ObjC Bool

Objective-C

Source code

#import <Foundation/Foundation.h>

@interface BoolTest: NSObject
  -(void) testcbool: (_Bool) avalue;
  -(void) testobjcbool: (BOOL) avalue;
@end

@implementation BoolTest
-(void) testcbool: (_Bool) avalue
{
    NSLog(@" cbool %s", avalue ? "true" : "false");
}

-(void) testobjcbool: (BOOL) avalue
{
    NSLog(@" objcbool %s", avalue ? "true" : "false");
}
@end

void simpleC(_Bool avalue)
{
    NSLog(@" plainc %s", avalue ? "true" : "false");
    return;
}

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        int a = 10;
        int b = 10;
        BoolTest* tt = [[BoolTest alloc] init];
        [tt testcbool:(a==b)];
        [tt testobjcbool:(a==b)];
        simpleC(a==b);
   }
    return 0;
}

Disassembly x86_54

Boolean parameters, no matter BOOL (signed char) or _Bool are always passed in the entired register

    0x100000e5d <+93>:  movl   -0x14(%rbp), %edx
    0x100000e60 <+96>:  cmpl   -0x18(%rbp), %edx
    0x100000e63 <+99>:  sete   %r8b
    0x100000e67 <+103>: movq   0x31a(%rip), %rsi         ; "testcbool:"
    0x100000e6e <+110>: andb   $0x1, %r8b

    0x100000e72 <+114>: movzbl %r8b, %edx

    0x100000e76 <+118>: movq   0x183(%rip), %rcx         ; (void *)0x00007fff7e936e80: objc_msgSend
    0x100000e7d <+125>: movq   %rax, %rdi
    0x100000e80 <+128>: callq  *%rcx
    0x100000e82 <+130>: movq   -0x20(%rbp), %rax

    0x100000e86 <+134>: movl   -0x14(%rbp), %edx
    0x100000e89 <+137>: cmpl   -0x18(%rbp), %edx
    0x100000e8c <+140>: sete   %r8b
    0x100000e90 <+144>: andb   $0x1, %r8b

    0x100000e94 <+148>: movzbl %r8b, %edx

    0x100000e98 <+152>: movb   %dl, %r8b
    0x100000e9b <+155>: movq   0x2ee(%rip), %rsi         ; "testobjcbool:"
    0x100000ea2 <+162>: movq   %rax, %rdi
    0x100000ea5 <+165>: movsbl %r8b, %edx
    0x100000ea9 <+169>: callq  0x100000ef8               ; symbol stub for: objc_msgSend


    0x100000eae <+174>: movl   -0x14(%rbp), %edx
    0x100000eb1 <+177>: cmpl   -0x18(%rbp), %edx
    0x100000eb4 <+180>: sete   %r8b
    0x100000eb8 <+184>: andb   $0x1, %r8b

    0x100000ebc <+188>: movzbl %r8b, %edi

    0x100000ec0 <+192>: callq  0x100000db0               ; simpleC at main.m:29