LLVM 19.0.0git
DeadStoreElimination.cpp
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1//===- DeadStoreElimination.cpp - MemorySSA Backed Dead Store Elimination -===//
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// The code below implements dead store elimination using MemorySSA. It uses
10// the following general approach: given a MemoryDef, walk upwards to find
11// clobbering MemoryDefs that may be killed by the starting def. Then check
12// that there are no uses that may read the location of the original MemoryDef
13// in between both MemoryDefs. A bit more concretely:
14//
15// For all MemoryDefs StartDef:
16// 1. Get the next dominating clobbering MemoryDef (MaybeDeadAccess) by walking
17// upwards.
18// 2. Check that there are no reads between MaybeDeadAccess and the StartDef by
19// checking all uses starting at MaybeDeadAccess and walking until we see
20// StartDef.
21// 3. For each found CurrentDef, check that:
22// 1. There are no barrier instructions between CurrentDef and StartDef (like
23// throws or stores with ordering constraints).
24// 2. StartDef is executed whenever CurrentDef is executed.
25// 3. StartDef completely overwrites CurrentDef.
26// 4. Erase CurrentDef from the function and MemorySSA.
27//
28//===----------------------------------------------------------------------===//
29
31#include "llvm/ADT/APInt.h"
32#include "llvm/ADT/DenseMap.h"
33#include "llvm/ADT/MapVector.h"
35#include "llvm/ADT/SetVector.h"
38#include "llvm/ADT/Statistic.h"
39#include "llvm/ADT/StringRef.h"
52#include "llvm/IR/Argument.h"
53#include "llvm/IR/BasicBlock.h"
54#include "llvm/IR/Constant.h"
55#include "llvm/IR/Constants.h"
56#include "llvm/IR/DataLayout.h"
57#include "llvm/IR/DebugInfo.h"
58#include "llvm/IR/Dominators.h"
59#include "llvm/IR/Function.h"
60#include "llvm/IR/IRBuilder.h"
62#include "llvm/IR/InstrTypes.h"
63#include "llvm/IR/Instruction.h"
66#include "llvm/IR/Module.h"
67#include "llvm/IR/PassManager.h"
69#include "llvm/IR/Value.h"
72#include "llvm/Support/Debug.h"
79#include <algorithm>
80#include <cassert>
81#include <cstdint>
82#include <iterator>
83#include <map>
84#include <optional>
85#include <utility>
86
87using namespace llvm;
88using namespace PatternMatch;
89
90#define DEBUG_TYPE "dse"
91
92STATISTIC(NumRemainingStores, "Number of stores remaining after DSE");
93STATISTIC(NumRedundantStores, "Number of redundant stores deleted");
94STATISTIC(NumFastStores, "Number of stores deleted");
95STATISTIC(NumFastOther, "Number of other instrs removed");
96STATISTIC(NumCompletePartials, "Number of stores dead by later partials");
97STATISTIC(NumModifiedStores, "Number of stores modified");
98STATISTIC(NumCFGChecks, "Number of stores modified");
99STATISTIC(NumCFGTries, "Number of stores modified");
100STATISTIC(NumCFGSuccess, "Number of stores modified");
101STATISTIC(NumGetDomMemoryDefPassed,
102 "Number of times a valid candidate is returned from getDomMemoryDef");
103STATISTIC(NumDomMemDefChecks,
104 "Number iterations check for reads in getDomMemoryDef");
105
106DEBUG_COUNTER(MemorySSACounter, "dse-memoryssa",
107 "Controls which MemoryDefs are eliminated.");
108
109static cl::opt<bool>
110EnablePartialOverwriteTracking("enable-dse-partial-overwrite-tracking",
111 cl::init(true), cl::Hidden,
112 cl::desc("Enable partial-overwrite tracking in DSE"));
113
114static cl::opt<bool>
115EnablePartialStoreMerging("enable-dse-partial-store-merging",
116 cl::init(true), cl::Hidden,
117 cl::desc("Enable partial store merging in DSE"));
118
120 MemorySSAScanLimit("dse-memoryssa-scanlimit", cl::init(150), cl::Hidden,
121 cl::desc("The number of memory instructions to scan for "
122 "dead store elimination (default = 150)"));
124 "dse-memoryssa-walklimit", cl::init(90), cl::Hidden,
125 cl::desc("The maximum number of steps while walking upwards to find "
126 "MemoryDefs that may be killed (default = 90)"));
127
129 "dse-memoryssa-partial-store-limit", cl::init(5), cl::Hidden,
130 cl::desc("The maximum number candidates that only partially overwrite the "
131 "killing MemoryDef to consider"
132 " (default = 5)"));
133
135 "dse-memoryssa-defs-per-block-limit", cl::init(5000), cl::Hidden,
136 cl::desc("The number of MemoryDefs we consider as candidates to eliminated "
137 "other stores per basic block (default = 5000)"));
138
140 "dse-memoryssa-samebb-cost", cl::init(1), cl::Hidden,
141 cl::desc(
142 "The cost of a step in the same basic block as the killing MemoryDef"
143 "(default = 1)"));
144
146 MemorySSAOtherBBStepCost("dse-memoryssa-otherbb-cost", cl::init(5),
148 cl::desc("The cost of a step in a different basic "
149 "block than the killing MemoryDef"
150 "(default = 5)"));
151
153 "dse-memoryssa-path-check-limit", cl::init(50), cl::Hidden,
154 cl::desc("The maximum number of blocks to check when trying to prove that "
155 "all paths to an exit go through a killing block (default = 50)"));
156
157// This flags allows or disallows DSE to optimize MemorySSA during its
158// traversal. Note that DSE optimizing MemorySSA may impact other passes
159// downstream of the DSE invocation and can lead to issues not being
160// reproducible in isolation (i.e. when MemorySSA is built from scratch). In
161// those cases, the flag can be used to check if DSE's MemorySSA optimizations
162// impact follow-up passes.
163static cl::opt<bool>
164 OptimizeMemorySSA("dse-optimize-memoryssa", cl::init(true), cl::Hidden,
165 cl::desc("Allow DSE to optimize memory accesses."));
166
167//===----------------------------------------------------------------------===//
168// Helper functions
169//===----------------------------------------------------------------------===//
170using OverlapIntervalsTy = std::map<int64_t, int64_t>;
172
173/// Returns true if the end of this instruction can be safely shortened in
174/// length.
176 // Don't shorten stores for now
177 if (isa<StoreInst>(I))
178 return false;
179
180 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
181 switch (II->getIntrinsicID()) {
182 default: return false;
183 case Intrinsic::memset:
184 case Intrinsic::memcpy:
185 case Intrinsic::memcpy_element_unordered_atomic:
186 case Intrinsic::memset_element_unordered_atomic:
187 // Do shorten memory intrinsics.
188 // FIXME: Add memmove if it's also safe to transform.
189 return true;
190 }
191 }
192
193 // Don't shorten libcalls calls for now.
194
195 return false;
196}
197
198/// Returns true if the beginning of this instruction can be safely shortened
199/// in length.
201 // FIXME: Handle only memset for now. Supporting memcpy/memmove should be
202 // easily done by offsetting the source address.
203 return isa<AnyMemSetInst>(I);
204}
205
206static std::optional<TypeSize> getPointerSize(const Value *V,
207 const DataLayout &DL,
208 const TargetLibraryInfo &TLI,
209 const Function *F) {
211 ObjectSizeOpts Opts;
213
214 if (getObjectSize(V, Size, DL, &TLI, Opts))
215 return TypeSize::getFixed(Size);
216 return std::nullopt;
217}
218
219namespace {
220
221enum OverwriteResult {
222 OW_Begin,
223 OW_Complete,
224 OW_End,
225 OW_PartialEarlierWithFullLater,
226 OW_MaybePartial,
227 OW_None,
228 OW_Unknown
229};
230
231} // end anonymous namespace
232
233/// Check if two instruction are masked stores that completely
234/// overwrite one another. More specifically, \p KillingI has to
235/// overwrite \p DeadI.
236static OverwriteResult isMaskedStoreOverwrite(const Instruction *KillingI,
237 const Instruction *DeadI,
238 BatchAAResults &AA) {
239 const auto *KillingII = dyn_cast<IntrinsicInst>(KillingI);
240 const auto *DeadII = dyn_cast<IntrinsicInst>(DeadI);
241 if (KillingII == nullptr || DeadII == nullptr)
242 return OW_Unknown;
243 if (KillingII->getIntrinsicID() != DeadII->getIntrinsicID())
244 return OW_Unknown;
245 if (KillingII->getIntrinsicID() == Intrinsic::masked_store) {
246 // Type size.
247 VectorType *KillingTy =
248 cast<VectorType>(KillingII->getArgOperand(0)->getType());
249 VectorType *DeadTy = cast<VectorType>(DeadII->getArgOperand(0)->getType());
250 if (KillingTy->getScalarSizeInBits() != DeadTy->getScalarSizeInBits())
251 return OW_Unknown;
252 // Element count.
253 if (KillingTy->getElementCount() != DeadTy->getElementCount())
254 return OW_Unknown;
255 // Pointers.
256 Value *KillingPtr = KillingII->getArgOperand(1)->stripPointerCasts();
257 Value *DeadPtr = DeadII->getArgOperand(1)->stripPointerCasts();
258 if (KillingPtr != DeadPtr && !AA.isMustAlias(KillingPtr, DeadPtr))
259 return OW_Unknown;
260 // Masks.
261 // TODO: check that KillingII's mask is a superset of the DeadII's mask.
262 if (KillingII->getArgOperand(3) != DeadII->getArgOperand(3))
263 return OW_Unknown;
264 return OW_Complete;
265 }
266 return OW_Unknown;
267}
268
269/// Return 'OW_Complete' if a store to the 'KillingLoc' location completely
270/// overwrites a store to the 'DeadLoc' location, 'OW_End' if the end of the
271/// 'DeadLoc' location is completely overwritten by 'KillingLoc', 'OW_Begin'
272/// if the beginning of the 'DeadLoc' location is overwritten by 'KillingLoc'.
273/// 'OW_PartialEarlierWithFullLater' means that a dead (big) store was
274/// overwritten by a killing (smaller) store which doesn't write outside the big
275/// store's memory locations. Returns 'OW_Unknown' if nothing can be determined.
276/// NOTE: This function must only be called if both \p KillingLoc and \p
277/// DeadLoc belong to the same underlying object with valid \p KillingOff and
278/// \p DeadOff.
279static OverwriteResult isPartialOverwrite(const MemoryLocation &KillingLoc,
280 const MemoryLocation &DeadLoc,
281 int64_t KillingOff, int64_t DeadOff,
282 Instruction *DeadI,
284 const uint64_t KillingSize = KillingLoc.Size.getValue();
285 const uint64_t DeadSize = DeadLoc.Size.getValue();
286 // We may now overlap, although the overlap is not complete. There might also
287 // be other incomplete overlaps, and together, they might cover the complete
288 // dead store.
289 // Note: The correctness of this logic depends on the fact that this function
290 // is not even called providing DepWrite when there are any intervening reads.
292 KillingOff < int64_t(DeadOff + DeadSize) &&
293 int64_t(KillingOff + KillingSize) >= DeadOff) {
294
295 // Insert our part of the overlap into the map.
296 auto &IM = IOL[DeadI];
297 LLVM_DEBUG(dbgs() << "DSE: Partial overwrite: DeadLoc [" << DeadOff << ", "
298 << int64_t(DeadOff + DeadSize) << ") KillingLoc ["
299 << KillingOff << ", " << int64_t(KillingOff + KillingSize)
300 << ")\n");
301
302 // Make sure that we only insert non-overlapping intervals and combine
303 // adjacent intervals. The intervals are stored in the map with the ending
304 // offset as the key (in the half-open sense) and the starting offset as
305 // the value.
306 int64_t KillingIntStart = KillingOff;
307 int64_t KillingIntEnd = KillingOff + KillingSize;
308
309 // Find any intervals ending at, or after, KillingIntStart which start
310 // before KillingIntEnd.
311 auto ILI = IM.lower_bound(KillingIntStart);
312 if (ILI != IM.end() && ILI->second <= KillingIntEnd) {
313 // This existing interval is overlapped with the current store somewhere
314 // in [KillingIntStart, KillingIntEnd]. Merge them by erasing the existing
315 // intervals and adjusting our start and end.
316 KillingIntStart = std::min(KillingIntStart, ILI->second);
317 KillingIntEnd = std::max(KillingIntEnd, ILI->first);
318 ILI = IM.erase(ILI);
319
320 // Continue erasing and adjusting our end in case other previous
321 // intervals are also overlapped with the current store.
322 //
323 // |--- dead 1 ---| |--- dead 2 ---|
324 // |------- killing---------|
325 //
326 while (ILI != IM.end() && ILI->second <= KillingIntEnd) {
327 assert(ILI->second > KillingIntStart && "Unexpected interval");
328 KillingIntEnd = std::max(KillingIntEnd, ILI->first);
329 ILI = IM.erase(ILI);
330 }
331 }
332
333 IM[KillingIntEnd] = KillingIntStart;
334
335 ILI = IM.begin();
336 if (ILI->second <= DeadOff && ILI->first >= int64_t(DeadOff + DeadSize)) {
337 LLVM_DEBUG(dbgs() << "DSE: Full overwrite from partials: DeadLoc ["
338 << DeadOff << ", " << int64_t(DeadOff + DeadSize)
339 << ") Composite KillingLoc [" << ILI->second << ", "
340 << ILI->first << ")\n");
341 ++NumCompletePartials;
342 return OW_Complete;
343 }
344 }
345
346 // Check for a dead store which writes to all the memory locations that
347 // the killing store writes to.
348 if (EnablePartialStoreMerging && KillingOff >= DeadOff &&
349 int64_t(DeadOff + DeadSize) > KillingOff &&
350 uint64_t(KillingOff - DeadOff) + KillingSize <= DeadSize) {
351 LLVM_DEBUG(dbgs() << "DSE: Partial overwrite a dead load [" << DeadOff
352 << ", " << int64_t(DeadOff + DeadSize)
353 << ") by a killing store [" << KillingOff << ", "
354 << int64_t(KillingOff + KillingSize) << ")\n");
355 // TODO: Maybe come up with a better name?
356 return OW_PartialEarlierWithFullLater;
357 }
358
359 // Another interesting case is if the killing store overwrites the end of the
360 // dead store.
361 //
362 // |--dead--|
363 // |-- killing --|
364 //
365 // In this case we may want to trim the size of dead store to avoid
366 // generating stores to addresses which will definitely be overwritten killing
367 // store.
369 (KillingOff > DeadOff && KillingOff < int64_t(DeadOff + DeadSize) &&
370 int64_t(KillingOff + KillingSize) >= int64_t(DeadOff + DeadSize)))
371 return OW_End;
372
373 // Finally, we also need to check if the killing store overwrites the
374 // beginning of the dead store.
375 //
376 // |--dead--|
377 // |-- killing --|
378 //
379 // In this case we may want to move the destination address and trim the size
380 // of dead store to avoid generating stores to addresses which will definitely
381 // be overwritten killing store.
383 (KillingOff <= DeadOff && int64_t(KillingOff + KillingSize) > DeadOff)) {
384 assert(int64_t(KillingOff + KillingSize) < int64_t(DeadOff + DeadSize) &&
385 "Expect to be handled as OW_Complete");
386 return OW_Begin;
387 }
388 // Otherwise, they don't completely overlap.
389 return OW_Unknown;
390}
391
392/// Returns true if the memory which is accessed by the second instruction is not
393/// modified between the first and the second instruction.
394/// Precondition: Second instruction must be dominated by the first
395/// instruction.
396static bool
398 BatchAAResults &AA, const DataLayout &DL,
399 DominatorTree *DT) {
400 // Do a backwards scan through the CFG from SecondI to FirstI. Look for
401 // instructions which can modify the memory location accessed by SecondI.
402 //
403 // While doing the walk keep track of the address to check. It might be
404 // different in different basic blocks due to PHI translation.
