考虑以下代码:
#include <stdio.h>
typedef void (^block)();
block foo() {
char a = 'a';
return [^{
printf("%c\n", a);
} copy];
}
block bar() {
const char a = 'a';
return [^{
printf("%c\n", a);
} copy];
}
这是为 armv7 编译的内容:
_foo:
@ BB#0:
push {r7, lr}
mov r7, sp
sub sp, #24
movw r3, :lower16:(L__NSConcreteStackBlock$non_lazy_ptr-(LPC0_0+4))
movt r3, :upper16:(L__NSConcreteStackBlock$non_lazy_ptr-(LPC0_0+4))
movw r1, :lower16:(___foo_block_invoke_0-(LPC0_1+4))
LPC0_0:
add r3, pc
movt r1, :upper16:(___foo_block_invoke_0-(LPC0_1+4))
movw r0, :lower16:(L_OBJC_SELECTOR_REFERENCES_-(LPC0_2+4))
LPC0_1:
add r1, pc
movt r0, :upper16:(L_OBJC_SELECTOR_REFERENCES_-(LPC0_2+4))
movw r2, :lower16:(___block_descriptor_tmp-(LPC0_3+4))
ldr r3, [r3]
movt r2, :upper16:(___block_descriptor_tmp-(LPC0_3+4))
str r3, [sp]
mov.w r3, #1073741824
LPC0_2:
add r0, pc
str r3, [sp, #4]
movs r3, #0
LPC0_3:
add r2, pc
str r3, [sp, #8]
str r1, [sp, #12]
ldr r1, [r0]
mov r0, sp
str r2, [sp, #16]
movs r2, #97
strb.w r2, [sp, #20]
blx _objc_msgSend
add sp, #24
pop {r7, pc}
_bar:
@ BB#0:
movw r1, :lower16:(L_OBJC_SELECTOR_REFERENCES_-(LPC2_0+4))
movt r1, :upper16:(L_OBJC_SELECTOR_REFERENCES_-(LPC2_0+4))
movw r0, :lower16:(___block_literal_global-(LPC2_1+4))
LPC2_0:
add r1, pc
movt r0, :upper16:(___block_literal_global-(LPC2_1+4))
LPC2_1:
add r0, pc
ldr r1, [r1]
b.w _objc_msgSend
让我困惑的是第一个块不是全局块。它是一个堆栈块,然后被复制。这对我来说没有意义。我在 C 标准中忽略了为什么编译器不能自动推断出a
实际上可以考虑的东西const
吗?
我正在构建这个Os
,启用了 ARC,这是我的 clang 版本:
$ clang -v
Apple clang version 4.1 (tags/Apple/clang-421.11.66) (based on LLVM 3.1svn)
Target: x86_64-apple-darwin12.4.0
Thread model: posix