From: Richard Biener <richard.guenther@gmail.com>
To: Jeff Law <law@redhat.com>
Cc: Andreas Schwab <schwab@linux-m68k.org>,
GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH][PR tree-optimization/67892] Use FSM threader to handle backedges
Date: Mon, 02 Nov 2015 09:43:00 -0000 [thread overview]
Message-ID: <CAFiYyc14DKh9KKGS6X1iSqDi=naCkeFQzYSp9-g36SMwnAP4Aw@mail.gmail.com> (raw)
In-Reply-To: <5633D2B6.4080201@redhat.com>
On Fri, Oct 30, 2015 at 9:27 PM, Jeff Law <law@redhat.com> wrote:
> On 10/30/2015 07:57 AM, Andreas Schwab wrote:
>>
>> I'm getting this regression on m68k:
>>
>> FAIL: gcc.dg/tree-ssa/ssa-thread-11.c scan-tree-dump vrp2 "FSM"
>>
>> The generated code looks equivalent, though.
>
> Definitely an artifact of differences in branch costing. Pondering the best
> way to fix.
The usual list of targets and a dg-skip ...
Or work towards eliminating those "early" target dependences
introduced in our IL.
Major effects are from LOGICAL_OP_NON_SHORT_CIRCUIT (boiling down to
BRANCH_COST as default) and from PUSH_ARGS_REVERSED. Esp. the
logical-op-non-short-circuit decisions are done a bit early (before
profile-reading
for example). So I'd rather keep the short-circuiting for all targets (for the
GENERIC folding) and let ifcombine do the "heavy" lifting also taking
into account
branch predictability (and target preferences).
Richard.
> jeff
prev parent reply other threads:[~2015-11-02 9:43 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-29 16:20 Jeff Law
2015-10-30 14:08 ` Andreas Schwab
2015-10-30 14:34 ` Jeff Law
2015-10-30 17:56 ` Jeff Law
2015-10-30 20:20 ` Jeff Law
2015-10-30 20:45 ` Jeff Law
2015-11-02 9:43 ` Richard Biener [this message]
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