run.sh

$ clang -fobjc-arc -O2 -arch x86_64 test.m -framework Foundation
$ ./a.out b: 0x104011710
Segmentation fault: 11

test.m

#import <Foundation/Foundation.h>

typedef void (^B)(void);

@interface A : NSObject
@end

@implementation A

- (NSArray *)f
{
	B tmp = ^{
		printf("a: %p\n", self);
	};
	return [NSArray arrayWithObjects:tmp, nil];
}

- (NSArray *)g
{
	return [NSArray arrayWithObjects:^{
		printf("b: %p\n", self);
	}, nil];
}

@end

int main()
{
	@autoreleasepool {
		A *a = [A new];
		((B)[[a g]objectAtIndex:0])();
		((B)[[a f]objectAtIndex:0])();
	}
	return 0;
}