[PATCH] D31598: [SCEV] Try to get RHS from sext in implication via operations

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
Herald added a subscriber: mzolotukhin.

When proving implication via operations and LHS was taken from sext, it makes sense to try
to take RHS from extension also in case of type sizes mismatch.


https://reviews.llvm.org/D31598

Files:
  lib/Analysis/ScalarEvolution.cpp


Index: lib/Analysis/ScalarEvolution.cpp
===================================================================
--- lib/Analysis/ScalarEvolution.cpp
+++ lib/Analysis/ScalarEvolution.cpp
@@ -8617,17 +8617,23 @@
     // going to compare the operands to RHS, we should be certain that we don't
     // need any size extensions for this. So let's decline all cases when the
     // sizes of types of LHS and RHS do not match.
-    // TODO: Maybe try to get RHS from sext to catch more cases?
-    if (getTypeSizeInBits(LHS->getType()) != getTypeSizeInBits(RHS->getType()))
+    auto *LTy = LHS->getType();
+    // If RHS has a wider type, there is a chance that RHS can be stripped from
+    // extension.
+    if (getTypeSizeInBits(LTy) < getTypeSizeInBits(RHS->getType()))
+      RHS = GetOpFromSExt(RHS);
+
+    // If the sizes still don't match, there is nothing we can do.
+    if (getTypeSizeInBits(LTy) != getTypeSizeInBits(RHS->getType()))
       return false;
 
     // Should not overflow.
     if (!LHSAddExpr->hasNoSignedWrap())
       return false;
 
     auto *LL = LHSAddExpr->getOperand(0);
     auto *LR = LHSAddExpr->getOperand(1);
-    auto *MinusOne = getNegativeSCEV(getOne(RHS->getType()));
+    auto *MinusOne = getNegativeSCEV(getOne(LTy));
 
     // Checks that S1 >= 0 && S2 > RHS, trivially or using the found context.
     auto IsSumGreaterThanRHS = [&](const SCEV *S1, const SCEV *S2) {


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