Depends on how fussy you want to be I guess.
RR instructions are, as I recall, the fastest instructions, with the RI
being just behind it.
As someone else mentioned...for readability the RR is more common and known.
Dale
On 7/10/2025 12:39 PM, Mark Hammack wrote:
Is there any advantage to using:
LA Rx,1(,Rx) vs.
AHI Rx,1
Back in the old days (I started on S/370 with MVS right before XA came
out), to increment a register, you had to use option 1. Now, either will
work. I prefer the latter because I think it is clearer what you intend
but since it sets the CC flags, I'm not sure it is any "better" and may be
(slightly) slower.
Really, the same question can be asked about:
BCTR Rx,0 vs.
AHI Rx,-1
and
LA Rx,value
LHI Rx,value
Same thing, the latter is much clearer, especially for new-to-assembler
programmers. In the LA vs LHI case, LA is limited to 4095 whereas LHI can
go to 32767 so there is an advantage in some situations.
IDK, maybe it's the closet C programmer in me...
*Mark Hammack*
