[ObjC] Expand isClassLayoutKnownStatically to base classes as long as the implementation of it is known #85465

AZero13 · 2024-03-15T20:44:07Z

Only NSObject we can trust the layout of won't change even though we cannot directly see its @implementation

llvmbot · 2024-03-15T20:44:38Z

@llvm/pr-subscribers-clang-codegen

Author: AtariDreams (AtariDreams)

Changes

Only NSObject we can trust the layout of won't change even though we cannot directly see its @implementation

Full diff: https://github.com/llvm/llvm-project/pull/85465.diff

2 Files Affected:

(modified) clang/lib/CodeGen/CGObjCMac.cpp (+8-1)
(modified) clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m (+29-1)

diff --git a/clang/lib/CodeGen/CGObjCMac.cpp b/clang/lib/CodeGen/CGObjCMac.cpp
index e815e097e1fb48..da47ef786cf816 100644
--- a/clang/lib/CodeGen/CGObjCMac.cpp
+++ b/clang/lib/CodeGen/CGObjCMac.cpp
@@ -1595,6 +1595,11 @@ class CGObjCNonFragileABIMac : public CGObjCCommonMac {
   bool isClassLayoutKnownStatically(const ObjCInterfaceDecl *ID) {
     // Test a class by checking its superclasses up to
     // its base class if it has one.
+
+    // Cannot check a null class
+    if (!ID)
+      return false;
+
     for (; ID; ID = ID->getSuperClass()) {
       // The layout of base class NSObject
       // is guaranteed to be statically known
@@ -1606,7 +1611,9 @@ class CGObjCNonFragileABIMac : public CGObjCCommonMac {
       if (!ID->getImplementation())
         return false;
     }
-    return false;
+
+    // We know the layout of all the intermediate classes and superclasses.
+    return true;
   }
 
 public:
diff --git a/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m b/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
index 8d55e6c7d23081..ee4034e4b7f205 100644
--- a/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
+++ b/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
@@ -8,6 +8,12 @@
 // CHECK: @"OBJC_IVAR_$_IntermediateClass._intermediateProperty" = hidden constant i64 48
 // CHECK: @"OBJC_IVAR_$_SubClass.subClassIvar" = constant i64 56
 // CHECK: @"OBJC_IVAR_$_SubClass._subClassProperty" = hidden constant i64 64
+
+// CHECK: @"OBJC_IVAR_$_RootClass.these" = constant i64 0
+// CHECK: @"OBJC_IVAR_$_RootClass.dont" = constant i64 4
+// CHECK: @"OBJC_IVAR_$_RootClass.change" = constant i64 4
+// CHECK: @"OBJC_IVAR_$_StillStaticLayout.static_layout_ivar" = hidden global i32 12
+
 // CHECK: @"OBJC_IVAR_$_NotStaticLayout.not_static_layout_ivar" = hidden global i64 12
 
 @interface NSObject {
@@ -120,7 +126,29 @@ -(void)intermediateSubclassVar {
 // CHECK: getelementptr inbounds i8, ptr %1, i64 64
 @end
 
-@interface NotNSObject {
+ __attribute((objc_root_class))  @interface RootClass {
+  int these, dont, change;
+}
+@end
+
+@implementation RootClass 
+@end
+
+@interface StillStaticLayout : RootClass
+@end
+
+@implementation StillStaticLayout {
+  int static_layout_ivar;
+}
+
+// CHECK-LABEL: define internal void @"\01-[StillStaticLayout meth]"
+-(void)meth {
+  static_layout_ivar = 0;
+  // CHECK-NOT: load i64, ptr @"OBJC_IVAR_$StillStaticLayout.static_layout_ivar
+}
+@end
+
+__attribute((objc_root_class))  @interface NotNSObject {
   int these, might, change;
 }
 @end

llvmbot · 2024-03-15T20:44:38Z

@llvm/pr-subscribers-clang

Author: AtariDreams (AtariDreams)

Changes

Only NSObject we can trust the layout of won't change even though we cannot directly see its @implementation

Full diff: https://github.com/llvm/llvm-project/pull/85465.diff

2 Files Affected:

(modified) clang/lib/CodeGen/CGObjCMac.cpp (+8-1)
(modified) clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m (+29-1)

diff --git a/clang/lib/CodeGen/CGObjCMac.cpp b/clang/lib/CodeGen/CGObjCMac.cpp
index e815e097e1fb48..da47ef786cf816 100644
--- a/clang/lib/CodeGen/CGObjCMac.cpp
+++ b/clang/lib/CodeGen/CGObjCMac.cpp
@@ -1595,6 +1595,11 @@ class CGObjCNonFragileABIMac : public CGObjCCommonMac {
   bool isClassLayoutKnownStatically(const ObjCInterfaceDecl *ID) {
     // Test a class by checking its superclasses up to
     // its base class if it has one.
+
+    // Cannot check a null class
+    if (!ID)
+      return false;
+
     for (; ID; ID = ID->getSuperClass()) {
       // The layout of base class NSObject
       // is guaranteed to be statically known
@@ -1606,7 +1611,9 @@ class CGObjCNonFragileABIMac : public CGObjCCommonMac {
       if (!ID->getImplementation())
         return false;
     }
-    return false;
+
+    // We know the layout of all the intermediate classes and superclasses.
+    return true;
   }
 
