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Status Not under consideration
Workspace IBM High Level Assembler for z/OS and z/VM
Categories Assembler
Created by Guest
Created on Apr 7, 2023

RELATED IDEAS

Flag RX instructions with index but no base register

It has been a common malpractice since more than half a century not to use a base register but the index register in rx instructions, e.g. L Ra,100(Rb) instead of L Ra,100(,Rb).

Historically, this implied some performance penalty (AFAIR), nowadays there are at least rumours that cache logic is impacted. Furthermore, in AR mode, this can lead to not so obvious errors.

The suggestion is to add a warning in such a situation. In case that it is really desirable to have register 0 as a base, the instruction could be coded as L Ra,100(Rb,0) in order to avoid a false positive.

A somewhat comparable test is done for page0 access.



Idea priority Medium
  • Guest
    Reply
    |     Apr 27, 2023
    Firstly, we should point out that any performance difference went away long ago, except in AR mode, where there is a functional difference such that use of an index register is likely to be intentional.

    The suggestion appears valid, but as stated it appears to be of very limited value, so it would not be likely to be considered for implementation in the near future.
  • Guest
    Reply
    |     Apr 10, 2023
    Development team will review the Idea.

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