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Re: [PATCH] Don't bypass blocks with multiple latch edges (PR middle-end/54838)
- From: Marek Polacek <polacek at redhat dot com>
- To: Eric Botcazou <ebotcazou at adacore dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Wed, 28 Nov 2012 19:24:57 +0100
- Subject: Re: [PATCH] Don't bypass blocks with multiple latch edges (PR middle-end/54838)
- References: <20121126142843.GH17362@redhat.com> <1544820.Re9E01eJrW@polaris>
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:
--- 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)
- gcc_assert (cfun->curr_properties & PROP_loops);
/* Ensure that the dominators are computed, like flow_loops_find does. */
This quashes the ICE. I've regtested it, it caused one
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,