[llvm] [InstCombine] Refine nuw propagation in `OptimizePointerDifference` (PR #147059)

[Nikita Popov via llvm-commits]

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@@ -2164,10 +2164,13 @@ Value *InstCombinerImpl::OptimizePointerDifference(Value *LHS, Value *RHS,
 
   // If this is a single inbounds GEP and the original sub was nuw,
   // then the final multiplication is also nuw.
-  if (auto *I = dyn_cast<Instruction>(Result))
+  if (auto *I = dyn_cast<OverflowingBinaryOperator>(Result))
     if (IsNUW && match(Offset2, m_Zero()) && Base.LHSNW.isInBounds() &&
-        I->getOpcode() == Instruction::Mul)
-      I->setHasNoUnsignedWrap();
+        I->hasNoSignedWrap() && !I->hasNoUnsignedWrap() &&
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nikic wrote:

I think we're also missing a one-use check? Otherwise there may be another use of the instruction that's not nuw.

https://github.com/llvm/llvm-project/pull/147059