[Clang] Add the ability to map DLL storage class to visibility

For PlayStation we offer source code compatibility with
Microsoft's dllimport/export annotations; however, our file
format is based on ELF.

To support this we translate from DLL storage class to ELF
visibility at the end of codegen in Clang.

Other toolchains have used similar strategies (e.g. see the
documentation for this ARM toolchain:

https://developer.arm.com/documentation/dui0530/i/migrating-from-rvct-v3-1-to-rvct-v4-0/changes-to-symbol-visibility-between-rvct-v3-1-and-rvct-v4-0)

This patch adds the ability to perform this translation. Options
are provided to support customizing the mapping behaviour.

Differential Revision: https://reviews.llvm.org/D89970

1 files changed, 41 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 66a3c57..9512b35 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -401,6 +401,41 @@ void InstrProfStats::reportDiagnostics(DiagnosticsEngine &Diags,
   }
 }
 
+static void setVisibilityFromDLLStorageClass(const clang::LangOptions &LO,
+                                             llvm::Module &M) {
+  if (!LO.VisibilityFromDLLStorageClass)
+    return;
+
+  llvm::GlobalValue::VisibilityTypes DLLExportVisibility =
+      CodeGenModule::GetLLVMVisibility(LO.getDLLExportVisibility());
+  llvm::GlobalValue::VisibilityTypes NoDLLStorageClassVisibility =
+      CodeGenModule::GetLLVMVisibility(LO.getNoDLLStorageClassVisibility());
+  llvm::GlobalValue::VisibilityTypes ExternDeclDLLImportVisibility =
+      CodeGenModule::GetLLVMVisibility(LO.getExternDeclDLLImportVisibility());
+  llvm::GlobalValue::VisibilityTypes ExternDeclNoDLLStorageClassVisibility =
+      CodeGenModule::GetLLVMVisibility(
+          LO.getExternDeclNoDLLStorageClassVisibility());
+
+  for (llvm::GlobalValue &GV : M.global_values()) {
+    if (GV.hasAppendingLinkage() || GV.hasLocalLinkage())
+      return;
+
+    if (GV.isDeclarationForLinker()) {
+      GV.setVisibility(GV.getDLLStorageClass() ==
+                               llvm::GlobalValue::DLLImportStorageClass
+                           ? ExternDeclDLLImportVisibility
+                           : ExternDeclNoDLLStorageClassVisibility);
+    } else {
+      GV.setVisibility(GV.getDLLStorageClass() ==
+                               llvm::GlobalValue::DLLExportStorageClass
+                           ? DLLExportVisibility
+                           : NoDLLStorageClassVisibility);
+    }
+
+    GV.setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
+  }
+}
+
 void CodeGenModule::Release() {
   EmitDeferred();
   EmitVTablesOpportunistically();
@@ -688,6 +723,12 @@ void CodeGenModule::Release() {
   getTargetCodeGenInfo().emitTargetMetadata(*this, MangledDeclNames);
 
   EmitBackendOptionsMetadata(getCodeGenOpts());
+
+  // Set visibility from DLL export class
+  // We do this at the end of LLVM IR generation; after any operation
+  // that might affect the DLL storage class or the visibility, and
+  // before anything that might act on these.
+  setVisibilityFromDLLStorageClass(LangOpts, getModule());
 }
 
 void CodeGenModule::EmitOpenCLMetadata() {