[llvm] [ConstraintElim] Add NSW to ADD if one op is nneg and other npos. (PR #221487)

[Florian Hahn via llvm-commits]

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@@ -1356,6 +1370,21 @@ static bool tryToStrengthenFlags(Instruction *I, ConstraintInfo &Info,
     I->setHasNoUnsignedWrap();
     return true;
   }
+  case Instruction::Add: {
+    // Op0 + Op1 does not wrap signed, if one operand is non-negative and the
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fhahn wrote:

Yep, we can effectively re-use the Mul/Shl range logic for those cases.

We still miss some cases (I think we the boundary we check is signed min, which cannot be decomposed, but overall we get a number of additional flags for cheaper (fewer queries) https://github.com/dtcxzyw/llvm-opt-benchmark-nightly/pull/1215

https://github.com/llvm/llvm-project/pull/221487