 public:
diff --git a/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m b/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
index 8d55e6c7d23081..ee4034e4b7f205 100644
--- a/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
+++ b/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
@@ -8,6 +8,12 @@
 // CHECK: @"OBJC_IVAR_$_IntermediateClass._intermediateProperty" = hidden constant i64 48
 // CHECK: @"OBJC_IVAR_$_SubClass.subClassIvar" = constant i64 56
 // CHECK: @"OBJC_IVAR_$_SubClass._subClassProperty" = hidden constant i64 64
+
+// CHECK: @"OBJC_IVAR_$_RootClass.these" = constant i64 0
+// CHECK: @"OBJC_IVAR_$_RootClass.dont" = constant i64 4
+// CHECK: @"OBJC_IVAR_$_RootClass.change" = constant i64 4
+// CHECK: @"OBJC_IVAR_$_StillStaticLayout.static_layout_ivar" = hidden global i32 12
+
 // CHECK: @"OBJC_IVAR_$_NotStaticLayout.not_static_layout_ivar" = hidden global i64 12
 
 @interface NSObject {
@@ -120,7 +126,29 @@ -(void)intermediateSubclassVar {
 // CHECK: getelementptr inbounds i8, ptr %1, i64 64
 @end
 
-@interface NotNSObject {
+ __attribute((objc_root_class))  @interface RootClass {
+  int these, dont, change;
+}
+@end
+
+@implementation RootClass 
+@end
+
+@interface StillStaticLayout : RootClass
+@end
+
+@implementation StillStaticLayout {
+  int static_layout_ivar;
+}
+
+// CHECK-LABEL: define internal void @"\01-[StillStaticLayout meth]"
+-(void)meth {
+  static_layout_ivar = 0;
+  // CHECK-NOT: load i64, ptr @"OBJC_IVAR_$StillStaticLayout.static_layout_ivar
+}
+@end
+
+__attribute((objc_root_class))  @interface NotNSObject {
   int these, might, change;
 }
 @end

AZero13 · 2024-11-17T22:46:20Z

Going to ping @rjmccall

AZero13 · 2025-02-10T01:34:20Z

@adrian-prantl thoughts on this?

AZero13 · 2025-02-11T15:44:39Z

@davidchisnall thoughts?

clang/lib/CodeGen/CGObjCMac.cpp

ahatanak

We can remove the null check when we prove ID is never null.

AZero13 · 2025-02-25T14:19:48Z

@ahatanak Okay I removed the null check.

AZero13 · 2025-03-03T18:17:14Z

@ahatanak Can we please merge this?

ahatanak · 2025-03-03T22:24:16Z

Can we assert that ID isn't null at the beginning of isClassLayoutKnownStatically?

@implementation

… the implementation of it is known Only NSObject we can trust the layout of won't change even though we cannot directly see its @implementation.

AZero13 · 2025-03-04T14:10:59Z

Can we assert that ID isn't null at the beginning of isClassLayoutKnownStatically?

Done! @ahatanak!

llvmbot added clang Clang issues not falling into any other category clang:codegen IR generation bugs: mangling, exceptions, etc. labels Mar 15, 2024

AZero13 force-pushed the what-if branch 3 times, most recently from d778404 to 3e11da6 Compare March 16, 2024 23:25

AZero13 force-pushed the what-if branch from 3e11da6 to 1c241dd Compare June 2, 2024 01:48

AZero13 mentioned this pull request Jul 15, 2024

We know the layout of base classes and their subclasses that we can see the @implementation of #98930

Closed

AZero13 force-pushed the what-if branch from 1c241dd to 50f321e Compare July 23, 2024 14:07

AZero13 closed this Sep 10, 2024

AZero13 reopened this Oct 28, 2024

AZero13 force-pushed the what-if branch from 50f321e to 5872f59 Compare October 28, 2024 17:57

AZero13 force-pushed the what-if branch 2 times, most recently from 357b8ca to ffbc1da Compare November 17, 2024 02:21

AZero13 force-pushed the what-if branch from ffbc1da to bd44589 Compare February 10, 2025 01:34

efriedma-quic requested review from ahatanak, davidchisnall and rjmccall February 10, 2025 23:26

AZero13 mentioned this pull request Feb 10, 2025

[CodeGen][ObjC] Invalidate cached ObjC class layout information after parsing ObjC class implementations if new ivars are added to the interface #126591

Merged

ahatanak reviewed Feb 12, 2025

View reviewed changes

clang/lib/CodeGen/CGObjCMac.cpp Outdated Show resolved Hide resolved

ahatanak approved these changes Feb 17, 2025

View reviewed changes

AZero13 force-pushed the what-if branch 4 times, most recently from 0572dd0 to 9cb7c41 Compare February 25, 2025 14:39

[ObjC] Expand isClassLayoutKnownStatically to base classes as long as…

b0eba86

… the implementation of it is known Only NSObject we can trust the layout of won't change even though we cannot directly see its @implementation.

AZero13 force-pushed the what-if branch from 9cb7c41 to b0eba86 Compare March 4, 2025 14:11

ahatanak merged commit 6720465 into llvm:main Mar 4, 2025
11 checks passed

AZero13 deleted the what-if branch March 4, 2025 16:54

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[ObjC] Expand isClassLayoutKnownStatically to base classes as long as the implementation of it is known #85465

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[ObjC] Expand isClassLayoutKnownStatically to base classes as long as the implementation of it is known #85465

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