mirror of
https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207196 91177308-0d34-0410-b5e6-96231b3b80d8
849 lines
33 KiB
C++
849 lines
33 KiB
C++
//===- InstCombineLoadStoreAlloca.cpp -------------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the visit functions for load, store and alloca.
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//
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//===----------------------------------------------------------------------===//
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#include "InstCombine.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/Loads.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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using namespace llvm;
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#define DEBUG_TYPE "instcombine"
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STATISTIC(NumDeadStore, "Number of dead stores eliminated");
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STATISTIC(NumGlobalCopies, "Number of allocas copied from constant global");
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/// pointsToConstantGlobal - Return true if V (possibly indirectly) points to
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/// some part of a constant global variable. This intentionally only accepts
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/// constant expressions because we can't rewrite arbitrary instructions.
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static bool pointsToConstantGlobal(Value *V) {
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if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
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return GV->isConstant();
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if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
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if (CE->getOpcode() == Instruction::BitCast ||
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CE->getOpcode() == Instruction::AddrSpaceCast ||
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CE->getOpcode() == Instruction::GetElementPtr)
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return pointsToConstantGlobal(CE->getOperand(0));
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}
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return false;
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}
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/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived)
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/// pointer to an alloca. Ignore any reads of the pointer, return false if we
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/// see any stores or other unknown uses. If we see pointer arithmetic, keep
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/// track of whether it moves the pointer (with IsOffset) but otherwise traverse
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/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to
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/// the alloca, and if the source pointer is a pointer to a constant global, we
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/// can optimize this.
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static bool
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isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy,
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SmallVectorImpl<Instruction *> &ToDelete,
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bool IsOffset = false) {
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// We track lifetime intrinsics as we encounter them. If we decide to go
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// ahead and replace the value with the global, this lets the caller quickly
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// eliminate the markers.
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for (Use &U : V->uses()) {
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Instruction *I = cast<Instruction>(U.getUser());
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if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
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// Ignore non-volatile loads, they are always ok.
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if (!LI->isSimple()) return false;
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continue;
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}
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if (isa<BitCastInst>(I) || isa<AddrSpaceCastInst>(I)) {
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// If uses of the bitcast are ok, we are ok.
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if (!isOnlyCopiedFromConstantGlobal(I, TheCopy, ToDelete, IsOffset))
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return false;
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continue;
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}
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if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
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// If the GEP has all zero indices, it doesn't offset the pointer. If it
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// doesn't, it does.
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if (!isOnlyCopiedFromConstantGlobal(
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GEP, TheCopy, ToDelete, IsOffset || !GEP->hasAllZeroIndices()))
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return false;
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continue;
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}
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if (CallSite CS = I) {
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// If this is the function being called then we treat it like a load and
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// ignore it.
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if (CS.isCallee(&U))
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continue;
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// Inalloca arguments are clobbered by the call.
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unsigned ArgNo = CS.getArgumentNo(&U);
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if (CS.isInAllocaArgument(ArgNo))
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return false;
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// If this is a readonly/readnone call site, then we know it is just a
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// load (but one that potentially returns the value itself), so we can
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// ignore it if we know that the value isn't captured.
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if (CS.onlyReadsMemory() &&
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(CS.getInstruction()->use_empty() || CS.doesNotCapture(ArgNo)))
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continue;
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// If this is being passed as a byval argument, the caller is making a
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// copy, so it is only a read of the alloca.
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if (CS.isByValArgument(ArgNo))
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continue;
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}
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// Lifetime intrinsics can be handled by the caller.
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if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
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if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
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II->getIntrinsicID() == Intrinsic::lifetime_end) {
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assert(II->use_empty() && "Lifetime markers have no result to use!");
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ToDelete.push_back(II);
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continue;
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}
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}
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// If this is isn't our memcpy/memmove, reject it as something we can't
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// handle.
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MemTransferInst *MI = dyn_cast<MemTransferInst>(I);
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if (!MI)
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return false;
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// If the transfer is using the alloca as a source of the transfer, then
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// ignore it since it is a load (unless the transfer is volatile).
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if (U.getOperandNo() == 1) {
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if (MI->isVolatile()) return false;
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continue;
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}
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// If we already have seen a copy, reject the second one.
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if (TheCopy) return false;
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// If the pointer has been offset from the start of the alloca, we can't
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// safely handle this.
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if (IsOffset) return false;
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// If the memintrinsic isn't using the alloca as the dest, reject it.
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if (U.getOperandNo() != 0) return false;
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// If the source of the memcpy/move is not a constant global, reject it.
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if (!pointsToConstantGlobal(MI->getSource()))
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return false;
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// Otherwise, the transform is safe. Remember the copy instruction.
