1 //===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass performs various transformations related to eliminating memcpy
11 // calls, or transforming sets of stores into memset's.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "memcpyopt"
16 #include "llvm/Transforms/Scalar.h"
17 #include "llvm/IntrinsicInst.h"
18 #include "llvm/Instructions.h"
19 #include "llvm/LLVMContext.h"
20 #include "llvm/ADT/SmallVector.h"
21 #include "llvm/ADT/Statistic.h"
22 #include "llvm/Analysis/Dominators.h"
23 #include "llvm/Analysis/AliasAnalysis.h"
24 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/GetElementPtrTypeIterator.h"
27 #include "llvm/Support/raw_ostream.h"
28 #include "llvm/Target/TargetData.h"
32 STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted");
33 STATISTIC(NumMemSetInfer, "Number of memsets inferred");
34 STATISTIC(NumMoveToCpy, "Number of memmoves converted to memcpy");
36 /// isBytewiseValue - If the specified value can be set by repeating the same
37 /// byte in memory, return the i8 value that it is represented with. This is
38 /// true for all i8 values obviously, but is also true for i32 0, i32 -1,
39 /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
40 /// byte store (e.g. i16 0x1234), return null.
41 static Value *isBytewiseValue(Value *V) {
42 LLVMContext &Context = V->getContext();
44 // All byte-wide stores are splatable, even of arbitrary variables.
45 if (V->getType()->isIntegerTy(8)) return V;
47 // Constant float and double values can be handled as integer values if the
48 // corresponding integer value is "byteable". An important case is 0.0.
49 if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
50 if (CFP->getType()->isFloatTy())
51 V = ConstantExpr::getBitCast(CFP, Type::getInt32Ty(Context));
52 if (CFP->getType()->isDoubleTy())
53 V = ConstantExpr::getBitCast(CFP, Type::getInt64Ty(Context));
54 // Don't handle long double formats, which have strange constraints.
57 // We can handle constant integers that are power of two in size and a
58 // multiple of 8 bits.
59 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
60 unsigned Width = CI->getBitWidth();
61 if (isPowerOf2_32(Width) && Width > 8) {
62 // We can handle this value if the recursive binary decomposition is the
63 // same at all levels.
64 APInt Val = CI->getValue();
66 while (Val.getBitWidth() != 8) {
67 unsigned NextWidth = Val.getBitWidth()/2;
68 Val2 = Val.lshr(NextWidth);
69 Val2.trunc(Val.getBitWidth()/2);
70 Val.trunc(Val.getBitWidth()/2);
72 // If the top/bottom halves aren't the same, reject it.
76 return ConstantInt::get(Context, Val);
80 // Conceptually, we could handle things like:
81 // %a = zext i8 %X to i16
84 // but until there is an example that actually needs this, it doesn't seem
85 // worth worrying about.
89 static int64_t GetOffsetFromIndex(const GetElementPtrInst *GEP, unsigned Idx,
90 bool &VariableIdxFound, TargetData &TD) {
91 // Skip over the first indices.
92 gep_type_iterator GTI = gep_type_begin(GEP);
93 for (unsigned i = 1; i != Idx; ++i, ++GTI)
96 // Compute the offset implied by the rest of the indices.
98 for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
99 ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
101 return VariableIdxFound = true;
102 if (OpC->isZero()) continue; // No offset.
104 // Handle struct indices, which add their field offset to the pointer.
105 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
106 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
110 // Otherwise, we have a sequential type like an array or vector. Multiply
111 // the index by the ElementSize.
112 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
113 Offset += Size*OpC->getSExtValue();
119 /// IsPointerOffset - Return true if Ptr1 is provably equal to Ptr2 plus a
120 /// constant offset, and return that constant offset. For example, Ptr1 might
121 /// be &A[42], and Ptr2 might be &A[40]. In this case offset would be -8.
