[Patch, ping] Emit error for negative _Alignas alignment values

[Senthil Kumar Selvaraj <senthil_kumar dot selvaraj at atmel dot com>]

Ping.

http://gcc.gnu.org/ml/gcc-patches/2013-04/msg00163.html

Regards
Senthil

On Wed, Apr 03, 2013 at 07:18:20PM +0530, Senthil Kumar Selvaraj wrote:
> This patch detects and emits an error if the value provided in _Alignas
> is negative. The fix was approved pending full regression testing in a
> previous discussion (http://gcc.gnu.org/ml/gcc/2013-03/msg00282.html). 
> To add to that patch, I have added a testcase that explicitly checks for the
> error for a negative power of 2.
> 
> Bootstrapped and regression tested with x86_64-unknown-linux-gnu with no new
> failures.
> 
> If ok, could someone commit please? I don't have commit access.
> 
> Regards
> Senthil
> 
> ChangeLog
> 
> 2013-04-03	Senthil Kumar Selvaraj	<senthil_kumar.selvaraj@atmel.com>
> 
> 	* c-common.c (check_user_alignment): Emit error for negative values
>     
> 	* gcc.dg/c1x-align-3.c: Add test for negative power of 2
> 
> diff --git gcc/c-family/c-common.c gcc/c-family/c-common.c
> index c7cdd0f..dfdfbb6 100644
> --- gcc/c-family/c-common.c
> +++ gcc/c-family/c-common.c
> @@ -7308,9 +7308,10 @@ check_user_alignment (const_tree align, bool allow_zero)
>      }
>    else if (allow_zero && integer_zerop (align))
>      return -1;
> -  else if ((i = tree_log2 (align)) == -1)
> +  else if (tree_int_cst_sgn (align) == -1
> +           || (i = tree_log2 (align)) == -1)
>      {
> -      error ("requested alignment is not a power of 2");
> +      error ("requested alignment is not a positive power of 2");
>        return -1;
>      }
>    else if (i >= HOST_BITS_PER_INT - BITS_PER_UNIT_LOG)
> diff --git gcc/testsuite/gcc.dg/c1x-align-3.c gcc/testsuite/gcc.dg/c1x-align-3.c
> index 0b2a77f..b97351c 100644
> --- gcc/testsuite/gcc.dg/c1x-align-3.c
> +++ gcc/testsuite/gcc.dg/c1x-align-3.c
> @@ -23,6 +23,7 @@ _Alignas (-(__LONG_LONG_MAX__-1)/4) char i3; /* { dg-error "too large|power of 2
>  _Alignas (-(__LONG_LONG_MAX__-1)/8) char i4; /* { dg-error "too large|power of 2" } */
>  _Alignas (-(__LONG_LONG_MAX__-1)/16) char i5; /* { dg-error "too large|power of 2" } */
>  _Alignas (-1) char j; /* { dg-error "power of 2" } */
> +_Alignas (-2) char j; /* { dg-error "positive power of 2" } */
>  _Alignas (3) char k; /* { dg-error "power of 2" } */
>  
>  _Alignas ((void *) 1) char k; /* { dg-error "integer constant" } */