7042fcc638
Add an `fastMathAttr` on `arith::extf` and `arith::truncf`. If these two ops are inserted by some promotion passes (like legalize-to-f32 / emulate-unsupported-floats), they will be labeled as `FastMathFlags::contract`, denoting that they can be then `eliminated by canonicalizer`. The `elimination` can help improve performance, while may introduce some numerical differences.