X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FLoopDeletion.cpp;h=48817ab9d5ad923f56c15b89fa1122689c5961e5;hb=040056fd11693ffc41ce9b777281c71705d0dc1f;hp=ac807a4c9b20e11664a0df38046b18595941cc86;hpb=e2abdd3ff0dd54a59edbd114ebb1d7728040a2d9;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/LoopDeletion.cpp b/lib/Transforms/Scalar/LoopDeletion.cpp index ac807a4c9b2..48817ab9d5a 100644 --- a/lib/Transforms/Scalar/LoopDeletion.cpp +++ b/lib/Transforms/Scalar/LoopDeletion.cpp @@ -15,19 +15,17 @@ //===----------------------------------------------------------------------===// #define DEBUG_TYPE "loop-delete" - #include "llvm/Transforms/Scalar.h" #include "llvm/Analysis/LoopPass.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(&ID) {} @@ -35,12 +33,10 @@ namespace { // 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(); @@ -53,6 +49,7 @@ namespace { AU.addPreserved(); AU.addPreservedID(LoopSimplifyID); AU.addPreservedID(LCSSAID); + AU.addPreserved(); } }; } @@ -64,51 +61,13 @@ 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 /// checked for unique exit and exiting blocks, and that the code is in LCSSA /// form. bool LoopDeletion::IsLoopDead(Loop* L, SmallVector& exitingBlocks, - SmallVector& exitBlocks) { + SmallVector& exitBlocks, + bool &Changed, BasicBlock *Preheader) { BasicBlock* exitingBlock = exitingBlocks[0]; BasicBlock* exitBlock = exitBlocks[0]; @@ -121,7 +80,7 @@ bool LoopDeletion::IsLoopDead(Loop* L, while (PHINode* P = dyn_cast(BI)) { Value* incoming = P->getIncomingValueForBlock(exitingBlock); if (Instruction* I = dyn_cast(incoming)) - if (!IsLoopInvariantInst(I, L)) + if (!L->makeLoopInvariant(I, Changed, Preheader->getTerminator())) return false; BI++; @@ -135,11 +94,8 @@ 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; } } @@ -159,6 +115,10 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) { 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()) @@ -177,21 +137,21 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) { 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)) + // Loops with multiple exits are too complicated to handle correctly. + if (exitingBlocks.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(); - SCEVHandle S = SE.getIterationCount(L); + 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. @@ -201,18 +161,12 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) { // 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(); TI->replaceUsesOfWith(L->getHeader(), exitBlock); @@ -228,6 +182,7 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) { // 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; for (Loop::block_iterator LI = L->block_begin(), LE = L->block_end(); LI != LE; ++LI) { @@ -235,19 +190,15 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) { // 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) + DE = ChildNodes.end(); DI != DE; ++DI) { DT.changeImmediateDominator(*DI, DT[preheader]); + if (DF) DF->changeImmediateDominator((*DI)->getBlock(), preheader, &DT); + } ChildNodes.clear(); DT.eraseNode(*LI); - - // Remove instructions that we're deleting from ScalarEvolution. - for (BasicBlock::iterator BI = (*LI)->begin(), BE = (*LI)->end(); - BI != BE; ++BI) - SE.deleteValueFromRecords(BI); - - SE.deleteValueFromRecords(*LI); - + if (DF) DF->removeBlock(*LI); + // Remove the block from the reference counting scheme, so that we can // delete it freely later. (*LI)->dropAllReferences(); @@ -261,9 +212,6 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) { LI != LE; ++LI) (*LI)->eraseFromParent(); - // Tell ScalarEvolution that the loop is deleted. - SE.forgetLoopIterationCount(L); - // Finally, the blocks from loopinfo. This has to happen late because // otherwise our loop iterators won't work. LoopInfo& loopInfo = getAnalysis(); @@ -276,8 +224,9 @@ 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++; - return true; + return Changed; }