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TheCopy = MI;
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}
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return true;
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}
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/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only
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/// modified by a copy from a constant global. If we can prove this, we can
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/// replace any uses of the alloca with uses of the global directly.
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static MemTransferInst *
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isOnlyCopiedFromConstantGlobal(AllocaInst *AI,
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SmallVectorImpl<Instruction *> &ToDelete) {
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MemTransferInst *TheCopy = nullptr;
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if (isOnlyCopiedFromConstantGlobal(AI, TheCopy, ToDelete))
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return TheCopy;
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return nullptr;
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}
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Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
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// Ensure that the alloca array size argument has type intptr_t, so that
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// any casting is exposed early.
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if (DL) {
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Type *IntPtrTy = DL->getIntPtrType(AI.getType());
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if (AI.getArraySize()->getType() != IntPtrTy) {
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Value *V = Builder->CreateIntCast(AI.getArraySize(),
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IntPtrTy, false);
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AI.setOperand(0, V);
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return &AI;
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}
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}
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// Convert: alloca Ty, C - where C is a constant != 1 into: alloca [C x Ty], 1
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if (AI.isArrayAllocation()) { // Check C != 1
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if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) {
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Type *NewTy =
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ArrayType::get(AI.getAllocatedType(), C->getZExtValue());
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AllocaInst *New = Builder->CreateAlloca(NewTy, nullptr, AI.getName());
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New->setAlignment(AI.getAlignment());
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// Scan to the end of the allocation instructions, to skip over a block of
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// allocas if possible...also skip interleaved debug info
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//
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BasicBlock::iterator It = New;
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while (isa<AllocaInst>(*It) || isa<DbgInfoIntrinsic>(*It)) ++It;
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// Now that I is pointing to the first non-allocation-inst in the block,
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// insert our getelementptr instruction...
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//
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Type *IdxTy = DL
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? DL->getIntPtrType(AI.getType())
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: Type::getInt64Ty(AI.getContext());
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Value *NullIdx = Constant::getNullValue(IdxTy);
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Value *Idx[2] = { NullIdx, NullIdx };
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Instruction *GEP =
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GetElementPtrInst::CreateInBounds(New, Idx, New->getName() + ".sub");
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InsertNewInstBefore(GEP, *It);
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// Now make everything use the getelementptr instead of the original
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// allocation.
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return ReplaceInstUsesWith(AI, GEP);
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} else if (isa<UndefValue>(AI.getArraySize())) {
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return ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
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}
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}
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if (DL && AI.getAllocatedType()->isSized()) {
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// If the alignment is 0 (unspecified), assign it the preferred alignment.
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if (AI.getAlignment() == 0)
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AI.setAlignment(DL->getPrefTypeAlignment(AI.getAllocatedType()));
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// Move all alloca's of zero byte objects to the entry block and merge them
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// together. Note that we only do this for alloca's, because malloc should
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// allocate and return a unique pointer, even for a zero byte allocation.
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if (DL->getTypeAllocSize(AI.getAllocatedType()) == 0) {
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// For a zero sized alloca there is no point in doing an array allocation.
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// This is helpful if the array size is a complicated expression not used
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// elsewhere.
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if (AI.isArrayAllocation()) {
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AI.setOperand(0, ConstantInt::get(AI.getArraySize()->getType(), 1));
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return &AI;
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}
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// Get the first instruction in the entry block.
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BasicBlock &EntryBlock = AI.getParent()->getParent()->getEntryBlock();
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Instruction *FirstInst = EntryBlock.getFirstNonPHIOrDbg();
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if (FirstInst != &AI) {
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// If the entry block doesn't start with a zero-size alloca then move
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// this one to the start of the entry block. There is no problem with
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// dominance as the array size was forced to a constant earlier already.
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AllocaInst *EntryAI = dyn_cast<AllocaInst>(FirstInst);
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if (!EntryAI || !EntryAI->getAllocatedType()->isSized() ||
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DL->getTypeAllocSize(EntryAI->getAllocatedType()) != 0) {
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AI.moveBefore(FirstInst);
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return &AI;
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}
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// If the alignment of the entry block alloca is 0 (unspecified),
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// assign it the preferred alignment.
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if (EntryAI->getAlignment() == 0)
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EntryAI->setAlignment(
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DL->getPrefTypeAlignment(EntryAI->getAllocatedType()));
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// Replace this zero-sized alloca with the one at the start of the entry
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// block after ensuring that the address will be aligned enough for both
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// types.
