X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FADCE.cpp;h=3423fdd492974836a11dae368654c45341d9dd29;hb=a5f4103931346d7abc33f5a2dd21a5cf7666c9cb;hp=ffb57d0d6aeb449dc1ec88d4d8b5576b70ca19f9;hpb=ef6a6a69ff1e1b709d0acb315b9f6c926c67a778;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/ADCE.cpp b/lib/Transforms/Scalar/ADCE.cpp index ffb57d0d6ae..3423fdd4929 100644 --- a/lib/Transforms/Scalar/ADCE.cpp +++ b/lib/Transforms/Scalar/ADCE.cpp @@ -1,4 +1,11 @@ //===- ADCE.cpp - Code to perform aggressive dead code elimination --------===// +// +// The LLVM Compiler Infrastructure +// +// This file was developed by the LLVM research group and is distributed under +// the University of Illinois Open Source License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// // // This file implements "aggressive" dead code elimination. ADCE is DCe where // values are assumed to be dead until proven otherwise. This is similar to @@ -7,23 +14,26 @@ //===----------------------------------------------------------------------===// #include "llvm/Transforms/Scalar.h" -#include "llvm/Transforms/Utils/Local.h" -#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Constant.h" +#include "llvm/Instructions.h" #include "llvm/Type.h" +#include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/PostDominators.h" -#include "llvm/iTerminators.h" -#include "llvm/iPHINode.h" -#include "llvm/Constant.h" #include "llvm/Support/CFG.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h" #include "Support/Debug.h" #include "Support/DepthFirstIterator.h" #include "Support/Statistic.h" #include "Support/STLExtras.h" #include +using namespace llvm; namespace { Statistic<> NumBlockRemoved("adce", "Number of basic blocks removed"); Statistic<> NumInstRemoved ("adce", "Number of instructions removed"); + Statistic<> NumCallRemoved ("adce", "Number of calls and invokes removed"); //===----------------------------------------------------------------------===// // ADCE Class @@ -52,6 +62,10 @@ public: // getAnalysisUsage - We require post dominance frontiers (aka Control // Dependence Graph) virtual void getAnalysisUsage(AnalysisUsage &AU) const { + // We require that all function nodes are unified, because otherwise code + // can be marked live that wouldn't necessarily be otherwise. + AU.addRequired(); + AU.addRequired(); AU.addRequired(); AU.addRequired(); } @@ -84,15 +98,15 @@ private: } inline void markTerminatorLive(const BasicBlock *BB) { - DEBUG(std::cerr << "Terminat Live: " << BB->getTerminator()); - markInstructionLive((Instruction*)BB->getTerminator()); + DEBUG(std::cerr << "Terminator Live: " << BB->getTerminator()); + markInstructionLive(const_cast(BB->getTerminator())); } }; RegisterOpt X("adce", "Aggressive Dead Code Elimination"); } // End of anonymous namespace -Pass *createAggressiveDCEPass() { return new ADCE(); } +Pass *llvm::createAggressiveDCEPass() { return new ADCE(); } void ADCE::markBlockAlive(BasicBlock *BB) { // Mark the basic block as being newly ALIVE... and mark all branches that @@ -128,10 +142,12 @@ bool ADCE::dropReferencesOfDeadInstructionsInLiveBlock(BasicBlock *BB) { // #arguments != #predecessors, so we remove them now. // PN->replaceAllUsesWith(Constant::getNullValue(PN->getType())); - + // Delete the instruction... - I = BB->getInstList().erase(I); + ++I; + BB->getInstList().erase(PN); Changed = true; + ++NumInstRemoved; } else { ++I; } @@ -166,6 +182,33 @@ TerminatorInst *ADCE::convertToUnconditionalBranch(TerminatorInst *TI) { bool ADCE::doADCE() { bool MadeChanges = false; + AliasAnalysis &AA = getAnalysis(); + + + // Iterate over all invokes in the function, turning invokes into calls if + // they cannot throw. + for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB) + if (InvokeInst *II = dyn_cast(BB->getTerminator())) + if (Function *F = II->getCalledFunction()) + if (AA.onlyReadsMemory(F)) { + // The function cannot unwind. Convert it to a call with a branch + // after it to the normal destination. + std::vector Args(II->op_begin()+3, II->op_end()); + std::string Name = II->getName(); II->setName(""); + Instruction *NewCall = new CallInst(F, Args, Name, II); + II->replaceAllUsesWith(NewCall); + new BranchInst(II->getNormalDest(), II); + + // Update PHI nodes in the unwind destination + II->getUnwindDest()->removePredecessor(BB); + BB->getInstList().erase(II); + + if (NewCall->use_empty()) { + BB->getInstList().erase(NewCall); + ++NumCallRemoved; + } + } + // Iterate over all of the instructions in the function, eliminating trivially // dead instructions, and marking instructions live that are known to be // needed. Perform the walk in depth first order so that we avoid marking any @@ -176,16 +219,24 @@ bool ADCE::doADCE() { BBI != BBE; ++BBI) { BasicBlock *BB = *BBI; for (BasicBlock::iterator II = BB->begin(), EI = BB->end(); II != EI; ) { - if (II->mayWriteToMemory() || II->getOpcode() == Instruction::Ret) { - markInstructionLive(II); - ++II; // Increment the