[clang][AIX] Don't ignore XCOFF visibility by default

D87451 added -mignore-xcoff-visibility for AIX targets and made it the default (which mimicked the behaviour of the XL 16.1 compiler on AIX).

However, ignoring hidden visibility has unwanted side effects and some libraries depend on visibility to hide non-ABI facing entities from user headers and
reserve the right to change these implementation details based on this (https://libcxx.llvm.org/DesignDocs/VisibilityMacros.html). This forces us to use
internal linkage fallbacks for these cases on AIX and creates an unwanted divergence in implementations on the plaform.

For these reasons, it's preferable to not add -mignore-xcoff-visibility by default, which is what this patch does.

Reviewed By: DiggerLin

Differential Revision: https://reviews.llvm.org/D125141

1 files changed, 1 insertions, 22 deletions

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 847766a..2e205f34 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -3739,28 +3739,7 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
     Opts.GNUCVersion = Major * 100 * 100 + Minor * 100 + Patch;
   }
 
-  // In AIX OS, the -mignore-xcoff-visibility is enable by default if there is
-  // no -fvisibility=* option.
-  // This is the reason why '-fvisibility' needs to be always generated:
-  // its absence implies '-mignore-xcoff-visibility'.
-  //
-  // Suppose the original cc1 command line does contain '-fvisibility default':
-  // '-mignore-xcoff-visibility' should not be implied.
-  // * If '-fvisibility' is not generated (as most options with default values
-  //   don't), its absence would imply '-mignore-xcoff-visibility'. This changes
-  //   the command line semantics.
-  // * If '-fvisibility' is generated regardless of its presence and value,
-  //   '-mignore-xcoff-visibility' won't be implied and the command line
-  //   semantics are kept intact.
-  //
-  // When the original cc1 command line does **not** contain '-fvisibility',
-  // '-mignore-xcoff-visibility' is implied. The generated command line will
-  // contain both '-fvisibility default' and '-mignore-xcoff-visibility' and
-  // subsequent calls to `CreateFromArgs`/`generateCC1CommandLine` will always
-  // produce the same arguments.
-
-  if (T.isOSAIX() && (Args.hasArg(OPT_mignore_xcoff_visibility) ||
-                      !Args.hasArg(OPT_fvisibility)))
+  if (T.isOSAIX() && (Args.hasArg(OPT_mignore_xcoff_visibility)))
     Opts.IgnoreXCOFFVisibility = 1;
 
   if (Args.hasArg(OPT_ftrapv)) {