[Dwarf-Discuss] Representing the location of smaller values in vector registers

Cary Coutant ccoutant at gmail.com
Wed Mar 9 19:42:51 PST 2016


We're straying even further off topic now...

>> [...]  We're not discussing "how ABIs tell you how to interpret
>> [location lists]". We're discussing whether the consumer is expected
>> to turn to the ABI to find out how a smaller value is stored in a
>> larger register. [...]
>
> Given that the ABI constraints apply only at function call boundaries,

Sure, calling conventions and register usage and such apply only at
function call boundaries, but an ABI covers far more than just that.
Whatever it says for representation of values in registers would apply
in general...

> it's possible that a compiler would choose to store values in a
> different way in the function's interior.  For example, it could put
> several small scalars into a wider register.

...and we have DW_OP_bit_piece for exceptional circumstances like that.

-cary


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