Re: [PATCH] testsuite: xfail scev-[35].c on ia32

[Richard Biener <rguenther@suse.de>]

On Wed, 8 Nov 2023, Alexandre Oliva wrote:

> 
> These gimplefe tests never got the desired optimization on ia32, but
> they only started visibly failing when the representation of MEMs in
> dumps changed from printing 'symbol: a' to '&a'.
> 
> The transformation is not considered profitable on ia32, that's why it
> doesn't take place.  Maybe that's a bug in itself, but it's not a
> regression, and not something to be noisy about.
> 
> Regstrapped on x86_64-linux-gnu, also tested with gcc-13 on i686- and
> x86_64-.  Ok to install?

OK.

> (Richi, is the non-optimization choice on ia32 something unexpected that
> ought to be looked into?  I could file a PR, and maybe even look into it
> a bit further.)

There might be even a PR already.  The testcase expects that IVOPTs
chooses an IV that satisfies both

 a_p = &a[i_12];

and

 *&a[i_12] = 100;

basically code-generating a LEA, a store of the address and an
register indirect memory access.  That's what happens for 64bit
(and presumably on all other archs).  For some reason (I can only
guess costing), on ia32 we choose to prioritize using a single
induction variable (we need the original GIV for the exit test)
and so we get an obfuscated LEA for the address store and a
base with scaled index access for the store.

Note the testcase is a bit "bad" because we later sink the store
to a_p, so the generated assembly for the ia32 looks actually better.

Richard.


> 
> for  gcc/testsuite/ChangeLog
> 
> 	* gcc.dg/tree-ssa/scev-3.c: xfail on ia32.
> 	* gcc.dg/tree-ssa/scev-5.c: Likewise.
> 
> Issue: gcc#155
> TN: W517-007
> ---
>  gcc/testsuite/gcc.dg/tree-ssa/scev-3.c |    2 +-
>  gcc/testsuite/gcc.dg/tree-ssa/scev-5.c |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/scev-3.c b/gcc/testsuite/gcc.dg/tree-ssa/scev-3.c
> index 4babd33f5c062..ac8c8d4519e30 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/scev-3.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/scev-3.c
> @@ -40,4 +40,4 @@ __BB(6):
>  
>  }
>  
> -/* { dg-final { scan-tree-dump-times "&a" 1 "ivopts" } } */
> +/* { dg-final { scan-tree-dump-times "&a" 1 "ivopts" { xfail ia32 } } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/scev-5.c b/gcc/testsuite/gcc.dg/tree-ssa/scev-5.c
> index c2feebdfc2489..c911a9298866f 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/scev-5.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/scev-5.c
> @@ -40,4 +40,4 @@ __BB(6):
>  
>  }
>  
> -/* { dg-final { scan-tree-dump-times "&a" 1 "ivopts" } } */
> +/* { dg-final { scan-tree-dump-times "&a" 1 "ivopts" { xfail ia32 } } } */
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)