ObjC Bool: what changed

Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.

Title: ObjC Bool

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

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