[GNU ObjC] Clang 14 regression: access violation when building with ARC and optimization

[triplef]

Building the following Objective-C code using using Automatic Reference Counting and the GNU Objective-C 2.0 runtime and -O1 or better optimization using Clang 14.0.5 causes an access violation at runtime.

This does not happen with Clang 13.0.1, or when using -O0, or when not using ARC.

#import "objc/runtime.h"

__attribute__((objc_root_class))
@interface Test {
  id isa;
}
+ (id)new;
@end

@implementation Test
+ (id)new {
  return class_createInstance(self, 0);
}
@end

int main(void) {
  [Test new];
  return 0;
}

Building:

"C:\Program Files\LLVM-14\bin\clang" -IC:\libobjc2\include -LC:\libobjc2\lib -fobjc-runtime=gnustep-2.0 -fobjc-arc -fuse-ld=lld -lobjc -O2 -o test.exe test.m

Result:

* thread #1, stop reason = Exception 0xc0000005 encountered at address 0x7ffb16aea405: Access violation reading location 0xffffffffffffffff
    frame #0: 0x00007ffb16aea405 objc.dll`objc_retain + 149
objc.dll`objc_retain:
->  0x7ffb16aea405 <+149>: movq   (%rax), %rcx
    0x7ffb16aea408 <+152>: movl   $0x4000, %edx             ; imm = 0x4000
    0x7ffb16aea40d <+157>: callq  0x7ffb16aeacb0            ; objc_storeWeak + 1472
    0x7ffb16aea412 <+162>: movl   %eax, 0x54(%rsp)

[triplef]

Interestingly the access violation does not happen when using NSObject from GNUstep Base instead of the locally defined Test class, and it even works to call [Test new] after [NSObject new]. However calling [Test new] before [NSObject new] still reproduces the bug.

#import "objc/runtime.h"
#import <Foundation/Foundation.h>

__attribute__((objc_root_class))
@interface Test {
  id isa;
}
+ (id)new;
@end

@implementation Test
+ (id)new {
  return class_createInstance(self, 0);
}
@end

// does not crash:
int main(void) {
  [NSObject new];
  [Test new];
  return 0;
}

// crashes:
/*
int main(void) {
  [Test new];
  [NSObject new];
  return 0;
}
*/

Built with the following using the pre-built GNUstep toolchain:

"C:\Program Files\LLVM-14\bin\clang" -I C:\GNUstep\x64\Debug\include -L C:\GNUstep\x64\Debug\lib -fobjc-runtime=gnustep-2.0 -lobjc -fobjc-arc -fuse-ld=lld -fexceptions -fobjc-exceptions -fblocks -DGNUSTEP -DGNUSTEP_WITH_DLL -DGNUSTEP_RUNTIME=1 -D_NONFRAGILE_ABI=1 -D_NATIVE_OBJC_EXCEPTIONS -lobjc -lgnustep-base -O2 -o test.exe test.m

[davidchisnall]

I believe that this is caused by libobjc2 not having the ns_returns_retained attribute on class_createInstance. Closing and fixing it over there. Please reopen if this turns out to be a clang bug.