forked from OSchip/llvm-project
496 lines
17 KiB
C++
496 lines
17 KiB
C++
//===- SSAUpdater.cpp - Unstructured SSA Update Tool ----------------------===//
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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 SSAUpdater class.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/SSAUpdater.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/ADT/TinyPtrVector.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DebugLoc.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/Use.h"
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#include "llvm/IR/Value.h"
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#include "llvm/IR/ValueHandle.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
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#include <cassert>
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#include <utility>
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using namespace llvm;
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#define DEBUG_TYPE "ssaupdater"
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typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
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static AvailableValsTy &getAvailableVals(void *AV) {
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return *static_cast<AvailableValsTy*>(AV);
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}
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SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
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: InsertedPHIs(NewPHI) {}
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SSAUpdater::~SSAUpdater() {
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delete static_cast<AvailableValsTy*>(AV);
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}
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void SSAUpdater::Initialize(Type *Ty, StringRef Name) {
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if (!AV)
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AV = new AvailableValsTy();
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else
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getAvailableVals(AV).clear();
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ProtoType = Ty;
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ProtoName = Name;
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}
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bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
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return getAvailableVals(AV).count(BB);
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}
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void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
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assert(ProtoType && "Need to initialize SSAUpdater");
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assert(ProtoType == V->getType() &&
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"All rewritten values must have the same type");
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getAvailableVals(AV)[BB] = V;
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}
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static bool IsEquivalentPHI(PHINode *PHI,
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SmallDenseMap<BasicBlock*, Value*, 8> &ValueMapping) {
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unsigned PHINumValues = PHI->getNumIncomingValues();
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if (PHINumValues != ValueMapping.size())
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return false;
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// Scan the phi to see if it matches.
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for (unsigned i = 0, e = PHINumValues; i != e; ++i)
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if (ValueMapping[PHI->getIncomingBlock(i)] !=
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PHI->getIncomingValue(i)) {
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return false;
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}
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return true;
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}
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Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
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Value *Res = GetValueAtEndOfBlockInternal(BB);
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return Res;
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}
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Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
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// If there is no definition of the renamed variable in this block, just use
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// GetValueAtEndOfBlock to do our work.
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if (!HasValueForBlock(BB))
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return GetValueAtEndOfBlock(BB);
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// Otherwise, we have the hard case. Get the live-in values for each
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// predecessor.
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SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
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Value *SingularValue = nullptr;
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// We can get our predecessor info by walking the pred_iterator list, but it
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// is relatively slow. If we already have PHI nodes in this block, walk one
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// of them to get the predecessor list instead.
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if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
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for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
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BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
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Value *PredVal = GetValueAtEndOfBlock(PredBB);
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PredValues.push_back(std::make_pair(PredBB, PredVal));
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// Compute SingularValue.
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if (i == 0)
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SingularValue = PredVal;
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else if (PredVal != SingularValue)
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SingularValue = nullptr;
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}
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} else {
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bool isFirstPred = true;
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for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
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BasicBlock *PredBB = *PI;
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Value *PredVal = GetValueAtEndOfBlock(PredBB);
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PredValues.push_back(std::make_pair(PredBB, PredVal));
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// Compute SingularValue.
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if (isFirstPred) {
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SingularValue = PredVal;
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isFirstPred = false;
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} else if (PredVal != SingularValue)
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SingularValue = nullptr;
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}
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}
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// If there are no predecessors, just return undef.
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if (PredValues.empty())
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return UndefValue::get(ProtoType);
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// Otherwise, if all the merged values are the same, just use it.
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if (SingularValue)
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return SingularValue;
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// Otherwise, we do need a PHI: check to see if we already have one available
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// in this block that produces the right value.
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if (isa<PHINode>(BB->begin())) {
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SmallDenseMap<BasicBlock*, Value*, 8> ValueMapping(PredValues.begin(),
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PredValues.end());
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PHINode *SomePHI;
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for (BasicBlock::iterator It = BB->begin();
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(SomePHI = dyn_cast<PHINode>(It)); ++It) {
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if (IsEquivalentPHI(SomePHI, ValueMapping))
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return SomePHI;
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}
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}
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// Ok, we have no way out, insert a new one now.
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PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
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ProtoName, &BB->front());
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// Fill in all the predecessors of the PHI.
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for (const auto &PredValue : PredValues)
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InsertedPHI->addIncoming(PredValue.second, PredValue.first);
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// See if the PHI node can be merged to a single value. This can happen in
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// loop cases when we get a PHI of itself and one other value.
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if (Value *V =
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SimplifyInstruction(InsertedPHI, BB->getModule()->getDataLayout())) {
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InsertedPHI->eraseFromParent();
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return V;
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}
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// Set the DebugLoc of the inserted PHI, if available.
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DebugLoc DL;
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if (const Instruction *I = BB->getFirstNonPHI())
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DL = I->getDebugLoc();
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InsertedPHI->setDebugLoc(DL);
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// If the client wants to know about all new instructions, tell it.
