[ObjCARC] Add an new attribute, objc_externally_retained
This attribute, called "objc_externally_retained", exposes clang's
notion of pseudo-__strong variables in ARC. Pseudo-strong variables
"borrow" their initializer, meaning that they don't retain/release
it, instead assuming that someone else is keeping their value alive.
If a function is annotated with this attribute, implicitly strong
parameters of that function aren't implicitly retained/released in
the function body, and are implicitly const. This is useful to expose
for performance reasons, most functions don't need the extra safety
of the retain/release, so programmers can opt out as needed.
This attribute can also apply to declarations of local variables,
with similar effect.
Differential revision: https://reviews.llvm.org/D55865
llvm-svn: 350422
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 2262c99..5959d88 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -797,15 +797,21 @@
case Qualifiers::OCL_None:
llvm_unreachable("present but none");
+ case Qualifiers::OCL_Strong: {
+ if (!D || !isa<VarDecl>(D) || !cast<VarDecl>(D)->isARCPseudoStrong()) {
+ value = EmitARCRetainScalarExpr(init);
+ break;
+ }
+ // If D is pseudo-strong, treat it like __unsafe_unretained here. This means
+ // that we omit the retain, and causes non-autoreleased return values to be
+ // immediately released.
+ LLVM_FALLTHROUGH;
+ }
+
case Qualifiers::OCL_ExplicitNone:
value = EmitARCUnsafeUnretainedScalarExpr(init);
break;
- case Qualifiers::OCL_Strong: {
- value = EmitARCRetainScalarExpr(init);
- break;
- }
-
case Qualifiers::OCL_Weak: {
// If it's not accessed by the initializer, try to emit the
// initialization with a copy or move.
@@ -2324,15 +2330,11 @@
// cleanup to do the release at the end of the function.
bool isConsumed = D.hasAttr<NSConsumedAttr>();
- // 'self' is always formally __strong, but if this is not an
- // init method then we don't want to retain it.
+ // If a parameter is pseudo-strong then we can omit the implicit retain.
if (D.isARCPseudoStrong()) {
- const ObjCMethodDecl *method = cast<ObjCMethodDecl>(CurCodeDecl);
- assert(&D == method->getSelfDecl());
- assert(lt == Qualifiers::OCL_Strong);
- assert(qs.hasConst());
- assert(method->getMethodFamily() != OMF_init);
- (void) method;
+ assert(lt == Qualifiers::OCL_Strong &&
+ "pseudo-strong variable isn't strong?");
+ assert(qs.hasConst() && "pseudo-strong variable should be const!");
lt = Qualifiers::OCL_ExplicitNone;
}