[all-commits] [llvm/llvm-project] f041e9: CWG2352: Allow qualification conversions during re...

[Richard Smith via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: f041e9ad706aee7987c5299427c33424fcabbd0d
      https://github.com/llvm/llvm-project/commit/f041e9ad706aee7987c5299427c33424fcabbd0d
  Author: Richard Smith <richard at metafoo.co.uk>
  Date:   2020-01-09 (Thu, 09 Jan 2020)

  Changed paths:
    M clang/include/clang/Basic/DiagnosticSemaKinds.td
    M clang/include/clang/Sema/Sema.h
    M clang/lib/Sema/SemaExprCXX.cpp
    M clang/lib/Sema/SemaInit.cpp
    M clang/lib/Sema/SemaOverload.cpp
    M clang/test/CXX/drs/dr23xx.cpp
    M clang/test/CXX/drs/dr4xx.cpp
    M clang/test/SemaCXX/ref-init-ambiguous.cpp
    M clang/test/SemaObjCXX/arc-overloading.mm
    M clang/test/SemaOpenCL/address-spaces-conversions-cl2.0.cl
    M clang/www/cxx_dr_status.html
    M clang/www/make_cxx_dr_status

  Log Message:
  -----------
  CWG2352: Allow qualification conversions during reference binding.

The language wording change forgot to update overload resolution to rank
implicit conversion sequences based on qualification conversions in
reference bindings. The anticipated resolution for that oversight is
implemented here -- we order candidates based on qualification
conversion, not only on top-level cv-qualifiers, including ranking
reference bindings against non-reference bindings if they differ in
non-top-level qualification conversions.

For OpenCL/C++, this allows reference binding between pointers with
differing (nested) address spaces. This makes the behavior of reference
binding consistent with that of implicit pointer conversions, as is the
purpose of this change, but that pre-existing behavior for pointer
conversions is itself probably not correct. In any case, it's now
consistently the same behavior and implemented in only one place.

This reinstates commit de21704ba96fa80d3e9402f12c6505917a3885f4,
reverted in commit d8018233d1ea4234de68d5b4593abd773db79484, with
workarounds for some overload resolution ordering problems introduced by
CWG2352.