[llvm] [X86][Codegen] - Introduce a new tuning for X86 backend to control FMA generation (PR #210343)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> No new hook, but give the existing one the information it lacks: pass the
SDNode (or the FMUL's SDNodeFlags) to isFMAFasterThanFMulAndFAdd so targets
can answer per-node. That extends an existing hook instead of adding a knob,
at the cost of touching all implementors.

The flags don't help, isFMAFasterThanFMulAndFAdd is meaningless if the contraction isn't legal to perform in the first place 

I think 2 is the only viable option 


> If you consider "global -ffp-contract=fast I

There is no global mode, all of this needs to be specific to a particular instruction. New global-ish controls should not be added 

https://github.com/llvm/llvm-project/pull/210343