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RE: Restrict qualifier still not working?


> -----Original Message-----
> From: Alexander Monakov [mailto:amonakov@ispras.ru]
> Sent: 02 August 2010 17:48
> To: Bingfeng Mei
> Cc: gcc@gcc.gnu.org; Richard Guenther
> Subject: Re: Restrict qualifier still not working?
> 
> 
> 
> On Mon, 2 Aug 2010, Bingfeng Mei wrote:
> 
> > Hi,
> > I ran a small test to see how the trunk/4.5 works
> > with the rewritten restrict qualified pointer code. But it doesn't
> > seem to work on both x86-64 and our port.
> >
> > tst.c:
> > void foo (int * restrict a, int * restrict b,
> >           int * restrict c, int * restrict d)
> > {
> >   *c = *a + 1;
> >   *d = *b + 1;
> > }
> [snip]
> > foo:
> > .LFB0:
> > 	.cfi_startproc
> > 	movl	(%rdi), %eax
> > 	addl	$1, %eax
> > 	movl	%eax, (%rdx)
> > 	movl	(%rsi), %eax
> > 	addl	$1, %eax
> > 	movl	%eax, (%rcx)
> > 	ret
> >
> > In the finally generated code, the second load should have
> > been moved before the first store if restrict qualifiers
> > are handled correctly.
> >
> > Am I missing something here? Thanks.
> 
> The second load is moved for me with -fschedule-insns, -frename-
> registers or
> -fselective-scheduling2 (all of which are disabled by default on x86-64
> -O2).
> Without those flags, second scheduler alone cannot lift the load due to
> dependency on %eax.
> 
> Hope that helps.

Thanks, I can reproduce it with trunk compiler but not 4.5.0. 
Do you know how alias set are represented and used now. It used to 
be each alias set is assigned a unique number and there won't 
be a dependence edge drawn between different alias set. It seems not
to be the case anymore. [2 *a_1(D)+0 S4 A32] The second field 
must play a role in disambiguate the memory access. 

BTW, why these two intermediate variables are both assigned to eax
without these non-default options? This example has no register pressure.
It looks like an issue with IRA. 


Cheers,
Bingfeng



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