Re: [PATCH] Unswitching outer loops.

[Yuri Rumyantsev <ysrumyan at gmail dot com>]

Hi Richard,

I checked that both test-cases from 23855 are sucessfully unswitched
by proposed patch. I understand that it does not catch deeper loop
nest as
   for (i=0; i<10; i++)
     for (j=0;j<n;j++)
        for (k=0;k<20;k++)
  ...
but duplication of middle-loop does not look reasonable.

Here is dump for your second test-case:

void foo(int *ie, int *je, double *x)
{
  int i, j;
  for (j=0; j<*je; ++j)
    for (i=0; i<*ie; ++i)
      x[i+j] = 0.0;
}
grep -i unswitch t6.c.119t.unswitch
;; Unswitching outer loop

Yuri.

2015-07-14 14:06 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
> On Fri, Jul 10, 2015 at 12:02 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>> Hi All,
>>
>> Here is presented simple transformation which tries to hoist out of
>> outer-loop a check on zero trip count for inner-loop. This is very
>> restricted transformation since it accepts outer-loops with very
>> simple cfg, as for example:
>>     acc = 0;
>>    for (i = 1; i <= m; i++) {
>>       for (j = 0; j < n; j++)
>>          if (l[j] == i) { v[j] = acc; acc++; };
>>       acc <<= 1;
>>    }
>>
>> Note that degenerative outer loop (without inner loop) will be
>> completely deleted as dead code.
>> The main goal of this transformation was to convert outer-loop to form
>> accepted by outer-loop vectorization (such test-case is also included
>> to patch).
>>
>> Bootstrap and regression testing did not show any new failures.
>>
>> Is it OK for trunk?
>
> I think this is
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=23855
>
> as well.  It has a patch adding a invariant loop guard hoisting
> phase to loop-header copying.  Yeah, it needs updating to
> trunk again I suppose.  It's always non-stage1 when I come
> back to that patch.
>
> Your patch seems to be very specific and only handles outer
> loops of innermost loops.
>
> Richard.
>
>> ChangeLog:
>> 2015-07-10  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>
>> * tree-ssa-loop-unswitch.c: Include "tree-cfgcleanup.h" and
>> "gimple-iterator.h", add prototype for tree_unswitch_outer_loop.
>> (tree_ssa_unswitch_loops): Add invoke of tree_unswitch_outer_loop.
>> (tree_unswitch_outer_loop): New function.
>>
>> gcc/testsuite/ChangeLog:
>> * gcc.dg/tree-ssa/unswitch-outer-loop-1.c: New test.
>> * gcc.dg/vect/vect-outer-simd-3.c: New test.