X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FLoopDeletion.cpp;h=4971ab88ab46c332f0eb2414c58926591e598d95;hb=47be3618f189879a22ceb060548a6a47d124f3f7;hp=76a773a80815dcf8f51983ed66a318b10aea98b9;hpb=0bba49cebc50c7bd4662a4807bcb3ee7f42cb470;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/LoopDeletion.cpp b/lib/Transforms/Scalar/LoopDeletion.cpp index 76a773a8081..4971ab88ab4 100644 --- a/lib/Transforms/Scalar/LoopDeletion.cpp +++ b/lib/Transforms/Scalar/LoopDeletion.cpp @@ -14,120 +14,102 @@ // //===----------------------------------------------------------------------===// -#define DEBUG_TYPE "loop-delete" - #include "llvm/Transforms/Scalar.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/GlobalsModRef.h" #include "llvm/Analysis/LoopPass.h" #include "llvm/Analysis/ScalarEvolution.h" -#include "llvm/ADT/Statistic.h" -#include "llvm/ADT/SmallVector.h" - +#include "llvm/IR/Dominators.h" using namespace llvm; +#define DEBUG_TYPE "loop-delete" + STATISTIC(NumDeleted, "Number of loops deleted"); namespace { - class VISIBILITY_HIDDEN LoopDeletion : public LoopPass { + class LoopDeletion : public LoopPass { public: static char ID; // Pass ID, replacement for typeid - LoopDeletion() : LoopPass(&ID) {} - + LoopDeletion() : LoopPass(ID) { + initializeLoopDeletionPass(*PassRegistry::getPassRegistry()); + } + // Possibly eliminate loop L if it is dead. - bool runOnLoop(Loop* L, LPPassManager& LPM); - - bool SingleDominatingExit(Loop* L, - SmallVector& exitingBlocks); - bool IsLoopDead(Loop* L, SmallVector& exitingBlocks, - SmallVector& exitBlocks); - bool IsLoopInvariantInst(Instruction *I, Loop* L); - - virtual void getAnalysisUsage(AnalysisUsage& AU) const { - AU.addRequired(); - AU.addRequired(); - AU.addRequired(); + bool runOnLoop(Loop *L, LPPassManager &LPM) override; + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.addRequired(); + AU.addRequired(); + AU.addRequired(); AU.addRequiredID(LoopSimplifyID); AU.addRequiredID(LCSSAID); - - AU.addPreserved(); - AU.addPreserved(); - AU.addPreserved(); + + AU.addPreserved(); + AU.addPreserved(); + AU.addPreserved(); + AU.addPreserved(); AU.addPreservedID(LoopSimplifyID); AU.addPreservedID(LCSSAID); - AU.addPreserved(); } + + private: + bool isLoopDead(Loop *L, SmallVectorImpl &exitingBlocks, + SmallVectorImpl &exitBlocks, + bool &Changed, BasicBlock *Preheader); + }; } - + char LoopDeletion::ID = 0; -static RegisterPass X("loop-deletion", "Delete dead loops"); +INITIALIZE_PASS_BEGIN(LoopDeletion, "loop-deletion", + "Delete dead loops", false, false) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) +INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass) +INITIALIZE_PASS_DEPENDENCY(LoopSimplify) +INITIALIZE_PASS_DEPENDENCY(LCSSA) +INITIALIZE_PASS_END(LoopDeletion, "loop-deletion", + "Delete dead loops", false, false) -Pass* llvm::createLoopDeletionPass() { +Pass *llvm::createLoopDeletionPass() { return new LoopDeletion(); } -/// SingleDominatingExit - Checks that there is only a single blocks that -/// branches out of the loop, and that it also g the latch block. Loops -/// with multiple or non-latch-dominating exiting blocks could be dead, but we'd -/// have to do more extensive analysis to make sure, for instance, that the -/// control flow logic involved was or could be made loop-invariant. -bool LoopDeletion::SingleDominatingExit(Loop* L, - SmallVector& exitingBlocks) { - - if (exitingBlocks.size() != 1) - return false; - - BasicBlock* latch = L->getLoopLatch(); - if (!latch) - return false; - - DominatorTree& DT = getAnalysis(); - return DT.dominates(exitingBlocks[0], latch); -} - -/// IsLoopInvariantInst - Checks if an instruction is invariant with respect to -/// a loop, which is defined as being true if all of its operands are defined -/// outside of the loop. These instructions can be hoisted out of the loop -/// if their results are needed. This could be made more aggressive by -/// recursively checking the operands for invariance, but it's not clear that -/// it's worth it. -bool LoopDeletion::IsLoopInvariantInst(Instruction *I, Loop* L) { - // PHI nodes are not loop invariant if defined in the loop. - if (isa(I) && L->contains(I->getParent())) - return false; - - // The instruction is loop invariant if all of its operands are loop-invariant - for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) - if (!L->isLoopInvariant(I->getOperand(i))) - return false; - - // If we got this far, the