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@55779 91177308-0d34-0410-b5e6-96231b3b80d8
594 lines
21 KiB
C++
594 lines
21 KiB
C++
//===- DeadStoreElimination.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 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 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/Constants.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.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/Dominators.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 DSE : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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DSE() : FunctionPass(&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,
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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, uint64_t killPointerSize,
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BasicBlock::iterator& BBI,
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SmallPtrSet<Value*, 64>& 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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/// Find the base pointer that a pointer came from
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/// Because this is used to find pointers that originate
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/// from allocas, it is safe to ignore GEP indices, since
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/// either the store will be in the alloca, and thus dead,
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/// or beyond the end of the alloca, and thus undefined.
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void TranslatePointerBitCasts(Value*& v, bool zeroGepsOnly = false) {
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assert(isa<PointerType>(v->getType()) &&
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"Translating a non-pointer type?");
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while (true) {
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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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if (!zeroGepsOnly || G->hasAllZeroIndices()) {
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v = G->getOperand(0);
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} else {
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break;
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}
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else
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break;
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}
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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<DominatorTree>();
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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<DominatorTree>();
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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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}
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char DSE::ID = 0;
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static RegisterPass<DSE> X("dse", "Dead Store Elimination");
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FunctionPass *llvm::createDeadStoreEliminationPass() { return new DSE(); }
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bool DSE::runOnBasicBlock(BasicBlock &BB) {
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MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
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TargetData &TD = getAnalysis<TargetData>();
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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();
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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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continue;
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Value* pointer = 0;
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if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
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if (!S->isVolatile())
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pointer = S->getPointerOperand();
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else
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continue;
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} else
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pointer = cast<FreeInst>(BBI)->getPointerOperand();
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TranslatePointerBitCasts(pointer, true);
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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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TD.getTypeStoreSize(last->getOperand(0)->getType()) >
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TD.getTypeStoreSize(BBI->getOperand(0)->getType())) {
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dep = MD.getDependency(BBI, dep);
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continue;
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}
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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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}
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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,
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MD.getDependency(F),
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possiblyDead);
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// No known stores after the free
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last = 0;
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} else {
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StoreInst* S = cast<StoreInst>(BBI);
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// If we're storing the same value back to a pointer that we just
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// loaded from, then the store can be removed;
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if (LoadInst* L = dyn_cast<LoadInst>(S->getOperand(0))) {
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Instruction* dep = MD.getDependency(S);
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DominatorTree& DT = getAnalysis<DominatorTree>();
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if (!S->isVolatile() && S->getParent() == L->getParent() &&
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S->getPointerOperand() == L->getPointerOperand() &&
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( dep == MemoryDependenceAnalysis::None ||
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dep == MemoryDependenceAnalysis::NonLocal ||
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DT.dominates(dep, L))) {
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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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// Avoid iterator invalidation.
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BBI--;
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MD.removeInstruction(S);
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S->eraseFromParent();
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NumFastStores++;
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MadeChange = true;
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} else
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// Update our most-recent-store map.
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last = S;
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} else
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// Update our most-recent-store map.
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last = S;
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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 DSE::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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else if (dependency->isVolatile())
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return false;
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Value* depPointer = dependency->getPointerOperand();
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const Type* depType = dependency->getOperand(0)->getType();
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unsigned depPointerSize = TD.getTypeStoreSize(depType);
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// Check for aliasing
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AliasAnalysis::AliasResult A = AA.alias(F->getPointerOperand(), ~0U,
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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
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/// function end block. Ex:
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/// %A = alloca i32
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/// ...
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/// store i32 1, i32* %A
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/// ret void
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bool DSE::handleEndBlock(BasicBlock& BB,
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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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// Pointers alloca'd in this function are dead in the end block
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SmallPtrSet<Value*, 64> 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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for (Function::arg_iterator AI = BB.getParent()->arg_begin(),
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AE = BB.getParent()->arg_end(); AI != AE; ++AI)
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if (AI->hasByValAttr())
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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 we find a store whose pointer is dead...
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if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
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if (!S->isVolatile()) {
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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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// Alloca'd pointers or byval arguments (which are functionally like
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// alloca's) are valid candidates for removal.
