[all-commits] [llvm/llvm-project] 52aab0: [clang] Re-apply change to avoid passing -stdlib=l...

[Louis Dionne via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 52aab0e4b4a5d6728f4bb9c7b3340133f585fc15
      https://github.com/llvm/llvm-project/commit/52aab0e4b4a5d6728f4bb9c7b3340133f585fc15
  Author: Louis Dionne <ldionne.2 at gmail.com>
  Date:   2022-12-20 (Tue, 20 Dec 2022)

  Changed paths:
    M clang/include/clang/Basic/DiagnosticDriverKinds.td
    M clang/lib/Driver/ToolChains/Darwin.cpp
    M clang/test/Driver/darwin-header-search-libcxx.cpp
    A clang/test/Driver/darwin-stdlib-dont-pass-in-c.c
    M clang/test/Driver/darwin-stdlib.cpp
    M compiler-rt/test/profile/lit.cfg.py

  Log Message:
  -----------
  [clang] Re-apply change to avoid passing -stdlib=libc++ spuriously to CC1 on Darwin

Previously, we would be passing down -stdlib=libc++ from the Driver
to CC1 whenever the default standard library on the platform was libc++,
even if -stdlib= had not been passed to the Driver. This meant that we
would pass -stdlib=libc++ in nonsensical circumstances, such as when
compiling C code.

This logic had been added in b534ce46bd40 to make sure that header
search paths were set up properly. However, since libc++ is now the
default Standard Library on Darwin, passing this explicitly is not
required anymore. Indeed, if no -stdlib= is specified, CC1 will end
up using libc++ if it queries which standard library to use, without
having to be told.

Not passing -stdlib= at all to CC1 on Darwin should become possible
once CC1 stops relying on it to set up framework search paths.

Furthermore, this commit also removes a diagnostic checking whether the
deployment target is too old to support libc++. Nowadays, all supported
deployment targets use libc++ and compiling with libstdc++ is not
supported anymore. The Driver was the wrong place to issue this
diagnostic since it doesn't know whether libc++ will actually be linked
against (e.g. C vs C++), which would lead to spurious diagnostics.
Given that these targets are not supported anymore, we simply drop
the diagnostic instead of trying to refactor it into CC1.

This is a re-application of 6540f32db09c which had been reverted in
49dd02bd0819 because it broke a compiler-rt test. The test had broken
because we were compiling C code and passing -stdlib=libc++, which Clang
will now warn about.

rdar://103198514

Differential Revision: https://reviews.llvm.org/D139938