i8x16.popcnt instruction

Author: Maratyszcza

proposals/simd/BinarySIMD.md

@@ -240,6 +240,7 @@ For example, `ImmLaneIdx16` is a byte with values in the range 0-15 (inclusive).
 | `i64x2.extmul_low_i32x4_u`  |   `0x11a`| -                        |
 | `i64x2.extmul_high_i32x4_u` |   `0x11b`| -                        |
 | `i16x8.q15mulr_sat_s`       |     `TBD`| -                        |
+| `i8x16.popcnt`              |     `TBD`| -                        |
 | `v128.any_true`             |     `TBD`| -                        |
 | `v128.load8_lane`           |     `TBD`| m:memarg, i:ImmLaneIdx16 |
 | `v128.load16_lane`          |     `TBD`| m:memarg, i:ImmLaneIdx8  |

proposals/simd/ImplementationStatus.md

@@ -103,6 +103,7 @@
 | `i8x16.max_s`               |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
 | `i8x16.max_u`               |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
 | `i8x16.avgr_u`              |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
+| `i8x16.popcnt`              |                           |                    |                    |                    |                    |
 | `i16x8.abs`                 |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
 | `i16x8.neg`                 |               `-msimd128` | :heavy_check_mark: |                    | :heavy_check_mark: | :heavy_check_mark: |
 | `i16x8.all_true`            |               `-msimd128` | :heavy_check_mark: |                    | :heavy_check_mark: | :heavy_check_mark: |

proposals/simd/SIMD.md

@@ -662,6 +662,15 @@ Note that the normal WebAssembly `select` instruction also works with vector
 types. It selects between two whole vectors controlled by a single scalar value,
 rather than selecting bits controlled by a control mask vector.
 
+### Lane-wise Population Count
+* `i8x16.popcnt(v: v128) -> v128`
+
+Count the number of bits set to one within each lane.
+
+```python
+def S.popcnt(v):
+    return S.lanewise_unary(popcnt, v)
+```
 
 ## Boolean horizontal reductions