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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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MD.removeInstruction(S);
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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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}
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continue;
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// We can also remove memcpy's to local variables at the end of a function
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} else if (MemCpyInst* M = dyn_cast<MemCpyInst>(BBI)) {
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Value* dest = M->getDest();
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TranslatePointerBitCasts(dest);
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if (deadPointers.count(dest)) {
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MD.removeInstruction(M);
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// DCE instructions only used to calculate that memcpy
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if (Instruction* D = dyn_cast<Instruction>(M->getRawSource()))
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possiblyDead.insert(D);
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if (Instruction* D = dyn_cast<Instruction>(M->getLength()))
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possiblyDead.insert(D);
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if (Instruction* D = dyn_cast<Instruction>(M->getRawDest()))
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possiblyDead.insert(D);
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BBI++;
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M->eraseFromParent();
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NumFastOther++;
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MadeChange = true;
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continue;
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}
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// Because a memcpy is also a load, we can't skip it if we didn't remove it
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}
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Value* killPointer = 0;
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uint64_t killPointerSize = ~0UL;
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// If we encounter a use of the pointer, it is no longer considered dead
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if (LoadInst* L = dyn_cast<LoadInst>(BBI)) {
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// However, if this load is unused and not volatile, we can go ahead and
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// remove it, and not have to worry about it making our pointer undead!
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if (L->use_empty() && !L->isVolatile()) {
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MD.removeInstruction(L);
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// DCE instructions only used to calculate that load
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if (Instruction* D = dyn_cast<Instruction>(L->getPointerOperand()))
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possiblyDead.insert(D);
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BBI++;
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L->eraseFromParent();
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NumFastOther++;
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MadeChange = true;
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possiblyDead.remove(L);
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continue;
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}
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killPointer = L->getPointerOperand();
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} else if (VAArgInst* V = dyn_cast<VAArgInst>(BBI)) {
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killPointer = V->getOperand(0);
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} else if (isa<MemCpyInst>(BBI) &&
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isa<ConstantInt>(cast<MemCpyInst>(BBI)->getLength())) {
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killPointer = cast<MemCpyInst>(BBI)->getSource();
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killPointerSize = cast<ConstantInt>(
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cast<MemCpyInst>(BBI)->getLength())->getZExtValue();
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} else if (AllocaInst* A = dyn_cast<AllocaInst>(BBI)) {
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deadPointers.erase(A);
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// Dead alloca's can be DCE'd when we reach them
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if (A->use_empty()) {
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MD.removeInstruction(A);
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// DCE instructions only used to calculate that load
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if (Instruction* D = dyn_cast<Instruction>(A->getArraySize()))
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possiblyDead.insert(D);
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BBI++;
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A->eraseFromParent();
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NumFastOther++;
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MadeChange = true;
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possiblyDead.remove(A);
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}
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continue;
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} else if (CallSite::get(BBI).getInstruction() != 0) {
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// If this call does not access memory, it can't
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// be undeadifying any of our pointers.
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CallSite CS = CallSite::get(BBI);
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if (AA.doesNotAccessMemory(CS))
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continue;
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unsigned modRef = 0;
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unsigned other = 0;
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// Remove any pointers made undead by the call from the dead set
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std::vector<Value*> dead;
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for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
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E = deadPointers.end(); I != E; ++I) {
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// HACK: if we detect that our AA is imprecise, it's not
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// worth it to scan the rest of the deadPointers set. Just
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// assume that the AA will return ModRef for everything, and
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// go ahead and bail.
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if (modRef >= 16 && other == 0) {
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deadPointers.clear();
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return MadeChange;
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}
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// Get size information for the alloca
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unsigned pointerSize = ~0U;
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if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) {
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if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize()))
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pointerSize = C->getZExtValue() * \
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TD.getABITypeSize(A->getAllocatedType());
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} else {
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const PointerType* PT = cast<PointerType>(
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cast<Argument>(*I)->getType());
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pointerSize = TD.getABITypeSize(PT->getElementType());
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}
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// See if the call site touches it
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AliasAnalysis::ModRefResult A = AA.getModRefInfo(CS, *I, pointerSize);
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if (A == AliasAnalysis::ModRef)
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modRef++;
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else
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other++;
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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<Value*>::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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} else {
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// For any non-memory-affecting non-terminators, DCE them as we reach them
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Instruction *CI = BBI;
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if (!CI->isTerminator() && CI->use_empty() && !isa<FreeInst>(CI)) {
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// DCE instructions only used to calculate that load
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for (Instruction::op_iterator OI = CI->op_begin(), OE = CI->op_end();
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OI != OE; ++OI)
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if (Instruction* D = dyn_cast<Instruction>(OI))
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possiblyDead.insert(D);
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BBI++;
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CI->eraseFromParent();
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NumFastOther++;
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MadeChange = true;
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possiblyDead.remove(CI);
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continue;
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}
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}
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if (!killPointer)
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continue;
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TranslatePointerBitCasts(killPointer);
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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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/// RemoveUndeadPointers - check for uses of a pointer that make it
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/// undead when scanning for dead stores to alloca's.
