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Re: [patch] h8300.md: Optimize one case of zero_extract.
- From: Hans-Peter Nilsson <hp at bitrange dot com>
- To: Kazu Hirata <kazu at cs dot umass dot edu>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Mon, 3 Mar 2003 08:28:44 -0500 (EST)
- Subject: Re: [patch] h8300.md: Optimize one case of zero_extract.
On Mon, 3 Mar 2003, Kazu Hirata wrote:
> but this can be optimized to
>
> sub.l er0,er0
> mov.b r3h,r0l
>
> if X and Y are different registers.
For reference, this is usually done through constraints.
Simple usage example:
..._operand:SI 0 "r,r"
..._operand:SI 1 "?0,r"
...
"@
same
different"
Shorter than C and IMHO less error-prone. The "?" is to make
GCC penalize that alternative a bit (not prefer it over the
other case due to the order), since the same-register
alternative IIUC would be more costly in this particular case.
brgds, H-P