Re: [PATCH] PR45834: make restrict qualifier work for char pointer type.

[Richard Guenther <richard.guenther@gmail.com>]

On Thu, Oct 21, 2010 at 4:26 PM, Bingfeng Mei <bmei@broadcom.com> wrote:
> Hi,
>
> This patch fixes bug PR45834. In alias.c, a check for QImode prevents later
> alias analysis based on restrict qualifier for char pointer type.
> This check is based on ancient code (at least 1997), and other modern
> way has been implemented for dealing that (MEM_ALIAS_SET == 0)
> according to Richard.
>
> Bootstrapped and tested for x86_64-unknown-linux-gnu.
>
> Before the patch  powerpc-elf-gcc -O2 tst.c -S
>
> void foo (char * __restrict a, char *__restrict b, char * __restrict c)
> {
>  *a = *b;
>  *(a+1) = *c;
> }
> foo:
>        lbz 0,0(4)
>        stb 0,0(3)
>        lbz 0,0(5)
>        stb 0,1(3)
>        blr
>
> After the patch
> foo:
>        lbz 0,0(4)
>        lbz 9,0(5)
>        stb 0,0(3)
>        stb 9,1(3)
>        blr
>
> Not sure how to add it into testsuite though.
>
> Cheers,
> Bingfeng Mei
>
> 2010-10-21  Bingfeng Mei  <bmei@broadcom.com>
>        * alias.c (true_dependence_1): Remove check for QImode,
>        which prevents accurate alias info of char pointer type
>        with restrict qualifier. The check is handled by
>        better and more modern method now.
>        (may_alias_p): Ditto.

Just say

        * alias.c (true_dependence_1): Remove obsolete check for QImode.

Ok with that change.

Richard.


> Index: alias.c
> ===================================================================
> --- alias.c     (revision 165637)
> +++ alias.c     (working copy)
> @@ -2459,7 +2459,7 @@ true_dependence_1 (const_rtx mem, enum m
>
>   /* We cannot use aliases_everything_p to test MEM, since we must look
>      at MEM_ADDR, rather than XEXP (mem, 0).  */
> -  if (mem_mode == QImode || GET_CODE (mem_addr) == AND)
> +  if (GET_CODE (mem_addr) == AND)
>     return 1;
>
>   /* ??? In true_dependence we also allow BLKmode to alias anything.  Why
> @@ -2655,7 +2655,7 @@ may_alias_p (const_rtx mem, const_rtx x)
>
>   /* We cannot use aliases_everything_p to test MEM, since we must look
>      at MEM_ADDR, rather than XEXP (mem, 0).  */
> -  if (GET_MODE (mem) == QImode || GET_CODE (mem_addr) == AND)
> +  if (GET_CODE (mem_addr) == AND)
>     return 1;
>
>   if (fixed_scalar_and_varying_struct_p (mem, x, mem_addr, x_addr,
>
>
>
>