Re: Expansion of narrowing math built-ins into power instructions

[Joseph Myers <joseph@codesourcery.com>]

On Thu, 8 Aug 2019, Segher Boessenkool wrote:

> These current patterns all take the same mode for all inputs and outputs
> (that's what <mode>3 indicates, say, fadddf3).  You will need to define
> something that takes two SFs in and produces a DF.  That cannot really

For example, md.texi describes standard patterns such as mulhisi3 that 
multiply two HImode values and produce an SImode result (widening integer 
multiply).

Using a similar naming pattern, you might have a pattern adddfsf3 that 
multiplies two DFmode values and produces an SFmode result (or you could 
call it something like add_truncdfsf3 if you wish to emphasise the 
truncation involved, for example).  Similarly addtfsf3 that multiplies 
TFmode and produces an SFmode result, and so on.  Of course these names 
need documenting (and you need corresponding RTL for them to generate that 
distinguishes the fused add+truncate from the different RTL for separate 
addition and truncation with double rounding).  In cases where long double 
and double have the same mode, the daddl function should use the existing 
adddf3 pattern.

-- 
Joseph S. Myers
joseph@codesourcery.com