cmd/compile: fix noder.Addr() to not call typechecker

Simple change to avoid calling the old typechecker in noder.Addr(). This
fixes cases where generic code calls a pointer method with a non-pointer
receiver.

Added test typeparam/lockable.go that now works with this change.

For lockable.go to work, also fix incorrect check to decide whether to
translate an OXDOT now or later. We should delay translating an OXDOT
until instantiation (because we don't know how embedding, etc. will
work) if the receiver has any typeparam, not just if the receiver type
is a simple typeparam. We also have to handle OXDOT for now in
IsAddressable(), until we can remove calls to the old typechecker in
(*irgen).funcBody().

Change-Id: I77ee5efcef9a8f6c7133564106a32437e36ba4bb
Reviewed-on: https://go-review.googlesource.com/c/go/+/300990
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -740,6 +740,13 @@ func IsAddressable(n Node) bool {
 	case ODEREF, ODOTPTR:
 		return true
 
+	case OXDOT:
+		// TODO(danscales): remove this case as we remove calls to the old
+		// typechecker in (*irgen).funcBody().
+		if base.Flag.G == 0 {
+			return false
+		}
+		fallthrough
 	case ODOT:
 		n := n.(*SelectorExpr)
 		return IsAddressable(n.X)

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

@@ -188,7 +188,7 @@ func (g *irgen) expr0(typ types2.Type, expr syntax.Expr) ir.Node {
 // than in typecheck.go.
 func (g *irgen) selectorExpr(pos src.XPos, typ types2.Type, expr *syntax.SelectorExpr) ir.Node {
 	x := g.expr(expr.X)
-	if x.Type().Kind() == types.TTYPEPARAM {
+	if x.Type().HasTParam() {
 		// Leave a method call on a type param as an OXDOT, since it can
 		// only be fully transformed once it has an instantiated type.
 		n := ir.NewSelectorExpr(pos, ir.OXDOT, x, typecheck.Lookup(expr.Sel.Value))

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

@@ -54,8 +54,11 @@ func Nil(pos src.XPos, typ *types.Type) ir.Node {
 // Expressions
 
 func Addr(pos src.XPos, x ir.Node) *ir.AddrExpr {
-	// TODO(mdempsky): Avoid typecheck.Expr. Probably just need to set OPTRLIT when appropriate.
-	n := typecheck.Expr(typecheck.NodAddrAt(pos, x)).(*ir.AddrExpr)
+	n := typecheck.NodAddrAt(pos, x)
+	switch x.Op() {
+	case ir.OARRAYLIT, ir.OMAPLIT, ir.OSLICELIT, ir.OSTRUCTLIT:
+		n.SetOp(ir.OPTRLIT)
+	}
 	typed(types.NewPtr(x.Type()), n)
 	return n
 }
@@ -125,7 +128,7 @@ func Call(pos src.XPos, typ *types.Type, fun ir.Node, args []ir.Node, dots bool)
 	n.IsDDD = dots
 
 	if fun.Op() == ir.OXDOT {
-		if fun.(*ir.SelectorExpr).X.Type().Kind() != types.TTYPEPARAM {
+		if !fun.(*ir.SelectorExpr).X.Type().HasTParam() {
 			base.FatalfAt(pos, "Expecting type param receiver in %v", fun)
 		}
 		// For methods called in a generic function, don't do any extra

test/typeparam/lockable.go

@@ -0,0 +1,50 @@
+// run -gcflags=-G=3
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "sync"
+
+// A _Lockable is a value that may be safely simultaneously accessed
+// from multiple goroutines via the Get and Set methods.
+type _Lockable[T any] struct {
+	T
+	mu sync.Mutex
+}
+
+// Get returns the value stored in a _Lockable.
+func (l *_Lockable[T]) get() T {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	return l.T
+}
+
+// set sets the value in a _Lockable.
+func (l *_Lockable[T]) set(v T) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	l.T = v
+}
+
+func main() {
+	sl := _Lockable[string]{T: "a"}
+	if got := sl.get(); got != "a" {
+		panic(got)
+	}
+	sl.set("b")
+	if got := sl.get(); got != "b" {
+		panic(got)
+	}
+
+	il := _Lockable[int]{T: 1}
+	if got := il.get(); got != 1 {
+		panic(got)
+	}
+	il.set(2)
+	if got := il.get(); got != 2 {
+		panic(got)
+	}
+}