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Re: [rs6000] Add documentation for __builtin_mtfsf

On 7/21/19 1:13 PM, Segher Boessenkool wrote:
> On Sun, Jul 21, 2019 at 04:06:32AM -0500, Paul Clarke wrote:
>> +@code{__builtin_mtfsf} takes a constant 8-bit integer field mask and a
>> +representation of the new value of the FPSCR and generates the @code{mtfsf}
>> +instruction to copy the supplied value into the FPSCR, subject to the field
>> +mask, each bit of which represents a nibble of the FPSCR.  The

> "A representation of the new value"?  I guess you want to say that it
> sits in an FPR?

It's the 2nd parameter to the builtin, so a "double".  It may or may not be in an FPR, but the user of the builtin doesn't really know or care.  (It'll eventually be in an FPR, of course, but the user has it in a variable.)  It's a "representation" because it's not actually the new value, because it gets written under mask.

> Before we document __builtin_mtfsf, maybe we should make it work with
> the W and/or L fields first, or at least, decide how we want that?

It's been available but undocumented for ages.  Do you want me to thus document how it is currently implemented by including something like "...generates the mtfsf (extended mnemonic) instruction ..." ?

If you think the basic mnemonic form needs to be supported, that's a whole other piece of work ;-)


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