[PATCH] Fix Fortran DO loop fallback

[Martin Liška]

On 07/12/2016 12:14 PM, Richard Biener wrote:
> On Mon, Jul 11, 2016 at 4:44 PM, Jeff Law <law@redhat.com> wrote:
>> On 07/08/2016 08:26 AM, Martin Liška wrote:
>>>
>>> Hello
>>>
>>> Following patch fixes fallout caused by the patch set:
>>> https://gcc.gnu.org/ml/gcc-regression/2016-07/msg00097.html
>>>
>>> Ready after it finished regression tests?
>>> Thanks,
>>> Martin
>>>
>>>
>>> 0001-Fix-Fortran-DO-loop-fallback.patch
>>>
>>>
>>> From c5dd7ad62f795cce560c7f1bb8767b7ed9298d8a Mon Sep 17 00:00:00 2001
>>> From: marxin <mliska@suse.cz>
>>> Date: Fri, 8 Jul 2016 15:51:54 +0200
>>> Subject: [PATCH] Fix Fortran DO loop fallback
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>> 2016-07-08  Martin Liska  <mliska@suse.cz>
>>>
>>>         * gfortran.dg/ldist-1.f90: Update expected dump scan.
>>>         * gfortran.dg/pr42108.f90: Likewise.
>>>         * gfortran.dg/vect/pr62283.f: Likewise.
>>
>> Shouldn't ldist-1.f90 be scan-tree-dump-not?  It seems like you change it
>> from that just last week, but it wasn't mentioned in the ChangeLog.
> 
> gfortran.dg/pr42108.f90 also looks pointless now?  I suppose there is nothing
> to hoist after the change?  Do we now have an option to revert back to old
> behavior?  If so it would be better to use that flag here.

No, there's no option. So, as the test-case now looks pointless, should I mark it
with xfail now?

> 
> diff --git a/gcc/testsuite/gfortran.dg/vect/pr62283.f
> b/gcc/testsuite/gfortran.dg/vect/pr62283.f
> index 7df3d99..2933f51 100644
> --- a/gcc/testsuite/gfortran.dg/vect/pr62283.f
> +++ b/gcc/testsuite/gfortran.dg/vect/pr62283.f
> @@ -13,4 +13,4 @@ C { dg-additional-options "-fvect-cost-model=dynamic" }
>        beta=3.141593
>        y=y+beta*x
>        end
> -C { dg-final { scan-tree-dump-times "vectorized 1 loops" 2 "vect" {
> target { vect_hw_misalign } } } }
> +C { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { target {
> vect_hw_misalign } } } }
> 
> so why do we no longer vectorize 1 loops in two functions?  The
> testcase works for me
> unchanged.

Yeah, it works on -m64, however as we're able to merge the functions with -m32 (-fipa-icf),
then I recommend to disable ICF for the test-case.

Reason why the pair of functions on x86_64 is that:

test3 (real(kind=4)[4] * restrict x, real(kind=4)[4] * restrict y)
{
  <bb 2>:

  <bb 3>:
  # S.0_6 = PHI <1(2), S.0_12(4)>
  if (S.0_6 > 4)
    goto <bb 5>;
  else
    goto <bb 4>;
...

test2 (real(kind=4)[4] * restrict x, real(kind=4)[4] * restrict y)
{
  integer(kind=4) i;

  <bb 2>:

  <bb 3>:
  # i_6 = PHI <1(2), i_12(4)>
...

On x86_64 types of 'S.0_6' and 'i' are not compatible. As I've just read tree dump files,
  # S.0_6 = PHI <1(2), S.0_12(4)>
  if (S.0_6 > 4)

is optimized out by VRP, which runs after IPA ICF.

I'll send patch right after we'll agree on pr42108.f90.

Thanks,
Martin

> 
> Richard.
> 
>> OK with that change.
>>
>> jeff
>>
>>