cmd/compile/internal/ir: simplify printing of OLITERALs

This formatting used to be relevant to user error diagnostics and
(much earlier) even to the old textual export data format, but now
it's only relevant to backend debugging. So we can simplify a lot,
adjusting a few test expectations accordingly.

Change-Id: Ibe8e029284ce6150bfa24ef794d8d9eff66dbdea
Reviewed-on: https://go-review.googlesource.com/c/go/+/526375
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -133,10 +133,14 @@ type BasicLit struct {
 }
 
 func NewBasicLit(pos src.XPos, val constant.Value) Node {
+	if val == nil || val.Kind() == constant.Unknown {
+		base.FatalfAt(pos, "bad value: %v", val)
+	}
+
 	n := &BasicLit{val: val}
 	n.op = OLITERAL
 	n.pos = pos
-	n.SetType(idealType(val.Kind()))
+	n.SetType(types.UntypedTypes[val.Kind()])
 	n.SetTypecheck(1)
 	return n
 }

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

@@ -580,46 +580,29 @@ func exprFmt(n Node, s fmt.State, prec int) {
 	case ONIL:
 		fmt.Fprint(s, "nil")
 
-	case OLITERAL: // this is a bit of a mess
-		if !exportFormat && n.Sym() != nil {
+	case OLITERAL:
+		if n.Sym() != nil {
 			fmt.Fprint(s, n.Sym())
 			return
 		}
 
-		needUnparen := false
-		if n.Type() != nil && !n.Type().IsUntyped() {
-			// Need parens when type begins with what might
-			// be misinterpreted as a unary operator: * or <-.
-			if n.Type().IsPtr() || (n.Type().IsChan() && n.Type().ChanDir() == types.Crecv) {
-				fmt.Fprintf(s, "(%v)(", n.Type())
-			} else {
-				fmt.Fprintf(s, "%v(", n.Type())
-			}
-			needUnparen = true
-		}
+		typ := n.Type()
+		val := n.Val()
 
-		if n.Type() == types.UntypedRune {
-			switch x, ok := constant.Uint64Val(n.Val()); {
-			case !ok:
-				fallthrough
-			default:
-				fmt.Fprintf(s, "('\\x00' + %v)", n.Val())
-
-			case x < utf8.RuneSelf:
+		// Special case for rune constants.
+		if typ == types.RuneType || typ == types.UntypedRune {
+			if x, ok := constant.Uint64Val(val); ok && x <= utf8.MaxRune {
 				fmt.Fprintf(s, "%q", x)
-
-			case x < 1<<16:
-				fmt.Fprintf(s, "'\\u%04x'", x)
-
-			case x <= utf8.MaxRune:
-				fmt.Fprintf(s, "'\\U%08x'", x)
+				return
 			}
-		} else {
-			fmt.Fprint(s, types.FmtConst(n.Val(), s.Flag('#')))
 		}
 
-		if needUnparen {
-			fmt.Fprintf(s, ")")
+		// Only include typ if it's neither the default nor untyped type
+		// for the constant value.
+		if k := val.Kind(); typ == types.Types[types.DefaultKinds[k]] || typ == types.UntypedTypes[k] {
+			fmt.Fprint(s, val)
+		} else {
+			fmt.Fprintf(s, "%v(%v)", typ, val)
 		}
 
 	case ODCLFUNC:

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

@@ -60,23 +60,6 @@ func ValidTypeForConst(t *types.Type, v constant.Value) bool {
 	panic("unreachable")
 }
 
-func idealType(ct constant.Kind) *types.Type {
-	switch ct {
-	case constant.String:
-		return types.UntypedString
-	case constant.Bool:
-		return types.UntypedBool
-	case constant.Int:
-		return types.UntypedInt
-	case constant.Float:
-		return types.UntypedFloat
-	case constant.Complex:
-		return types.UntypedComplex
-	}
-	base.Fatalf("unexpected Ctype: %v", ct)
-	return nil
-}
-
 var OKForConst [types.NTYPE]bool
 
 // Int64Val returns n as an int64.

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

@@ -8,7 +8,6 @@ import (
 	"bytes"
 	"encoding/binary"
 	"fmt"
-	"go/constant"
 	"strconv"
 	"strings"
 	"sync"
@@ -683,41 +682,6 @@ func SplitVargenSuffix(name string) (base, suffix string) {
 	return name, ""
 }
 
-// Val
-
-func FmtConst(v constant.Value, sharp bool) string {
-	if !sharp && v.Kind() == constant.Complex {
-		real, imag := constant.Real(v), constant.Imag(v)
-
-		var re string
-		sre := constant.Sign(real)
-		if sre != 0 {
-			re = real.String()
-		}
-
-		var im string
-		sim := constant.Sign(imag)
-		if sim != 0 {
-			im = imag.String()
-		}
-
-		switch {
-		case sre == 0 && sim == 0:
-			return "0"
-		case sre == 0:
-			return im + "i"
-		case sim == 0:
-			return re
-		case sim < 0:
-			return fmt.Sprintf("(%s%si)", re, im)
-		default:
-			return fmt.Sprintf("(%s+%si)", re, im)
-		}
-	}
-
-	return v.String()
-}
-
 // TypeHash computes a hash value for type t to use in type switch statements.
 func TypeHash(t *Type) uint32 {
 	p := t.LinkString()

src/cmd/compile/internal/types/type.go

@@ -9,6 +9,7 @@ import (
 	"cmd/internal/objabi"
 	"cmd/internal/src"
 	"fmt"
+	"go/constant"
 	"internal/types/errors"
 	"sync"
 )
@@ -128,6 +129,25 @@ var (
 	UntypedComplex = newType(TIDEAL)
 )
 
+// UntypedTypes maps from a constant.Kind to its untyped Type
+// representation.
+var UntypedTypes = [...]*Type{
+	constant.Bool:    UntypedBool,
+	constant.String:  UntypedString,
+	constant.Int:     UntypedInt,
+	constant.Float:   UntypedFloat,
+	constant.Complex: UntypedComplex,
+}
+
+// DefaultKinds maps from a constant.Kind to its default Kind.
+var DefaultKinds = [...]Kind{
+	constant.Bool:    TBOOL,
+	constant.String:  TSTRING,
+	constant.Int:     TINT,
+	constant.Float:   TFLOAT64,
+	constant.Complex: TCOMPLEX128,
+}
+
 // A Type represents a Go type.
 //
 // There may be multiple unnamed types with identical structure. However, there must