1 files changed, 21 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 1b142f1..5aa6df4 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -1985,7 +1985,28 @@ PHINode *WidenIV::createWideIV(SCEVExpander &Rewriter) {
       // increment to the new (widened) increment.
       auto *OrigInc =
           cast<Instruction>(OrigPhi->getIncomingValueForBlock(LatchBlock));
+
       WideInc->setDebugLoc(OrigInc->getDebugLoc());
+      // We are replacing a narrow IV increment with a wider IV increment. If
+      // the original (narrow) increment did not wrap, the wider increment one
+      // should not wrap either. Set the flags to be the union of both wide
+      // increment and original increment; this ensures we preserve flags SCEV
+      // could infer for the wider increment. Limit this only to cases where
+      // both increments directly increment the corresponding PHI nodes and have
+      // the same opcode. It is not safe to re-use the flags from the original
+      // increment, if it is more complex and SCEV expansion may have yielded a
+      // more simplified wider increment.
+      bool MatchingOps =
+          match(OrigInc, m_c_BinOp(m_Specific(OrigPhi), m_Value())) &&
+          match(WideInc, m_c_BinOp(m_Specific(WidePhi), m_Value())) &&
+          OrigInc->getOpcode() == WideInc->getOpcode();
+      if (MatchingOps && isa<OverflowingBinaryOperator>(OrigInc) &&
+          isa<OverflowingBinaryOperator>(WideInc)) {
+        WideInc->setHasNoUnsignedWrap(WideInc->hasNoUnsignedWrap() ||
+                                      OrigInc->hasNoUnsignedWrap());
+        WideInc->setHasNoSignedWrap(WideInc->hasNoSignedWrap() ||
+                                    OrigInc->hasNoSignedWrap());
+      }
     }
   }