rex &= 0x40 | Rxr
	if a.Offset != int64(int32(a.Offset)) {
		// The rules are slightly different for 386 and AMD64,
		// mostly for historical reasons. We may unify them later,
		// but it must be discussed beforehand.
		//
		// For 64bit mode only LEAL is allowed to overflow.
		// It's how https://golang.org/cl/59630 made it.
		// crypto/sha1/sha1block_amd64.s depends on this feature.
		//