Skip to content

Commit 923ddf6

Browse files
AZero13AZero13
authored
[ObjC] Check entire chain of superclasses to see if class layout is statically known (#81335)
As of now, we only check if a class directly inherits from NSObject to determine if said class has fixed offsets and can therefore "opt-out" from the non-fragile ABI for ivars. However, if an NSObject subclass has fixed offsets, then so must the subclasses of that subclass, so this allows us to optimize instances of subclasses of subclasses that inherit from NSObject and so on. To determine this, we need to find that the compiler can see the implementation of each intermediate class, as that means it is statically linked. Fixes: #81369
1 parent 762f762 commit 923ddf6

File tree

2 files changed

+116
-6
lines changed

2 files changed

+116
-6
lines changed

‎clang/lib/CodeGen/CGObjCMac.cpp‎

Lines changed: 14 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1593,12 +1593,20 @@ class CGObjCNonFragileABIMac : public CGObjCCommonMac {
15931593
}
15941594

15951595
bool isClassLayoutKnownStatically(const ObjCInterfaceDecl *ID) {
1596-
// NSObject is a fixed size. If we can see the @implementation of a class
1597-
// which inherits from NSObject then we know that all it's offsets also must
1598-
// be fixed. FIXME: Can we do this if see a chain of super classes with
1599-
// implementations leading to NSObject?
1600-
return ID->getImplementation() && ID->getSuperClass() &&
1601-
ID->getSuperClass()->getName() == "NSObject";
1596+
// Test a class by checking its superclasses up to
1597+
// its base class if it has one.
1598+
for (; ID; ID = ID->getSuperClass()) {
1599+
// The layout of base class NSObject
1600+
// is guaranteed to be statically known
1601+
if (ID->getIdentifier()->getName() == "NSObject")
1602+
return true;
1603+
1604+
// If we cannot see the @implementation of a class,
1605+
// we cannot statically know the class layout.
1606+
if (!ID->getImplementation())
1607+
return false;
1608+
}
1609+
return false;
16021610
}
16031611

16041612
public:

‎clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m‎

Lines changed: 102 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,13 @@
11
// RUN: %clang_cc1 -triple x86_64-apple-macosx10.14.0 -emit-llvm %s -o - | FileCheck %s
22

33
// CHECK: @"OBJC_IVAR_$_StaticLayout.static_layout_ivar" = hidden constant i64 20
4+
// CHECK: @"OBJC_IVAR_$_SuperClass.superClassIvar" = hidden constant i64 20
5+
// CHECK: @"OBJC_IVAR_$_SuperClass._superClassProperty" = hidden constant i64 24
6+
// CHECK: @"OBJC_IVAR_$_IntermediateClass.intermediateClassIvar" = constant i64 32
7+
// CHECK: @"OBJC_IVAR_$_IntermediateClass.intermediateClassIvar2" = constant i64 40
8+
// CHECK: @"OBJC_IVAR_$_IntermediateClass._intermediateProperty" = hidden constant i64 48
9+
// CHECK: @"OBJC_IVAR_$_SubClass.subClassIvar" = constant i64 56
10+
// CHECK: @"OBJC_IVAR_$_SubClass._subClassProperty" = hidden constant i64 64
411
// CHECK: @"OBJC_IVAR_$_NotStaticLayout.not_static_layout_ivar" = hidden global i64 12
512

