[llvm] Use DIExpression::foldConstantMath at the result of a Salvaged expression (PR #71721)

[Fangrui Song via llvm-commits]

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+//===- llvm/IR/DIExpressionOptimizer.h - Constant folding of DIExpressions --*-
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MaskRay wrote:

80 columns and avoid wrapping

You can remove `llvm/IR/` to get more columns.

https://github.com/llvm/llvm-project/pull/71721