strict_low_part question

[Richard Henderson]

On Mon, May 05, 2003 at 07:02:18PM +0200, Falk Hueffner wrote:
> I'm playing with a byteswap builtin, and I would like to expand
> bswap:SI in optabs.c to 3 rotations (rotate low 16 bits by 8, rotate
> 32 bits by 16, rotate low 16 bits by 8; that should give optimal code
> on m68k and i386). However, the rotations of the low bits need to
> leave the high bits unchanged, and I can't seem to be able to emit RTL
> that does this. Can I use strict_low_part somehow? Or do I need iors
> etc? Any hints appreciated...

Yes,

	(set (strict_low_part (subreg:HI (reg:SI x) 0))
	     (rot:HI (subreg:HI (reg:SI x) 0)
		     (const_int 16)))

should describe exactly what you want.

Though I do suggest that you not expose this before reload.


r~