Use LVI to eliminate conditional branches where we've tested a related condition previously. Update tests for this change.
This fixes PR5652.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112270 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 8abd842..3d4db28 100644
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -669,6 +669,45 @@
}
}
}
+
+ // For a comparison where the LHS is outside this block, it's possible
+ // that we've branch on it before. Used LVI to see if we can simplify
+ // the branch based on that.
+ BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
+ Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
+ if (LVI && CondBr && CondConst && CondBr->isConditional() &&
+ (!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.
+ unsigned Trues = 0, Falses = 0, predcount = 0;
+ for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB);PI != PE; ++PI){
+ ++predcount;
+ LazyValueInfo::Tristate Ret =
+ LVI->getPredicateOnEdge(CondCmp->getPredicate(),
+ CondCmp->getOperand(0), CondConst, *PI, BB);
+ if (Ret == LazyValueInfo::True)
+ ++Trues;
+ else if (Ret == LazyValueInfo::False)
+ ++Falses;
+ }
+
+ // If we can determine the branch direction statically, converted
+ // the conditional branch to an unconditional one.
+ if (Trues && Trues == predcount) {
+ RemovePredecessorAndSimplify(CondBr->getSuccessor(1), BB, TD);
+ BranchInst::Create(CondBr->getSuccessor(0), CondBr);
+ CondBr->eraseFromParent();
+ return true;
+ } else if (Falses && Falses == predcount) {
+ RemovePredecessorAndSimplify(CondBr->getSuccessor(0), BB, TD);
+ BranchInst::Create(CondBr->getSuccessor(1), CondBr);
+ CondBr->eraseFromParent();
+ return true;
+ }
+ }
}
// Check for some cases that are worth simplifying. Right now we want to look