runtime: add test case for checkptr alignment with nested expression

Discover while working on moving checkptr instrumentation from walk to
SSA generation.

Change-Id: I3f4a41fe4ad308b86c7c57d14b6ccc7c613e7f98
Reviewed-on: https://go-review.googlesource.com/c/go/+/345432
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/runtime/checkptr_test.go

@@ -55,3 +55,40 @@ func TestCheckPtr(t *testing.T) {
 		})
 	}
 }
+
+func TestCheckPtr2(t *testing.T) {
+	t.Parallel()
+	testenv.MustHaveGoRun(t)
+
+	exe, err := buildTestProg(t, "testprog", "-gcflags=all=-d=checkptr=2")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	testCases := []struct {
+		cmd  string
+		want string
+	}{
+		{"CheckPtrAlignmentNested", "fatal error: checkptr: converted pointer straddles multiple allocations\n"},
+	}
+
+	for _, tc := range testCases {
+		tc := tc
+		t.Run(tc.cmd, func(t *testing.T) {
+			t.Parallel()
+			got, err := testenv.CleanCmdEnv(exec.Command(exe, tc.cmd)).CombinedOutput()
+			if err != nil {
+				t.Log(err)
+			}
+			if tc.want == "" {
+				if len(got) > 0 {
+					t.Errorf("output:\n%s\nwant no output", got)
+				}
+				return
+			}
+			if !strings.HasPrefix(string(got), tc.want) {
+				t.Errorf("output:\n%s\n\nwant output starting with: %s", got, tc.want)
+			}
+		})
+	}
+}

src/runtime/testdata/testprog/checkptr.go

@@ -20,6 +20,7 @@ func init() {
 	register("CheckPtrSmall", CheckPtrSmall)
 	register("CheckPtrSliceOK", CheckPtrSliceOK)
 	register("CheckPtrSliceFail", CheckPtrSliceFail)
+	register("CheckPtrAlignmentNested", CheckPtrAlignmentNested)
 }
 
 func CheckPtrAlignmentNoPtr() {
@@ -96,3 +97,10 @@ func CheckPtrSliceFail() {
 	sink2 = p
 	sink2 = unsafe.Slice(p, 100)
 }
+
+func CheckPtrAlignmentNested() {
+	s := make([]int8, 100)
+	p := unsafe.Pointer(&s[0])
+	n := 9
+	_ = ((*[10]int8)(unsafe.Pointer((*[10]int64)(unsafe.Pointer(&p)))))[:n:n]
+}