405 using BlockAddressPair = std::pair<BasicBlock *, PHITransAddr>;
407 // Keep track of the address we visited each block with. Bail out if we
408 // visit a block with different addresses.
410
411 BasicBlock::iterator FirstBBI(FirstI);
412 ++FirstBBI;
413 BasicBlock::iterator SecondBBI(SecondI);
414 BasicBlock *FirstBB = FirstI->getParent();
415 BasicBlock *SecondBB = SecondI->getParent();
416 MemoryLocation MemLoc;
417 if (auto *MemSet = dyn_cast<MemSetInst>(SecondI))
418 MemLoc = MemoryLocation::getForDest(MemSet);
419 else
420 MemLoc = MemoryLocation::get(SecondI);
421
422 auto *MemLocPtr = const_cast<Value *>(MemLoc.Ptr);
423
424 // Start checking the SecondBB.
425 WorkList.push_back(
426 std::make_pair(SecondBB, PHITransAddr(MemLocPtr, DL, nullptr)));
427 bool isFirstBlock = true;
428
429 // Check all blocks going backward until we reach the FirstBB.
430 while (!WorkList.empty()) {
431 BlockAddressPair Current = WorkList.pop_back_val();
432 BasicBlock *B = Current.first;
433 PHITransAddr &Addr = Current.second;
434 Value *Ptr = Addr.getAddr();
435
436 // Ignore instructions before FirstI if this is the FirstBB.
437 BasicBlock::iterator BI = (B == FirstBB ? FirstBBI : B->begin());
438
440 if (isFirstBlock) {
441 // Ignore instructions after SecondI if this is the first visit of SecondBB.
442 assert(B == SecondBB && "first block is not the store block");
443 EI = SecondBBI;
444 isFirstBlock = false;
445 } else {
446 // It's not SecondBB or (in case of a loop) the second visit of SecondBB.
447 // In this case we also have to look at instructions after SecondI.
448 EI = B->end();
449 }
450 for (; BI != EI; ++BI) {
451 Instruction *I = &*BI;
452 if (I->mayWriteToMemory() && I != SecondI)
453 if (isModSet(AA.getModRefInfo(I, MemLoc.getWithNewPtr(Ptr))))
454 return false;
455 }
456 if (B != FirstBB) {
457 assert(B != &FirstBB->getParent()->getEntryBlock() &&
458 "Should not hit the entry block because SI must be dominated by LI");
459 for (BasicBlock *Pred : predecessors(B)) {
460 PHITransAddr PredAddr = Addr;
461 if (PredAddr.needsPHITranslationFromBlock(B)) {
462 if (!PredAddr.isPotentiallyPHITranslatable())
463 return false;
464 if (!PredAddr.translateValue(B, Pred, DT, false))
465 return false;
466 }
467 Value *TranslatedPtr = PredAddr.getAddr();
468 auto Inserted = Visited.insert(std::make_pair(Pred, TranslatedPtr));
469 if (!Inserted.second) {
470 // We already visited this block before. If it was with a different
471 // address - bail out!
472 if (TranslatedPtr != Inserted.first->second)
473 return false;
474 // ... otherwise just skip it.
475 continue;
476 }
477 WorkList.push_back(std::make_pair(Pred, PredAddr));
478 }
479 }
480 }
481 return true;
482}
483
484static void shortenAssignment(Instruction *Inst, Value *OriginalDest,
485 uint64_t OldOffsetInBits, uint64_t OldSizeInBits,
486 uint64_t NewSizeInBits, bool IsOverwriteEnd) {
487 const DataLayout &DL = Inst->getModule()->getDataLayout();
488 uint64_t DeadSliceSizeInBits = OldSizeInBits - NewSizeInBits;
489 uint64_t DeadSliceOffsetInBits =
490 OldOffsetInBits + (IsOverwriteEnd ? NewSizeInBits : 0);
491 auto SetDeadFragExpr = [](auto *Assign,
492 DIExpression::FragmentInfo DeadFragment) {
493 // createFragmentExpression expects an offset relative to the existing
494 // fragment offset if there is one.
495 uint64_t RelativeOffset = DeadFragment.OffsetInBits -
496 Assign->getExpression()
497 ->getFragmentInfo()
498 .value_or(DIExpression::FragmentInfo(0, 0))
499 .OffsetInBits;
501 Assign->getExpression(), RelativeOffset, DeadFragment.SizeInBits)) {
502 Assign->setExpression(*NewExpr);
503 return;
504 }
505 // Failed to create a fragment expression for this so discard the value,
506 // making this a kill location.
508 DIExpression::get(Assign->getContext(), std::nullopt),
509 DeadFragment.OffsetInBits, DeadFragment.SizeInBits);
510 Assign->setExpression(Expr);
511 Assign->setKillLocation();
512 };
513
514 // A DIAssignID to use so that the inserted dbg.assign intrinsics do not
515 // link to any instructions. Created in the loop below (once).
516 DIAssignID *LinkToNothing = nullptr;
517 LLVMContext &Ctx = Inst->getContext();
518 auto GetDeadLink = [&Ctx, &LinkToNothing]() {
519 if (!LinkToNothing)
520 LinkToNothing = DIAssignID::getDistinct(Ctx);
521 return LinkToNothing;
522 };
523
524 // Insert an unlinked dbg.assign intrinsic for the dead fragment after each
525 // overlapping dbg.assign intrinsic. The loop invalidates the iterators
526 // returned by getAssignmentMarkers so save a copy of the markers to iterate
527 // over.
528 auto LinkedRange = at::getAssignmentMarkers(Inst);
530 SmallVector<DbgAssignIntrinsic *> Linked(LinkedRange.begin(),
531 LinkedRange.end());
532 auto InsertAssignForOverlap = [&](auto *Assign) {
533 std::optional<DIExpression::FragmentInfo> NewFragment;
534 if (!at::calculateFragmentIntersect(DL, OriginalDest, DeadSliceOffsetInBits,
535 DeadSliceSizeInBits, Assign,
536 NewFragment) ||
537 !NewFragment) {
538 // We couldn't calculate the intersecting fragment for some reason. Be
539 // cautious and unlink the whole assignment from the store.
540 Assign->setKillAddress();
541 Assign->setAssignId(GetDeadLink());
542 return;
543 }
544 // No intersect.
545 if (NewFragment->SizeInBits == 0)
546 return;
547
548 // Fragments overlap: insert a new dbg.assign for this dead part.
549 auto *NewAssign = static_cast<decltype(Assign)>(Assign->clone());
550 NewAssign->insertAfter(Assign);
551 NewAssign->setAssignId(GetDeadLink());
552 if (NewFragment)
553 SetDeadFragExpr(NewAssign, *NewFragment);
554 NewAssign->setKillAddress();
555 };
556 for_each(Linked, InsertAssignForOverlap);
557 for_each(LinkedDPVAssigns, InsertAssignForOverlap);
558}
559
560static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart,
561 uint64_t &DeadSize, int64_t KillingStart,
562 uint64_t KillingSize, bool IsOverwriteEnd) {
563 auto *DeadIntrinsic = cast<AnyMemIntrinsic>(DeadI);
564 Align PrefAlign = DeadIntrinsic->getDestAlign().valueOrOne();
565
566 // We assume that memet/memcpy operates in chunks of the "largest" native
567 // type size and aligned on the same value. That means optimal start and size
568 // of memset/memcpy should be modulo of preferred alignment of that type. That
569 // is it there is no any sense in trying to reduce store size any further
570 // since any "extra" stores comes for free anyway.
571 // On the other hand, maximum alignment we can achieve is limited by alignment
572 // of initial store.
573
574 // TODO: Limit maximum alignment by preferred (or abi?) alignment of the
575 // "largest" native type.
576 // Note: What is the proper way to get that value?
577 // Should TargetTransformInfo::getRegisterBitWidth be used or anything else?
578 // PrefAlign = std::min(DL.getPrefTypeAlign(LargestType), PrefAlign);
579
580 int64_t ToRemoveStart = 0;
581 uint64_t ToRemoveSize = 0;
582 // Compute start and size of the region to remove. Make sure 'PrefAlign' is
583 // maintained on the remaining store.
584 if (IsOverwriteEnd) {
585 // Calculate required adjustment for 'KillingStart' in order to keep
586 // remaining store size aligned on 'PerfAlign'.
587 uint64_t Off =
588 offsetToAlignment(uint64_t(KillingStart - DeadStart), PrefAlign);
589 ToRemoveStart = KillingStart + Off;
590 if (DeadSize <= uint64_t(ToRemoveStart - DeadStart))
591 return false;
592 ToRemoveSize = DeadSize - uint64_t(ToRemoveStart - DeadStart);
593 } else {
594 ToRemoveStart = DeadStart;
595 assert(KillingSize >= uint64_t(DeadStart - KillingStart) &&
596 "Not overlapping accesses?");
597 ToRemoveSize = KillingSize - uint64_t(DeadStart - KillingStart);
598 // Calculate required adjustment for 'ToRemoveSize'in order to keep
599 // start of the remaining store aligned on 'PerfAlign'.
600 uint64_t Off = offsetToAlignment(ToRemoveSize, PrefAlign);
601 if (Off != 0) {
602 if (ToRemoveSize <= (PrefAlign.value() - Off))
603 return false;
604 ToRemoveSize -= PrefAlign.value() - Off;
605 }
606 assert(isAligned(PrefAlign, ToRemoveSize) &&
607 "Should preserve selected alignment");
608 }
609
610 assert(ToRemoveSize > 0 && "Shouldn't reach here if nothing to remove");
611 assert(DeadSize > ToRemoveSize && "Can't remove more than original size");
612
613 uint64_t NewSize = DeadSize - ToRemoveSize;
614 if (auto *AMI = dyn_cast<AtomicMemIntrinsic>(DeadI)) {
615 // When shortening an atomic memory intrinsic, the newly shortened
616 // length must remain an integer multiple of the element size.
617 const uint32_t ElementSize = AMI->getElementSizeInBytes();
618 if (0 != NewSize % ElementSize)
619 return false;
620 }
621
622 LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n OW "
623 << (IsOverwriteEnd ? "END" : "BEGIN") << ": " << *DeadI
624 << "\n KILLER [" << ToRemoveStart << ", "
625 << int64_t(ToRemoveStart + ToRemoveSize) << ")\n");
626
627 Value *DeadWriteLength = DeadIntrinsic->getLength();
628 Value *TrimmedLength = ConstantInt::get(DeadWriteLength->getType(), NewSize);
629 DeadIntrinsic->setLength(TrimmedLength);
630 DeadIntrinsic->setDestAlignment(PrefAlign);
631
632 Value *OrigDest = DeadIntrinsic->getRawDest();
633 if (!IsOverwriteEnd) {
634 Value *Indices[1] = {
635 ConstantInt::get(DeadWriteLength->getType(), ToRemoveSize)};
637 Type::getInt8Ty(DeadIntrinsic->getContext()), OrigDest, Indices, "", DeadI);
638 NewDestGEP->setDebugLoc(DeadIntrinsic->getDebugLoc());
639 DeadIntrinsic->setDest(NewDestGEP);
640 }
641
642 // Update attached dbg.assign intrinsics. Assume 8-bit byte.
643 shortenAssignment(DeadI, OrigDest, DeadStart * 8, DeadSize * 8, NewSize * 8,
644 IsOverwriteEnd);
645
646 // Finally update start and size of dead access.
647 if (!IsOverwriteEnd)
648 DeadStart += ToRemoveSize;
649 DeadSize = NewSize;
650
651 return true;
652}
653
655 int64_t &DeadStart, uint64_t &DeadSize) {
656 if (IntervalMap.empty() || !isShortenableAtTheEnd(DeadI))
657 return false;
658
659 OverlapIntervalsTy::iterator OII = --IntervalMap.end();
660 int64_t KillingStart = OII->second;
661 uint64_t KillingSize = OII->first - KillingStart;
662
663 assert(OII->first - KillingStart >= 0 && "Size expected to be positive");
664
665 if (KillingStart > DeadStart &&
666 // Note: "KillingStart - KillingStart" is known to be positive due to
667 // preceding check.
668 (uint64_t)(KillingStart - DeadStart) < DeadSize &&
669 // Note: "DeadSize - (uint64_t)(KillingStart - DeadStart)" is known to
670 // be non negative due to preceding checks.
671 KillingSize >= DeadSize - (uint64_t)(KillingStart - DeadStart)) {
672 if (tryToShorten(DeadI, DeadStart, DeadSize, KillingStart, KillingSize,
673 true)) {
674 IntervalMap.erase(OII);
675 return true;
676 }
677 }
678 return false;
679}
680
683 int64_t &DeadStart, uint64_t &DeadSize) {
685 return false;
686
687 OverlapIntervalsTy::iterator OII = IntervalMap.begin();
688 int64_t KillingStart = OII->second;
689 uint64_t KillingSize = OII->first - KillingStart;
690
691 assert(OII->first - KillingStart >= 0 && "Size expected to be positive");
692
693 if (KillingStart <= DeadStart &&
694 // Note: "DeadStart - KillingStart" is known to be non negative due to
695 // preceding check.
696 KillingSize > (uint64_t)(DeadStart - KillingStart)) {
697 // Note: "KillingSize - (uint64_t)(DeadStart - DeadStart)" is known to
698 // be positive due to preceding checks.
699 assert(KillingSize - (uint64_t)(DeadStart - KillingStart) < DeadSize &&
700 "Should have been handled as OW_Complete");
701 if (tryToShorten(DeadI, DeadStart, DeadSize, KillingStart, KillingSize,
702 false)) {
703 IntervalMap.erase(OII);
704 return true;
705 }
706 }
707 return false;
708}
709
710static Constant *
712 int64_t KillingOffset, int64_t DeadOffset,
713 const DataLayout &DL, BatchAAResults &AA,
714 DominatorTree *DT) {
715
716 if (DeadI && isa<ConstantInt>(DeadI->getValueOperand()) &&
717 DL.typeSizeEqualsStoreSize(DeadI->getValueOperand()->getType()) &&
718 KillingI && isa<ConstantInt>(KillingI->getValueOperand()) &&
719 DL.typeSizeEqualsStoreSize(KillingI->getValueOperand()->getType()) &&
720 memoryIsNotModifiedBetween(DeadI, KillingI, AA, DL, DT)) {
721 // If the store we find is:
722 // a) partially overwritten by the store to 'Loc'
723 // b) the killing store is fully contained in the dead one and
724 // c) they both have a constant value
725 // d) none of the two stores need padding
726 // Merge the two stores, replacing the dead store's value with a
727 // merge of both values.
728 // TODO: Deal with other constant types (vectors, etc), and probably
729 // some mem intrinsics (if needed)
730
731 APInt DeadValue = cast<ConstantInt>(DeadI->getValueOperand())->getValue();
732 APInt KillingValue =
733 cast<ConstantInt>(KillingI->getValueOperand())->getValue();
734 unsigned KillingBits = KillingValue.getBitWidth();
735 assert(DeadValue.getBitWidth() > KillingValue.getBitWidth());
736 KillingValue = KillingValue.zext(DeadValue.getBitWidth());
737
738 // Offset of the smaller store inside the larger store
739 unsigned BitOffsetDiff = (KillingOffset - DeadOffset) * 8;
740 unsigned LShiftAmount =
741 DL.isBigEndian() ? DeadValue.getBitWidth() - BitOffsetDiff - KillingBits
742 : BitOffsetDiff;
743 APInt Mask = APInt::getBitsSet(DeadValue.getBitWidth(), LShiftAmount,
744 LShiftAmount + KillingBits);
745 // Clear the bits we'll be replacing, then OR with the smaller
746 // store, shifted appropriately.
747 APInt Merged = (DeadValue & ~Mask) | (KillingValue << LShiftAmount);
748 LLVM_DEBUG(dbgs() << "DSE: Merge Stores:\n Dead: " << *DeadI
749 << "\n Killing: " << *KillingI
750 << "\n Merged Value: " << Merged << '\n');
751 return ConstantInt::get(DeadI->getValueOperand()->getType(), Merged);
752 }
753 return nullptr;
754}
755
756namespace {
757// Returns true if \p I is an intrinsic that does not read or write memory.
