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https://github.com/c64scene-ar/llvm-6502.git
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Move FastDSE in to DeadStoreElimination.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40667 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson
387
lib/Transforms/Scalar/DeadStoreElimination.cpp
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387
lib/Transforms/Scalar/DeadStoreElimination.cpp
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//===- FastDSE.cpp - Fast 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 Owen Anderson 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 "fdse"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Pass.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/MemoryDependenceAnalysis.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/Support/Compiler.h"
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using namespace llvm;
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STATISTIC(NumFastStores, "Number of stores deleted");
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STATISTIC(NumFastOther , "Number of other instrs removed");
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namespace {
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struct VISIBILITY_HIDDEN FDSE : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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FDSE() : 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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bool handleFreeWithNonTrivialDependency(FreeInst* F, Instruction* dependency,
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SetVector<Instruction*>& possiblyDead);
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bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead);
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bool RemoveUndeadPointers(Value* pointer, unsigned pointerSize,
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BasicBlock::iterator& BBI,
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SmallPtrSet<AllocaInst*, 4>& deadPointers,
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SetVector<Instruction*>& possiblyDead);
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void DeleteDeadInstructionChains(Instruction *I,
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SetVector<Instruction*> &DeadInsts);
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void TranslatePointerBitCasts(Value*& v) {
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assert(isa<PointerType>(v->getType()) && "Translating a non-pointer type?");
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// See through pointer-to-pointer bitcasts
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while (isa<BitCastInst>(v) || isa<GetElementPtrInst>(v))
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if (BitCastInst* C = dyn_cast<BitCastInst>(v))
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v = C->getOperand(0);
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else if (GetElementPtrInst* G = dyn_cast<GetElementPtrInst>(v))
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v = G->getOperand(0);
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}
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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.addRequired<MemoryDependenceAnalysis>();
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AU.addPreserved<AliasAnalysis>();
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AU.addPreserved<MemoryDependenceAnalysis>();
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}
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};
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char FDSE::ID = 0;
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RegisterPass<FDSE> X("fdse", "Fast Dead Store Elimination");
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}
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FunctionPass *llvm::createFastDeadStoreEliminationPass() { return new FDSE(); }
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bool FDSE::runOnBasicBlock(BasicBlock &BB) {
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MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
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// Record the last-seen store to this pointer
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DenseMap<Value*, StoreInst*> lastStore;
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// Record instructions possibly made dead by deleting a store
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SetVector<Instruction*> possiblyDead;
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bool MadeChange = false;
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// Do a top-down walk on the BB
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for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end(); BBI != BBE; ++BBI) {
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// If we find a store or a free...
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if (isa<StoreInst>(BBI) || isa<FreeInst>(BBI)) {
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Value* pointer = 0;
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if (StoreInst* S = dyn_cast<StoreInst>(BBI))
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pointer = S->getPointerOperand();
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else if (FreeInst* F = dyn_cast<FreeInst>(BBI))
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pointer = F->getPointerOperand();
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assert(pointer && "Not a free or a store?");
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StoreInst*& last = lastStore[pointer];
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bool deletedStore = false;
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// ... to a pointer that has been stored to before...
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if (last) {
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Instruction* dep = MD.getDependency(BBI);
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// ... and no other memory dependencies are between them....
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while (dep != MemoryDependenceAnalysis::None &&
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dep != MemoryDependenceAnalysis::NonLocal &&
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isa<StoreInst>(dep)) {
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if (dep == last) {
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// Remove it!
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MD.removeInstruction(last);
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// DCE instructions only used to calculate that store
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if (Instruction* D = dyn_cast<Instruction>(last->getOperand(0)))
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possiblyDead.insert(D);
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if (Instruction* D = dyn_cast<Instruction>(last->getOperand(1)))
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possiblyDead.insert(D);
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last->eraseFromParent();
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NumFastStores++;
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deletedStore = true;
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MadeChange = true;
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break;
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} else {
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dep = MD.getDependency(BBI, dep);
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}
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}
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}
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// Handle frees whose dependencies are non-trivial
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if (FreeInst* F = dyn_cast<FreeInst>(BBI))
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if (!deletedStore)
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MadeChange |= handleFreeWithNonTrivialDependency(F, MD.getDependency(F),
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possiblyDead);
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// Update our most-recent-store map
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if (StoreInst* S = dyn_cast<StoreInst>(BBI))
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last = S;
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else
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last = 0;
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}
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}
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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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MadeChange |= handleEndBlock(BB, possiblyDead);
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// Do a trivial DCE
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while (!possiblyDead.empty()) {
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Instruction *I = possiblyDead.back();
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possiblyDead.pop_back();
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DeleteDeadInstructionChains(I, possiblyDead);
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}
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return MadeChange;
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}
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/// handleFreeWithNonTrivialDependency - Handle frees of entire structures whose
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/// dependency is a store to a field of that structure
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bool FDSE::handleFreeWithNonTrivialDependency(FreeInst* F, Instruction* dep,
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SetVector<Instruction*>& possiblyDead) {
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TargetData &TD = getAnalysis<TargetData>();
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AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
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MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
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if (dep == MemoryDependenceAnalysis::None ||
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dep == MemoryDependenceAnalysis::NonLocal)
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return false;
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StoreInst* dependency = dyn_cast<StoreInst>(dep);
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if (!dependency)
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return false;
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Value* depPointer = dependency->getPointerOperand();
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unsigned depPointerSize = TD.getTypeSize(dependency->getOperand(0)->getType());
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// Check for aliasing
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AliasAnalysis::AliasResult A = AA.alias(F->getPointerOperand(), ~0UL,
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depPointer, depPointerSize);
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if (A == AliasAnalysis::MustAlias) {
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// Remove it!
