[LLVMdev] Question about FMA formation

[Eli Friedman]

On Wed, Dec 12, 2012 at 3:40 PM, Shuxin Yang <shuxin.llvm at gmail.com> wrote:
> Hi, Dear All:
>
>    I'm going implement FMA formation. On some architectures, "FMA a, b, c"
> is more precise than
> "a * b + c".

If it isn't more accurate, it isn't an FMA, at least not in the
commonly used sense.  (ARM has an instruction which does a multiply
and add which isn't more precise, but it would just be confusing to
refer to that as an FMA.)

> In the former
> case, can we enable FMA
>  formation despite restrictive FP mode?

No.  There have already been very long discussions about fma; try
searching the llvmdev archives.

-Eli