758bool isNoopIntrinsic(Instruction *I) {
759 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
760 switch (II->getIntrinsicID()) {
761 case Intrinsic::lifetime_start:
762 case Intrinsic::lifetime_end:
763 case Intrinsic::invariant_end:
764 case Intrinsic::launder_invariant_group:
765 case Intrinsic::assume:
766 return true;
767 case Intrinsic::dbg_declare:
768 case Intrinsic::dbg_label:
769 case Intrinsic::dbg_value:
770 llvm_unreachable("Intrinsic should not be modeled in MemorySSA");
771 default:
772 return false;
773 }
774 }
775 return false;
776}
777
778// Check if we can ignore \p D for DSE.
779bool canSkipDef(MemoryDef *D, bool DefVisibleToCaller) {
780 Instruction *DI = D->getMemoryInst();
781 // Calls that only access inaccessible memory cannot read or write any memory
782 // locations we consider for elimination.
783 if (auto *CB = dyn_cast<CallBase>(DI))
784 if (CB->onlyAccessesInaccessibleMemory())
785 return true;
786
787 // We can eliminate stores to locations not visible to the caller across
788 // throwing instructions.
789 if (DI->mayThrow() && !DefVisibleToCaller)
790 return true;
791
792 // We can remove the dead stores, irrespective of the fence and its ordering
793 // (release/acquire/seq_cst). Fences only constraints the ordering of
794 // already visible stores, it does not make a store visible to other
795 // threads. So, skipping over a fence does not change a store from being
796 // dead.
797 if (isa<FenceInst>(DI))
798 return true;
799
800 // Skip intrinsics that do not really read or modify memory.
801 if (isNoopIntrinsic(DI))
802 return true;
803
804 return false;
805}
806
807struct DSEState {
808 Function &F;
809 AliasAnalysis &AA;
811
812 /// The single BatchAA instance that is used to cache AA queries. It will
813 /// not be invalidated over the whole run. This is safe, because:
814 /// 1. Only memory writes are removed, so the alias cache for memory
815 /// locations remains valid.
816 /// 2. No new instructions are added (only instructions removed), so cached
817 /// information for a deleted value cannot be accessed by a re-used new
818 /// value pointer.
819 BatchAAResults BatchAA;
820
821 MemorySSA &MSSA;
822 DominatorTree &DT;
824 const TargetLibraryInfo &TLI;
825 const DataLayout &DL;
826 const LoopInfo &LI;
827
828 // Whether the function contains any irreducible control flow, useful for
829 // being accurately able to detect loops.
830 bool ContainsIrreducibleLoops;
831
832 // All MemoryDefs that potentially could kill other MemDefs.
834 // Any that should be skipped as they are already deleted
836 // Keep track whether a given object is captured before return or not.
837 DenseMap<const Value *, bool> CapturedBeforeReturn;
838 // Keep track of all of the objects that are invisible to the caller after
839 // the function returns.
840 DenseMap<const Value *, bool> InvisibleToCallerAfterRet;
841 // Keep track of blocks with throwing instructions not modeled in MemorySSA.
842 SmallPtrSet<BasicBlock *, 16> ThrowingBlocks;
843 // Post-order numbers for each basic block. Used to figure out if memory
844 // accesses are executed before another access.
845 DenseMap<BasicBlock *, unsigned> PostOrderNumbers;
846
847 /// Keep track of instructions (partly) overlapping with killing MemoryDefs per
848 /// basic block.
850 // Check if there are root nodes that are terminated by UnreachableInst.
851 // Those roots pessimize post-dominance queries. If there are such roots,
852 // fall back to CFG scan starting from all non-unreachable roots.
853 bool AnyUnreachableExit;
854
855 // Whether or not we should iterate on removing dead stores at the end of the
856 // function due to removing a store causing a previously captured pointer to
857 // no longer be captured.
858 bool ShouldIterateEndOfFunctionDSE;
859
860 // Class contains self-reference, make sure it's not copied/moved.
861 DSEState(const DSEState &) = delete;
862 DSEState &operator=(const DSEState &) = delete;
863
864 DSEState(Function &F, AliasAnalysis &AA, MemorySSA &MSSA, DominatorTree &DT,
865 PostDominatorTree &PDT, const TargetLibraryInfo &TLI,
866 const LoopInfo &LI)
867 : F(F), AA(AA), EI(DT, &LI), BatchAA(AA, &EI), MSSA(MSSA), DT(DT),
868 PDT(PDT), TLI(TLI), DL(F.getParent()->getDataLayout()), LI(LI) {
869 // Collect blocks with throwing instructions not modeled in MemorySSA and
870 // alloc-like objects.
871 unsigned PO = 0;
872 for (BasicBlock *BB : post_order(&F)) {
873 PostOrderNumbers[BB] = PO++;
874 for (Instruction &I : *BB) {
875 MemoryAccess *MA = MSSA.getMemoryAccess(&I);
876 if (I.mayThrow() && !MA)
877 ThrowingBlocks.insert(I.getParent());
878
879 auto *MD = dyn_cast_or_null<MemoryDef>(MA);
880 if (MD && MemDefs.size() < MemorySSADefsPerBlockLimit &&
881 (getLocForWrite(&I) || isMemTerminatorInst(&I)))
882 MemDefs.push_back(MD);
883 }
884 }
885
886 // Treat byval or inalloca arguments the same as Allocas, stores to them are
887 // dead at the end of the function.
888 for (Argument &AI : F.args())
889 if (AI.hasPassPointeeByValueCopyAttr())
890 InvisibleToCallerAfterRet.insert({&AI, true});
891
892 // Collect whether there is any irreducible control flow in the function.
893 ContainsIrreducibleLoops = mayContainIrreducibleControl(F, &LI);
894
895 AnyUnreachableExit = any_of(PDT.roots(), [](const BasicBlock *E) {
896 return isa<UnreachableInst>(E->getTerminator());
897 });
898 }
899
900 LocationSize strengthenLocationSize(const Instruction *I,
901 LocationSize Size) const {
902 if (auto *CB = dyn_cast<CallBase>(I)) {
903 LibFunc F;
904 if (TLI.getLibFunc(*CB, F) && TLI.has(F) &&
905 (F == LibFunc_memset_chk || F == LibFunc_memcpy_chk)) {
906 // Use the precise location size specified by the 3rd argument
907 // for determining KillingI overwrites DeadLoc if it is a memset_chk
908 // instruction. memset_chk will write either the amount specified as 3rd
909 // argument or the function will immediately abort and exit the program.
910 // NOTE: AA may determine NoAlias if it can prove that the access size
911 // is larger than the allocation size due to that being UB. To avoid
912 // returning potentially invalid NoAlias results by AA, limit the use of
913 // the precise location size to isOverwrite.
914 if (const auto *Len = dyn_cast<ConstantInt>(CB->getArgOperand(2)))
915 return LocationSize::precise(Len->getZExtValue());
916 }
917 }
918 return Size;
919 }
920
921 /// Return 'OW_Complete' if a store to the 'KillingLoc' location (by \p
922 /// KillingI instruction) completely overwrites a store to the 'DeadLoc'
923 /// location (by \p DeadI instruction).
924 /// Return OW_MaybePartial if \p KillingI does not completely overwrite
925 /// \p DeadI, but they both write to the same underlying object. In that
926 /// case, use isPartialOverwrite to check if \p KillingI partially overwrites
927 /// \p DeadI. Returns 'OR_None' if \p KillingI is known to not overwrite the
928 /// \p DeadI. Returns 'OW_Unknown' if nothing can be determined.
929 OverwriteResult isOverwrite(const Instruction *KillingI,
930 const Instruction *DeadI,
931 const MemoryLocation &KillingLoc,
932 const MemoryLocation &DeadLoc,
933 int64_t &KillingOff, int64_t &DeadOff) {
934 // AliasAnalysis does not always account for loops. Limit overwrite checks
935 // to dependencies for which we can guarantee they are independent of any
936 // loops they are in.
937 if (!isGuaranteedLoopIndependent(DeadI, KillingI, DeadLoc))
938 return OW_Unknown;
939
940 LocationSize KillingLocSize =
941 strengthenLocationSize(KillingI, KillingLoc.Size);
942 const Value *DeadPtr = DeadLoc.Ptr->stripPointerCasts();
943 const Value *KillingPtr = KillingLoc.Ptr->stripPointerCasts();
944 const Value *DeadUndObj = getUnderlyingObject(DeadPtr);
945 const Value *KillingUndObj = getUnderlyingObject(KillingPtr);
946
947 // Check whether the killing store overwrites the whole object, in which
948 // case the size/offset of the dead store does not matter.
949 if (DeadUndObj == KillingUndObj && KillingLocSize.isPrecise() &&
950 isIdentifiedObject(KillingUndObj)) {
951 std::optional<TypeSize> KillingUndObjSize =
952 getPointerSize(KillingUndObj, DL, TLI, &F);
953 if (KillingUndObjSize && *KillingUndObjSize == KillingLocSize.getValue())
954 return OW_Complete;
955 }
956
957 // FIXME: Vet that this works for size upper-bounds. Seems unlikely that we'll
958 // get imprecise values here, though (except for unknown sizes).
959 if (!KillingLocSize.isPrecise() || !DeadLoc.Size.isPrecise()) {
960 // In case no constant size is known, try to an IR values for the number
961 // of bytes written and check if they match.
962 const auto *KillingMemI = dyn_cast<MemIntrinsic>(KillingI);
963 const auto *DeadMemI = dyn_cast<MemIntrinsic>(DeadI);
964 if (KillingMemI && DeadMemI) {
965 const Value *KillingV = KillingMemI->getLength();
966 const Value *DeadV = DeadMemI->getLength();
967 if (KillingV == DeadV && BatchAA.isMustAlias(DeadLoc, KillingLoc))
968 return OW_Complete;
969 }
970
971 // Masked stores have imprecise locations, but we can reason about them
972 // to some extent.
973 return isMaskedStoreOverwrite(KillingI, DeadI, BatchAA);
974 }
975
976 const TypeSize KillingSize = KillingLocSize.getValue();
977 const TypeSize DeadSize = DeadLoc.Size.getValue();
978 // Bail on doing Size comparison which depends on AA for now
979 // TODO: Remove AnyScalable once Alias Analysis deal with scalable vectors
980 const bool AnyScalable =
981 DeadSize.isScalable() || KillingLocSize.isScalable();
982
983 if (AnyScalable)
984 return OW_Unknown;
985 // Query the alias information
986 AliasResult AAR = BatchAA.alias(KillingLoc, DeadLoc);
987
988 // If the start pointers are the same, we just have to compare sizes to see if
989 // the killing store was larger than the dead store.
990 if (AAR == AliasResult::MustAlias) {
991 // Make sure that the KillingSize size is >= the DeadSize size.
992 if (KillingSize >= DeadSize)
993 return OW_Complete;
994 }
995
996 // If we hit a partial alias we may have a full overwrite
997 if (AAR == AliasResult::PartialAlias && AAR.hasOffset()) {
998 int32_t Off = AAR.getOffset();
999 if (Off >= 0 && (uint64_t)Off + DeadSize <= KillingSize)
1000 return OW_Complete;
1001 }
1002
1003 // If we can't resolve the same pointers to the same object, then we can't
1004 // analyze them at all.
1005 if (DeadUndObj != KillingUndObj) {
1006 // Non aliasing stores to different objects don't overlap. Note that
1007 // if the killing store is known to overwrite whole object (out of
1008 // bounds access overwrites whole object as well) then it is assumed to
1009 // completely overwrite any store to the same object even if they don't
1010 // actually alias (see next check).
1011 if (AAR == AliasResult::NoAlias)
1012 return OW_None;
1013 return OW_Unknown;
1014 }
1015
1016 // Okay, we have stores to two completely different pointers. Try to
1017 // decompose the pointer into a "base + constant_offset" form. If the base
1018 // pointers are equal, then we can reason about the two stores.
1019 DeadOff = 0;
1020 KillingOff = 0;
1021 const Value *DeadBasePtr =
1022 GetPointerBaseWithConstantOffset(DeadPtr, DeadOff, DL);
1023 const Value *KillingBasePtr =
1024 GetPointerBaseWithConstantOffset(KillingPtr, KillingOff, DL);
1025
1026 // If the base pointers still differ, we have two completely different
1027 // stores.
1028 if (DeadBasePtr != KillingBasePtr)
1029 return OW_Unknown;
1030
1031 // The killing access completely overlaps the dead store if and only if
1032 // both start and end of the dead one is "inside" the killing one:
1033 // |<->|--dead--|<->|
1034 // |-----killing------|
1035 // Accesses may overlap if and only if start of one of them is "inside"
1036 // another one:
1037 // |<->|--dead--|<-------->|
1038 // |-------killing--------|
1039 // OR
1040 // |-------dead-------|
1041 // |<->|---killing---|<----->|
1042 //
1043 // We have to be careful here as *Off is signed while *.Size is unsigned.
1044
1045 // Check if the dead access starts "not before" the killing one.
1046 if (DeadOff >= KillingOff) {
1047 // If the dead access ends "not after" the killing access then the
1048 // dead one is completely overwritten by the killing one.
1049 if (uint64_t(DeadOff - KillingOff) + DeadSize <= KillingSize)
1050 return OW_Complete;
1051 // If start of the dead access is "before" end of the killing access
1052 // then accesses overlap.
1053 else if ((uint64_t)(DeadOff - KillingOff) < KillingSize)
1054 return OW_MaybePartial;
1055 }
1056 // If start of the killing access is "before" end of the dead access then
1057 // accesses overlap.
1058 else if ((uint64_t)(KillingOff - DeadOff) < DeadSize) {
1059 return OW_MaybePartial;
1060 }
1061
1062 // Can reach here only if accesses are known not to overlap.
1063 return OW_None;
1064 }
1065
1066 bool isInvisibleToCallerAfterRet(const Value *V) {
1067 if (isa<AllocaInst>(V))
1068 return true;
1069 auto I = InvisibleToCallerAfterRet.insert({V, false});
1070 if (I.second) {
1071 if (!isInvisibleToCallerOnUnwind(V)) {
1072 I.first->second = false;
1073 } else if (isNoAliasCall(V)) {
1074 I.first->second = !PointerMayBeCaptured(V, true, false);
1075 }
1076 }
1077 return I.first->second;
1078 }
1079
1080 bool isInvisibleToCallerOnUnwind(const Value *V) {
1081 bool RequiresNoCaptureBeforeUnwind;
1082 if (!isNotVisibleOnUnwind(V, RequiresNoCaptureBeforeUnwind))
1083 return false;
1084 if (!RequiresNoCaptureBeforeUnwind)
1085 return true;
1086
1087 auto I = CapturedBeforeReturn.insert({V, true});
1088 if (I.second)
1089 // NOTE: This could be made more precise by PointerMayBeCapturedBefore
1090 // with the killing MemoryDef. But we refrain from doing so for now to
1091 // limit compile-time and this does not cause any changes to the number
1092 // of stores removed on a large test set in practice.
1093 I.first->second = PointerMayBeCaptured(V, false, true);
1094 return !I.first->second;
1095 }
1096
1097 std::optional<MemoryLocation> getLocForWrite(Instruction *I) const {
1098 if (!I->mayWriteToMemory())
1099 return std::nullopt;
1100
1101 if (auto *CB = dyn_cast<CallBase>(I))
1102 return MemoryLocation::getForDest(CB, TLI);
1103
1105 }
1106
1107 /// Assuming this instruction has a dead analyzable write, can we delete
1108 /// this instruction?
1109 bool isRemovable(Instruction *I) {
1110 assert(getLocForWrite(I) && "Must have analyzable write");
1111
1112 // Don't remove volatile/atomic stores.
1113 if (StoreInst *SI = dyn_cast<StoreInst>(I))
1114 return SI->isUnordered();
1115
1116 if (auto *CB = dyn_cast<CallBase>(I)) {
1117 // Don't remove volatile memory intrinsics.