122 static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
124 // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
125 // base. After that base, they may have some number of common (and
126 // potentially variable) indices. After that they handle some constant
127 // offset, which determines their offset from each other. At this point, we
128 // handle no other case.
129 GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(Ptr1);
130 GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(Ptr2);
131 if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0))
134 // Skip any common indices and track the GEP types.
136 for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
137 if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
140 bool VariableIdxFound = false;
141 int64_t Offset1 = GetOffsetFromIndex(GEP1, Idx, VariableIdxFound, TD);
142 int64_t Offset2 = GetOffsetFromIndex(GEP2, Idx, VariableIdxFound, TD);
143 if (VariableIdxFound) return false;
145 Offset = Offset2-Offset1;
150 /// MemsetRange - Represents a range of memset'd bytes with the ByteVal value.
151 /// This allows us to analyze stores like:
156 /// which sometimes happens with stores to arrays of structs etc. When we see
157 /// the first store, we make a range [1, 2). The second store extends the range
158 /// to [0, 2). The third makes a new range [2, 3). The fourth store joins the
159 /// two ranges into [0, 3) which is memset'able.
162 // Start/End - A semi range that describes the span that this range covers.
163 // The range is closed at the start and open at the end: [Start, End).
166 /// StartPtr - The getelementptr instruction that points to the start of the
170 /// Alignment - The known alignment of the first store.
173 /// TheStores - The actual stores that make up this range.
174 SmallVector<StoreInst*, 16> TheStores;
176 bool isProfitableToUseMemset(const TargetData &TD) const;
179 } // end anon namespace
181 bool MemsetRange::isProfitableToUseMemset(const TargetData &TD) const {
182 // If we found more than 8 stores to merge or 64 bytes, use memset.
183 if (TheStores.size() >= 8 || End-Start >= 64) return true;
185 // Assume that the code generator is capable of merging pairs of stores
186 // together if it wants to.
187 if (TheStores.size() <= 2) return false;
189 // If we have fewer than 8 stores, it can still be worthwhile to do this.
190 // For example, merging 4 i8 stores into an i32 store is useful almost always.
191 // However, merging 2 32-bit stores isn't useful on a 32-bit architecture (the
192 // memset will be split into 2 32-bit stores anyway) and doing so can
193 // pessimize the llvm optimizer.
195 // Since we don't have perfect knowledge here, make some assumptions: assume
196 // the maximum GPR width is the same size as the pointer size and assume that
197 // this width can be stored. If so, check to see whether we will end up
198 // actually reducing the number of stores used.
199 unsigned Bytes = unsigned(End-Start);
200 unsigned NumPointerStores = Bytes/TD.getPointerSize();
202 // Assume the remaining bytes if any are done a byte at a time.
203 unsigned NumByteStores = Bytes - NumPointerStores*TD.getPointerSize();
205 // If we will reduce the # stores (according to this heuristic), do the
206 // transformation. This encourages merging 4 x i8 -> i32 and 2 x i16 -> i32
208 return TheStores.size() > NumPointerStores+NumByteStores;
214 /// Ranges - A sorted list of the memset ranges. We use std::list here
215 /// because each element is relatively large and expensive to copy.
216 std::list<MemsetRange> Ranges;
217 typedef std::list<MemsetRange>::iterator range_iterator;
220 MemsetRanges(TargetData &td) : TD(td) {}
222 typedef std::list<MemsetRange>::const_iterator const_iterator;
223 const_iterator begin() const { return Ranges.begin(); }
224 const_iterator end() const { return Ranges.end(); }
225 bool empty() const { return Ranges.empty(); }
227 void addStore(int64_t OffsetFromFirst, StoreInst *SI);
230 } // end anon namespace
233 /// addStore - Add a new store to the MemsetRanges data structure. This adds a
234 /// new range for the specified store at the specified offset, merging into
235 /// existing ranges as appropriate.
