[all-commits] [llvm/llvm-project] f16941: [clang] Simplify the overload resolution logic for...

[Oliver Hunt via All-commits]

  Branch: refs/heads/users/ojhunt/simplify-operator-new-overload-resolution
  Home:   https://github.com/llvm/llvm-project
  Commit: f16941b1d0b21c665d23ffce3c8da64e919df99d
      https://github.com/llvm/llvm-project/commit/f16941b1d0b21c665d23ffce3c8da64e919df99d
  Author: Oliver Hunt <oliver at apple.com>
  Date:   2026-08-08 (Sat, 08 Aug 2026)

  Changed paths:
    M clang/include/clang/Basic/DiagnosticSemaKinds.td
    A clang/include/clang/Sema/DynamicAllocationArgumentsCXX.h
    M clang/include/clang/Sema/Sema.h
    M clang/lib/Sema/SemaCoroutine.cpp
    M clang/lib/Sema/SemaExprCXX.cpp
    A clang/test/SemaCXX/microsoft-new-array-fallback.cpp
    A clang/test/SemaCXX/type-aware-new-invalid-alignvalt-cache.cpp
    M clang/test/SemaCXX/type-aware-new-invalid-type-identity.cpp

  Log Message:
  -----------
  [clang] Simplify the overload resolution logic for operator new and new[]

This PR replaces the current spec-equivalent argument list mutation with
direct iteration of the correctly ordered set of argument lists for a
given allocation.

This adds a bit of architectural work around the argument list construction
but the overall effect is substantially simplified search of the overload
candidates.

* We now simply enumerate correctly ordered candidates for the implicit
  arguments. This means no more re-entrant modification of the argument
  list to handle addition and removal of type-identity or alignment
  parameters.
* We no longer mutate the primary LookupResult when attempting the MSVC
  array fallback. This also lays the groundwork for correct diagnostics
  of such cases. For now we have a minor improvement of correctly
  reporting the operator we were trying to resolve originally, and tell
  the user that we have attempted the MSVC fallback if applicable.

LLM usage:
  Depressingly claude actually did something right:
  - Identified align_val_t being cached alongside size_t was likely
    unsound, which was easy enough to create a test for.
  - It also noted that tryBuildStdTypeIdentity could be reentrant,
    and was able to construct a test case when I could not. That is
    now test #5 in type-aware-new-invalid-type-identity.cpp.
    An invalid type_identity defined as:
    ```cpp
    template <class T> struct type_identity {
       using type = decltype(new T);
    };
    ```
    triggers re-entrant evaluation of getTypeIdentityArgument
    invalidating the insertion slot.



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