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

[Uros Bizjak <ubizjak@gmail.com>]

On Fri, Sep 2, 2016 at 7:17 PM, Richard Henderson <rth@twiddle.net> wrote:
> 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.

Thanks!

>> (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.

FYI, after some more involved deep searching (and luck ;) I found one
at [1]. It is under "Programming Documentation Bookshelf" section, the
document is called "Calling Standard for Alpha Systems" [2].

[1] http://h41361.www4.hpe.com/docs/pub_page/V51B_DOCS/v51b_doclist.htm
[2] http://h41361.www4.hpe.com/docs/base_doc/DOCUMENTATION/V51B_ACRO_DUX/ARH9MCTE.PDF

Uros.