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_BEGIN(MemCpyOpt, "memcpyopt", "MemCpy Optimization",
336 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
337 INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis)
338 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
339 INITIALIZE_PASS_END(MemCpyOpt, "memcpyopt", "MemCpy Optimization",
343 /// processStore - When GVN is scanning forward over instructions, we look for
344 /// some other patterns to fold away. In particular, this looks for stores to
345 /// neighboring locations of memory. If it sees enough consequtive ones
346 /// (currently 4) it attempts to merge them together into a memcpy/memset.
347 bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
348 if (SI->isVolatile()) return false;
350 LLVMContext &Context = SI->getContext();
352 // There are two cases that are interesting for this code to handle: memcpy
353 // and memset. Right now we only handle memset.
355 // Ensure that the value being stored is something that can be memset'able a
356 // byte at a time like "0" or "-1" or any width, as well as things like
357 // 0xA0A0A0A0 and 0.0.
358 Value *ByteVal = isBytewiseValue(SI->getOperand(0));
362 TargetData *TD = getAnalysisIfAvailable<TargetData>();
363 if (!TD) return false;
364 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
365 Module *M = SI->getParent()->getParent()->getParent();
367 // Okay, so we now have a single store that can be splatable. Scan to find
368 // all subsequent stores of the same value to offset from the same pointer.
369 // Join these together into ranges, so we can decide whether contiguous blocks
371 MemsetRanges Ranges(*TD);
373 Value *StartPtr = SI->getPointerOperand();
375 BasicBlock::iterator BI = SI;
376 for (++BI; !isa<TerminatorInst>(BI); ++BI) {
377 if (isa<CallInst>(BI) || isa<InvokeInst>(BI)) {
378 // If the call is readnone, ignore it, otherwise bail out. We don't even
379 // allow readonly here because we don't want something like:
380 // A[1] = 2; strlen(A); A[2] = 2; -> memcpy(A, ...); strlen(A).
381 if (AA.getModRefBehavior(CallSite(BI)) ==
382 AliasAnalysis::DoesNotAccessMemory)
385 // TODO: If this is a memset, try to join it in.
388 } else if (isa<VAArgInst>(BI) || isa<LoadInst>(BI))
391 // If this is a non-store instruction it is fine, ignore it.
392 StoreInst *NextStore = dyn_cast<StoreInst>(BI);
393 if (NextStore == 0) continue;
395 // If this is a store, see if we can merge it in.
396 if (NextStore->isVolatile()) break;
398 // Check to see if this stored value is of the same byte-splattable value.
399 if (ByteVal != isBytewiseValue(NextStore->getOperand(0)))
402 // Check to see if this store is to a constant offset from the start ptr.
404 if (!IsPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset, *TD))
407 Ranges.addStore(Offset, NextStore);
410 // If we have no ranges, then we just had a single store with nothing that
411 // could be merged in. This is a very common case of course.
415 // If we had at least one store that could be merged in, add the starting
416 // store as well. We try to avoid this unless there is at least something
417 // interesting as a small compile-time optimization.
418 Ranges.addStore(0, SI);
421 // Now that we have full information about ranges, loop over the ranges and
422 // emit memset's for anything big enough to be worthwhile.
423 bool MadeChange = false;
424 for (MemsetRanges::const_iterator I = Ranges.begin(), E = Ranges.end();
426 const MemsetRange &Range = *I;
428 if (Range.TheStores.size() == 1) continue;
430 // If it is profitable to lower this range to memset, do so now.
431 if (!Range.isProfitableToUseMemset(*TD))
434 // Otherwise, we do want to transform this! Create a new memset. We put
435 // the memset right before the first instruction that isn't part of this
436 // memset block. This ensure that the memset is dominated by any addressing
437 // instruction needed by the start of the block.
438 BasicBlock::iterator InsertPt = BI;
440 // Get the starting pointer of the block.
441 StartPtr = Range.StartPtr;
443 // Determine alignment
444 unsigned Alignment = Range.Alignment;
445 if (Alignment == 0) {
446 const Type *EltType =
447 cast<PointerType>(StartPtr->getType())->getElementType();
448 Alignment = TD->getABITypeAlignment(EltType);
451 // Cast the start ptr to be i8* as memset requires.
