[ARM] Enable __fp16 as a function parameter and return type.

[Joseph Myers]

On Tue, 3 May 2016, Matthew Wahab wrote:

> > This patch addresses one incompatibility of the original __fp16 
> > specification with the more recent ACLE specification and the 
> > specification in ISO/IEC TS 18661-3 for how such types should work. 
> > Another such incompatibility is the peculiar rule in the original 
> > specification that conversions from double to __fp16 go via float, 
> > with double rounding.  Do you have plans to eliminate that and move to 
> > the single-rounding semantics that are in current specifications?
> 
> The patch aims to preserve the __fp16 semantics currently used by GCC, 
> except for the obvious argument/return value in registers change. This 
> is to avoid any changes to the values calculated by existing __fp16 code 
> that might be introduced if things like the conversion rules are 
> changed.

My question wasn't about what this patch does - it makes sense for each 
patch to do just one thing (so this patch only deals with allowing certain 
cases that were disallowed by the original __fp16 specification but are 
allowed by ACLE).  My question was about future intent - do you intend 
other patches to address other incompatibilities between ACLE and GCC 
__fp16, one incompatibility at a time?

-- 
Joseph S. Myers
joseph@codesourcery.com