go/callgraph/vta: use core type for channels

When adding edges to the type graph for channel operations, we need the
*types.Chan object for the channel's type.  The underlying type of a
channel may only be a type parameter, so use the core type instead to
get the *types.Chan.

Change-Id: I08078dbbb480363a372024161f0efb72a54c36a9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/568735
Reviewed-by: Zvonimir Pavlinovic <[email protected]>
Reviewed-by: Tim King <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Tim King <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: John Dethridge

go/callgraph/vta/graph.go

@@ -390,7 +390,7 @@ func (b *builder) unop(u *ssa.UnOp) {
 		// Multiplication operator * is used here as a dereference operator.
 		b.addInFlowAliasEdges(b.nodeFromVal(u), b.nodeFromVal(u.X))
 	case token.ARROW:
-		t := u.X.Type().Underlying().(*types.Chan).Elem()
+		t := typeparams.CoreType(u.X.Type()).(*types.Chan).Elem()
 		b.addInFlowAliasEdges(b.nodeFromVal(u), channelElem{typ: t})
 	default:
 		// There is no interesting type flow otherwise.
@@ -444,7 +444,7 @@ func (b *builder) fieldAddr(f *ssa.FieldAddr) {
 }
 
 func (b *builder) send(s *ssa.Send) {
-	t := s.Chan.Type().Underlying().(*types.Chan).Elem()
+	t := typeparams.CoreType(s.Chan.Type()).(*types.Chan).Elem()
 	b.addInFlowAliasEdges(channelElem{typ: t}, b.nodeFromVal(s.X))
 }
 
@@ -458,7 +458,7 @@ func (b *builder) send(s *ssa.Send) {
 func (b *builder) selekt(s *ssa.Select) {
 	recvIndex := 0
 	for _, state := range s.States {
-		t := state.Chan.Type().Underlying().(*types.Chan).Elem()
+		t := typeparams.CoreType(state.Chan.Type()).(*types.Chan).Elem()
 
 		if state.Dir == types.SendOnly {
 			b.addInFlowAliasEdges(channelElem{typ: t}, b.nodeFromVal(state.Send))

go/callgraph/vta/graph_test.go

@@ -181,6 +181,7 @@ func TestVTAGraphConstruction(t *testing.T) {
 		"testdata/src/store_load_alias.go",
 		"testdata/src/phi_alias.go",
 		"testdata/src/channels.go",
+		"testdata/src/generic_channels.go",
 		"testdata/src/select.go",
 		"testdata/src/stores_arrays.go",
 		"testdata/src/maps.go",

go/callgraph/vta/testdata/src/generic_channels.go

@@ -0,0 +1,33 @@
+// 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.
+
+// go:build ignore
+
+package testdata
+
+type I1 interface{}
+type I2 interface{}
+type I3 interface{}
+
+func Foo[C interface{ ~chan I1 | ~chan<- I1 }](c C, j int) {
+	c <- j
+}
+
+func Bar[C interface{ ~chan I2 | ~<-chan I2 }](c C) {
+	x := <-c
+	print(x)
+}
+
+func Baz[C interface{ ~chan I3 | ~<-chan I3 }](c C) {
+	select {
+	case x := <-c:
+		print(x)
+	default:
+	}
+}
+
+// WANT:
+// Local(t0) -> Channel(chan testdata.I1)
+// Channel(chan testdata.I2) -> Local(t0)
+// Channel(chan testdata.I3) -> Local(t0[2])