Re: [PATCH] Unswitching outer loops.

[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.