[llvm] [ConstraintElim] Decompose shl nsw for signed predicates (PR #76961)

[Florian Hahn via llvm-commits]

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@@ -517,6 +517,17 @@ static Decomposition decompose(Value *V,
       return Result;
     }
 
+    // shl nsw x, shift is mul nsw x, (1<<shift),
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fhahn wrote:

nit: might be good to wrap the expressions in `()` or something else to separate them from the interleave text

https://github.com/llvm/llvm-project/pull/76961