//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Constant.h"
+#include "llvm/Constants.h"
#include "llvm/Instructions.h"
-#include "llvm/Type.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/PostDominators.h"
#include "llvm/Support/CFG.h"
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);
+ // deleteDeadInstructionsInLiveBlock - Loop over all of the instructions in
+ // the specified basic block, deleting ones that are dead according to
+ // LiveSet.
+ bool deleteDeadInstructionsInLiveBlock(BasicBlock *BB);
TerminatorInst *convertToUnconditionalBranch(TerminatorInst *TI);
inline void markInstructionLive(Instruction *I) {
- if (LiveSet.count(I)) return;
+ if (!LiveSet.insert(I).second) return;
DEBUG(std::cerr << "Insn Live: " << *I);
- LiveSet.insert(I);
WorkList.push_back(I);
}
RegisterOpt<ADCE> X("adce", "Aggressive Dead Code Elimination");
} // End of anonymous namespace
-Pass *llvm::createAggressiveDCEPass() { return new ADCE(); }
+FunctionPass *llvm::createAggressiveDCEPass() { return new ADCE(); }
void ADCE::markBlockAlive(BasicBlock *BB) {
// Mark the basic block as being newly ALIVE... and mark all branches that
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) {
+// deleteDeadInstructionsInLiveBlock - Loop over all of the instructions in the
+// specified basic block, deleting ones that are dead according to LiveSet.
+bool ADCE::deleteDeadInstructionsInLiveBlock(BasicBlock *BB) {
bool Changed = false;
- for (BasicBlock::iterator I = BB->begin(), E = --BB->end(); I != E; )
+ for (BasicBlock::iterator II = BB->begin(), E = --BB->end(); II != E; ) {
+ Instruction *I = II++;
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(PN);
- Changed = true;
+ if (!I->use_empty())
+ I->replaceAllUsesWith(UndefValue::get(I->getType()));
+
+ // Nope... remove the instruction from it's basic block...
+ if (isa<CallInst>(I))
+ ++NumCallRemoved;
+ else
++NumInstRemoved;
- } else {
- ++I;
- }
- } else {
- ++I;
+ BB->getInstList().erase(I);
+ Changed = true;
}
+ }
return Changed;
}
markInstructionLive(I);
}
} else if (I->mayWriteToMemory() || isa<ReturnInst>(I) ||
- isa<UnwindInst>(I)) {
+ isa<UnwindInst>(I) || isa<UnreachableInst>(I)) {
+ // FIXME: Unreachable instructions should not be marked intrinsically
+ // live here.
markInstructionLive(I);
} else if (isInstructionTriviallyDead(I)) {
// Remove the instruction from it's basic block...
for (pred_iterator PI = pred_begin(I), E = pred_end(I); PI != E; ++PI)
markInstructionLive((*PI)->getTerminator());
-
-
DEBUG(std::cerr << "Processing work list\n");
// AliveBlocks - Set of basic blocks that we know have instructions that are
BasicBlock *BB = I->getParent();
if (!ReachableBBs.count(BB)) continue;
- if (!AliveBlocks.count(BB)) { // Basic block not alive yet...
- AliveBlocks.insert(BB); // Block is now ALIVE!
+ if (AliveBlocks.insert(BB).second) // Basic block not alive yet.
markBlockAlive(BB); // Make it so now!
- }
// PHI nodes are a special case, because the incoming values are actually
// defined in the predecessor nodes of this block, meaning that the PHI
// makes the predecessors alive.
//
if (PHINode *PN = dyn_cast<PHINode>(I))
- for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE; ++PI)
- if (!AliveBlocks.count(*PI)) {
- AliveBlocks.insert(BB); // Block is now ALIVE!
- markBlockAlive(*PI);
- }
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (AliveBlocks.insert(PN->getIncomingBlock(i)).second)
+ markBlockAlive(PN->getIncomingBlock(i)); // Block is newly ALIVE!
// Loop over all of the operands of the live instruction, making sure that
- // they are known to be alive as well...
+ // they are known to be alive as well.
//
for (unsigned op = 0, End = I->getNumOperands(); op != End; ++op)
if (Instruction *Operand = dyn_cast<Instruction>(I->getOperand(op)))
}
});
- // Find the first postdominator of the entry node that is alive. Make it the
- // new entry node...
