cmd/compile: simplify OPTRLIT handling

Previously, we would recognize &(T{...}) expressions during type
checking, rewrite them into (*T){...}, and then do a lot of extra work
to make sure the user doesn't write (*T){...} themselves and
resynthesizing the OPTRLIT later on.

This CL simply handles &T{...} directly in the straight forward
manner, by changing OADDR directly to OPTRLIT when appropriate.

While here, match go/types's invalid composite literal type error
message.

Passes toolstash-check.

Change-Id: I902b14c7e2cd9fa93e6915dd58272d2352ba38f8
Reviewed-on: https://go-review.googlesource.com/c/go/+/197120
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

7 files changed, 67 insertions, 113 deletions

diff --git a/src/cmd/compile/internal/gc/closure.go b/src/cmd/compile/internal/gc/closure.go
index 21b3461b47..6080777e8e 100644
--- a/src/cmd/compile/internal/gc/closure.go
+++ b/src/cmd/compile/internal/gc/closure.go
@@ -395,18 +395,16 @@ func walkclosure(clo *Node, init *Nodes) *Node {
 
 	typ := closureType(clo)
 
-	clos := nod(OCOMPLIT, nil, nod(ODEREF, typenod(typ), nil))
+	clos := nod(OCOMPLIT, nil, typenod(typ))
 	clos.Esc = clo.Esc
-	clos.Right.SetImplicit(true)
 	clos.List.Set(append([]*Node{nod(OCFUNC, xfunc.Func.Nname, nil)}, clo.Func.Enter.Slice()...))
 
+	clos = nod(OADDR, clos, nil)
+	clos.Esc = clo.Esc
+
 	// Force type conversion from *struct to the func type.
 	clos = convnop(clos, clo.Type)
 
-	// typecheck will insert a PTRLIT node under CONVNOP,
-	// tag it with escape analysis result.
-	clos.Left.Esc = clo.Esc
-
 	// non-escaping temp to use, if any.
 	if x := prealloc[clo]; x != nil {
 		if !types.Identical(typ, x.Type) {
@@ -547,18 +545,16 @@ func walkpartialcall(n *Node, init *Nodes) *Node {
 
 	typ := partialCallType(n)
 
-	clos := nod(OCOMPLIT, nil, nod(ODEREF, typenod(typ), nil))
+	clos := nod(OCOMPLIT, nil, typenod(typ))
 	clos.Esc = n.Esc
-	clos.Right.SetImplicit(true)
 	clos.List.Set2(nod(OCFUNC, n.Func.Nname, nil), n.Left)
 
+	clos = nod(OADDR, clos, nil)
+	clos.Esc = n.Esc
+
 	// Force type conversion from *struct to the func type.
 	clos = convnop(clos, n.Type)
 
-	// The typecheck inside convnop will insert a PTRLIT node under CONVNOP.
-	// Tag it with escape analysis result.
-	clos.Left.Esc = n.Esc
-
 	// non-escaping temp to use, if any.
 	if x := prealloc[n]; x != nil {
 		if !types.Identical(typ, x.Type) {
diff --git a/src/cmd/compile/internal/gc/fmt.go b/src/cmd/compile/internal/gc/fmt.go
index e7a2def950..e449444ca5 100644
--- a/src/cmd/compile/internal/gc/fmt.go
+++ b/src/cmd/compile/internal/gc/fmt.go
@@ -1304,12 +1304,8 @@ func (n *Node) exprfmt(s fmt.State, prec int, mode fmtMode) {
 
 	case OCOMPLIT:
 		if mode == FErr {
-			if n.Right != nil && n.Right.Type != nil && !n.Implicit() {
-				if n.Right.Implicit() && n.Right.Type.IsPtr() {
-					mode.Fprintf(s, "&%v literal", n.Right.Type.Elem())
-					return
-				}
-				mode.Fprintf(s, "%v literal", n.Right.Type)
+			if n.Right != nil {
+				mode.Fprintf(s, "%v literal", n.Right)
 				return
 			}
 
diff --git a/src/cmd/compile/internal/gc/iexport.go b/src/cmd/compile/internal/gc/iexport.go
index eeca0b4083..da0a8be30e 100644
--- a/src/cmd/compile/internal/gc/iexport.go
+++ b/src/cmd/compile/internal/gc/iexport.go
@@ -1181,10 +1181,10 @@ func (w *exportWriter) expr(n *Node) {
 	// 	should have been resolved by typechecking - handled by default case
 
 	case OPTRLIT:
-		w.op(OPTRLIT)
+		w.op(OPTRLIT) // TODO(mdempsky): Replace with OADDR.
 		w.pos(n.Pos)
 		w.expr(n.Left)
-		w.bool(n.Implicit())
+		w.bool(false)
 
