cmd/internal/obj/arm64: materialize float constant 0 from zero register

Materialize float constant 0 from integer zero register, instead
of loading from constant pool.

Also fix assembling FMOV from zero register to FP register.

Change-Id: Ie413dd342cedebdb95ba8cfc220e23ed2a39e885
Reviewed-on: https://go-review.googlesource.com/32250
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -2380,13 +2380,15 @@ func asmout(ctxt *obj.Link, p *obj.Prog, o *Optab, out []uint32) {
 		o2 |= uint32(p.To.Reg & 31)
 
 	case 29: /* op Rn, Rd */
-		if (p.As == AFMOVD || p.As == AFMOVS) && (aclass(ctxt, &p.From) == C_REG || aclass(ctxt, &p.To) == C_REG) {
+		fc := aclass(ctxt, &p.From)
+		tc := aclass(ctxt, &p.To)
+		if (p.As == AFMOVD || p.As == AFMOVS) && (fc == C_REG || fc == C_ZCON || tc == C_REG || tc == C_ZCON) {
 			// FMOV Rx, Fy or FMOV Fy, Rx
 			o1 = FPCVTI(0, 0, 0, 0, 6)
 			if p.As == AFMOVD {
 				o1 |= 1<<31 | 1<<22 // 64-bit
 			}
-			if aclass(ctxt, &p.From) == C_REG {
+			if fc == C_REG || fc == C_ZCON {
 				o1 |= 1 << 16 // FMOV Rx, Fy
 			}
 		} else {

src/cmd/internal/obj/arm64/obj7.go

@@ -262,6 +262,11 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 		if p.From.Type == obj.TYPE_FCONST {
 			f32 := float32(p.From.Val.(float64))
 			i32 := math.Float32bits(f32)
+			if i32 == 0 {
+				p.From.Type = obj.TYPE_REG
+				p.From.Reg = REGZERO
+				break
+			}
 			literal := fmt.Sprintf("$f32.%08x", i32)
 			s := obj.Linklookup(ctxt, literal, 0)
 			s.Size = 4
@@ -275,6 +280,11 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 	case AFMOVD:
 		if p.From.Type == obj.TYPE_FCONST {
 			i64 := math.Float64bits(p.From.Val.(float64))
+			if i64 == 0 {
+				p.From.Type = obj.TYPE_REG
+				p.From.Reg = REGZERO
+				break
+			}
 			literal := fmt.Sprintf("$f64.%016x", i64)
 			s := obj.Linklookup(ctxt, literal, 0)
 			s.Size = 8