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Date: Thu, 05 Jul 2012 12:46:00 -0000
Message-ID: <CAFiYyc1OHhD7SOXB_D3RN0_zkEo3k39+vJDnBDEy-MuVnceGRA@mail.gmail.com>
Subject: Re: Tree tail merging breaks __builtin_unreachable optimization
From: Richard Guenther <richard.guenther@gmail.com>
To: Michael Matz <matz@suse.de>
Cc: Steven Bosscher <stevenb.gcc@gmail.com>, Ulrich Weigand <uweigand@de.ibm.com>, gcc-patches@gcc.gnu.org, 	tom@codesourcery.com
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On Thu, Jul 5, 2012 at 2:44 PM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Wed, 4 Jul 2012, Steven Bosscher wrote:
>
>> On Wed, Jul 4, 2012 at 7:02 PM, Ulrich Weigand <uweigand@de.ibm.com> wrote:
>> > Any suggestions how to fix this?  Should tail merging detect
>> > __builtin_unreachable and not merge such block?
>>
>> That seems to be the most straight-forward thing to do. I don't think
>> there are any other passes that do this kind of code merging.
>
> What do we gain by delaying to remove these blocks until RTL?  AFAICS not
> much if anything.  So removing those on the tree level would make more
> sense.

The gain is to derive assertions from the conditional guarding these blocks
and optimize using that knowledge.

Richard.

>
> Ciao,
> Michael.