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unsigned MaxAlign = std::max(EntryAI->getAlignment(),
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AI.getAlignment());
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EntryAI->setAlignment(MaxAlign);
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if (AI.getType() != EntryAI->getType())
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return new BitCastInst(EntryAI, AI.getType());
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return ReplaceInstUsesWith(AI, EntryAI);
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}
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}
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}
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if (AI.getAlignment()) {
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// Check to see if this allocation is only modified by a memcpy/memmove from
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// a constant global whose alignment is equal to or exceeds that of the
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// allocation. If this is the case, we can change all users to use
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// the constant global instead. This is commonly produced by the CFE by
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// constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A'
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// is only subsequently read.
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SmallVector<Instruction *, 4> ToDelete;
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if (MemTransferInst *Copy = isOnlyCopiedFromConstantGlobal(&AI, ToDelete)) {
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unsigned SourceAlign = getOrEnforceKnownAlignment(Copy->getSource(),
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AI.getAlignment(), DL);
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if (AI.getAlignment() <= SourceAlign) {
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DEBUG(dbgs() << "Found alloca equal to global: " << AI << '\n');
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DEBUG(dbgs() << " memcpy = " << *Copy << '\n');
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for (unsigned i = 0, e = ToDelete.size(); i != e; ++i)
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EraseInstFromFunction(*ToDelete[i]);
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Constant *TheSrc = cast<Constant>(Copy->getSource());
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Constant *Cast
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= ConstantExpr::getPointerBitCastOrAddrSpaceCast(TheSrc, AI.getType());
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Instruction *NewI = ReplaceInstUsesWith(AI, Cast);
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EraseInstFromFunction(*Copy);
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++NumGlobalCopies;
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return NewI;
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}
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}
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}
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// At last, use the generic allocation site handler to aggressively remove
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// unused allocas.
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return visitAllocSite(AI);
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}
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/// InstCombineLoadCast - Fold 'load (cast P)' -> cast (load P)' when possible.
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static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI,
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const DataLayout *DL) {
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User *CI = cast<User>(LI.getOperand(0));
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Value *CastOp = CI->getOperand(0);
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PointerType *DestTy = cast<PointerType>(CI->getType());
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Type *DestPTy = DestTy->getElementType();
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if (PointerType *SrcTy = dyn_cast<PointerType>(CastOp->getType())) {
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// If the address spaces don't match, don't eliminate the cast.
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if (DestTy->getAddressSpace() != SrcTy->getAddressSpace())
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return nullptr;
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Type *SrcPTy = SrcTy->getElementType();
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if (DestPTy->isIntegerTy() || DestPTy->isPointerTy() ||
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DestPTy->isVectorTy()) {
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// If the source is an array, the code below will not succeed. Check to
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// see if a trivial 'gep P, 0, 0' will help matters. Only do this for
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// constants.
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if (ArrayType *ASrcTy = dyn_cast<ArrayType>(SrcPTy))
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if (Constant *CSrc = dyn_cast<Constant>(CastOp))
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if (ASrcTy->getNumElements() != 0) {
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Type *IdxTy = DL
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? DL->getIntPtrType(SrcTy)
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: Type::getInt64Ty(SrcTy->getContext());
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Value *Idx = Constant::getNullValue(IdxTy);
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Value *Idxs[2] = { Idx, Idx };
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CastOp = ConstantExpr::getGetElementPtr(CSrc, Idxs);
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SrcTy = cast<PointerType>(CastOp->getType());
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SrcPTy = SrcTy->getElementType();
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}
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if (IC.getDataLayout() &&
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(SrcPTy->isIntegerTy() || SrcPTy->isPointerTy() ||
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SrcPTy->isVectorTy()) &&
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// Do not allow turning this into a load of an integer, which is then
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// casted to a pointer, this pessimizes pointer analysis a lot.
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(SrcPTy->isPtrOrPtrVectorTy() ==
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LI.getType()->isPtrOrPtrVectorTy()) &&
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IC.getDataLayout()->getTypeSizeInBits(SrcPTy) ==
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IC.getDataLayout()->getTypeSizeInBits(DestPTy)) {
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// Okay, we are casting from one integer or pointer type to another of
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// the same size. Instead of casting the pointer before the load, cast
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// the result of the loaded value.
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LoadInst *NewLoad =
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IC.Builder->CreateLoad(CastOp, LI.isVolatile(), CI->getName());
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NewLoad->setAlignment(LI.getAlignment());
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NewLoad->setAtomic(LI.getOrdering(), LI.getSynchScope());
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// Now cast the result of the load.
