Pseudo-Minimum and Pseudo-Maximum instructions (#122)

Introduce Pseudo-Minimum (`f32x4.pmin` and `f64x2.pmin`) and Pseudo-Maximum (`f32x4.pmax` and `f64x2.pmax`) instructions, which implement Pseudo-Minimum and Pseudo-Maximum operations with slightly different semantics than the Minimum and Maximum in the current spec. Pseudo-Minimum is defined as `pmin(a, b) := b < a ? b : a` and Pseudo-Maximum is defined as `pmax(a, b) := a < b ? b : a`. "Pseudo" in the name refers to the fact that these operations may not return the minimum in case of signed zero inputs, in particular:
- `pmin(+0.0, -0.0) == +0.0`
- `pmax(-0.0, +0.0) == -0.0`

Author: Maratyszcza

proposals/simd/BinarySIMD.md

@@ -197,6 +197,8 @@ For example, `ImmLaneIdx16` is a byte with values in the range 0-15 (inclusive).
 | `f32x4.div`                |    `0xe7`| -                  |
 | `f32x4.min`                |    `0xe8`| -                  |
 | `f32x4.max`                |    `0xe9`| -                  |
+| `f32x4.pmin`               |    `0xea`| -                  |
+| `f32x4.pmax`               |    `0xeb`| -                  |
 | `f64x2.abs`                |    `0xec`| -                  |
 | `f64x2.neg`                |    `0xed`| -                  |
 | `f64x2.sqrt`               |    `0xef`| -                  |
@@ -206,6 +208,8 @@ For example, `ImmLaneIdx16` is a byte with values in the range 0-15 (inclusive).
 | `f64x2.div`                |    `0xf3`| -                  |
 | `f64x2.min`                |    `0xf4`| -                  |
 | `f64x2.max`                |    `0xf5`| -                  |
+| `f64x2.pmin`               |    `0xf6`| -                  |
+| `f64x2.pmax`               |    `0xf7`| -                  |
 | `i32x4.trunc_sat_f32x4_s`  |    `0xf8`| -                  |
 | `i32x4.trunc_sat_f32x4_u`  |    `0xf9`| -                  |
 | `f32x4.convert_i32x4_s`    |    `0xfa`| -                  |

proposals/simd/SIMD.md

@@ -867,6 +867,18 @@ Lane-wise minimum value, propagating NaNs.
 
 Lane-wise maximum value, propagating NaNs.
 
+### Pseudo-minimum
+* `f32x4.pmin(a: v128, b: v128) -> v128`
+* `f64x2.pmin(a: v128, b: v128) -> v128`
+
+Lane-wise minimum value, defined as `b < a ? b : a`.
+
+### Pseudo-maximum
+* `f32x4.pmax(a: v128, b: v128) -> v128`
+* `f64x2.pmax(a: v128, b: v128) -> v128`
+
+Lane-wise maximum value, defined as `a < b ? b : a`.
+
 ## Floating-point arithmetic
 
 The floating-point arithmetic operations are all lane-wise versions of the