cmd/compile: simplify value coding for unified IR

In indexed export, values are always exported along with their type
and are encoded in a type-sensitive manner, because this matches how
cmd/compile handled constants internally.

However, go/types intentionally differs from this, decoupling type
from value representation. As unified IR strives to be more
go/types-centric, it makes sense to embrace this and make values a
more first-class encoding.

Change-Id: If21d849c4f610358bd776d5665469d180bcd5f6e
Reviewed-on: https://go-review.googlesource.com/c/go/+/348014
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

src/cmd/compile/internal/noder/decoder.go

@@ -255,7 +255,8 @@ func (r *decoder) strings() []string {
 	return res
 }
 
-func (r *decoder) rawValue() constant.Value {
+func (r *decoder) value() constant.Value {
+	r.sync(syncValue)
 	isComplex := r.bool()
 	val := r.scalar()
 	if isComplex {

src/cmd/compile/internal/noder/encoder.go

@@ -237,7 +237,8 @@ func (w *encoder) strings(ss []string) {
 	}
 }
 
-func (w *encoder) rawValue(val constant.Value) {
+func (w *encoder) value(val constant.Value) {
+	w.sync(syncValue)
 	if w.bool(val.Kind() == constant.Complex) {
 		w.scalar(constant.Real(val))
 		w.scalar(constant.Imag(val))

src/cmd/compile/internal/noder/reader.go

@@ -626,7 +626,8 @@ func (pr *pkgReader) objIdx(idx int, implicits, explicits []*types.Type) ir.Node
 
 	case objConst:
 		name := do(ir.OLITERAL, false)
-		typ, val := r.value()
+		typ := r.typ()
+		val := FixValue(typ, r.value())
 		setType(name, typ)
 		setValue(name, val)
 		return name
@@ -755,12 +756,6 @@ func (r *reader) typeParamNames() {
 	}
 }
 
-func (r *reader) value() (*types.Type, constant.Value) {
-	r.sync(syncValue)
-	typ := r.typ()
-	return typ, FixValue(typ, r.rawValue())
-}
-
 func (r *reader) method() *types.Field {
 	r.sync(syncMethod)
 	pos := r.pos()
@@ -1556,7 +1551,8 @@ func (r *reader) expr() (res ir.Node) {
 
 	case exprConst:
 		pos := r.pos()
-		typ, val := r.value()
+		typ := r.typ()
+		val := FixValue(typ, r.value())
 		op := r.op()
 		orig := r.string()
 		return typecheck.Expr(OrigConst(pos, typ, val, op, orig))

src/cmd/compile/internal/noder/reader2.go

@@ -7,8 +7,6 @@
 package noder
 
 import (
-	"go/constant"
-
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/syntax"
 	"cmd/compile/internal/types2"
@@ -388,7 +386,8 @@ func (pr *pkgReader2) objIdx(idx int) (*types2.Package, string) {
 
 		case objConst:
 			pos := r.pos()
-			typ, val := r.value()
+			typ := r.typ()
+			val := r.value()
 			return types2.NewConst(pos, objPkg, objName, typ, val)
 
 		case objFunc:
@@ -428,11 +427,6 @@ func (pr *pkgReader2) objIdx(idx int) (*types2.Package, string) {
 	return objPkg, objName
 }
 
-func (r *reader2) value() (types2.Type, constant.Value) {
-	r.sync(syncValue)
-	return r.typ(), r.rawValue()
-}
-
 func (pr *pkgReader2) objDictIdx(idx int) *reader2Dict {
 	r := pr.newReader(relocObjDict, idx, syncObject1)
 

src/cmd/compile/internal/noder/writer.go

@@ -542,7 +542,8 @@ func (w *writer) doObj(obj types2.Object) codeObj {
 
 	case *types2.Const:
 		w.pos(obj)
-		w.value(obj.Type(), obj.Val())
+		w.typ(obj.Type())
+		w.value(obj.Val())
 		return objConst
 
 	case *types2.Func:
@@ -598,12 +599,6 @@ func (w *writer) typExpr(expr syntax.Expr) {
 	w.typ(tv.Type)
 }
 
-func (w *writer) value(typ types2.Type, val constant.Value) {
-	w.sync(syncValue)
-	w.typ(typ)
-	w.rawValue(val)
-}
-
 // objDict writes the dictionary needed for reading the given object.
 func (w *writer) objDict(obj types2.Object, dict *writerDict) {
 	// TODO(mdempsky): Split objDict into multiple entries? reader.go
@@ -1199,7 +1194,8 @@ func (w *writer) expr(expr syntax.Expr) {
 
 			w.code(exprConst)
 			w.pos(pos)
-			w.value(tv.Type, tv.Value)
+			w.typ(tv.Type)
+			w.value(tv.Value)
 
 			// TODO(mdempsky): These details are only important for backend
 			// diagnostics. Explore writing them out separately.