452 const PointerType* StartPTy = cast<PointerType>(StartPtr->getType());
453 const PointerType *i8Ptr = Type::getInt8PtrTy(Context,
454 StartPTy->getAddressSpace());
455 if (StartPTy!= i8Ptr)
456 StartPtr = new BitCastInst(StartPtr, i8Ptr, StartPtr->getName(),
460 StartPtr, ByteVal, // Start, value
462 ConstantInt::get(Type::getInt64Ty(Context), Range.End-Range.Start),
464 ConstantInt::get(Type::getInt32Ty(Context), Alignment),
466 ConstantInt::get(Type::getInt1Ty(Context), 0),
468 const Type *Tys[] = { Ops[0]->getType(), Ops[2]->getType() };
470 Function *MemSetF = Intrinsic::getDeclaration(M, Intrinsic::memset, Tys, 2);
472 Value *C = CallInst::Create(MemSetF, Ops, Ops+5, "", InsertPt);
473 DEBUG(dbgs() << "Replace stores:\n";
474 for (unsigned i = 0, e = Range.TheStores.size(); i != e; ++i)
475 dbgs() << *Range.TheStores[i];
476 dbgs() << "With: " << *C); C=C;
478 // Don't invalidate the iterator
481 // Zap all the stores.
482 for (SmallVector<StoreInst*, 16>::const_iterator
483 SI = Range.TheStores.begin(),
484 SE = Range.TheStores.end(); SI != SE; ++SI)
485 (*SI)->eraseFromParent();
494 /// performCallSlotOptzn - takes a memcpy and a call that it depends on,
495 /// and checks for the possibility of a call slot optimization by having
496 /// the call write its result directly into the destination of the memcpy.
497 bool MemCpyOpt::performCallSlotOptzn(MemCpyInst *cpy, CallInst *C) {
498 // The general transformation to keep in mind is
500 // call @func(..., src, ...)
501 // memcpy(dest, src, ...)
505 // memcpy(dest, src, ...)
506 // call @func(..., dest, ...)
508 // Since moving the memcpy is technically awkward, we additionally check that
509 // src only holds uninitialized values at the moment of the call, meaning that
510 // the memcpy can be discarded rather than moved.
512 // Deliberately get the source and destination with bitcasts stripped away,
513 // because we'll need to do type comparisons based on the underlying type.
514 Value *cpyDest = cpy->getDest();
515 Value *cpySrc = cpy->getSource();
518 // We need to be able to reason about the size of the memcpy, so we require
519 // that it be a constant.
520 ConstantInt *cpyLength = dyn_cast<ConstantInt>(cpy->getLength());
524 // Require that src be an alloca. This simplifies the reasoning considerably.
525 AllocaInst *srcAlloca = dyn_cast<AllocaInst>(cpySrc);
529 // Check that all of src is copied to dest.
530 TargetData *TD = getAnalysisIfAvailable<TargetData>();
531 if (!TD) return false;
533 ConstantInt *srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize());
537 uint64_t srcSize = TD->getTypeAllocSize(srcAlloca->getAllocatedType()) *
538 srcArraySize->getZExtValue();
540 if (cpyLength->getZExtValue() < srcSize)
543 // Check that accessing the first srcSize bytes of dest will not cause a
544 // trap. Otherwise the transform is invalid since it might cause a trap
545 // to occur earlier than it otherwise would.
546 if (AllocaInst *A = dyn_cast<AllocaInst>(cpyDest)) {
547 // The destination is an alloca. Check it is larger than srcSize.
548 ConstantInt *destArraySize = dyn_cast<ConstantInt>(A->getArraySize());
552 uint64_t destSize = TD->getTypeAllocSize(A->getAllocatedType()) *
553 destArraySize->getZExtValue();
555 if (destSize < srcSize)
557 } else if (Argument *A = dyn_cast<Argument>(cpyDest)) {
558 // If the destination is an sret parameter then only accesses that are
559 // outside of the returned struct type can trap.
