.erase(Pair.first->getParent());
702 PredecessorBlocks.erase(Pair.first->getSuccessor(1));
703 } else if (Pair.first->getSuccessor(1) == BB) {
704 PredecessorBlocks.erase(Pair.first->getParent());
705 PredecessorBlocks.erase(Pair.first->getSuccessor(0));
706 } else {
707 PredecessorBlocks.erase(Pair.first->getSuccessor(0));
708 PredecessorBlocks.erase(Pair.first->getSuccessor(1));
709 }
710 }
711 }
712 // PredecessorBlocks will now be empty if for every predecessor of BB we
713 // found a hoistable branch source.
714 return PredecessorBlocks.empty();
715 }
716
getOrCreateHoistedBlock(BasicBlock * BB)717 BasicBlock *getOrCreateHoistedBlock(BasicBlock *BB) {
718 if (!ControlFlowHoisting)
719 return CurLoop->getLoopPreheader();
720 // If BB has already been hoisted, return that
721 if (HoistDestinationMap.count(BB))
722 return HoistDestinationMap[BB];
723
724 // Check if this block is conditional based on a pending branch
725 auto HasBBAsSuccessor =
726 [&](DenseMap<BranchInst *, BasicBlock *>::value_type &Pair) {
727 return BB != Pair.second && (Pair.first->getSuccessor(0) == BB ||
728 Pair.first->getSuccessor(1) == BB);
729 };
730 auto It = llvm::find_if(HoistableBranches, HasBBAsSuccessor);
731
732 // If not involved in a pending branch, hoist to preheader
733 BasicBlock *InitialPreheader = CurLoop->getLoopPreheader();
734 if (It == HoistableBranches.end()) {
735 LLVM_DEBUG(dbgs() << "LICM using "
736 << InitialPreheader->getNameOrAsOperand()
737 << " as hoist destination for "
738 << BB->getNameOrAsOperand() << "\n");
739 HoistDestinationMap[BB] = InitialPreheader;
740 return InitialPreheader;
741 }
742 BranchInst *BI = It->first;
743 assert(std::find_if(++It, HoistableBranches.end(), HasBBAsSuccessor) ==
744 HoistableBranches.end() &&
745 "BB is expected to be the target of at most one branch");
746
747 LLVMContext &C = BB->getContext();
748 BasicBlock *TrueDest = BI->getSuccessor(0);
749 BasicBlock *FalseDest = BI->getSuccessor(1);
750 BasicBlock *CommonSucc = HoistableBranches[BI];
751 BasicBlock *HoistTarget = getOrCreateHoistedBlock(BI->getParent());
752
753 // Create hoisted versions of blocks that currently don't have them
754 auto CreateHoistedBlock = [&](BasicBlock *Orig) {
755 if (HoistDestinationMap.count(Orig))
756 return HoistDestinationMap[Orig];
757 BasicBlock *New =
758 BasicBlock::Create(C, Orig->getName() + ".licm", Orig->getParent());
759 HoistDestinationMap[Orig] = New;
760 DT->addNewBlock(New, HoistTarget);
761 if (CurLoop->getParentLoop())
762 CurLoop->getParentLoop()->addBasicBlockToLoop(New, *LI);
763 ++NumCreatedBlocks;
764 LLVM_DEBUG(dbgs() << "LICM created " << New->getName()
765 << " as hoist destination for " << Orig->getName()
766 << "\n");
767 return New;
768 };
769 BasicBlock *HoistTrueDest = CreateHoistedBlock(TrueDest);
770 BasicBlock *HoistFalseDest = CreateHoistedBlock(FalseDest);
771 BasicBlock *HoistCommonSucc = CreateHoistedBlock(CommonSucc);
772
773 // Link up these blocks with branches.
774 if (!HoistCommonSucc->getTerminator()) {
775 // The new common successor we've generated will branch to whatever that
776 // hoist target branched to.
777 BasicBlock *TargetSucc = HoistTarget->getSingleSuccessor();
778 assert(TargetSucc && "Expected hoist target to have a single successor");
779 HoistCommonSucc->moveBefore(TargetSucc);
780 BranchInst::Create(TargetSucc, HoistCommonSucc);
781 }
782 if (!HoistTrueDest->getTerminator()) {
783 HoistTrueDest->moveBefore(HoistCommonSucc);
784 BranchInst::Create(HoistCommonSucc, HoistTrueDest);
785 }
786 if (!HoistFalseDest->getTerminator()) {
787 HoistFalseDest->moveBefore(HoistCommonSucc);
788 BranchInst::Create(HoistCommonSucc, HoistFalseDest);
789 }
790
791 // If BI is being cloned to what was originally the preheader then
792 // HoistCommonSucc will now be the new preheader.
793 if (HoistTarget == InitialPreheader) {
794 // Phis in the loop header now need to use the new preheader.
795 InitialPreheader->replaceSuccessorsPhiUsesWith(HoistCommonSucc);
796 MSSAU->wireOldPredecessorsToNewImmediatePredecessor(
797 HoistTarget->getSingleSuccessor(), HoistCommonSucc, {HoistTarget});
798 // The new preheader dominates the loop header.
799 DomTreeNode *PreheaderNode = DT->getNode(HoistCommonSucc);
800 DomTreeNode *HeaderNode = DT->getNode(CurLoop->getHeader());
801 DT->changeImmediateDominator(HeaderNode, PreheaderNode);
802 // The preheader hoist destination is now the new preheader, with the
803 // exception of the hoist destination of this branch.
804 for (auto &Pair : HoistDestinationMap)
805 if (Pair.second == InitialPreheader && Pair.first != BI->getParent())
806 Pair.second = HoistCommonSucc;
807 }
808
809 // Now finally clone BI.
810 ReplaceInstWithInst(
811 HoistTarget->getTerminator(),
812 BranchInst::Create(HoistTrueDest, HoistFalseDest, BI->getCondition()));
813 ++NumClonedBranches;
814
815 assert(CurLoop->getLoopPreheader() &&
816 "Hoisting blocks should not have destroyed preheader");
817 return HoistDestinationMap[BB];
818 }
819 };
820 } // namespace
821
822 // Hoisting/sinking instruction out of a loop isn't always beneficial. It's only
823 // only worthwhile if the destination block is actually colder than current
824 // block.
worthSinkOrHoistInst(Instruction & I,BasicBlock * DstBlock,OptimizationRemarkEmitter * ORE,BlockFrequencyInfo * BFI)825 static bool worthSinkOrHoistInst(Instruction &I, BasicBlock *DstBlock,
826 OptimizationRemarkEmitter *ORE,
827 BlockFrequencyInfo *BFI) {
828 // Check block frequency only when runtime profile is available
829 // to avoid pathological cases. With static profile, lean towards
830 // hosting because it helps canonicalize the loop for vectorizer.
831 if (!DstBlock->getParent()->hasProfileData())
832 return true;
833
834 if (!HoistSinkColdnessThreshold || !BFI)
835 return true;
836
837 BasicBlock *SrcBlock = I.getParent();
838 if (BFI->getBlockFreq(DstBlock).getFrequency() / HoistSinkColdnessThreshold >
839 BFI->getBlockFreq(SrcBlock).getFrequency()) {
840 ORE->emit([&]() {
841 return OptimizationRemarkMissed(DEBUG_TYPE, "SinkHoistInst", &I)
842 << "failed to sink or hoist instruction because containing block "
843 "has lower frequency than destination block";
844 });
845 return false;
846 }
847
848 return true;
849 }
850
851 /// Walk the specified region of the CFG (defined by all blocks dominated by
852 /// the specified block, and that are in the current loop) in depth first
853 /// order w.r.t the DominatorTree. This allows us to visit definitions before
854 /// uses, allowing us to hoist a loop body in one pass without iteration.
855 ///
hoistRegion(DomTreeNode * N,AAResults * AA,LoopInfo * LI,DominatorTree * DT,BlockFrequencyInfo * BFI,TargetLibraryInfo * TLI,Loop * CurLoop,MemorySSAUpdater * MSSAU,ScalarEvolution * SE,ICFLoopSafetyInfo * SafetyInfo,SinkAndHoistLICMFlags & Flags,OptimizationRemarkEmitter * ORE,bool LoopNestMode)856 bool llvm::hoistRegion(DomTreeNode *N, AAResults *AA, LoopInfo *LI,
857 DominatorTree *DT, BlockFrequencyInfo *BFI,
858 TargetLibraryInfo *TLI, Loop *CurLoop,
859 MemorySSAUpdater *MSSAU, ScalarEvolution *SE,
860 ICFLoopSafetyInfo *SafetyInfo,
861 SinkAndHoistLICMFlags &Flags,
862 OptimizationRemarkEmitter *ORE, bool LoopNestMode) {
863 // Verify inputs.
864 assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
865 CurLoop != nullptr && MSSAU != nullptr && SafetyInfo != nullptr &&
866 "Unexpected input to hoistRegion.");
867
868 ControlFlowHoister CFH(LI, DT, CurLoop, MSSAU);
869
870 // Keep track of instructions that have been hoisted, as they may need to be
871 // re-hoisted if they end up not dominating all of their uses.
872 SmallVector<Instruction *, 16> HoistedInstructions;
873
874 // For PHI hoisting to work we need to hoist blocks before their successors.
875 // We can do this by iterating through the blocks in the loop in reverse
876 // post-order.
877 LoopBlocksRPO Worklist(CurLoop);
878 Worklist.perform(LI);
879 bool Changed = false;
880 for (BasicBlock *BB : Worklist) {
881 // Only need to process the contents of this block if it is not part of a
882 // subloop (which would already have been processed).
883 if (!LoopNestMode && inSubLoop(BB, CurLoop, LI))
884 continue;
885
886 for (Instruction &I : llvm::make_early_inc_range(*BB)) {
887 // Try constant folding this instruction. If all the operands are
888 // constants, it is technically hoistable, but it would be better to
889 // just fold it.
890 if (Constant *C = ConstantFoldInstruction(
891 &I, I.getModule()->getDataLayout(), TLI)) {
892 LLVM_DEBUG(dbgs() << "LICM folding inst: " << I << " --> " << *C
893 << '\n');
894 // FIXME MSSA: Such replacements may make accesses unoptimized (D51960).
895 I.replaceAllUsesWith(C);
896 if (isInstructionTriviallyDead(&I, TLI))
897 eraseInstruction(I, *SafetyInfo, MSSAU);
898 Changed = true;
899 continue;
900 }
901
902 // Try hoisting the instruction out to the preheader. We can only do
903 // this if all of the operands of the instruction are loop invariant and
904 // if it is safe to hoist the instruction. We also check block frequency
905 // to make sure instruction only gets hoisted into colder blocks.
906 // TODO: It may be safe to hoist if we are hoisting to a conditional block
907 // and we have accurately duplicated the control flow from the loop header
908 // to that block.