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PointerType *OldTy = dyn_cast<PointerType>(NewLoad->getType());
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PointerType *NewTy = dyn_cast<PointerType>(LI.getType());
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if (OldTy && NewTy &&
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OldTy->getAddressSpace() != NewTy->getAddressSpace()) {
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return new AddrSpaceCastInst(NewLoad, LI.getType());
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}
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return new BitCastInst(NewLoad, LI.getType());
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}
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}
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}
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return nullptr;
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}
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Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
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Value *Op = LI.getOperand(0);
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// Attempt to improve the alignment.
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if (DL) {
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unsigned KnownAlign =
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getOrEnforceKnownAlignment(Op, DL->getPrefTypeAlignment(LI.getType()),DL);
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unsigned LoadAlign = LI.getAlignment();
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unsigned EffectiveLoadAlign = LoadAlign != 0 ? LoadAlign :
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DL->getABITypeAlignment(LI.getType());
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if (KnownAlign > EffectiveLoadAlign)
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LI.setAlignment(KnownAlign);
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else if (LoadAlign == 0)
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LI.setAlignment(EffectiveLoadAlign);
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}
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// load (cast X) --> cast (load X) iff safe.
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if (isa<CastInst>(Op))
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if (Instruction *Res = InstCombineLoadCast(*this, LI, DL))
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return Res;
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// None of the following transforms are legal for volatile/atomic loads.
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// FIXME: Some of it is okay for atomic loads; needs refactoring.
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if (!LI.isSimple()) return nullptr;
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// Do really simple store-to-load forwarding and load CSE, to catch cases
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// where there are several consecutive memory accesses to the same location,
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// separated by a few arithmetic operations.
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BasicBlock::iterator BBI = &LI;
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if (Value *AvailableVal = FindAvailableLoadedValue(Op, LI.getParent(), BBI,6))
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return ReplaceInstUsesWith(LI, AvailableVal);
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// load(gep null, ...) -> unreachable
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if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) {
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const Value *GEPI0 = GEPI->getOperand(0);
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// TODO: Consider a target hook for valid address spaces for this xform.
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if (isa<ConstantPointerNull>(GEPI0) && GEPI->getPointerAddressSpace() == 0){
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// Insert a new store to null instruction before the load to indicate
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// that this code is not reachable. We do this instead of inserting
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// an unreachable instruction directly because we cannot modify the
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// CFG.
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new StoreInst(UndefValue::get(LI.getType()),
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Constant::getNullValue(Op->getType()), &LI);
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return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType()));
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}
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}
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// load null/undef -> unreachable
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// TODO: Consider a target hook for valid address spaces for this xform.
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if (isa<UndefValue>(Op) ||
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(isa<ConstantPointerNull>(Op) && LI.getPointerAddressSpace() == 0)) {
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// Insert a new store to null instruction before the load to indicate that
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// this code is not reachable. We do this instead of inserting an
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// unreachable instruction directly because we cannot modify the CFG.
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new StoreInst(UndefValue::get(LI.getType()),
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Constant::getNullValue(Op->getType()), &LI);
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return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType()));
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}
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// Instcombine load (constantexpr_cast global) -> cast (load global)
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if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Op))
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if (CE->isCast())
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if (Instruction *Res = InstCombineLoadCast(*this, LI, DL))
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return Res;
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if (Op->hasOneUse()) {
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// Change select and PHI nodes to select values instead of addresses: this
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// helps alias analysis out a lot, allows many others simplifications, and
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// exposes redundancy in the code.
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//
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// Note that we cannot do the transformation unless we know that the
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// introduced loads cannot trap! Something like this is valid as long as
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// the condition is always false: load (select bool %C, int* null, int* %G),
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// but it would not be valid if we transformed it to load from null
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// unconditionally.
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//
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if (SelectInst *SI = dyn_cast<SelectInst>(Op)) {
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// load (select (Cond, &V1, &V2)) --> select(Cond, load &V1, load &V2).
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unsigned Align = LI.getAlignment();
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if (isSafeToLoadUnconditionally(SI->getOperand(1), SI, Align, DL) &&
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isSafeToLoadUnconditionally(SI->getOperand(2), SI, Align, DL)) {
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LoadInst *V1 = Builder->CreateLoad(SI->getOperand(1),
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SI->getOperand(1)->getName()+".val");
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LoadInst *V2 = Builder->CreateLoad(SI->getOperand(2),
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SI->getOperand(2)->getName()+".val");
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V1->setAlignment(Align);
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V2->setAlignment(Align);
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return SelectInst::Create(SI->getCondition(), V1, V2);
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|
}
|
|
|
|
// load (select (cond, null, P)) -> load P
|
|
if (Constant *C = dyn_cast<Constant>(SI->getOperand(1)))
|
|
if (C->isNullValue()) {
|
|
LI.setOperand(0, SI->getOperand(2));
|
|
return &LI;
|
|
}
|
|
|
|
// load (select (cond, P, null)) -> load P
|
|
if (Constant *C = dyn_cast<Constant>(SI->getOperand(2)))
|
|
if (C->isNullValue()) {
|
|
LI.setOperand(0, SI->getOperand(1));
|
|
return &LI;
|
|
}
|
|
}
|
|
}
|
|
return nullptr;
|
|
}
|
|
|
|
/// InstCombineStoreToCast - Fold store V, (cast P) -> store (cast V), P
|
|
/// when possible. This makes it generally easy to do alias analysis and/or
|
|
/// SROA/mem2reg of the memory object.
