cmd/compile: ensure FuncForPC works on closures that start with NOPs

A 0-sized no-op shouldn't prevent us from detecting that the first
instruction is from an inlined callee.

Update #58300

Change-Id: Ic5f6ed108c54a32c05e9b2264b516f2cc17e4619
Reviewed-on: https://go-review.googlesource.com/c/go/+/467977
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/compile/internal/ssagen/ssa.go

@@ -7171,7 +7171,7 @@ func genssa(f *ssa.Func, pp *objw.Progs) {
 			// This ensures that runtime.FuncForPC(uintptr(reflect.ValueOf(fn).Pointer())).Name()
 			// returns the right answer. See issue 58300.
 			for p := pp.Text; p != nil; p = p.Link {
-				if p.As == obj.AFUNCDATA || p.As == obj.APCDATA || p.As == obj.ATEXT {
+				if p.As == obj.AFUNCDATA || p.As == obj.APCDATA || p.As == obj.ATEXT || p.As == obj.ANOP {
 					continue
 				}
 				if base.Ctxt.PosTable.Pos(p.Pos).Base().InliningIndex() >= 0 {

test/fixedbugs/issue58300b.go

@@ -0,0 +1,35 @@
+// run
+
+// Copyright 2023 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 (
+	"reflect"
+	"runtime"
+)
+
+type T struct {
+	a, b int
+}
+
+func f(t *T) int {
+	if t != nil {
+		return t.b
+	}
+	return 0
+}
+
+func g(t *T) int {
+	return f(t) + 5
+}
+
+func main() {
+	x(f)
+	x(g)
+}
+func x(v any) {
+	println(runtime.FuncForPC(reflect.ValueOf(v).Pointer()).Name())
+}

test/fixedbugs/issue58300b.out

@@ -0,0 +1,2 @@
+main.f
+main.g