llvm dev - Jul 2010 - [LLVMdev] Proposal for adding rounding variant of fpto?i instructions

On Jul 12, 2010, at 9:28 AM, Anton Lokhmotov wrote:
> Hi Peter,
> 
>> I would appreciate comments/feedback on this proposal to extend the
>> fpto?i instructions to support rounding.
> I think this might be useful. Actually, LLVM specifies that fpto?i convert
> their operand into the nearest (rounding towards zero) signed integer
value.
> Do you have other rounding modes in mind? Currently I use custom metadata
to
> represent conversions with other rounding modes.
My high level thought on this is that it would be great to have, but is a major
new feature.  In addition to adding rounding mode selection to fpto?i, we should
add it to all the rest of the fp operators.  We also want to eventually add
support for the optimizer to know that the user is messing around with rounding
modes (which needs to disable inexact constant folding and other optimizations)
as well.  Modeling this properly will require some fairly substantial changes
throughout the compiler similar to when NUW/NSW were added on the integer side.

-Chris