[dev.typeparams] cmd/compile: slightly more incremental unified typecheck

This CL pushes the typecheck.Expr calls further down to the IR
construction points. It turns out we don't really care about
typecheck.AssignExpr, because it's only used to distinguish whether
ir.BlankNode is allowed. We can avoid that issue by just skipping the
call to typecheck.Expr for blank nodes.

Similarly, for typecheck.Callee, only two details matter: (1) don't
report errors for builtin functions (which aren't allowed outside of
callee contexts); and (2) method-value selector expressions need to
have Op ODOTMETH/ODOTINTER rather than OMETHVALUE. The first can be
handled by simply skipping typecheck on Names (as with ir.BlankNode,
we don't need to typecheck these). The second currently requires
adding a 'callee bool' parameter to disambiguate the context.

The other option would be for exprCall to reset the fun's Op from
OMETHVALUE to OXDOT and let typecheck handle it a second time. But I
anticipate needing to add extra logic in the exprSelector case which
would be harder to undo, so this seems somewhat better.

Change-Id: I1a8dfb6af04265ab466fd7f4cb6ee8b479e92282
Reviewed-on: https://go-review.googlesource.com/c/go/+/333769
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Matthew Dempsky <mdempsky@google.com>

1 files changed, 42 insertions, 34 deletions

diff --git a/src/cmd/compile/internal/noder/reader.go b/src/cmd/compile/internal/noder/reader.go
index 19e51d9eba..25aac6c026 100644
--- a/src/cmd/compile/internal/noder/reader.go
+++ b/src/cmd/compile/internal/noder/reader.go
@@ -1252,7 +1252,7 @@ func (r *reader) assignList() ([]*ir.Name, []ir.Node) {
 			continue
 		}
 
-		lhs[i] = typecheck.AssignExpr(r.expr0())
+		lhs[i] = r.expr()
 	}
 
 	return names, lhs
@@ -1447,18 +1447,13 @@ func (r *reader) initDefn(defn ir.InitNode, names []*ir.Name) bool {
 // @@@ Expressions
 
 // expr reads and returns a typechecked expression.
-func (r *reader) expr() ir.Node {
-	n := r.expr0()
-	if n == nil || n.Op() == ir.OTYPE {
-		// TODO(mdempsky): Push this responsibility up to callers?
-		return n
-	}
-	return typecheck.Expr(n)
-}
+func (r *reader) expr() (res ir.Node) {
+	defer func() {
+		if res != nil && res.Typecheck() == 0 {
+			base.FatalfAt(res.Pos(), "%v missed typecheck", res)
+		}
+	}()
 
-// expr0 reads and returns an expression, possibly untypechecked.
-// The caller must typecheck the result as appropriate for its context.
-func (r *reader) expr0() ir.Node {
 	switch tag := codeExpr(r.code(syncExpr)); tag {
 	default:
 		panic("unhandled expression")
@@ -1467,23 +1462,30 @@ func (r *reader) expr0() ir.Node {
 		return nil
 
 	case exprBlank:
-		return ir.BlankNode
+		// blank only allowed in LHS of assignments
+		// TODO(mdempsky): Handle directly in assignList instead?
+		return typecheck.AssignExpr(ir.BlankNode)
 
 	case exprLocal:
-		return r.useLocal()
+		return typecheck.Expr(r.useLocal())
 
 	case exprName:
-		return r.obj()
+		// Callee instead of Expr allows builtins
+		// TODO(mdempsky): Handle builtins directly in exprCall, like method calls?
+		return typecheck.Callee(r.obj())
 
 	case exprType:
-		return ir.TypeNode(r.typ())
+		// TODO(mdempsky): ir.TypeNode should probably return a typecheck'd node.
+		n := ir.TypeNode(r.typ())
+		n.SetTypecheck(1)
+		return n
 
 	case exprConst:
 		pos := r.pos()
 		typ, val := r.value()
 		op := r.op()
 		orig := r.string()
-		return OrigConst(pos, typ, val, op, orig)
+		return typecheck.Expr(OrigConst(pos, typ, val, op, orig))
 