|
|
static Instruction *InstCombineStoreToCast(InstCombiner &IC, StoreInst &SI) {
|
|
User *CI = cast<User>(SI.getOperand(1));
|
|
Value *CastOp = CI->getOperand(0);
|
|
|
|
Type *DestPTy = cast<PointerType>(CI->getType())->getElementType();
|
|
PointerType *SrcTy = dyn_cast<PointerType>(CastOp->getType());
|
|
if (!SrcTy) return nullptr;
|
|
|
|
Type *SrcPTy = SrcTy->getElementType();
|
|
|
|
if (!DestPTy->isIntegerTy() && !DestPTy->isPointerTy())
|
|
return nullptr;
|
|
|
|
/// NewGEPIndices - If SrcPTy is an aggregate type, we can emit a "noop gep"
|
|
/// to its first element. This allows us to handle things like:
|
|
/// store i32 xxx, (bitcast {foo*, float}* %P to i32*)
|
|
/// on 32-bit hosts.
|
|
SmallVector<Value*, 4> NewGEPIndices;
|
|
|
|
// If the source is an array, the code below will not succeed. Check to
|
|
// see if a trivial 'gep P, 0, 0' will help matters. Only do this for
|
|
// constants.
|
|
if (SrcPTy->isArrayTy() || SrcPTy->isStructTy()) {
|
|
// Index through pointer.
|
|
Constant *Zero = Constant::getNullValue(Type::getInt32Ty(SI.getContext()));
|
|
NewGEPIndices.push_back(Zero);
|
|
|
|
while (1) {
|
|
if (StructType *STy = dyn_cast<StructType>(SrcPTy)) {
|
|
if (!STy->getNumElements()) /* Struct can be empty {} */
|
|
break;
|
|
NewGEPIndices.push_back(Zero);
|
|
SrcPTy = STy->getElementType(0);
|
|
} else if (ArrayType *ATy = dyn_cast<ArrayType>(SrcPTy)) {
|
|
NewGEPIndices.push_back(Zero);
|
|
SrcPTy = ATy->getElementType();
|
|
} else {
|
|
break;
|
|
}
|
|
}
|
|
|
|
SrcTy = PointerType::get(SrcPTy, SrcTy->getAddressSpace());
|
|
}
|
|
|
|
if (!SrcPTy->isIntegerTy() && !SrcPTy->isPointerTy())
|
|
return nullptr;
|
|
|
|
// If the pointers point into different address spaces don't do the
|
|
// transformation.
|
|
if (SrcTy->getAddressSpace() !=
|
|
cast<PointerType>(CI->getType())->getAddressSpace())
|
|
return nullptr;
|
|
|
|
// If the pointers point to values of different sizes don't do the
|
|
// transformation.
|
|
if (!IC.getDataLayout() ||
|
|
IC.getDataLayout()->getTypeSizeInBits(SrcPTy) !=
|
|
IC.getDataLayout()->getTypeSizeInBits(DestPTy))
|
|
return nullptr;
|
|
|
|
// If the pointers point to pointers to different address spaces don't do the
|
|
// transformation. It is not safe to introduce an addrspacecast instruction in
|
|
// this case since, depending on the target, addrspacecast may not be a no-op
|
|
// cast.
|
|
if (SrcPTy->isPointerTy() && DestPTy->isPointerTy() &&
|
|
SrcPTy->getPointerAddressSpace() != DestPTy->getPointerAddressSpace())
|
|
return nullptr;
|
|
|
|
// Okay, we are casting from one integer or pointer type to another of
|
|
// the same size. Instead of casting the pointer before
|
|
// the store, cast the value to be stored.