1118 if (auto *MI = dyn_cast<MemIntrinsic>(CB))
1119 return !MI->isVolatile();
1120
1121 // Never remove dead lifetime intrinsics, e.g. because they are followed
1122 // by a free.
1123 if (CB->isLifetimeStartOrEnd())
1124 return false;
1125
1126 return CB->use_empty() && CB->willReturn() && CB->doesNotThrow() &&
1127 !CB->isTerminator();
1128 }
1129
1130 return false;
1131 }
1132
1133 /// Returns true if \p UseInst completely overwrites \p DefLoc
1134 /// (stored by \p DefInst).
1135 bool isCompleteOverwrite(const MemoryLocation &DefLoc, Instruction *DefInst,
1136 Instruction *UseInst) {
1137 // UseInst has a MemoryDef associated in MemorySSA. It's possible for a
1138 // MemoryDef to not write to memory, e.g. a volatile load is modeled as a
1139 // MemoryDef.
1140 if (!UseInst->mayWriteToMemory())
1141 return false;
1142
1143 if (auto *CB = dyn_cast<CallBase>(UseInst))
1144 if (CB->onlyAccessesInaccessibleMemory())
1145 return false;
1146
1147 int64_t InstWriteOffset, DepWriteOffset;
1148 if (auto CC = getLocForWrite(UseInst))
1149 return isOverwrite(UseInst, DefInst, *CC, DefLoc, InstWriteOffset,
1150 DepWriteOffset) == OW_Complete;
1151 return false;
1152 }
1153
1154 /// Returns true if \p Def is not read before returning from the function.
1155 bool isWriteAtEndOfFunction(MemoryDef *Def) {
1156 LLVM_DEBUG(dbgs() << " Check if def " << *Def << " ("
1157 << *Def->getMemoryInst()
1158 << ") is at the end the function \n");
1159
1160 auto MaybeLoc = getLocForWrite(Def->getMemoryInst());
1161 if (!MaybeLoc) {
1162 LLVM_DEBUG(dbgs() << " ... could not get location for write.\n");
1163 return false;
1164 }
1165
1168 auto PushMemUses = [&WorkList, &Visited](MemoryAccess *Acc) {
1169 if (!Visited.insert(Acc).second)
1170 return;
1171 for (Use &U : Acc->uses())
1172 WorkList.push_back(cast<MemoryAccess>(U.getUser()));
1173 };
1174 PushMemUses(Def);
1175 for (unsigned I = 0; I < WorkList.size(); I++) {
1176 if (WorkList.size() >= MemorySSAScanLimit) {
1177 LLVM_DEBUG(dbgs() << " ... hit exploration limit.\n");
1178 return false;
1179 }
1180
1181 MemoryAccess *UseAccess = WorkList[I];
1182 if (isa<MemoryPhi>(UseAccess)) {
1183 // AliasAnalysis does not account for loops. Limit elimination to
1184 // candidates for which we can guarantee they always store to the same
1185 // memory location.
1186 if (!isGuaranteedLoopInvariant(MaybeLoc->Ptr))
1187 return false;
1188
1189 PushMemUses(cast<MemoryPhi>(UseAccess));
1190 continue;
1191 }
1192 // TODO: Checking for aliasing is expensive. Consider reducing the amount
1193 // of times this is called and/or caching it.
1194 Instruction *UseInst = cast<MemoryUseOrDef>(UseAccess)->getMemoryInst();
1195 if (isReadClobber(*MaybeLoc, UseInst)) {
1196 LLVM_DEBUG(dbgs() << " ... hit read clobber " << *UseInst << ".\n");
1197 return false;
1198 }
1199
1200 if (MemoryDef *UseDef = dyn_cast<MemoryDef>(UseAccess))
1201 PushMemUses(UseDef);
1202 }
1203 return true;
1204 }
1205
1206 /// If \p I is a memory terminator like llvm.lifetime.end or free, return a
1207 /// pair with the MemoryLocation terminated by \p I and a boolean flag
1208 /// indicating whether \p I is a free-like call.
1209 std::optional<std::pair<MemoryLocation, bool>>
1210 getLocForTerminator(Instruction *I) const {
1211 uint64_t Len;
1212 Value *Ptr;
1213 if (match(I, m_Intrinsic<Intrinsic::lifetime_end>(m_ConstantInt(Len),
1214 m_Value(Ptr))))
1215 return {std::make_pair(MemoryLocation(Ptr, Len), false)};
1216
1217 if (auto *CB = dyn_cast<CallBase>(I)) {
1218 if (Value *FreedOp = getFreedOperand(CB, &TLI))
1219 return {std::make_pair(MemoryLocation::getAfter(FreedOp), true)};
1220 }
1221
1222 return std::nullopt;
1223 }
1224
1225 /// Returns true if \p I is a memory terminator instruction like
1226 /// llvm.lifetime.end or free.
1227 bool isMemTerminatorInst(Instruction *I) const {
1228 auto *CB = dyn_cast<CallBase>(I);
1229 return CB && (CB->getIntrinsicID() == Intrinsic::lifetime_end ||
1230 getFreedOperand(CB, &TLI) != nullptr);
1231 }
1232
1233 /// Returns true if \p MaybeTerm is a memory terminator for \p Loc from
1234 /// instruction \p AccessI.
1235 bool isMemTerminator(const MemoryLocation &Loc, Instruction *AccessI,
1236 Instruction *MaybeTerm) {
1237 std::optional<std::pair<MemoryLocation, bool>> MaybeTermLoc =
1238 getLocForTerminator(MaybeTerm);
1239
1240 if (!MaybeTermLoc)
1241 return false;
1242
1243 // If the terminator is a free-like call, all accesses to the underlying
1244 // object can be considered terminated.
1245 if (getUnderlyingObject(Loc.Ptr) !=
1246 getUnderlyingObject(MaybeTermLoc->first.Ptr))
1247 return false;
1248
1249 auto TermLoc = MaybeTermLoc->first;
1250 if (MaybeTermLoc->second) {
1251 const Value *LocUO = getUnderlyingObject(Loc.Ptr);
1252 return BatchAA.isMustAlias(TermLoc.Ptr, LocUO);
1253 }
1254 int64_t InstWriteOffset = 0;
1255 int64_t DepWriteOffset = 0;
1256 return isOverwrite(MaybeTerm, AccessI, TermLoc, Loc, InstWriteOffset,
1257 DepWriteOffset) == OW_Complete;
1258 }
1259
1260 // Returns true if \p Use may read from \p DefLoc.
1261 bool isReadClobber(const MemoryLocation &DefLoc, Instruction *UseInst) {
1262 if (isNoopIntrinsic(UseInst))
1263 return false;
1264
1265 // Monotonic or weaker atomic stores can be re-ordered and do not need to be
1266 // treated as read clobber.
1267 if (auto SI = dyn_cast<StoreInst>(UseInst))
1268 return isStrongerThan(SI->getOrdering(), AtomicOrdering::Monotonic);
1269
1270 if (!UseInst->mayReadFromMemory())
1271 return false;
1272
1273 if (auto *CB = dyn_cast<CallBase>(UseInst))
1274 if (CB->onlyAccessesInaccessibleMemory())
1275 return false;
1276
1277 return isRefSet(BatchAA.getModRefInfo(UseInst, DefLoc));
1278 }
1279
1280 /// Returns true if a dependency between \p Current and \p KillingDef is
1281 /// guaranteed to be loop invariant for the loops that they are in. Either
1282 /// because they are known to be in the same block, in the same loop level or
1283 /// by guaranteeing that \p CurrentLoc only references a single MemoryLocation
1284 /// during execution of the containing function.
1285 bool isGuaranteedLoopIndependent(const Instruction *Current,
1286 const Instruction *KillingDef,
1287 const MemoryLocation &CurrentLoc) {
1288 // If the dependency is within the same block or loop level (being careful
1289 // of irreducible loops), we know that AA will return a valid result for the
1290 // memory dependency. (Both at the function level, outside of any loop,
1291 // would also be valid but we currently disable that to limit compile time).
1292 if (Current->getParent() == KillingDef->getParent())
1293 return true;
1294 const Loop *CurrentLI = LI.getLoopFor(Current->getParent());
1295 if (!ContainsIrreducibleLoops && CurrentLI &&
1296 CurrentLI == LI.getLoopFor(KillingDef->getParent()))
1297 return true;
1298 // Otherwise check the memory location is invariant to any loops.
1299 return isGuaranteedLoopInvariant(CurrentLoc.Ptr);
1300 }
1301
1302 /// Returns true if \p Ptr is guaranteed to be loop invariant for any possible
1303 /// loop. In particular, this guarantees that it only references a single
1304 /// MemoryLocation during execution of the containing function.
1305 bool isGuaranteedLoopInvariant(const Value *Ptr) {
1306 Ptr = Ptr->stripPointerCasts();
1307 if (auto *GEP = dyn_cast<GEPOperator>(Ptr))
1308 if (GEP->hasAllConstantIndices())
1309 Ptr = GEP->getPointerOperand()->stripPointerCasts();
1310
1311 if (auto *I = dyn_cast<Instruction>(Ptr)) {
1312 return I->getParent()->isEntryBlock() ||
1313 (!ContainsIrreducibleLoops && !LI.getLoopFor(I->getParent()));
1314 }
1315 return true;
1316 }
1317
1318 // Find a MemoryDef writing to \p KillingLoc and dominating \p StartAccess,
1319 // with no read access between them or on any other path to a function exit
1320 // block if \p KillingLoc is not accessible after the function returns. If
1321 // there is no such MemoryDef, return std::nullopt. The returned value may not
1322 // (completely) overwrite \p KillingLoc. Currently we bail out when we
1323 // encounter an aliasing MemoryUse (read).
1324 std::optional<MemoryAccess *>
1325 getDomMemoryDef(MemoryDef *KillingDef, MemoryAccess *StartAccess,
1326 const MemoryLocation &KillingLoc, const Value *KillingUndObj,
1327 unsigned &ScanLimit, unsigned &WalkerStepLimit,
1328 bool IsMemTerm, unsigned &PartialLimit) {
1329 if (ScanLimit == 0 || WalkerStepLimit == 0) {
1330 LLVM_DEBUG(dbgs() << "\n ... hit scan limit\n");
1331 return std::nullopt;
1332 }
1333
1334 MemoryAccess *Current = StartAccess;
1335 Instruction *KillingI = KillingDef->getMemoryInst();
1336 LLVM_DEBUG(dbgs() << " trying to get dominating access\n");
1337
1338 // Only optimize defining access of KillingDef when directly starting at its
1339 // defining access. The defining access also must only access KillingLoc. At
1340 // the moment we only support instructions with a single write location, so
1341 // it should be sufficient to disable optimizations for instructions that
1342 // also read from memory.
1343 bool CanOptimize = OptimizeMemorySSA &&
1344 KillingDef->getDefiningAccess() == StartAccess &&
1345 !KillingI->mayReadFromMemory();
1346
1347 // Find the next clobbering Mod access for DefLoc, starting at StartAccess.
1348 std::optional<MemoryLocation> CurrentLoc;
1349 for (;; Current = cast<MemoryDef>(Current)->getDefiningAccess()) {
1350 LLVM_DEBUG({
1351 dbgs() << " visiting " << *Current;
1352 if (!MSSA.isLiveOnEntryDef(Current) && isa<MemoryUseOrDef>(Current))
1353 dbgs() << " (" << *cast<MemoryUseOrDef>(Current)->getMemoryInst()
1354 << ")";
1355 dbgs() << "\n";
1356 });
1357
1358 // Reached TOP.
1359 if (MSSA.isLiveOnEntryDef(Current)) {
1360 LLVM_DEBUG(dbgs() << " ... found LiveOnEntryDef\n");
1361 if (CanOptimize && Current != KillingDef->getDefiningAccess())
1362 // The first clobbering def is... none.
1363 KillingDef->setOptimized(Current);
1364 return std::nullopt;
1365 }
1366
1367 // Cost of a step. Accesses in the same block are more likely to be valid
1368 // candidates for elimination, hence consider them cheaper.
1369 unsigned StepCost = KillingDef->getBlock() == Current->getBlock()
1372 if (WalkerStepLimit <= StepCost) {
1373 LLVM_DEBUG(dbgs() << " ... hit walker step limit\n");
1374 return std::nullopt;
1375 }
1376 WalkerStepLimit -= StepCost;
1377
1378 // Return for MemoryPhis. They cannot be eliminated directly and the
1379 // caller is responsible for traversing them.
1380 if (isa<MemoryPhi>(Current)) {
1381 LLVM_DEBUG(dbgs() << " ... found MemoryPhi\n");
1382 return Current;
1383 }
1384
1385 // Below, check if CurrentDef is a valid candidate to be eliminated by
1386 // KillingDef. If it is not, check the next candidate.
1387 MemoryDef *CurrentDef = cast<MemoryDef>(Current);
1388 Instruction *CurrentI = CurrentDef->getMemoryInst();
1389
1390 if (canSkipDef(CurrentDef, !isInvisibleToCallerOnUnwind(KillingUndObj))) {
1391 CanOptimize = false;
1392 continue;
1393 }
1394
1395 // Before we try to remove anything, check for any extra throwing
1396 // instructions that block us from DSEing
1397 if (mayThrowBetween(KillingI, CurrentI, KillingUndObj)) {
1398 LLVM_DEBUG(dbgs() << " ... skip, may throw!\n");
1399 return std::nullopt;
1400 }
1401
1402 // Check for anything that looks like it will be a barrier to further
1403 // removal
1404 if (isDSEBarrier(KillingUndObj, CurrentI)) {
1405 LLVM_DEBUG(dbgs() << " ... skip, barrier\n");
1406 return std::nullopt;
1407 }
1408
1409 // If Current is known to be on path that reads DefLoc or is a read
1410 // clobber, bail out, as the path is not profitable. We skip this check
1411 // for intrinsic calls, because the code knows how to handle memcpy
1412 // intrinsics.
1413 if (!isa<IntrinsicInst>(CurrentI) && isReadClobber(KillingLoc, CurrentI))
1414 return std::nullopt;
1415
1416 // Quick check if there are direct uses that are read-clobbers.
1417 if (any_of(Current->uses(), [this, &KillingLoc, StartAccess](Use &U) {
1418 if (auto *UseOrDef = dyn_cast<MemoryUseOrDef>(U.getUser()))
1419 return !MSSA.dominates(StartAccess, UseOrDef) &&
1420 isReadClobber(KillingLoc, UseOrDef->getMemoryInst());
1421 return false;
1422 })) {
1423 LLVM_DEBUG(dbgs() << " ... found a read clobber\n");
1424 return std::nullopt;
1425 }
1426
1427 // If Current does not have an analyzable write location or is not
1428 // removable, skip it.
1429 CurrentLoc = getLocForWrite(CurrentI);
1430 if (!CurrentLoc || !isRemovable(CurrentI)) {
1431 CanOptimize = false;
1432 continue;
1433 }
1434
1435 // AliasAnalysis does not account for loops. Limit elimination to
1436 // candidates for which we can guarantee they always store to the same
1437 // memory location and not located in different loops.
1438 if (!isGuaranteedLoopIndependent(CurrentI, KillingI, *CurrentLoc)) {
1439 LLVM_DEBUG(dbgs() << " ... not guaranteed loop independent\n");
1440 CanOptimize = false;
1441 continue;
1442 }
1443
1444 if (IsMemTerm) {
1445 // If the killing def is a memory terminator (e.g. lifetime.end), check
1446 // the next candidate if the current Current does not write the same
1447 // underlying object as the terminator.
1448 if (!isMemTerminator(*CurrentLoc, CurrentI, KillingI)) {
1449 CanOptimize = false;
1450 continue;
1451 }
1452 } else {
1453 int64_t KillingOffset = 0;
1454 int64_t DeadOffset = 0;
1455 auto OR = isOverwrite(KillingI, CurrentI, KillingLoc, *CurrentLoc,
1456 KillingOffset, DeadOffset);
1457 if (CanOptimize) {
1458 // CurrentDef is the earliest write clobber of KillingDef. Use it as
1459 // optimized access. Do not optimize if CurrentDef is already the
1460 // defining access of KillingDef.
