[LLVMdev] RFC: Add ISD nodes for mad

[Owen Anderson]

> On Jan 28, 2015, at 3:47 PM, Hal Finkel <hfinkel at anl.gov> wrote:
> 
> ----- Original Message -----
>> From: "Matt Arsenault" <Matthew.Arsenault at amd.com>
>> To: "llvmdev at cs.uiuc.edu" <LLVMdev at cs.uiuc.edu>
>> Sent: Wednesday, January 28, 2015 1:52:59 PM
>> Subject: [LLVMdev] RFC: Add ISD nodes for mad
>> 
>> Hi,
>> 
>> I would like to add an ISD node for an fmad operation (named either
>> FMAD
>> or FMULADD). It will have the semantics of returning the same result
>> as
>> the separate multiply and add with the intermediate rounding step,
>> and
>> not a differently rounded result.  The motivation is to share code
>> with
>> the various FMA forming DAG combines, but will be generally more
>> useful
>> on targets that support it since it is OK to form without non-default
>> -fp-contract modes.
> 
> Why not just reuse the existing FMA node, but add an additional parameter to indicate whether enhanced intermediate precision is required?

Because that would break a lot of existing backends?

—Owen
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