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Re: A question about UNSPEC expression and register allocation
- From: Paul Brook <paul at codesourcery dot com>
- To: gcc at gcc dot gnu dot org
- Cc: "Mohamed Shafi" <shafitvm at gmail dot com>
- Date: Sun, 18 May 2008 01:30:35 +0100
- Subject: Re: A question about UNSPEC expression and register allocation
- References: <ba0bd44d0805162310s2a0d4340qa03b4d84dba9b0d1@mail.gmail.com>
On Saturday 17 May 2008, Mohamed Shafi wrote:
> Hello all,
>
> Recently i noticed that register allocation for the operands in a
> unspec pattern was going wrong.
> This was because there was no conflict between the registers used in
> the unspec pattern and the other registers which should have been
> there.
> During debugging i found out that the code is written in such a way
> that it doesn't consider registers used inside an unspec expression.
> So i rewrote the patten so that the unspec is in the source rather
> than in the destination of the pattern. That solved the issue. But is
> this expected?
> Will the allocation also go wrong for the source operands if they
> contain registers inside an unpsec expression? I still haven't
> encountered this.
Registers in an unspec are no different to registers used anywhere else.
All the normal rues about overallping operands, early clobbers, etc. apply.
Paul