613
@interface NSObject {
@@ -14,12 +21,105 @@ @interface StaticLayout : NSObject
1421
@implementation StaticLayout {
1522
int static_layout_ivar;
1623
}
24+
25+
// CHECK-LABEL: define internal void @"\01-[StaticLayout meth]"
1726
-(void)meth {
1827
static_layout_ivar = 0;
1928
// CHECK-NOT: load i64, ptr @"OBJC_IVAR_$_StaticLayout
29+
// CHECK: getelementptr inbounds i8, ptr %0, i64 20
30+
}
31+
@end
32+
33+
@interface SuperClass : NSObject
34+
@property (nonatomic, assign) int superClassProperty;
35+
@end
36+
37+
@implementation SuperClass {
38+
int superClassIvar; // Declare an ivar
39+
}
40+
41+
// CHECK-LABEL: define internal void @"\01-[SuperClass superClassMethod]"
42+
- (void)superClassMethod {
43+
_superClassProperty = 42;
44+
superClassIvar = 10;
45+
// CHECK-NOT: load i64, ptr @"OBJC_IVAR_$_SuperClass
46+
// CHECK: getelementptr inbounds i8, ptr %1, i64 20
47+
}
48+
49+
// Implicitly synthesized method here
50+
// CHECK-LABEL: define internal i32 @"\01-[SuperClass superClassProperty]"
51+
// CHECK: getelementptr inbounds i8, ptr %0, i64 24
52+
53+
// CHECK-LABEL: define internal void @"\01-[SuperClass setSuperClassProperty:]"
54+
// CHECK: getelementptr inbounds i8, ptr %1, i64 24
55+
@end
56+
57+
@interface IntermediateClass : SuperClass {
58+
double intermediateClassIvar;
59+
60+
@protected
61+
int intermediateClassIvar2;
62+
}
63+
@property (nonatomic, strong) SuperClass *intermediateProperty;
64+
@end
65+
66+
@implementation IntermediateClass
67+
@synthesize intermediateProperty = _intermediateProperty;
68+
69+
// CHECK-LABEL: define internal void @"\01-[IntermediateClass intermediateClassMethod]"
70+
- (void)intermediateClassMethod {
71+
intermediateClassIvar = 3.14;
72+
// CHECK-NOT: load i64, ptr @"OBJC_IVAR_$_IntermediateClass
73+
// CHECK: getelementptr inbounds i8, ptr %0, i64 32
74+
}
75+
76+
// CHECK-LABEL: define internal void @"\01-[IntermediateClass intermediateClassPropertyMethod]"
77+
- (void)intermediateClassPropertyMethod {
78+
self.intermediateProperty = 0;
79+
// CHECK: load ptr, ptr @OBJC_SELECTOR_REFERENCES_
80+
// CHECK: call void @objc_msgSend(ptr noundef %0, ptr noundef %1, ptr noundef null)
81+
}
82+
83+
// CHECK-LABEL: define internal void @"\01-[IntermediateClass intermediateClassPropertyMethodDirect]"
84+
- (void)intermediateClassPropertyMethodDirect {
85+
_intermediateProperty = 0;
86+
// CHECK-NOT: load i64, ptr @"OBJC_IVAR_$_IntermediateClass._intermediateProperty"
87+
// CHECK: getelementptr inbounds i8, ptr %0, i64 48
2088
}
2189
@end
2290

91+
@interface SubClass : IntermediateClass {
92+
double subClassIvar;
93+
}
94+
@property (nonatomic, assign) SubClass *subClassProperty;
95+
@end
96+
97+
@implementation SubClass
98+
99+
// CHECK-LABEL: define internal void @"\01-[SubClass subclassVar]"
100+
- (void)subclassVar {
101+
subClassIvar = 6.28;
102+
// CHECK-NOT: load i64, ptr @"OBJC_IVAR_$_SubClass
103+
// CHECK: getelementptr inbounds i8, ptr %0, i64 56
104+
}
105+
106+
// CHECK-LABEL: define internal void @"\01-[SubClass intermediateSubclassVar]"
107+
-(void)intermediateSubclassVar {
108+
intermediateClassIvar = 3.14;
109+
// CHECK-NOT: load i64, ptr @"OBJC_IVAR_$_IntermediateClass
110+
// CHECK: getelementptr inbounds i8, ptr %0, i64 32
111+
}
112+
113+
// Implicit synthesized method here:
114+
// CHECK-LABEL: define internal ptr @"\01-[SubClass subClassProperty]"
115+
// CHECK-NOT: load i64, ptr @"OBJC_IVAR_$_SubClass._subClassProperty"
116+
// CHECK: getelementptr inbounds i8, ptr %0, i64 64
117+
118+
// CHECK-LABEL: define internal void @"\01-[SubClass setSubClassProperty:]"
119+
// CHECK-NOT: load i64, ptr @"OBJC_IVAR_$_SubClass._subClassProperty"
120+
// CHECK: getelementptr inbounds i8, ptr %1, i64 64
121+
@end
122+
23123
@interface NotNSObject {
24124
int these, might, change;
25125
}
@@ -31,6 +131,8 @@ @interface NotStaticLayout : NotNSObject
31131
@implementation NotStaticLayout {
32132
int not_static_layout_ivar;
33133
}
134+
135+
// CHECK-LABEL: define internal void @"\01-[NotStaticLayout meth]"
34136
-(void)meth {
35137
not_static_layout_ivar = 0;
36138
// CHECK: load i64, ptr @"OBJC_IVAR_$_NotStaticLayout.not_static_layout_ivar

0 commit comments

Comments
 (0)