A respectful correction, Brian.
On 4/20/2012 4:50 AM, Brian Leach wrote:
it's all the same to the compiler.
-----Original Message-----
BEGIN CASE
CASE A = "TEST"; GOSUB DO.SOMETHING
CASE 1; GOSUB DO.SOMETHING.ELSE
END CASE
versus this
IF A = "TEST" THEN GOSUB DO.SOMETHING ELSE GOSUB DO.SOMETHING.ELSE
-----
Since we seem to be finding every nit in the bottom of this empty
barrel, here's one more.
There are 2 compiler difference as shown by VLIST (UV10.2):
00001: BEGIN CASE
00002: CASE A = "TEST"; GOSUB DO.SOMETHING
00002 00000 : 06E eq A "TEST" => $R0
00002 00008 : 2DE testfw $R0 00020:
00002 00010 : 0A4 gosub 00060:
00003: CASE 1; GOSUB DO.SOMETHING.ELSE
00003 00018 : 0C2 jump 00038:
00003 00020 : 2DE testfw 1 00038: <-------------- Extra
worthless test
00003 00028 : 0A4 gosub 00062:
00004: END CASE
00004 00030 : 0C2 jump 00038: <-------------- Extra worthless
jump (to next line)
(Source lineup is goofy. This jump is really part
of source line 3. RAID is confusing, too.
A
discussion for a different thread.)
00005: IF A = "TEST" THEN GOSUB DO.SOMETHING ELSE GOSUB DO.SOMETHING.ELSE
00005 00038 : 06E eq A "TEST" => $R0
00005 00040 : 2DE testfw $R0 00058:
00005 00048 : 0A4 gosub 00060:
00005 00050 : 0C2 jump 00060:
00005 00058 : 0A4 gosub 00062:
00006: STOP
00006 00060 : 190 stop
With the speed of today's machines it would be hard to find a place
where that performance makes a difference.
Rocket could theoretically clean up both (or either independently) if
the compiler was smart enough:
1. to know that a logical test outcome was predestined at compile time
(It already does that sort of thing in other situations.). Then it
could compile only 1 of the 2 paths the testfw takes. (e.g. 0020x).
Same for IF, WHILE, or UNTIL constructs.
2. To recognize the final CASE before the END CASE never needs to jump
(e.g., 0030x).
I wonder if we've already wasted more electrical & biological energy by
me writing this email, dispersing it around the globe, and you reading
it, than all the machine cycles wasted executing the 2 worthless tests
in all the object scattered around the universe that Rocket could
theoretically optimize.
cds
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