909 if (CurLoop->hasLoopInvariantOperands(&I) &&
910 canSinkOrHoistInst(I, AA, DT, CurLoop, /*CurAST*/ nullptr, MSSAU,
911 true, &Flags, ORE) &&
912 worthSinkOrHoistInst(I, CurLoop->getLoopPreheader(), ORE, BFI) &&
913 isSafeToExecuteUnconditionally(
914 I, DT, TLI, CurLoop, SafetyInfo, ORE,
915 CurLoop->getLoopPreheader()->getTerminator())) {
916 hoist(I, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo,
917 MSSAU, SE, ORE);
918 HoistedInstructions.push_back(&I);
919 Changed = true;
920 continue;
921 }
922
923 // Attempt to remove floating point division out of the loop by
924 // converting it to a reciprocal multiplication.
925 if (I.getOpcode() == Instruction::FDiv && I.hasAllowReciprocal() &&
926 CurLoop->isLoopInvariant(I.getOperand(1))) {
927 auto Divisor = I.getOperand(1);
928 auto One = llvm::ConstantFP::get(Divisor->getType(), 1.0);
929 auto ReciprocalDivisor = BinaryOperator::CreateFDiv(One, Divisor);
930 ReciprocalDivisor->setFastMathFlags(I.getFastMathFlags());
931 SafetyInfo->insertInstructionTo(ReciprocalDivisor, I.getParent());
932 ReciprocalDivisor->insertBefore(&I);
933
934 auto Product =
935 BinaryOperator::CreateFMul(I.getOperand(0), ReciprocalDivisor);
936 Product->setFastMathFlags(I.getFastMathFlags());
937 SafetyInfo->insertInstructionTo(Product, I.getParent());
938 Product->insertAfter(&I);
939 I.replaceAllUsesWith(Product);
940 eraseInstruction(I, *SafetyInfo, MSSAU);
941
942 hoist(*ReciprocalDivisor, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB),
943 SafetyInfo, MSSAU, SE, ORE);
944 HoistedInstructions.push_back(ReciprocalDivisor);
945 Changed = true;
946 continue;
947 }
948
949 auto IsInvariantStart = [&](Instruction &I) {
950 using namespace PatternMatch;
951 return I.use_empty() &&
952 match(&I, m_Intrinsic<Intrinsic::invariant_start>());
953 };
954 auto MustExecuteWithoutWritesBefore = [&](Instruction &I) {
955 return SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop) &&
956 SafetyInfo->doesNotWriteMemoryBefore(I, CurLoop);
957 };
958 if ((IsInvariantStart(I) || isGuard(&I)) &&
959 CurLoop->hasLoopInvariantOperands(&I) &&
960 MustExecuteWithoutWritesBefore(I)) {
961 hoist(I, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo,
962 MSSAU, SE, ORE);
963 HoistedInstructions.push_back(&I);
964 Changed = true;
965 continue;
966 }
967
968 if (PHINode *PN = dyn_cast<PHINode>(&I)) {
969 if (CFH.canHoistPHI(PN)) {
970 // Redirect incoming blocks first to ensure that we create hoisted
971 // versions of those blocks before we hoist the phi.
972 for (unsigned int i = 0; i < PN->getNumIncomingValues(); ++i)
973 PN->setIncomingBlock(
974 i, CFH.getOrCreateHoistedBlock(PN->getIncomingBlock(i)));
975 hoist(*PN, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo,
976 MSSAU, SE, ORE);
977 assert(DT->dominates(PN, BB) && "Conditional PHIs not expected");
978 Changed = true;
979 continue;
980 }
981 }
982
983 // Remember possibly hoistable branches so we can actually hoist them
984 // later if needed.
985 if (BranchInst *BI = dyn_cast<BranchInst>(&I))
986 CFH.registerPossiblyHoistableBranch(BI);
987 }
988 }
989
990 // If we hoisted instructions to a conditional block they may not dominate
991 // their uses that weren't hoisted (such as phis where some operands are not
992 // loop invariant). If so make them unconditional by moving them to their
993 // immediate dominator. We iterate through the instructions in reverse order
994 // which ensures that when we rehoist an instruction we rehoist its operands,
995 // and also keep track of where in the block we are rehoisting to to make sure
996 // that we rehoist instructions before the instructions that use them.
997 Instruction *HoistPoint = nullptr;
998 if (ControlFlowHoisting) {
999 for (Instruction *I : reverse(HoistedInstructions)) {
1000 if (!llvm::all_of(I->uses(),
1001 [&](Use &U) { return DT->dominates(I, U); })) {
1002 BasicBlock *Dominator =
1003 DT->getNode(I->getParent())->getIDom()->getBlock();
1004 if (!HoistPoint || !DT->dominates(HoistPoint->getParent(), Dominator)) {
1005 if (HoistPoint)
1006 assert(DT->dominates(Dominator, HoistPoint->getParent()) &&
1007 "New hoist point expected to dominate old hoist point");
1008 HoistPoint = Dominator->getTerminator();
1009 }
1010 LLVM_DEBUG(dbgs() << "LICM rehoisting to "
1011 << HoistPoint->getParent()->getNameOrAsOperand()
1012 << ": " << *I << "\n");
1013 moveInstructionBefore(*I, *HoistPoint, *SafetyInfo, MSSAU, SE);
1014 HoistPoint = I;
1015 Changed = true;
1016 }
1017 }
1018 }
1019 if (VerifyMemorySSA)
1020 MSSAU->getMemorySSA()->verifyMemorySSA();
1021
1022 // Now that we've finished hoisting make sure that LI and DT are still
1023 // valid.
1024 #ifdef EXPENSIVE_CHECKS
1025 if (Changed) {
1026 assert(DT->verify(DominatorTree::VerificationLevel::Fast) &&
1027 "Dominator tree verification failed");
1028 LI->verify(*DT);
1029 }
1030 #endif
1031
1032 return Changed;
1033 }
1034
1035 // Return true if LI is invariant within scope of the loop. LI is invariant if
1036 // CurLoop is dominated by an invariant.start representing the same memory
1037 // location and size as the memory location LI loads from, and also the
1038 // invariant.start has no uses.
isLoadInvariantInLoop(LoadInst * LI,DominatorTree * DT,Loop * CurLoop)1039 static bool isLoadInvariantInLoop(LoadInst *LI, DominatorTree *DT,
1040 Loop *CurLoop) {
1041 Value *Addr = LI->getOperand(0);
1042 const DataLayout &DL = LI->getModule()->getDataLayout();
1043 const TypeSize LocSizeInBits = DL.getTypeSizeInBits(LI->getType());
1044
1045 // It is not currently possible for clang to generate an invariant.start
1046 // intrinsic with scalable vector types because we don't support thread local
1047 // sizeless types and we don't permit sizeless types in structs or classes.
1048 // Furthermore, even if support is added for this in future the intrinsic
1049 // itself is defined to have a size of -1 for variable sized objects. This
1050 // makes it impossible to verify if the intrinsic envelops our region of
1051 // interest. For example, both <vscale x 32 x i8> and <vscale x 16 x i8>
1052 // types would have a -1 parameter, but the former is clearly double the size
1053 // of the latter.
1054 if (LocSizeInBits.isScalable())
1055 return false;
1056
1057 // if the type is i8 addrspace(x)*, we know this is the type of
1058 // llvm.invariant.start operand
1059 auto *PtrInt8Ty = PointerType::get(Type::getInt8Ty(LI->getContext()),
1060 LI->getPointerAddressSpace());
1061 unsigned BitcastsVisited = 0;
1062 // Look through bitcasts until we reach the i8* type (this is invariant.start
1063 // operand type).
1064 while (Addr->getType() != PtrInt8Ty) {
1065 auto *BC = dyn_cast<BitCastInst>(Addr);
1066 // Avoid traversing high number of bitcast uses.
1067 if (++BitcastsVisited > MaxNumUsesTraversed || !BC)
1068 return false;
1069 Addr = BC->getOperand(0);
1070 }
1071 // If we've ended up at a global/constant, bail. We shouldn't be looking at
1072 // uselists for non-local Values in a loop pass.
1073 if (isa<Constant>(Addr))
1074 return false;
1075
1076 unsigned UsesVisited = 0;
1077 // Traverse all uses of the load operand value, to see if invariant.start is
1078 // one of the uses, and whether it dominates the load instruction.
1079 for (auto *U : Addr->users()) {
1080 // Avoid traversing for Load operand with high number of users.
1081 if (++UsesVisited > MaxNumUsesTraversed)
1082 return false;
1083 IntrinsicInst *II = dyn_cast<IntrinsicInst>(U);
1084 // If there are escaping uses of invariant.start instruction, the load maybe
1085 // non-invariant.
1086 if (!II || II->getIntrinsicID() != Intrinsic::invariant_start ||
1087 !II->use_empty())
1088 continue;
1089 ConstantInt *InvariantSize = cast<ConstantInt>(II->getArgOperand(0));
1090 // The intrinsic supports having a -1 argument for variable sized objects
1091 // so we should check for that here.
1092 if (InvariantSize->isNegative())
1093 continue;
1094 uint64_t InvariantSizeInBits = InvariantSize->getSExtValue() * 8;
1095 // Confirm the invariant.start location size contains the load operand size
1096 // in bits. Also, the invariant.start should dominate the load, and we
1097 // should not hoist the load out of a loop that contains this dominating
1098 // invariant.start.
1099 if (LocSizeInBits.getFixedSize() <= InvariantSizeInBits &&
1100 DT->properlyDominates(II->getParent(), CurLoop->getHeader()))
1101 return true;
1102 }
1103
1104 return false;
1105 }
1106
1107 namespace {
1108 /// Return true if-and-only-if we know how to (mechanically) both hoist and
1109 /// sink a given instruction out of a loop. Does not address legality
1110 /// concerns such as aliasing or speculation safety.
isHoistableAndSinkableInst(Instruction & I)1111 bool isHoistableAndSinkableInst(Instruction &I) {
1112 // Only these instructions are hoistable/sinkable.
