Re: [PATCH] Don't bypass blocks with multiple latch edges (PR middle-end/54838)

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Nov 28, 2012 at 7:24 PM, Marek Polacek <polacek@redhat.com> wrote:
> On Wed, Nov 28, 2012 at 10:52:17AM +0100, Eric Botcazou wrote:
>> No, I don't think that's the problem.  The above messages are admittedly a bit
>> terse, they should say:
>>
>> JUMP-BYPASS: Proved reg 59 in jump_insn 15 equals constant (const_int 3 [0x3])
>>              when BB 4 is entered from BB 9.  Redirect edge 9->4 to 5.
>>
>> so you can have different constants for BB 3 and BB 9.  The patch to tweak the
>> dump messages along these lines is pre-approved.
>
> Ouch.  Okay, I'll post a separate patch for improving the message.
>
>> The ICE in merge_latch_edges means that the loop structure and the CFG aren't
>> in sync anymore.  Does the cprop pass modify the former without declaring it?
>
> I admit I'm not sure what to look at, maybe cprop should have in
> properties_destroyed PROP_loops?  Well, then we need to remove one
> assert in loop-init.c.  So something like:

Definitely not - that means to not preserve loops until after cprop.  The goal
is to preserve loops everywhere!

Richard.

> --- gcc/cprop.c.mp      2012-11-28 16:55:03.520375191 +0100
> +++ gcc/cprop.c 2012-11-28 16:55:35.992246623 +0100
> @@ -1927,7 +1927,7 @@ struct rtl_opt_pass pass_rtl_cprop =
>    TV_CPROP,                             /* tv_id */
>    PROP_cfglayout,                       /* properties_required */
>    0,                                    /* properties_provided */
> -  0,                                    /* properties_destroyed */
> +  PROP_loops,                           /* properties_destroyed */
>    0,                                    /* todo_flags_start */
>    TODO_df_finish | TODO_verify_rtl_sharing |
>    TODO_verify_flow | TODO_ggc_collect   /* todo_flags_finish */
> --- gcc/loop-init.c.mp  2012-11-28 16:55:08.924398879 +0100
> +++ gcc/loop-init.c     2012-11-28 16:55:17.684437276 +0100
> @@ -54,8 +54,6 @@ loop_optimizer_init (unsigned flags)
>      }
>    else
>      {
> -      gcc_assert (cfun->curr_properties & PROP_loops);
> -
>        /* Ensure that the dominators are computed, like flow_loops_find does.  */
>        calculate_dominance_info (CDI_DOMINATORS);
>
> This quashes the ICE.  I've regtested it, it caused one
> regression though:
> FAIL: gcc.dg/unroll_5.c scan-rtl-dump-times loop2_unroll "realistic
> bound: 2999999" 1
>
> But there probably is something else.
>
> Thanks for the review,
>
>         Marek