On Tue, Oct 28, 2014 at 5:22 AM, Yangfei (Felix) <felix.yang@huawei.com> wrote:
> Hi Sterling,
>   How do you think about this issue?
>   As c6x/bfin port handles this the same way, is it OK for the patch to be applied?
>   Thanks.

I have committed this patch as attached. I made a couple of minor
cleanups, plus some small fixes to the ChangeLog entry.

The new code generated is better than the old code, but I'm not
particularly happy with the result. In particular, it is way too
conservative around spilling the trip count, and it still maintains
the trip count inside the loop, in spite of the trip count being dead
at that point. It won't always be dead, but when it is, it should be
eliminated.

So there is quite a bit of performance that could still be gained here.

Thanks for the patch Felix.

Sterling

2014-10-10  Felix Yang  <felix.yang@huawei.com>

    * config/xtensa/xtensa.h (TARGET_LOOPS): New Macro.
    * config/xtensa/xtensa.c: Include dumpfile.h and hw-doloop.h.
    (xtensa_reorg, xtensa_reorg_loops): New.
    (xtensa_can_use_doloop_p, xtensa_invalid_within_doloop): New.
    (hwloop_optimize, hwloop_fail, hwloop_pattern_reg): New.
    (xtensa_emit_loop_end): Emit the zero-overhead loop end label.
    (xtensa_doloop_hooks): Define.
    * config/xtensa/xtensa.md (doloop_end, loop_end): New
    (zero_cost_loop_start): Rewritten.
    (zero_cost_loop_end): Likewise.