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Re: [PATCH GCC]Allow cfgcleanup to remove forwarder loop preheaders and latches
- From: "Bin.Cheng" <amker dot cheng at gmail dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: "bin.cheng" <bin dot cheng at arm dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Fri, 28 Feb 2014 09:45:06 +0800
- Subject: Re: [PATCH GCC]Allow cfgcleanup to remove forwarder loop preheaders and latches
- Authentication-results: sourceware.org; auth=none
- References: <001901cf31e8$2218ad50$664a07f0$ at arm dot com> <CAMe9rOqOh90HV-evw62XCc8FzvTEZmK51r4+8nQ-5fYDAaFaeA at mail dot gmail dot com>
Thanks for reporting this, I will look into it.
Thanks,
bin
On Fri, Feb 28, 2014 at 8:52 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Feb 24, 2014 at 9:12 PM, bin.cheng <bin.cheng@arm.com> wrote:
>> Hi,
>> This patch is to fix regression reported in PR60280 by removing forward loop
>> headers/latches in cfg cleanup if possible. Several tests are broken by
>> this change since cfg cleanup is shared by all optimizers. Some tests has
>> already been fixed by recent patches, I went through and fixed the others.
>> One case needs to be clarified is "gcc.dg/tree-prof/update-loopch.c". When
>> GCC removing a basic block, it checks profile information by calling
>> check_bb_profile after redirecting incoming edges of the bb. This certainly
>> results in warnings about invalid profile information and causes the case to
>> fail. I will send a patch to skip checking profile information for a
>> removing basic block in stage 1 if it sounds reasonable. For now I just
>> twisted the case itself.
>>
>> Bootstrap and tested on x86_64 and arm_a15.
>>
>> Is it OK?
>>
>>
>> 2014-02-25 Bin Cheng <bin.cheng@arm.com>
>>
>> PR target/60280
>> * tree-cfgcleanup.c (tree_forwarder_block_p): Protect loop
>> preheaders and latches only if requested. Fix latch if it
>> is removed.
>> * tree-ssa-dom.c (tree_ssa_dominator_optimize): Set
>> LOOPS_HAVE_PREHEADERS.
>>
>
> This change:
>
> if (dest->loop_father->header == dest)
> - return false;
> + {
> + if (loops_state_satisfies_p (LOOPS_HAVE_PREHEADERS)
> + && bb->loop_father->header != dest)
> + return false;
> +
> + if (loops_state_satisfies_p (LOOPS_HAVE_SIMPLE_LATCHES)
> + && bb->loop_father->header == dest)
> + return false;
> + }
> }
>
> miscompiled 435.gromacs in SPEC CPU 2006 on x32 with
>
> -O3 -funroll-loops -ffast-math -fwhole-program -flto=jobserver
> -fuse-linker-plugin
>
> This patch changes loops without LOOPS_HAVE_PREHEADERS
> nor LOOPS_HAVE_SIMPLE_LATCHES from returning false to returning
> true. I don't have a small testcase. But this patch:
>
> diff --git a/gcc/tree-cfgcleanup.c b/gcc/tree-cfgcleanup.c
> index b5c384b..2ba673c 100644
> --- a/gcc/tree-cfgcleanup.c
> +++ b/gcc/tree-cfgcleanup.c
> @@ -323,6 +323,10 @@ tree_forwarder_block_p (basic_block bb, bool phi_wanted)
> if (loops_state_satisfies_p (LOOPS_HAVE_SIMPLE_LATCHES)
> && bb->loop_father->header == dest)
> return false;
> +
> + if (!loops_state_satisfies_p (LOOPS_HAVE_PREHEADERS)
> + && !loops_state_satisfies_p (LOOPS_HAVE_SIMPLE_LATCHES))
> + return false;
> }
> }
>
> fixes the regression. Does it make any senses?
>
>
> --
> H.J.
--
Best Regards.