560 if (!A->hasStructRetAttr())
563 const Type *StructTy = cast<PointerType>(A->getType())->getElementType();
564 uint64_t destSize = TD->getTypeAllocSize(StructTy);
566 if (destSize < srcSize)
572 // Check that src is not accessed except via the call and the memcpy. This
573 // guarantees that it holds only undefined values when passed in (so the final
574 // memcpy can be dropped), that it is not read or written between the call and
575 // the memcpy, and that writing beyond the end of it is undefined.
576 SmallVector<User*, 8> srcUseList(srcAlloca->use_begin(),
577 srcAlloca->use_end());
578 while (!srcUseList.empty()) {
579 User *UI = srcUseList.pop_back_val();
581 if (isa<BitCastInst>(UI)) {
582 for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
584 srcUseList.push_back(*I);
585 } else if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(UI)) {
586 if (G->hasAllZeroIndices())
587 for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
589 srcUseList.push_back(*I);
592 } else if (UI != C && UI != cpy) {
597 // Since we're changing the parameter to the callsite, we need to make sure
598 // that what would be the new parameter dominates the callsite.
599 DominatorTree &DT = getAnalysis<DominatorTree>();
600 if (Instruction *cpyDestInst = dyn_cast<Instruction>(cpyDest))
601 if (!DT.dominates(cpyDestInst, C))
604 // In addition to knowing that the call does not access src in some
605 // unexpected manner, for example via a global, which we deduce from
606 // the use analysis, we also need to know that it does not sneakily
607 // access dest. We rely on AA to figure this out for us.
608 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
609 if (AA.getModRefInfo(C, cpy->getRawDest(), srcSize) !=
610 AliasAnalysis::NoModRef)
613 // All the checks have passed, so do the transformation.
614 bool changedArgument = false;
615 for (unsigned i = 0; i < CS.arg_size(); ++i)
616 if (CS.getArgument(i)->stripPointerCasts() == cpySrc) {
617 if (cpySrc->getType() != cpyDest->getType())
618 cpyDest = CastInst::CreatePointerCast(cpyDest, cpySrc->getType(),
619 cpyDest->getName(), C);
620 changedArgument = true;
621 if (CS.getArgument(i)->getType() == cpyDest->getType())
622 CS.setArgument(i, cpyDest);
624 CS.setArgument(i, CastInst::CreatePointerCast(cpyDest,
625 CS.getArgument(i)->getType(), cpyDest->getName(), C));
628 if (!changedArgument)
631 // Drop any cached information about the call, because we may have changed
632 // its dependence information by changing its parameter.
633 MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
634 MD.removeInstruction(C);
637 MD.removeInstruction(cpy);
638 cpy->eraseFromParent();
644 /// processMemCpy - perform simplification of memcpy's. If we have memcpy A
645 /// which copies X to Y, and memcpy B which copies Y to Z, then we can rewrite
646 /// B to be a memcpy from X to Z (or potentially a memmove, depending on
647 /// circumstances). This allows later passes to remove the first memcpy
649 bool MemCpyOpt::processMemCpy(MemCpyInst *M) {
650 MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
652 // The are two possible optimizations we can do for memcpy:
653 // a) memcpy-memcpy xform which exposes redundance for DSE.
654 // b) call-memcpy xform for return slot optimization.
655 MemDepResult dep = MD.getDependency(M);
656 if (!dep.isClobber())
658 if (!isa<MemCpyInst>(dep.getInst())) {
659 if (CallInst *C = dyn_cast<CallInst>(dep.getInst()))
660 return performCallSlotOptzn(M, C);
664 MemCpyInst *MDep = cast<MemCpyInst>(dep.getInst());
666 // We can only transforms memcpy's where the dest of one is the source of the
668 if (M->getSource() != MDep->getDest())
671 // Second, the length of the memcpy's must be the same, or the preceeding one
672 // must be larger than the following one.