1113 return (isa<LoadInst>(I) || isa<StoreInst>(I) || isa<CallInst>(I) ||
1114 isa<FenceInst>(I) || isa<CastInst>(I) || isa<UnaryOperator>(I) ||
1115 isa<BinaryOperator>(I) || isa<SelectInst>(I) ||
1116 isa<GetElementPtrInst>(I) || isa<CmpInst>(I) ||
1117 isa<InsertElementInst>(I) || isa<ExtractElementInst>(I) ||
1118 isa<ShuffleVectorInst>(I) || isa<ExtractValueInst>(I) ||
1119 isa<InsertValueInst>(I) || isa<FreezeInst>(I));
1120 }
1121 /// Return true if all of the alias sets within this AST are known not to
1122 /// contain a Mod, or if MSSA knows there are no MemoryDefs in the loop.
isReadOnly(AliasSetTracker * CurAST,const MemorySSAUpdater * MSSAU,const Loop * L)1123 bool isReadOnly(AliasSetTracker *CurAST, const MemorySSAUpdater *MSSAU,
1124 const Loop *L) {
1125 if (CurAST) {
1126 for (AliasSet &AS : *CurAST) {
1127 if (!AS.isForwardingAliasSet() && AS.isMod()) {
1128 return false;
1129 }
1130 }
1131 return true;
1132 } else { /*MSSAU*/
1133 for (auto *BB : L->getBlocks())
1134 if (MSSAU->getMemorySSA()->getBlockDefs(BB))
1135 return false;
1136 return true;
1137 }
1138 }
1139
1140 /// Return true if I is the only Instruction with a MemoryAccess in L.
isOnlyMemoryAccess(const Instruction * I,const Loop * L,const MemorySSAUpdater * MSSAU)1141 bool isOnlyMemoryAccess(const Instruction *I, const Loop *L,
1142 const MemorySSAUpdater *MSSAU) {
1143 for (auto *BB : L->getBlocks())
1144 if (auto *Accs = MSSAU->getMemorySSA()->getBlockAccesses(BB)) {
1145 int NotAPhi = 0;
1146 for (const auto &Acc : *Accs) {
1147 if (isa<MemoryPhi>(&Acc))
1148 continue;
1149 const auto *MUD = cast<MemoryUseOrDef>(&Acc);
1150 if (MUD->getMemoryInst() != I || NotAPhi++ == 1)
1151 return false;
1152 }
1153 }
1154 return true;
1155 }
1156 }
1157
canSinkOrHoistInst(Instruction & I,AAResults * AA,DominatorTree * DT,Loop * CurLoop,AliasSetTracker * CurAST,MemorySSAUpdater * MSSAU,bool TargetExecutesOncePerLoop,SinkAndHoistLICMFlags * Flags,OptimizationRemarkEmitter * ORE)1158 bool llvm::canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT,
1159 Loop *CurLoop, AliasSetTracker *CurAST,
1160 MemorySSAUpdater *MSSAU,
1161 bool TargetExecutesOncePerLoop,
1162 SinkAndHoistLICMFlags *Flags,
1163 OptimizationRemarkEmitter *ORE) {
1164 assert(((CurAST != nullptr) ^ (MSSAU != nullptr)) &&
1165 "Either AliasSetTracker or MemorySSA should be initialized.");
1166
1167 // If we don't understand the instruction, bail early.
1168 if (!isHoistableAndSinkableInst(I))
1169 return false;
1170
1171 MemorySSA *MSSA = MSSAU ? MSSAU->getMemorySSA() : nullptr;
1172 if (MSSA)
1173 assert(Flags != nullptr && "Flags cannot be null.");
1174
1175 // Loads have extra constraints we have to verify before we can hoist them.
1176 if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
1177 if (!LI->isUnordered())
1178 return false; // Don't sink/hoist volatile or ordered atomic loads!
1179
1180 // Loads from constant memory are always safe to move, even if they end up
1181 // in the same alias set as something that ends up being modified.
1182 if (AA->pointsToConstantMemory(LI->getOperand(0)))
1183 return true;
1184 if (LI->hasMetadata(LLVMContext::MD_invariant_load))
1185 return true;
1186
1187 if (LI->isAtomic() && !TargetExecutesOncePerLoop)
1188 return false; // Don't risk duplicating unordered loads
1189
1190 // This checks for an invariant.start dominating the load.
1191 if (isLoadInvariantInLoop(LI, DT, CurLoop))
1192 return true;
1193
1194 bool Invalidated;
1195 if (CurAST)
1196 Invalidated = pointerInvalidatedByLoop(MemoryLocation::get(LI), CurAST,
1197 CurLoop, AA);
1198 else
1199 Invalidated = pointerInvalidatedByLoopWithMSSA(
1200 MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(LI)), CurLoop, I, *Flags);
1201 // Check loop-invariant address because this may also be a sinkable load
1202 // whose address is not necessarily loop-invariant.
1203 if (ORE && Invalidated && CurLoop->isLoopInvariant(LI->getPointerOperand()))
1204 ORE->emit([&]() {
1205 return OptimizationRemarkMissed(
1206 DEBUG_TYPE, "LoadWithLoopInvariantAddressInvalidated", LI)
1207 << "failed to move load with loop-invariant address "
1208 "because the loop may invalidate its value";
1209 });
1210
1211 return !Invalidated;
1212 } else if (CallInst *CI = dyn_cast<CallInst>(&I)) {
1213 // Don't sink or hoist dbg info; it's legal, but not useful.
1214 if (isa<DbgInfoIntrinsic>(I))
1215 return false;
1216
1217 // Don't sink calls which can throw.
1218 if (CI->mayThrow())
1219 return false;
1220
1221 // Convergent attribute has been used on operations that involve
1222 // inter-thread communication which results are implicitly affected by the
1223 // enclosing control flows. It is not safe to hoist or sink such operations
1224 // across control flow.
1225 if (CI->isConvergent())
1226 return false;
1227
1228 using namespace PatternMatch;
1229 if (match(CI, m_Intrinsic<Intrinsic::assume>()))
1230 // Assumes don't actually alias anything or throw
1231 return true;
1232
1233 if (match(CI, m_Intrinsic<Intrinsic::experimental_widenable_condition>()))
1234 // Widenable conditions don't actually alias anything or throw
1235 return true;
1236
1237 // Handle simple cases by querying alias analysis.
1238 FunctionModRefBehavior Behavior = AA->getModRefBehavior(CI);
1239 if (Behavior == FMRB_DoesNotAccessMemory)
1240 return true;
1241 if (AAResults::onlyReadsMemory(Behavior)) {
1242 // A readonly argmemonly function only reads from memory pointed to by
1243 // it's arguments with arbitrary offsets. If we can prove there are no
1244 // writes to this memory in the loop, we can hoist or sink.
1245 if (AAResults::onlyAccessesArgPointees(Behavior)) {
1246 // TODO: expand to writeable arguments
1247 for (Value *Op : CI->args())
1248 if (Op->getType()->isPointerTy()) {
1249 bool Invalidated;
1250 if (CurAST)
1251 Invalidated = pointerInvalidatedByLoop(
1252 MemoryLocation::getBeforeOrAfter(Op), CurAST, CurLoop, AA);
1253 else
1254 Invalidated = pointerInvalidatedByLoopWithMSSA(
1255 MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(CI)), CurLoop, I,
1256 *Flags);
1257 if (Invalidated)
1258 return false;
1259 }
1260 return true;
1261 }
1262
1263 // If this call only reads from memory and there are no writes to memory
1264 // in the loop, we can hoist or sink the call as appropriate.
1265 if (isReadOnly(CurAST, MSSAU, CurLoop))
1266 return true;
1267 }
1268
1269 // FIXME: This should use mod/ref information to see if we can hoist or
1270 // sink the call.
1271
1272 return false;
1273 } else if (auto *FI = dyn_cast<FenceInst>(&I)) {
1274 // Fences alias (most) everything to provide ordering. For the moment,
1275 // just give up if there are any other memory operations in the loop.
1276 if (CurAST) {
1277 auto Begin = CurAST->begin();
1278 assert(Begin != CurAST->end() && "must contain FI");
1279 if (std::next(Begin) != CurAST->end())
1280 // constant memory for instance, TODO: handle better
1281 return false;
1282 auto *UniqueI = Begin->getUniqueInstruction();
1283 if (!UniqueI)
1284 // other memory op, give up
1285 return false;
1286 (void)FI; // suppress unused variable warning
1287 assert(UniqueI == FI && "AS must contain FI");
1288 return true;
1289 } else // MSSAU
1290 return isOnlyMemoryAccess(FI, CurLoop, MSSAU);
1291 } else if (auto *SI = dyn_cast<StoreInst>(&I)) {
1292 if (!SI->isUnordered())
1293 return false; // Don't sink/hoist volatile or ordered atomic store!
1294
1295 // We can only hoist a store that we can prove writes a value which is not
1296 // read or overwritten within the loop. For those cases, we fallback to
1297 // load store promotion instead. TODO: We can extend this to cases where
1298 // there is exactly one write to the location and that write dominates an
1299 // arbitrary number of reads in the loop.
1300 if (CurAST) {
1301 auto &AS = CurAST->getAliasSetFor(MemoryLocation::get(SI));
1302
1303 if (AS.isRef() || !AS.isMustAlias())
1304 // Quick exit test, handled by the full path below as well.
1305 return false;
1306 auto *UniqueI = AS.getUniqueInstruction();
1307 if (!UniqueI)
1308 // other memory op, give up
1309 return false;
1310 assert(UniqueI == SI && "AS must contain SI");
1311 return true;
1312 } else { // MSSAU
1313 if (isOnlyMemoryAccess(SI, CurLoop, MSSAU))
1314 return true;
1315 // If there are more accesses than the Promotion cap or no "quota" to
1316 // check clobber, then give up as we're not walking a list that long.
1317 if (Flags->tooManyMemoryAccesses() || Flags->tooManyClobberingCalls())
1318 return false;
1319 // If there are interfering Uses (i.e. their defining access is in the
1320 // loop), or ordered loads (stored as Defs!), don't move this store.
1321 // Could do better here, but this is conservatively correct.
1322 // TODO: Cache set of Uses on the first walk in runOnLoop, update when
1323 // moving accesses. Can also extend to dominating uses.
1324 auto *SIMD = MSSA->getMemoryAccess(SI);
1325 for (auto *BB : CurLoop->getBlocks())
1326 if (auto *Accesses = MSSA->getBlockAccesses(BB)) {
1327 for (const auto &MA : *Accesses)
1328 if (const auto *MU = dyn_cast<MemoryUse>(&MA)) {
1329 auto *MD = MU->getDefiningAccess();
1330 if (!MSSA->isLiveOnEntryDef(MD) &&
1331 CurLoop->contains(MD->getBlock()))
1332 return false;
1333 // Disable hoisting past potentially interfering loads. Optimized
1334 // Uses may point to an access outside the loop, as getClobbering
1335 // checks the previous iteration when walking the backedge.
1336 // FIXME: More precise: no Uses that alias SI.
1337 if (!Flags->getIsSink() && !MSSA->dominates(SIMD, MU))
1338 return false;
1339 } else if (const auto *MD = dyn_cast<MemoryDef>(&MA)) {
1340 if (auto *LI = dyn_cast<LoadInst>(MD->getMemoryInst())) {
1341 (void)LI; // Silence warning.
1342 assert(!LI->isUnordered() && "Expected unordered load");
1343 return false;
1344 }
1345 // Any call, while it may not be clobbering SI, it may be a use.