- //
+ // All blocks being live is a common case, handle it specially.
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 referring to them.
- //
- dropReferencesOfDeadInstructionsInLiveBlock(I);
+ // Loop over all of the instructions in the function deleting instructions
+ // to drop their references.
+ deleteDeadInstructionsInLiveBlock(I);
// Check to make sure the terminator instruction is live. If it isn't,
// this means that the condition that it branches on (we know it is not an
// unconditional branch), is not needed to make the decision of where to
// go to, because all outgoing edges go to the same place. We must remove
// the use of the condition (because it's probably dead), so we convert
- // the terminator to a conditional branch.
+ // the terminator to an unconditional branch.
//
TerminatorInst *TI = I->getTerminator();
if (!LiveSet.count(TI))
convertToUnconditionalBranch(TI);
}
+
+ return MadeChanges;
+ }
+
+
+ // If the entry node is dead, insert a new entry node to eliminate the entry
+ // node as a special case.
+ //
+ if (!AliveBlocks.count(&Func->front())) {
+ BasicBlock *NewEntry = new BasicBlock();
+ new BranchInst(&Func->front(), NewEntry);
+ Func->getBasicBlockList().push_front(NewEntry);
+ AliveBlocks.insert(NewEntry); // This block is always alive!
+ LiveSet.insert(NewEntry->getTerminator()); // The branch is live
+ }
- } else { // If there are some blocks dead...
- // If the entry node is dead, insert a new entry node to eliminate the entry
- // node as a special case.
- //
- if (!AliveBlocks.count(&Func->front())) {
- BasicBlock *NewEntry = new BasicBlock();
- new BranchInst(&Func->front(), NewEntry);
- Func->getBasicBlockList().push_front(NewEntry);
- AliveBlocks.insert(NewEntry); // This block is always alive!
- LiveSet.insert(NewEntry->getTerminator()); // The branch is live
- }
-
- // Loop over all of the alive blocks in the function. If any successor
- // blocks are not alive, we adjust the outgoing branches to branch to the
- // first live postdominator of the live block, adjusting any PHI nodes in
- // the block to reflect this.
- //
- for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I)
- if (AliveBlocks.count(I)) {
- BasicBlock *BB = I;
- TerminatorInst *TI = BB->getTerminator();
+ // Loop over all of the alive blocks in the function. If any successor
+ // blocks are not alive, we adjust the outgoing branches to branch to the
+ // first live postdominator of the live block, adjusting any PHI nodes in
+ // the block to reflect this.
+ //
+ for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I)
+ if (AliveBlocks.count(I)) {
+ BasicBlock *BB = I;
+ TerminatorInst *TI = BB->getTerminator();
- // If the terminator instruction is alive, but the block it is contained
- // in IS alive, this means that this terminator is a conditional branch
- // on a condition that doesn't matter. Make it an unconditional branch
- // to ONE of the successors. This has the side effect of dropping a use
- // of the conditional value, which may also be dead.
- if (!LiveSet.count(TI))
- TI = convertToUnconditionalBranch(TI);
-
- // Loop over all of the successors, looking for ones that are not alive.
- // We cannot save the number of successors in the terminator instruction
- // here because we may remove them if we don't have a postdominator...
- //
- for (unsigned i = 0; i != TI->getNumSuccessors(); ++i)
- if (!AliveBlocks.count(TI->getSuccessor(i))) {
- // Scan up the postdominator tree, looking for the first
- // postdominator that is alive, and the last postdominator that is
- // dead...
+ // If the terminator instruction is alive, but the block it is contained
+ // in IS alive, this means that this terminator is a conditional branch on
+ // a condition that doesn't matter. Make it an unconditional branch to
+ // ONE of the successors. This has the side effect of dropping a use of
+ // the conditional value, which may also be dead.
+ if (!LiveSet.count(TI))
+ TI = convertToUnconditionalBranch(TI);
+
+ // Loop over all of the successors, looking for ones that are not alive.
+ // We cannot save the number of successors in the terminator instruction
+ // here because we may remove them if we don't have a postdominator...
+ //
+ for (unsigned i = 0; i != TI->getNumSuccessors(); ++i)
+ if (!AliveBlocks.count(TI->getSuccessor(i))) {
+ // Scan up the postdominator tree, looking for the first
+ // postdominator that is alive, and the last postdominator that is
+ // dead...
