What did you do?

I compiled the following code on tip, which generated the assembly code below:

package test

import "encoding/binary"

func test(x uint64) (out [8]byte) {
	binary.LittleEndian.PutUint64(out[:], x)
	return out
}

movq    $0, "".out+16(SP)
xchgl   AX, AX
movq    "".x+8(SP), AX
movq    AX, "".out+16(SP)
ret

What did you expect to see?

I expected the XCHGL instruction to not be there, as I don't think it makes much sense.
In version 1.11, the assembly code looks like this:

movq    $0, "".out+16(SP)
movq    "".x+8(SP), AX
movq    AX, "".out+16(SP)
ret

What did you see instead?

Instead, the XCHGL instruction is present, as shown in the first assembly snippet