From 8c8a2679a20f621994fa904bcfc68775e7345edc Mon Sep 17 00:00:00 2001
From: David Tenty <daltenty@ibm.com>
Date: Tue, 10 May 2022 11:39:58 -0400
Subject: [clang][AIX] add option mdefault-visibility-export-mapping

The option mdefault-visibility-export-mapping is created to allow
mapping default visibility to an explicit shared library export
(e.g. dllexport). Exactly how and if this is manifested is target
dependent (since it depends on how they map dllexport in the IR).

Three values are provided for the option:

* none: the default and behavior without the option, no additional export linkage information is created.
* explicit: add the export for entities with explict default visibility from the source, including RTTI
* all: add the export for all entities with default visibility

This option is useful for targets which do not export symbols as part of
their usual default linkage behaviour (e.g. AIX), such targets
traditionally specified such information in external files (e.g. export
lists), but this mapping allows them to use the visibility information
typically used for this purpose on other (e.g. ELF) platforms.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D126340
---
 clang/lib/CodeGen/CodeGenModule.cpp | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

(limited to 'clang/lib/CodeGen/CodeGenModule.cpp')

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index b4ae266f8988..090055dc532d 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1212,12 +1212,22 @@ void CodeGenModule::setDLLImportDLLExport(llvm::GlobalValue *GV,
   setDLLImportDLLExport(GV, D);
 }
 
+bool CodeGenModule::shouldMapVisibilityToDLLExport(const NamedDecl *D) const {
+  return D &&
+         (D->getLinkageAndVisibility().getVisibility() == DefaultVisibility) &&
+         ((D->getLinkageAndVisibility().isVisibilityExplicit() &&
+           getLangOpts().isExplicitDefaultVisibilityExportMapping()) ||
+          getLangOpts().isAllDefaultVisibilityExportMapping());
+}
+
 void CodeGenModule::setDLLImportDLLExport(llvm::GlobalValue *GV,
                                           const NamedDecl *D) const {
   if (D && D->isExternallyVisible()) {
     if (D->hasAttr<DLLImportAttr>())
       GV->setDLLStorageClass(llvm::GlobalVariable::DLLImportStorageClass);
-    else if (D->hasAttr<DLLExportAttr>() && !GV->isDeclarationForLinker())
+    else if ((D->hasAttr<DLLExportAttr>() ||
+              shouldMapVisibilityToDLLExport(D)) &&
+             !GV->isDeclarationForLinker())
       GV->setDLLStorageClass(llvm::GlobalVariable::DLLExportStorageClass);
   }
 }
@@ -3793,7 +3803,8 @@ llvm::Constant *CodeGenModule::GetOrCreateLLVMFunction(
     }
 
     // Handle dropped DLL attributes.
-    if (D && !D->hasAttr<DLLImportAttr>() && !D->hasAttr<DLLExportAttr>()) {
+    if (D && !D->hasAttr<DLLImportAttr>() && !D->hasAttr<DLLExportAttr>() &&
+        !shouldMapVisibilityToDLLExport(cast_or_null<NamedDecl>(D))) {
       Entry->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
       setDSOLocal(Entry);
     }
@@ -4105,7 +4116,8 @@ CodeGenModule::GetOrCreateLLVMGlobal(StringRef MangledName, llvm::Type *Ty,
     }
 
     // Handle dropped DLL attributes.
-    if (D && !D->hasAttr<DLLImportAttr>() && !D->hasAttr<DLLExportAttr>())
+    if (D && !D->hasAttr<DLLImportAttr>() && !D->hasAttr<DLLExportAttr>() &&
+        !shouldMapVisibilityToDLLExport(D))
       Entry->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
 
     if (LangOpts.OpenMP && !LangOpts.OpenMPSimd && D)
-- 
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