cmd/asm: fix operand order of ARM's MULA instruction

As discussion in issue #19141, the addend should be the third
argument of MULA. This patch fixes it in both the front end
and the back end of the assembler. And also tests are added to
the encoding test.

Fixes #19141

Change-Id: Idbc6f338b8fdfcad97a135f27a98c5b375b27d43
Reviewed-on: https://go-review.googlesource.com/42028
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

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

@@ -639,12 +639,12 @@ func (p *Parser) asmInstruction(op obj.As, cond string, a []obj.Addr) {
 			// All must be registers.
 			p.getRegister(prog, op, &a[0])
 			r1 := p.getRegister(prog, op, &a[1])
-			p.getRegister(prog, op, &a[2])
-			r3 := p.getRegister(prog, op, &a[3])
+			r2 := p.getRegister(prog, op, &a[2])
+			p.getRegister(prog, op, &a[3])
 			prog.From = a[0]
-			prog.To = a[2]
+			prog.To = a[3]
 			prog.To.Type = obj.TYPE_REGREG2
-			prog.To.Offset = int64(r3)
+			prog.To.Offset = int64(r2)
 			prog.Reg = r1
 			break
 		}

src/cmd/asm/internal/asm/testdata/arm.s

@@ -951,6 +951,8 @@ jmp_label_3:
 	MULAWT	R1, R2, R3, R4       // c23124e1
 	MULAWB	R1, R2, R3, R4       // 823124e1
 	MULS	R1, R2, R3, R4       // 923164e0
+	MULA	R1, R2, R3, R4       // 923124e0
+	MULA.S	R1, R2, R3, R4       // 923134e0
 	MMULA	R1, R2, R3, R4       // 123154e7
 	MMULS	R1, R2, R3, R4       // d23154e7
 	MULABB	R1, R2, R3, R4       // 823104e1

src/cmd/internal/obj/arm/asm5.go

@@ -165,7 +165,6 @@ var optab = []Optab{
 	{ADIVHW, C_REG, C_REG, C_REG, 105, 4, 0, 0, 0},
 	{ADIVHW, C_REG, C_NONE, C_REG, 105, 4, 0, 0, 0},
 	{AMULL, C_REG, C_REG, C_REGREG, 17, 4, 0, 0, 0},
-	{AMULA, C_REG, C_REG, C_REGREG2, 17, 4, 0, 0, 0},
 	{AMOVW, C_REG, C_NONE, C_SAUTO, 20, 4, REGSP, 0, 0},
 	{AMOVW, C_REG, C_NONE, C_SOREG, 20, 4, 0, 0, 0},
 	{AMOVB, C_REG, C_NONE, C_SAUTO, 20, 4, REGSP, 0, 0},
@@ -1526,6 +1525,7 @@ func buildop(ctxt *obj.Link) {
 		case AMULAWT:
 			opset(AMULAWB, r0)
 			opset(AMULABB, r0)
+			opset(AMULA, r0)
 			opset(AMULS, r0)
 			opset(AMMULA, r0)
 			opset(AMMULS, r0)
@@ -1536,12 +1536,10 @@ func buildop(ctxt *obj.Link) {
 			opset(AREVSH, r0)
 			opset(ARBIT, r0)
 
-		case AMULA,
-			ALDREX,
+		case ALDREX,
 			ASTREX,
 			ALDREXD,
 			ASTREXD,
-			ATST,
 			APLD,
 			obj.AUNDEF,
 			obj.AFUNCDATA,
@@ -2489,10 +2487,10 @@ func (c *ctxt5) asmout(p *obj.Prog, o *Optab, out []uint32) {
 	case 99: /* MULAW{T,B} Rs, Rm, Rn, Rd */
 		o1 = c.oprrr(p, p.As, int(p.Scond))
 
-		o1 |= (uint32(p.To.Reg) & 15) << 12
+		o1 |= (uint32(p.To.Reg) & 15) << 16
 		o1 |= (uint32(p.From.Reg) & 15) << 8
 		o1 |= (uint32(p.Reg) & 15) << 0
-		o1 |= uint32((p.To.Offset & 15) << 16)
+		o1 |= uint32((p.To.Offset & 15) << 12)
 
 	// DATABUNDLE: BKPT $0x5be0, signify the start of NaCl data bundle;
 	// DATABUNDLEEND: zero width alignment marker

src/cmd/internal/obj/util.go

@@ -240,7 +240,7 @@ func Dconv(p *Prog, a *Addr) string {
 		str = fmt.Sprintf("(%v, %v)", Rconv(int(a.Reg)), Rconv(int(a.Offset)))
 
 	case TYPE_REGREG2:
-		str = fmt.Sprintf("%v, %v", Rconv(int(a.Reg)), Rconv(int(a.Offset)))
+		str = fmt.Sprintf("%v, %v", Rconv(int(a.Offset)), Rconv(int(a.Reg)))
 
 	case TYPE_REGLIST:
 		str = regListConv(int(a.Offset))