236 void MemsetRanges::addStore(int64_t Start, StoreInst *SI) {
237 int64_t End = Start+TD.getTypeStoreSize(SI->getOperand(0)->getType());
239 // Do a linear search of the ranges to see if this can be joined and/or to
240 // find the insertion point in the list. We keep the ranges sorted for
241 // simplicity here. This is a linear search of a linked list, which is ugly,
242 // however the number of ranges is limited, so this won't get crazy slow.
243 range_iterator I = Ranges.begin(), E = Ranges.end();
245 while (I != E && Start > I->End)
248 // We now know that I == E, in which case we didn't find anything to merge
249 // with, or that Start <= I->End. If End < I->Start or I == E, then we need
250 // to insert a new range. Handle this now.
251 if (I == E || End < I->Start) {
252 MemsetRange &R = *Ranges.insert(I, MemsetRange());
255 R.StartPtr = SI->getPointerOperand();
256 R.Alignment = SI->getAlignment();
257 R.TheStores.push_back(SI);
261 // This store overlaps with I, add it.
262 I->TheStores.push_back(SI);
264 // At this point, we may have an interval that completely contains our store.
265 // If so, just add it to the interval and return.
266 if (I->Start <= Start && I->End >= End)
269 // Now we know that Start <= I->End and End >= I->Start so the range overlaps
270 // but is not entirely contained within the range.
272 // See if the range extends the start of the range. In this case, it couldn't
273 // possibly cause it to join the prior range, because otherwise we would have
275 if (Start < I->Start) {
277 I->StartPtr = SI->getPointerOperand();
278 I->Alignment = SI->getAlignment();
281 // Now we know that Start <= I->End and Start >= I->Start (so the startpoint
282 // is in or right at the end of I), and that End >= I->Start. Extend I out to
286 range_iterator NextI = I;
287 while (++NextI != E && End >= NextI->Start) {
288 // Merge the range in.
289 I->TheStores.append(NextI->TheStores.begin(), NextI->TheStores.end());
290 if (NextI->End > I->End)
298 //===----------------------------------------------------------------------===//
300 //===----------------------------------------------------------------------===//
303 class MemCpyOpt : public FunctionPass {
304 bool runOnFunction(Function &F);
306 static char ID; // Pass identification, replacement for typeid
307 MemCpyOpt() : FunctionPass(ID) {}
310 // This transformation requires dominator postdominator info
311 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
312 AU.setPreservesCFG();
313 AU.addRequired<DominatorTree>();
314 AU.addRequired<MemoryDependenceAnalysis>();
315 AU.addRequired<AliasAnalysis>();
316 AU.addPreserved<AliasAnalysis>();
317 AU.addPreserved<MemoryDependenceAnalysis>();
321 bool processStore(StoreInst *SI, BasicBlock::iterator &BBI);
322 bool processMemCpy(MemCpyInst *M);
323 bool processMemMove(MemMoveInst *M);
324 bool performCallSlotOptzn(MemCpyInst *cpy, CallInst *C);
325 bool iterateOnFunction(Function &F);
328 char MemCpyOpt::ID = 0;
331 // createMemCpyOptPass - The public interface to this file...
332 FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOpt(); }
334 INITIALIZE_PASS(MemCpyOpt, "memcpyopt", "MemCpy Optimization", false, false);
338 /// processStore - When GVN is scanning forward over instructions, we look for
339 /// some other patterns to fold away. In particular, this looks for stores to
340 /// neighboring locations of memory. If it sees enough consequtive ones
341 /// (currently 4) it attempts to merge them together into a memcpy/memset.
342 bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
343 if (SI->isVolatile()) return false;
345 LLVMContext &Context = SI->getContext();
347 // There are two cases that are interesting for this code to handle: memcpy
348 // and memset. Right now we only handle memset.
350 // Ensure that the value being stored is something that can be memset'able a
351 // byte at a time like "0" or "-1" or any width, as well as things like
352 // 0xA0A0A0A0 and 0.0.
