A __attribute__ decorator that causes method calls to become implicit dispatches could be interesting: __attribute__((dispatch, async, priority))

gistfile1.m

#import <Foundation/Foundation.h>
#include <objc/message.h>

typedef void (*DISPATCH_IMP_NOARGS_NORETURN)(id, SEL);
typedef id (*DISPATCH_IMP_NOARGS)(id, SEL);

@interface Foo : NSObject

@end

@implementation Foo

- (void)foo //__attribute__((dispatch, true, DISPATCH_QUEUE_PRIORITY_HIGH))
{
	NSLog(@"%@", NSStringFromSelector(_cmd));
}

// Async would probably have to be a build error on return values
- (id)bar //__attribute__((dispatch, async, priority)) i.e. __attribute__((dispatch, false, DISPATCH_QUEUE_PRIORITY_HIGH))
{
	return NSStringFromSelector(_cmd);
}

@end

void _dispatch_async_objc_msgSend_noArgs_noReturn(int priority, id self, SEL _cmd)
{
	dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
		DISPATCH_IMP_NOARGS_NORETURN f = (DISPATCH_IMP_NOARGS_NORETURN)&objc_msgSend;
		f(self, _cmd);
	});
}

id _dispatch_sync_objc_msgSend_noArgs(int priority, id self, SEL _cmd)
{
	__block id val;
	dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
		DISPATCH_IMP_NOARGS f = (DISPATCH_IMP_NOARGS)&objc_msgSend;
		val = f(self, _cmd);
	});
	return val;
}

int main(int argc, const char * argv[])
{
	@autoreleasepool {
	    Foo *foo = [Foo new];
		// With this (madeup) attribute, instead of emitting objc_msgSend
		// the compiler could emit something like these
		// Where [foo foo] becomes
		_dispatch_async_objc_msgSend_noArgs_noReturn(DISPATCH_QUEUE_PRIORITY_HIGH, foo, @selector(foo));
		// and [foo bar becomes
		id val = _dispatch_sync_objc_msgSend_noArgs(DISPATCH_QUEUE_PRIORITY_HIGH, foo, @selector(bar));
		NSLog(@"%@", val);
		dispatch_main();
	}
    return 0;
}