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From: Zdenek Dvorak <rakdver@kam.mff.cuni.cz>
To: Steven Bosscher <stevenb.gcc@gmail.com>
Cc: Alain Ketterlin <alain.ketterlin@gmail.com>, gcc@gcc.gnu.org
Subject: Re: Irreducible loops in generated code
Date: Fri, 20 Aug 2010 00:11:00 -0000	[thread overview]
Message-ID: <20100819232827.GA19049@kam.mff.cuni.cz> (raw)
In-Reply-To: <AANLkTikQTXv5=Fs05zYBCC=ASX9aRoqGDqkWh8_z62=6@mail.gmail.com>

Hi,

> > I'm working on decompiling x86-64 binary programs, using branches to rebuild
> > a control-flow graph and looking for loops. I've found a significant number
> > of irreducible loops in gcc-produced code (irreducible loops are loops with
> > more than one entry point), especially in -O3 optimized binaries, even when
> > the source code is "well" structured. My experiments are done mainly on the
> > SPEC CPU-2006 benchmarks.
> >
> > My question is: where do these irreducible loops come from? Which
> > optimization pass leads to irreducible regions? Thanks in advance for any
> > pointer.
> 
> Questions right back at you: What compiler version are you using? Got
> a specific exampe (test case)?
> 
> In older releases of GCC4, jump threading sometimes resulted in
> irreducible regions, but more recent GCCs carefully try to avoid them.

I am not sure that is actually true.  Afaik, we only avoid this on gimple,
while rtl jump threading does not care,

Zdenek

      parent reply	other threads:[~2010-08-19 23:28 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-08-18 13:06 Alain Ketterlin
2010-08-18 13:11 ` Steven Bosscher
2010-08-18 16:51   ` Alain Ketterlin
2010-08-20  0:11   ` Zdenek Dvorak [this message]

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