if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
- // For a comparison where the LHS is outside this block, it's possible
- // that we've branched on it before. Used LVI to see if we can simplify
- // the branch based on that.
+ // If we're branching on a conditional, LVI might be able to determine
+ // it's value at the branch instruction. We only handle comparisons
+ // against a constant at this time.
+ // TODO: This should be extended to handle switches as well.
BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
- pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
- if (CondBr && CondConst && CondBr->isConditional() && PI != PE &&
- (!isa<Instruction>(CondCmp->getOperand(0)) ||
- cast<Instruction>(CondCmp->getOperand(0))->getParent() != BB)) {
- // For predecessor edge, determine if the comparison is true or false
- // on that edge. If they're all true or all false, we can simplify the
- // branch.
- // FIXME: We could handle mixed true/false by duplicating code.
- LazyValueInfo::Tristate Baseline =
- LVI->getPredicateOnEdge(CondCmp->getPredicate(), CondCmp->getOperand(0),
- CondConst, *PI, BB, CondCmp);
- if (Baseline != LazyValueInfo::Unknown) {
- // Check that all remaining incoming values match the first one.
- while (++PI != PE) {
- LazyValueInfo::Tristate Ret =
- LVI->getPredicateOnEdge(CondCmp->getPredicate(),
- CondCmp->getOperand(0), CondConst, *PI, BB,
- CondCmp);
- if (Ret != Baseline) break;
- }
-
- // If we terminated early, then one of the values didn't match.
- if (PI == PE) {
- unsigned ToRemove = Baseline == LazyValueInfo::True ? 1 : 0;
- unsigned ToKeep = Baseline == LazyValueInfo::True ? 0 : 1;
- CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true);
- BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
- CondBr->eraseFromParent();
- if (CondCmp->use_empty())
- CondCmp->eraseFromParent();
- else if (CondCmp->getParent() == BB) {
- // If the fact we just learned is true for all uses of the
- // condition, replace it with a constant value
- auto *CI = Baseline == LazyValueInfo::True ?
- ConstantInt::getTrue(CondCmp->getType()) :
- ConstantInt::getFalse(CondCmp->getType());
- CondCmp->replaceAllUsesWith(CI);
- CondCmp->eraseFromParent();
- }
- return true;
- }
- }
-
- } else if (CondBr && CondConst && CondBr->isConditional()) {
- // There might be an invariant in the same block with the conditional
- // that can determine the predicate.
-
+ if (CondBr && CondConst && CondBr->isConditional()) {
LazyValueInfo::Tristate Ret =
LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0),
- CondConst, CondCmp);
+ CondConst, CondBr);
if (Ret != LazyValueInfo::Unknown) {
unsigned ToRemove = Ret == LazyValueInfo::True ? 1 : 0;
unsigned ToKeep = Ret == LazyValueInfo::True ? 0 : 1;
CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true);
BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
CondBr->eraseFromParent();
+ if (CondCmp->use_empty())
+ CondCmp->eraseFromParent();
+ else if (CondCmp->getParent() == BB) {
+ // If the fact we just learned is true for all uses of the
+ // condition, replace it with a constant value
+ auto *CI = Ret == LazyValueInfo::True ?
+ ConstantInt::getTrue(CondCmp->getType()) :
+ ConstantInt::getFalse(CondCmp->getType());
+ CondCmp->replaceAllUsesWith(CI);
+ CondCmp->eraseFromParent();
+ }
return true;
}
}