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if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
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DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
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return InsertedPHI;
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}
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void SSAUpdater::RewriteUse(Use &U) {
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Instruction *User = cast<Instruction>(U.getUser());
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Value *V;
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if (PHINode *UserPN = dyn_cast<PHINode>(User))
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V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
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else
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V = GetValueInMiddleOfBlock(User->getParent());
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// Notify that users of the existing value that it is being replaced.
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Value *OldVal = U.get();
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if (OldVal != V && OldVal->hasValueHandle())
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ValueHandleBase::ValueIsRAUWd(OldVal, V);
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U.set(V);
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}
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void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
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Instruction *User = cast<Instruction>(U.getUser());
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Value *V;
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if (PHINode *UserPN = dyn_cast<PHINode>(User))
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V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
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else
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V = GetValueAtEndOfBlock(User->getParent());
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U.set(V);
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}
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namespace llvm {
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template<>
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class SSAUpdaterTraits<SSAUpdater> {
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public:
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typedef BasicBlock BlkT;
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typedef Value *ValT;
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typedef PHINode PhiT;
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typedef succ_iterator BlkSucc_iterator;
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static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
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static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
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class PHI_iterator {
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private:
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PHINode *PHI;
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unsigned idx;
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public:
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explicit PHI_iterator(PHINode *P) // begin iterator
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: PHI(P), idx(0) {}
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PHI_iterator(PHINode *P, bool) // end iterator
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: PHI(P), idx(PHI->getNumIncomingValues()) {}
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PHI_iterator &operator++() { ++idx; return *this; }
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bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
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bool operator!=(const PHI_iterator& x) const { return !operator==(x); }
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Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
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BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
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};
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static PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
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static PHI_iterator PHI_end(PhiT *PHI) {
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return PHI_iterator(PHI, true);
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}
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/// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
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/// vector, set Info->NumPreds, and allocate space in Info->Preds.
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static void FindPredecessorBlocks(BasicBlock *BB,
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SmallVectorImpl<BasicBlock*> *Preds) {
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// We can get our predecessor info by walking the pred_iterator list,
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// but it is relatively slow. If we already have PHI nodes in this
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// block, walk one of them to get the predecessor list instead.
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if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
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Preds->append(SomePhi->block_begin(), SomePhi->block_end());
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} else {
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for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
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Preds->push_back(*PI);
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}
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}
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/// GetUndefVal - Get an undefined value of the same type as the value
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/// being handled.
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static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
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return UndefValue::get(Updater->ProtoType);
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}
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/// CreateEmptyPHI - Create a new PHI instruction in the specified block.
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/// Reserve space for the operands but do not fill them in yet.
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static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
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SSAUpdater *Updater) {
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PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds,
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Updater->ProtoName, &BB->front());
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return PHI;
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}
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/// AddPHIOperand - Add the specified value as an operand of the PHI for
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/// the specified predecessor block.
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static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
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PHI->addIncoming(Val, Pred);
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}
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/// InstrIsPHI - Check if an instruction is a PHI.
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///
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static PHINode *InstrIsPHI(Instruction *I) {
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return dyn_cast<PHINode>(I);
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}
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/// ValueIsPHI - Check if a value is a PHI.
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///
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static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
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return dyn_cast<PHINode>(Val);
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}
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/// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
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/// operands, i.e., it was just added.
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static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
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PHINode *PHI = ValueIsPHI(Val, Updater);
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if (PHI && PHI->getNumIncomingValues() == 0)
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return PHI;
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return nullptr;
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}
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/// GetPHIValue - For the specified PHI instruction, return the value
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/// that it defines.
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static Value *GetPHIValue(PHINode *PHI) {
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return PHI;
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}
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};
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} // end namespace llvm
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/// Check to see if AvailableVals has an entry for the specified BB and if so,
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/// return it. If not, construct SSA form by first calculating the required
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/// placement of PHIs and then inserting new PHIs where needed.
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Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
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AvailableValsTy &AvailableVals = getAvailableVals(AV);
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if (Value *V = AvailableVals[BB])
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return V;
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SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
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return Impl.GetValue(BB);
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}
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//===----------------------------------------------------------------------===//
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// LoadAndStorePromoter Implementation
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//===----------------------------------------------------------------------===//
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LoadAndStorePromoter::
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LoadAndStorePromoter(ArrayRef<const Instruction*> Insts,
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SSAUpdater &S, StringRef BaseName) : SSA(S) {
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if (Insts.empty()) return;
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const Value *SomeVal;
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if (const LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
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SomeVal = LI;
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else
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SomeVal = cast<StoreInst>(Insts[0])->getOperand(0);
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if (BaseName.empty())
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BaseName = SomeVal->getName();
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SSA.Initialize(SomeVal->getType(), BaseName);
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}
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void LoadAndStorePromoter::
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run(const SmallVectorImpl<Instruction*> &Insts) const {
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// First step: bucket up uses of the alloca by the block they occur in.
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// This is important because we have to handle multiple defs/uses in a block
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// ourselves: SSAUpdater is purely for cross-block references.
