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

[Fangrui Song via llvm-commits]

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@@ -0,0 +1,81 @@
+//===- llvm/IR/DIExpressionOptimizer.h - Constant folding of DIExpressions --*-
+//C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Declarations for functions to constant fold DIExpressions.
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MaskRay wrote:

This can use more descriptions.

 The similar comment in the .cpp file might not be that useful.

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