[CodeGen] tighten objc ivar invariant.load attribution

An ivar ofset cannot be marked as invariant load in all cases.  The ivar offset
is a lazily initialised constant, which is dependent on an objc_msgSend
invocation to perform a fixup of the offset.  If the load is being performed on
a method implemented by the class then this load can safely be marked as an
inviarant because a message must have been passed to the class at some point,
forcing the ivar offset to be resolved.

An additional heuristic that can be used to identify an invariant load would be
if the ivar offset base is a parameter to an objc method.  However, without the
parameters available at hand, this is currently not possible.

Reviewed-by: John McCall <rjmccall@apple.com>
Signed-off-by: Saleem Abdulrasool <compnerd@compnerd.org>
llvm-svn: 175386

1 files changed, 53 insertions, 0 deletions

diff --git a/clang/test/CodeGenObjC/ivar-invariant.m b/clang/test/CodeGenObjC/ivar-invariant.m
new file mode 100644
index 0000000..f592654
--- /dev/null
+++ b/clang/test/CodeGenObjC/ivar-invariant.m
@@ -0,0 +1,53 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -x objective-c %s -o - | FileCheck %s
+
+@interface NSObject
++ (id) new;
+- (id) init;
+@end
+
+@interface Base : NSObject @end
+
+// @implementation Base
+// {
+//     int dummy;
+// }
+// @end
+
+@interface Derived : Base
+{
+    @public int member;
+}
+@end
+
+@implementation Derived
+- (id) init
+{
+    self = [super init];
+    member = 42;
+    return self;
+}
+@end
+
+// CHECK: [[IVAR:%.*]] = load i64* @"OBJC_IVAR_$_Derived.member", !invariant.load
+
+void * variant_load_1(int i) {
+    void *ptr;
+    while (i--) {
+        Derived *d = [Derived new];
+        ptr = &d->member;
+    }
+    return ptr;
+}
+
+// CHECK: [[IVAR:%.*]] = load i64* @"OBJC_IVAR_$_Derived.member"{{$}}
+
+@interface Container : Derived @end
+@implementation Container
+- (void *) invariant_load_1
+{
+    return &self->member;
+}
+@end
+
+// CHECK: [[IVAR:%.*]] = load i64* @"OBJC_IVAR_$_Derived.member", !invariant.load
+