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Re: [PATCH, LRA] Remove REG_DEAD and REG_UNUSED notes.
- From: Vladimir Makarov <vmakarov at redhat dot com>
- To: Mike Stump <mikestump at comcast dot net>
- Cc: Steven Bosscher <stevenb dot gcc at gmail dot com>, Eric Botcazou <ebotcazou at adacore dot com>, Yvan Roux <yvan dot roux at linaro dot org>, GCC Patches <gcc-patches at gcc dot gnu dot org>, Patch Tracking <patches at linaro dot org>
- Date: Wed, 25 Sep 2013 10:55:31 -0400
- Subject: Re: [PATCH, LRA] Remove REG_DEAD and REG_UNUSED notes.
- Authentication-results: sourceware.org; auth=none
- References: <CAD57uCdOYQAkj+M3pVncqNpadeBFrxqn=yuRETHJ=Uy_GBoYow at mail dot gmail dot com> <4163413 dot 18cp2JSUdS at polaris> <CABu31nN2wF3R=DAf2dP9CS7prkrLtGeQw_yvU3VF--4AP5e1=A at mail dot gmail dot com> <BA43ED5C-BFB0-4A66-9117-4B60B19F86A1 at comcast dot net>
On 09/24/2013 03:40 PM, Mike Stump wrote:
> On Sep 24, 2013, at 12:23 PM, Steven Bosscher <firstname.lastname@example.org> wrote:
>> On Tue, Sep 24, 2013 at 5:03 PM, Eric Botcazou wrote:
>>>> This patch removes REG_DEAD and REG_UNUSED notes
>>> DF framework is supposed to do it for you.
>> Unfortunately LRA uses its own DF framework.
I'd say fortunately. Otherwise, LRA would decrease whole compiler speed
by upto 10%. I can say it because of the first version of LRA was based
on DF framework.
I guess that was one reason why reload was never moved to DF too.
LRA/reload is the most live analysis intensive passes (too many changes
on several sub-passes).
LRA uses also REG notes internally and recreates them several time as a
by-product of pseudo live-range analysis used for (reload) pseudo
I'd be glad if we move to DF without compilation time degradation.
I already wrote that DF-design (although it has a nice API which is good
for prototyping) has a bad design with resource usage point of view.
Keeping a lot of duplicated info by RTL side increases memory footprint
very much, worsens data locality, and slows down the compiler. As I
remember correctly, GCC steering committing permitted 5% compiler time
degradation as a criterium to include it into the trunk and DF achieved
this with difficulties.
> Is that a bug, or a feature?