[SCEV] Make isImpliedCondOperandsViaRanges smarter

This change lets us prove things like

  "{X,+,10} s< 5000" implies "{X+7,+,10} does not sign overflow"

It does this by replacing replacing getConstantDifference by
computeConstantDifference (which is smarter) in
isImpliedCondOperandsViaRanges.

llvm-svn: 276505

1 files changed, 1 insertions, 11 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 89c09a8..d881e81 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -8571,16 +8571,6 @@ ScalarEvolution::isImpliedCondOperandsHelper(ICmpInst::Predicate Pred,
   return false;
 }
 
-Optional<APInt> ScalarEvolution::getConstantDifference(const SCEV *LHS,
-                                                       const SCEV *RHS) {
-  if (const SCEVAddExpr *AddLHS = dyn_cast<SCEVAddExpr>(LHS))
-    if (AddLHS->getOperand(1) == RHS)
-      if (auto *Addend = dyn_cast<SCEVConstant>(AddLHS->getOperand(0)))
-        return Addend->getAPInt();
-
-  return None;
-}
-
 bool ScalarEvolution::isImpliedCondOperandsViaRanges(ICmpInst::Predicate Pred,
                                                      const SCEV *LHS,
                                                      const SCEV *RHS,
@@ -8591,7 +8581,7 @@ bool ScalarEvolution::isImpliedCondOperandsViaRanges(ICmpInst::Predicate Pred,
     // reduce the compile time impact of this optimization.
     return false;
 
-  Optional<APInt> Addend = getConstantDifference(LHS, FoundLHS);
+  Optional<APInt> Addend = computeConstantDifference(LHS, FoundLHS);
   if (!Addend)
     return false;