On 6 November 2014 17:20, Jonathan Scott <[email protected]>
wrote:
>Paul Gilmartin wrote:
>> Are dependent USINGs referring to the same base register
>> allowed to overlap? There should be no objection to this
>> provided that they resolve to identical base and displacement
>> regardless which USING is used. But this introduces an
>> ambiguity in "DROP by address" when that address can be
>> resolved, albeit equivalently, by either of two dependent
>> USINGs.
>
> When all else is equal a new dependent USING for a given location
> should supersede any older one for the same location and base
> USING.
1) This is not the way non-dependent USINGs work. There can be multiple
"right-part"s (registers, =bases, in some sense) with at worst a warning.
Why should this be different?
2) Having multiple overlapping dependent USINGs can be useful. For example:
xCBAREA DS XL...
...
USING IHADCB,xCBAREA
USING IFGACB,xCBAREA
...
MVC DCBDDNAM,some_ddname Works for DCB or ACB
...
TM DCBOFLGS,DCBOPEN Works for DCB or ACB
...
TM ACBDSOR2,ACBDORGA Is this an ACB?
JO Handle_ACB Go do ACB-only stuff
...
DROP ???
I'm not claiming this is the "right" technique -- clearly there are other
ways of doing it -- but it's a use case.
Tony H.
