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Use a worklist-driven algorithm instead of a recursive one. 

llvm-svn: 35680
This commit is contained in:
Chris Lattner 2007-04-05 01:27:02 +00:00
parent 85460acfbf
commit 108083edff
1 changed files with 33 additions and 24 deletions
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57
llvm/lib/Transforms/Scalar/SimplifyCFG.cpp
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@ -47,36 +47,45 @@ FunctionPass *llvm::createCFGSimplificationPass() {
static bool MarkAliveBlocks(BasicBlock *BB,
SmallPtrSet<BasicBlock*, 16> &Reachable) {
if (!Reachable.insert(BB)) return false;
std::vector<BasicBlock*> Worklist;
Worklist.push_back(BB);
bool Changed = false;
while (!Worklist.empty()) {
BB = Worklist.back();
Worklist.pop_back();
if (!Reachable.insert(BB))
continue;
// Do a quick scan of the basic block, turning any obviously unreachable
// instructions into LLVM unreachable insts. The instruction combining pass
// canonnicalizes unreachable insts into stores to null or undef.
for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E; ++BBI)
if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
if (isa<ConstantPointerNull>(SI->getOperand(1)) ||
isa<UndefValue>(SI->getOperand(1))) {
// Loop over all of the successors, removing BB's entry from any PHI
// nodes.
for (succ_iterator I = succ_begin(BB), SE = succ_end(BB); I != SE; ++I)
(*I)->removePredecessor(BB);
// Do a quick scan of the basic block, turning any obviously unreachable
// instructions into LLVM unreachable insts. The instruction combining pass
// canonnicalizes unreachable insts into stores to null or undef.
for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E; ++BBI)
if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
if (isa<ConstantPointerNull>(SI->getOperand(1)) ||
isa<UndefValue>(SI->getOperand(1))) {
// Loop over all of the successors, removing BB's entry from any PHI
// nodes.
for (succ_iterator I = succ_begin(BB), SE = succ_end(BB); I != SE;++I)
(*I)->removePredecessor(BB);
new UnreachableInst(SI);
new UnreachableInst(SI);
// All instructions after this are dead.
for (; BBI != E; ) {
if (!BBI->use_empty())
BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
BB->getInstList().erase(BBI++);
// All instructions after this are dead.
while (BBI != E) {
if (!BBI->use_empty())
BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
BB->getInstList().erase(BBI++);
}
break;
}
break;
}
bool Changed = ConstantFoldTerminator(BB);
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
Changed |= MarkAliveBlocks(*SI, Reachable);
Changed |= ConstantFoldTerminator(BB);
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
Worklist.push_back(*SI);
}
return Changed;
}