1 files changed, 10 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index dc2d32856cc..88686427127 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -8138,6 +8138,16 @@ const SCEV *ScalarEvolution::computeSCEVAtScope(const SCEV *V, const Loop *L) {
             if (RV) return getSCEV(RV);
           }
         }
+
+        // If there is a single-input Phi, evaluate it at our scope. If we can
+        // prove that this replacement does not break LCSSA form, use new value.
+        if (PN->getNumOperands() == 1) {
+          const SCEV *Input = getSCEV(PN->getOperand(0));
+          const SCEV *InputAtScope = getSCEVAtScope(Input, L);
+          // TODO: We can generalize it using LI.replacementPreservesLCSSAForm,
+          // for the simplest case just support constants.
+          if (isa<SCEVConstant>(InputAtScope)) return InputAtScope;
+        }
       }
 
       // Okay, this is an expression that we cannot symbolically evaluate