more on C optimization

[chris at umcp-cs.UUCP]

All right, how come no one has replied yet???  I posted something
a while ago about something /lib/c2 did that was "neat", namely,
change

	movl	$7,r11
	...
	bicl3	$-256,r11,r1

into

	movl	$7,r11
	...
	extzv	$0,r11,r11,r1	# look closely now

(instead of "extzv $0,$7,r11,r1").  If you just think for a minute,
the "extzv" is unnecessary in the first place!  If c2 does limited
flow analysis to watch over register contents, how come it doesn't
eliminate instructions that are effectively no-ops?  (That's a
rhetorical question, by the way.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci
UUCP:	{seismo,allegra,brl-bmd}!umcp-cs!chris
CSNet:	chris at umcp-cs		ARPA:	chris.umcp-cs at CSNet-Relay