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

[ldionne]

Summary

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

[arphaman]

Great, thank you!

[hans]

This seems to have broken the instrprof-darwin-exports.c test, see e.g. https://green.lab.llvm.org/green/job/clang-stage1-RA/32351/

I'll revert for now.

[steven_wu]

In D139938#4008232, @hans wrote:

This seems to have broken the instrprof-darwin-exports.c test, see e.g. https://green.lab.llvm.org/green/job/clang-stage1-RA/32351/

I'll revert for now.

It seems you still need to claim OPT_stdlib_EQ so it doesn't complain about unused argument when you pass stdlib when compiling C code.

[ldionne]

In D139938#4008909, @steven_wu wrote:

In D139938#4008232, @hans wrote:

This seems to have broken the instrprof-darwin-exports.c test, see e.g. https://green.lab.llvm.org/green/job/clang-stage1-RA/32351/

I'll revert for now.

It seems you still need to claim OPT_stdlib_EQ so it doesn't complain about unused argument when you pass stdlib when compiling C code.

Thanks for taking a look. I actually think that the current behavior is correct -- we don't use -stdlib=libc++ in C mode, and I don't think we should be silencing the warning. If someone compiles C code with -stdlib=libc++, I think it's OK to tell them that we're ignoring the flag.

Instead, I think the "fix" needs to be done within compiler-rt.

[ldionne]

Fix compiler-rt test.

[ldionne]

compiler-rt/test/profile/lit.cfg.py

45–51

This is not great, but I think this is OK as a stopgap. I don't want to remove -stdlib=libc++ from target_cflags in this patch since it may cause other issues in the test suite.

[ldionne]

I'll ship this now since CI seems happy and I reproduced the issue and saw it was fixed by my new change.

clang/include/clang/Basic/DiagnosticDriverKinds.td

 def err_drv_missing_arg_mtp : Error<
   "missing argument to '%0'">;
 def warn_drv_missing_plugin_name : Warning<
   "missing plugin name in %0">,
   InGroup<InvalidCommandLineArgument>;
 def warn_drv_missing_plugin_arg : Warning<
   "missing plugin argument for plugin %0 in %1">,
   InGroup<InvalidCommandLineArgument>;
-def err_drv_invalid_libcxx_deployment : Error<
-  "invalid deployment target for -stdlib=libc++ (requires %0 or later)">;
 def err_drv_invalid_argument_to_option : Error<
   "invalid argument '%0' to -%1">;
 def err_drv_missing_sanitizer_ignorelist : Error<
   "missing sanitizer ignorelist: '%0'">;
 def err_drv_malformed_sanitizer_ignorelist : Error<
   "malformed sanitizer ignorelist: '%0'">;
 def err_drv_malformed_sanitizer_coverage_allowlist : Error<
   "malformed sanitizer coverage allowlist: '%0'">;

clang/lib/Driver/ToolChains/Darwin.cpp

 }
 
 DerivedArgList *
 Darwin::TranslateArgs(const DerivedArgList &Args, StringRef BoundArch,
                       Action::OffloadKind DeviceOffloadKind) const {
   // First get the generic Apple args, before moving onto Darwin-specific ones.
   DerivedArgList *DAL =
       MachO::TranslateArgs(Args, BoundArch, DeviceOffloadKind);
-  const OptTable &Opts = getDriver().getOpts();
 
   // If no architecture is bound, none of the translations here are relevant.
   if (BoundArch.empty())
     return DAL;
 
   // Add an explicit version min argument for the deployment target. We do this
   // after argument translation because -Xarch_ arguments may add a version min
   // argument.
for (ArgList::iterator it = DAL->begin(), ie = DAL->end(); it != ie; ) {
       A = *it;
       assert(A->getOption().getID() == options::OPT_static &&
              "missing expected -static argument");
       *it = nullptr;
       ++it;
     }
   }
 
