[cfe-dev] Clangs equivalent to GCCs -Og flag?

[Xinliang David Li]

-fdump-passes? The dump result can be misleading. For instance, the post
ipa optimization is grouped under *all_optimization or *all_optimization_g
groups. With -Og, *all_optimization is off, but all the nested
optimizations that are turned on normally under opt level 1 is still marked
as 'ON' -- that is why you don't see many difference. The optimizations
included in *all_optimization_g group is a much smaller set.

The early optimization pipelines are very similar. WIth -Og, early SRA pass
is disabled.

David


On Fri, Jul 31, 2015 at 3:28 PM, Robinson, Paul <
Paul_Robinson at playstation.sony.com> wrote:

> I remember using gcc's "tell me what optimizations you ran" flag, which
> does something like print out the list of –f switches you would need to use
> to get the same effect as the optimization flags you actually provided.
> Comparing –O1 to –Og I saw only one difference. Hence my statement that
> gcc's –O1 and –Og are 99% equivalent.  It is a very black-box experiment
> but I think it's indicative. Or at least instructive.
>
> --paulr
>
>
>
> *From:* Xinliang David Li [mailto:xinliangli at gmail.com]
> *Sent:* Friday, July 31, 2015 11:49 AM
> *To:* Robinson, Paul
> *Cc:* David Blaikie; Dan Walmsley; cfe-dev Developers
>
> *Subject:* Re: [cfe-dev] Clangs equivalent to GCCs -Og flag?
>
>
>
>
>
>
>
> On Fri, Jul 31, 2015 at 7:27 AM, Robinson, Paul <
> Paul_Robinson at playstation.sony.com> wrote:
>
> People ask about this from time to time, but we've never done anything
> about it.
>
> One thing I noticed about GCC –Og is that it's 99% identical to their –O1.
>
>
>
> Not really. The optimization level is set to 1, but the pass pipeline
> setup is very different between O1 and Og.
>
>
>
> David
>
>
>
>
>
> I'd be curious about people's experience using Clang –O1 –g and whether
> that experience is somewhere close to reasonable.
>
> --paulr
>
>
>
> *From:* cfe-dev-bounces at cs.uiuc.edu [mailto:cfe-dev-bounces at cs.uiuc.edu] *On
> Behalf Of *David Blaikie
> *Sent:* Wednesday, July 29, 2015 10:13 AM
> *To:* Dan Walmsley; cfe-dev Developers
> *Subject:* Re: [cfe-dev] Clangs equivalent to GCCs -Og flag?
>
>
>
>
>
>
>
> On Wed, Jul 29, 2015 at 8:42 AM, Dan Walmsley <dan at walms.co.uk> wrote:
>
> Thanks,
>
>
>
>     Perhaps there might be some documentation somewhere that would give me
> an idea of which optimizations to enable individually?
>
>
> Not really - optimized debug info is still pretty lacking in Clang. Even
> the most common/basic optimizations (SROA, for example) are going to pretty
> heavily impact debuggability today.
>
> - Dave
>
>
>
>
> Dan
> ------------------------------
>
> Date: Wed, 29 Jul 2015 06:40:06 -0700
> Subject: Re: [cfe-dev] Clangs equivalent to GCCs -Og flag?
> From: dblaikie at gmail.com
> To: dan at walms.co.uk
> CC: cfe-dev at cs.uiuc.edu
>
>
>
>
> On Jul 29, 2015 3:23 AM, "Dan Walmsley" <dan at walms.co.uk> wrote:
> >
> > GCC has a debug level flag of -Og which enables all optimizers that
> won't degrade the debugging experience greatly.
> >
> > Does clang have an equivalent?
>
> No, clang had no equivalent at this time.
>
> >
> > Thanks in advance.
> >
> > Dan
> >
> > _______________________________________________
> > cfe-dev mailing list
> > cfe-dev at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
> >
>
>
>
>
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