[dev.typeparams] cmd/compile: add and use ir.RawOrigExpr

This CL adds ir.RawOrigExpr, which can be used to represent arbitrary
constant expressions without needing to build and carry around an
entire IR representation of the original expression. It also allows
distinguishing how the constant was originally written by the
user (e.g., "0xff" vs "255").

This CL then also updates irgen to make use of this functionality for
expressions that were constant folded by types2.

Change-Id: I41e04e228e715ae2735c357b75633a2d08ee7021
Reviewed-on: https://go-review.googlesource.com/c/go/+/323210
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

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

@@ -448,6 +448,20 @@ func (n *ParenExpr) SetOTYPE(t *types.Type) {
 	t.SetNod(n)
 }
 
+// A RawOrigExpr represents an arbitrary Go expression as a string value.
+// When printed in diagnostics, the string value is written out exactly as-is.
+type RawOrigExpr struct {
+	miniExpr
+	Raw string
+}
+
+func NewRawOrigExpr(pos src.XPos, op Op, raw string) *RawOrigExpr {
+	n := &RawOrigExpr{Raw: raw}
+	n.pos = pos
+	n.op = op
+	return n
+}
+
 // A ResultExpr represents a direct access to a result.
 type ResultExpr struct {
 	miniExpr

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

@@ -567,6 +567,11 @@ func exprFmt(n Node, s fmt.State, prec int) {
 		return
 	}
 
+	if n, ok := n.(*RawOrigExpr); ok {
+		fmt.Fprint(s, n.Raw)
+		return
+	}
+
 	switch n.Op() {
 	case OPAREN:
 		n := n.(*ParenExpr)

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

@@ -947,6 +947,22 @@ func (n *RangeStmt) editChildren(edit func(Node) Node) {
 	}
 }
 
+func (n *RawOrigExpr) Format(s fmt.State, verb rune) { fmtNode(n, s, verb) }
+func (n *RawOrigExpr) copy() Node {
+	c := *n
+	c.init = copyNodes(c.init)
+	return &c
+}
+func (n *RawOrigExpr) doChildren(do func(Node) bool) bool {
+	if doNodes(n.init, do) {
+		return true
+	}
+	return false
+}
+func (n *RawOrigExpr) editChildren(edit func(Node) Node) {
+	editNodes(n.init, edit)
+}
+
 func (n *ResultExpr) Format(s fmt.State, verb rune) { fmtNode(n, s, verb) }
 func (n *ResultExpr) copy() Node {
 	c := *n

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

@@ -66,7 +66,7 @@ func Float64Val(v constant.Value) float64 {
 
 func AssertValidTypeForConst(t *types.Type, v constant.Value) {
 	if !ValidTypeForConst(t, v) {
-		base.Fatalf("%v does not represent %v (%v)", t, v, v.Kind())
+		base.Fatalf("%v (%v) does not represent %v (%v)", t, t.Kind(), v, v.Kind())
 	}
 }
 

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

@@ -5,6 +5,8 @@
 package noder
 
 import (
+	"fmt"
+
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/ir"
 	"cmd/compile/internal/syntax"
@@ -15,6 +17,8 @@ import (
 )
 
 func (g *irgen) expr(expr syntax.Expr) ir.Node {
+	expr = unparen(expr) // skip parens; unneeded after parse+typecheck
+
 	if expr == nil {
 		return nil
 	}
@@ -67,7 +71,9 @@ func (g *irgen) expr(expr syntax.Expr) ir.Node {
 
 	// Constant expression.
 	if tv.Value != nil {
-		return Const(g.pos(expr), g.typ(typ), tv.Value)
+		typ := g.typ(typ)
+		value := FixValue(typ, tv.Value)
+		return OrigConst(g.pos(expr), typ, value, constExprOp(expr), syntax.String(expr))
 	}
 
 	n := g.expr0(typ, expr)
@@ -161,9 +167,6 @@ func (g *irgen) expr0(typ types2.Type, expr syntax.Expr) ir.Node {
 		typed(g.typ(typ), n)
 		return n
 
-	case *syntax.ParenExpr:
-		return g.expr(expr.X) // skip parens; unneeded after parse+typecheck
-
 	case *syntax.SelectorExpr:
 		// Qualified identifier.
 		if name, ok := expr.X.(*syntax.Name); ok {
@@ -317,13 +320,17 @@ func getTargs(selinfo *types2.Selection) []types2.Type {
 }
 
 func (g *irgen) exprList(expr syntax.Expr) []ir.Node {
+	return g.exprs(unpackListExpr(expr))
+}
+
+func unpackListExpr(expr syntax.Expr) []syntax.Expr {
 	switch expr := expr.(type) {
 	case nil:
 		return nil
 	case *syntax.ListExpr:
-		return g.exprs(expr.ElemList)
+		return expr.ElemList
 	default:
-		return []ir.Node{g.expr(expr)}
+		return []syntax.Expr{expr}
 	}
 }
 
@@ -402,3 +409,35 @@ func (g *irgen) typeExpr(typ syntax.Expr) *types.Type {
 	}
 	return n.Type()
 }
+
+// constExprOp returns an ir.Op that represents the outermost
+// operation of the given constant expression. It's intended for use
+// with ir.RawOrigExpr.
+func constExprOp(expr syntax.Expr) ir.Op {
+	switch expr := expr.(type) {
+	default:
+		panic(fmt.Sprintf("%s: unexpected expression: %T", expr.Pos(), expr))
+
+	case *syntax.BasicLit:
+		return ir.OLITERAL
+	case *syntax.Name, *syntax.SelectorExpr:
+		return ir.ONAME
+	case *syntax.CallExpr:
+		return ir.OCALL
+	case *syntax.Operation:
+		if expr.Y == nil {
+			return unOps[expr.Op]
+		}
+		return binOps[expr.Op]
+	}
+}
+
+func unparen(expr syntax.Expr) syntax.Expr {
+	for {
+		paren, ok := expr.(*syntax.ParenExpr)
+		if !ok {
+			return expr
+		}
+		expr = paren.X
+	}
+}

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

@@ -43,6 +43,32 @@ func Const(pos src.XPos, typ *types.Type, val constant.Value) ir.Node {
 	return typed(typ, ir.NewBasicLit(pos, val))
 }
 
+func OrigConst(pos src.XPos, typ *types.Type, val constant.Value, op ir.Op, raw string) ir.Node {
+	orig := ir.NewRawOrigExpr(pos, op, raw)
+	return ir.NewConstExpr(val, typed(typ, orig))
+}
+
+// FixValue returns val after converting and truncating it as
+// appropriate for typ.
+func FixValue(typ *types.Type, val constant.Value) constant.Value {
+	assert(typ.Kind() != types.TFORW)
+	switch {
+	case typ.IsInteger():
+		val = constant.ToInt(val)
+	case typ.IsFloat():
+		val = constant.ToFloat(val)
+	case typ.IsComplex():
+		val = constant.ToComplex(val)
+	}
+	if !typ.IsUntyped() {
+		val = typecheck.DefaultLit(ir.NewBasicLit(src.NoXPos, val), typ).Val()
+	}
+	if typ.Kind() != types.TTYPEPARAM {
+		ir.AssertValidTypeForConst(typ, val)
+	}
+	return val
+}
+
 func Nil(pos src.XPos, typ *types.Type) ir.Node {
 	return typed(typ, ir.NewNilExpr(pos))
 }