From: "Rupert Reynolds" <[email protected]> Sent: Tuesday, August 11, 2020 11:03 AM
I've not seen SLR, but my comment based on 1990s knowledge is that it's best to keep it simple. Don't access storage unnecessarily (such as L Rn,=F'0') and any of the more obvious methods (such as "LA Rn,0" "SR Rn,Rn" or "XR Rn,Rn") is likely to be optimised as a special case. XR and SR use less memory for the instruction, but LA was the preferred way where I learned most of what I know--perhaps that was because it doesn't set the condition code.
Shortest is best. The only reason for using LA r,0 would be to avoid changing the CC, as you suggest below.
I suspect (I mean guess!) that optimisation for the special case of zeroing a register may mean the advantage of not setting CC is lost in that case.
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