[RFC PATCH, alpha]: ABI change: pass SFmode and SCmode variable arguments by reference

[Richard Henderson]

On 09/02/2016 02:35 AM, Uros Bizjak wrote:
> --q--
>   /* Pass float and _Complex float variable arguments by reference.
>      This avoids 64-bit store from a FP register to a pretend args save area
>      and subsequent 32-bit load from the saved location to a FP register.
> 
>      Note that 32-bit loads and stores to/from a FP register on alpha reorder
>      bits to form a canonical 64-bit value in the FP register.  This fact
>      invalidates compiler assumption that 32-bit FP value lives in the lower
>      32-bits of the passed 64-bit FP value, so loading the 32-bit value from
>      the stored 64-bit location using 32-bit FP load is invalid on alpha.
> 
>      This introduces sort of ABI incompatibility, but until _Float32 was
>      introduced, C-family languages promoted 32-bit float variable arg to
>      a 64-bit double, and it was not allowed to pass float as a varible
>      argument.  Passing _Complex float as a variable argument never
>      worked on alpha.  Thus, we have no backward compatibility issues
>      to worry about, and passing un-promoted _Float32 and _Complex float
>      as a variable argument will actually work in the future.  */
> --/q--

This sounds like a good plan to me.

> (I was not able to find the
> authoritative OSF/1 ABI document on the net...)

As far as I know, it was never available online.
I have a paper copy.


r~