misc, runtime, test: extra tests and benchmarks for defer

Add a bunch of extra tests and benchmarks for defer, in preparation for new
low-cost (open-coded) implementation of defers (see #34481),

 - New file defer_test.go that tests a bunch more unusual defer scenarios,
   including things that might have problems for open-coded defers.
 - Additions to callers_test.go actually verifying what the stack trace looks like
   for various panic or panic-recover scenarios.
 - Additions to crash_test.go testing several more crash scenarios involving
   recursive panics.
 - New benchmark in runtime_test.go measuring speed of panic-recover
 - New CGo benchmark in cgo_test.go calling from Go to C back to Go that
   shows defer overhead

Updates #34481

Change-Id: I423523f3e05fc0229d4277dd00073289a5526188
Reviewed-on: https://go-review.googlesource.com/c/go/+/197017
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

1 files changed, 176 insertions, 0 deletions

diff --git a/src/runtime/defer_test.go b/src/runtime/defer_test.go
new file mode 100644
index 0000000000..0d3e8e9d63
--- /dev/null
+++ b/src/runtime/defer_test.go
@@ -0,0 +1,176 @@
+// Copyright 2019 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 runtime_test
+
+import (
+	"fmt"
+	"reflect"
+	"runtime"
+	"testing"
+)
+
+// Make sure open-coded defer exit code is not lost, even when there is an
+// unconditional panic (hence no return from the function)
+func TestUnconditionalPanic(t *testing.T) {
+	defer func() {
+		if recover() == nil {
+			t.Fatal("expected unconditional panic")
+		}
+	}()
+	panic("panic should be recovered")
+}
+
+var glob int = 3
+
+// Test an open-coded defer and non-open-coded defer - make sure both defers run
+// and call recover()
+func TestOpenAndNonOpenDefers(t *testing.T) {
+	for {
+		// Non-open defer because in a loop
+		defer func(n int) {
+			if recover() == nil {
+				t.Fatal("expected testNonOpen panic")
+			}
+		}(3)
+		if glob > 2 {
+			break
+		}
+	}
+	testOpen(t, 47)
+	panic("testNonOpenDefer")
+}
+
+//go:noinline
+func testOpen(t *testing.T, arg int) {
+	defer func(n int) {
+		if recover() == nil {
+			t.Fatal("expected testOpen panic")
+		}
+	}(4)
+	if arg > 2 {
+		panic("testOpenDefer")
+	}
+}
+
+// Test a non-open-coded defer and an open-coded defer - make sure both defers run
+// and call recover()
+func TestNonOpenAndOpenDefers(t *testing.T) {
+	testOpen(t, 47)
+	for {
+		// Non-open defer because in a loop
+		defer func(n int) {
+			if recover() == nil {
+				t.Fatal("expected testNonOpen panic")
+			}
+		}(3)
+		if glob > 2 {
+			break
+		}
+	}
+	panic("testNonOpenDefer")
+}
+
+var list []int
+
+// Make sure that conditional open-coded defers are activated correctly and run in
+// the correct order.
+func TestConditionalDefers(t *testing.T) {
+	list = make([]int, 0, 10)
+
+	defer func() {
+		if recover() == nil {
+			t.Fatal("expected panic")
+		}
+		want := []int{4, 2, 1}
+		if !reflect.DeepEqual(want, list) {
+			t.Fatal(fmt.Sprintf("wanted %v, got %v", want, list))
+		}
+
+	}()
+	testConditionalDefers(8)
+}
+
+func testConditionalDefers(n int) {
+	doappend := func(i int) {
+		list = append(list, i)
+	}
+
+	defer doappend(1)
+	if n > 5 {
+		defer doappend(2)
+		if n > 8 {
+			defer doappend(3)
+		} else {
+			defer doappend(4)
+		}
+	}
+	panic("test")
+}
+
+// Test that there is no compile-time or run-time error if an open-coded defer
+// call is removed by constant propagation and dead-code elimination.
+func TestDisappearingDefer(t *testing.T) {
+	switch runtime.GOOS {
+	case "invalidOS":
+		defer func() {
+			t.Fatal("Defer shouldn't run")
+		}()
+	}
+}
+
+// This tests an extra recursive panic behavior that is only specified in the
+// code.  Suppose a first panic P1 happens and starts processing defer calls.  If
+// a second panic P2 happens while processing defer call D in frame F, then defer
+// call processing is restarted (with some potentially new defer calls created by
+// D or its callees).  If the defer processing reaches the started defer call D
+// again in the defer stack, then the original panic P1 is aborted and cannot
+// continue panic processing or be recovered.  If the panic P2 does a recover at
+// some point, it will naturally the original panic P1 from the stack, since the
+// original panic had to be in frame F or a descendant of F.
+func TestAbortedPanic(t *testing.T) {
+	defer func() {
+		// The first panic should have been "aborted", so there is
+		// no other panic to recover
+		r := recover()
+		if r != nil {
+			t.Fatal(fmt.Sprintf("wanted nil recover, got %v", r))
+		}
+	}()
+	defer func() {
+		r := recover()
+		if r != "panic2" {
+			t.Fatal(fmt.Sprintf("wanted %v, got %v", "panic2", r))
+		}
+	}()
+	defer func() {
+		panic("panic2")
+	}()
+	panic("panic1")
+}
+
+// This tests that recover() does not succeed unless it is called directly from a
+// defer function that is directly called by the panic.  Here, we first call it
+// from a defer function that is created by the defer function called directly by
+// the panic.  In
+func TestRecoverMatching(t *testing.T) {
+	defer func() {
+		r := recover()
+		if r != "panic1" {
+			t.Fatal(fmt.Sprintf("wanted %v, got %v", "panic1", r))
+		}
+	}()
+	defer func() {
+		defer func() {
+			// Shouldn't succeed, even though it is called directly
+			// from a defer function, since this defer function was
+			// not directly called by the panic.
+			r := recover()
+			if r != nil {
+				t.Fatal(fmt.Sprintf("wanted nil recover, got %v", r))
+			}
+		}()
+	}()
+	panic("panic1")
+}