+++ /dev/null
-//===- DeadLoopElimination.cpp - Dead Loop Elimination Pass ---------------===//
-//
-// The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This file implements the Dead Loop Elimination Pass.
-//
-//===----------------------------------------------------------------------===//
-
-#define DEBUG_TYPE "dead-loop"
-
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/Instruction.h"
-#include "llvm/Analysis/LoopInfo.h"
-#include "llvm/Analysis/LoopPass.h"
-#include "llvm/ADT/Statistic.h"
-#include "llvm/ADT/SmallVector.h"
-
-using namespace llvm;
-
-STATISTIC(NumDeleted, "Number of loops deleted");
-
-namespace {
- class VISIBILITY_HIDDEN DeadLoopElimination : public LoopPass {
- public:
- static char ID; // Pass ID, replacement for typeid
- DeadLoopElimination() : LoopPass((intptr_t)&ID) { }
-
- // Possibly eliminate loop L if it is dead.
- bool runOnLoop(Loop* L, LPPassManager& LPM);
-
- bool SingleDominatingExit(Loop* L);
- bool IsLoopDead(Loop* L);
- bool IsLoopInvariantInst(Instruction *I, Loop* L);
-
- virtual void getAnalysisUsage(AnalysisUsage& AU) const {
- AU.addRequired<DominatorTree>();
- AU.addRequired<LoopInfo>();
- AU.addRequiredID(LoopSimplifyID);
- AU.addRequiredID(LCSSAID);
-
- AU.addPreserved<DominatorTree>();
- AU.addPreserved<LoopInfo>();
- AU.addPreservedID(LoopSimplifyID);
- AU.addPreservedID(LCSSAID);
- }
- };
-
- char DeadLoopElimination::ID = 0;
- RegisterPass<DeadLoopElimination> X ("dead-loop", "Eliminate dead loops");
-}
-
-LoopPass* llvm::createDeadLoopEliminationPass() {
- return new DeadLoopElimination();
-}
-
-bool DeadLoopElimination::SingleDominatingExit(Loop* L) {
- SmallVector<BasicBlock*, 4> exitingBlocks;
- L->getExitingBlocks(exitingBlocks);
-
- if (exitingBlocks.size() != 1)
- return 0;
-
- BasicBlock* latch = L->getLoopLatch();
- if (!latch)
- return 0;
-
- DominatorTree& DT = getAnalysis<DominatorTree>();
- if (DT.dominates(exitingBlocks[0], latch))
- return exitingBlocks[0];
- else
- return 0;
-}
-
-bool DeadLoopElimination::IsLoopInvariantInst(Instruction *I, Loop* L) {
- // PHI nodes are not loop invariant if defined in the loop.
- if (isa<PHINode>(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;
-}
-
-bool DeadLoopElimination::IsLoopDead(Loop* L) {
- SmallVector<BasicBlock*, 1> exitingBlocks;
- L->getExitingBlocks(exitingBlocks);
- BasicBlock* exitingBlock = exitingBlocks[0];
-
- // Get the set of out-of-loop blocks that the exiting block branches to.
- SmallVector<BasicBlock*, 8> exitBlocks;
- L->getUniqueExitBlocks(exitBlocks);
- if (exitBlocks.size() > 1)
- return false;
- BasicBlock* exitBlock = exitBlocks[0];
-
- // Make sure that all PHI entries coming from the loop are loop invariant.
- BasicBlock::iterator BI = exitBlock->begin();
- while (PHINode* P = dyn_cast<PHINode>(BI)) {
- Value* incoming = P->getIncomingValueForBlock(exitingBlock);
- if (Instruction* I = dyn_cast<Instruction>(incoming))
- if (!IsLoopInvariantInst(I, L))
- return false;
-
- BI++;
- }
-
- // Make sure that no instructions in the block have potential side-effects.
- 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; ++BI) {
- if (BI->mayWriteToMemory())
- 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
-/// 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.
-bool DeadLoopElimination::runOnLoop(Loop* L, LPPassManager& LPM) {
- // 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;
-
- // 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;
-
- // 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;
-
- // Loops with multiple exits or exits that don't dominate the latch
- // are too complicated to handle correctly.
- if (!SingleDominatingExit(L))
- return false;
-
- // Finally, we have to check that the loop really is dead.
- if (!IsLoopDead(L))
- return false;
-
- // Now that we know the removal is safe, change the branch from the preheader
- // to go to the single exiting block.
- SmallVector<BasicBlock*, 1> exitingBlocks;
- L->getExitingBlocks(exitingBlocks);
- BasicBlock* exitingBlock = exitingBlocks[0];
-
- SmallVector<BasicBlock*, 1> exitBlocks;
- L->getUniqueExitBlocks(exitBlocks);
- 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->getNumUses() > 0 && IsLoopInvariantInst(I, L))
- I->moveBefore(preheader->getTerminator());
- }
-
- // Connect the preheader directly to the exit block.
