suboptimal_flops in const functions

[leonardo-m]

On this code:

#![feature(const_fn_floating_point_arithmetic)]
#![allow(dead_code)]

#![warn(clippy::nursery)]

const fn mul_add(a: f32, b: f32, c: f32) -> f32 { a * b + c }

fn main() {}

Clippy gives me:

Checking foo1 v0.1.0 (...\foo1)
warning: multiply and add expressions can be calculated more efficiently and accurately
 --> src\main.rs:6:51
  |
6 | const fn mul_add(a: f32, b: f32, c: f32) -> f32 { a * b + c }
  |                                                   ^^^^^^^^^ help: consider using: `a.mul_add(b, c)`
  |
note: the lint level is defined here
 --> src\main.rs:4:9
  |
4 | #![warn(clippy::nursery)]
  |         ^^^^^^^^^^^^^^^
  = note: `#[warn(clippy::suboptimal_flops)]` implied by `#[warn(clippy::nursery)]`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#suboptimal_flops

But currently mul_add doesn't work in const functions.

[xFrednet]

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