[llvm] [InstCombine] Fold adds + shifts with nsw and nuw flags (PR #88193)

[Yingwei Zheng via llvm-commits]

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@@ -1259,6 +1259,18 @@ Instruction *InstCombinerImpl::visitLShr(BinaryOperator &I) {
       match(Op1, m_SpecificIntAllowPoison(BitWidth - 1)))
     return new ZExtInst(Builder.CreateIsNotNeg(X, "isnotneg"), Ty);
 
+  // If both the add and the shift are nuw, then:
+  // ((X << Z) + Y) nuw >>u Z --> X + (Y >>u Z) nuw
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dtcxzyw wrote:

```suggestion
  // ((X <<nuw Z) +nuw Y) >>u Z --> X +nuw (Y >>u Z)
```


https://github.com/llvm/llvm-project/pull/88193