353 Value *ByteVal = isBytewiseValue(SI->getOperand(0));
357 TargetData *TD = getAnalysisIfAvailable<TargetData>();
358 if (!TD) return false;
359 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
360 Module *M = SI->getParent()->getParent()->getParent();
362 // Okay, so we now have a single store that can be splatable. Scan to find
363 // all subsequent stores of the same value to offset from the same pointer.
364 // Join these together into ranges, so we can decide whether contiguous blocks
366 MemsetRanges Ranges(*TD);
368 Value *StartPtr = SI->getPointerOperand();
370 BasicBlock::iterator BI = SI;
371 for (++BI; !isa<TerminatorInst>(BI); ++BI) {
372 if (isa<CallInst>(BI) || isa<InvokeInst>(BI)) {
373 // If the call is readnone, ignore it, otherwise bail out. We don't even
374 // allow readonly here because we don't want something like:
375 // A[1] = 2; strlen(A); A[2] = 2; -> memcpy(A, ...); strlen(A).
376 if (AA.getModRefBehavior(CallSite(BI)) ==
377 AliasAnalysis::DoesNotAccessMemory)
380 // TODO: If this is a memset, try to join it in.
383 } else if (isa<VAArgInst>(BI) || isa<LoadInst>(BI))
386 // If this is a non-store instruction it is fine, ignore it.
387 StoreInst *NextStore = dyn_cast<StoreInst>(BI);
388 if (NextStore == 0) continue;
390 // If this is a store, see if we can merge it in.
391 if (NextStore->isVolatile()) break;
393 // Check to see if this stored value is of the same byte-splattable value.
394 if (ByteVal != isBytewiseValue(NextStore->getOperand(0)))
397 // Check to see if this store is to a constant offset from the start ptr.
399 if (!IsPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset, *TD))
402 Ranges.addStore(Offset, NextStore);
405 // If we have no ranges, then we just had a single store with nothing that
406 // could be merged in. This is a very common case of course.
410 // If we had at least one store that could be merged in, add the starting
411 // store as well. We try to avoid this unless there is at least something
412 // interesting as a small compile-time optimization.
413 Ranges.addStore(0, SI);
416 // Now that we have full information about ranges, loop over the ranges and
417 // emit memset's for anything big enough to be worthwhile.
418 bool MadeChange = false;
419 for (MemsetRanges::const_iterator I = Ranges.begin(), E = Ranges.end();
421 const MemsetRange &Range = *I;
423 if (Range.TheStores.size() == 1) continue;
425 // If it is profitable to lower this range to memset, do so now.
426 if (!Range.isProfitableToUseMemset(*TD))
429 // Otherwise, we do want to transform this! Create a new memset. We put
430 // the memset right before the first instruction that isn't part of this
431 // memset block. This ensure that the memset is dominated by any addressing
432 // instruction needed by the start of the block.
433 BasicBlock::iterator InsertPt = BI;
435 // Get the starting pointer of the block.
436 StartPtr = Range.StartPtr;
438 // Determine alignment
439 unsigned Alignment = Range.Alignment;
440 if (Alignment == 0) {
441 const Type *EltType =
442 cast<PointerType>(StartPtr->getType())->getElementType();
443 Alignment = TD->getABITypeAlignment(EltType);
446 // Cast the start ptr to be i8* as memset requires.
447 const PointerType* StartPTy = cast<PointerType>(StartPtr->getType());
448 const PointerType *i8Ptr = Type::getInt8PtrTy(Context,
449 StartPTy->getAddressSpace());
450 if (StartPTy!= i8Ptr)
451 StartPtr = new BitCastInst(StartPtr, i8Ptr, StartPtr->getName(),
455 StartPtr, ByteVal, // Start, value
457 ConstantInt::get(Type::getInt64Ty(Context), Range.End-Range.Start),
459 ConstantInt::get(Type::getInt32Ty(Context), Alignment),
461 ConstantInt::get(Type::getInt1Ty(Context), 0),
463 const Type *Tys[] = { Ops[0]->getType(), Ops[2]->getType() };
465 Function *MemSetF = Intrinsic::getDeclaration(M, Intrinsic::memset, Tys, 2);
467 Value *C = CallInst::Create(MemSetF, Ops, Ops+5, "", InsertPt);
468 DEBUG(dbgs() << "Replace stores:\n";
469 for (unsigned i = 0, e = Range.TheStores.size(); i != e; ++i)
470 dbgs() << *Range.TheStores[i];
471 dbgs() << "With: " << *C); C=C;
473 // Don't invalidate the iterator
476 // Zap all the stores.
