cmd/compile: resurrect clobberdead mode

This CL resurrects the clobberdead debugging mode (CL 23924).
When -clobberdead flag is set (TODO: make it GOEXPERIMENT?), the
compiler inserts code that clobbers all dead stack slots that
contains pointers.

Mark windows syscall functions cgo_unsafe_args, as the code
actually does that, by taking the address of one argument and
passing it to cgocall.

Change-Id: Ie09a015f4bd14ae6053cc707866e30ae509b9d6f
Reviewed-on: https://go-review.googlesource.com/c/go/+/301791
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

1 files changed, 47 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/test/clobberdead_test.go b/src/cmd/compile/internal/test/clobberdead_test.go
new file mode 100644
index 0000000000..3e2aadcbf5
--- /dev/null
+++ b/src/cmd/compile/internal/test/clobberdead_test.go
@@ -0,0 +1,47 @@
+// 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 test
+
+import (
+	"internal/testenv"
+	"io/ioutil"
+	"os/exec"
+	"path/filepath"
+	"testing"
+)
+
+const helloSrc = `
+package main
+import "fmt"
+func main() { fmt.Println("hello") }
+`
+
+func TestClobberDead(t *testing.T) {
+	// Test that clobberdead mode generates correct program.
+
+	if testing.Short() {
+		// This test rebuilds the runtime with a special flag, which
+		// takes a while.
+		t.Skip("skip in short mode")
+	}
+	testenv.MustHaveGoRun(t)
+	t.Parallel()
+
+	tmpdir := t.TempDir()
+	src := filepath.Join(tmpdir, "x.go")
+	err := ioutil.WriteFile(src, []byte(helloSrc), 0644)
+	if err != nil {
+		t.Fatalf("write file failed: %v", err)
+	}
+
+	cmd := exec.Command(testenv.GoToolPath(t), "run", "-gcflags=all=-clobberdead", src)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("go run failed: %v\n%s", err, out)
+	}
+	if string(out) != "hello\n" {
+		t.Errorf("wrong output: got %q, want %q", out, "hello\n")
+	}
+}