[CodeGen][ObjC] Annotate retain-agnostic ObjC globals with attribute

'objc_arc_inert'

The attribute enables the ARC optimizer to delete ObjC ARC runtime calls
on the annotated globals (see https://reviews.llvm.org/D62433). We
currently only annotate global variables for string literals and global
blocks with the attribute.

rdar://problem/49839633

Differential Revision: https://reviews.llvm.org/D62831

llvm-svn: 363467

2 files changed, 4 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGBlocks.cpp b/clang/lib/CodeGen/CGBlocks.cpp
index 2a317fc956d..c3ee7129d9d 100644
--- a/clang/lib/CodeGen/CGBlocks.cpp
+++ b/clang/lib/CodeGen/CGBlocks.cpp
@@ -1434,10 +1434,12 @@ static llvm::Constant *buildGlobalBlock(CodeGenModule &CGM,
   if (CGM.getContext().getLangOpts().OpenCL)
     AddrSpace = CGM.getContext().getTargetAddressSpace(LangAS::opencl_global);
 
-  llvm::Constant *literal = fields.finishAndCreateGlobal(
+  llvm::GlobalVariable *literal = fields.finishAndCreateGlobal(
       "__block_literal_global", blockInfo.BlockAlign,
       /*constant*/ !IsWindows, llvm::GlobalVariable::InternalLinkage, AddrSpace);
 
+  literal->addAttribute("objc_arc_inert");
+
   // Windows does not allow globals to be initialised to point to globals in
   // different DLLs.  Any such variables must run code to initialise them.
   if (IsWindows) {
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index bd44a493a28..7edac4d0114 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -4652,6 +4652,7 @@ CodeGenModule::GetAddrOfConstantCFString(const StringLiteral *Literal) {
   GV = Fields.finishAndCreateGlobal("_unnamed_cfstring_", Alignment,
                                     /*isConstant=*/false,
                                     llvm::GlobalVariable::PrivateLinkage);
+  GV->addAttribute("objc_arc_inert");
   switch (Triple.getObjectFormat()) {
   case llvm::Triple::UnknownObjectFormat:
     llvm_unreachable("unknown file format");