477 for (SmallVector<StoreInst*, 16>::const_iterator
478 SI = Range.TheStores.begin(),
479 SE = Range.TheStores.end(); SI != SE; ++SI)
480 (*SI)->eraseFromParent();
489 /// performCallSlotOptzn - takes a memcpy and a call that it depends on,
490 /// and checks for the possibility of a call slot optimization by having
491 /// the call write its result directly into the destination of the memcpy.
492 bool MemCpyOpt::performCallSlotOptzn(MemCpyInst *cpy, CallInst *C) {
493 // The general transformation to keep in mind is
495 // call @func(..., src, ...)
496 // memcpy(dest, src, ...)
500 // memcpy(dest, src, ...)
501 // call @func(..., dest, ...)
503 // Since moving the memcpy is technically awkward, we additionally check that
504 // src only holds uninitialized values at the moment of the call, meaning that
505 // the memcpy can be discarded rather than moved.
507 // Deliberately get the source and destination with bitcasts stripped away,
508 // because we'll need to do type comparisons based on the underlying type.
509 Value *cpyDest = cpy->getDest();
510 Value *cpySrc = cpy->getSource();
513 // We need to be able to reason about the size of the memcpy, so we require
514 // that it be a constant.
515 ConstantInt *cpyLength = dyn_cast<ConstantInt>(cpy->getLength());
519 // Require that src be an alloca. This simplifies the reasoning considerably.
520 AllocaInst *srcAlloca = dyn_cast<AllocaInst>(cpySrc);
524 // Check that all of src is copied to dest.
525 TargetData *TD = getAnalysisIfAvailable<TargetData>();
526 if (!TD) return false;
528 ConstantInt *srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize());
532 uint64_t srcSize = TD->getTypeAllocSize(srcAlloca->getAllocatedType()) *
533 srcArraySize->getZExtValue();
535 if (cpyLength->getZExtValue() < srcSize)
538 // Check that accessing the first srcSize bytes of dest will not cause a
539 // trap. Otherwise the transform is invalid since it might cause a trap
540 // to occur earlier than it otherwise would.
541 if (AllocaInst *A = dyn_cast<AllocaInst>(cpyDest)) {
542 // The destination is an alloca. Check it is larger than srcSize.
543 ConstantInt *destArraySize = dyn_cast<ConstantInt>(A->getArraySize());
547 uint64_t destSize = TD->getTypeAllocSize(A->getAllocatedType()) *
548 destArraySize->getZExtValue();
550 if (destSize < srcSize)
552 } else if (Argument *A = dyn_cast<Argument>(cpyDest)) {
553 // If the destination is an sret parameter then only accesses that are
554 // outside of the returned struct type can trap.
555 if (!A->hasStructRetAttr())
558 const Type *StructTy = cast<PointerType>(A->getType())->getElementType();
559 uint64_t destSize = TD->getTypeAllocSize(StructTy);
561 if (destSize < srcSize)
567 // Check that src is not accessed except via the call and the memcpy. This
568 // guarantees that it holds only undefined values when passed in (so the final
569 // memcpy can be dropped), that it is not read or written between the call and
570 // the memcpy, and that writing beyond the end of it is undefined.
