From a425623dd9907bf5433e2bf0f64b7e0dcb2b4a8a Mon Sep 17 00:00:00 2001
From: Ivan Krasin <krasin@chromium.org>
Date: Fri, 5 Aug 2016 01:45:54 +0000
Subject: [PATCH] CFI: add XFAIL test for a future optimization of two vcalls.

Summary:
Often, a code will call multiple virtual methods of a given object.
If they go in a linear block, it should be possible to check vtable
before the first call, then store vtable pointer and reuse it for
the second vcall without any additional checks.

This is expected to have a positive performance impact on a hot
path in Blink, see https://crbug.com/634139.

Reviewers: kcc

Differential Revision: https://reviews.llvm.org/D23151

llvm-svn: 277795
---
 compiler-rt/test/cfi/two-vcalls.cpp | 60 +++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 compiler-rt/test/cfi/two-vcalls.cpp

diff --git a/compiler-rt/test/cfi/two-vcalls.cpp b/compiler-rt/test/cfi/two-vcalls.cpp
new file mode 100644
index 000000000000..854b3e0059c1
--- /dev/null
+++ b/compiler-rt/test/cfi/two-vcalls.cpp
@@ -0,0 +1,60 @@
+// RUN: %clangxx_cfi_diag -o %t %s
+// RUN: %t 2>&1 | FileCheck %s
+
+// This test checks that we don't generate two type checks,
+// if two virtual calls are in the same function.
+
+// UNSUPPORTED: win32
+// REQUIRES: cxxabi
+
+// TODO(krasin): implement the optimization to not emit two type checks.
+// XFAIL: *
+#include <stdio.h>
+
+class Base {
+ public:
+  virtual void Foo() {
+    fprintf(stderr, "Base::Foo\n");
+  }
+
+  virtual void Bar() {
+    fprintf(stderr, "Base::Bar\n");
+  }
+};
+
+class Derived : public Base {
+ public:
+  void Foo() override {
+    fprintf(stderr, "Derived::Foo\n");
+  }
+
+  void Bar() override {
+    printf("Derived::Bar\n");
+  }
+};
+
+__attribute__((noinline)) void print(Base* ptr) {
+  ptr->Foo();
+  // Corrupt the vtable pointer. We expect that the optimization will
+  // check vtable before the first vcall then store it in a local
+  // variable, and reuse it for the second vcall. With no optimization,
+  // CFI will complain about the virtual table being corrupted.
+  *reinterpret_cast<void**>(ptr) = 0;
+  ptr->Bar();
+}
+
+
+int main() {
+  Base b;
+  Derived d;
+  // CHECK: Base::Foo
+  // CHECK: Base::Bar
+  print(&b);
+
+  // CHECK: Derived::Foo
+  // CHECK-NOT: runtime error
+  // CHECK: Derived::Bar
+  print(&d);
+
+  return 0;
+}