instruction is loop invariant! - return true; -} - -/// IsLoopDead - Determined if a loop is dead. This assumes that we've already +/// isLoopDead - Determined if a loop is dead. This assumes that we've already /// checked for unique exit and exiting blocks, and that the code is in LCSSA /// form. -bool LoopDeletion::IsLoopDead(Loop* L, - SmallVector& exitingBlocks, - SmallVector& exitBlocks) { - BasicBlock* exitingBlock = exitingBlocks[0]; - BasicBlock* exitBlock = exitBlocks[0]; - +bool LoopDeletion::isLoopDead(Loop *L, + SmallVectorImpl &exitingBlocks, + SmallVectorImpl &exitBlocks, + bool &Changed, BasicBlock *Preheader) { + BasicBlock *exitBlock = exitBlocks[0]; + // Make sure that all PHI entries coming from the loop are loop invariant. // Because the code is in LCSSA form, any values used outside of the loop // must pass through a PHI in the exit block, meaning that this check is // sufficient to guarantee that no loop-variant values are used outside // of the loop. BasicBlock::iterator BI = exitBlock->begin(); - while (PHINode* P = dyn_cast(BI)) { - Value* incoming = P->getIncomingValueForBlock(exitingBlock); - if (Instruction* I = dyn_cast(incoming)) - if (!IsLoopInvariantInst(I, L)) + while (PHINode *P = dyn_cast(BI)) { + Value *incoming = P->getIncomingValueForBlock(exitingBlocks[0]); + + // Make sure all exiting blocks produce the same incoming value for the exit + // block. If there are different incoming values for different exiting + // blocks, then it is impossible to statically determine which value should + // be used. + for (unsigned i = 1, e = exitingBlocks.size(); i < e; ++i) { + if (incoming != P->getIncomingValueForBlock(exitingBlocks[i])) + return false; + } + + if (Instruction *I = dyn_cast(incoming)) + if (!L->makeLoopInvariant(I, Changed, Preheader->getTerminator())) return false; - - BI++; + + ++BI; } - + // Make sure that no instructions in the block have potential side-effects. // This includes instructions that could write to memory, and loads that are // marked volatile. This could be made more aggressive by using aliasing @@ -140,118 +122,111 @@ bool LoopDeletion::IsLoopDead(Loop* L, return false; } } - + return true; } /// runOnLoop - Remove dead loops, by which we mean loops that do not impact the -/// observable behavior of the program other than finite running time. Note +/// observable behavior of the program other than finite running time. Note /// we do ensure that this never remove a loop that might be infinite, as doing /// so could change the halting/non-halting nature of a program. /// NOTE: This entire process relies pretty heavily on LoopSimplify and LCSSA /// in order to make various safety checks work. -bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) { - // We can only remove the loop if there is a preheader that we can +bool LoopDeletion::runOnLoop(Loop *L, LPPassManager &LPM) { + if (skipOptnoneFunction(L)) + return false; + + // We can only remove the loop if there is a preheader that we can // branch from after removing it. - BasicBlock* preheader = L->getLoopPreheader(); + BasicBlock *preheader = L->getLoopPreheader(); if (!preheader) return false; - + + // If LoopSimplify form is not available, stay out of trouble. + if (!L->hasDedicatedExits()) + return false; + // We can't remove loops that contain subloops. If the subloops were dead, // they would already have been removed in earlier executions of this pass. if (L->begin() != L->end()) return false; - + SmallVector exitingBlocks; L->getExitingBlocks(exitingBlocks); - + SmallVector exitBlocks; L->getUniqueExitBlocks(exitBlocks); - + // We require that the loop only have a single exit block. Otherwise, we'd // be in the situation of needing to be able to solve statically which exit // block will be branched to, or trying to preserve the branching logic in // a loop invariant manner. if (exitBlocks.size() != 1) return false; - - // Loops with multiple exits or exits that don't dominate the latch - // are too complicated to handle correctly. - if (!SingleDominatingExit(L, exitingBlocks)) - return false; - + // Finally, we have to check that the loop really is dead. - if (!IsLoopDead(L, exitingBlocks, exitBlocks)) - return false; - + bool Changed = false; + if (!isLoopDead(L, exitingBlocks, exitBlocks, Changed, preheader)) + return Changed; + // Don't remove loops for which we can't solve the trip count. // They could be infinite, in which case we'd be changing program