 	case exprCompLit:
 		return r.compLit()
@@ -1495,13 +1497,13 @@ func (r *reader) expr0() ir.Node {
 		x := r.expr()
 		pos := r.pos()
 		_, sym := r.selector()
-		return ir.NewSelectorExpr(pos, ir.OXDOT, x, sym)
+		return typecheck.Expr(ir.NewSelectorExpr(pos, ir.OXDOT, x, sym))
 
 	case exprIndex:
 		x := r.expr()
 		pos := r.pos()
 		index := r.expr()
-		return ir.NewIndexExpr(pos, x, index)
+		return typecheck.Expr(ir.NewIndexExpr(pos, x, index))
 
 	case exprSlice:
 		x := r.expr()
@@ -1514,13 +1516,13 @@ func (r *reader) expr0() ir.Node {
 		if index[2] != nil {
 			op = ir.OSLICE3
 		}
-		return ir.NewSliceExpr(pos, op, x, index[0], index[1], index[2])
+		return typecheck.Expr(ir.NewSliceExpr(pos, op, x, index[0], index[1], index[2]))
 
 	case exprAssert:
 		x := r.expr()
 		pos := r.pos()
 		typ := r.expr().(ir.Ntype)
-		return ir.NewTypeAssertExpr(pos, x, typ)
+		return typecheck.Expr(ir.NewTypeAssertExpr(pos, x, typ))
 
 	case exprUnaryOp:
 		op := r.op()
@@ -1529,11 +1531,11 @@ func (r *reader) expr0() ir.Node {
 
 		switch op {
 		case ir.OADDR:
-			return typecheck.NodAddrAt(pos, x)
+			return typecheck.Expr(typecheck.NodAddrAt(pos, x))
 		case ir.ODEREF:
-			return ir.NewStarExpr(pos, x)
+			return typecheck.Expr(ir.NewStarExpr(pos, x))
 		}
-		return ir.NewUnaryExpr(pos, op, x)
+		return typecheck.Expr(ir.NewUnaryExpr(pos, op, x))
 
 	case exprBinaryOp:
 		op := r.op()
@@ -1543,12 +1545,17 @@ func (r *reader) expr0() ir.Node {
 
 		switch op {
 		case ir.OANDAND, ir.OOROR:
-			return ir.NewLogicalExpr(pos, op, x, y)
+			return typecheck.Expr(ir.NewLogicalExpr(pos, op, x, y))
 		}
-		return ir.NewBinaryExpr(pos, op, x, y)
+		return typecheck.Expr(ir.NewBinaryExpr(pos, op, x, y))
 
 	case exprCall:
-		fun := typecheck.Callee(r.expr0())
+		fun := r.expr()
+		if r.bool() { // method call
+			pos := r.pos()
+			_, sym := r.selector()
+			fun = typecheck.Callee(ir.NewSelectorExpr(pos, ir.OXDOT, fun, sym))
+		}
 		pos := r.pos()
 		args := r.exprs()
 		dots := r.bool()
@@ -1558,17 +1565,17 @@ func (r *reader) expr0() ir.Node {
 		typ := r.typ()
 		pos := r.pos()
 		x := r.expr()
-		return ir.NewConvExpr(pos, ir.OCONV, typ, x)
+		return typecheck.Expr(ir.NewConvExpr(pos, ir.OCONV, typ, x))
 	}
 }
 
 func (r *reader) compLit() ir.Node {
 	r.sync(syncCompLit)
 	pos := r.pos()
-	typ := r.typ()
+	typ0 := r.typ()
 
-	isPtrLit := typ.IsPtr()
-	if isPtrLit {
+	typ := typ0
+	if typ.IsPtr() {
 		typ = typ.Elem()
 	}
 	if typ.Kind() == types.TFORW {
@@ -1591,9 +1598,10 @@ func (r *reader) compLit() ir.Node {
 		*elemp = wrapName(r.pos(), r.expr())
 	}
 
-	lit := ir.NewCompLitExpr(pos, ir.OCOMPLIT, ir.TypeNode(typ), elems)
-	if isPtrLit {
-		return typecheck.NodAddrAt(pos, lit)
+	lit := typecheck.Expr(ir.NewCompLitExpr(pos, ir.OCOMPLIT, ir.TypeNode(typ), elems))
+	if typ0.IsPtr() {
+		lit = typecheck.Expr(typecheck.NodAddrAt(pos, lit))
+		lit.SetType(typ0)
 	}
 	return lit
 }