|
|
Value *NewCast;
|
|
Instruction::CastOps opcode = Instruction::BitCast;
|
|
Type* CastSrcTy = DestPTy;
|
|
Type* CastDstTy = SrcPTy;
|
|
if (CastDstTy->isPointerTy()) {
|
|
if (CastSrcTy->isIntegerTy())
|
|
opcode = Instruction::IntToPtr;
|
|
} else if (CastDstTy->isIntegerTy()) {
|
|
if (CastSrcTy->isPointerTy())
|
|
opcode = Instruction::PtrToInt;
|
|
}
|
|
|
|
// SIOp0 is a pointer to aggregate and this is a store to the first field,
|
|
// emit a GEP to index into its first field.
|
|
if (!NewGEPIndices.empty())
|
|
CastOp = IC.Builder->CreateInBoundsGEP(CastOp, NewGEPIndices);
|
|
|
|
Value *SIOp0 = SI.getOperand(0);
|
|
NewCast = IC.Builder->CreateCast(opcode, SIOp0, CastDstTy,
|
|
SIOp0->getName()+".c");
|
|
SI.setOperand(0, NewCast);
|
|
SI.setOperand(1, CastOp);
|
|
return &SI;
|
|
}
|
|
|
|
/// equivalentAddressValues - Test if A and B will obviously have the same
|
|
/// value. This includes recognizing that %t0 and %t1 will have the same
|
|
/// value in code like this:
|
|
/// %t0 = getelementptr \@a, 0, 3
|
|
/// store i32 0, i32* %t0
|
|
/// %t1 = getelementptr \@a, 0, 3
|
|
/// %t2 = load i32* %t1
|
|
///
|
|
static bool equivalentAddressValues(Value *A, Value *B) {
|
|
// Test if the values are trivially equivalent.
|
|
if (A == B) return true;
|
|
|
|
// Test if the values come form identical arithmetic instructions.
|
|
// This uses isIdenticalToWhenDefined instead of isIdenticalTo because
|
|
// its only used to compare two uses within the same basic block, which
|
|
// means that they'll always either have the same value or one of them
|
|
// will have an undefined value.
|
|
if (isa<BinaryOperator>(A) ||
|
|
isa<CastInst>(A) ||
|
|
isa<PHINode>(A) ||
|
|
isa<GetElementPtrInst>(A))
|
|
if (Instruction *BI = dyn_cast<Instruction>(B))
|
|
if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI))
|
|
return true;
|
|
|
|
// Otherwise they may not be equivalent.
|
|
return false;
|
|
}
|
|
|
|
Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
|
|
Value *Val = SI.getOperand(0);
|
|
Value *Ptr = SI.getOperand(1);
|
|
|
|
// Attempt to improve the alignment.
|
|
if (DL) {
|
|
unsigned KnownAlign =
|
|
getOrEnforceKnownAlignment(Ptr, DL->getPrefTypeAlignment(Val->getType()),
|
|
DL);
|
|
unsigned StoreAlign = SI.getAlignment();
|
|
unsigned EffectiveStoreAlign = StoreAlign != 0 ? StoreAlign :
|
|
DL->getABITypeAlignment(Val->getType());
|
|
|
|
if (KnownAlign > EffectiveStoreAlign)
|
|
SI.setAlignment(KnownAlign);
|
|
else if (StoreAlign == 0)
|
|
SI.setAlignment(EffectiveStoreAlign);
|
|
}
|
|
|
|
// Don't hack volatile/atomic stores.
|
|
// FIXME: Some bits are legal for atomic stores; needs refactoring.
|
|
if (!SI.isSimple()) return nullptr;
|
|
|
|
// If the RHS is an alloca with a single use, zapify the store, making the
|
|
// alloca dead.
|
|
if (Ptr->hasOneUse()) {
|
|
if (isa<AllocaInst>(Ptr))
|
|
return EraseInstFromFunction(SI);
|
|
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) {
|
|
if (isa<AllocaInst>(GEP->getOperand(0))) {
|
|
if (GEP->getOperand(0)->hasOneUse())
|
|
return EraseInstFromFunction(SI);
|
|
}
|
|
}
|
|
}
|
|
|
|
// Do really simple DSE, to catch cases where there are several consecutive
|
|
// stores to the same location, separated by a few arithmetic operations. This
|
|
// situation often occurs with bitfield accesses.
|
|
BasicBlock::iterator BBI = &SI;
|
|
for (unsigned ScanInsts = 6; BBI != SI.getParent()->begin() && ScanInsts;
|
|
--ScanInsts) {
|
|
--BBI;
|
|
// Don't count debug info directives, lest they affect codegen,
|
|
// and we skip pointer-to-pointer bitcasts, which are NOPs.
|
|
if (isa<DbgInfoIntrinsic>(BBI) ||
|
|
(isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
|
|
ScanInsts++;
|
|
continue;
|
|
}
|
|
|
|
if (StoreInst *PrevSI = dyn_cast<StoreInst>(BBI)) {
|
|
// Prev store isn't volatile, and stores to the same location?
|
|
if (PrevSI->isSimple() && equivalentAddressValues(PrevSI->getOperand(1),
|
|
SI.getOperand(1))) {
|
|
++NumDeadStore;
|
|
++BBI;
|
|
EraseInstFromFunction(*PrevSI);
|
|
continue;
|
|
}
|
|
break;
|
|
}
|
|
|
|
// If this is a load, we have to stop. However, if the loaded value is from
|
|
// the pointer we're loading and is producing the pointer we're storing,
|
|
// then *this* store is dead (X = load P; store X -> P).
