Prefetch instructions

Author: Maratyszcza

proposals/simd/BinarySIMD.md

@@ -222,3 +222,5 @@ For example, `ImmLaneIdx16` is a byte with values in the range 0-15 (inclusive).
 | `i32x4.trunc_sat_f32x4_u`  |    `0xf9`| -                  |
 | `f32x4.convert_i32x4_s`    |    `0xfa`| -                  |
 | `f32x4.convert_i32x4_u`    |    `0xfb`| -                  |
+| `prefetch.t`               |      TBA | -                  |
+| `prefetch.nt`              |      TBA | -                  |

proposals/simd/SIMD.md

@@ -1023,3 +1023,13 @@ def S.widen_low_T_u(a):
 def S.widen_high_T_u(a):
     return S.widen_high_T(Zext, a)
 ```
+
+### Prefetch
+
+* `prefetch.t(memarg)`
+* `prefetch.nt(memarg)`
+
+Prefetch memory location into lowest-level cache. Prefetch with temporal hint
+(`prefetch.t`) should be used for data that will be used only once, and
+prefetch with non-temporal (`prefetch.nt`) hint for data that will be reused
+multiple times.