[compiler-rt] [clang-tools-extra] [llvm] [clang] [InferAddressSpaces] Fix constant replace to avoid modifying other functions (PR #70611)

[Nikita Popov via cfe-commits]

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@@ -334,6 +335,15 @@ template<> struct simplify_type<User::const_op_iterator> {
   }
 };
 
+template <> struct GraphTraits<User *> {
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nikic wrote:

> What's the issue with putting this here? Seems nicer than inlining yet another DFS in another place.

I have a couple of concerns about exposing it here.

The first is that "DFS walk on `User *`" is not a well-defined operation. You can perform a DFS walk either in the direction of users or in the direction of operands. Keep in mind that, despite the name, the defining property of a `User` is that it has operands, not that it has users. Having users is a property of `Value *`.

The second is that even if we say that it should be a walk in the direction of users, we still have the choice between doing the walk on `User *` or on `Use &`.

The third is that doing an unbounded DFS walk on values is just a bad idea in general, and we should not encourage it.

For the specific problem here, I'd consider expanding all constant expressions in the function upfront, and then not having to deal with it.

https://github.com/llvm/llvm-project/pull/70611