1 files changed, 17 insertions, 0 deletions
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index b0654f9..89e485a 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1831,6 +1831,23 @@ bool CompilerInvocation::ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args,
     }
   }
 
+  // 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)))
     Opts.IgnoreXCOFFVisibility = 1;