1461 if (CurrentDef != KillingDef->getDefiningAccess() &&
1462 (OR == OW_Complete || OR == OW_MaybePartial))
1463 KillingDef->setOptimized(CurrentDef);
1464
1465 // Once a may-aliasing def is encountered do not set an optimized
1466 // access.
1467 if (OR != OW_None)
1468 CanOptimize = false;
1469 }
1470
1471 // If Current does not write to the same object as KillingDef, check
1472 // the next candidate.
1473 if (OR == OW_Unknown || OR == OW_None)
1474 continue;
1475 else if (OR == OW_MaybePartial) {
1476 // If KillingDef only partially overwrites Current, check the next
1477 // candidate if the partial step limit is exceeded. This aggressively
1478 // limits the number of candidates for partial store elimination,
1479 // which are less likely to be removable in the end.
1480 if (PartialLimit <= 1) {
1481 WalkerStepLimit -= 1;
1482 LLVM_DEBUG(dbgs() << " ... reached partial limit ... continue with next access\n");
1483 continue;
1484 }
1485 PartialLimit -= 1;
1486 }
1487 }
1488 break;
1489 };
1490
1491 // Accesses to objects accessible after the function returns can only be
1492 // eliminated if the access is dead along all paths to the exit. Collect
1493 // the blocks with killing (=completely overwriting MemoryDefs) and check if
1494 // they cover all paths from MaybeDeadAccess to any function exit.
1496 KillingDefs.insert(KillingDef->getMemoryInst());
1497 MemoryAccess *MaybeDeadAccess = Current;
1498 MemoryLocation MaybeDeadLoc = *CurrentLoc;
1499 Instruction *MaybeDeadI = cast<MemoryDef>(MaybeDeadAccess)->getMemoryInst();
1500 LLVM_DEBUG(dbgs() << " Checking for reads of " << *MaybeDeadAccess << " ("
1501 << *MaybeDeadI << ")\n");
1502
1504 auto PushMemUses = [&WorkList](MemoryAccess *Acc) {
1505 for (Use &U : Acc->uses())
1506 WorkList.insert(cast<MemoryAccess>(U.getUser()));
1507 };
1508 PushMemUses(MaybeDeadAccess);
1509
1510 // Check if DeadDef may be read.
1511 for (unsigned I = 0; I < WorkList.size(); I++) {
1512 MemoryAccess *UseAccess = WorkList[I];
1513
1514 LLVM_DEBUG(dbgs() << " " << *UseAccess);
1515 // Bail out if the number of accesses to check exceeds the scan limit.
1516 if (ScanLimit < (WorkList.size() - I)) {
1517 LLVM_DEBUG(dbgs() << "\n ... hit scan limit\n");
1518 return std::nullopt;
1519 }
1520 --ScanLimit;
1521 NumDomMemDefChecks++;
1522
1523 if (isa<MemoryPhi>(UseAccess)) {
1524 if (any_of(KillingDefs, [this, UseAccess](Instruction *KI) {
1525 return DT.properlyDominates(KI->getParent(),
1526 UseAccess->getBlock());
1527 })) {
1528 LLVM_DEBUG(dbgs() << " ... skipping, dominated by killing block\n");
1529 continue;
1530 }
1531 LLVM_DEBUG(dbgs() << "\n ... adding PHI uses\n");
1532 PushMemUses(UseAccess);
1533 continue;
1534 }
1535
1536 Instruction *UseInst = cast<MemoryUseOrDef>(UseAccess)->getMemoryInst();
1537 LLVM_DEBUG(dbgs() << " (" << *UseInst << ")\n");
1538
1539 if (any_of(KillingDefs, [this, UseInst](Instruction *KI) {
1540 return DT.dominates(KI, UseInst);
1541 })) {
1542 LLVM_DEBUG(dbgs() << " ... skipping, dominated by killing def\n");
1543 continue;
1544 }
1545
1546 // A memory terminator kills all preceeding MemoryDefs and all succeeding
1547 // MemoryAccesses. We do not have to check it's users.
1548 if (isMemTerminator(MaybeDeadLoc, MaybeDeadI, UseInst)) {
1549 LLVM_DEBUG(
1550 dbgs()
1551 << " ... skipping, memterminator invalidates following accesses\n");
1552 continue;
1553 }
1554
1555 if (isNoopIntrinsic(cast<MemoryUseOrDef>(UseAccess)->getMemoryInst())) {
1556 LLVM_DEBUG(dbgs() << " ... adding uses of intrinsic\n");
1557 PushMemUses(UseAccess);
1558 continue;
1559 }
1560
1561 if (UseInst->mayThrow() && !isInvisibleToCallerOnUnwind(KillingUndObj)) {
1562 LLVM_DEBUG(dbgs() << " ... found throwing instruction\n");
1563 return std::nullopt;
1564 }
1565
1566 // Uses which may read the original MemoryDef mean we cannot eliminate the
1567 // original MD. Stop walk.
1568 if (isReadClobber(MaybeDeadLoc, UseInst)) {
1569 LLVM_DEBUG(dbgs() << " ... found read clobber\n");
1570 return std::nullopt;
1571 }
1572
1573 // If this worklist walks back to the original memory access (and the
1574 // pointer is not guarenteed loop invariant) then we cannot assume that a
1575 // store kills itself.
1576 if (MaybeDeadAccess == UseAccess &&
1577 !isGuaranteedLoopInvariant(MaybeDeadLoc.Ptr)) {
1578 LLVM_DEBUG(dbgs() << " ... found not loop invariant self access\n");
1579 return std::nullopt;
1580 }
1581 // Otherwise, for the KillingDef and MaybeDeadAccess we only have to check
1582 // if it reads the memory location.
1583 // TODO: It would probably be better to check for self-reads before
1584 // calling the function.
1585 if (KillingDef == UseAccess || MaybeDeadAccess == UseAccess) {
1586 LLVM_DEBUG(dbgs() << " ... skipping killing def/dom access\n");
1587 continue;
1588 }
1589
1590 // Check all uses for MemoryDefs, except for defs completely overwriting
1591 // the original location. Otherwise we have to check uses of *all*
1592 // MemoryDefs we discover, including non-aliasing ones. Otherwise we might
1593 // miss cases like the following
1594 // 1 = Def(LoE) ; <----- DeadDef stores [0,1]
1595 // 2 = Def(1) ; (2, 1) = NoAlias, stores [2,3]
1596 // Use(2) ; MayAlias 2 *and* 1, loads [0, 3].
1597 // (The Use points to the *first* Def it may alias)
1598 // 3 = Def(1) ; <---- Current (3, 2) = NoAlias, (3,1) = MayAlias,
1599 // stores [0,1]
1600 if (MemoryDef *UseDef = dyn_cast<MemoryDef>(UseAccess)) {
1601 if (isCompleteOverwrite(MaybeDeadLoc, MaybeDeadI, UseInst)) {
1602 BasicBlock *MaybeKillingBlock = UseInst->getParent();
1603 if (PostOrderNumbers.find(MaybeKillingBlock)->second <
1604 PostOrderNumbers.find(MaybeDeadAccess->getBlock())->second) {
1605 if (!isInvisibleToCallerAfterRet(KillingUndObj)) {
1607 << " ... found killing def " << *UseInst << "\n");
1608 KillingDefs.insert(UseInst);
1609 }
1610 } else {
1612 << " ... found preceeding def " << *UseInst << "\n");
1613 return std::nullopt;
1614 }
1615 } else
1616 PushMemUses(UseDef);
1617 }
1618 }
1619
1620 // For accesses to locations visible after the function returns, make sure
1621 // that the location is dead (=overwritten) along all paths from
1622 // MaybeDeadAccess to the exit.
1623 if (!isInvisibleToCallerAfterRet(KillingUndObj)) {
1624 SmallPtrSet<BasicBlock *, 16> KillingBlocks;
1625 for (Instruction *KD : KillingDefs)
1626 KillingBlocks.insert(KD->getParent());
1627 assert(!KillingBlocks.empty() &&
1628 "Expected at least a single killing block");
1629
1630 // Find the common post-dominator of all killing blocks.
1631 BasicBlock *CommonPred = *KillingBlocks.begin();
1632 for (BasicBlock *BB : llvm::drop_begin(KillingBlocks)) {
1633 if (!CommonPred)
1634 break;
1635 CommonPred = PDT.findNearestCommonDominator(CommonPred, BB);
1636 }
1637
1638 // If the common post-dominator does not post-dominate MaybeDeadAccess,
1639 // there is a path from MaybeDeadAccess to an exit not going through a
1640 // killing block.
1641 if (!PDT.dominates(CommonPred, MaybeDeadAccess->getBlock())) {
1642 if (!AnyUnreachableExit)
1643 return std::nullopt;
1644
1645 // Fall back to CFG scan starting at all non-unreachable roots if not
1646 // all paths to the exit go through CommonPred.
1647 CommonPred = nullptr;
1648 }
1649
1650 // If CommonPred itself is in the set of killing blocks, we're done.
1651 if (KillingBlocks.count(CommonPred))
1652 return {MaybeDeadAccess};
1653
1654 SetVector<BasicBlock *> WorkList;
1655 // If CommonPred is null, there are multiple exits from the function.
1656 // They all have to be added to the worklist.
1657 if (CommonPred)
1658 WorkList.insert(CommonPred);
1659 else
1660 for (BasicBlock *R : PDT.roots()) {
1661 if (!isa<UnreachableInst>(R->getTerminator()))
1662 WorkList.insert(R);
1663 }
1664
1665 NumCFGTries++;
1666 // Check if all paths starting from an exit node go through one of the
1667 // killing blocks before reaching MaybeDeadAccess.
1668 for (unsigned I = 0; I < WorkList.size(); I++) {
1669 NumCFGChecks++;
1670 BasicBlock *Current = WorkList[I];
1671 if (KillingBlocks.count(Current))
1672 continue;
1673 if (Current == MaybeDeadAccess->getBlock())
1674 return std::nullopt;
1675
1676 // MaybeDeadAccess is reachable from the entry, so we don't have to
1677 // explore unreachable blocks further.
1678 if (!DT.isReachableFromEntry(Current))
1679 continue;
1680
1681 for (BasicBlock *Pred : predecessors(Current))
1682 WorkList.insert(Pred);
1683
1684 if (WorkList.size() >= MemorySSAPathCheckLimit)
1685 return std::nullopt;
1686 }
1687 NumCFGSuccess++;
1688 }
1689
1690 // No aliasing MemoryUses of MaybeDeadAccess found, MaybeDeadAccess is
1691 // potentially dead.
1692 return {MaybeDeadAccess};
1693 }
1694
1695 // Delete dead memory defs
1697 MemorySSAUpdater Updater(&MSSA);
1698 SmallVector<Instruction *, 32> NowDeadInsts;
1699 NowDeadInsts.push_back(SI);
1700 --NumFastOther;
1701
1702 while (!NowDeadInsts.empty()) {
1703 Instruction *DeadInst = NowDeadInsts.pop_back_val();
1704 ++NumFastOther;
1705
1706 // Try to preserve debug information attached to the dead instruction.
1707 salvageDebugInfo(*DeadInst);
1708 salvageKnowledge(DeadInst);
1709
1710 // Remove the Instruction from MSSA.
1711 if (MemoryAccess *MA = MSSA.getMemoryAccess(DeadInst)) {
1712 if (MemoryDef *MD = dyn_cast<MemoryDef>(MA)) {
1713 SkipStores.insert(MD);
1714 if (auto *SI = dyn_cast<StoreInst>(MD->getMemoryInst())) {
1715 if (SI->getValueOperand()->getType()->isPointerTy()) {
1716 const Value *UO = getUnderlyingObject(SI->getValueOperand());
1717 if (CapturedBeforeReturn.erase(UO))
1718 ShouldIterateEndOfFunctionDSE = true;
1719 InvisibleToCallerAfterRet.erase(UO);
1720 }
1721 }
1722 }
1723
1724 Updater.removeMemoryAccess(MA);
1725 }
1726
1727 auto I = IOLs.find(DeadInst->getParent());
1728 if (I != IOLs.end())
1729 I->second.erase(DeadInst);
1730 // Remove its operands
1731 for (Use &O : DeadInst->operands())
1732 if (Instruction *OpI = dyn_cast<Instruction>(O)) {
1733 O = nullptr;
1734 if (isInstructionTriviallyDead(OpI, &TLI))
1735 NowDeadInsts.push_back(OpI);
1736 }
1737
1738 EI.removeInstruction(DeadInst);
1739 DeadInst->eraseFromParent();
1740 }
1741 }
1742
1743 // Check for any extra throws between \p KillingI and \p DeadI that block
1744 // DSE. This only checks extra maythrows (those that aren't MemoryDef's).
1745 // MemoryDef that may throw are handled during the walk from one def to the
1746 // next.
1747 bool mayThrowBetween(Instruction *KillingI, Instruction *DeadI,
1748 const Value *KillingUndObj) {
1749 // First see if we can ignore it by using the fact that KillingI is an
1750 // alloca/alloca like object that is not visible to the caller during
1751 // execution of the function.
1752 if (KillingUndObj && isInvisibleToCallerOnUnwind(KillingUndObj))
1753 return false;
1754
1755 if (KillingI->getParent() == DeadI->getParent())
1756 return ThrowingBlocks.count(KillingI->getParent());
1757 return !ThrowingBlocks.empty();
1758 }
1759
1760 // Check if \p DeadI acts as a DSE barrier for \p KillingI. The following
1761 // instructions act as barriers:
1762 // * A memory instruction that may throw and \p KillingI accesses a non-stack
1763 // object.
1764 // * Atomic stores stronger that monotonic.
1765 bool isDSEBarrier(const Value *KillingUndObj, Instruction *DeadI) {
1766 // If DeadI may throw it acts as a barrier, unless we are to an
1767 // alloca/alloca like object that does not escape.
1768 if (DeadI->mayThrow() && !isInvisibleToCallerOnUnwind(KillingUndObj))
1769 return true;
1770
1771 // If DeadI is an atomic load/store stronger than monotonic, do not try to
1772 // eliminate/reorder it.
1773 if (DeadI->isAtomic()) {
1774 if (auto *LI = dyn_cast<LoadInst>(DeadI))
1775 return isStrongerThanMonotonic(LI->getOrdering());
1776 if (auto *SI = dyn_cast<StoreInst>(DeadI))
1777 return isStrongerThanMonotonic(SI->getOrdering());
1778 if (auto *ARMW = dyn_cast<AtomicRMWInst>(DeadI))
1779 return isStrongerThanMonotonic(ARMW->getOrdering());
1780 if (auto *CmpXchg = dyn_cast<AtomicCmpXchgInst>(DeadI))
1781 return isStrongerThanMonotonic(CmpXchg->getSuccessOrdering()) ||
1782 isStrongerThanMonotonic(CmpXchg->getFailureOrdering());
1783 llvm_unreachable("other instructions should be skipped in MemorySSA");
1784 }
1785 return false;
1786 }
1787
1788 /// Eliminate writes to objects that are not visible in the caller and are not
1789 /// accessed before returning from the function.
1790 bool eliminateDeadWritesAtEndOfFunction() {
1791 bool MadeChange = false;
1792 LLVM_DEBUG(
1793 dbgs()
1794 << "Trying to eliminate MemoryDefs at the end of the function\n");
1795 do {
1796 ShouldIterateEndOfFunctionDSE = false;
1797 for (MemoryDef *Def : llvm::reverse(MemDefs)) {
1798 if (SkipStores.contains(Def))
1799 continue;
1800
1801 Instruction *DefI = Def->getMemoryInst();
1802 auto DefLoc = getLocForWrite(DefI);
1803 if (!DefLoc || !isRemovable(DefI))
1804 continue;
1805
1806 // NOTE: Currently eliminating writes at the end of a function is
1807 // limited to MemoryDefs with a single underlying object, to save
1808 // compile-time. In practice it appears the case with multiple
1809 // underlying objects is very uncommon. If it turns out to be important,
1810 // we can use getUnderlyingObjects here instead.