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bool DSE::RemoveUndeadPointers(Value* killPointer, uint64_t killPointerSize,
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BasicBlock::iterator& BBI,
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SmallPtrSet<Value*, 64>& 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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// If the kill pointer can be easily reduced to an alloca,
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// don't bother doing extraneous AA queries
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if (deadPointers.count(killPointer)) {
|
|
deadPointers.erase(killPointer);
|
|
return false;
|
|
} else if (isa<GlobalValue>(killPointer)) {
|
|
// A global can't be in the dead pointer set
|
|
return false;
|
|
}
|
|
|
|
bool MadeChange = false;
|
|
|
|
std::vector<Value*> undead;
|
|
|
|
for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
|
|
E = deadPointers.end(); I != E; ++I) {
|
|
// Get size information for the alloca
|
|
unsigned pointerSize = ~0U;
|
|
if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) {
|
|
if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize()))
|
|
pointerSize = C->getZExtValue() * \
|
|
TD.getABITypeSize(A->getAllocatedType());
|
|
} else {
|
|
const PointerType* PT = cast<PointerType>(
|
|
cast<Argument>(*I)->getType());
|
|
pointerSize = TD.getABITypeSize(PT->getElementType());
|
|
}
|
|
|
|
// See if this pointer could alias it
|
|
AliasAnalysis::AliasResult A = AA.alias(*I, pointerSize,
|
|
killPointer, killPointerSize);
|
|
|
|
// If it must-alias and a store, we can delete it
|
|
if (isa<StoreInst>(BBI) && A == AliasAnalysis::MustAlias) {
|
|
StoreInst* S = cast<StoreInst>(BBI);
|
|
|
|
// Remove it!
|
|
MD.removeInstruction(S);
|
|
|
|
// DCE instructions only used to calculate that store
|
|
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
|
|
possiblyDead.insert(D);
|
|
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
|
|
possiblyDead.insert(D);
|
|
|
|
BBI++;
|
|
S->eraseFromParent();
|
|
NumFastStores++;
|
|
MadeChange = true;
|
|
|
|
continue;
|
|
|
|
// Otherwise, it is undead
|
|
} else if (A != AliasAnalysis::NoAlias)
|
|
undead.push_back(*I);
|
|
}
|
|
|
|
for (std::vector<Value*>::iterator I = undead.begin(), E = undead.end();
|
|
I != E; ++I)
|
|
deadPointers.erase(*I);
|
|
|
|
return MadeChange;
|
|
}
|
|
|
|
/// DeleteDeadInstructionChains - takes an instruction and a setvector of
|
|
/// dead instructions. If I is dead, it is erased, and its operands are
|
|
/// checked for deadness. If they are dead, they are added to the dead
|
|
/// setvector.
|
|
void DSE::DeleteDeadInstructionChains(Instruction *I,
|
|
SetVector<Instruction*> &DeadInsts) {
|
|
// Instruction must be dead.
|
|
if (!I->use_empty() || !isInstructionTriviallyDead(I)) return;
|
|
|
|
// Let the memory dependence know
|
|
getAnalysis<MemoryDependenceAnalysis>().removeInstruction(I);
|
|
|
|
// See if this made any operands dead. We do it this way in case the
|
|
// instruction uses the same operand twice. We don't want to delete a
|
|
// value then reference it.
|
|
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
|
|
if (I->getOperand(i)->hasOneUse())
|
|
if (Instruction* Op = dyn_cast<Instruction>(I->getOperand(i)))
|
|
DeadInsts.insert(Op); // Attempt to nuke it later.
|
|
|
|
I->setOperand(i, 0); // Drop from the operand list.
|
|
}
|
|
|
|
I->eraseFromParent();
|
|
++NumFastOther;
|
|
}
|