673 ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength());
674 ConstantInt *C2 = dyn_cast<ConstantInt>(M->getLength());
678 uint64_t DepSize = C1->getValue().getZExtValue();
679 uint64_t CpySize = C2->getValue().getZExtValue();
681 if (DepSize < CpySize)
684 // Finally, we have to make sure that the dest of the second does not
685 // alias the source of the first
686 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
687 if (AA.alias(M->getRawDest(), CpySize, MDep->getRawSource(), DepSize) !=
688 AliasAnalysis::NoAlias)
690 else if (AA.alias(M->getRawDest(), CpySize, M->getRawSource(), CpySize) !=
691 AliasAnalysis::NoAlias)
693 else if (AA.alias(MDep->getRawDest(), DepSize, MDep->getRawSource(), DepSize)
694 != AliasAnalysis::NoAlias)
697 // If all checks passed, then we can transform these memcpy's
698 const Type *ArgTys[3] = { M->getRawDest()->getType(),
699 MDep->getRawSource()->getType(),
700 M->getLength()->getType() };
701 Function *MemCpyFun = Intrinsic::getDeclaration(
702 M->getParent()->getParent()->getParent(),
703 M->getIntrinsicID(), ArgTys, 3);
705 // Make sure to use the lesser of the alignment of the source and the dest
706 // since we're changing where we're reading from, but don't want to increase
707 // the alignment past what can be read from or written to.
708 // TODO: Is this worth it if we're creating a less aligned memcpy? For
709 // example we could be moving from movaps -> movq on x86.
710 unsigned Align = std::min(MDep->getAlignmentCst()->getZExtValue(),
711 M->getAlignmentCst()->getZExtValue());
712 LLVMContext &Context = M->getContext();
713 ConstantInt *AlignCI = ConstantInt::get(Type::getInt32Ty(Context), Align);
715 M->getRawDest(), MDep->getRawSource(), M->getLength(),
716 AlignCI, M->getVolatileCst()
718 CallInst *C = CallInst::Create(MemCpyFun, Args, Args+5, "", M);
720 // If C and M don't interfere, then this is a valid transformation. If they
721 // did, this would mean that the two sources overlap, which would be bad.
722 if (MD.getDependency(C) == dep) {
723 MD.removeInstruction(M);
724 M->eraseFromParent();
729 // Otherwise, there was no point in doing this, so we remove the call we
730 // inserted and act like nothing happened.
731 MD.removeInstruction(C);
732 C->eraseFromParent();
736 /// processMemMove - Transforms memmove calls to memcpy calls when the src/dst
737 /// are guaranteed not to alias.
738 bool MemCpyOpt::processMemMove(MemMoveInst *M) {
739 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
741 // If the memmove is a constant size, use it for the alias query, this allows
742 // us to optimize things like: memmove(P, P+64, 64);
743 uint64_t MemMoveSize = ~0ULL;
744 if (ConstantInt *Len = dyn_cast<ConstantInt>(M->getLength()))
745 MemMoveSize = Len->getZExtValue();
747 // See if the pointers alias.
748 if (AA.alias(M->getRawDest(), MemMoveSize, M->getRawSource(), MemMoveSize) !=
749 AliasAnalysis::NoAlias)
752 DEBUG(dbgs() << "MemCpyOpt: Optimizing memmove -> memcpy: " << *M << "\n");
754 // If not, then we know we can transform this.
755 Module *Mod = M->getParent()->getParent()->getParent();
756 const Type *ArgTys[3] = { M->getRawDest()->getType(),
757 M->getRawSource()->getType(),
758 M->getLength()->getType() };
759 M->setCalledFunction(Intrinsic::getDeclaration(Mod, Intrinsic::memcpy,
762 // MemDep may have over conservative information about this instruction, just
763 // conservatively flush it from the cache.
764 getAnalysis<MemoryDependenceAnalysis>().removeInstruction(M);
771 // MemCpyOpt::iterateOnFunction - Executes one iteration of GVN.
772 bool MemCpyOpt::iterateOnFunction(Function &F) {
773 bool MadeChange = false;
775 // Walk all instruction in the function.
776 for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
777 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
779 // Avoid invalidating the iterator.
780 Instruction *I = BI++;
782 if (StoreInst *SI = dyn_cast<StoreInst>(I))
783 MadeChange |= processStore(SI, BI);
784 else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I))
785 MadeChange |= processMemCpy(M);
786 else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I)) {
787 if (processMemMove(M)) {
788 --BI; // Reprocess the new memcpy.
798 // MemCpyOpt::runOnFunction - This is the main transformation entry point for a
801 bool MemCpyOpt::runOnFunction(Function &F) {
802 bool MadeChange = false;
804 if (!iterateOnFunction(F))