wasm-encoder: Wrong encoding of i64x2.le_s instruction

[adambratschikaye]

The following example encodes the i64x2.le_s instruction using wasm-encoder and then reads it back using wasmparser, but doesn't round trip:

use wasm_encoder::{Encode, Function, Instruction};
use wasmparser::FunctionBody;

fn main() {
    let mut function = Function::new(vec![]);
    function.instruction(&Instruction::I64x2LeS);

    let mut buf = vec![];
    function.encode(&mut buf);
    println!("{:x?}", buf);

    // Skip leading byte containing the function body length.
    let body = FunctionBody::new(0, &buf[1..]);
    let mut reader = body.get_operators_reader().unwrap();
    println!("{:?}", reader.read().unwrap());
}

output:

[4, 0, fd, dd, 1]
I64x2ExtMulHighI32x4S

[alexcrichton]

Fixed in #811