cmd/asm: fix encoding errors for FMOVD and FMOVS instructions on arm64

The encoding of instructions "FMOVD F1, ZR" and "FMOVS F1, ZR" is wrong,
the assembler encodes them as "FMOVD F1, F31" and "FMOVS F1, F31". This
CL fixes the bug.

Change-Id: I2d31520b58f9950ce2534a04f4a3275bf103a673
Reviewed-on: https://go-review.googlesource.com/c/go/+/503135
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: David Chase <[email protected]>
Run-TryBot: Eric Fang <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: eric fang

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

@@ -238,6 +238,8 @@ TEXT	foo(SB), DUPOK|NOSPLIT, $-8
 	FMOVS	$0, F0                          // e003271e
 	FMOVD	ZR, F0                          // e003679e
 	FMOVS	ZR, F0                          // e003271e
+	FMOVD	F1, ZR                          // 3f00669e
+	FMOVS	F1, ZR                          // 3f00261e
 	VUADDW	V9.B8, V12.H8, V14.H8           // 8e11292e
 	VUADDW	V13.H4, V10.S4, V11.S4          // 4b116d2e
 	VUADDW	V21.S2, V24.D2, V29.D2          // 1d13b52e

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

@@ -3880,7 +3880,7 @@ func (c *ctxt7) asmout(p *obj.Prog, o *Optab, out []uint32) {
 	case 29: /* op Rn, Rd */
 		fc := c.aclass(&p.From)
 		tc := c.aclass(&p.To)
-		if (p.As == AFMOVD || p.As == AFMOVS) && (fc == C_REG || fc == C_ZREG || tc == C_REG) {
+		if (p.As == AFMOVD || p.As == AFMOVS) && (fc == C_REG || fc == C_ZREG || tc == C_REG || tc == C_ZREG) {
 			// FMOV Rx, Fy or FMOV Fy, Rx
 			o1 = FPCVTI(0, 0, 0, 0, 6)
 			if p.As == AFMOVD {