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Re: Postreload and STRICT_LOW_PART
- From: Richard Guenther <richard dot guenther at gmail dot com>
- To: Andreas Schwab <schwab at linux-m68k dot org>
- Cc: gcc at gcc dot gnu dot org
- Date: Sun, 20 Sep 2009 18:31:23 +0200
- Subject: Re: Postreload and STRICT_LOW_PART
- References: <m27hvtbnrf.fsf@igel.home>
On Sun, Sep 20, 2009 at 6:10 PM, Andreas Schwab <schwab@linux-m68k.org> wrote:
> Why is postreload converting (set (REGX) (CONST_INT A)) ... (set (REGX)
> (CONST_INT B)) into (set (STRICT_LOW_PART (REGX)) (CONST_INT B))? ?That
> looks like a pessimisation especially if the constants are small, since
> STRICT_LOW_PART must not touch the high part. ?Is there a way for the
> backend to stop postreload from doing this if the constants are in some
> range? ?On the m68k, loading a constant in the range -128..127 in SI
> mode is better than loading it in strict QI mode.
It's probably an omission of a check if A & ~GET_MODE_MASK (narrow_mode)
is equal to zero. And of course a cost check is completely missing.
Richard.
> Andreas.
>
> --
> Andreas Schwab, schwab@linux-m68k.org
> GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 ?01D3 44D5 214B 8276 4ED5
> "And now for something completely different."
>