ObjC Bool: what changed

Revision 1 to 2. Removed lines have a minus sign; added lines have a plus sign.

Old	New		Line
1	1		## Objective-C
2	2
3	3		### Source code
4	4
5	5		main.m
6	6
7	7		```objc
8	8		#import <Foundation/Foundation.h>
9	9
10	10		@interface BoolTest: NSObject
11	11		-(void) testcbool: (_Bool) avalue;
12	12		-(void) testobjcbool: (BOOL) avalue;
13	13		@end
14	14
15	15		@implementation BoolTest
16	16		-(void) testcbool: (_Bool) avalue
17	17		{
18	18		NSLog(@" cbool %s", avalue ? "true" : "false");
19	19		}
20	20
21	21		-(void) testobjcbool: (BOOL) avalue
22	22		{
23	23		NSLog(@" objcbool %s", avalue ? "true" : "false");
24	24		}
25	25		@end
26	26
27	27		void simpleC(_Bool avalue)
28	28		{
29	29		NSLog(@" plainc %s", avalue ? "true" : "false");
30	30		return;
31	31		}
32	32
33	33		int main(int argc, const char * argv[]) {
34	34		@autoreleasepool {
35	35		// insert code here...
36	36		int a = 10;
37	37		int b = 10;
38	38		BoolTest* tt = [[BoolTest alloc] init];
39	39		[tt testcbool:(a==b)];
40	40		[tt testobjcbool:(a==b)];
41	41		simpleC(a==b);
42	42		}
43	43		return 0;
44	44		}
45	45		```
46	46
47	47		### Compile
48	48
49	49		You need to have Xcode command-line tools installed
50	50
51		-	~~`clang -framework Foundation -arch x86_64 main.m -o main`~~
	51	+	```text
	52	+	clang -framework Foundation -arch x86_64 main.m -o main
	53	+	```
52	54
53	55		produces the executable. (The executable can be debugged and lldb can show the disassebly)
54	56
55	57		In order to get assembly file from the compiler the following command-line could be used
56	58
57		-	~~`clang -framework Foundation -arch x86_64 main.m --assemble -o main.as`~~
	59	+	```text
	60	+	clang -framework Foundation -arch x86_64 main.m --assemble -o main.as
	61	+	```
58	62
59	63		## Disassembly x86_64
60	64
61	65		Boolean parameters, no matter BOOL (signed char) or _Bool are always passed in the entire register
62	66
63	67		### No optimization
64	68
65	69		``` asm
66	70		0x100000e5d <+93>: movl -0x14(%rbp), %edx
67	71		0x100000e60 <+96>: cmpl -0x18(%rbp), %edx
68	72		0x100000e63 <+99>: sete %r8b
69	73		0x100000e67 <+103>: movq 0x31a(%rip), %rsi ; "testcbool:"
70	74		0x100000e6e <+110>: andb $0x1, %r8b
71	75
72	76		0x100000e72 <+114>: movzbl %r8b, %edx
73	77
74	78		0x100000e76 <+118>: movq 0x183(%rip), %rcx ; (void *)0x00007fff7e936e80: objc_msgSend
75	79		0x100000e7d <+125>: movq %rax, %rdi
76	80		0x100000e80 <+128>: callq *%rcx
77	81		0x100000e82 <+130>: movq -0x20(%rbp), %rax
78	82
79	83		0x100000e86 <+134>: movl -0x14(%rbp), %edx
80	84		0x100000e89 <+137>: cmpl -0x18(%rbp), %edx
81	85		0x100000e8c <+140>: sete %r8b
82	86		0x100000e90 <+144>: andb $0x1, %r8b
83	87
84	88		0x100000e94 <+148>: movzbl %r8b, %edx
85	89
86	90		0x100000e98 <+152>: movb %dl, %r8b
87	91		0x100000e9b <+155>: movq 0x2ee(%rip), %rsi ; "testobjcbool:"
88	92		0x100000ea2 <+162>: movq %rax, %rdi
89	93		0x100000ea5 <+165>: movsbl %r8b, %edx
90	94		0x100000ea9 <+169>: callq 0x100000ef8 ; symbol stub for: objc_msgSend
91	95
92	96		0x100000eae <+174>: movl -0x14(%rbp), %edx
93	97		0x100000eb1 <+177>: cmpl -0x18(%rbp), %edx
94	98		0x100000eb4 <+180>: sete %r8b
95	99		0x100000eb8 <+184>: andb $0x1, %r8b
96	100
97	101		0x100000ebc <+188>: movzbl %r8b, %edi
98	102
99	103		0x100000ec0 <+192>: callq 0x100000db0 ; simpleC at main.m:29
100	104		```
101	105
102	106		### O3
103	107
104	108		As expected, O3 evaluates constant expressions and puts the end result into the code. Still boolean parameters are being written as long values into registers.
105	109
106	110		``` asm
107	111		0x100000e97 <+55>: movq %rax, %rbx
108	112		0x100000e9a <+58>: movq 0x2df(%rip), %rsi ; "testcbool:"
109	113		0x100000ea1 <+65>: movl $0x1, %edx
110	114		0x100000ea6 <+70>: movq %rbx, %rdi
111	115		0x100000ea9 <+73>: callq *%r15
112	116		0x100000eac <+76>: movq 0x2d5(%rip), %rsi ; "testobjcbool:"
113	117		0x100000eb3 <+83>: movl $0x1, %edx
114	118		0x100000eb8 <+88>: movq %rbx, %rdi
115	119		0x100000ebb <+91>: callq *%r15
116	120		0x100000ebe <+94>: leaq 0x1b3(%rip), %rdi ; @" plainc %s"
117	121		0x100000ec5 <+101>: leaq 0x70(%rip), %rsi ; "true"
118	122		0x100000ecc <+108>: xorl %eax, %eax
119	123		0x100000ece <+110>: callq 0x100000ef2 ; symbol stub for: NSLog
120	124		0x100000ed3 <+115>: movq %rbx, %rdi
121	125		```
122	126
123	127		---
124	128		From the Free Pascal wiki, page "ObjC Bool", as it stood on 2022-05-04 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).
125	129		Category: Objective-C
126	130		Category: macOS

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