behavior. - ScalarEvolution& SE = getAnalysis(); - const SCEV *S = SE.getBackedgeTakenCount(L); + ScalarEvolution &SE = getAnalysis().getSE(); + const SCEV *S = SE.getMaxBackedgeTakenCount(L); if (isa(S)) - return false; - + return Changed; + // Now that we know the removal is safe, remove the loop by changing the - // branch from the preheader to go to the single exit block. - BasicBlock* exitBlock = exitBlocks[0]; - BasicBlock* exitingBlock = exitingBlocks[0]; - + // branch from the preheader to go to the single exit block. + BasicBlock *exitBlock = exitBlocks[0]; + // Because we're deleting a large chunk of code at once, the sequence in which // we remove things is very important to avoid invalidation issues. Don't // mess with this unless you have good reason and know what you're doing. - - // Move simple loop-invariant expressions out of the loop, since they - // might be needed by the exit phis. - for (Loop::block_iterator LI = L->block_begin(), LE = L->block_end(); - LI != LE; ++LI) - for (BasicBlock::iterator BI = (*LI)->begin(), BE = (*LI)->end(); - BI != BE; ) { - Instruction* I = BI++; - if (!I->use_empty() && IsLoopInvariantInst(I, L)) - I->moveBefore(preheader->getTerminator()); - } - + + // Tell ScalarEvolution that the loop is deleted. Do this before + // deleting the loop so that ScalarEvolution can look at the loop + // to determine what it needs to clean up. + SE.forgetLoop(L); + // Connect the preheader directly to the exit block. - TerminatorInst* TI = preheader->getTerminator(); + TerminatorInst *TI = preheader->getTerminator(); TI->replaceUsesOfWith(L->getHeader(), exitBlock); // Rewrite phis in the exit block to get their inputs from // the preheader instead of the exiting block. + BasicBlock *exitingBlock = exitingBlocks[0]; BasicBlock::iterator BI = exitBlock->begin(); - while (PHINode* P = dyn_cast(BI)) { - P->replaceUsesOfWith(exitingBlock, preheader); - BI++; + while (PHINode *P = dyn_cast(BI)) { + int j = P->getBasicBlockIndex(exitingBlock); + assert(j >= 0 && "Can't find exiting block in exit block's phi node!"); + P->setIncomingBlock(j, preheader); + for (unsigned i = 1; i < exitingBlocks.size(); ++i) + P->removeIncomingValue(exitingBlocks[i]); + ++BI; } - + // Update the dominator tree and remove the instructions and blocks that will // be deleted from the reference counting scheme. - DominatorTree& DT = getAnalysis(); - DominanceFrontier* DF = getAnalysisIfAvailable(); - SmallPtrSet ChildNodes; + DominatorTree &DT = getAnalysis().getDomTree(); + SmallVector ChildNodes; for (Loop::block_iterator LI = L->block_begin(), LE = L->block_end(); LI != LE; ++LI) { // Move all of the block's children to be children of the preheader, which // allows us to remove the domtree entry for the block. - ChildNodes.insert(DT[*LI]->begin(), DT[*LI]->end()); - for (SmallPtrSet::iterator DI = ChildNodes.begin(), + ChildNodes.insert(ChildNodes.begin(), DT[*LI]->begin(), DT[*LI]->end()); + for (SmallVectorImpl::iterator DI = ChildNodes.begin(), DE = ChildNodes.end(); DI != DE; ++DI) { DT.changeImmediateDominator(*DI, DT[preheader]); - if (DF) DF->changeImmediateDominator((*DI)->getBlock(), preheader, &DT); } - + ChildNodes.clear(); DT.eraseNode(*LI); - if (DF) DF->removeBlock(*LI); // Remove the block from the reference counting scheme, so that we can // delete it freely later. (*LI)->dropAllReferences(); } - - // Tell ScalarEvolution that the loop is deleted. Do this before - // deleting the loop so that ScalarEvolution can look at the loop - // to determine what it needs to clean up. - SE.forgetLoopBackedgeTakenCount(L); // Erase the instructions and the blocks without having to worry // about ordering because we already dropped the references. @@ -263,18 +238,18 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) { // Finally, the blocks from loopinfo. This has to happen late because // otherwise our loop iterators won't work. - LoopInfo& loopInfo = getAnalysis(); + LoopInfo &loopInfo = getAnalysis().getLoopInfo(); SmallPtrSet blocks; blocks.insert(L->block_begin(), L->block_end()); - for (SmallPtrSet::iterator I = blocks.begin(), - E = blocks.end(); I != E; ++I) - loopInfo.removeBlock(*I); - + for (BasicBlock *BB : blocks) + loopInfo.removeBlock(BB); + // The last step is to inform the loop pass manager that we've // eliminated this loop. LPM.deleteLoopFromQueue(L); - - NumDeleted++; - - return true; + Changed = true; + + ++NumDeleted; + + return Changed; }