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Remove old DSE.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40666 91177308-0d34-0410-b5e6-96231b3b80d8
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Owen Anderson
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//===- DeadStoreElimination.cpp - Dead Store Elimination ------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source 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 a trivial dead store elimination that only considers
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// basic-block local redundant stores.
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//
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// FIXME: This should eventually be extended to be a post-dominator tree
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// traversal. Doing so would be pretty trivial.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "dse"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/AliasSetTracker.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Support/Compiler.h"
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using namespace llvm;
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STATISTIC(NumStores, "Number of stores deleted");
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STATISTIC(NumOther , "Number of other instrs removed");
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namespace {
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struct VISIBILITY_HIDDEN DSE : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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DSE() : FunctionPass((intptr_t)&ID) {}
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virtual bool runOnFunction(Function &F) {
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bool Changed = false;
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for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
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Changed |= runOnBasicBlock(*I);
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return Changed;
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}
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bool runOnBasicBlock(BasicBlock &BB);
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void DeleteDeadInstructionChains(Instruction *I,
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SetVector<Instruction*> &DeadInsts);
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// getAnalysisUsage - We require post dominance frontiers (aka Control
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// Dependence Graph)
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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AU.addRequired<TargetData>();
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AU.addRequired<AliasAnalysis>();
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AU.addPreserved<AliasAnalysis>();
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}
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};
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char DSE::ID = 0;
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RegisterPass<DSE> X("dse", "Dead Store Elimination");
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}
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FunctionPass *llvm::createDeadStoreEliminationPass() { return new DSE(); }
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bool DSE::runOnBasicBlock(BasicBlock &BB) {
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TargetData &TD = getAnalysis<TargetData>();
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AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
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AliasSetTracker KillLocs(AA);
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// If this block ends in a return, unwind, unreachable, and eventually
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// tailcall, then all allocas are dead at its end.
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if (BB.getTerminator()->getNumSuccessors() == 0) {
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BasicBlock *Entry = BB.getParent()->begin();
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for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I)
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if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
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unsigned Size = ~0U;
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if (!AI->isArrayAllocation() &&
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AI->getType()->getElementType()->isSized())
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Size = (unsigned)TD.getTypeSize(AI->getType()->getElementType());
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KillLocs.add(AI, Size);
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}
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}
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// PotentiallyDeadInsts - Deleting dead stores from the program can make other
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// instructions die if they were only used as operands to stores. Keep track
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// of the operands to stores so that we can try deleting them at the end of
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// the traversal.
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SetVector<Instruction*> PotentiallyDeadInsts;
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bool MadeChange = false;
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for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ) {
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Instruction *I = --BBI; // Keep moving iterator backwards
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// If this is a free instruction, it makes the free'd location dead!
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if (FreeInst *FI = dyn_cast<FreeInst>(I)) {
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// Free instructions make any stores to the free'd location dead.
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KillLocs.add(FI);
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continue;
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}
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if (!isa<StoreInst>(I) || cast<StoreInst>(I)->isVolatile()) {
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// If this is a vaarg instruction, it reads its operand. We don't model
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// it correctly, so just conservatively remove all entries.
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if (isa<VAArgInst>(I)) {
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KillLocs.clear();
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continue;
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}
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// If this is a non-store instruction, it makes everything referenced no
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// longer killed. Remove anything aliased from the alias set tracker.
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KillLocs.remove(I);
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continue;
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}
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// If this is a non-volatile store instruction, and if it is already in
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// the stored location is already in the tracker, then this is a dead
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// store. We can just delete it here, but while we're at it, we also
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// delete any trivially dead expression chains.
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unsigned ValSize = (unsigned)TD.getTypeSize(I->getOperand(0)->getType());
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Value *Ptr = I->getOperand(1);
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if (AliasSet *AS = KillLocs.getAliasSetForPointerIfExists(Ptr, ValSize))
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for (AliasSet::iterator ASI = AS->begin(), E = AS->end(); ASI != E; ++ASI)
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if (ASI.getSize() >= ValSize && // Overwriting all of this store.
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AA.alias(ASI.getPointer(), ASI.getSize(), Ptr, ValSize)
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== AliasAnalysis::MustAlias) {
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// If we found a must alias in the killed set, then this store really
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// is dead. Remember that the various operands of the store now have
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// fewer users. At the end we will see if we can delete any values
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// that are dead as part of the store becoming dead.
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if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(0)))
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PotentiallyDeadInsts.insert(Op);
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if (Instruction *Op = dyn_cast<Instruction>(Ptr))
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PotentiallyDeadInsts.insert(Op);
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// Delete it now.
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++BBI; // Don't invalidate iterator.
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BB.getInstList().erase(I); // Nuke the store!
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++NumStores;
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MadeChange = true;
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goto BigContinue;
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}
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// Otherwise, this is a non-dead store just add it to the set of dead
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// locations.
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KillLocs.add(cast<StoreInst>(I));
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BigContinue:;
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}
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while (!PotentiallyDeadInsts.empty()) {
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Instruction *I = PotentiallyDeadInsts.back();
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PotentiallyDeadInsts.pop_back();
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DeleteDeadInstructionChains(I, PotentiallyDeadInsts);
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}
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return MadeChange;
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}
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void DSE::DeleteDeadInstructionChains(Instruction *I,
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SetVector<Instruction*> &DeadInsts) {
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// Instruction must be dead.
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if (!I->use_empty() || !isInstructionTriviallyDead(I)) return;
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// Let the alias analysis know that we have nuked a value.
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getAnalysis<AliasAnalysis>().deleteValue(I);
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// See if this made any operands dead. We do it this way in case the
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// instruction uses the same operand twice. We don't want to delete a
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// value then reference it.
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
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if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
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DeadInsts.insert(Op); // Attempt to nuke it later.
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I->setOperand(i, 0); // Drop from the operand list.
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}
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I->eraseFromParent();
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++NumOther;
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}
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