1346 if (auto *CI = dyn_cast<CallInst>(MD->getMemoryInst())) {
1347 // Check if the call may read from the memory location written
1348 // to by SI. Check CI's attributes and arguments; the number of
1349 // such checks performed is limited above by NoOfMemAccTooLarge.
1350 ModRefInfo MRI = AA->getModRefInfo(CI, MemoryLocation::get(SI));
1351 if (isModOrRefSet(MRI))
1352 return false;
1353 }
1354 }
1355 }
1356 auto *Source = MSSA->getSkipSelfWalker()->getClobberingMemoryAccess(SI);
1357 Flags->incrementClobberingCalls();
1358 // If there are no clobbering Defs in the loop, store is safe to hoist.
1359 return MSSA->isLiveOnEntryDef(Source) ||
1360 !CurLoop->contains(Source->getBlock());
1361 }
1362 }
1363
1364 assert(!I.mayReadOrWriteMemory() && "unhandled aliasing");
1365
1366 // We've established mechanical ability and aliasing, it's up to the caller
1367 // to check fault safety
1368 return true;
1369 }
1370
1371 /// Returns true if a PHINode is a trivially replaceable with an
1372 /// Instruction.
1373 /// This is true when all incoming values are that instruction.
1374 /// This pattern occurs most often with LCSSA PHI nodes.
1375 ///
isTriviallyReplaceablePHI(const PHINode & PN,const Instruction & I)1376 static bool isTriviallyReplaceablePHI(const PHINode &PN, const Instruction &I) {
1377 for (const Value *IncValue : PN.incoming_values())
1378 if (IncValue != &I)
1379 return false;
1380
1381 return true;
1382 }
1383
1384 /// Return true if the instruction is free in the loop.
isFreeInLoop(const Instruction & I,const Loop * CurLoop,const TargetTransformInfo * TTI)1385 static bool isFreeInLoop(const Instruction &I, const Loop *CurLoop,
1386 const TargetTransformInfo *TTI) {
1387
1388 if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(&I)) {
1389 if (TTI->getUserCost(GEP, TargetTransformInfo::TCK_SizeAndLatency) !=
1390 TargetTransformInfo::TCC_Free)
1391 return false;
1392 // For a GEP, we cannot simply use getUserCost because currently it
1393 // optimistically assume that a GEP will fold into addressing mode
1394 // regardless of its users.
1395 const BasicBlock *BB = GEP->getParent();
1396 for (const User *U : GEP->users()) {
1397 const Instruction *UI = cast<Instruction>(U);
1398 if (CurLoop->contains(UI) &&
1399 (BB != UI->getParent() ||
1400 (!isa<StoreInst>(UI) && !isa<LoadInst>(UI))))
1401 return false;
1402 }
1403 return true;
1404 } else
1405 return TTI->getUserCost(&I, TargetTransformInfo::TCK_SizeAndLatency) ==
1406 TargetTransformInfo::TCC_Free;
1407 }
1408
1409 /// Return true if the only users of this instruction are outside of
1410 /// the loop. If this is true, we can sink the instruction to the exit
1411 /// blocks of the loop.
1412 ///
1413 /// We also return true if the instruction could be folded away in lowering.
1414 /// (e.g., a GEP can be folded into a load as an addressing mode in the loop).
isNotUsedOrFreeInLoop(const Instruction & I,const Loop * CurLoop,const LoopSafetyInfo * SafetyInfo,TargetTransformInfo * TTI,bool & FreeInLoop,bool LoopNestMode)1415 static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop,
1416 const LoopSafetyInfo *SafetyInfo,
1417 TargetTransformInfo *TTI, bool &FreeInLoop,
1418 bool LoopNestMode) {
1419 const auto &BlockColors = SafetyInfo->getBlockColors();
1420 bool IsFree = isFreeInLoop(I, CurLoop, TTI);
1421 for (const User *U : I.users()) {
1422 const Instruction *UI = cast<Instruction>(U);
1423 if (const PHINode *PN = dyn_cast<PHINode>(UI)) {
1424 const BasicBlock *BB = PN->getParent();
1425 // We cannot sink uses in catchswitches.
1426 if (isa<CatchSwitchInst>(BB->getTerminator()))
1427 return false;
1428
1429 // We need to sink a callsite to a unique funclet. Avoid sinking if the
1430 // phi use is too muddled.
1431 if (isa<CallInst>(I))
1432 if (!BlockColors.empty() &&
1433 BlockColors.find(const_cast<BasicBlock *>(BB))->second.size() != 1)
1434 return false;
1435
1436 if (LoopNestMode) {
1437 while (isa<PHINode>(UI) && UI->hasOneUser() &&
1438 UI->getNumOperands() == 1) {
1439 if (!CurLoop->contains(UI))
1440 break;
1441 UI = cast<Instruction>(UI->user_back());
1442 }
1443 }
1444 }
1445
1446 if (CurLoop->contains(UI)) {
1447 if (IsFree) {
1448 FreeInLoop = true;
1449 continue;
1450 }
1451 return false;
1452 }
1453 }
1454 return true;
1455 }
1456
cloneInstructionInExitBlock(Instruction & I,BasicBlock & ExitBlock,PHINode & PN,const LoopInfo * LI,const LoopSafetyInfo * SafetyInfo,MemorySSAUpdater * MSSAU)1457 static Instruction *cloneInstructionInExitBlock(
1458 Instruction &I, BasicBlock &ExitBlock, PHINode &PN, const LoopInfo *LI,
1459 const LoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU) {
1460 Instruction *New;
1461 if (auto *CI = dyn_cast<CallInst>(&I)) {
1462 const auto &BlockColors = SafetyInfo->getBlockColors();
1463
1464 // Sinking call-sites need to be handled differently from other
1465 // instructions. The cloned call-site needs a funclet bundle operand
1466 // appropriate for its location in the CFG.
1467 SmallVector<OperandBundleDef, 1> OpBundles;
1468 for (unsigned BundleIdx = 0, BundleEnd = CI->getNumOperandBundles();
1469 BundleIdx != BundleEnd; ++BundleIdx) {
1470 OperandBundleUse Bundle = CI->getOperandBundleAt(BundleIdx);
1471 if (Bundle.getTagID() == LLVMContext::OB_funclet)
1472 continue;
1473
1474 OpBundles.emplace_back(Bundle);
1475 }
1476
1477 if (!BlockColors.empty()) {
1478 const ColorVector &CV = BlockColors.find(&ExitBlock)->second;
1479 assert(CV.size() == 1 && "non-unique color for exit block!");
1480 BasicBlock *BBColor = CV.front();
1481 Instruction *EHPad = BBColor->getFirstNonPHI();
1482 if (EHPad->isEHPad())
1483 OpBundles.emplace_back("funclet", EHPad);
1484 }
1485
1486 New = CallInst::Create(CI, OpBundles);
1487 } else {
1488 New = I.clone();
1489 }
1490
1491 ExitBlock.getInstList().insert(ExitBlock.getFirstInsertionPt(), New);
1492 if (!I.getName().empty())
1493 New->setName(I.getName() + ".le");
1494
1495 if (MSSAU && MSSAU->getMemorySSA()->getMemoryAccess(&I)) {
1496 // Create a new MemoryAccess and let MemorySSA set its defining access.
1497 MemoryAccess *NewMemAcc = MSSAU->createMemoryAccessInBB(
1498 New, nullptr, New->getParent(), MemorySSA::Beginning);
1499 if (NewMemAcc) {
1500 if (auto *MemDef = dyn_cast<MemoryDef>(NewMemAcc))
1501 MSSAU->insertDef(MemDef, /*RenameUses=*/true);
1502 else {
1503 auto *MemUse = cast<MemoryUse>(NewMemAcc);
1504 MSSAU->insertUse(MemUse, /*RenameUses=*/true);
1505 }
1506 }
1507 }
1508
1509 // Build LCSSA PHI nodes for any in-loop operands (if legal). Note that
1510 // this is particularly cheap because we can rip off the PHI node that we're
1511 // replacing for the number and blocks of the predecessors.
1512 // OPT: If this shows up in a profile, we can instead finish sinking all
1513 // invariant instructions, and then walk their operands to re-establish
1514 // LCSSA. That will eliminate creating PHI nodes just to nuke them when
1515 // sinking bottom-up.
1516 for (Use &Op : New->operands())
1517 if (LI->wouldBeOutOfLoopUseRequiringLCSSA(Op.get(), PN.getParent())) {
1518 auto *OInst = cast<Instruction>(Op.get());
1519 PHINode *OpPN =
1520 PHINode::Create(OInst->getType(), PN.getNumIncomingValues(),
1521 OInst->getName() + ".lcssa", &ExitBlock.front());
1522 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
1523 OpPN->addIncoming(OInst, PN.getIncomingBlock(i));
1524 Op = OpPN;
1525 }
1526 return New;
1527 }
1528
eraseInstruction(Instruction & I,ICFLoopSafetyInfo & SafetyInfo,MemorySSAUpdater * MSSAU)1529 static void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo,
1530 MemorySSAUpdater *MSSAU) {
1531 if (MSSAU)
1532 MSSAU->removeMemoryAccess(&I);
1533 SafetyInfo.removeInstruction(&I);
1534 I.eraseFromParent();
1535 }
1536
moveInstructionBefore(Instruction & I,Instruction & Dest,ICFLoopSafetyInfo & SafetyInfo,MemorySSAUpdater * MSSAU,ScalarEvolution * SE)1537 static void moveInstructionBefore(Instruction &I, Instruction &Dest,
1538 ICFLoopSafetyInfo &SafetyInfo,
1539 MemorySSAUpdater *MSSAU,
1540 ScalarEvolution *SE) {
1541 SafetyInfo.removeInstruction(&I);
1542 SafetyInfo.insertInstructionTo(&I, Dest.getParent());
1543 I.moveBefore(&Dest);
1544 if (MSSAU)
1545 if (MemoryUseOrDef *OldMemAcc = cast_or_null<MemoryUseOrDef>(
1546 MSSAU->getMemorySSA()->getMemoryAccess(&I)))
1547 MSSAU->moveToPlace(OldMemAcc, Dest.getParent(),
1548 MemorySSA::BeforeTerminator);
1549 if (SE)
1550 SE->forgetValue(&I);
1551 }
1552
sinkThroughTriviallyReplaceablePHI(PHINode * TPN,Instruction * I,LoopInfo * LI,SmallDenseMap<BasicBlock *,Instruction *,32> & SunkCopies,const LoopSafetyInfo * SafetyInfo,const Loop * CurLoop,MemorySSAUpdater * MSSAU)1553 static Instruction *sinkThroughTriviallyReplaceablePHI(
1554 PHINode *TPN, Instruction *I, LoopInfo *LI,
1555 SmallDenseMap<BasicBlock *, Instruction *, 32> &SunkCopies,
1556 const LoopSafetyInfo *SafetyInfo, const Loop *CurLoop,
1557 MemorySSAUpdater *MSSAU) {
1558 assert(isTriviallyReplaceablePHI(*TPN, *I) &&
1559 "Expect only trivially replaceable PHI");
1560 BasicBlock *ExitBlock = TPN->getParent();
1561 Instruction *New;
1562 auto It = SunkCopies.find(ExitBlock);
1563 if (It != SunkCopies.end())
1564 New = It->second;
1565 else
1566 New = SunkCopies[ExitBlock] = cloneInstructionInExitBlock(
1567 *I, *ExitBlock, *TPN, LI, SafetyInfo, MSSAU);
1568 return New;
1569 }
1570
canSplitPredecessors(PHINode * PN,LoopSafetyInfo * SafetyInfo)1571 static bool canSplitPredecessors(PHINode *PN, LoopSafetyInfo *SafetyInfo) {
1572 BasicBlock *BB = PN->getParent();
1573 if (!BB->canSplitPredecessors())
1574 return false;
1575 // It's not impossible to split EHPad blocks, but if BlockColors already exist
1576 // it require updating BlockColors for all offspring blocks accordingly. By
1577 // skipping such corner case, we can make updating BlockColors after splitting
1578 // predecessor fairly simple.