1811 const Value *UO = getUnderlyingObject(DefLoc->Ptr);
1812 if (!isInvisibleToCallerAfterRet(UO))
1813 continue;
1814
1815 if (isWriteAtEndOfFunction(Def)) {
1816 // See through pointer-to-pointer bitcasts
1817 LLVM_DEBUG(dbgs() << " ... MemoryDef is not accessed until the end "
1818 "of the function\n");
1820 ++NumFastStores;
1821 MadeChange = true;
1822 }
1823 }
1824 } while (ShouldIterateEndOfFunctionDSE);
1825 return MadeChange;
1826 }
1827
1828 /// If we have a zero initializing memset following a call to malloc,
1829 /// try folding it into a call to calloc.
1830 bool tryFoldIntoCalloc(MemoryDef *Def, const Value *DefUO) {
1831 Instruction *DefI = Def->getMemoryInst();
1832 MemSetInst *MemSet = dyn_cast<MemSetInst>(DefI);
1833 if (!MemSet)
1834 // TODO: Could handle zero store to small allocation as well.
1835 return false;
1836 Constant *StoredConstant = dyn_cast<Constant>(MemSet->getValue());
1837 if (!StoredConstant || !StoredConstant->isNullValue())
1838 return false;
1839
1840 if (!isRemovable(DefI))
1841 // The memset might be volatile..
1842 return false;
1843
1844 if (F.hasFnAttribute(Attribute::SanitizeMemory) ||
1845 F.hasFnAttribute(Attribute::SanitizeAddress) ||
1846 F.hasFnAttribute(Attribute::SanitizeHWAddress) ||
1847 F.getName() == "calloc")
1848 return false;
1849 auto *Malloc = const_cast<CallInst *>(dyn_cast<CallInst>(DefUO));
1850 if (!Malloc)
1851 return false;
1852 auto *InnerCallee = Malloc->getCalledFunction();
1853 if (!InnerCallee)
1854 return false;
1855 LibFunc Func;
1856 if (!TLI.getLibFunc(*InnerCallee, Func) || !TLI.has(Func) ||
1857 Func != LibFunc_malloc)
1858 return false;
1859 // Gracefully handle malloc with unexpected memory attributes.
1860 auto *MallocDef = dyn_cast_or_null<MemoryDef>(MSSA.getMemoryAccess(Malloc));
1861 if (!MallocDef)
1862 return false;
1863
1864 auto shouldCreateCalloc = [](CallInst *Malloc, CallInst *Memset) {
1865 // Check for br(icmp ptr, null), truebb, falsebb) pattern at the end
1866 // of malloc block
1867 auto *MallocBB = Malloc->getParent(),
1868 *MemsetBB = Memset->getParent();
1869 if (MallocBB == MemsetBB)
1870 return true;
1871 auto *Ptr = Memset->getArgOperand(0);
1872 auto *TI = MallocBB->getTerminator();
1874 BasicBlock *TrueBB, *FalseBB;
1875 if (!match(TI, m_Br(m_ICmp(Pred, m_Specific(Ptr), m_Zero()), TrueBB,
1876 FalseBB)))
1877 return false;
1878 if (Pred != ICmpInst::ICMP_EQ || MemsetBB != FalseBB)
1879 return false;
1880 return true;
1881 };
1882
1883 if (Malloc->getOperand(0) != MemSet->getLength())
1884 return false;
1885 if (!shouldCreateCalloc(Malloc, MemSet) ||
1886 !DT.dominates(Malloc, MemSet) ||
1887 !memoryIsNotModifiedBetween(Malloc, MemSet, BatchAA, DL, &DT))
1888 return false;
1889 IRBuilder<> IRB(Malloc);
1890 Type *SizeTTy = Malloc->getArgOperand(0)->getType();
1891 auto *Calloc = emitCalloc(ConstantInt::get(SizeTTy, 1),
1892 Malloc->getArgOperand(0), IRB, TLI);
1893 if (!Calloc)
1894 return false;
1895 MemorySSAUpdater Updater(&MSSA);
1896 auto *NewAccess =
1897 Updater.createMemoryAccessAfter(cast<Instruction>(Calloc), nullptr,
1898 MallocDef);
1899 auto *NewAccessMD = cast<MemoryDef>(NewAccess);
1900 Updater.insertDef(NewAccessMD, /*RenameUses=*/true);
1901 Updater.removeMemoryAccess(Malloc);
1902 Malloc->replaceAllUsesWith(Calloc);
1903 Malloc->eraseFromParent();
1904 return true;
1905 }
1906
1907 // Check if there is a dominating condition, that implies that the value
1908 // being stored in a ptr is already present in the ptr.
1909 bool dominatingConditionImpliesValue(MemoryDef *Def) {
1910 auto *StoreI = cast<StoreInst>(Def->getMemoryInst());
1911 BasicBlock *StoreBB = StoreI->getParent();
1912 Value *StorePtr = StoreI->getPointerOperand();
1913 Value *StoreVal = StoreI->getValueOperand();
1914
1915 DomTreeNode *IDom = DT.getNode(StoreBB)->getIDom();
1916 if (!IDom)
1917 return false;
1918
1919 auto *BI = dyn_cast<BranchInst>(IDom->getBlock()->getTerminator());
1920 if (!BI || !BI->isConditional())
1921 return false;
1922
1923 // In case both blocks are the same, it is not possible to determine
1924 // if optimization is possible. (We would not want to optimize a store
1925 // in the FalseBB if condition is true and vice versa.)
1926 if (BI->getSuccessor(0) == BI->getSuccessor(1))
1927 return false;
1928
1929 Instruction *ICmpL;
1931 if (!match(BI->getCondition(),
1932 m_c_ICmp(Pred,
1933 m_CombineAnd(m_Load(m_Specific(StorePtr)),
1934 m_Instruction(ICmpL)),
1935 m_Specific(StoreVal))) ||
1936 !ICmpInst::isEquality(Pred))
1937 return false;
1938
1939 // In case the else blocks also branches to the if block or the other way
1940 // around it is not possible to determine if the optimization is possible.
1941 if (Pred == ICmpInst::ICMP_EQ &&
1942 !DT.dominates(BasicBlockEdge(BI->getParent(), BI->getSuccessor(0)),
1943 StoreBB))
1944 return false;
1945
1946 if (Pred == ICmpInst::ICMP_NE &&
1947 !DT.dominates(BasicBlockEdge(BI->getParent(), BI->getSuccessor(1)),
1948 StoreBB))
1949 return false;
1950
1951 MemoryAccess *LoadAcc = MSSA.getMemoryAccess(ICmpL);
1952 MemoryAccess *ClobAcc =
1953 MSSA.getSkipSelfWalker()->getClobberingMemoryAccess(Def, BatchAA);
1954
1955 return MSSA.dominates(ClobAcc, LoadAcc);
1956 }
1957
1958 /// \returns true if \p Def is a no-op store, either because it
1959 /// directly stores back a loaded value or stores zero to a calloced object.
1960 bool storeIsNoop(MemoryDef *Def, const Value *DefUO) {
1961 Instruction *DefI = Def->getMemoryInst();
1962 StoreInst *Store = dyn_cast<StoreInst>(DefI);
1963 MemSetInst *MemSet = dyn_cast<MemSetInst>(DefI);
1964 Constant *StoredConstant = nullptr;
1965 if (Store)
1966 StoredConstant = dyn_cast<Constant>(Store->getOperand(0));
1967 else if (MemSet)
1968 StoredConstant = dyn_cast<Constant>(MemSet->getValue());
1969 else
1970 return false;
1971
1972 if (!isRemovable(DefI))
1973 return false;
1974
1975 if (StoredConstant) {
1976 Constant *InitC =
1977 getInitialValueOfAllocation(DefUO, &TLI, StoredConstant->getType());
1978 // If the clobbering access is LiveOnEntry, no instructions between them
1979 // can modify the memory location.
1980 if (InitC && InitC == StoredConstant)
1981 return MSSA.isLiveOnEntryDef(
1982 MSSA.getSkipSelfWalker()->getClobberingMemoryAccess(Def, BatchAA));
1983 }
1984
1985 if (!Store)
1986 return false;
1987
1988 if (dominatingConditionImpliesValue(Def))
1989 return true;
1990
1991 if (auto *LoadI = dyn_cast<LoadInst>(Store->getOperand(0))) {
1992 if (LoadI->getPointerOperand() == Store->getOperand(1)) {
1993 // Get the defining access for the load.
1994 auto *LoadAccess = MSSA.getMemoryAccess(LoadI)->getDefiningAccess();
1995 // Fast path: the defining accesses are the same.
1996 if (LoadAccess == Def->getDefiningAccess())
1997 return true;
1998
1999 // Look through phi accesses. Recursively scan all phi accesses by
2000 // adding them to a worklist. Bail when we run into a memory def that
2001 // does not match LoadAccess.
2003 MemoryAccess *Current =
2004 MSSA.getWalker()->getClobberingMemoryAccess(Def, BatchAA);
2005 // We don't want to bail when we run into the store memory def. But,
2006 // the phi access may point to it. So, pretend like we've already
2007 // checked it.
2008 ToCheck.insert(Def);
2009 ToCheck.insert(Current);
2010 // Start at current (1) to simulate already having checked Def.
2011 for (unsigned I = 1; I < ToCheck.size(); ++I) {
2012 Current = ToCheck[I];
2013 if (auto PhiAccess = dyn_cast<MemoryPhi>(Current)) {
2014 // Check all the operands.
2015 for (auto &Use : PhiAccess->incoming_values())
2016 ToCheck.insert(cast<MemoryAccess>(&Use));
2017 continue;
2018 }
2019
2020 // If we found a memory def, bail. This happens when we have an
2021 // unrelated write in between an otherwise noop store.
2022 assert(isa<MemoryDef>(Current) &&
2023 "Only MemoryDefs should reach here.");
2024 // TODO: Skip no alias MemoryDefs that have no aliasing reads.
2025 // We are searching for the definition of the store's destination.
2026 // So, if that is the same definition as the load, then this is a
2027 // noop. Otherwise, fail.
2028 if (LoadAccess != Current)
2029 return false;
2030 }
2031 return true;
2032 }
2033 }
2034
2035 return false;
2036 }
2037
2038 bool removePartiallyOverlappedStores(InstOverlapIntervalsTy &IOL) {
2039 bool Changed = false;
2040 for (auto OI : IOL) {
2041 Instruction *DeadI = OI.first;
2042 MemoryLocation Loc = *getLocForWrite(DeadI);
2043 assert(isRemovable(DeadI) && "Expect only removable instruction");
2044
2045 const Value *Ptr = Loc.Ptr->stripPointerCasts();
2046 int64_t DeadStart = 0;
2047 uint64_t DeadSize = Loc.Size.getValue();
2048 GetPointerBaseWithConstantOffset(Ptr, DeadStart, DL);
2049 OverlapIntervalsTy &IntervalMap = OI.second;
2050 Changed |= tryToShortenEnd(DeadI, IntervalMap, DeadStart, DeadSize);
2051 if (IntervalMap.empty())
2052 continue;
2053 Changed |= tryToShortenBegin(DeadI, IntervalMap, DeadStart, DeadSize);
2054 }
2055 return Changed;
2056 }
2057
2058 /// Eliminates writes to locations where the value that is being written
2059 /// is already stored at the same location.
2060 bool eliminateRedundantStoresOfExistingValues() {
2061 bool MadeChange = false;
2062 LLVM_DEBUG(dbgs() << "Trying to eliminate MemoryDefs that write the "
2063 "already existing value\n");
2064 for (auto *Def : MemDefs) {
2065 if (SkipStores.contains(Def) || MSSA.isLiveOnEntryDef(Def))
2066 continue;
2067
2068 Instruction *DefInst = Def->getMemoryInst();
2069 auto MaybeDefLoc = getLocForWrite(DefInst);
2070 if (!MaybeDefLoc || !isRemovable(DefInst))
2071 continue;
2072
2073 MemoryDef *UpperDef;
2074 // To conserve compile-time, we avoid walking to the next clobbering def.
2075 // Instead, we just try to get the optimized access, if it exists. DSE
2076 // will try to optimize defs during the earlier traversal.
2077 if (Def->isOptimized())
2078 UpperDef = dyn_cast<MemoryDef>(Def->getOptimized());
2079 else
2080 UpperDef = dyn_cast<MemoryDef>(Def->getDefiningAccess());
2081 if (!UpperDef || MSSA.isLiveOnEntryDef(UpperDef))
2082 continue;
2083
2084 Instruction *UpperInst = UpperDef->getMemoryInst();
2085 auto IsRedundantStore = [&]() {
2086 if (DefInst->isIdenticalTo(UpperInst))
2087 return true;
2088 if (auto *MemSetI = dyn_cast<MemSetInst>(UpperInst)) {
2089 if (auto *SI = dyn_cast<StoreInst>(DefInst)) {
2090 // MemSetInst must have a write location.
2091 MemoryLocation UpperLoc = *getLocForWrite(UpperInst);
2092 int64_t InstWriteOffset = 0;
2093 int64_t DepWriteOffset = 0;
2094 auto OR = isOverwrite(UpperInst, DefInst, UpperLoc, *MaybeDefLoc,
2095 InstWriteOffset, DepWriteOffset);
2096 Value *StoredByte = isBytewiseValue(SI->getValueOperand(), DL);
2097 return StoredByte && StoredByte == MemSetI->getOperand(1) &&
2098 OR == OW_Complete;
2099 }
2100 }
2101 return false;
2102 };
2103
2104 if (!IsRedundantStore() || isReadClobber(*MaybeDefLoc, DefInst))
2105 continue;
2106 LLVM_DEBUG(dbgs() << "DSE: Remove No-Op Store:\n DEAD: " << *DefInst
2107 << '\n');
2108 deleteDeadInstruction(DefInst);
2109 NumRedundantStores++;
2110 MadeChange = true;
2111 }
2112 return MadeChange;
2113 }
2114};
2115
2116static bool eliminateDeadStores(Function &F, AliasAnalysis &AA, MemorySSA &MSSA,
2118 const TargetLibraryInfo &TLI,
2119 const LoopInfo &LI) {
2120 bool MadeChange = false;
2121
2122 DSEState State(F, AA, MSSA, DT, PDT, TLI, LI);
2123 // For each store:
2124 for (unsigned I = 0; I < State.MemDefs.size(); I++) {
2125 MemoryDef *KillingDef = State.MemDefs[I];
2126 if (State.SkipStores.count(KillingDef))
2127 continue;
2128 Instruction *KillingI = KillingDef->getMemoryInst();
2129
2130 std::optional<MemoryLocation> MaybeKillingLoc;
2131 if (State.isMemTerminatorInst(KillingI)) {
2132 if (auto KillingLoc = State.getLocForTerminator(KillingI))
2133 MaybeKillingLoc = KillingLoc->first;
2134 } else {
2135 MaybeKillingLoc = State.getLocForWrite(KillingI);
2136 }
2137
2138 if (!MaybeKillingLoc) {
2139 LLVM_DEBUG(dbgs() << "Failed to find analyzable write location for "
2140 << *KillingI << "\n");
2141 continue;
2142 }
2143 MemoryLocation KillingLoc = *MaybeKillingLoc;
2144 assert(KillingLoc.Ptr && "KillingLoc should not be null");
2145 const Value *KillingUndObj = getUnderlyingObject(KillingLoc.Ptr);
2146 LLVM_DEBUG(dbgs() << "Trying to eliminate MemoryDefs killed by "
2147 << *KillingDef << " (" << *KillingI << ")\n");
2148
2149 unsigned ScanLimit = MemorySSAScanLimit;
2150 unsigned WalkerStepLimit = MemorySSAUpwardsStepLimit;
2151 unsigned PartialLimit = MemorySSAPartialStoreLimit;
2152 // Worklist of MemoryAccesses that may be killed by KillingDef.
