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Re: df.c and partial writes/REG_EQUAL notes
- To: law at redhat dot com
- Subject: Re: df.c and partial writes/REG_EQUAL notes
- From: Richard Henderson <rth at redhat dot com>
- Date: Wed, 24 Oct 2001 13:00:19 -0700
- Cc: Jan Hubicka <jh at suse dot cz>, gcc at gcc dot gnu dot org, m dot hayes at elec dot canterbury dot ac dot nz, matzmich at cs dot tu-berlin dot de, dan at cgsoftware dot com
- References: <20010925161602.C13734@atrey.karlin.mff.cuni.cz> <3257.1003952277@localhost.localdomain>
On Wed, Oct 24, 2001 at 01:37:57PM -0600, law@redhat.com wrote:
> Right. Review the movxx section in the Machine Descriptions part of the
> manual. Quoting:
[...]
> If operand 0 is a @code{subreg} with mode @var{m} of a register whose
> own mode is wider than @var{m}, the effect of this instruction is
> to store the specified value in the part of the register that corresponds
> to mode @var{m}. The effect on the rest of the register is undefined.
>
> Based on that I believe there should be no dependency since insn #2
> leaves the rest of the DI register undefined.
The documentation is incomplete. The rest of the register up to
BITS_PER_WORD are undefined. Other words of a multi-word pseudo
are no undefined.
r~