Implementation in LLVM and various engines

Instruction	LLVM [1]	V8 [2]	SpiderMonkey [3]
`i8x16.relaxed_swizzle`	-mrelaxed-simd	✔️	✔️
`i32x4.relaxed_trunc_f32x4_s`	-mrelaxed-simd	✔️	✔️
`i32x4.relaxed_trunc_f32x4_u`	-mrelaxed-simd	✔️	✔️
`i32x4.relaxed_trunc_f64x2_s_zero`	-mrelaxed-simd	✔️	✔️
`i32x4.relaxed_trunc_f64x2_u_zero`	-mrelaxed-simd	✔️	✔️
`f32x4.relaxed_madd`	-mrelaxed-simd	✔️	✔️
`f32x4.relaxed_nmadd`	-mrelaxed-simd	✔️	✔️
`f64x2.relaxed_madd`	-mrelaxed-simd	✔️	✔️
`f64x2.relaxed_nmadd`	-mrelaxed-simd	✔️	✔️
`i8x16.relaxed_laneselect`	-mrelaxed-simd	✔️	✔️
`i16x8.relaxed_laneselect`	-mrelaxed-simd	✔️	✔️
`i32x4.relaxed_laneselect`	-mrelaxed-simd	✔️	✔️
`i64x2.relaxed_laneselect`	-mrelaxed-simd	✔️	✔️
`f32x4.relaxed_min`	-mrelaxed-simd	✔️	✔️
`f32x4.relaxed_max`	-mrelaxed-simd	✔️	✔️
`f64x2.relaxed_min`	-mrelaxed-simd	✔️	✔️
`f64x2.relaxed_max`	-mrelaxed-simd	✔️	✔️
`i16x8.relaxed_q15mulr_s`	-mrelaxed-simd	✔️	✔️
`i16x8.relaxed_dot_i8x16_i7x16_s`	-mrelaxed-simd	✔️	✔️
`i32x4.relaxed_dot_i8x16_i7x16_add_s`	-mrelaxed-simd	✔️	✔️

[1] Tip of tree LLVM as of 2021-10-28

[2] V8 9.7.75 (only implemented on x64)

[3] SpiderMonkey as of 2021-10-18 implemented on x86, x64 and Aarch64

Name of builtins in LLVM

Instruction	LLVM
`i8x16.relaxed_swizzle`	`__builtin_wasm_relaxed_swizzle_i8x16`
`i32x4.relaxed_trunc_f32x4_s`	`__builtin_wasm_relaxed_trunc_s_i32x4_f32x4`
`i32x4.relaxed_trunc_f32x4_u`	`__builtin_wasm_relaxed_trunc_u_i32x4_f32x4`
`i32x4.relaxed_trunc_f64x2_s_zero`	`__builtin_wasm_relaxed_trunc_zero_s_i32x4_f64x2`
`i32x4.relaxed_trunc_f64x2_u_zero`	`__builtin_wasm_relaxed_trunc_zero_u_i32x4_f64x2`
`f32x4.relaxed_madd`	`__builtin_wasm_fma_f32x4`
`f32x4.relaxed_nmadd`	`__builtin_wasm_fnma_f32x4`
`f64x2.relaxed_madd`	`__builtin_wasm_fma_f64x2`
`f64x2.relaxed_nmadd`	`__builtin_wasm_fnma_f64x2`
`i8x16.relaxed_laneselect`	`__builtin_wasm_laneselect_i8x16`
`i16x8.relaxed_laneselect`	`__builtin_wasm_laneselect_i16x8`
`i32x4.relaxed_laneselect`	`__builtin_wasm_laneselect_i32x4`
`i64x2.relaxed_laneselect`	`__builtin_wasm_laneselect_i64x2`
`f32x4.relaxed_min`	`__builtin_wasm_relaxed_min_f32x4`
`f32x4.relaxed_max`	`__builtin_wasm_relaxed_max_f32x4`
`f64x2.relaxed_min`	`__builtin_wasm_relaxed_min_f64x2`
`f64x2.relaxed_max`	`__builtin_wasm_relaxed_max_f64x2`
`i16x8.relaxed_q15mulr_s`	`__builtin_wasm_relaxed_q15mulr_s_i16x8`
`i16x8.relaxed_dot_i8x16_i7x16_s`	`__builtin_wasm_dot_i8x16_i7x16_s_i16x8`
`i32x4.relaxed_dot_i8x16_i7x16_add_s`	`__builtin_wasm_dot_i8x16_i7x16_add_s_i32x4`