X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FLoopDeletion.cpp;h=f7f32981baa77e6e46c394fa4042e68a7781b05f;hb=b05fdd6babada25da2ec3ba54bb462c2ecfc42a8;hp=02a5ca98d97761e803d1ef98ffe9d0d163af85b4;hpb=a8a118b68fa3ca1632e7280cd6994aa0f8f1eec1;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/LoopDeletion.cpp b/lib/Transforms/Scalar/LoopDeletion.cpp index 02a5ca98d97..f7f32981baa 100644 --- a/lib/Transforms/Scalar/LoopDeletion.cpp +++ b/lib/Transforms/Scalar/LoopDeletion.cpp @@ -15,92 +15,60 @@ //===----------------------------------------------------------------------===// #define DEBUG_TYPE "loop-delete" - #include "llvm/Transforms/Scalar.h" #include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/Dominators.h" +#include "llvm/Analysis/ScalarEvolution.h" #include "llvm/ADT/Statistic.h" #include "llvm/ADT/SmallVector.h" - using namespace llvm; 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((intptr_t)&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); - + SmallVector& exitBlocks, + bool &Changed, BasicBlock *Preheader); + virtual void getAnalysisUsage(AnalysisUsage& AU) const { AU.addRequired(); AU.addRequired(); + AU.addRequired(); AU.addRequiredID(LoopSimplifyID); AU.addRequiredID(LCSSAID); + AU.addPreserved(); AU.addPreserved(); AU.addPreserved(); AU.addPreservedID(LoopSimplifyID); AU.addPreservedID(LCSSAID); } }; - - char LoopDeletion::ID = 0; - RegisterPass X ("loop-deletion", "Delete dead loops"); } - -LoopPass* llvm::createLoopDeletionPass() { - return new LoopDeletion(); -} - -/// SingleDominatingExit - Checks that there is only a single blocks that -/// branches out of the loop, and that it also dominates 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 involves 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(); - if (DT.dominates(exitingBlocks[0], latch)) - return true; - else - return false; -} +char LoopDeletion::ID = 0; +INITIALIZE_PASS_BEGIN(LoopDeletion, "loop-deletion", + "Delete dead loops", false, false) +INITIALIZE_PASS_DEPENDENCY(DominatorTree) +INITIALIZE_PASS_DEPENDENCY(LoopInfo) +INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) +INITIALIZE_PASS_DEPENDENCY(LoopSimplify) +INITIALIZE_PASS_DEPENDENCY(LCSSA) +INITIALIZE_PASS_END(LoopDeletion, "loop-deletion", + "Delete dead loops", false, false) -/// 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; +Pass* llvm::createLoopDeletionPass() { + return new LoopDeletion(); } /// IsLoopDead - Determined if a loop is dead. This assumes that we've already @@ -108,8 +76,8 @@ bool LoopDeletion::IsLoopInvariantInst(Instruction *I, Loop* L) { /// form. bool LoopDeletion::IsLoopDead(Loop* L, SmallVector& exitingBlocks, - SmallVector& exitBlocks) { - BasicBlock* exitingBlock = exitingBlocks[0]; + SmallVector& exitBlocks, + bool &Changed, BasicBlock *Preheader) { BasicBlock* exitBlock = exitBlocks[0]; // Make sure that all PHI entries coming from the loop are loop invariant. @@ -119,12 +87,22 @@ bool LoopDeletion::IsLoopDead(Loop* L, // 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)) + 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; i < exitingBlocks.size(); ++i) { + if (incoming != P->getIncomingValueForBlock(exitingBlocks[i])) return false; + } - BI++; + if (Instruction* I = dyn_cast(incoming)) + if (!L->makeLoopInvariant(I, Changed, Preheader->getTerminator())) + return false; + + ++BI; } // Make sure that no instructions in the block have potential side-effects. @@ -135,11 +113,8 @@ bool LoopDeletion::IsLoopDead(Loop* L, LI != LE; ++LI) { for (BasicBlock::iterator BI = (*LI)->begin(), BE = (*LI)->end(); BI != BE; ++BI) { - if (BI->mayWriteToMemory()) + if (BI->mayHaveSideEffects()) return false; - else if (LoadInst* L = dyn_cast(BI)) - if (L->isVolatile()) - return false; } } @@ -153,99 +128,95 @@ bool LoopDeletion::IsLoopDead(Loop* L, /// 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) { - 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 branced to, or trying to preserve the branching logic in - // a loop invariant manner. - if (exitBlocks.size() != 1) - 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(); 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; - // 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. - if (!L->getTripCount()) - return false; + SmallVector exitingBlocks; + L->getExitingBlocks(exitingBlocks); - // Loops with multiple exits or exits that don't dominate the latch - // are too complicated to handle correctly. - if (!SingleDominatingExit(L, 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; // 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.getMaxBackedgeTakenCount(L); + if (isa(S)) + 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]; // 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->getNumUses() > 0 && 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(); 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++; + 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(); - SmallPtrSet ChildNodes; + 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(), - DE = ChildNodes.end(); DI != DE; ++DI) + ChildNodes.insert(ChildNodes.begin(), DT[*LI]->begin(), DT[*LI]->end()); + for (SmallVector::iterator DI = ChildNodes.begin(), + DE = ChildNodes.end(); DI != DE; ++DI) { DT.changeImmediateDominator(*DI, DT[preheader]); + } ChildNodes.clear(); DT.eraseNode(*LI); - - // Drop all references between the instructions and the block so - // that we don't have reference counting problems later. - for (BasicBlock::iterator BI = (*LI)->begin(), BE = (*LI)->end(); - BI != BE; ++BI) { - BI->dropAllReferences(); - } - + + // Remove the block from the reference counting scheme, so that we can + // delete it freely later. (*LI)->dropAllReferences(); } @@ -254,13 +225,9 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) { // NOTE: This iteration is safe because erasing the block does not remove its // entry from the loop's block list. We do that in the next section. for (Loop::block_iterator LI = L->block_begin(), LE = L->block_end(); - LI != LE; ++LI) { - for (Value::use_iterator UI = (*LI)->use_begin(), UE = (*LI)->use_end(); - UI != UE; ++UI) - (*UI)->dump(); + LI != LE; ++LI) (*LI)->eraseFromParent(); - } - + // Finally, the blocks from loopinfo. This has to happen late because // otherwise our loop iterators won't work. LoopInfo& loopInfo = getAnalysis(); @@ -273,8 +240,9 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) { // The last step is to inform the loop pass manager that we've // eliminated this loop. LPM.deleteLoopFromQueue(L); + Changed = true; - NumDeleted++; + ++NumDeleted; - return true; + return Changed; }