runtime: skip cgo check for non-pointer slice elements

Fixes #14387.

Change-Id: Icc98be80f549c5e1f55c5e693bfea97b456a6c41
Reviewed-on: https://go-review.googlesource.com/19621
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-on: https://go-review.googlesource.com/22036Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/cgocall.go

@@ -463,6 +463,9 @@ func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) {
 		if !top {
 			panic(errorString(msg))
 		}
+		if st.elem.kind&kindNoPointers != 0 {
+			return
+		}
 		for i := 0; i < s.cap; i++ {
 			cgoCheckArg(st.elem, p, true, false, msg)
 			p = add(p, st.elem.size)

src/runtime/crash_cgo_test.go

@@ -7,10 +7,12 @@
 package runtime_test
 
 import (
+	"internal/testenv"
 	"os/exec"
 	"runtime"
 	"strings"
 	"testing"
+	"time"
 )
 
 func TestCgoCrashHandler(t *testing.T) {
@@ -147,3 +149,32 @@ func TestEnsureDropM(t *testing.T) {
 		t.Errorf("expected %q, got %v", want, got)
 	}
 }
+
+// Test for issue 14387.
+// Test that the program that doesn't need any cgo pointer checking
+// takes about the same amount of time with it as without it.
+func TestCgoCheckBytes(t *testing.T) {
+	// Make sure we don't count the build time as part of the run time.
+	testenv.MustHaveGoBuild(t)
+	exe, err := buildTestProg(t, "testprogcgo")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	cmd := testEnv(exec.Command(exe, "CgoCheckBytes"))
+
+	start := time.Now()
+	cmd.Run()
+	d1 := time.Since(start)
+
+	cmd = testEnv(exec.Command(exe, "CgoCheckBytes"))
+	cmd.Env = append(cmd.Env, "GODEBUG=cgocheck=0")
+
+	start = time.Now()
+	cmd.Run()
+	d2 := time.Since(start)
+
+	if d2*10 < d1 {
+		t.Errorf("cgo check too slow: got %v, expected at most %v", d1, d2*10)
+	}
+}

src/runtime/testdata/testprogcgo/cgo.go

@@ -6,17 +6,20 @@ package main
 
 /*
 void foo1(void) {}
+void foo2(void* p) {}
 */
 import "C"
 import (
 	"fmt"
 	"runtime"
 	"time"
+	"unsafe"
 )
 
 func init() {
 	register("CgoSignalDeadlock", CgoSignalDeadlock)
 	register("CgoTraceback", CgoTraceback)
+	register("CgoCheckBytes", CgoCheckBytes)
 }
 
 func CgoSignalDeadlock() {
@@ -78,3 +81,10 @@ func CgoTraceback() {
 	runtime.Stack(buf, true)
 	fmt.Printf("OK\n")
 }
+
+func CgoCheckBytes() {
+	b := make([]byte, 1e6)
+	for i := 0; i < 1e3; i++ {
+		C.foo2(unsafe.Pointer(&b[0]))
+	}
+}