[IndVars] Provide eliminateIVComparison with context

We can prove more predicates when we have a context when eliminating ICmp.
As first (and very obvious) approximation we can use the ICmp instruction itself,
though in the future we are going to use a common dominator of all its users.
Need some refactoring before that.

Observed ~0.5% negative compile time impact.

Differential Revision: https://reviews.llvm.org/D98697
Reviewed By: lebedev.ri

1 files changed, 4 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index d0c43bb..120556f 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -261,9 +261,10 @@ void SimplifyIndvar::eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) {
   const SCEV *S = SE->getSCEVAtScope(ICmp->getOperand(IVOperIdx), ICmpLoop);
   const SCEV *X = SE->getSCEVAtScope(ICmp->getOperand(1 - IVOperIdx), ICmpLoop);
 
-  // If the condition is always true or always false, replace it with
-  // a constant value.
-  if (auto Ev = SE->evaluatePredicate(Pred, S, X)) {
+  // If the condition is always true or always false in the given context,
+  // replace it with a constant value.
+  // TODO: We can sharpen the context to common dominator of all ICmp's users.
+  if (auto Ev = SE->evaluatePredicateAt(Pred, S, X, ICmp)) {
     ICmp->replaceAllUsesWith(ConstantInt::getBool(ICmp->getContext(), *Ev));
     DeadInsts.emplace_back(ICmp);
     LLVM_DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');