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MD.removeInstruction(dependency);
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// DCE instructions only used to calculate that store
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if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(0)))
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possiblyDead.insert(D);
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if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(1)))
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possiblyDead.insert(D);
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dependency->eraseFromParent();
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NumFastStores++;
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return true;
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}
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return false;
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}
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/// handleEndBlock - Remove dead stores to stack-allocated locations in the function
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/// end block
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bool FDSE::handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead) {
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TargetData &TD = getAnalysis<TargetData>();
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AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
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MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
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bool MadeChange = false;
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// Pointers alloca'd in this function are dead in the end block
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SmallPtrSet<AllocaInst*, 4> deadPointers;
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// Find all of the alloca'd pointers in the entry block
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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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deadPointers.insert(AI);
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// Scan the basic block backwards
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for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
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--BBI;
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if (deadPointers.empty())
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break;
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Value* killPointer = 0;
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unsigned killPointerSize = 0;
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// If we find a store whose pointer is dead...
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if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
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Value* pointerOperand = S->getPointerOperand();
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// See through pointer-to-pointer bitcasts
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TranslatePointerBitCasts(pointerOperand);
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if (deadPointers.count(pointerOperand)){
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// Remove it!
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MD.removeInstruction(S);
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// DCE instructions only used to calculate that store
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if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
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possiblyDead.insert(D);
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if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
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possiblyDead.insert(D);
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BBI++;
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S->eraseFromParent();
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NumFastStores++;
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MadeChange = true;
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}
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// If we encounter a use of the pointer, it is no longer considered dead
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} else if (LoadInst* L = dyn_cast<LoadInst>(BBI)) {
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killPointer = L->getPointerOperand();
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killPointerSize = TD.getTypeSize(L->getType());
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} else if (VAArgInst* V = dyn_cast<VAArgInst>(BBI)) {
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killPointer = V->getOperand(0);
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killPointerSize = TD.getTypeSize(V->getType());
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} else if (FreeInst* F = dyn_cast<FreeInst>(BBI)) {
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killPointer = F->getPointerOperand();
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killPointerSize = ~0UL;
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} else if (AllocaInst* A = dyn_cast<AllocaInst>(BBI)) {
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deadPointers.erase(A);
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continue;
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} else if (CallSite::get(BBI).getInstruction() != 0) {
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// Remove any pointers made undead by the call from the dead set
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std::vector<Instruction*> dead;
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for (SmallPtrSet<AllocaInst*, 4>::iterator I = deadPointers.begin(),
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E = deadPointers.end(); I != E; ++I) {
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// Get size information for the alloca
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unsigned pointerSize = ~0UL;
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if (ConstantInt* C = dyn_cast<ConstantInt>((*I)->getArraySize()))
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pointerSize = C->getZExtValue() * TD.getTypeSize((*I)->getAllocatedType());
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// See if the call site touches it
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AliasAnalysis::ModRefResult A = AA.getModRefInfo(CallSite::get(BBI),
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*I, pointerSize);
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if (A == AliasAnalysis::ModRef || A == AliasAnalysis::Ref)
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dead.push_back(*I);
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}
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for (std::vector<Instruction*>::iterator I = dead.begin(), E = dead.end();
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I != E; ++I)
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deadPointers.erase(*I);
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continue;
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}
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if (!killPointer)
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continue;
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// Deal with undead pointers
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MadeChange |= RemoveUndeadPointers(killPointer, killPointerSize, BBI,
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deadPointers, possiblyDead);
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}
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return MadeChange;
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}
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bool FDSE::RemoveUndeadPointers(Value* killPointer, unsigned killPointerSize,
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BasicBlock::iterator& BBI,
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SmallPtrSet<AllocaInst*, 4>& deadPointers,
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SetVector<Instruction*>& possiblyDead) {
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TargetData &TD = getAnalysis<TargetData>();
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AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
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MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
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bool MadeChange = false;
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std::vector<Instruction*> undead;
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for (SmallPtrSet<AllocaInst*, 4>::iterator I = deadPointers.begin(),
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E = deadPointers.end(); I != E; ++I) {
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// Get size information for the alloca
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unsigned pointerSize = ~0UL;
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if (ConstantInt* C = dyn_cast<ConstantInt>((*I)->getArraySize()))
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pointerSize = C->getZExtValue() * TD.getTypeSize((*I)->getAllocatedType());
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// See if this pointer could alias it
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AliasAnalysis::AliasResult A = AA.alias(*I, pointerSize, killPointer, killPointerSize);
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// If it must-alias and a store, we can delete it
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if (isa<StoreInst>(BBI) && A == AliasAnalysis::MustAlias) {
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StoreInst* S = cast<StoreInst>(BBI);
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// Remove it!
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MD.removeInstruction(S);
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// DCE instructions only used to calculate that store
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if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
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possiblyDead.insert(D);
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if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
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possiblyDead.insert(D);
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BBI++;
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S->eraseFromParent();
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NumFastStores++;
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MadeChange = true;
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continue;
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// Otherwise, it is undead
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} else if (A != AliasAnalysis::NoAlias)
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undead.push_back(*I);
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}
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for (std::vector<Instruction*>::iterator I = undead.begin(), E = undead.end();
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I != E; ++I)
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deadPointers.erase(*I);
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return MadeChange;
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}
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void FDSE::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 memory dependence know
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getAnalysis<MemoryDependenceAnalysis>().removeInstruction(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 (I->getOperand(i)->hasOneUse())
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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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++NumFastOther;
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}
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