inst iterator if the inst wasn't deleted - } else if (isInstructionTriviallyDead(II)) { + Instruction *I = II++; + if (CallInst *CI = dyn_cast(I)) { + Function *F = CI->getCalledFunction(); + if (F && AA.onlyReadsMemory(F)) { + if (CI->use_empty()) { + BB->getInstList().erase(CI); + ++NumCallRemoved; + } + } else { + markInstructionLive(I); + } + } else if (I->mayWriteToMemory() || isa(I) || + isa(I)) { + markInstructionLive(I); + } else if (isInstructionTriviallyDead(I)) { // Remove the instruction from it's basic block... - II = BB->getInstList().erase(II); + BB->getInstList().erase(I); ++NumInstRemoved; - MadeChanges = true; - } else { - ++II; // Increment the inst iterator if the inst wasn't deleted } } } @@ -195,11 +246,23 @@ bool ADCE::doADCE() { // transformations safely. // PostDominatorTree &DT = getAnalysis(); - if (DT[&Func->getEntryNode()] == 0) { + if (DT[&Func->getEntryBlock()] == 0) { WorkList.clear(); return MadeChanges; } + // Scan the function marking blocks without post-dominance information as + // live. Blocks without post-dominance information occur when there is an + // infinite loop in the program. Because the infinite loop could contain a + // function which unwinds, exits or has side-effects, we don't want to delete + // the infinite loop or those blocks leading up to it. + for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I) + if (DT[I] == 0) + for (pred_iterator PI = pred_begin(I), E = pred_end(I); PI != E; ++PI) + markInstructionLive((*PI)->getTerminator()); + + + DEBUG(std::cerr << "Processing work list\n"); // AliveBlocks - Set of basic blocks that we know have instructions that are @@ -259,7 +322,7 @@ bool ADCE::doADCE() { // Loop over all of the instructions in the function, telling dead // instructions to drop their references. This is so that the next sweep // over the program can safely delete dead instructions without other dead - // instructions still refering to them. + // instructions still referring to them. // dropReferencesOfDeadInstructionsInLiveBlock(I); @@ -281,7 +344,7 @@ bool ADCE::doADCE() { // if (!AliveBlocks.count(&Func->front())) { BasicBlock *NewEntry = new BasicBlock(); - NewEntry->getInstList().push_back(new BranchInst(&Func->front())); + new BranchInst(&Func->front(), NewEntry); Func->getBasicBlockList().push_front(NewEntry); AliveBlocks.insert(NewEntry); // This block is always alive! LiveSet.insert(NewEntry->getTerminator()); // The branch is live @@ -328,9 +391,9 @@ bool ADCE::doADCE() { if (LastNode == 0) { // No postdominator! // Call RemoveSuccessor to transmogrify the terminator instruction // to not contain the outgoing branch, or to create a new - // terminator if the form fundementally changes (ie unconditional - // branch to return). Note that this will change a branch into an - // infinite loop into a return instruction! + // terminator if the form fundamentally changes (i.e., + // unconditional branch to return). Note that this will change a + // branch into an infinite loop into a return instruction! // RemoveSuccessor(TI, i); @@ -344,14 +407,14 @@ bool ADCE::doADCE() { } else { PostDominatorTree::Node *NextNode = LastNode->getIDom(); - while (!AliveBlocks.count(NextNode->getNode())) { + while (!AliveBlocks.count(NextNode->getBlock())) { LastNode = NextNode; NextNode = NextNode->getIDom(); } // Get the basic blocks that we need... - BasicBlock *LastDead = LastNode->getNode(); - BasicBlock *NextAlive = NextNode->getNode(); + BasicBlock *LastDead = LastNode->getBlock(); + BasicBlock *NextAlive = NextNode->getBlock(); // Make the conditional branch now go to the next alive block... TI->getSuccessor(i)->removePredecessor(BB); @@ -378,7 +441,7 @@ bool ADCE::doADCE() { // Now loop over all of the instructions in the basic block, telling // dead instructions to drop their references. This is so that the next // sweep over the program can safely delete dead instructions without - // other dead instructions still refering to them. + // other dead instructions still referring to them. // dropReferencesOfDeadInstructionsInLiveBlock(BB); } @@ -409,10 +472,14 @@ bool ADCE::doADCE() { } // Delete the old terminator instruction... + const Type *TermTy = BB->getTerminator()->getType(); + if (TermTy != Type::VoidTy) + BB->getTerminator()->replaceAllUsesWith( + Constant::getNullValue(TermTy)); BB->getInstList().pop_back(); const Type *RetTy = Func->getReturnType(); - BB->getInstList().push_back(new ReturnInst(RetTy != Type::VoidTy ? - Constant::getNullValue(RetTy) : 0)); + new ReturnInst(RetTy != Type::VoidTy ? + Constant::getNullValue(RetTy) : 0, BB); } } @@ -437,8 +504,11 @@ bool ADCE::doADCE() { for (BasicBlock::iterator II = BI->begin(); II != --BI->end(); ) if (!LiveSet.count(II)) { // Is this instruction alive? // Nope... remove the instruction from it's basic block... + if (isa(II)) + ++NumCallRemoved; + else + ++NumInstRemoved; II = BI->getInstList().erase(II); - ++NumInstRemoved; MadeChanges = true; } else { ++II;