571 SmallVector<User*, 8> srcUseList(srcAlloca->use_begin(),
572 srcAlloca->use_end());
573 while (!srcUseList.empty()) {
574 User *UI = srcUseList.pop_back_val();
576 if (isa<BitCastInst>(UI)) {
577 for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
579 srcUseList.push_back(*I);
580 } else if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(UI)) {
581 if (G->hasAllZeroIndices())
582 for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
584 srcUseList.push_back(*I);
587 } else if (UI != C && UI != cpy) {
592 // Since we're changing the parameter to the callsite, we need to make sure
593 // that what would be the new parameter dominates the callsite.
594 DominatorTree &DT = getAnalysis<DominatorTree>();
595 if (Instruction *cpyDestInst = dyn_cast<Instruction>(cpyDest))
596 if (!DT.dominates(cpyDestInst, C))
599 // In addition to knowing that the call does not access src in some
600 // unexpected manner, for example via a global, which we deduce from
601 // the use analysis, we also need to know that it does not sneakily
602 // access dest. We rely on AA to figure this out for us.
603 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
604 if (AA.getModRefInfo(C, cpy->getRawDest(), srcSize) !=
605 AliasAnalysis::NoModRef)
608 // All the checks have passed, so do the transformation.
609 bool changedArgument = false;
610 for (unsigned i = 0; i < CS.arg_size(); ++i)
611 if (CS.getArgument(i)->stripPointerCasts() == cpySrc) {
612 if (cpySrc->getType() != cpyDest->getType())
613 cpyDest = CastInst::CreatePointerCast(cpyDest, cpySrc->getType(),
614 cpyDest->getName(), C);
615 changedArgument = true;
616 if (CS.getArgument(i)->getType() == cpyDest->getType())
617 CS.setArgument(i, cpyDest);
619 CS.setArgument(i, CastInst::CreatePointerCast(cpyDest,
620 CS.getArgument(i)->getType(), cpyDest->getName(), C));
623 if (!changedArgument)
626 // Drop any cached information about the call, because we may have changed
627 // its dependence information by changing its parameter.
628 MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
629 MD.removeInstruction(C);
632 MD.removeInstruction(cpy);
633 cpy->eraseFromParent();
639 /// processMemCpy - perform simplification of memcpy's. If we have memcpy A
640 /// which copies X to Y, and memcpy B which copies Y to Z, then we can rewrite
641 /// B to be a memcpy from X to Z (or potentially a memmove, depending on
642 /// circumstances). This allows later passes to remove the first memcpy
644 bool MemCpyOpt::processMemCpy(MemCpyInst *M) {
645 MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
647 // The are two possible optimizations we can do for memcpy:
648 // a) memcpy-memcpy xform which exposes redundance for DSE.
649 // b) call-memcpy xform for return slot optimization.
650 MemDepResult dep = MD.getDependency(M);
651 if (!dep.isClobber())
653 if (!isa<MemCpyInst>(dep.getInst())) {
654 if (CallInst *C = dyn_cast<CallInst>(dep.getInst()))
655 return performCallSlotOptzn(M, C);
659 MemCpyInst *MDep = cast<MemCpyInst>(dep.getInst());
661 // We can only transforms memcpy's where the dest of one is the source of the
663 if (M->getSource() != MDep->getDest())
666 // Second, the length of the memcpy's must be the same, or the preceeding one
667 // must be larger than the following one.
668 ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength());
669 ConstantInt *C2 = dyn_cast<ConstantInt>(M->getLength());
673 uint64_t DepSize = C1->getValue().getZExtValue();
674 uint64_t CpySize = C2->getValue().getZExtValue();
676 if (DepSize < CpySize)
679 // Finally, we have to make sure that the dest of the second does not
680 // alias the source of the first
681 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
682 if (AA.alias(M->getRawDest(), CpySize, MDep->getRawSource(), DepSize) !=
683 AliasAnalysis::NoAlias)
685 else if (AA.alias(M->getRawDest(), CpySize, M->getRawSource(), CpySize) !=
686 AliasAnalysis::NoAlias)
688 else if (AA.alias(MDep->getRawDest(), DepSize, MDep->getRawSource(), DepSize)
689 != AliasAnalysis::NoAlias)
692 // If all checks passed, then we can transform these memcpy's
693 const Type *ArgTys[3] = { M->getRawDest()->getType(),
694 MDep->getRawSource()->getType(),
695 M->getLength()->getType() };
696 Function *MemCpyFun = Intrinsic::getDeclaration(
697 M->getParent()->getParent()->getParent(),
698 M->getIntrinsicID(), ArgTys, 3);
700 // Make sure to use the lesser of the alignment of the source and the dest
701 // since we're changing where we're reading from, but don't want to increase
702 // the alignment past what can be read from or written to.
