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Date: Mon, 29 Jun 2015 11:50:16 -0600
From: Jens Axboe <axboe@kernel.dk>
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Subject: Re: competime_assert failure without -O3 optimization flag expected
 ?
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To: Alireza Haghdoost <haghdoost@gmail.com>
Cc: "fio@vger.kernel.org" <fio@vger.kernel.org>
List-ID: <fio@vger.kernel.org>

On 06/29/2015 11:42 AM, Alireza Haghdoost wrote:
> Jens,
>
> Sounds like the compiletime_assert() method was not function and is
> relying on the optimizer performing dead code elimination to remove
> the call to prefix ## suffix
>
> How about this solution: I guess we have to work around it to make it
> more portable since it works with C11.
>
> diff --git a/fio-arh/compiler/compiler.h b/fio-arh/compiler/compiler.h
> index 40e857c..7c9ba57 100644
> --- a/fio-arh/compiler/compiler.h
> +++ b/fio-arh/compiler/compiler.h
> @@ -33,26 +33,6 @@
>    1; \
>   })
>
> -#ifndef __compiletime_error
> -#define __compiletime_error(message)
> -#endif
> -#ifndef __compiletime_error_fallback
> -#define __compiletime_error_fallback(condition) do { } while (0)
> -#endif
> -
> -#define __compiletime_assert(condition, msg, prefix, suffix) \
> - do { \
> - int __cond = !(condition); \
> - extern void prefix ## suffix(void) __compiletime_error(msg); \
> - if (__cond) \
> - prefix ## suffix(); \
> - __compiletime_error_fallback(__cond); \
> - } while (0)
> -
> -#define _compiletime_assert(condition, msg, prefix, suffix) \
> - __compiletime_assert(condition, msg, prefix, suffix)
> -
> -#define compiletime_assert(condition, msg) \
> - _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
> +#define compiletime_assert(condition, msg) _Static_assert(condition, msg)
>
>   #endif

But now it's more compiler dependent, which is worse than before. At 
least it only broke if people fiddled with the optimizations before, 
otherwise it was fine.

Add a configure test for this, use _Static_assert() if it's available, 
the old method if not.

-- 
Jens Axboe