// mneg by constant
(MNEG x (MOVDconst [-1])) => x
(MNEG _ (MOVDconst [0])) => (MOVDconst [0])
(MNEG x (MOVDconst [1])) => (NEG x)
(MNEG x (MOVDconst [c])) && isPowerOfTwo64(c) => (NEG (SLLconst <x.Type> [log64(c)] x))
(MNEG x (MOVDconst [c])) && isPowerOfTwo64(c-1) && c >= 3 => (NEG (ADDshiftLL <x.Type> x x [log64(c-1)]))

			rel := obj.Addrel(c.cursym)

			rel.Off = int32(c.pc)
			rel.Siz = 4
			rel.Sym = p.To.Sym
			rel.Add = p.To.Offset
			rel.Type = objabi.R_ADDR
			o1 = 0
		}

	case 15: /* mul/mneg/umulh/umull r,[r,]r; madd/msub/fmadd/fmsub/fnmadd/fnmsub Rm,Ra,Rn,Rd */
		o1 = c.oprrr(p, p.As)

		rf := int(p.From.Reg)
		rt := int(p.To.Reg)
		var r int
		var ra int
		if p.From3Type() == obj.TYPE_REG {