CodeGen: annotate ObjC ARC functions with ABI constraints

Certain ARC runtime functions have an ABI contract of being forwarding.
Annotate the functions with the appropriate `returned` attribute on the
arguments.  This hoists some of the runtime ABI contract information
into the frontend rather than the backend transformations.

The test adjustments are to mark the returned function parameter as
such.  The minor change to the IR output is due to the fact that the
returned reference of the object causes it to extend the lifetime of the
object by returning an autoreleased return value.  The result is that
the explicit objc_autorelease call is no longer formed, as autorelease
elision is now possible on the return.

llvm-svn: 294872

2 files changed, 36 insertions, 11 deletions

diff --git a/clang/lib/CodeGen/CGObjC.cpp b/clang/lib/CodeGen/CGObjC.cpp
index 1ca56df37ff..304288de6da 100644
--- a/clang/lib/CodeGen/CGObjC.cpp
+++ b/clang/lib/CodeGen/CGObjC.cpp
@@ -1802,6 +1802,22 @@ void CodeGenFunction::EmitARCIntrinsicUse(ArrayRef<llvm::Value*> values) {
 }
 
 
+static bool IsForwarding(StringRef Name) {
+  return llvm::StringSwitch<bool>(Name)
+      .Cases("objc_autoreleaseReturnValue",             // ARCInstKind::AutoreleaseRV
+             "objc_autorelease",                        // ARCInstKind::Autorelease
+             "objc_retainAutoreleaseReturnValue",       // ARCInstKind::FusedRetainAutoreleaseRV
+             "objc_retainAutoreleasedReturnValue",      // ARCInstKind::RetainRV
+             "objc_retainAutorelease",                  // ARCInstKind::FusedRetainAutorelease
+             "objc_retainedObject",                     // ARCInstKind::NoopCast
+             "objc_retain",                             // ARCInstKind::Retain
+             "objc_unretainedObject",                   // ARCInstKind::NoopCast
+             "objc_unretainedPointer",                  // ARCInstKind::NoopCast
+             "objc_unsafeClaimAutoreleasedReturnValue", // ARCInstKind::ClaimRV
+             true)
+      .Default(false);
+}
+
 static llvm::Constant *createARCRuntimeFunction(CodeGenModule &CGM,
                                                 llvm::FunctionType *FTy,
                                                 StringRef Name) {
@@ -1819,6 +1835,13 @@ static llvm::Constant *createARCRuntimeFunction(CodeGenModule &CGM,
       // performance.
       F->addFnAttr(llvm::Attribute::NonLazyBind);
     }
+
+    if (IsForwarding(Name)) {
+      llvm::AttrBuilder B;
+      B.addAttribute(llvm::Attribute::Returned);
+
+      F->arg_begin()->addAttr(llvm::AttributeSet::get(F->getContext(), 1, B));
+    }
   }
 
   return RTF;
diff --git a/clang/test/CodeGenObjC/arc.m b/clang/test/CodeGenObjC/arc.m
index bed91c99535..fc135af6d31 100644
--- a/clang/test/CodeGenObjC/arc.m
+++ b/clang/test/CodeGenObjC/arc.m
@@ -7,30 +7,30 @@
 // RUN: %clang_cc1 -fobjc-runtime=macosx-10.7.0 -triple x86_64-apple-darwin11 -Wno-objc-root-class -Wno-incompatible-pointer-types -Wno-arc-unsafe-retained-assign -emit-llvm -fblocks -fobjc-arc -fobjc-runtime-has-weak -o - %s | FileCheck -check-prefix=ARC-NATIVE %s
 
