[llvm] [ConstraintElim] Do not allow overflows in `Decomposition` (PR #140541)

[Florian Hahn via llvm-commits]

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@@ -534,20 +536,21 @@ static Decomposition decompose(Value *V,
     }
 
     if (match(V, m_NSWAdd(m_Value(Op0), m_Value(Op1))))
-      return MergeResults(Op0, Op1, IsSigned);
+      if (auto Decomp = MergeResults(Op0, Op1, IsSigned))
+        return *Decomp;
 
     if (match(V, m_NSWSub(m_Value(Op0), m_Value(Op1)))) {
       auto ResA = decompose(Op0, Preconditions, IsSigned, DL);
       auto ResB = decompose(Op1, Preconditions, IsSigned, DL);
-      ResA.sub(ResB);
-      return ResA;
+      if (!ResA.sub(ResB))
+        return ResA;
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fhahn wrote:

Does it make sense to continue below after overflow? Should we just return std::nullopt?

Same for the others

https://github.com/llvm/llvm-project/pull/140541