1579 if (!SafetyInfo->getBlockColors().empty() && BB->getFirstNonPHI()->isEHPad())
1580 return false;
1581 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1582 BasicBlock *BBPred = *PI;
1583 if (isa<IndirectBrInst>(BBPred->getTerminator()) ||
1584 isa<CallBrInst>(BBPred->getTerminator()))
1585 return false;
1586 }
1587 return true;
1588 }
1589
splitPredecessorsOfLoopExit(PHINode * PN,DominatorTree * DT,LoopInfo * LI,const Loop * CurLoop,LoopSafetyInfo * SafetyInfo,MemorySSAUpdater * MSSAU)1590 static void splitPredecessorsOfLoopExit(PHINode *PN, DominatorTree *DT,
1591 LoopInfo *LI, const Loop *CurLoop,
1592 LoopSafetyInfo *SafetyInfo,
1593 MemorySSAUpdater *MSSAU) {
1594 #ifndef NDEBUG
1595 SmallVector<BasicBlock *, 32> ExitBlocks;
1596 CurLoop->getUniqueExitBlocks(ExitBlocks);
1597 SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(),
1598 ExitBlocks.end());
1599 #endif
1600 BasicBlock *ExitBB = PN->getParent();
1601 assert(ExitBlockSet.count(ExitBB) && "Expect the PHI is in an exit block.");
1602
1603 // Split predecessors of the loop exit to make instructions in the loop are
1604 // exposed to exit blocks through trivially replaceable PHIs while keeping the
1605 // loop in the canonical form where each predecessor of each exit block should
1606 // be contained within the loop. For example, this will convert the loop below
1607 // from
1608 //
1609 // LB1:
1610 // %v1 =
1611 // br %LE, %LB2
1612 // LB2:
1613 // %v2 =
1614 // br %LE, %LB1
1615 // LE:
1616 // %p = phi [%v1, %LB1], [%v2, %LB2] <-- non-trivially replaceable
1617 //
1618 // to
1619 //
1620 // LB1:
1621 // %v1 =
1622 // br %LE.split, %LB2
1623 // LB2:
1624 // %v2 =
1625 // br %LE.split2, %LB1
1626 // LE.split:
1627 // %p1 = phi [%v1, %LB1] <-- trivially replaceable
1628 // br %LE
1629 // LE.split2:
1630 // %p2 = phi [%v2, %LB2] <-- trivially replaceable
1631 // br %LE
1632 // LE:
1633 // %p = phi [%p1, %LE.split], [%p2, %LE.split2]
1634 //
1635 const auto &BlockColors = SafetyInfo->getBlockColors();
1636 SmallSetVector<BasicBlock *, 8> PredBBs(pred_begin(ExitBB), pred_end(ExitBB));
1637 while (!PredBBs.empty()) {
1638 BasicBlock *PredBB = *PredBBs.begin();
1639 assert(CurLoop->contains(PredBB) &&
1640 "Expect all predecessors are in the loop");
1641 if (PN->getBasicBlockIndex(PredBB) >= 0) {
1642 BasicBlock *NewPred = SplitBlockPredecessors(
1643 ExitBB, PredBB, ".split.loop.exit", DT, LI, MSSAU, true);
1644 // Since we do not allow splitting EH-block with BlockColors in
1645 // canSplitPredecessors(), we can simply assign predecessor's color to
1646 // the new block.
1647 if (!BlockColors.empty())
1648 // Grab a reference to the ColorVector to be inserted before getting the
1649 // reference to the vector we are copying because inserting the new
1650 // element in BlockColors might cause the map to be reallocated.
1651 SafetyInfo->copyColors(NewPred, PredBB);
1652 }
1653 PredBBs.remove(PredBB);
1654 }
1655 }
1656
1657 /// When an instruction is found to only be used outside of the loop, this
1658 /// function moves it to the exit blocks and patches up SSA form as needed.
1659 /// This method is guaranteed to remove the original instruction from its
1660 /// position, and may either delete it or move it to outside of the loop.
1661 ///
sink(Instruction & I,LoopInfo * LI,DominatorTree * DT,BlockFrequencyInfo * BFI,const Loop * CurLoop,ICFLoopSafetyInfo * SafetyInfo,MemorySSAUpdater * MSSAU,OptimizationRemarkEmitter * ORE)1662 static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
1663 BlockFrequencyInfo *BFI, const Loop *CurLoop,
1664 ICFLoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU,
1665 OptimizationRemarkEmitter *ORE) {
1666 bool Changed = false;
1667 LLVM_DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n");
1668
1669 // Iterate over users to be ready for actual sinking. Replace users via
1670 // unreachable blocks with undef and make all user PHIs trivially replaceable.
1671 SmallPtrSet<Instruction *, 8> VisitedUsers;
1672 for (Value::user_iterator UI = I.user_begin(), UE = I.user_end(); UI != UE;) {
1673 auto *User = cast<Instruction>(*UI);
1674 Use &U = UI.getUse();
1675 ++UI;
1676
1677 if (VisitedUsers.count(User) || CurLoop->contains(User))
1678 continue;
1679
1680 if (!DT->isReachableFromEntry(User->getParent())) {
1681 U = UndefValue::get(I.getType());
1682 Changed = true;
1683 continue;
1684 }
1685
1686 // The user must be a PHI node.
1687 PHINode *PN = cast<PHINode>(User);
1688
1689 // Surprisingly, instructions can be used outside of loops without any
1690 // exits. This can only happen in PHI nodes if the incoming block is
1691 // unreachable.
1692 BasicBlock *BB = PN->getIncomingBlock(U);
1693 if (!DT->isReachableFromEntry(BB)) {
1694 U = UndefValue::get(I.getType());
1695 Changed = true;
1696 continue;
1697 }
1698
1699 VisitedUsers.insert(PN);
1700 if (isTriviallyReplaceablePHI(*PN, I))
1701 continue;
1702
1703 if (!canSplitPredecessors(PN, SafetyInfo))
1704 return Changed;
1705
1706 // Split predecessors of the PHI so that we can make users trivially
1707 // replaceable.
1708 splitPredecessorsOfLoopExit(PN, DT, LI, CurLoop, SafetyInfo, MSSAU);
1709
1710 // Should rebuild the iterators, as they may be invalidated by
1711 // splitPredecessorsOfLoopExit().
1712 UI = I.user_begin();
1713 UE = I.user_end();
1714 }
1715
1716 if (VisitedUsers.empty())
1717 return Changed;
1718
1719 ORE->emit([&]() {
1720 return OptimizationRemark(DEBUG_TYPE, "InstSunk", &I)
1721 << "sinking " << ore::NV("Inst", &I);
1722 });
1723 if (isa<LoadInst>(I))
1724 ++NumMovedLoads;
1725 else if (isa<CallInst>(I))
1726 ++NumMovedCalls;
1727 ++NumSunk;
1728
1729 #ifndef NDEBUG
1730 SmallVector<BasicBlock *, 32> ExitBlocks;
1731 CurLoop->getUniqueExitBlocks(ExitBlocks);
1732 SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(),
1733 ExitBlocks.end());
1734 #endif
1735
1736 // Clones of this instruction. Don't create more than one per exit block!
1737 SmallDenseMap<BasicBlock *, Instruction *, 32> SunkCopies;
1738
1739 // If this instruction is only used outside of the loop, then all users are
1740 // PHI nodes in exit blocks due to LCSSA form. Just RAUW them with clones of
1741 // the instruction.
1742 // First check if I is worth sinking for all uses. Sink only when it is worth
1743 // across all uses.
1744 SmallSetVector<User*, 8> Users(I.user_begin(), I.user_end());
1745 SmallVector<PHINode *, 8> ExitPNs;
1746 for (auto *UI : Users) {
1747 auto *User = cast<Instruction>(UI);
1748
1749 if (CurLoop->contains(User))
1750 continue;
1751
1752 PHINode *PN = cast<PHINode>(User);
1753 assert(ExitBlockSet.count(PN->getParent()) &&
1754 "The LCSSA PHI is not in an exit block!");
1755 if (!worthSinkOrHoistInst(I, PN->getParent(), ORE, BFI)) {
1756 return Changed;
1757 }
1758
1759 ExitPNs.push_back(PN);
1760 }
1761
1762 for (auto *PN : ExitPNs) {
1763
1764 // The PHI must be trivially replaceable.
1765 Instruction *New = sinkThroughTriviallyReplaceablePHI(
1766 PN, &I, LI, SunkCopies, SafetyInfo, CurLoop, MSSAU);
1767 PN->replaceAllUsesWith(New);
1768 eraseInstruction(*PN, *SafetyInfo, nullptr);
1769 Changed = true;
1770 }
1771 return Changed;
1772 }
1773
1774 /// When an instruction is found to only use loop invariant operands that
1775 /// is safe to hoist, this instruction is called to do the dirty work.
1776 ///
hoist(Instruction & I,const DominatorTree * DT,const Loop * CurLoop,BasicBlock * Dest,ICFLoopSafetyInfo * SafetyInfo,MemorySSAUpdater * MSSAU,ScalarEvolution * SE,OptimizationRemarkEmitter * ORE)1777 static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
1778 BasicBlock *Dest, ICFLoopSafetyInfo *SafetyInfo,
1779 MemorySSAUpdater *MSSAU, ScalarEvolution *SE,
1780 OptimizationRemarkEmitter *ORE) {
1781 LLVM_DEBUG(dbgs() << "LICM hoisting to " << Dest->getNameOrAsOperand() << ": "
1782 << I << "\n");
1783 ORE->emit([&]() {
1784 return OptimizationRemark(DEBUG_TYPE, "Hoisted", &I) << "hoisting "
1785 << ore::NV("Inst", &I);
1786 });
1787
1788 // Metadata can be dependent on conditions we are hoisting above.
