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Re: Ping: PR25514: A problem with note distribution in combine
- From: Alan Modra <amodra at bigpond dot net dot au>
- To: gcc-patches at gcc dot gnu dot org, richard at codesourcery dot com
- Date: Thu, 11 May 2006 10:14:46 +0930
- Subject: Re: Ping: PR25514: A problem with note distribution in combine
- References: <87aca9br5r.fsf@talisman.home> <873bfidp24.fsf@talisman.home>
On Wed, May 10, 2006 at 01:47:31PM +0100, Richard Sandiford wrote:
> > Alan added the comment:
> >
> > /* You might think you could search back from FROM_INSN
> > rather than from I3, but combine tries to split invalid
> > combined instructions. This can result in the old I2
> > or I1 moving later in the insn sequence. */
If I remember correctly, I was seeing this sequence
i2
other insns
i3
being combined to
deleted
other insns
i2+i3
but i2+i3 was invalid so it was split to
deleted
other insns
i2
i3
A rather useless exercise on the part of combine but illustrates why a
from_insn pointing to the old i2 can't be used. (Perhaps there was an
i1 involved too, I can't remember.)
--
Alan Modra
IBM OzLabs - Linux Technology Centre