On Thu, Jul 11, 2013 at 11:17 PM, Alex Markin <alexanius@xxxxxxxxx> wrote:
>
> I've noticed the difference in gcc and llvm behaviour with the following code:
>
> $ cat test.c
> #include <stdio.h>
> int main()
> {
> for(int i = 0;; ({break;}))
> printf("Hello, world\n");
> }
>
> $ clang test.c -pedantic && ./a.out
> test.c:5:22: warning: use of GNU statement expression extension [-Wgnu]
> for(int i = 0;; ({break;}))
> ^
> 1 warning generated.
> Hello, world
>
> $ gcc test.c -std=gnu11 -pedantic && ./a.out
> test.c: In function 'main':
> test.c:5:23: error: break statement not within loop or switch
> for(int i = 0;; ({break;}))
> ^
> test.c:5:21: warning: ISO C forbids braced-groups within expressions
> [-Wpedantic]
> for(int i = 0;; ({break;}))
>
>
> So, llvm thinks that this is GNU extension (seems like it really is),
> but compiles it, and gcc does not, even if the standard is specified
> as gnu11. Is it a bug?
Yes.
But probably you wanted to know whether it is a bug in LLVM or in GCC.
It's a bug in LLVM. You can't use break in a statement expression to
break out of a loop that is not in the statement expression.
Statement expressions are their own thing; they don't inherit the
surrounding context, except that using a goto statement to a label
outside the statement expression is permitted.
Ian