 // ARC-ALIEN: declare extern_weak void @objc_storeStrong(i8**, i8*)
-// ARC-ALIEN: declare extern_weak i8* @objc_retain(i8*)
-// ARC-ALIEN: declare extern_weak i8* @objc_autoreleaseReturnValue(i8*)
+// ARC-ALIEN: declare extern_weak i8* @objc_retain(i8* returned)
+// ARC-ALIEN: declare extern_weak i8* @objc_autoreleaseReturnValue(i8* returned)
 // ARC-ALIEN: declare i8* @objc_msgSend(i8*, i8*, ...) [[NLB:#[0-9]+]]
 // ARC-ALIEN: declare extern_weak void @objc_release(i8*)
-// ARC-ALIEN: declare extern_weak i8* @objc_retainAutoreleasedReturnValue(i8*)
+// ARC-ALIEN: declare extern_weak i8* @objc_retainAutoreleasedReturnValue(i8* returned)
 // ARC-ALIEN: declare extern_weak i8* @objc_initWeak(i8**, i8*)
 // ARC-ALIEN: declare extern_weak i8* @objc_storeWeak(i8**, i8*)
 // ARC-ALIEN: declare extern_weak i8* @objc_loadWeakRetained(i8**)
 // ARC-ALIEN: declare extern_weak void @objc_destroyWeak(i8**)
-// ARC-ALIEN: declare extern_weak i8* @objc_autorelease(i8*)
-// ARC-ALIEN: declare extern_weak i8* @objc_retainAutorelease(i8*)
+// declare extern_weak i8* @objc_autorelease(i8*)
+// ARC-ALIEN: declare extern_weak i8* @objc_retainAutorelease(i8* returned)
 
 // ARC-NATIVE: declare void @objc_storeStrong(i8**, i8*)
-// ARC-NATIVE: declare i8* @objc_retain(i8*) [[NLB:#[0-9]+]]
-// ARC-NATIVE: declare i8* @objc_autoreleaseReturnValue(i8*)
+// ARC-NATIVE: declare i8* @objc_retain(i8* returned) [[NLB:#[0-9]+]]
+// ARC-NATIVE: declare i8* @objc_autoreleaseReturnValue(i8* returned)
 // ARC-NATIVE: declare i8* @objc_msgSend(i8*, i8*, ...) [[NLB]]
 // ARC-NATIVE: declare void @objc_release(i8*) [[NLB]]
-// ARC-NATIVE: declare i8* @objc_retainAutoreleasedReturnValue(i8*)
+// ARC-NATIVE: declare i8* @objc_retainAutoreleasedReturnValue(i8* returned)
 // ARC-NATIVE: declare i8* @objc_initWeak(i8**, i8*)
 // ARC-NATIVE: declare i8* @objc_storeWeak(i8**, i8*)
 // ARC-NATIVE: declare i8* @objc_loadWeakRetained(i8**)
 // ARC-NATIVE: declare void @objc_destroyWeak(i8**)
-// ARC-NATIVE: declare i8* @objc_autorelease(i8*)
-// ARC-NATIVE: declare i8* @objc_retainAutorelease(i8*)
+// declare i8* @objc_autorelease(i8*)
+// ARC-NATIVE: declare i8* @objc_retainAutorelease(i8* returned)
 
 // CHECK-LABEL: define void @test0
 void test0(id x) {
@@ -1504,7 +1504,9 @@ void test68(void) {
 // CHECK:      [[SELF:%.*]] = alloca [[TEST69:%.*]]*, align 8
 // CHECK:      [[T0:%.*]] = load [[TEST69]]*, [[TEST69]]** [[SELF]], align 8
 // CHECK-NEXT: [[T1:%.*]] = bitcast [[TEST69]]* [[T0]] to i8*
-// CHECK-NEXT: ret i8* [[T1]]
+// CHECK-NEXT: [[RETAIN:%.*]] = call i8* @objc_retain(i8* [[T1]])
+// CHECK-NEXT: [[AUTORELEASE:%.*]] = tail call i8* @objc_autoreleaseReturnValue(i8* [[RETAIN]])
+// CHECK-NEXT: ret i8* [[AUTORELEASE]]
 
 // rdar://problem/10907547
 void test70(id i) {