[PATCH] Unswitching outer loops.

[Yuri Rumyantsev]

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?

ChangeLog:
2015-07-10  Yuri Rumyantsev  <ysrum...@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.

patch.3
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