 	case OSTRUCTLIT:
 		w.op(OSTRUCTLIT)
diff --git a/src/cmd/compile/internal/gc/iimport.go b/src/cmd/compile/internal/gc/iimport.go
index 4862f86344..dd35b9ba46 100644
--- a/src/cmd/compile/internal/gc/iimport.go
+++ b/src/cmd/compile/internal/gc/iimport.go
@@ -802,17 +802,8 @@ func (r *importReader) node() *Node {
 	//	unimplemented
 
 	case OPTRLIT:
-		pos := r.pos()
-		n := npos(pos, r.expr())
-		if !r.bool() /* !implicit, i.e. '&' operator */ {
-			if n.Op == OCOMPLIT {
-				// Special case for &T{...}: turn into (*T){...}.
-				n.Right = nodl(pos, ODEREF, n.Right, nil)
-				n.Right.SetImplicit(true)
-			} else {
-				n = nodl(pos, OADDR, n, nil)
-			}
-		}
+		n := nodl(r.pos(), OADDR, r.expr(), nil)
+		_ = r.bool()
 		return n
 
 	case OSTRUCTLIT:
diff --git a/src/cmd/compile/internal/gc/noder.go b/src/cmd/compile/internal/gc/noder.go
index 91c7fd49b1..2922f9a872 100644
--- a/src/cmd/compile/internal/gc/noder.go
+++ b/src/cmd/compile/internal/gc/noder.go
@@ -662,15 +662,6 @@ func (p *noder) expr(expr syntax.Expr) *Node {
 		}
 		x := p.expr(expr.X)
 		if expr.Y == nil {
-			if expr.Op == syntax.And {
-				x = unparen(x) // TODO(mdempsky): Needed?
-				if x.Op == OCOMPLIT {
-					// Special case for &T{...}: turn into (*T){...}.
-					x.Right = p.nod(expr, ODEREF, x.Right, nil)
-					x.Right.SetImplicit(true)
-					return x
-				}
-			}
 			return p.nod(expr, p.unOp(expr.Op), x, nil)
 		}
 		return p.nod(expr, p.binOp(expr.Op), x, p.expr(expr.Y))
diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index 7d0d5f35be..989805c1df 100644
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -830,36 +830,38 @@ func typecheck1(n *Node, top int) (res *Node) {
 			n.Type = nil
 			return n
 		}
-		checklvalue(n.Left, "take the address of")
-		r := outervalue(n.Left)
-		var l *Node
-		for l = n.Left; l != r; l = l.Left {
-			l.SetAddrtaken(true)
-			if l.IsClosureVar() && !capturevarscomplete {
-				// Mark the original variable as Addrtaken so that capturevars
-				// knows not to pass it by value.
-				// But if the capturevars phase is complete, don't touch it,
-				// in case l.Name's containing function has not yet been compiled.
-				l.Name.Defn.SetAddrtaken(true)
+
+		switch n.Left.Op {
+		case OARRAYLIT, OMAPLIT, OSLICELIT, OSTRUCTLIT:
+			n.Op = OPTRLIT
+
+		default:
+			checklvalue(n.Left, "take the address of")
+			r := outervalue(n.Left)
+			if r.Orig != r && r.Op == ONAME {
+				Fatalf("found non-orig name node %v", r) // TODO(mdempsky): What does this mean?
+			}
+			for l := n.Left; ; l = l.Left {
+				l.SetAddrtaken(true)
+				if l.IsClosureVar() && !capturevarscomplete {
+					// Mark the original variable as Addrtaken so that capturevars
+					// knows not to pass it by value.
+					// But if the capturevars phase is complete, don't touch it,
+					// in case l.Name's containing function has not yet been compiled.
+					l.Name.Defn.SetAddrtaken(true)
+				}
+				if l == r {
+					break
+				}
+			}
+			n.Left = defaultlit(n.Left, nil)
+			if n.Left.Type == nil {
+				n.Type = nil
+				return n
 			}
 		}
 
-		if l.Orig != l && l.Op == ONAME {
-			Fatalf("found non-orig name node %v", l)
-		}
-		l.SetAddrtaken(true)
-		if l.IsClosureVar() && !capturevarscomplete {
-			// See comments above about closure variables.
-			l.Name.Defn.SetAddrtaken(true)
-		}
-		n.Left = defaultlit(n.Left, nil)
-		l = n.Left
-		t := l.Type
-		if t == nil {
-			n.Type = nil
-			return n
-		}
-		n.Type = types.NewPtr(t)
+		n.Type = types.NewPtr(n.Left.Type)
 
 	case OCOMPLIT:
 		ok |= ctxExpr
@@ -2723,13 +2725,8 @@ func fielddup(name string, hash map[string]bool) {
 	hash[name] = true
 }
 
