cmd/compile: start using reflect.Value.IsZero

We now require Go 1.17.13 to bootstrap via make.bash,
and since reflect.Value.IsZero was added in Go 1.13,
we can now use it directly to save a bit of copy pasting.

Change-Id: I77eef782cbbf86c72a4505c8b4866c9658914a24
Reviewed-on: https://go-review.googlesource.com/c/go/+/479395
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>

src/cmd/compile/internal/ir/dump.go

@@ -218,7 +218,7 @@ func (p *dumper) dump(x reflect.Value, depth int) {
 					continue // Op field already printed for Nodes
 				}
 				x := x.Field(i)
-				if isZeroVal(x) {
+				if x.IsZero() {
 					omitted = true
 					continue // exclude zero-valued fields
 				}
@@ -248,22 +248,6 @@ func (p *dumper) dump(x reflect.Value, depth int) {
 	}
 }
 
-func isZeroVal(x reflect.Value) bool {
-	switch x.Kind() {
-	case reflect.Bool:
-		return !x.Bool()
-	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		return x.Int() == 0
-	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
-		return x.Uint() == 0
-	case reflect.String:
-		return x.String() == ""
-	case reflect.Interface, reflect.Ptr, reflect.Slice:
-		return x.IsNil()
-	}
-	return false
-}
-
 func commonPrefixLen(a, b string) (i int) {
 	for i < len(a) && i < len(b) && a[i] == b[i] {
 		i++

src/cmd/compile/internal/ir/fmt.go

@@ -9,7 +9,6 @@ import (
 	"fmt"
 	"go/constant"
 	"io"
-	"math"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -1022,7 +1021,7 @@ func dumpNodeHeader(w io.Writer, n Node) {
 			name := strings.TrimSuffix(tf.Name, "_")
 			vf := v.Field(i)
 			vfi := vf.Interface()
-			if name == "Offset" && vfi == types.BADWIDTH || name != "Offset" && isZero(vf) {
+			if name == "Offset" && vfi == types.BADWIDTH || name != "Offset" && vf.IsZero() {
 				continue
 			}
 			if vfi == true {
@@ -1261,40 +1260,3 @@ func dumpNodes(w io.Writer, list Nodes, depth int) {
 		dumpNode(w, n, depth)
 	}
 }
-
-// reflect.IsZero is not available in Go 1.4 (added in Go 1.13), so we use this copy instead.
-func isZero(v reflect.Value) bool {
-	switch v.Kind() {
-	case reflect.Bool:
-		return !v.Bool()
-	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		return v.Int() == 0
-	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
-		return v.Uint() == 0
-	case reflect.Float32, reflect.Float64:
-		return math.Float64bits(v.Float()) == 0
-	case reflect.Complex64, reflect.Complex128:
-		c := v.Complex()
-		return math.Float64bits(real(c)) == 0 && math.Float64bits(imag(c)) == 0
-	case reflect.Array:
-		for i := 0; i < v.Len(); i++ {
-			if !isZero(v.Index(i)) {
-				return false
-			}
-		}
-		return true
-	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice, reflect.UnsafePointer:
-		return v.IsNil()
-	case reflect.String:
-		return v.Len() == 0
-	case reflect.Struct:
-		for i := 0; i < v.NumField(); i++ {
-			if !isZero(v.Field(i)) {
-				return false
-			}
-		}
-		return true
-	default:
-		return false
-	}
-}