703 // TODO: Is this worth it if we're creating a less aligned memcpy? For
704 // example we could be moving from movaps -> movq on x86.
705 unsigned Align = std::min(MDep->getAlignmentCst()->getZExtValue(),
706 M->getAlignmentCst()->getZExtValue());
707 LLVMContext &Context = M->getContext();
708 ConstantInt *AlignCI = ConstantInt::get(Type::getInt32Ty(Context), Align);
710 M->getRawDest(), MDep->getRawSource(), M->getLength(),
711 AlignCI, M->getVolatileCst()
713 CallInst *C = CallInst::Create(MemCpyFun, Args, Args+5, "", M);
715 // If C and M don't interfere, then this is a valid transformation. If they
716 // did, this would mean that the two sources overlap, which would be bad.
717 if (MD.getDependency(C) == dep) {
718 MD.removeInstruction(M);
719 M->eraseFromParent();
724 // Otherwise, there was no point in doing this, so we remove the call we
725 // inserted and act like nothing happened.
726 MD.removeInstruction(C);
727 C->eraseFromParent();
731 /// processMemMove - Transforms memmove calls to memcpy calls when the src/dst
732 /// are guaranteed not to alias.
733 bool MemCpyOpt::processMemMove(MemMoveInst *M) {
734 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
736 // If the memmove is a constant size, use it for the alias query, this allows
737 // us to optimize things like: memmove(P, P+64, 64);
738 uint64_t MemMoveSize = ~0ULL;
739 if (ConstantInt *Len = dyn_cast<ConstantInt>(M->getLength()))
740 MemMoveSize = Len->getZExtValue();
742 // See if the pointers alias.
743 if (AA.alias(M->getRawDest(), MemMoveSize, M->getRawSource(), MemMoveSize) !=
744 AliasAnalysis::NoAlias)
747 DEBUG(dbgs() << "MemCpyOpt: Optimizing memmove -> memcpy: " << *M << "\n");
749 // If not, then we know we can transform this.
750 Module *Mod = M->getParent()->getParent()->getParent();
751 const Type *ArgTys[3] = { M->getRawDest()->getType(),
752 M->getRawSource()->getType(),
753 M->getLength()->getType() };
754 M->setCalledFunction(Intrinsic::getDeclaration(Mod, Intrinsic::memcpy,
757 // MemDep may have over conservative information about this instruction, just
758 // conservatively flush it from the cache.
759 getAnalysis<MemoryDependenceAnalysis>().removeInstruction(M);
766 // MemCpyOpt::iterateOnFunction - Executes one iteration of GVN.
767 bool MemCpyOpt::iterateOnFunction(Function &F) {
768 bool MadeChange = false;
770 // Walk all instruction in the function.
771 for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
772 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
774 // Avoid invalidating the iterator.
775 Instruction *I = BI++;
777 if (StoreInst *SI = dyn_cast<StoreInst>(I))
778 MadeChange |= processStore(SI, BI);
779 else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I))
780 MadeChange |= processMemCpy(M);
781 else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I)) {
782 if (processMemMove(M)) {
783 --BI; // Reprocess the new memcpy.
793 // MemCpyOpt::runOnFunction - This is the main transformation entry point for a
796 bool MemCpyOpt::runOnFunction(Function &F) {
797 bool MadeChange = false;
799 if (!iterateOnFunction(F))