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
|
|
if (LI == Val && equivalentAddressValues(LI->getOperand(0), Ptr) &&
|
|
LI->isSimple())
|
|
return EraseInstFromFunction(SI);
|
|
|
|
// Otherwise, this is a load from some other location. Stores before it
|
|
// may not be dead.
|
|
break;
|
|
}
|
|
|
|
// Don't skip over loads or things that can modify memory.
|
|
if (BBI->mayWriteToMemory() || BBI->mayReadFromMemory())
|
|
break;
|
|
}
|
|
|
|
// store X, null -> turns into 'unreachable' in SimplifyCFG
|
|
if (isa<ConstantPointerNull>(Ptr) && SI.getPointerAddressSpace() == 0) {
|
|
if (!isa<UndefValue>(Val)) {
|
|
SI.setOperand(0, UndefValue::get(Val->getType()));
|
|
if (Instruction *U = dyn_cast<Instruction>(Val))
|
|
Worklist.Add(U); // Dropped a use.
|
|
}
|
|
return nullptr; // Do not modify these!
|
|
}
|
|
|
|
// store undef, Ptr -> noop
|
|
if (isa<UndefValue>(Val))
|
|
return EraseInstFromFunction(SI);
|
|
|
|
// If the pointer destination is a cast, see if we can fold the cast into the
|
|
// source instead.
|
|
if (isa<CastInst>(Ptr))
|
|
if (Instruction *Res = InstCombineStoreToCast(*this, SI))
|
|
return Res;
|
|
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
|
|
if (CE->isCast())
|
|
if (Instruction *Res = InstCombineStoreToCast(*this, SI))
|
|
return Res;
|
|
|
|
|
|
// If this store is the last instruction in the basic block (possibly
|
|
// excepting debug info instructions), and if the block ends with an
|
|
// unconditional branch, try to move it to the successor block.
|
|
BBI = &SI;
|
|
do {
|
|
++BBI;
|
|
} while (isa<DbgInfoIntrinsic>(BBI) ||
|
|
(isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy()));
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(BBI))
|
|
if (BI->isUnconditional())
|
|
if (SimplifyStoreAtEndOfBlock(SI))
|
|
return nullptr; // xform done!
|
|
|
|
return nullptr;
|
|
}
|
|
|
|
/// SimplifyStoreAtEndOfBlock - Turn things like:
|
|
/// if () { *P = v1; } else { *P = v2 }
|
|
/// into a phi node with a store in the successor.
|
|
///
|
|
/// Simplify things like:
|
|
/// *P = v1; if () { *P = v2; }
|
|
/// into a phi node with a store in the successor.
|
|
///
|
|
bool InstCombiner::SimplifyStoreAtEndOfBlock(StoreInst &SI) {
|
|
BasicBlock *StoreBB = SI.getParent();
|
|
|
|
// Check to see if the successor block has exactly two incoming edges. If
|
|
// so, see if the other predecessor contains a store to the same location.
|
|
// if so, insert a PHI node (if needed) and move the stores down.
|
|
BasicBlock *DestBB = StoreBB->getTerminator()->getSuccessor(0);
|
|
|
|
// Determine whether Dest has exactly two predecessors and, if so, compute
|
|
// the other predecessor.
|
|
pred_iterator PI = pred_begin(DestBB);
|
|
BasicBlock *P = *PI;
|
|
BasicBlock *OtherBB = nullptr;
|
|
|
|
if (P != StoreBB)
|
|
OtherBB = P;
|
|
|
|
if (++PI == pred_end(DestBB))
|
|
return false;
|
|
|
|
P = *PI;
|
|
if (P != StoreBB) {
|
|
if (OtherBB)
|
|
return false;
|
|
OtherBB = P;
|
|
}
|
|
if (++PI != pred_end(DestBB))
|
|
return false;
|
|
|
|
// Bail out if all the relevant blocks aren't distinct (this can happen,
|
|
// for example, if SI is in an infinite loop)
|
|
if (StoreBB == DestBB || OtherBB == DestBB)
|
|
return false;
|
|
|
|
// Verify that the other block ends in a branch and is not otherwise empty.