2154 ToCheck.insert(KillingDef->getDefiningAccess());
2155
2156 bool Shortend = false;
2157 bool IsMemTerm = State.isMemTerminatorInst(KillingI);
2158 // Check if MemoryAccesses in the worklist are killed by KillingDef.
2159 for (unsigned I = 0; I < ToCheck.size(); I++) {
2160 MemoryAccess *Current = ToCheck[I];
2161 if (State.SkipStores.count(Current))
2162 continue;
2163
2164 std::optional<MemoryAccess *> MaybeDeadAccess = State.getDomMemoryDef(
2165 KillingDef, Current, KillingLoc, KillingUndObj, ScanLimit,
2166 WalkerStepLimit, IsMemTerm, PartialLimit);
2167
2168 if (!MaybeDeadAccess) {
2169 LLVM_DEBUG(dbgs() << " finished walk\n");
2170 continue;
2171 }
2172
2173 MemoryAccess *DeadAccess = *MaybeDeadAccess;
2174 LLVM_DEBUG(dbgs() << " Checking if we can kill " << *DeadAccess);
2175 if (isa<MemoryPhi>(DeadAccess)) {
2176 LLVM_DEBUG(dbgs() << "\n ... adding incoming values to worklist\n");
2177 for (Value *V : cast<MemoryPhi>(DeadAccess)->incoming_values()) {
2178 MemoryAccess *IncomingAccess = cast<MemoryAccess>(V);
2179 BasicBlock *IncomingBlock = IncomingAccess->getBlock();
2180 BasicBlock *PhiBlock = DeadAccess->getBlock();
2181
2182 // We only consider incoming MemoryAccesses that come before the
2183 // MemoryPhi. Otherwise we could discover candidates that do not
2184 // strictly dominate our starting def.
2185 if (State.PostOrderNumbers[IncomingBlock] >
2186 State.PostOrderNumbers[PhiBlock])
2187 ToCheck.insert(IncomingAccess);
2188 }
2189 continue;
2190 }
2191 auto *DeadDefAccess = cast<MemoryDef>(DeadAccess);
2192 Instruction *DeadI = DeadDefAccess->getMemoryInst();
2193 LLVM_DEBUG(dbgs() << " (" << *DeadI << ")\n");
2194 ToCheck.insert(DeadDefAccess->getDefiningAccess());
2195 NumGetDomMemoryDefPassed++;
2196
2197 if (!DebugCounter::shouldExecute(MemorySSACounter))
2198 continue;
2199
2200 MemoryLocation DeadLoc = *State.getLocForWrite(DeadI);
2201
2202 if (IsMemTerm) {
2203 const Value *DeadUndObj = getUnderlyingObject(DeadLoc.Ptr);
2204 if (KillingUndObj != DeadUndObj)
2205 continue;
2206 LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: " << *DeadI
2207 << "\n KILLER: " << *KillingI << '\n');
2208 State.deleteDeadInstruction(DeadI);
2209 ++NumFastStores;
2210 MadeChange = true;
2211 } else {
2212 // Check if DeadI overwrites KillingI.
2213 int64_t KillingOffset = 0;
2214 int64_t DeadOffset = 0;
2215 OverwriteResult OR = State.isOverwrite(
2216 KillingI, DeadI, KillingLoc, DeadLoc, KillingOffset, DeadOffset);
2217 if (OR == OW_MaybePartial) {
2218 auto Iter = State.IOLs.insert(
2219 std::make_pair<BasicBlock *, InstOverlapIntervalsTy>(
2220 DeadI->getParent(), InstOverlapIntervalsTy()));
2221 auto &IOL = Iter.first->second;
2222 OR = isPartialOverwrite(KillingLoc, DeadLoc, KillingOffset,
2223 DeadOffset, DeadI, IOL);
2224 }
2225
2226 if (EnablePartialStoreMerging && OR == OW_PartialEarlierWithFullLater) {
2227 auto *DeadSI = dyn_cast<StoreInst>(DeadI);
2228 auto *KillingSI = dyn_cast<StoreInst>(KillingI);
2229 // We are re-using tryToMergePartialOverlappingStores, which requires
2230 // DeadSI to dominate KillingSI.
2231 // TODO: implement tryToMergeParialOverlappingStores using MemorySSA.
2232 if (DeadSI && KillingSI && DT.dominates(DeadSI, KillingSI)) {
2234 KillingSI, DeadSI, KillingOffset, DeadOffset, State.DL,
2235 State.BatchAA, &DT)) {
2236
2237 // Update stored value of earlier store to merged constant.
2238 DeadSI->setOperand(0, Merged);
2239 ++NumModifiedStores;
2240 MadeChange = true;
2241
2242 Shortend = true;
2243 // Remove killing store and remove any outstanding overlap
2244 // intervals for the updated store.
2245 State.deleteDeadInstruction(KillingSI);
2246 auto I = State.IOLs.find(DeadSI->getParent());
2247 if (I != State.IOLs.end())
2248 I->second.erase(DeadSI);
2249 break;
2250 }
2251 }
2252 }
2253
2254 if (OR == OW_Complete) {
2255 LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: " << *DeadI
2256 << "\n KILLER: " << *KillingI << '\n');
2257 State.deleteDeadInstruction(DeadI);
2258 ++NumFastStores;
2259 MadeChange = true;
2260 }
2261 }
2262 }
2263
2264 // Check if the store is a no-op.
2265 if (!Shortend && State.storeIsNoop(KillingDef, KillingUndObj)) {
2266 LLVM_DEBUG(dbgs() << "DSE: Remove No-Op Store:\n DEAD: " << *KillingI
2267 << '\n');
2268 State.deleteDeadInstruction(KillingI);
2269 NumRedundantStores++;
2270 MadeChange = true;
2271 continue;
2272 }
2273
2274 // Can we form a calloc from a memset/malloc pair?
2275 if (!Shortend && State.tryFoldIntoCalloc(KillingDef, KillingUndObj)) {
2276 LLVM_DEBUG(dbgs() << "DSE: Remove memset after forming calloc:\n"
2277 << " DEAD: " << *KillingI << '\n');
2278 State.deleteDeadInstruction(KillingI);
2279 MadeChange = true;
2280 continue;
2281 }
2282 }
2283
2285 for (auto &KV : State.IOLs)
2286 MadeChange |= State.removePartiallyOverlappedStores(KV.second);
2287
2288 MadeChange |= State.eliminateRedundantStoresOfExistingValues();
2289 MadeChange |= State.eliminateDeadWritesAtEndOfFunction();
2290 return MadeChange;
2291}
2292} // end anonymous namespace
2293
2294//===----------------------------------------------------------------------===//
2295// DSE Pass
2296//===----------------------------------------------------------------------===//
2301 MemorySSA &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
2303 LoopInfo &LI = AM.getResult<LoopAnalysis>(F);
2304
2305 bool Changed = eliminateDeadStores(F, AA, MSSA, DT, PDT, TLI, LI);
2306
2307#ifdef LLVM_ENABLE_STATS
2309 for (auto &I : instructions(F))
2310 NumRemainingStores += isa<StoreInst>(&I);
2311#endif
2312
2313 if (!Changed)
2314 return PreservedAnalyses::all();
2315
2319 PA.preserve<LoopAnalysis>();
2320 return PA;
2321}
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL
This file implements a class to represent arbitrary precision integral constant values and operations...
static const Function * getParent(const Value *V)
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
static GCRegistry::Add< StatepointGC > D("statepoint-example", "an example strategy for statepoint")
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
This file contains the declarations for the subclasses of Constant, which represent the different fla...
static void shortenAssignment(Instruction *Inst, Value *OriginalDest, uint64_t OldOffsetInBits, uint64_t OldSizeInBits, uint64_t NewSizeInBits, bool IsOverwriteEnd)
static bool isShortenableAtTheEnd(Instruction *I)
Returns true if the end of this instruction can be safely shortened in length.
static cl::opt< bool > EnablePartialStoreMerging("enable-dse-partial-store-merging", cl::init(true), cl::Hidden, cl::desc("Enable partial store merging in DSE"))
static bool tryToShortenBegin(Instruction *DeadI, OverlapIntervalsTy &IntervalMap, int64_t &DeadStart, uint64_t &DeadSize)
std::map< int64_t, int64_t > OverlapIntervalsTy
static bool isShortenableAtTheBeginning(Instruction *I)
Returns true if the beginning of this instruction can be safely shortened in length.
static cl::opt< unsigned > MemorySSADefsPerBlockLimit("dse-memoryssa-defs-per-block-limit", cl::init(5000), cl::Hidden, cl::desc("The number of MemoryDefs we consider as candidates to eliminated " "other stores per basic block (default = 5000)"))
static Constant * tryToMergePartialOverlappingStores(StoreInst *KillingI, StoreInst *DeadI, int64_t KillingOffset, int64_t DeadOffset, const DataLayout &DL, BatchAAResults &AA, DominatorTree *DT)
static bool memoryIsNotModifiedBetween(Instruction *FirstI, Instruction *SecondI, BatchAAResults &AA, const DataLayout &DL, DominatorTree *DT)
Returns true if the memory which is accessed by the second instruction is not modified between the fi...
static OverwriteResult isMaskedStoreOverwrite(const Instruction *KillingI, const Instruction *DeadI, BatchAAResults &AA)
Check if two instruction are masked stores that completely overwrite one another.
static cl::opt< unsigned > MemorySSAOtherBBStepCost("dse-memoryssa-otherbb-cost", cl::init(5), cl::Hidden, cl::desc("The cost of a step in a different basic " "block than the killing MemoryDef" "(default = 5)"))
static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart, uint64_t &DeadSize, int64_t KillingStart, uint64_t KillingSize, bool IsOverwriteEnd)
static cl::opt< unsigned > MemorySSAScanLimit("dse-memoryssa-scanlimit", cl::init(150), cl::Hidden, cl::desc("The number of memory instructions to scan for " "dead store elimination (default = 150)"))
static cl::opt< unsigned > MemorySSASameBBStepCost("dse-memoryssa-samebb-cost", cl::init(1), cl::Hidden, cl::desc("The cost of a step in the same basic block as the killing MemoryDef" "(default = 1)"))
static cl::opt< bool > EnablePartialOverwriteTracking("enable-dse-partial-overwrite-tracking", cl::init(true), cl::Hidden, cl::desc("Enable partial-overwrite tracking in DSE"))
static OverwriteResult isPartialOverwrite(const MemoryLocation &KillingLoc, const MemoryLocation &DeadLoc, int64_t KillingOff, int64_t DeadOff, Instruction *DeadI, InstOverlapIntervalsTy &IOL)
Return 'OW_Complete' if a store to the 'KillingLoc' location completely overwrites a store to the 'De...
static cl::opt< unsigned > MemorySSAPartialStoreLimit("dse-memoryssa-partial-store-limit", cl::init(5), cl::Hidden, cl::desc("The maximum number candidates that only partially overwrite the " "killing MemoryDef to consider" " (default = 5)"))
static std::optional< TypeSize > getPointerSize(const Value *V, const DataLayout &DL, const TargetLibraryInfo &TLI, const Function *F)
static bool tryToShortenEnd(Instruction *DeadI, OverlapIntervalsTy &IntervalMap, int64_t &DeadStart, uint64_t &DeadSize)
static cl::opt< unsigned > MemorySSAUpwardsStepLimit("dse-memoryssa-walklimit", cl::init(90), cl::Hidden, cl::desc("The maximum number of steps while walking upwards to find " "MemoryDefs that may be killed (default = 90)"))
static cl::opt< bool > OptimizeMemorySSA("dse-optimize-memoryssa", cl::init(true), cl::Hidden, cl::desc("Allow DSE to optimize memory accesses."))
static cl::opt< unsigned > MemorySSAPathCheckLimit("dse-memoryssa-path-check-limit", cl::init(50), cl::Hidden, cl::desc("The maximum number of blocks to check when trying to prove that " "all paths to an exit go through a killing block (default = 50)"))
This file provides an implementation of debug counters.
#define DEBUG_COUNTER(VARNAME, COUNTERNAME, DESC)
Definition: DebugCounter.h:182
#define LLVM_DEBUG(X)
Definition: Debug.h:101
This file defines the DenseMap class.
uint64_t Addr
uint64_t Size
This is the interface for a simple mod/ref and alias analysis over globals.
Hexagon Common GEP
IRTranslator LLVM IR MI
Select target instructions out of generic instructions
static void deleteDeadInstruction(Instruction *I)
#define F(x, y, z)
Definition: MD5.cpp:55
#define I(x, y, z)
Definition: MD5.cpp:58
This file implements a map that provides insertion order iteration.
This file provides utility analysis objects describing memory locations.
This file exposes an interface to building/using memory SSA to walk memory instructions using a use/d...
Module.h This file contains the declarations for the Module class.
Contains a collection of routines for determining if a given instruction is guaranteed to execute if ...
This header defines various interfaces for pass management in LLVM.
This file builds on the ADT/GraphTraits.h file to build a generic graph post order iterator.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
This file implements a set that has insertion order iteration characteristics.
This file defines the SmallPtrSet class.
This file defines the SmallVector class.
This file defines the 'Statistic' class, which is designed to be an easy way to expose various metric...
#define STATISTIC(VARNAME, DESC)
Definition: Statistic.h:167
A manager for alias analyses.
Class for arbitrary precision integers.
Definition: APInt.h:76
APInt zext(unsigned width) const
Zero extend to a new width.
Definition: APInt.cpp:981
static APInt getBitsSet(unsigned numBits, unsigned loBit, unsigned hiBit)
Get a value with a block of bits set.
Definition: APInt.h:236
unsigned getBitWidth() const
Return the number of bits in the APInt.
Definition: APInt.h:1433
The possible results of an alias query.
Definition: AliasAnalysis.h:81
@ NoAlias
The two locations do not alias at all.
Definition: AliasAnalysis.h:99
@ PartialAlias
The two locations alias, but only due to a partial overlap.
@ MustAlias
The two locations precisely alias each other.
constexpr int32_t getOffset() const
constexpr bool hasOffset() const
A container for analyses that lazily runs them and caches their results.
Definition: PassManager.h:348
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:500
This class represents an incoming formal argument to a Function.
Definition: Argument.h:28
LLVM Basic Block Representation.
Definition: BasicBlock.h:60
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:214
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:173
const Instruction * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.h:229
This class is a wrapper over an AAResults, and it is intended to be used only when there are no IR ch...
AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB)
bool isMustAlias(const MemoryLocation &LocA, const MemoryLocation &LocB)
ModRefInfo getModRefInfo(const Instruction *I, const std::optional< MemoryLocation > &OptLoc)
Represents analyses that only rely on functions' control flow.
Definition: Analysis.h:70
This class represents a function call, abstracting a target machine's calling convention.
Predicate
This enumeration lists the possible predicates for CmpInst subclasses.
Definition: InstrTypes.h:780
static Constant * get(Type *Ty, uint64_t V, bool IsSigned=false)
If Ty is a vector type, return a Constant with a splat of the given value.
Definition: Constants.cpp:888
This is an important base class in LLVM.
Definition: Constant.h:41
bool isNullValue() const
Return true if this is the value that would be returned by getNullValue.
Definition: Constants.cpp:76
Assignment ID.
static DIAssignID * getDistinct(LLVMContext &Context)
static std::optional< DIExpression * > createFragmentExpression(const DIExpression *Expr, unsigned OffsetInBits, unsigned SizeInBits)
Create a DIExpression to describe one part of an aggregate variable that is fragmented across multipl...
PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM)
A parsed version of the target data layout string in and methods for querying it.
Definition: DataLayout.h:110
static bool shouldExecute(unsigned CounterName)
Definition: DebugCounter.h:72
iterator find(const_arg_type_t< KeyT > Val)
Definition: DenseMap.h:155
bool erase(const KeyT &Val)
Definition: DenseMap.h:329
std::pair< iterator, bool > insert(const std::pair< KeyT, ValueT > &KV)
Definition: DenseMap.h:220
DomTreeNodeBase * getIDom() const
NodeT * getBlock() const
Analysis pass which computes a DominatorTree.
