🚀 go-pugleaf

In article <6071@mimsy.UUCP>, chris@mimsy.UUCP (Chris Torek) writes:

> The proper way to speed strcpy() on a MicroVAX-II is no doubt to
> use the following assembly code:
> 
> 	_strcpy:.globl	_strcpy
> 		.word	0		# save no registers
> 		movq	4(ap),r1	# get s1 and s2 into r1 and r2
> 		movl	r1,r0		# save s1
> 	1:	movb	(r2)+,(r1)+	# *s1++ = *s2++
> 		bneq	1b		# loop until a zero is moved
> 		ret			# return original s1 in r0
> 
> Note that this is remarkably similar to the compiler's output
> for the original code, modified to have the proper return value:

> All one can improve on the locc-poor MicroVAX-II is the register
> usage and the parameter grabbing.  (c2, at least from 32V to 4.3BSD,
> will never turn two `movl's into a `movq'.  Ah well.)

Replacing your loop with:

	1:	movb	(r2)+,(r1)+
		bequ	2f
		movb	(r2)+,(r1)+
		bneq	1b
	2:

will almost certainly speed things up (say 15%). I haven't actually
tried it, but I've tried entirely analogous cases. Loop unrolling can
produce speed-up even when the instruction count is unchanged, if
taken branches are replaced by untaken branches. 

    Radford Neal