[objc-arc] Teach the ARC optimizer that objc_sync_enter/objc_sync_exit do not modify the ref count of an objc object and additionally are inert for modref purposes.

llvm-svn: 185769

2 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/ObjCARC/ObjCARCAliasAnalysis.cpp b/llvm/lib/Transforms/ObjCARC/ObjCARCAliasAnalysis.cpp
index 46b2de71374..1a3f383d4c0 100644
--- a/llvm/lib/Transforms/ObjCARC/ObjCARCAliasAnalysis.cpp
+++ b/llvm/lib/Transforms/ObjCARC/ObjCARCAliasAnalysis.cpp
@@ -150,6 +150,14 @@ ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS, const Location &Loc) {
     break;
   }
 
+  // Handle special objective c calls defaulting to chaining.
+  const Function *F = CS.getCalledFunction();
+  if (F)
+    return StringSwitch<AliasAnalysis::ModRefResult>(F->getName())
+      .Case("objc_sync_start", NoModRef)
+      .Case("objc_sync_stop", NoModRef)
+      .Default(AliasAnalysis::getModRefInfo(CS, Loc));
+
   return AliasAnalysis::getModRefInfo(CS, Loc);
 }
 
diff --git a/llvm/lib/Transforms/ObjCARC/ObjCARCUtil.cpp b/llvm/lib/Transforms/ObjCARC/ObjCARCUtil.cpp
index 03e12d4fd76..415e76355db 100644
--- a/llvm/lib/Transforms/ObjCARC/ObjCARCUtil.cpp
+++ b/llvm/lib/Transforms/ObjCARC/ObjCARCUtil.cpp
@@ -112,6 +112,8 @@ InstructionClass llvm::objcarc::GetFunctionClass(const Function *F) {
           .Case("objc_retain_autorelease",    IC_FusedRetainAutorelease)
           .Case("objc_retainAutorelease",     IC_FusedRetainAutorelease)
           .Case("objc_retainAutoreleaseReturnValue",IC_FusedRetainAutoreleaseRV)
+          .Case("objc_sync_enter", IC_User)
+          .Case("objc_sync_exit", IC_User)
           .Default(IC_CallOrUser);
 
       // Argument is i8**