1 files changed, 6 insertions, 1 deletions
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 2958a5054afc..c784c27d36b4 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -5917,8 +5917,13 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
   if (const SCEV *S = createNodeFromSelectLikePHI(PN))
     return S;
 
+  // If the PHI has a single incoming value, follow that value, unless the
+  // PHI's incoming blocks are in a different loop, in which case doing so
+  // risks breaking LCSSA form. Instcombine would normally zap these, but
+  // it doesn't have DominatorTree information, so it may miss cases.
   if (Value *V = simplifyInstruction(PN, {getDataLayout(), &TLI, &DT, &AC}))
-    return getSCEV(V);
+    if (LI.replacementPreservesLCSSAForm(PN, V))
+      return getSCEV(V);
 
   // If it's not a loop phi, we can't handle it yet.
   return getUnknown(PN);