1789 // Conservatively strip all metadata on the instruction unless we were
1790 // guaranteed to execute I if we entered the loop, in which case the metadata
1791 // is valid in the loop preheader.
1792 // Similarly, If I is a call and it is not guaranteed to execute in the loop,
1793 // then moving to the preheader means we should strip attributes on the call
1794 // that can cause UB since we may be hoisting above conditions that allowed
1795 // inferring those attributes. They may not be valid at the preheader.
1796 if ((I.hasMetadataOtherThanDebugLoc() || isa<CallInst>(I)) &&
1797 // The check on hasMetadataOtherThanDebugLoc is to prevent us from burning
1798 // time in isGuaranteedToExecute if we don't actually have anything to
1799 // drop. It is a compile time optimization, not required for correctness.
1800 !SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop))
1801 I.dropUndefImplyingAttrsAndUnknownMetadata();
1802
1803 if (isa<PHINode>(I))
1804 // Move the new node to the end of the phi list in the destination block.
1805 moveInstructionBefore(I, *Dest->getFirstNonPHI(), *SafetyInfo, MSSAU, SE);
1806 else
1807 // Move the new node to the destination block, before its terminator.
1808 moveInstructionBefore(I, *Dest->getTerminator(), *SafetyInfo, MSSAU, SE);
1809
1810 I.updateLocationAfterHoist();
1811
1812 if (isa<LoadInst>(I))
1813 ++NumMovedLoads;
1814 else if (isa<CallInst>(I))
1815 ++NumMovedCalls;
1816 ++NumHoisted;
1817 }
1818
1819 /// Only sink or hoist an instruction if it is not a trapping instruction,
1820 /// or if the instruction is known not to trap when moved to the preheader.
1821 /// or if it is a trapping instruction and is guaranteed to execute.
isSafeToExecuteUnconditionally(Instruction & Inst,const DominatorTree * DT,const TargetLibraryInfo * TLI,const Loop * CurLoop,const LoopSafetyInfo * SafetyInfo,OptimizationRemarkEmitter * ORE,const Instruction * CtxI)1822 static bool isSafeToExecuteUnconditionally(Instruction &Inst,
1823 const DominatorTree *DT,
1824 const TargetLibraryInfo *TLI,
1825 const Loop *CurLoop,
1826 const LoopSafetyInfo *SafetyInfo,
1827 OptimizationRemarkEmitter *ORE,
1828 const Instruction *CtxI) {
1829 if (isSafeToSpeculativelyExecute(&Inst, CtxI, DT, TLI))
1830 return true;
1831
1832 bool GuaranteedToExecute =
1833 SafetyInfo->isGuaranteedToExecute(Inst, DT, CurLoop);
1834
1835 if (!GuaranteedToExecute) {
1836 auto *LI = dyn_cast<LoadInst>(&Inst);
1837 if (LI && CurLoop->isLoopInvariant(LI->getPointerOperand()))
1838 ORE->emit([&]() {
1839 return OptimizationRemarkMissed(
1840 DEBUG_TYPE, "LoadWithLoopInvariantAddressCondExecuted", LI)
1841 << "failed to hoist load with loop-invariant address "
1842 "because load is conditionally executed";
1843 });
1844 }
1845
1846 return GuaranteedToExecute;
1847 }
1848
1849 namespace {
1850 class LoopPromoter : public LoadAndStorePromoter {
1851 Value *SomePtr; // Designated pointer to store to.
1852 const SmallSetVector<Value *, 8> &PointerMustAliases;
1853 SmallVectorImpl<BasicBlock *> &LoopExitBlocks;
1854 SmallVectorImpl<Instruction *> &LoopInsertPts;
1855 SmallVectorImpl<MemoryAccess *> &MSSAInsertPts;
1856 PredIteratorCache &PredCache;
1857 MemorySSAUpdater *MSSAU;
1858 LoopInfo &LI;
1859 DebugLoc DL;
1860 Align Alignment;
1861 bool UnorderedAtomic;
1862 AAMDNodes AATags;
1863 ICFLoopSafetyInfo &SafetyInfo;
1864
1865 // We're about to add a use of V in a loop exit block. Insert an LCSSA phi
1866 // (if legal) if doing so would add an out-of-loop use to an instruction
1867 // defined in-loop.
maybeInsertLCSSAPHI(Value * V,BasicBlock * BB) const1868 Value *maybeInsertLCSSAPHI(Value *V, BasicBlock *BB) const {
1869 if (!LI.wouldBeOutOfLoopUseRequiringLCSSA(V, BB))
1870 return V;
1871
1872 Instruction *I = cast<Instruction>(V);
1873 // We need to create an LCSSA PHI node for the incoming value and
1874 // store that.
1875 PHINode *PN = PHINode::Create(I->getType(), PredCache.size(BB),
1876 I->getName() + ".lcssa", &BB->front());
1877 for (BasicBlock *Pred : PredCache.get(BB))
1878 PN->addIncoming(I, Pred);
1879 return PN;
1880 }
1881
1882 public:
LoopPromoter(Value * SP,ArrayRef<const Instruction * > Insts,SSAUpdater & S,const SmallSetVector<Value *,8> & PMA,SmallVectorImpl<BasicBlock * > & LEB,SmallVectorImpl<Instruction * > & LIP,SmallVectorImpl<MemoryAccess * > & MSSAIP,PredIteratorCache & PIC,MemorySSAUpdater * MSSAU,LoopInfo & li,DebugLoc dl,Align Alignment,bool UnorderedAtomic,const AAMDNodes & AATags,ICFLoopSafetyInfo & SafetyInfo)1883 LoopPromoter(Value *SP, ArrayRef<const Instruction *> Insts, SSAUpdater &S,
1884 const SmallSetVector<Value *, 8> &PMA,
1885 SmallVectorImpl<BasicBlock *> &LEB,
1886 SmallVectorImpl<Instruction *> &LIP,
1887 SmallVectorImpl<MemoryAccess *> &MSSAIP, PredIteratorCache &PIC,
1888 MemorySSAUpdater *MSSAU, LoopInfo &li, DebugLoc dl,
1889 Align Alignment, bool UnorderedAtomic, const AAMDNodes &AATags,
1890 ICFLoopSafetyInfo &SafetyInfo)
1891 : LoadAndStorePromoter(Insts, S), SomePtr(SP), PointerMustAliases(PMA),
1892 LoopExitBlocks(LEB), LoopInsertPts(LIP), MSSAInsertPts(MSSAIP),
1893 PredCache(PIC), MSSAU(MSSAU), LI(li), DL(std::move(dl)),
1894 Alignment(Alignment), UnorderedAtomic(UnorderedAtomic), AATags(AATags),
1895 SafetyInfo(SafetyInfo) {}
1896
isInstInList(Instruction * I,const SmallVectorImpl<Instruction * > &) const1897 bool isInstInList(Instruction *I,
1898 const SmallVectorImpl<Instruction *> &) const override {
1899 Value *Ptr;
1900 if (LoadInst *LI = dyn_cast<LoadInst>(I))
1901 Ptr = LI->getOperand(0);
1902 else
1903 Ptr = cast<StoreInst>(I)->getPointerOperand();
1904 return PointerMustAliases.count(Ptr);
1905 }
1906
doExtraRewritesBeforeFinalDeletion()1907 void doExtraRewritesBeforeFinalDeletion() override {
1908 // Insert stores after in the loop exit blocks. Each exit block gets a
1909 // store of the live-out values that feed them. Since we've already told
1910 // the SSA updater about the defs in the loop and the preheader
1911 // definition, it is all set and we can start using it.
1912 for (unsigned i = 0, e = LoopExitBlocks.size(); i != e; ++i) {
1913 BasicBlock *ExitBlock = LoopExitBlocks[i];
1914 Value *LiveInValue = SSA.GetValueInMiddleOfBlock(ExitBlock);
1915 LiveInValue = maybeInsertLCSSAPHI(LiveInValue, ExitBlock);
1916 Value *Ptr = maybeInsertLCSSAPHI(SomePtr, ExitBlock);
1917 Instruction *InsertPos = LoopInsertPts[i];
1918 StoreInst *NewSI = new StoreInst(LiveInValue, Ptr, InsertPos);
1919 if (UnorderedAtomic)
1920 NewSI->setOrdering(AtomicOrdering::Unordered);
1921 NewSI->setAlignment(Alignment);
1922 NewSI->setDebugLoc(DL);
1923 if (AATags)
1924 NewSI->setAAMetadata(AATags);
1925
1926 MemoryAccess *MSSAInsertPoint = MSSAInsertPts[i];
1927 MemoryAccess *NewMemAcc;
1928 if (!MSSAInsertPoint) {
1929 NewMemAcc = MSSAU->createMemoryAccessInBB(
1930 NewSI, nullptr, NewSI->getParent(), MemorySSA::Beginning);
1931 } else {
1932 NewMemAcc =
1933 MSSAU->createMemoryAccessAfter(NewSI, nullptr, MSSAInsertPoint);
1934 }
1935 MSSAInsertPts[i] = NewMemAcc;
1936 MSSAU->insertDef(cast<MemoryDef>(NewMemAcc), true);
1937 // FIXME: true for safety, false may still be correct.
1938 }
1939 }
1940
instructionDeleted(Instruction * I) const1941 void instructionDeleted(Instruction *I) const override {
1942 SafetyInfo.removeInstruction(I);
1943 MSSAU->removeMemoryAccess(I);
1944 }
1945 };
1946
isNotCapturedBeforeOrInLoop(const Value * V,const Loop * L,DominatorTree * DT)1947 bool isNotCapturedBeforeOrInLoop(const Value *V, const Loop *L,
1948 DominatorTree *DT) {
1949 // We can perform the captured-before check against any instruction in the
1950 // loop header, as the loop header is reachable from any instruction inside
1951 // the loop.
1952 // TODO: ReturnCaptures=true shouldn't be necessary here.
1953 return !PointerMayBeCapturedBefore(V, /* ReturnCaptures */ true,
1954 /* StoreCaptures */ true,
1955 L->getHeader()->getTerminator(), DT);
1956 }
1957
1958 /// Return true iff we can prove that a caller of this function can not inspect
1959 /// the contents of the provided object in a well defined program.
isKnownNonEscaping(Value * Object,const Loop * L,const TargetLibraryInfo * TLI,DominatorTree * DT)1960 bool isKnownNonEscaping(Value *Object, const Loop *L,
1961 const TargetLibraryInfo *TLI, DominatorTree *DT) {
1962 if (isa<AllocaInst>(Object))
1963 // Since the alloca goes out of scope, we know the caller can't retain a
1964 // reference to it and be well defined. Thus, we don't need to check for
1965 // capture.
