[Bug c/106117] New: Use of option -fexcess-precision for operation-by-operation emulation for _Float16 arithmetics.

[Zahira.Ammarguellat at intel dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106117

            Bug ID: 106117
           Summary: Use of option -fexcess-precision for
                    operation-by-operation emulation for _Float16
                    arithmetics.
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Zahira.Ammarguellat at intel dot com
  Target Milestone: ---

We are adding in Clang the support of '_Float16' on X86 targets with SSE2
enabled. 
When the target supports AVX512-FP16, Clang performs '_Float16' arithmetic
using native support. Otherwise, '_Float16' arithmetic is performed by
promoting to 'float', then performing the operation, and finally truncating to
'_Float16'. 

This operation-by-operation emulation is the default in Clang, and is in line
with the C standard's rules for excess precision arithmetic. We would like to
adopt the option '-fexcess-precision' to request this operation-by-operation
emulation by setting '-fexcess-precision=none'. 
First are there any objections in using this option to request
operation-by-operation emulation for '_Float16' arithmetic? 
Second is 'none' the right value to use?
Thanks.