Aucbvax.6972
fa.info-vax
utzoo!decvax!ucbvax!info-vax
Wed Apr 28 12:01:45 1982
VAX Timing Question
>From PRJohnson@MIT-XX Wed Apr 28 11:39:15 1982
Does anyone know why the first of the two following code sequences
is slower on both the 780 and the 750?

Sequence 1:
	addl3	r1,r1,r3
	movw	r1,r3
	bicl2	$0x10000,r3
	addl3	r2,r2,r4
	movw	r2,r4
	bicl2	$0x10000,r4

Sequence 2 (a shuffle of sequence 1):
	addl3	r1,r1,r3
	addl3	r2,r2,r4
	movw	r1,r3
	movw	r2,r4
	bicl2	$0x10000,r3
	bicl2	$0x10000,r4

Do the Vaxes pipeline???

The percentage difference is not much on the 780 (about 1.5%
speed up), but is larger on the 750 (about 3.5%).  Note that the
differences still exist if the code sequences are long word
aligned, and have NOPs inserted to align all the listed
instructions (i.e.: a NOP after each MOVW and each BICL2).

Thanks for any insights.

---Paul Johnson
-------

-----------------------------------------------------------------
 gopher://quux.org/ conversion by John Goerzen <jgoerzen@complete.org>
 of http://communication.ucsd.edu/A-News/


This Usenet Oldnews Archive
article may be copied and distributed freely, provided:

1. There is no money collected for the text(s) of the articles.

2. The following notice remains appended to each copy:

The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 
 Bruce Jones, Henry Spencer, David Wiseman.