1966 return true;
1967
1968 // For all other objects we need to know that the caller can't possibly
1969 // have gotten a reference to the object. There are two components of
1970 // that:
1971 // 1) Object can't be escaped by this function. This is what
1972 // PointerMayBeCaptured checks.
1973 // 2) Object can't have been captured at definition site. For this, we
1974 // need to know the return value is noalias. At the moment, we use a
1975 // weaker condition and handle only AllocLikeFunctions (which are
1976 // known to be noalias). TODO
1977 return isAllocLikeFn(Object, TLI) &&
1978 isNotCapturedBeforeOrInLoop(Object, L, DT);
1979 }
1980
1981 } // namespace
1982
1983 /// Try to promote memory values to scalars by sinking stores out of the
1984 /// loop and moving loads to before the loop. We do this by looping over
1985 /// the stores in the loop, looking for stores to Must pointers which are
1986 /// loop invariant.
1987 ///
promoteLoopAccessesToScalars(const SmallSetVector<Value *,8> & PointerMustAliases,SmallVectorImpl<BasicBlock * > & ExitBlocks,SmallVectorImpl<Instruction * > & InsertPts,SmallVectorImpl<MemoryAccess * > & MSSAInsertPts,PredIteratorCache & PIC,LoopInfo * LI,DominatorTree * DT,const TargetLibraryInfo * TLI,Loop * CurLoop,MemorySSAUpdater * MSSAU,ICFLoopSafetyInfo * SafetyInfo,OptimizationRemarkEmitter * ORE)1988 bool llvm::promoteLoopAccessesToScalars(
1989 const SmallSetVector<Value *, 8> &PointerMustAliases,
1990 SmallVectorImpl<BasicBlock *> &ExitBlocks,
1991 SmallVectorImpl<Instruction *> &InsertPts,
1992 SmallVectorImpl<MemoryAccess *> &MSSAInsertPts, PredIteratorCache &PIC,
1993 LoopInfo *LI, DominatorTree *DT, const TargetLibraryInfo *TLI,
1994 Loop *CurLoop, MemorySSAUpdater *MSSAU, ICFLoopSafetyInfo *SafetyInfo,
1995 OptimizationRemarkEmitter *ORE) {
1996 // Verify inputs.
1997 assert(LI != nullptr && DT != nullptr && CurLoop != nullptr &&
1998 SafetyInfo != nullptr &&
1999 "Unexpected Input to promoteLoopAccessesToScalars");
2000
2001 Value *SomePtr = *PointerMustAliases.begin();
2002 BasicBlock *Preheader = CurLoop->getLoopPreheader();
2003
2004 // It is not safe to promote a load/store from the loop if the load/store is
2005 // conditional. For example, turning:
2006 //
2007 // for () { if (c) *P += 1; }
2008 //
2009 // into:
2010 //
2011 // tmp = *P; for () { if (c) tmp +=1; } *P = tmp;
2012 //
2013 // is not safe, because *P may only be valid to access if 'c' is true.
2014 //
2015 // The safety property divides into two parts:
2016 // p1) The memory may not be dereferenceable on entry to the loop. In this
2017 // case, we can't insert the required load in the preheader.
2018 // p2) The memory model does not allow us to insert a store along any dynamic
2019 // path which did not originally have one.
2020 //
2021 // If at least one store is guaranteed to execute, both properties are
2022 // satisfied, and promotion is legal.
2023 //
2024 // This, however, is not a necessary condition. Even if no store/load is
2025 // guaranteed to execute, we can still establish these properties.
2026 // We can establish (p1) by proving that hoisting the load into the preheader
2027 // is safe (i.e. proving dereferenceability on all paths through the loop). We
2028 // can use any access within the alias set to prove dereferenceability,
2029 // since they're all must alias.
2030 //
2031 // There are two ways establish (p2):
2032 // a) Prove the location is thread-local. In this case the memory model
2033 // requirement does not apply, and stores are safe to insert.
2034 // b) Prove a store dominates every exit block. In this case, if an exit
2035 // blocks is reached, the original dynamic path would have taken us through
2036 // the store, so inserting a store into the exit block is safe. Note that this
2037 // is different from the store being guaranteed to execute. For instance,
2038 // if an exception is thrown on the first iteration of the loop, the original
2039 // store is never executed, but the exit blocks are not executed either.
2040
2041 bool DereferenceableInPH = false;
2042 bool SafeToInsertStore = false;
2043
2044 SmallVector<Instruction *, 64> LoopUses;
2045
2046 // We start with an alignment of one and try to find instructions that allow
2047 // us to prove better alignment.
2048 Align Alignment;
2049 // Keep track of which types of access we see
2050 bool SawUnorderedAtomic = false;
2051 bool SawNotAtomic = false;
2052 AAMDNodes AATags;
2053
2054 const DataLayout &MDL = Preheader->getModule()->getDataLayout();
2055
2056 bool IsKnownThreadLocalObject = false;
2057 if (SafetyInfo->anyBlockMayThrow()) {
2058 // If a loop can throw, we have to insert a store along each unwind edge.
2059 // That said, we can't actually make the unwind edge explicit. Therefore,
2060 // we have to prove that the store is dead along the unwind edge. We do
2061 // this by proving that the caller can't have a reference to the object
2062 // after return and thus can't possibly load from the object.
2063 Value *Object = getUnderlyingObject(SomePtr);
2064 if (!isKnownNonEscaping(Object, CurLoop, TLI, DT))
2065 return false;
2066 // Subtlety: Alloca's aren't visible to callers, but *are* potentially
2067 // visible to other threads if captured and used during their lifetimes.
2068 IsKnownThreadLocalObject = !isa<AllocaInst>(Object);
2069 }
2070
2071 // Check that all of the pointers in the alias set have the same type. We
2072 // cannot (yet) promote a memory location that is loaded and stored in
2073 // different sizes. While we are at it, collect alignment and AA info.
2074 for (Value *ASIV : PointerMustAliases) {
2075 // Check that all of the pointers in the alias set have the same type. We
2076 // cannot (yet) promote a memory location that is loaded and stored in
2077 // different sizes.
2078 if (SomePtr->getType() != ASIV->getType())
2079 return false;
2080
2081 for (User *U : ASIV->users()) {
2082 // Ignore instructions that are outside the loop.
2083 Instruction *UI = dyn_cast<Instruction>(U);
2084 if (!UI || !CurLoop->contains(UI))
2085 continue;
2086
2087 // If there is an non-load/store instruction in the loop, we can't promote
2088 // it.
2089 if (LoadInst *Load = dyn_cast<LoadInst>(UI)) {
2090 if (!Load->isUnordered())
2091 return false;
2092
2093 SawUnorderedAtomic |= Load->isAtomic();
2094 SawNotAtomic |= !Load->isAtomic();
2095
2096 Align InstAlignment = Load->getAlign();
2097
2098 // Note that proving a load safe to speculate requires proving
2099 // sufficient alignment at the target location. Proving it guaranteed
2100 // to execute does as well. Thus we can increase our guaranteed
2101 // alignment as well.
2102 if (!DereferenceableInPH || (InstAlignment > Alignment))
2103 if (isSafeToExecuteUnconditionally(*Load, DT, TLI, CurLoop,
2104 SafetyInfo, ORE,
2105 Preheader->getTerminator())) {
2106 DereferenceableInPH = true;
2107 Alignment = std::max(Alignment, InstAlignment);
2108 }
2109 } else if (const StoreInst *Store = dyn_cast<StoreInst>(UI)) {
2110 // Stores *of* the pointer are not interesting, only stores *to* the
2111 // pointer.
2112 if (UI->getOperand(1) != ASIV)
2113 continue;
2114 if (!Store->isUnordered())
2115 return false;
2116
2117 SawUnorderedAtomic |= Store->isAtomic();
2118 SawNotAtomic |= !Store->isAtomic();
2119
2120 // If the store is guaranteed to execute, both properties are satisfied.
2121 // We may want to check if a store is guaranteed to execute even if we
2122 // already know that promotion is safe, since it may have higher
2123 // alignment than any other guaranteed stores, in which case we can
2124 // raise the alignment on the promoted store.
2125 Align InstAlignment = Store->getAlign();
2126
2127 if (!DereferenceableInPH || !SafeToInsertStore ||
2128 (InstAlignment > Alignment)) {
2129 if (SafetyInfo->isGuaranteedToExecute(*UI, DT, CurLoop)) {
2130 DereferenceableInPH = true;
2131 SafeToInsertStore = true;
2132 Alignment = std::max(Alignment, InstAlignment);
2133 }
2134 }
2135
2136 // If a store dominates all exit blocks, it is safe to sink.
2137 // As explained above, if an exit block was executed, a dominating
2138 // store must have been executed at least once, so we are not
2139 // introducing stores on paths that did not have them.
2140 // Note that this only looks at explicit exit blocks. If we ever
2141 // start sinking stores into unwind edges (see above), this will break.
2142 if (!SafeToInsertStore)
2143 SafeToInsertStore = llvm::all_of(ExitBlocks, [&](BasicBlock *Exit) {
2144 return DT->dominates(Store->getParent(), Exit);
2145 });
2146
2147 // If the store is not guaranteed to execute, we may still get
2148 // deref info through it.
2149 if (!DereferenceableInPH) {
2150 DereferenceableInPH = isDereferenceableAndAlignedPointer(
2151 Store->getPointerOperand(), Store->getValueOperand()->getType(),
2152 Store->getAlign(), MDL, Preheader->getTerminator(), DT, TLI);
2153 }
2154 } else
2155 return false; // Not a load or store.
2156
2157 // Merge the AA tags.
2158 if (LoopUses.empty()) {
2159 // On the first load/store, just take its AA tags.
2160 AATags = UI->getAAMetadata();
2161 } else if (AATags) {
2162 AATags = AATags.merge(UI->getAAMetadata());
2163 }
2164
2165 LoopUses.push_back(UI);
2166 }
2167 }
2168
2169 // If we found both an unordered atomic instruction and a non-atomic memory
2170 // access, bail. We can't blindly promote non-atomic to atomic since we
2171 // might not be able to lower the result. We can't downgrade since that
2172 // would violate memory model. Also, align 0 is an error for atomics.
2173 if (SawUnorderedAtomic && SawNotAtomic)
2174 return false;
2175
2176 // If we're inserting an atomic load in the preheader, we must be able to
2177 // lower it. We're only guaranteed to be able to lower naturally aligned
2178 // atomics.
2179 auto *SomePtrElemType = SomePtr->getType()->getPointerElementType();
2180 if (SawUnorderedAtomic &&
2181 Alignment < MDL.getTypeStoreSize(SomePtrElemType))
2182 return false;
2183
2184 // If we couldn't prove we can hoist the load, bail.