Definition: Dominators.h:275
NodeT * findNearestCommonDominator(NodeT *A, NodeT *B) const
Find nearest common dominator basic block for basic block A and B.
iterator_range< root_iterator > roots()
DomTreeNodeBase< NodeT > * getNode(const NodeT *BB) const
getNode - return the (Post)DominatorTree node for the specified basic block.
bool properlyDominates(const DomTreeNodeBase< NodeT > *A, const DomTreeNodeBase< NodeT > *B) const
properlyDominates - Returns true iff A dominates B and A != B.
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree.
Definition: Dominators.h:162
bool isReachableFromEntry(const Use &U) const
Provide an overload for a Use.
Definition: Dominators.cpp:321
bool dominates(const BasicBlock *BB, const Use &U) const
Return true if the (end of the) basic block BB dominates the use U.
Definition: Dominators.cpp:122
Context-sensitive CaptureInfo provider, which computes and caches the earliest common dominator closu...
void removeInstruction(Instruction *I)
const BasicBlock & getEntryBlock() const
Definition: Function.h:779
static GetElementPtrInst * CreateInBounds(Type *PointeeType, Value *Ptr, ArrayRef< Value * > IdxList, const Twine &NameStr="", Instruction *InsertBefore=nullptr)
Create an "inbounds" getelementptr.
Definition: Instructions.h:998
bool isEquality() const
Return true if this predicate is either EQ or NE.
This provides a uniform API for creating instructions and inserting them into a basic block: either a...
Definition: IRBuilder.h:2649
bool mayThrow(bool IncludePhaseOneUnwind=false) const LLVM_READONLY
Return true if this instruction may throw an exception.
bool mayWriteToMemory() const LLVM_READONLY
Return true if this instruction may modify memory.
const Module * getModule() const
Return the module owning the function this instruction belongs to or nullptr it the function does not...
Definition: Instruction.cpp:71
bool isAtomic() const LLVM_READONLY
Return true if this instruction has an AtomicOrdering of unordered or higher.
const BasicBlock * getParent() const
Definition: Instruction.h:150
InstListType::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
Definition: Instruction.cpp:93
bool mayReadFromMemory() const LLVM_READONLY
Return true if this instruction may read memory.
bool isIdenticalTo(const Instruction *I) const LLVM_READONLY
Return true if the specified instruction is exactly identical to the current one.
void setDebugLoc(DebugLoc Loc)
Set the debug location information for this instruction.
Definition: Instruction.h:449
const_iterator begin() const
Definition: IntervalMap.h:1146
bool empty() const
empty - Return true when no intervals are mapped.
Definition: IntervalMap.h:1101
const_iterator end() const
Definition: IntervalMap.h:1158
A wrapper class for inspecting calls to intrinsic functions.
Definition: IntrinsicInst.h:47
This is an important class for using LLVM in a threaded context.
Definition: LLVMContext.h:67
static LocationSize precise(uint64_t Value)
bool isScalable() const
TypeSize getValue() const
bool isPrecise() const
Analysis pass that exposes the LoopInfo for a function.
Definition: LoopInfo.h:566
LoopT * getLoopFor(const BlockT *BB) const
Return the inner most loop that BB lives in.
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:44
This class implements a map that also provides access to all stored values in a deterministic order.
Definition: MapVector.h:36
iterator end()
Definition: MapVector.h:71
iterator find(const KeyT &Key)
Definition: MapVector.h:167
Value * getLength() const
Value * getValue() const
This class wraps the llvm.memset and llvm.memset.inline intrinsics.
BasicBlock * getBlock() const
Definition: MemorySSA.h:164
Represents a read-write access to memory, whether it is a must-alias, or a may-alias.
Definition: MemorySSA.h:372
void setOptimized(MemoryAccess *MA)
Definition: MemorySSA.h:392
Representation for a specific memory location.
static MemoryLocation get(const LoadInst *LI)
Return a location with information about the memory reference by the given instruction.
LocationSize Size
The maximum size of the location, in address-units, or UnknownSize if the size is not known.
static MemoryLocation getAfter(const Value *Ptr, const AAMDNodes &AATags=AAMDNodes())
Return a location that may access any location after Ptr, while remaining within the underlying objec...
MemoryLocation getWithNewPtr(const Value *NewPtr) const
const Value * Ptr
The address of the start of the location.
static MemoryLocation getForDest(const MemIntrinsic *MI)
Return a location representing the destination of a memory set or transfer.
static std::optional< MemoryLocation > getOrNone(const Instruction *Inst)
An analysis that produces MemorySSA for a function.
Definition: MemorySSA.h:923
MemoryAccess * getClobberingMemoryAccess(const Instruction *I, BatchAAResults &AA)
Given a memory Mod/Ref/ModRef'ing instruction, calling this will give you the nearest dominating Memo...
Definition: MemorySSA.h:1040
Encapsulates MemorySSA, including all data associated with memory accesses.
Definition: MemorySSA.h:700
MemorySSAWalker * getSkipSelfWalker()
Definition: MemorySSA.cpp:1560
bool dominates(const MemoryAccess *A, const MemoryAccess *B) const
Given two memory accesses in potentially different blocks, determine whether MemoryAccess A dominates...
Definition: MemorySSA.cpp:2109
MemorySSAWalker * getWalker()
Definition: MemorySSA.cpp:1547
MemoryUseOrDef * getMemoryAccess(const Instruction *I) const
Given a memory Mod/Ref'ing instruction, get the MemorySSA access associated with it.
Definition: MemorySSA.h:717
bool isLiveOnEntryDef(const MemoryAccess *MA) const
Return true if MA represents the live on entry value.
Definition: MemorySSA.h:737
MemoryAccess * getDefiningAccess() const
Get the access that produces the memory state used by this Use.
Definition: MemorySSA.h:262
Instruction * getMemoryInst() const
Get the instruction that this MemoryUse represents.
Definition: MemorySSA.h:259
const DataLayout & getDataLayout() const
Get the data layout for the module's target platform.
Definition: Module.h:275
PHITransAddr - An address value which tracks and handles phi translation.
Definition: PHITransAddr.h:35
Value * translateValue(BasicBlock *CurBB, BasicBlock *PredBB, const DominatorTree *DT, bool MustDominate)
translateValue - PHI translate the current address up the CFG from CurBB to Pred, updating our state ...
bool isPotentiallyPHITranslatable() const
isPotentiallyPHITranslatable - If this needs PHI translation, return true if we have some hope of doi...
bool needsPHITranslationFromBlock(BasicBlock *BB) const
needsPHITranslationFromBlock - Return true if moving from the specified BasicBlock to its predecessor...
Definition: PHITransAddr.h:62
Value * getAddr() const
Definition: PHITransAddr.h:58
Analysis pass which computes a PostDominatorTree.
PostDominatorTree Class - Concrete subclass of DominatorTree that is used to compute the post-dominat...
bool dominates(const Instruction *I1, const Instruction *I2) const
Return true if I1 dominates I2.
A set of analyses that are preserved following a run of a transformation pass.
Definition: Analysis.h:109
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: Analysis.h:115
void preserveSet()
Mark an analysis set as preserved.
Definition: Analysis.h:144
void preserve()
Mark an analysis as preserved.
Definition: Analysis.h:129
A vector that has set insertion semantics.
Definition: SetVector.h:57
size_type size() const
Determine the number of elements in the SetVector.
Definition: SetVector.h:98
bool insert(const value_type &X)
Insert a new element into the SetVector.
Definition: SetVector.h:162
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:360
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:342
iterator begin() const
Definition: SmallPtrSet.h:380
bool contains(ConstPtrType Ptr) const
Definition: SmallPtrSet.h:366
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
Definition: SmallPtrSet.h:427
A SetVector that performs no allocations if smaller than a certain size.
Definition: SetVector.h:370
bool empty() const
Definition: SmallVector.h:94
size_t size() const
Definition: SmallVector.h:91
void push_back(const T &Elt)
Definition: SmallVector.h:426
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1209
An instruction for storing to memory.
Definition: Instructions.h:302
Value * getValueOperand()
Definition: Instructions.h:399
Analysis pass providing the TargetLibraryInfo.
Provides information about what library functions are available for the current target.
bool has(LibFunc F) const
Tests whether a library function is available.
bool getLibFunc(StringRef funcName, LibFunc &F) const
Searches for a particular function name.
static constexpr TypeSize getFixed(ScalarTy ExactSize)
Definition: TypeSize.h:332
The instances of the Type class are immutable: once they are created, they are never changed.
Definition: Type.h:45
static IntegerType * getInt8Ty(LLVMContext &C)
A Use represents the edge between a Value definition and its users.
Definition: Use.h:43
op_range operands()
Definition: User.h:242
LLVM Value Representation.
Definition: Value.h:74
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:255
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs and address space casts.
Definition: Value.cpp:693
LLVMContext & getContext() const
All values hold a context through their type.
Definition: Value.cpp:1074
iterator_range< use_iterator > uses()
Definition: Value.h:376
constexpr bool isScalable() const
Returns whether the quantity is scaled by a runtime quantity (vscale).
Definition: TypeSize.h:171
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
bool match(Val *V, const Pattern &P)
Definition: PatternMatch.h:49
bind_ty< Instruction > m_Instruction(Instruction *&I)
Match an instruction, capturing it if we match.
Definition: PatternMatch.h:724
specificval_ty m_Specific(const Value *V)
Match if we have a specific specified value.
Definition: PatternMatch.h:780
class_match< ConstantInt > m_ConstantInt()
Match an arbitrary ConstantInt and ignore it.
Definition: PatternMatch.h:147
match_combine_and< LTy, RTy > m_CombineAnd(const LTy &L, const RTy &R)
Combine two pattern matchers matching L && R.
Definition: PatternMatch.h:224
CmpClass_match< LHS, RHS, ICmpInst, ICmpInst::Predicate > m_ICmp(ICmpInst::Predicate &Pred, const LHS &L, const RHS &R)
OneOps_match< OpTy, Instruction::Load > m_Load(const OpTy &Op)
Matches LoadInst.
brc_match< Cond_t, bind_ty< BasicBlock >, bind_ty< BasicBlock > > m_Br(const Cond_t &C, BasicBlock *&T, BasicBlock *&F)
CmpClass_match< LHS, RHS, ICmpInst, ICmpInst::Predicate, true > m_c_ICmp(ICmpInst::Predicate &Pred, const LHS &L, const RHS &R)
Matches an ICmp with a predicate over LHS and RHS in either order.
class_match< Value > m_Value()
Match an arbitrary value and ignore it.
Definition: PatternMatch.h:76
is_zero m_Zero()
Match any null constant or a vector with all elements equal to 0.
Definition: PatternMatch.h:545
AssignmentMarkerRange getAssignmentMarkers(DIAssignID *ID)
Return a range of dbg.assign intrinsics which use \ID as an operand.
Definition: DebugInfo.cpp:1785
SmallVector< DPValue * > getDPVAssignmentMarkers(const Instruction *Inst)
Definition: DebugInfo.h:236
bool calculateFragmentIntersect(const DataLayout &DL, const Value *Dest, uint64_t SliceOffsetInBits, uint64_t SliceSizeInBits, const DbgAssignIntrinsic *DbgAssign, std::optional< DIExpression::FragmentInfo > &Result)
Calculate the fragment of the variable in DAI covered from (Dest + SliceOffsetInBits) to to (Dest + S...
Definition: DebugInfo.cpp:2008
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:450
NodeAddr< DefNode * > Def
Definition: RDFGraph.h:384
NodeAddr< FuncNode * > Func
Definition: RDFGraph.h:393
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
auto drop_begin(T &&RangeOrContainer, size_t N=1)
Return a range covering RangeOrContainer with the first N elements excluded.
Definition: STLExtras.h:329
UnaryFunction for_each(R &&Range, UnaryFunction F)
Provide wrappers to std::for_each which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1724
Constant * getInitialValueOfAllocation(const Value *V, const TargetLibraryInfo *TLI, Type *Ty)
If this is a call to an allocation function that initializes memory to a fixed value,...
bool isStrongerThanMonotonic(AtomicOrdering AO)
bool isAligned(Align Lhs, uint64_t SizeInBytes)
Checks that SizeInBytes is a multiple of the alignment.
Definition: Alignment.h:145
void salvageDebugInfo(const MachineRegisterInfo &MRI, MachineInstr &MI)
Assuming the instruction MI is going to be deleted, attempt to salvage debug users of MI by writing t...
Definition: Utils.cpp:1579
Value * emitCalloc(Value *Num, Value *Size, IRBuilderBase &B, const TargetLibraryInfo &TLI)
Emit a call to the calloc function.
Value * GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, const DataLayout &DL, bool AllowNonInbounds=true)
Analyze the specified pointer to see if it can be expressed as a base pointer plus a constant offset.
const Value * getUnderlyingObject(const Value *V, unsigned MaxLookup=6)
This method strips off any GEP address adjustments and pointer casts from the specified value,...
iterator_range< po_iterator< T > > post_order(const T &G)
bool isNoAliasCall(const Value *V)
Return true if this pointer is returned by a noalias function.
bool any_of(R &&range, UnaryPredicate P)
Provide wrappers to std::any_of which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1738
bool isInstructionTriviallyDead(Instruction *I, const TargetLibraryInfo *TLI=nullptr)
Return true if the result produced by the instruction is not used, and the instruction will return.
Definition: Local.cpp:399
bool getObjectSize(const Value *Ptr, uint64_t &Size, const DataLayout &DL, const TargetLibraryInfo *TLI, ObjectSizeOpts Opts={})
Compute the size of the object pointed by Ptr.
auto reverse(ContainerTy &&C)
Definition: STLExtras.h:428
bool isModSet(const ModRefInfo MRI)
Definition: ModRef.h:48
bool PointerMayBeCaptured(const Value *V, bool ReturnCaptures, bool StoreCaptures, unsigned MaxUsesToExplore=0)
PointerMayBeCaptured - Return true if this pointer value may be captured by the enclosing function (w...
bool NullPointerIsDefined(const Function *F, unsigned AS=0)
Check whether null pointer dereferencing is considered undefined behavior for a given function or an ...
Definition: Function.cpp:2010
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
bool AreStatisticsEnabled()
Check if statistics are enabled.
Definition: Statistic.cpp:139
bool isNotVisibleOnUnwind(const Value *Object, bool &RequiresNoCaptureBeforeUnwind)
Return true if Object memory is not visible after an unwind, in the sense that program semantics cann...
uint64_t offsetToAlignment(uint64_t Value, Align Alignment)
Returns the offset to the next integer (mod 2**64) that is greater than or equal to Value and is a mu...
Definition: Alignment.h:197
bool salvageKnowledge(Instruction *I, AssumptionCache *AC=nullptr, DominatorTree *DT=nullptr)
Calls BuildAssumeFromInst and if the resulting llvm.assume is valid insert if before I.
Value * getFreedOperand(const CallBase *CB, const TargetLibraryInfo *TLI)
If this if a call to a free function, return the freed operand.
Value * isBytewiseValue(Value *V, const DataLayout &DL)
If the specified value can be set by repeating the same byte in memory, return the i8 value that it i...
auto predecessors(const MachineBasicBlock *BB)
bool mayContainIrreducibleControl(const Function &F, const LoopInfo *LI)
bool isIdentifiedObject(const Value *V)
Return true if this pointer refers to a distinct and identifiable object.
bool isStrongerThan(AtomicOrdering AO, AtomicOrdering Other)
Returns true if ao is stronger than other as defined by the AtomicOrdering lattice,...
bool isRefSet(const ModRefInfo MRI)
Definition: ModRef.h:51
This struct is a compact representation of a valid (non-zero power of two) alignment.
Definition: Alignment.h:39
uint64_t value() const
This is a hole in the type system and should not be abused.
Definition: Alignment.h:85
Holds the characteristics of one fragment of a larger variable.
Various options to control the behavior of getObjectSize.
bool NullIsUnknownSize
If this is true, null pointers in address space 0 will be treated as though they can't be evaluated.