RE: [PATCH] [1/2] [ARM] [libgcc] Support RTABI half-precision conversion functions.

["Hale Wang" <hale.wang@arm.com>]

> -----Original Message-----
> From: gcc-patches-owner@gcc.gnu.org [mailto:gcc-patches-
> owner@gcc.gnu.org] On Behalf Of Joseph Myers
> Sent: Saturday, April 11, 2015 4:30 AM
> To: Hale Wang
> Cc: 'GCC Patches'
> Subject: Re: [PATCH] [1/2] [ARM] [libgcc] Support RTABI half-precision
> conversion functions.
> 
> On Fri, 10 Apr 2015, Hale Wang wrote:
> 
> > According to the run-time ABI for ARM architecture, this function is
> > allowed to corrupt only the integer core registers permitted to be
> > corrupted by the [AAPCS] (r0-r3, ip, lr, and CPSR). So we can't just
> > simply use the existing GNU conversion functions to implement this
> function.
> 
> I don't see that "only".  Indeed, at the bottom of page 15 in IHI0043D,
"If the
> FP instruction set is available, implementations of these functions may
use it.
> Consequently, FP hardware-using code that calls one of these helper
> functions directly, or indirectly by calling a function with a
base-standard
> interface, must assume that the FP parameter, result, scratch, and status
> registers might be altered by a call to it.".

Yes, you are right. It's my fault to add the "only" here. Thank you to point
out this.
Beside this, is this patch OK for you?

Hale
> 
> (Furthermore, the ideal result on implementations with VFP but not
> hardware half-precision support would be that the software conversions
> interact properly with hardware exceptions and rounding modes (so using
> FPSCR).)
> 
> --
> Joseph S. Myers
> joseph@codesourcery.com