[CodeGen][ObjC] Don't retain captured Objective-C pointers at block
creation that are const-qualified.
When a block captures an ObjC object pointer, clang retains the pointer
to prevent prematurely destroying the object the pointer points to
before the block is called or copied.
When the captured object pointer is const-qualified, we can avoid
emitting the retain/release pair since the pointer variable cannot be
modified in the scope in which the block literal is introduced.
For example:
void test(const id x) {
callee(^{ (void)x; });
}
This patch implements that optimization.
rdar://problem/28894510
Differential Revision: https://reviews.llvm.org/D32601
llvm-svn: 301667
diff --git a/clang/lib/CodeGen/CGBlocks.cpp b/clang/lib/CodeGen/CGBlocks.cpp
index 1a57b3e..791a57e 100644
--- a/clang/lib/CodeGen/CGBlocks.cpp
+++ b/clang/lib/CodeGen/CGBlocks.cpp
@@ -619,7 +619,13 @@
// Block captures count as local values and have imprecise semantics.
// They also can't be arrays, so need to worry about that.
- if (dtorKind == QualType::DK_objc_strong_lifetime) {
+ //
+ // For const-qualified captures, emit clang.arc.use to ensure the captured
+ // object doesn't get released while we are still depending on its validity
+ // within the block.
+ if (VT.isConstQualified() && VT.getObjCLifetime() == Qualifiers::OCL_Strong)
+ destroyer = CodeGenFunction::emitARCIntrinsicUse;
+ else if (dtorKind == QualType::DK_objc_strong_lifetime) {
destroyer = CodeGenFunction::destroyARCStrongImprecise;
} else {
destroyer = CGF.getDestroyer(dtorKind);
@@ -866,6 +872,12 @@
} else if (type->isReferenceType()) {
Builder.CreateStore(src.getPointer(), blockField);
+ // If type is const-qualified, copy the value into the block field.
+ } else if (type.isConstQualified() &&
+ type.getObjCLifetime() == Qualifiers::OCL_Strong) {
+ llvm::Value *value = Builder.CreateLoad(src, "captured");
+ Builder.CreateStore(value, blockField);
+
// If this is an ARC __strong block-pointer variable, don't do a
// block copy.
//