2185 if (!DereferenceableInPH)
2186 return false;
2187
2188 // We know we can hoist the load, but don't have a guaranteed store.
2189 // Check whether the location is thread-local. If it is, then we can insert
2190 // stores along paths which originally didn't have them without violating the
2191 // memory model.
2192 if (!SafeToInsertStore) {
2193 if (IsKnownThreadLocalObject)
2194 SafeToInsertStore = true;
2195 else {
2196 Value *Object = getUnderlyingObject(SomePtr);
2197 SafeToInsertStore =
2198 (isAllocLikeFn(Object, TLI) || isa<AllocaInst>(Object)) &&
2199 isNotCapturedBeforeOrInLoop(Object, CurLoop, DT);
2200 }
2201 }
2202
2203 // If we've still failed to prove we can sink the store, give up.
2204 if (!SafeToInsertStore)
2205 return false;
2206
2207 // Otherwise, this is safe to promote, lets do it!
2208 LLVM_DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " << *SomePtr
2209 << '\n');
2210 ORE->emit([&]() {
2211 return OptimizationRemark(DEBUG_TYPE, "PromoteLoopAccessesToScalar",
2212 LoopUses[0])
2213 << "Moving accesses to memory location out of the loop";
2214 });
2215 ++NumPromoted;
2216
2217 // Look at all the loop uses, and try to merge their locations.
2218 std::vector<const DILocation *> LoopUsesLocs;
2219 for (auto U : LoopUses)
2220 LoopUsesLocs.push_back(U->getDebugLoc().get());
2221 auto DL = DebugLoc(DILocation::getMergedLocations(LoopUsesLocs));
2222
2223 // We use the SSAUpdater interface to insert phi nodes as required.
2224 SmallVector<PHINode *, 16> NewPHIs;
2225 SSAUpdater SSA(&NewPHIs);
2226 LoopPromoter Promoter(SomePtr, LoopUses, SSA, PointerMustAliases, ExitBlocks,
2227 InsertPts, MSSAInsertPts, PIC, MSSAU, *LI, DL,
2228 Alignment, SawUnorderedAtomic, AATags, *SafetyInfo);
2229
2230 // Set up the preheader to have a definition of the value. It is the live-out
2231 // value from the preheader that uses in the loop will use.
2232 LoadInst *PreheaderLoad = new LoadInst(
2233 SomePtr->getType()->getPointerElementType(), SomePtr,
2234 SomePtr->getName() + ".promoted", Preheader->getTerminator());
2235 if (SawUnorderedAtomic)
2236 PreheaderLoad->setOrdering(AtomicOrdering::Unordered);
2237 PreheaderLoad->setAlignment(Alignment);
2238 PreheaderLoad->setDebugLoc(DebugLoc());
2239 if (AATags)
2240 PreheaderLoad->setAAMetadata(AATags);
2241 SSA.AddAvailableValue(Preheader, PreheaderLoad);
2242
2243 MemoryAccess *PreheaderLoadMemoryAccess = MSSAU->createMemoryAccessInBB(
2244 PreheaderLoad, nullptr, PreheaderLoad->getParent(), MemorySSA::End);
2245 MemoryUse *NewMemUse = cast<MemoryUse>(PreheaderLoadMemoryAccess);
2246 MSSAU->insertUse(NewMemUse, /*RenameUses=*/true);
2247
2248 if (VerifyMemorySSA)
2249 MSSAU->getMemorySSA()->verifyMemorySSA();
2250 // Rewrite all the loads in the loop and remember all the definitions from
2251 // stores in the loop.
2252 Promoter.run(LoopUses);
2253
2254 if (VerifyMemorySSA)
2255 MSSAU->getMemorySSA()->verifyMemorySSA();
2256 // If the SSAUpdater didn't use the load in the preheader, just zap it now.
2257 if (PreheaderLoad->use_empty())
2258 eraseInstruction(*PreheaderLoad, *SafetyInfo, MSSAU);
2259
2260 return true;
2261 }
2262
foreachMemoryAccess(MemorySSA * MSSA,Loop * L,function_ref<void (Instruction *)> Fn)2263 static void foreachMemoryAccess(MemorySSA *MSSA, Loop *L,
2264 function_ref<void(Instruction *)> Fn) {
2265 for (const BasicBlock *BB : L->blocks())
2266 if (const auto *Accesses = MSSA->getBlockAccesses(BB))
2267 for (const auto &Access : *Accesses)
2268 if (const auto *MUD = dyn_cast<MemoryUseOrDef>(&Access))
2269 Fn(MUD->getMemoryInst());
2270 }
2271
2272 static SmallVector<SmallSetVector<Value *, 8>, 0>
collectPromotionCandidates(MemorySSA * MSSA,AliasAnalysis * AA,Loop * L)2273 collectPromotionCandidates(MemorySSA *MSSA, AliasAnalysis *AA, Loop *L) {
2274 AliasSetTracker AST(*AA);
2275
2276 auto IsPotentiallyPromotable = [L](const Instruction *I) {
2277 if (const auto *SI = dyn_cast<StoreInst>(I))
2278 return L->isLoopInvariant(SI->getPointerOperand());
2279 if (const auto *LI = dyn_cast<LoadInst>(I))
2280 return L->isLoopInvariant(LI->getPointerOperand());
2281 return false;
2282 };
2283
2284 // Populate AST with potentially promotable accesses and remove them from
2285 // MaybePromotable, so they will not be checked again on the next iteration.
2286 SmallPtrSet<Value *, 16> AttemptingPromotion;
2287 foreachMemoryAccess(MSSA, L, [&](Instruction *I) {
2288 if (IsPotentiallyPromotable(I)) {
2289 AttemptingPromotion.insert(I);
2290 AST.add(I);
2291 }
2292 });
2293
2294 // We're only interested in must-alias sets that contain a mod.
2295 SmallVector<const AliasSet *, 8> Sets;
2296 for (AliasSet &AS : AST)
2297 if (!AS.isForwardingAliasSet() && AS.isMod() && AS.isMustAlias())
2298 Sets.push_back(&AS);
2299
2300 if (Sets.empty())
2301 return {}; // Nothing to promote...
2302
2303 // Discard any sets for which there is an aliasing non-promotable access.
2304 foreachMemoryAccess(MSSA, L, [&](Instruction *I) {
2305 if (AttemptingPromotion.contains(I))
2306 return;
2307
2308 llvm::erase_if(Sets, [&](const AliasSet *AS) {
2309 return AS->aliasesUnknownInst(I, *AA);
2310 });
2311 });
2312
2313 SmallVector<SmallSetVector<Value *, 8>, 0> Result;
2314 for (const AliasSet *Set : Sets) {
2315 SmallSetVector<Value *, 8> PointerMustAliases;
2316 for (const auto &ASI : *Set)
2317 PointerMustAliases.insert(ASI.getValue());
2318 Result.push_back(std::move(PointerMustAliases));
2319 }
2320
2321 return Result;
2322 }
2323
pointerInvalidatedByLoop(MemoryLocation MemLoc,AliasSetTracker * CurAST,Loop * CurLoop,AAResults * AA)2324 static bool pointerInvalidatedByLoop(MemoryLocation MemLoc,
2325 AliasSetTracker *CurAST, Loop *CurLoop,
2326 AAResults *AA) {
2327 return CurAST->getAliasSetFor(MemLoc).isMod();
2328 }
2329
pointerInvalidatedByLoopWithMSSA(MemorySSA * MSSA,MemoryUse * MU,Loop * CurLoop,Instruction & I,SinkAndHoistLICMFlags & Flags)2330 bool pointerInvalidatedByLoopWithMSSA(MemorySSA *MSSA, MemoryUse *MU,
2331 Loop *CurLoop, Instruction &I,
2332 SinkAndHoistLICMFlags &Flags) {
2333 // For hoisting, use the walker to determine safety
2334 if (!Flags.getIsSink()) {
2335 MemoryAccess *Source;
2336 // See declaration of SetLicmMssaOptCap for usage details.
2337 if (Flags.tooManyClobberingCalls())
2338 Source = MU->getDefiningAccess();
2339 else {
2340 Source = MSSA->getSkipSelfWalker()->getClobberingMemoryAccess(MU);
2341 Flags.incrementClobberingCalls();
2342 }
2343 return !MSSA->isLiveOnEntryDef(Source) &&
2344 CurLoop->contains(Source->getBlock());
2345 }
2346
2347 // For sinking, we'd need to check all Defs below this use. The getClobbering
2348 // call will look on the backedge of the loop, but will check aliasing with
2349 // the instructions on the previous iteration.
2350 // For example:
2351 // for (i ... )
2352 // load a[i] ( Use (LoE)
2353 // store a[i] ( 1 = Def (2), with 2 = Phi for the loop.
2354 // i++;
2355 // The load sees no clobbering inside the loop, as the backedge alias check
2356 // does phi translation, and will check aliasing against store a[i-1].
2357 // However sinking the load outside the loop, below the store is incorrect.
2358
2359 // For now, only sink if there are no Defs in the loop, and the existing ones
2360 // precede the use and are in the same block.
2361 // FIXME: Increase precision: Safe to sink if Use post dominates the Def;
2362 // needs PostDominatorTreeAnalysis.
2363 // FIXME: More precise: no Defs that alias this Use.
2364 if (Flags.tooManyMemoryAccesses())
2365 return true;
2366 for (auto *BB : CurLoop->getBlocks())
2367 if (pointerInvalidatedByBlockWithMSSA(*BB, *MSSA, *MU))
2368 return true;
2369 // When sinking, the source block may not be part of the loop so check it.
2370 if (!CurLoop->contains(&I))
2371 return pointerInvalidatedByBlockWithMSSA(*I.getParent(), *MSSA, *MU);
2372
2373 return false;
2374 }
2375
pointerInvalidatedByBlockWithMSSA(BasicBlock & BB,MemorySSA & MSSA,MemoryUse & MU)2376 bool pointerInvalidatedByBlockWithMSSA(BasicBlock &BB, MemorySSA &MSSA,
2377 MemoryUse &MU) {
2378 if (const auto *Accesses = MSSA.getBlockDefs(&BB))
2379 for (const auto &MA : *Accesses)
2380 if (const auto *MD = dyn_cast<MemoryDef>(&MA))
2381 if (MU.getBlock() != MD->getBlock() || !MSSA.locallyDominates(MD, &MU))
2382 return true;
2383 return false;
2384 }
2385
2386 /// Little predicate that returns true if the specified basic block is in
2387 /// a subloop of the current one, not the current one itself.
2388 ///
inSubLoop(BasicBlock * BB,Loop * CurLoop,LoopInfo * LI)2389 static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI) {
2390 assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop");
2391 return LI->getLoopFor(BB) != CurLoop;
2392 }
2393