1 files changed, 10 insertions, 3 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index a6c256f..4ae1c6d 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4955,11 +4955,18 @@ OverflowResult llvm::computeOverflowForUnsignedSub(const Value *LHS,
   // X - (X % ?)
   // The remainder of a value can't have greater magnitude than itself,
   // so the subtraction can't overflow.
+
+  // X - (X -nuw ?)
+  // In the minimal case, this would simplify to "?", so there's no subtract
+  // at all. But if this analysis is used to peek through casts, for example,
+  // then determining no-overflow may allow other transforms.
+
   // TODO: There are other patterns like this.
   //       See simplifyICmpWithBinOpOnLHS() for candidates.
-  if (match(RHS, m_URem(m_Specific(LHS), m_Value())) &&
-      isGuaranteedNotToBeUndefOrPoison(LHS, AC, CxtI, DT))
-    return OverflowResult::NeverOverflows;
+  if (match(RHS, m_URem(m_Specific(LHS), m_Value())) ||
+      match(RHS, m_NUWSub(m_Specific(LHS), m_Value())))
+    if (isGuaranteedNotToBeUndefOrPoison(LHS, AC, CxtI, DT))
+      return OverflowResult::NeverOverflows;
 
   // Checking for conditions implied by dominating conditions may be expensive.
   // Limit it to usub_with_overflow calls for now.