-// iscomptype reports whether type t is a composite literal type
-// or a pointer to one.
+// iscomptype reports whether type t is a composite literal type.
 func iscomptype(t *types.Type) bool {
-	if t.IsPtr() {
-		t = t.Elem()
-	}
-
 	switch t.Etype {
 	case TARRAY, TSLICE, TSTRUCT, TMAP:
 		return true
@@ -2738,16 +2735,27 @@ func iscomptype(t *types.Type) bool {
 	}
 }
 
-func pushtype(n *Node, t *types.Type) {
-	if n == nil || n.Op != OCOMPLIT || !iscomptype(t) {
-		return
+// pushtype adds elided type information for composite literals if
+// appropriate, and returns the resulting expression.
+func pushtype(n *Node, t *types.Type) *Node {
+	if n == nil || n.Op != OCOMPLIT || n.Right != nil {
+		return n
 	}
 
-	if n.Right == nil {
+	switch {
+	case iscomptype(t):
+		// For T, return T{...}.
 		n.Right = typenod(t)
-		n.SetImplicit(true)       // don't print
-		n.Right.SetImplicit(true) // * is okay
+
+	case t.IsPtr() && iscomptype(t.Elem()):
+		// For *T, return &T{...}.
+		n.Right = typenod(t.Elem())
+
+		n = nodl(n.Pos, OADDR, n, nil)
+		n.SetImplicit(true)
 	}
+
+	return n
 }
 
 // The result of typecheckcomplit MUST be assigned back to n, e.g.
@@ -2782,28 +2790,9 @@ func typecheckcomplit(n *Node) (res *Node) {
 	nerr := nerrors
 	n.Type = t
 
-	if t.IsPtr() {
-		// For better or worse, we don't allow pointers as the composite literal type,
-		// except when using the &T syntax, which sets implicit on the ODEREF.
-		if !n.Right.Implicit() {
-			yyerror("invalid pointer type %v for composite literal (use &%v instead)", t, t.Elem())
-			n.Type = nil
-			return n
-		}
-
-		// Also, the underlying type must be a struct, map, slice, or array.
-		if !iscomptype(t) {
-			yyerror("invalid pointer type %v for composite literal", t)
-			n.Type = nil
-			return n
-		}
-
-		t = t.Elem()
-	}
-
 	switch t.Etype {
 	default:
-		yyerror("invalid type for composite literal: %v", t)
+		yyerror("invalid composite literal type %v", t)
 		n.Type = nil
 
 	case TARRAY, TSLICE:
@@ -2850,7 +2839,7 @@ func typecheckcomplit(n *Node) (res *Node) {
 			}
 
 			r := *vp
-			pushtype(r, t.Elem())
+			r = pushtype(r, t.Elem())
 			r = typecheck(r, ctxExpr)
 			*vp = assignconv(r, t.Elem(), "array or slice literal")
 
@@ -2887,13 +2876,13 @@ func typecheckcomplit(n *Node) (res *Node) {
 			}
 
 			r := l.Left
-			pushtype(r, t.Key())
+			r = pushtype(r, t.Key())
 			r = typecheck(r, ctxExpr)
 			l.Left = assignconv(r, t.Key(), "map key")
 			cs.add(lineno, l.Left, "key", "map literal")
 
 			r = l.Right
-			pushtype(r, t.Elem())
+			r = pushtype(r, t.Elem())
 			r = typecheck(r, ctxExpr)
 			l.Right = assignconv(r, t.Elem(), "map value")
 		}
@@ -3025,15 +3014,6 @@ func typecheckcomplit(n *Node) (res *Node) {
 	}
 
 	n.Orig = norig
-	if n.Type.IsPtr() {
-		n = nodl(n.Pos, OPTRLIT, n, nil)
-		n.SetTypecheck(1)
-		n.Type = n.Left.Type
-		n.Left.Type = t
-		n.Left.SetTypecheck(1)
-	}
-
-	n.Orig = norig
 	return n
 }
 
diff --git a/test/complit1.go b/test/complit1.go
index 83695a9e88..eb0f920fcb 100644
--- a/test/complit1.go
+++ b/test/complit1.go
@@ -46,8 +46,8 @@ var (
 	_ = &T{0, 0, "", nil}               // ok
 	_ = &T{i: 0, f: 0, s: "", next: {}} // ERROR "missing type in composite literal|omit types within composite literal"
 	_ = &T{0, 0, "", {}}                // ERROR "missing type in composite literal|omit types within composite literal"
-	_ = TP{i: 0, f: 0, s: "", next: {}} // ERROR "invalid pointer type"
-	_ = &Ti{}                           // ERROR "invalid pointer type"
+	_ = TP{i: 0, f: 0, s: "", next: {}} // ERROR "invalid composite literal type TP"
+	_ = &Ti{}                           // ERROR "invalid composite literal type Ti"
 )
 
 type M map[T]T