- TerminatorInst* TI = preheader->getTerminator();
- if (BranchInst* BI = dyn_cast<BranchInst>(TI)) {
- if (BI->isUnconditional())
- BI->setSuccessor(0, exitBlock);
- else if (L->contains(BI->getSuccessor(0)))
- BI->setSuccessor(0, exitBlock);
- else
- BI->setSuccessor(1, exitBlock);
- } else {
- // FIXME: Support switches
- return false;
- }
-
- // Rewrite phis in the exit block to get their inputs from
- // the preheader instead of the exiting block.
- BasicBlock::iterator BI = exitBlock->begin();
- while (PHINode* P = dyn_cast<PHINode>(BI)) {
- unsigned i = P->getBasicBlockIndex(exitingBlock);
- P->setIncomingBlock(i, preheader);
- BI++;
- }
-
- // Update lots of internal structures...
- DominatorTree& DT = getAnalysis<DominatorTree>();
- 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.
- SmallPtrSet<DomTreeNode*, 8> childNodes;
- childNodes.insert(DT[*LI]->begin(), DT[*LI]->end());
- for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = childNodes.begin(),
- DE = childNodes.end(); DI != DE; ++DI)
- DT.changeImmediateDominator(*DI, DT[preheader]);
-
- 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();
- }
-
- (*LI)->dropAllReferences();
- }
-
- // Erase the instructions and the blocks without having to worry
- // about ordering because we already dropped the references.
- 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++;
- I->eraseFromParent();
- }
-
- (*LI)->eraseFromParent();
- }
-
- // Finally, the blocks from loopinfo. This has to happen late because
- // otherwise our loop iterators won't work.
- LoopInfo& loopInfo = getAnalysis<LoopInfo>();
- SmallPtrSet<BasicBlock*, 8> blocks;
- blocks.insert(L->block_begin(), L->block_end());
- for (SmallPtrSet<BasicBlock*,8>::iterator I = blocks.begin(),
- E = blocks.end(); I != E; ++I)
- loopInfo.removeBlock(*I);
-
- // The last step is to inform the loop pass manager that we've
- // eliminated this loop.
- LPM.deleteLoopFromQueue(L);
-
- NumDeleted++;
-
- return true;
-}
--- /dev/null
+//===- DeadLoopElimination.cpp - Dead Loop Elimination Pass ---------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the Dead Loop Elimination Pass.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "dead-loop"
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Instruction.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/SmallVector.h"
+
+using namespace llvm;
+
+STATISTIC(NumDeleted, "Number of loops deleted");
+
+namespace {
+ class VISIBILITY_HIDDEN DeadLoopElimination : public LoopPass {
+ public:
+ static char ID; // Pass ID, replacement for typeid
+ DeadLoopElimination() : LoopPass((intptr_t)&ID) { }
+
+ // Possibly eliminate loop L if it is dead.
+ bool runOnLoop(Loop* L, LPPassManager& LPM);
+
+ bool SingleDominatingExit(Loop* L);
+ bool IsLoopDead(Loop* L);
+ bool IsLoopInvariantInst(Instruction *I, Loop* L);
+
+ virtual void getAnalysisUsage(AnalysisUsage& AU) const {
+ AU.addRequired<DominatorTree>();
+ AU.addRequired<LoopInfo>();
+ AU.addRequiredID(LoopSimplifyID);
+ AU.addRequiredID(LCSSAID);
+
+ AU.addPreserved<DominatorTree>();
+ AU.addPreserved<LoopInfo>();
+ AU.addPreservedID(LoopSimplifyID);
+ AU.addPreservedID(LCSSAID);
+ }
+ };
+
+ char DeadLoopElimination::ID = 0;
+ RegisterPass<DeadLoopElimination> X ("dead-loop", "Eliminate dead loops");
+}
+
+LoopPass* llvm::createDeadLoopEliminationPass() {
+ return new DeadLoopElimination();
+}
+
+bool DeadLoopElimination::SingleDominatingExit(Loop* L) {
+ SmallVector<BasicBlock*, 4> exitingBlocks;
+ L->getExitingBlocks(exitingBlocks);
+
+ if (exitingBlocks.size() != 1)
+ return 0;
+
+ BasicBlock* latch = L->getLoopLatch();
+ if (!latch)
+ return 0;
+
+ DominatorTree& DT = getAnalysis<DominatorTree>();
+ if (DT.dominates(exitingBlocks[0], latch))
+ return exitingBlocks[0];
+ else
+ return 0;
+}
+
+bool DeadLoopElimination::IsLoopInvariantInst(Instruction *I, Loop* L) {
+ // PHI nodes are not loop invariant if defined in the loop.
