Keep only a single v8x16.shuffle instruction.

Remove all other swizzle and shuffle instructions since they can be
implemented in terms of the general v8x16.shuffle.

We can add more compact encodings of popular shuffles later if needed.

Author: Jakob Stoklund Olesen

proposals/simd/SIMD.md

@@ -208,27 +208,8 @@ def S.replace_lane(a, i, x):
 The input lane value, `x`, is interpreted the same way as for the splat
 instructions. For the `i8` and `i16` lanes, the high bits of `x` are ignored.
 
-### Swizzle lanes
-* `v8x16.swizzle(a: v128, s: LaneIdx16[16]) -> v128`
-* `v16x8.swizzle(a: v128, s: LaneIdx8[8]) -> v128`
-* `v32x4.swizzle(a: v128, s: LaneIdx4[4]) -> v128`
-* `v64x2.swizzle(a: v128, s: LaneIdx2[2]) -> v128`
-
-Create vector with lanes rearranged:
-
-```python
-def S.swizzle(a, s):
-    result = S.New()
-    for i in range(S.Lanes):
-        result[i] = a[s[i]]
-    return result
-```
-
 ### Shuffle lanes
 * `v8x16.shuffle(a: v128, b: v128, s: LaneIdx32[16]) -> v128`
-* `v16x8.shuffle(a: v128, b: v128, s: LaneIdx16[8]) -> v128`
-* `v32x4.shuffle(a: v128, b: v128, s: LaneIdx8[4]) -> v128`
-* `v64x2.shuffle(a: v128, b: v128, s: LaneIdx4[2]) -> v128`
 
 Create vector with lanes selected from the lanes of two input vectors: