Add -fapply-global-visibility-to-externs for -cc1

Introduce an option to request global visibility settings be applied to
declarations without a definition or an explicit visibility, rather than
the existing behavior of giving these default visibility. When the
visibility of all or most extern definitions are known this allows for
the same optimisations -fvisibility permits without updating source code
to annotate all declarations.

Differential Revision: https://reviews.llvm.org/D56868

llvm-svn: 352391

4 files changed, 11 insertions, 3 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 0be4bad7ee7..5a1b7cfe4fa 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -731,9 +731,11 @@ void CodeGenModule::setGlobalVisibility(llvm::GlobalValue *GV,
   }
   if (!D)
     return;
-  // Set visibility for definitions.
+  // Set visibility for definitions, and for declarations if requested globally
+  // or set explicitly.
   LinkageInfo LV = D->getLinkageAndVisibility();
-  if (LV.isVisibilityExplicit() || !GV->isDeclarationForLinker())
+  if (LV.isVisibilityExplicit() || getLangOpts().SetVisibilityForExternDecls ||
+      !GV->isDeclarationForLinker())
     GV->setVisibility(GetLLVMVisibility(LV.getVisibility()));
 }
 
diff --git a/clang/lib/Driver/ToolChains/AMDGPU.cpp b/clang/lib/Driver/ToolChains/AMDGPU.cpp
index a03a6073303..b9300bcc42e 100644
--- a/clang/lib/Driver/ToolChains/AMDGPU.cpp
+++ b/clang/lib/Driver/ToolChains/AMDGPU.cpp
@@ -108,5 +108,6 @@ void AMDGPUToolChain::addClangTargetOptions(
                          options::OPT_fvisibility_ms_compat)) {
     CC1Args.push_back("-fvisibility");
     CC1Args.push_back("hidden");
+    CC1Args.push_back("-fapply-global-visibility-to-externs");
   }
 }
diff --git a/clang/lib/Driver/ToolChains/HIP.cpp b/clang/lib/Driver/ToolChains/HIP.cpp
index f55dd2fc04f..cd8ed6118fe 100644
--- a/clang/lib/Driver/ToolChains/HIP.cpp
+++ b/clang/lib/Driver/ToolChains/HIP.cpp
@@ -293,8 +293,10 @@ void HIPToolChain::addClangTargetOptions(
   // Default to "hidden" visibility, as object level linking will not be
   // supported for the foreseeable future.
   if (!DriverArgs.hasArg(options::OPT_fvisibility_EQ,
-                         options::OPT_fvisibility_ms_compat))
+                         options::OPT_fvisibility_ms_compat)) {
     CC1Args.append({"-fvisibility", "hidden"});
+    CC1Args.push_back("-fapply-global-visibility-to-externs");
+  }
 }
 
 llvm::opt::DerivedArgList *
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 4d72924fad2..dbc29e24aee 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2501,6 +2501,9 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
   if (Args.hasArg(OPT_fvisibility_global_new_delete_hidden))
     Opts.GlobalAllocationFunctionVisibilityHidden = 1;
 
+  if (Args.hasArg(OPT_fapply_global_visibility_to_externs))
+    Opts.SetVisibilityForExternDecls = 1;
+
   if (Args.hasArg(OPT_ftrapv)) {
     Opts.setSignedOverflowBehavior(LangOptions::SOB_Trapping);
     // Set the handler, if one is specified.