|
|
BasicBlock::iterator BBI = OtherBB->getTerminator();
|
|
BranchInst *OtherBr = dyn_cast<BranchInst>(BBI);
|
|
if (!OtherBr || BBI == OtherBB->begin())
|
|
return false;
|
|
|
|
// If the other block ends in an unconditional branch, check for the 'if then
|
|
// else' case. there is an instruction before the branch.
|
|
StoreInst *OtherStore = nullptr;
|
|
if (OtherBr->isUnconditional()) {
|
|
--BBI;
|
|
// Skip over debugging info.
|
|
while (isa<DbgInfoIntrinsic>(BBI) ||
|
|
(isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
|
|
if (BBI==OtherBB->begin())
|
|
return false;
|
|
--BBI;
|
|
}
|
|
// If this isn't a store, isn't a store to the same location, or is not the
|
|
// right kind of store, bail out.
|
|
OtherStore = dyn_cast<StoreInst>(BBI);
|
|
if (!OtherStore || OtherStore->getOperand(1) != SI.getOperand(1) ||
|
|
!SI.isSameOperationAs(OtherStore))
|
|
return false;
|
|
} else {
|
|
// Otherwise, the other block ended with a conditional branch. If one of the
|
|
// destinations is StoreBB, then we have the if/then case.
|
|
if (OtherBr->getSuccessor(0) != StoreBB &&
|
|
OtherBr->getSuccessor(1) != StoreBB)
|
|
return false;
|
|
|
|
// Okay, we know that OtherBr now goes to Dest and StoreBB, so this is an
|
|
// if/then triangle. See if there is a store to the same ptr as SI that
|
|
// lives in OtherBB.
|
|
for (;; --BBI) {
|
|
// Check to see if we find the matching store.
|
|
if ((OtherStore = dyn_cast<StoreInst>(BBI))) {
|
|
if (OtherStore->getOperand(1) != SI.getOperand(1) ||
|
|
!SI.isSameOperationAs(OtherStore))
|
|
return false;
|
|
break;
|
|
}
|
|
// If we find something that may be using or overwriting the stored
|
|
// value, or if we run out of instructions, we can't do the xform.
|
|
if (BBI->mayReadFromMemory() || BBI->mayWriteToMemory() ||
|
|
BBI == OtherBB->begin())
|
|
return false;
|
|
}
|
|
|
|
// In order to eliminate the store in OtherBr, we have to
|
|
// make sure nothing reads or overwrites the stored value in
|
|
// StoreBB.
|
|
for (BasicBlock::iterator I = StoreBB->begin(); &*I != &SI; ++I) {
|
|
// FIXME: This should really be AA driven.
|
|
if (I->mayReadFromMemory() || I->mayWriteToMemory())
|
|
return false;
|
|
}
|
|
}
|
|
|
|
// Insert a PHI node now if we need it.
|
|
Value *MergedVal = OtherStore->getOperand(0);
|
|
if (MergedVal != SI.getOperand(0)) {
|
|
PHINode *PN = PHINode::Create(MergedVal->getType(), 2, "storemerge");
|
|
PN->addIncoming(SI.getOperand(0), SI.getParent());
|
|
PN->addIncoming(OtherStore->getOperand(0), OtherBB);
|
|
MergedVal = InsertNewInstBefore(PN, DestBB->front());
|
|
}
|
|
|
|
// Advance to a place where it is safe to insert the new store and
|
|
// insert it.
|
|
BBI = DestBB->getFirstInsertionPt();
|
|
StoreInst *NewSI = new StoreInst(MergedVal, SI.getOperand(1),
|
|
SI.isVolatile(),
|
|
SI.getAlignment(),
|
|
SI.getOrdering(),
|
|
SI.getSynchScope());
|
|
InsertNewInstBefore(NewSI, *BBI);
|
|
NewSI->setDebugLoc(OtherStore->getDebugLoc());
|
|
|
|
// If the two stores had the same TBAA tag, preserve it.
|
|
if (MDNode *TBAATag = SI.getMetadata(LLVMContext::MD_tbaa))
|
|
if ((TBAATag = MDNode::getMostGenericTBAA(TBAATag,
|
|
OtherStore->getMetadata(LLVMContext::MD_tbaa))))
|
|
NewSI->setMetadata(LLVMContext::MD_tbaa, TBAATag);
|
|
|
|
|
|
// Nuke the old stores.
|
|
EraseInstFromFunction(SI);
|
|
EraseInstFromFunction(*OtherStore);
|
|
return true;
|
|
}
|