-  if (!Args.getLastArg(options::OPT_stdlib_EQ) &&
-      GetCXXStdlibType(Args) == ToolChain::CST_Libcxx)
-    DAL->AddJoinedArg(nullptr, Opts.getOption(options::OPT_stdlib_EQ),
-                      "libc++");
-
-  // Validate the C++ standard library choice.
-  CXXStdlibType Type = GetCXXStdlibType(*DAL);
-  if (Type == ToolChain::CST_Libcxx) {
-    // Check whether the target provides libc++.
-    StringRef where;
-
-    // Complain about targeting iOS < 5.0 in any way.
-    if (isTargetIOSBased() && isIPhoneOSVersionLT(5, 0))
-      where = "iOS 5.0";
-
-    if (where != StringRef()) {
-      getDriver().Diag(clang::diag::err_drv_invalid_libcxx_deployment) << where;
-    }
-  }
-
   auto Arch = tools::darwin::getArchTypeForMachOArchName(BoundArch);
   if ((Arch == llvm::Triple::arm || Arch == llvm::Triple::thumb)) {
     if (Args.hasFlag(options::OPT_fomit_frame_pointer,
                      options::OPT_fno_omit_frame_pointer, false))
       getDriver().Diag(clang::diag::warn_drv_unsupported_opt_for_target)
           << "-fomit-frame-pointer" << BoundArch;
   }
 

clang/test/Driver/darwin-header-search-libcxx.cpp

 // RUN:     -ccc-install-dir %S/Inputs/basic_darwin_toolchain_no_libcxx/usr/bin \
 // RUN:     -isysroot %S/Inputs/basic_darwin_sdk_no_libcxx \
 // RUN:     -stdlib=libc++ \
 // RUN:   | FileCheck -DSYSROOT=%S/Inputs/basic_darwin_sdk_no_libcxx \
 // RUN:               -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain_no_libcxx \
 // RUN:               --check-prefix=CHECK-LIBCXX-MISSING-BOTH %s
 // CHECK-LIBCXX-MISSING-BOTH: ignoring nonexistent directory "[[TOOLCHAIN]]/usr/bin/../include/c++/v1"
 // CHECK-LIBCXX-MISSING-BOTH: ignoring nonexistent directory "[[SYSROOT]]/usr/include/c++/v1"
+
+// Make sure that on Darwin, we use libc++ header search paths by default even when
+// -stdlib= isn't passed.
+//
+// RUN: %clang -### %s -fsyntax-only 2>&1 \
+// RUN:     --target=x86_64-apple-darwin \
+// RUN:     -ccc-install-dir %S/Inputs/basic_darwin_toolchain_no_libcxx/usr/bin \
+// RUN:     -isysroot %S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
+// RUN:   | FileCheck -DSYSROOT=%S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
+// RUN:               -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain_no_libcxx \
+// RUN:               --check-prefix=CHECK-LIBCXX-STDLIB-UNSPECIFIED %s
+// CHECK-LIBCXX-STDLIB-UNSPECIFIED: "-cc1"
+// CHECK-LIBCXX-STDLIB-UNSPECIFIED: "-internal-isystem" "[[SYSROOT]]/usr/include/c++/v1"

clang/test/Driver/darwin-stdlib-dont-pass-in-c.c

-// This test will fail if CLANG_DEFAULT_CXX_STDLIB is set to libstdc++.
-// XFAIL: default-cxx-stdlib=libstdc++
+// This test ensures that the Driver doesn't pass -stdlib= down to CC1 when compiling C code.
 
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch arm64 -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck %s
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -mmacosx-version-min=10.9 %s -### 2>&1 | FileCheck %s
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7s -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck %s
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7k %s -### 2>&1 | FileCheck %s
 