+ if (isa<PHINode>(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;
+}
+
+bool DeadLoopElimination::IsLoopDead(Loop* L) {
+ SmallVector<BasicBlock*, 1> exitingBlocks;
+ L->getExitingBlocks(exitingBlocks);
+ BasicBlock* exitingBlock = exitingBlocks[0];
+
+ // Get the set of out-of-loop blocks that the exiting block branches to.
+ SmallVector<BasicBlock*, 8> exitBlocks;
+ L->getUniqueExitBlocks(exitBlocks);
+ if (exitBlocks.size() > 1)
+ return false;
+ BasicBlock* exitBlock = exitBlocks[0];
+
+ // Make sure that all PHI entries coming from the loop are loop invariant.
+ BasicBlock::iterator BI = exitBlock->begin();
+ while (PHINode* P = dyn_cast<PHINode>(BI)) {
+ Value* incoming = P->getIncomingValueForBlock(exitingBlock);
+ if (Instruction* I = dyn_cast<Instruction>(incoming))
+ if (!IsLoopInvariantInst(I, L))
+ return false;
+
+ BI++;
+ }
+
+ // Make sure that no instructions in the block have potential side-effects.
+ 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; ++BI) {
+ if (BI->mayWriteToMemory())
+ 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
+/// 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.
+bool DeadLoopElimination::runOnLoop(Loop* L, LPPassManager& LPM) {
+ // 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;
+
+ // 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;
+
+ // 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;
+
+ // Loops with multiple exits or exits that don't dominate the latch
+ // are too complicated to handle correctly.
+ if (!SingleDominatingExit(L))
+ return false;
+
+ // Finally, we have to check that the loop really is dead.
+ if (!IsLoopDead(L))
+ return false;
+
+ // Now that we know the removal is safe, change the branch from the preheader
+ // to go to the single exiting block.
+ SmallVector<BasicBlock*, 1> exitingBlocks;
+ L->getExitingBlocks(exitingBlocks);
+ BasicBlock* exitingBlock = exitingBlocks[0];
+
+ SmallVector<BasicBlock*, 1> exitBlocks;
+ L->getUniqueExitBlocks(exitBlocks);
+ 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->getNumUses() > 0 && IsLoopInvariantInst(I, L))
+ I->moveBefore(preheader->getTerminator());
+ }
+
+ // Connect the preheader directly to the exit block.
+ TerminatorInst* TI = preheader->getTerminator();
+ if (BranchInst* BI = dyn_cast<BranchInst>(TI)) {
+ if (BI->isUnconditional())
+ BI->setSuccessor(0, exitBlock);
+ else if (L->contains(BI->getSuccessor(0)))
+ BI->setSuccessor(0, exitBlock);
+ else
+ BI->setSuccessor(1, exitBlock);
+ } else {
+ // FIXME: Support switches
+ return false;
+ }
+
+ // Rewrite phis in the exit block to get their inputs from
+ // the preheader instead of the exiting block.
+ BasicBlock::iterator BI = exitBlock->begin();
+ while (PHINode* P = dyn_cast<PHINode>(BI)) {
+ unsigned i = P->getBasicBlockIndex(exitingBlock);
+ P->setIncomingBlock(i, preheader);
+ BI++;
+ }
+
+ // Update lots of internal structures...
+ DominatorTree& DT = getAnalysis<DominatorTree>();
+ 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.
+ SmallPtrSet<DomTreeNode*, 8> childNodes;
+ childNodes.insert(DT[*LI]->begin(), DT[*LI]->end());
+ for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = childNodes.begin(),
+ DE = childNodes.end(); DI != DE; ++DI)
+ DT.changeImmediateDominator(*DI, DT[preheader]);
+
+ 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();
+ }
+
+ (*LI)->dropAllReferences();
+ }
+
+ // Erase the instructions and the blocks without having to worry
+ // about ordering because we already dropped the references.
+ 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++;
+ I->eraseFromParent();
+ }
+
+ (*LI)->eraseFromParent();
+ }
+
+ // Finally, the blocks from loopinfo. This has to happen late because
+ // otherwise our loop iterators won't work.
+ LoopInfo& loopInfo = getAnalysis<LoopInfo>();
+ SmallPtrSet<BasicBlock*, 8> blocks;
+ blocks.insert(L->block_begin(), L->block_end());
+ for (SmallPtrSet<BasicBlock*,8>::iterator I = blocks.begin(),
+ E = blocks.end(); I != E; ++I)
+ loopInfo.removeBlock(*I);
+
+ // The last step is to inform the loop pass manager that we've
+ // eliminated this loop.
+ LPM.deleteLoopFromQueue(L);
+
+ NumDeleted++;
+
+ return true;
+}
projects / oota-llvm.git / commitdiff