[llvm] [WebAssembly] Implement more of getCastInstrCost (PR #164612)

[Sam Parker via llvm-commits]

================
@@ -1720,42 +1720,7 @@ for.body:                                         ; preds = %entry, %for.body
 }
 
 ; CHECK-LABEL: two_floats_two_bytes_same_op:
-; CHECK: loop
-; CHECK: v128.load
-; CHECK: v128.load
-; CHECK: i8x16.shuffle {{.*}} 0, 1, 2, 3, 8, 9, 10, 11, 16, 17, 18, 19, 24, 25, 26, 27
-; CHECK: v128.load
-; CHECK: v128.load
-; CHECK: i8x16.shuffle {{.*}} 0, 1, 2, 3, 8, 9, 10, 11, 16, 17, 18, 19, 24, 25, 26, 27
-; CHECK: f32x4.mul
-; CHECK: f32x4.extract_lane
-; CHECK: i32.trunc_sat_f32_s
-; CHECK: i8x16.splat
-; CHECK: i8x16.shuffle {{.*}} 4, 5, 6, 7, 12, 13, 14, 15, 20, 21, 22, 23, 28, 29, 30, 31
-; CHECK: i8x16.shuffle {{.*}} 4, 5, 6, 7, 12, 13, 14, 15, 20, 21, 22, 23, 28, 29, 30, 31
-; CHECK: f32x4.mul
-; CHECK: f32x4.extract_lane
-; CHECK: i32.trunc_sat_f32_s
----------------
sparker-arm wrote:

Looking at this again, couldn't we do (something like):
```
trunc_sat_f32x4_s
v128.and $MASK
narrow
shuffle
```

https://github.com/llvm/llvm-project/pull/164612