+ //
+ PostDominatorTree::Node *LastNode = DT[TI->getSuccessor(i)];
+
+ // There is a special case here... if there IS no post-dominator for
+ // the block we have no owhere to point our branch to. Instead,
+ // convert it to a return. This can only happen if the code branched
+ // into an infinite loop. Note that this may not be desirable,
+ // because we _are_ altering the behavior of the code. This is a well
+ // known drawback of ADCE, so in the future if we choose to revisit
+ // the decision, this is where it should be.
+ //
+ if (LastNode == 0) { // No postdominator!
+ // Call RemoveSuccessor to transmogrify the terminator instruction
+ // to not contain the outgoing branch, or to create a new terminator
+ // if the form fundamentally changes (i.e., unconditional branch to
+ // return). Note that this will change a branch into an infinite
+ // loop into a return instruction!
//
- PostDominatorTree::Node *LastNode = DT[TI->getSuccessor(i)];
-
- // There is a special case here... if there IS no post-dominator for
- // the block we have no owhere to point our branch to. Instead,
- // convert it to a return. This can only happen if the code
- // branched into an infinite loop. Note that this may not be
- // desirable, because we _are_ altering the behavior of the code.
- // This is a well known drawback of ADCE, so in the future if we
- // choose to revisit the decision, this is where it should be.
+ RemoveSuccessor(TI, i);
+
+ // RemoveSuccessor may replace TI... make sure we have a fresh
+ // pointer... and e variable.
//
- if (LastNode == 0) { // No postdominator!
- // Call RemoveSuccessor to transmogrify the terminator instruction
- // to not contain the outgoing branch, or to create a new
- // terminator if the form fundamentally changes (i.e.,
- // unconditional branch to return). Note that this will change a
- // branch into an infinite loop into a return instruction!
- //
- RemoveSuccessor(TI, i);
-
- // RemoveSuccessor may replace TI... make sure we have a fresh
- // pointer... and e variable.
- //
- TI = BB->getTerminator();
-
- // Rescan this successor...
- --i;
- } else {
- PostDominatorTree::Node *NextNode = LastNode->getIDom();
-
- while (!AliveBlocks.count(NextNode->getBlock())) {
- LastNode = NextNode;
- NextNode = NextNode->getIDom();
- }
+ TI = BB->getTerminator();
+
+ // Rescan this successor...
+ --i;
+ } else {
+ PostDominatorTree::Node *NextNode = LastNode->getIDom();
+
+ while (!AliveBlocks.count(NextNode->getBlock())) {
+ LastNode = NextNode;
+ NextNode = NextNode->getIDom();
+ }
- // Get the basic blocks that we need...
- BasicBlock *LastDead = LastNode->getBlock();
- BasicBlock *NextAlive = NextNode->getBlock();
-
- // Make the conditional branch now go to the next alive block...
- TI->getSuccessor(i)->removePredecessor(BB);
- TI->setSuccessor(i, NextAlive);
-
- // If there are PHI nodes in NextAlive, we need to add entries to
- // the PHI nodes for the new incoming edge. The incoming values
- // should be identical to the incoming values for LastDead.
- //
- for (BasicBlock::iterator II = NextAlive->begin();
- PHINode *PN = dyn_cast<PHINode>(II); ++II)
- if (LiveSet.count(PN)) { // Only modify live phi nodes
- // Get the incoming value for LastDead...
- int OldIdx = PN->getBasicBlockIndex(LastDead);
- assert(OldIdx != -1 &&"LastDead is not a pred of NextAlive!");
- Value *InVal = PN->getIncomingValue(OldIdx);
+ // Get the basic blocks that we need...
+ BasicBlock *LastDead = LastNode->getBlock();
+ BasicBlock *NextAlive = NextNode->getBlock();
+
+ // Make the conditional branch now go to the next alive block...
+ TI->getSuccessor(i)->removePredecessor(BB);
+ TI->setSuccessor(i, NextAlive);
+
+ // If there are PHI nodes in NextAlive, we need to add entries to
+ // the PHI nodes for the new incoming edge. The incoming values
+ // should be identical to the incoming values for LastDead.
+ //
+ for (BasicBlock::iterator II = NextAlive->begin();
+ isa<PHINode>(II); ++II) {
+ PHINode *PN = cast<PHINode>(II);
+ if (LiveSet.count(PN)) { // Only modify live phi nodes
+ // Get the incoming value for LastDead...
+ int OldIdx = PN->getBasicBlockIndex(LastDead);
+ assert(OldIdx != -1 &&"LastDead is not a pred of NextAlive!");
+ Value *InVal = PN->getIncomingValue(OldIdx);
- // Add an incoming value for BB now...
- PN->addIncoming(InVal, BB);
- }
+ // Add an incoming value for BB now...
+ PN->addIncoming(InVal, BB);
+ }
}
}
-
- // Now loop over all of the instructions in the basic block, 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 referring to them.
- //
- dropReferencesOfDeadInstructionsInLiveBlock(BB);
- }
- }
-
- // We make changes if there are any dead blocks in the function...
- if (unsigned NumDeadBlocks = Func->size() - AliveBlocks.size()) {
- MadeChanges = true;
- NumBlockRemoved += NumDeadBlocks;
- }
-
- // Loop over all of the basic blocks in the function, removing control flow
- // edges to live blocks (also eliminating any entries in PHI functions in
- // referenced blocks).
- //
- for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB)
- if (!AliveBlocks.count(BB)) {
- // Remove all outgoing edges from this basic block and convert the
- // terminator into a return instruction.
- std::vector<BasicBlock*> Succs(succ_begin(BB), succ_end(BB));
-
- if (!Succs.empty()) {
- // Loop over all of the successors, removing this block from PHI node
- // entries that might be in the block...
- while (!Succs.empty()) {
- Succs.back()->removePredecessor(BB);
- Succs.pop_back();
}
-
- // Delete the old terminator instruction...
- const Type *TermTy = BB->getTerminator()->getType();
- if (TermTy != Type::VoidTy)
- BB->getTerminator()->replaceAllUsesWith(
- Constant::getNullValue(TermTy));
- BB->getInstList().pop_back();
- const Type *RetTy = Func->getReturnType();
- new ReturnInst(RetTy != Type::VoidTy ?
- Constant::getNullValue(RetTy) : 0, BB);
- }
- }
+ // Now loop over all of the instructions in the basic block, deleting
+ // dead instructions. This is so that the next sweep over the program
+ // can safely delete dead instructions without other dead instructions
+ // still referring to them.
+ //
+ deleteDeadInstructionsInLiveBlock(BB);
+ }
// Loop over all of the basic blocks in the function, dropping references of
// the dead basic blocks. We must do this after the previous step to avoid
// dropping references to PHIs which still have entries...
//
+ std::vector<BasicBlock*> DeadBlocks;
for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB)
- if (!AliveBlocks.count(BB))
+ if (!AliveBlocks.count(BB)) {
+ // Remove PHI node entries for this block in live successor blocks.
+ for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
+ if (!SI->empty() && isa<PHINode>(SI->front()) && AliveBlocks.count(*SI))
+ (*SI)->removePredecessor(BB);
+
BB->dropAllReferences();
+ MadeChanges = true;
+ DeadBlocks.push_back(BB);
+ }
+
+ NumBlockRemoved += DeadBlocks.size();
// Now loop through all of the blocks and delete the dead ones. We can safely
// do this now because we know that there are no references to dead blocks
- // (because they have dropped all of their references... we also remove dead
- // instructions from alive blocks.
- //
- for (Function::iterator BI = Func->begin(); BI != Func->end(); )
- if (!AliveBlocks.count(BI)) { // Delete dead blocks...
- BI = Func->getBasicBlockList().erase(BI);
- } 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...
- if (isa<CallInst>(II))
- ++NumCallRemoved;
- else
- ++NumInstRemoved;
- II = BI->getInstList().erase(II);
- MadeChanges = true;
- } else {
- ++II;
- }
-
- ++BI; // Increment iterator...
- }
+ // (because they have dropped all of their references).
+ for (std::vector<BasicBlock*>::iterator I = DeadBlocks.begin(),
+ E = DeadBlocks.end(); I != E; ++I)
+ Func->getBasicBlockList().erase(*I);
return MadeChanges;
}
projects / oota-llvm.git / blobdiff