-// CHECK: "-stdlib=libc++"
-// CHECK-NOT: "-stdlib=libstdc++"
+// CHECK-NOT: "-stdlib="

clang/test/Driver/darwin-stdlib.cpp

-// This test will fail if CLANG_DEFAULT_CXX_STDLIB is set to libstdc++.
-// XFAIL: default-cxx-stdlib=libstdc++
+// Make sure that the Driver passes down -stdlib=libc++ to CC1 when specified explicitly.
+//
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch arm64  -miphoneos-version-min=7.0 -stdlib=libc++ %s -### 2>&1 | FileCheck --check-prefix=CHECK-LIBCXX %s
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/              -mmacosx-version-min=10.9  -stdlib=libc++ %s -### 2>&1 | FileCheck --check-prefix=CHECK-LIBCXX %s
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7s -miphoneos-version-min=7.0 -stdlib=libc++ %s -### 2>&1 | FileCheck --check-prefix=CHECK-LIBCXX %s
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7k                            -stdlib=libc++ %s -### 2>&1 | FileCheck --check-prefix=CHECK-LIBCXX %s
+// CHECK-LIBCXX: "-stdlib=libc++"
+// CHECK-LIBCXX-NOT: "-stdlib=libstdc++"
 
-// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch arm64 -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck %s
-// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -mmacosx-version-min=10.9 %s -### 2>&1 | FileCheck %s
-// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7s -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck %s
-// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7k %s -### 2>&1 | FileCheck %s
+// Make sure that the Driver passes down -stdlib=libstdc++ to CC1 when specified explicitly. Note that this
+// shouldn't really be used on Darwin because libstdc++ is not supported anymore, but we still pin down the
+// Driver behavior for now.
+//
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch arm64  -miphoneos-version-min=7.0 -stdlib=libstdc++ %s -### 2>&1 | FileCheck --check-prefix=CHECK-LIBSTDCXX %s
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/              -mmacosx-version-min=10.9  -stdlib=libstdc++ %s -### 2>&1 | FileCheck --check-prefix=CHECK-LIBSTDCXX %s
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7s -miphoneos-version-min=7.0 -stdlib=libstdc++ %s -### 2>&1 | FileCheck --check-prefix=CHECK-LIBSTDCXX %s
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7k                            -stdlib=libstdc++ %s -### 2>&1 | FileCheck --check-prefix=CHECK-LIBSTDCXX %s
+// CHECK-LIBSTDCXX: "-stdlib=libstdc++"
+// CHECK-LIBSTDCXX-NOT: "-stdlib=libc++"
 
-// CHECK: "-stdlib=libc++"
-// CHECK-NOT: "-stdlib=libstdc++"
+// Make sure that the Driver does not spuriously pass down any -stdlib=<...> option to CC1 if none is
+// specified on the command-line. In that case, CC1 should use the default standard library, which is
+// going to be libc++.
+//
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch arm64  -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck --check-prefix=CHECK-NONE %s
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/              -mmacosx-version-min=10.9  %s -### 2>&1 | FileCheck --check-prefix=CHECK-NONE %s
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7s -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck --check-prefix=CHECK-NONE %s
+// RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7k                            %s -### 2>&1 | FileCheck --check-prefix=CHECK-NONE %s
+// CHECK-NONE-NOT: "-stdlib="

compiler-rt/test/profile/lit.cfg.py

 # What to exclude.
 config.excludes = ['Inputs']
 
 # Clang flags.
 target_cflags=[get_required_attr(config, "target_cflags")]
 clang_cflags = target_cflags + extra_link_flags
 clang_cxxflags = config.cxx_mode_flags + clang_cflags
 
+# TODO: target_cflags can sometimes contain C++ only flags like -stdlib=<FOO>, which are
+#       ignored when compiling as C code. Passing this flag when compiling as C results in
+#       warnings that break tests that use -Werror.
+#       We remove -stdlib= from the cflags here to avoid problems, but the interaction between
+#       CMake and compiler-rt's tests should be reworked so that cflags don't contain C++ only
+#       flags.
+clang_cflags = [flag.replace('-stdlib=libc++', '').replace('-stdlib=libstdc++', '') for flag in clang_cflags]
+
 def build_invocation(compile_flags, with_lto = False):
   lto_flags = []
   if with_lto and config.lto_supported:
     lto_flags += config.lto_flags
   return " " + " ".join([config.clang] + lto_flags + compile_flags) + " "
 
 def exclude_unsupported_files_for_aix(dirname):
    for filename in os.listdir(dirname):