[dev.cc] cmd/asm: implement FMADD for ppc64

Missed this one instruction in the previous pass.

Change-Id: Ic8cdae4d3bfd626c6bbe0ce49fce28b53db2ad1c
Reviewed-on: https://go-review.googlesource.com/5420Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/asm/internal/arch/ppc64.go

@@ -20,12 +20,18 @@ func jumpPPC64(word string) bool {
 
 // IsPPC64RLD reports whether the op (as defined by an ppc64.A* constant) is
 // one of the RLD-like instructions that require special handling.
+// The FMADD-like instructions behave similarly.
 func IsPPC64RLD(op int) bool {
 	switch op {
 	case ppc64.ARLDC, ppc64.ARLDCCC, ppc64.ARLDCL, ppc64.ARLDCLCC,
 		ppc64.ARLDCR, ppc64.ARLDCRCC, ppc64.ARLDMI, ppc64.ARLDMICC,
 		ppc64.ARLWMI, ppc64.ARLWMICC, ppc64.ARLWNM, ppc64.ARLWNMCC:
 		return true
+	case ppc64.AFMADD, ppc64.AFMADDCC, ppc64.AFMADDS, ppc64.AFMADDSCC,
+		ppc64.AFMSUB, ppc64.AFMSUBCC, ppc64.AFMSUBS, ppc64.AFMSUBSCC,
+		ppc64.AFNMADD, ppc64.AFNMADDCC, ppc64.AFNMADDS, ppc64.AFNMADDSCC,
+		ppc64.AFNMSUB, ppc64.AFNMSUBCC, ppc64.AFNMSUBS, ppc64.AFNMSUBSCC:
+		return true
 	}
 	return false
 }

src/cmd/asm/internal/asm/asm.go

@@ -549,7 +549,9 @@ func (p *Parser) asmInstruction(op int, cond string, a []obj.Addr) {
 			break
 		}
 		if p.arch.Thechar == '9' && arch.IsPPC64RLD(op) {
-			// 2nd operand is always a register.
+			// 2nd operand must always be a register.
+			// TODO: Do we need to guard this with the instruction type?
+			// That is, are there 4-operand instructions without this property?
 			prog.From = a[0]
 			prog.Reg = p.getRegister(prog, op, &a[1])
 			prog.From3 = a[2]