go/callgraph/vta: do not assume that recovers cannot be deferred

Otherwise, one has a panic.

Change-Id: I850d99ad373ac877bfbc2a8c2ef0c8ac98992dff
Reviewed-on: https://go-review.googlesource.com/c/tools/+/420914
Run-TryBot: Zvonimir Pavlinovic <zpavlinovic@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Tim King <taking@google.com>

go/callgraph/vta/graph.go

@@ -568,7 +568,9 @@ func (b *builder) panic(p *ssa.Panic) {
 func (b *builder) call(c ssa.CallInstruction) {
 	// When c is r := recover() call register instruction, we add Recover -> r.
 	if bf, ok := c.Common().Value.(*ssa.Builtin); ok && bf.Name() == "recover" {
-		b.addInFlowEdge(recoverReturn{}, b.nodeFromVal(c.(*ssa.Call)))
+		if v, ok := c.(ssa.Value); ok {
+			b.addInFlowEdge(recoverReturn{}, b.nodeFromVal(v))
+		}
 		return
 	}
 

go/callgraph/vta/testdata/src/panic.go

@@ -27,12 +27,12 @@ func recover2() {
 
 func Baz(a A) {
 	defer recover1()
+	defer recover()
 	panic(a)
 }
 
 // Relevant SSA:
 // func recover1():
-// 	0:
 //   t0 = print("only this recover...":string)
 //   t1 = recover()
 //   t2 = typeassert,ok t1.(I)
@@ -53,6 +53,7 @@ func Baz(a A) {
 //   t0 = local A (a)
 //   *t0 = a
 //   defer recover1()
+//   defer recover()
 //   t1 = *t0
 //   t2 = make interface{} <- A (t1)
 //   panic t2