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DenseMap<BasicBlock*, TinyPtrVector<Instruction*>> UsesByBlock;
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for (Instruction *User : Insts)
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UsesByBlock[User->getParent()].push_back(User);
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// Okay, now we can iterate over all the blocks in the function with uses,
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// processing them. Keep track of which loads are loading a live-in value.
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// Walk the uses in the use-list order to be determinstic.
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SmallVector<LoadInst*, 32> LiveInLoads;
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DenseMap<Value*, Value*> ReplacedLoads;
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for (Instruction *User : Insts) {
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BasicBlock *BB = User->getParent();
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TinyPtrVector<Instruction*> &BlockUses = UsesByBlock[BB];
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// If this block has already been processed, ignore this repeat use.
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if (BlockUses.empty()) continue;
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// Okay, this is the first use in the block. If this block just has a
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// single user in it, we can rewrite it trivially.
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if (BlockUses.size() == 1) {
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// If it is a store, it is a trivial def of the value in the block.
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if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
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updateDebugInfo(SI);
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SSA.AddAvailableValue(BB, SI->getOperand(0));
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} else
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// Otherwise it is a load, queue it to rewrite as a live-in load.
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LiveInLoads.push_back(cast<LoadInst>(User));
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BlockUses.clear();
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continue;
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}
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// Otherwise, check to see if this block is all loads.
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bool HasStore = false;
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for (Instruction *I : BlockUses) {
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if (isa<StoreInst>(I)) {
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HasStore = true;
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break;
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}
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}
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// If so, we can queue them all as live in loads. We don't have an
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// efficient way to tell which on is first in the block and don't want to
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// scan large blocks, so just add all loads as live ins.
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if (!HasStore) {
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for (Instruction *I : BlockUses)
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LiveInLoads.push_back(cast<LoadInst>(I));
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BlockUses.clear();
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continue;
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}
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// Otherwise, we have mixed loads and stores (or just a bunch of stores).
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// Since SSAUpdater is purely for cross-block values, we need to determine
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// the order of these instructions in the block. If the first use in the
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// block is a load, then it uses the live in value. The last store defines
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// the live out value. We handle this by doing a linear scan of the block.
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Value *StoredValue = nullptr;
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for (Instruction &I : *BB) {
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if (LoadInst *L = dyn_cast<LoadInst>(&I)) {
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// If this is a load from an unrelated pointer, ignore it.
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if (!isInstInList(L, Insts)) continue;
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// If we haven't seen a store yet, this is a live in use, otherwise
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// use the stored value.
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if (StoredValue) {
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replaceLoadWithValue(L, StoredValue);
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L->replaceAllUsesWith(StoredValue);
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ReplacedLoads[L] = StoredValue;
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} else {
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LiveInLoads.push_back(L);
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}
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continue;
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}
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if (StoreInst *SI = dyn_cast<StoreInst>(&I)) {
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// If this is a store to an unrelated pointer, ignore it.
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if (!isInstInList(SI, Insts)) continue;
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updateDebugInfo(SI);
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// Remember that this is the active value in the block.
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StoredValue = SI->getOperand(0);
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}
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}
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// The last stored value that happened is the live-out for the block.
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assert(StoredValue && "Already checked that there is a store in block");
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SSA.AddAvailableValue(BB, StoredValue);
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BlockUses.clear();
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}
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// Okay, now we rewrite all loads that use live-in values in the loop,
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// inserting PHI nodes as necessary.
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for (LoadInst *ALoad : LiveInLoads) {
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Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
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replaceLoadWithValue(ALoad, NewVal);
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// Avoid assertions in unreachable code.
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if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType());
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ALoad->replaceAllUsesWith(NewVal);
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ReplacedLoads[ALoad] = NewVal;
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}
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// Allow the client to do stuff before we start nuking things.
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doExtraRewritesBeforeFinalDeletion();
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// Now that everything is rewritten, delete the old instructions from the
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// function. They should all be dead now.
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for (Instruction *User : Insts) {
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// If this is a load that still has uses, then the load must have been added
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// as a live value in the SSAUpdate data structure for a block (e.g. because
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// the loaded value was stored later). In this case, we need to recursively
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// propagate the updates until we get to the real value.
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if (!User->use_empty()) {
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Value *NewVal = ReplacedLoads[User];
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assert(NewVal && "not a replaced load?");
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// Propagate down to the ultimate replacee. The intermediately loads
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// could theoretically already have been deleted, so we don't want to
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// dereference the Value*'s.
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DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
|
|
while (RLI != ReplacedLoads.end()) {
|
|
NewVal = RLI->second;
|
|
RLI = ReplacedLoads.find(NewVal);
|
|
}
|
|
|
|
replaceLoadWithValue(cast<LoadInst>(User), NewVal);
|
|
User->replaceAllUsesWith(NewVal);
|
|
}
|
|
|
|
instructionDeleted(User);
|
|
User->eraseFromParent();
|
|
}
|
|
}
|
|
|
|
bool
|
|
LoadAndStorePromoter::isInstInList(Instruction *I,
|
|
const SmallVectorImpl<Instruction*> &Insts)
|
|
const {
|
|
return is_contained(Insts, I);
|
|
}
|