cmd/internal/obj/arm64: fix an encoding error of CMPW instruction

For arm64 CMP, ADD and other similar extended register instructions,
if there is no extension, the default extion is LSL<<0, but the default
encoding value (the value of 'option' field) of 32-bit instruction and
64-bit instruction is different, 32-bit is 2 and 64-bit is 3. But the
current assembler incorrectly encodes the value of 32-bit instruction
to 3. This CL fixes this error.

Change-Id: I0e09af2c9c5047a4ed2db7d1183290283db9c31c
Reviewed-on: https://go-review.googlesource.com/c/go/+/329749
Reviewed-by: eric fang <eric.fang@arm.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: eric fang <eric.fang@arm.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Trust: Dmitri Shuralyov <dmitshur@golang.org>

Author: eric fang

src/cmd/asm/internal/asm/testdata/arm64.s

@@ -89,7 +89,7 @@ TEXT	foo(SB), DUPOK|NOSPLIT, $-8
 	CMP	R1<<33, R2
 	CMP	R22.SXTX, RSP                    // ffe336eb
 	CMP	$0x22220000, RSP                 // CMP $572653568, RSP   // 5b44a4d2ff633beb
-	CMPW	$0x22220000, RSP                 // CMPW $572653568, RSP  // 5b44a452ff633b6b
+	CMPW	$0x22220000, RSP                 // CMPW $572653568, RSP  // 5b44a452ff433b6b
 	CCMN	MI, ZR, R1, $4	                 // e44341ba
 	// MADD Rn,Rm,Ra,Rd
 	MADD	R1, R2, R3, R4                   // 6408019b
@@ -377,6 +377,7 @@ TEXT	foo(SB), DUPOK|NOSPLIT, $-8
 	MOVD	$0x1000100010001000, RSP      // MOVD	$1152939097061330944, RSP   // ff8304b2
 	MOVW	$0x10001000, RSP              // MOVW	$268439552, RSP             // ff830432
 	ADDW	$0x10001000, R1               // ADDW	$268439552, R1              // fb83043221001b0b
+	ADDW	$0x22220000, RSP, R3          // ADDW	$572653568, RSP, R3         // 5b44a452e3433b0b
 
 // move a large constant to a Vd.
 	VMOVS	$0x80402010, V11                                      // VMOVS	$2151686160, V11

src/cmd/internal/obj/arm64/asm7.go

@@ -4333,8 +4333,10 @@ func (c *ctxt7) asmout(p *obj.Prog, o *Optab, out []uint32) {
 		if p.To.Reg == REG_RSP && isADDSop(p.As) {
 			c.ctxt.Diag("illegal destination register: %v\n", p)
 		}
+		lsl0 := LSL0_64
 		if isADDWop(p.As) || isANDWop(p.As) {
 			o1 = c.omovconst(AMOVW, p, &p.From, REGTMP)
+			lsl0 = LSL0_32
 		} else {
 			o1 = c.omovconst(AMOVD, p, &p.From, REGTMP)
 		}
@@ -4350,7 +4352,7 @@ func (c *ctxt7) asmout(p *obj.Prog, o *Optab, out []uint32) {
 		if p.To.Reg == REGSP || r == REGSP {
 			o2 = c.opxrrr(p, p.As, false)
 			o2 |= REGTMP & 31 << 16
-			o2 |= LSL0_64
+			o2 |= uint32(lsl0)
 		} else {
 			o2 = c.oprrr(p, p.As)
 			o2 |= REGTMP & 31 << 16 /* shift is 0 */