diff options
Diffstat (limited to 'lib/Transforms')
| -rw-r--r-- | lib/Transforms/Scalar/ADCE.cpp | 67 |
1 files changed, 46 insertions, 21 deletions
diff --git a/lib/Transforms/Scalar/ADCE.cpp b/lib/Transforms/Scalar/ADCE.cpp index 56b219a..126a32b 100644 --- a/lib/Transforms/Scalar/ADCE.cpp +++ b/lib/Transforms/Scalar/ADCE.cpp @@ -71,6 +71,12 @@ private: void markBlockAlive(BasicBlock *BB); + + // dropReferencesOfDeadInstructionsInLiveBlock - Loop over all of the + // instructions in the specified basic block, dropping references on + // instructions that are dead according to LiveSet. + bool dropReferencesOfDeadInstructionsInLiveBlock(BasicBlock *BB); + inline void markInstructionLive(Instruction *I) { if (LiveSet.count(I)) return; DEBUG(cerr << "Insn Live: " << I); @@ -107,6 +113,32 @@ void ADCE::markBlockAlive(BasicBlock *BB) { markTerminatorLive(BB); } +// dropReferencesOfDeadInstructionsInLiveBlock - Loop over all of the +// instructions in the specified basic block, dropping references on +// instructions that are dead according to LiveSet. +bool ADCE::dropReferencesOfDeadInstructionsInLiveBlock(BasicBlock *BB) { + bool Changed = false; + for (BasicBlock::iterator I = BB->begin(), E = --BB->end(); I != E; ) + if (!LiveSet.count(I)) { // Is this instruction alive? + I->dropAllReferences(); // Nope, drop references... + if (PHINode *PN = dyn_cast<PHINode>(&*I)) { + // We don't want to leave PHI nodes in the program that have + // #arguments != #predecessors, so we remove them now. + // + PN->replaceAllUsesWith(Constant::getNullValue(PN->getType())); + + // Delete the instruction... + I = BB->getInstList().erase(I); + Changed = true; + } else { + ++I; + } + } else { + ++I; + } + return Changed; +} + // doADCE() - Run the Aggressive Dead Code Elimination algorithm, returning // true if the function was modified. @@ -192,8 +224,17 @@ bool ADCE::doADCE() { // PostDominatorTree &DT = getAnalysis<PostDominatorTree>(); - // If there are some blocks dead... - if (AliveBlocks.size() != Func->size()) { + + if (AliveBlocks.size() == Func->size()) { // No dead blocks? + for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I) + // 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. + // + dropReferencesOfDeadInstructionsInLiveBlock(I); + + } else { // If there are some blocks dead... // Insert a new entry node to eliminate the entry node as a special case. BasicBlock *NewEntry = new BasicBlock(); NewEntry->getInstList().push_back(new BranchInst(&Func->front())); @@ -284,23 +325,7 @@ bool ADCE::doADCE() { // sweep over the program can safely delete dead instructions without // other dead instructions still refering to them. // - for (BasicBlock::iterator I = BB->begin(), E = --BB->end(); I != E; ) - if (!LiveSet.count(I)) { // Is this instruction alive? - I->dropAllReferences(); // Nope, drop references... - if (PHINode *PN = dyn_cast<PHINode>(&*I)) { - // We don't want to leave PHI nodes in the program that have - // #arguments != #predecessors, so we remove them now. - // - PN->replaceAllUsesWith(Constant::getNullValue(PN->getType())); - - // Delete the instruction... - I = BB->getInstList().erase(I); - } else { - ++I; - } - } else { - ++I; - } + dropReferencesOfDeadInstructionsInLiveBlock(BB); } } @@ -341,9 +366,9 @@ bool ADCE::doADCE() { // instructions from alive blocks. // for (Function::iterator BI = Func->begin(); BI != Func->end(); ) - if (!AliveBlocks.count(BI)) + if (!AliveBlocks.count(BI)) { // Delete dead blocks... BI = Func->getBasicBlockList().erase(BI); - else { + } else { // Scan alive blocks... 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... |