The two instructions were generated by an IBM software product. The code
doesn't
use the extra 120 bytes of spaces used to initialize the COBOL string
field. So I
think it would hurt if every "move space to ..." will define an additional
number
of spaces.
Tobias
P.S. the move would be MVC 254(120,3),=120c' '
Am 07.08.2009, 23:31 Uhr, schrieb Bill Fairchild <[email protected]>:
It certainly can't hurt to change the MVI/MVC to a single instruction:
MVC 254(3,120),=120c' '
And, if possible, align the 120c' ' on at least a double word boundary.
Bill Fairchild
Software Developer
Rocket Software
275 Grove Street * Newton, MA 02466-2272 * USA
Tel: +1.617.614.4503 * Mobile: +1.508.341.1715
Email: [email protected]
Web: www.rocketsoftware.com
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On
Behalf Of Farley, Peter x23353
Sent: Friday, August 07, 2009 2:50 PM
To: [email protected]
Subject: z10 and overlapping/destructive moves
I am in the midst of a CPU optimization exercise for a COBOL program and
ran across the following code sequence generated by the compiler:
MVI 254(3),X'40'
MVC 255(119,3),254(3)
This code is generated in response to a simple COBOL "MOVE SPACES TO
variable" instruction, where the variable is 120 bytes long.
Did I or did I not see some discussion here or perhaps in a SHARE
presentation that on a z10 machine overlapping/destructive moves wreck
the pipeline and take *much* longer to execute as a result? Or am I
imagining that?
The reason I ask is that Strobe highlights this place in the code as a
high-usage point, and I am struggling to understand why.
TIA for any info you can provide.
Peter
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