cmd/cgo/internal/test: benchmark for #cgo noescape directive

case: passing a single Go string object to C function.
result: 87 ns vs 61 ns.

BenchmarkCgoCall/string-pointer-escape
BenchmarkCgoCall/string-pointer-escape-12        67731663   87.02 ns/op
BenchmarkCgoCall/string-pointer-noescape
BenchmarkCgoCall/string-pointer-noescape-12    99424776   61.30 ns/op

For #56378

Change-Id: Iff5c69d8deedfa248f5d7399e1921a5cb0dc8b16
GitHub-Last-Rev: fc67d5a
GitHub-Pull-Request: #62297
Reviewed-on: https://go-review.googlesource.com/c/go/+/522939
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>

src/cmd/cgo/internal/test/test.go

@@ -115,6 +115,13 @@ int add(int x, int y) {
 	return x+y;
 };
 
+// escape vs noescape
+
+#cgo noescape handleGoStringPointerNoescape
+void handleGoStringPointerNoescape(void *s) {}
+
+void handleGoStringPointerEscape(void *s) {}
+
 // Following mimics vulkan complex definitions for benchmarking cgocheck overhead.
 
 typedef uint32_t VkFlags;
@@ -1106,6 +1113,18 @@ func benchCgoCall(b *testing.B) {
 			C.handleComplexPointer(&a0)
 		}
 	})
+	b.Run("string-pointer-escape", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			var s string
+			C.handleGoStringPointerEscape(unsafe.Pointer(&s))
+		}
+	})
+	b.Run("string-pointer-noescape", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			var s string
+			C.handleGoStringPointerNoescape(unsafe.Pointer(&s))
+		}
+	})
 	b.Run("eight-pointers", func(b *testing.B) {
 		var a0, a1, a2, a3, a4, a5, a6, a7 C.VkDeviceCreateInfo
 		for i := 0; i < b.N; i++ {