Optimizing COBOL generated assembler
Consider the cobol statements:
000034 02 R-CNTR PIC S99 COMP SYNC VALUE +0.
...
0000072 ADD 1 to R-CNTR
Which generated the following assembler code:
000620 4830 A012 LH 3,18(0,10) PGMLIT AT
+6
000624 4A30 9028 AH 3,40(0,9) R-CNTR
000628 1823 LR 2,3
00062A 8E20 0020 SRDA 2,32(0)
00062E 5D20 C000 D 2,0(0,12) SYSLIT AT
+0
000632 4020 9028 STH 2,40(0,9) R-CNTR
This snippet of code is from the following COBOL/370 generated assembler
LIST option:
http://www.cs.niu.edu/~t90jfl1/class/job2.htm
I think the LR, SRDA, and D instructions could be surpressed by specifying the
option NOTRUNC to allow values greater than the PIC digits 99.
With the new z10 instruction ADD LOGICAL WITH SIGNED IMMEDIATE, the
entire 6 instruction sequence could be reduced to a single instruction:
ALSI R-CNTR,1
Of course this would require that the COBOL compile have such a z10
optimization option. For compute intensive applications, such optimizations
along with the new z10 compare and branch instructions could be significant.
To aid in analyzing mainframe COBOL programs a new z390 COBOL Portable
Assembler option has been added in z390 PTF v1.4.01b. With this option
installed, you can convert Enterprise COBOL or COBOL for OS/390 generated
assembler listings into z390 assembler source programs which can be
assembled, linked, and executed specifying starting and ending line numbers in
order to unit test or benchmark specific generated code or supported COBOL
statments with called functions. In this initial release only DISPLAY and STOP
RUN function calls are supported, but requests for additional functions are
welcome. Support for COBOL/370, COBOL for MVS, and VS COBOL II are also
in development. For example generation and execution of DISPLAY and STOP
RUN demo, install z390 v1.4.01, v1.4.01b PTF, and then enter the command
cobol\paos\OSDEMO1.
Don Higgins
[EMAIL PROTECTED]
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