Define weak and __weak to mean ARC-style weak references, even in MRC.
Previously, __weak was silently accepted and ignored in MRC mode.
That makes this a potentially source-breaking change that we have to
roll out cautiously. Accordingly, for the time being, actual support
for __weak references in MRC is experimental, and the compiler will
reject attempts to actually form such references. The intent is to
eventually enable the feature by default in all non-GC modes.
(It is, of course, incompatible with ObjC GC's interpretation of
__weak.)
If you like, you can enable this feature with
-Xclang -fobjc-weak
but like any -Xclang option, this option may be removed at any point,
e.g. if/when it is eventually enabled by default.
This patch also enables the use of the ARC __unsafe_unretained qualifier
in MRC. Unlike __weak, this is being enabled immediately. Since
variables are essentially __unsafe_unretained by default in MRC,
the only practical uses are (1) communication and (2) changing the
default behavior of by-value block capture.
As an implementation matter, this means that the ObjC ownership
qualifiers may appear in any ObjC language mode, and so this patch
removes a number of checks for getLangOpts().ObjCAutoRefCount
that were guarding the processing of these qualifiers. I don't
expect this to be a significant drain on performance; it may even
be faster to just check for these qualifiers directly on a type
(since it's probably in a register anyway) than to do N dependent
loads to grab the LangOptions.
rdar://9674298
llvm-svn: 251041
diff --git a/clang/lib/CodeGen/CGObjC.cpp b/clang/lib/CodeGen/CGObjC.cpp
index 5890e7f..fce7409 100644
--- a/clang/lib/CodeGen/CGObjC.cpp
+++ b/clang/lib/CodeGen/CGObjC.cpp
@@ -323,6 +323,21 @@
llvm_unreachable("invalid receiver kind");
}
+/// Given an expression of ObjC pointer type, check whether it was
+/// immediately loaded from an ARC __weak l-value.
+static const Expr *findWeakLValue(const Expr *E) {
+ assert(E->getType()->isObjCRetainableType());
+ E = E->IgnoreParens();
+ if (auto CE = dyn_cast<CastExpr>(E)) {
+ if (CE->getCastKind() == CK_LValueToRValue) {
+ if (CE->getSubExpr()->getType().getObjCLifetime() == Qualifiers::OCL_Weak)
+ return CE->getSubExpr();
+ }
+ }
+
+ return nullptr;
+}
+
RValue CodeGenFunction::EmitObjCMessageExpr(const ObjCMessageExpr *E,
ReturnValueSlot Return) {
// Only the lookup mechanism and first two arguments of the method
@@ -333,6 +348,17 @@
const ObjCMethodDecl *method = E->getMethodDecl();
+ // If the method is -retain, and the receiver's being loaded from
+ // a __weak variable, peephole the entire operation to objc_loadWeakRetained.
+ if (method && E->getReceiverKind() == ObjCMessageExpr::Instance &&
+ method->getMethodFamily() == OMF_retain) {
+ if (auto lvalueExpr = findWeakLValue(E->getInstanceReceiver())) {
+ LValue lvalue = EmitLValue(lvalueExpr);
+ llvm::Value *result = EmitARCLoadWeakRetained(lvalue.getAddress());
+ return AdjustObjCObjectType(*this, E->getType(), RValue::get(result));
+ }
+ }
+
// We don't retain the receiver in delegate init calls, and this is
// safe because the receiver value is always loaded from 'self',
// which we zero out. We don't want to Block_copy block receivers,
@@ -976,7 +1002,11 @@
} else {
// We want to load and autoreleaseReturnValue ARC __weak ivars.
if (LV.getQuals().getObjCLifetime() == Qualifiers::OCL_Weak) {
- value = emitARCRetainLoadOfScalar(*this, LV, ivarType);
+ if (getLangOpts().ObjCAutoRefCount) {
+ value = emitARCRetainLoadOfScalar(*this, LV, ivarType);
+ } else {
+ value = EmitARCLoadWeak(LV.getAddress());
+ }
// Otherwise we want to do a simple load, suppressing the
// final autorelease.