PH07068: ARCH(12) programs may exhibit poor performance if many decimal overflows in environments where overflow is enabled

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Code generated by the compiler at ARCH(12) (ie. targeting the
  z14) using the new vector packed decimal instructions is
  truncating numbers for assignment to smaller data items in a way
  that's generating more overflows than code used at lower ARCH()
  levels.
  
  If the COBOL code does a lot of such truncations and is running
  in an environment where overflow is enabled, for example in a
  enclave that also uses C/C++, the CPU cost of ignoring the
  overflows can lead to poorer performance.
  

Local fix

• Compile at ARCH(11).
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: Users of Enterprise COBOL V6.2 compiling     *
  *                 programs at ARCH(12) for use in an           *
  *                 application with other programming           *
  *                 languages, that move data from PACKED-       *
  *                 DECIMAL to USAGE DISPLAY data items where    *
  *                 the sender has more digits than the          *
  *                 receiver or that contain COMPUTE statements  *
  *                 with PACKED-DECIMAL and USAGE DISPLAY        *
  *                 senders and unsigned PACKED-DECIMAL or       *
  *                 USAGE-DISPLAY receivers where the senders or *
  *                 intermediate results have more digits than   *
  *                 the receiver.                                *
  ****************************************************************
  * PROBLEM DESCRIPTION: Performance may be lower than expected  *
  ****************************************************************
  * RECOMMENDATION: Apply the provided PTF.                      *
  ****************************************************************
  z14/ARCH(12) introduce instructions that can perform packed
  arithmetic in registers instead of in memory. One of these
  instructions, VPSOP, can be used to truncate. The optimizer was
  using this instruction to truncate earlier than was strictly
  necessary, because the optimizer is designed to keep
  intermediate results as small as possible. The new instruction
  causes an overflow exception when truncating. In a pure COBOL
  application, this is fine, because the hardware is set to
  suppress overflow exceptions. In a mixed-language application,
  other languages may instruct the hardware to allow the overflow
  instruction. This causes no behaviour change in COBOL, because
  the COBOL runtime detects that the exception happened in a
  COBOL program and suppresses the exception, but this extra work
  causes a performance degradation.
  

Problem conclusion

• The compiler was fixed to avoid truncating with a VPSOP if the
  truncation could be done in a subsequent instruction without
  triggering an overflow exception.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Modules/Macros

• IGY8RWTU IGYCASMB IGYCCBE  IGYCCCRT IGYCCICS IGYCCSRV IGYCDGEN
  IGYCDIAG IGYCDMAP IGYCEN$0 IGYCEN$1 IGYCEN$2 IGYCEN$3 IGYCEN$4
  IGYCEN$5 IGYCEN$8 IGYCEN$D IGYCEN$R IGYCFGEN IGYCFREE IGYCINIT
  IGYCJA$0 IGYCJA$1 IGYCJA$2 IGYCJA$3 IGYCJA$4 IGYCJA$5 IGYCJA$8
  IGYCJA$D IGYCJA$R IGYCLIBH IGYCLIBO IGYCLIBR IGYCLSTR IGYCLVL0
  IGYCLVL1 IGYCLVL2 IGYCLVL3 IGYCLVL8 IGYCMALL IGYCOB2  IGYCOB2E
  IGYCOPI  IGYCOPT  IGYCOSCN IGYCPGEN IGYCRCTL IGYCRDPR IGYCRDSC
  IGYCREAL IGYCRWT  IGYCSCAN IGYCSIMD IGYCUE$0 IGYCUE$1 IGYCUE$2
  IGYCUE$3 IGYCUE$4 IGYCUE$5 IGYCUE$8 IGYCUE$D IGYCUE$R IGYCXREF
  IGYDRV   IGYEQCWI IGYMSGE  IGYMSGK  IGYMSGT  IGYQCBE  IGYZQDRV
  IGYZQENU IGYZQJPN
  

Fix information

• Fixed component name

  ENT COBOL FOR Z

• Fixed component ID

  5655EC600

Applicable component levels

• R620 PSY UI62019

     UP19/03/29 P F903

• R621 PSY UI62020

     UP19/03/29 P F903

• R622 PSY UI62021

     UP19/03/29 P F903

• R62H PSY UI62022

     UP19/03/29 P F903

Fix is available

• Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.