[PATCH] [UBsan] Skip -fsanitize=vptr instrumentations when the pointer value is null

[Byoungyoung Lee]

Update the patch as commented except the test cast folding. Richard, could you please point which file should I fold into for the testcase? As far as I checked, all existing ubsan tests are written in C (except type-blacklist one), but this case has to be done in C++.

http://reviews.llvm.org/D4412

Files:
  lib/CodeGen/CGExpr.cpp
  test/CodeGen/ubsan-vptr-null.cpp

Index: test/CodeGen/ubsan-vptr-null.cpp
===================================================================
--- test/CodeGen/ubsan-vptr-null.cpp
+++ test/CodeGen/ubsan-vptr-null.cpp
@@ -0,0 +1,18 @@
+// Verify ubsan vptr skip null pointer value cases.
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsanitize=vptr -emit-llvm %s -o - | FileCheck %s
+
+class Bar {
+public:
+  virtual ~Bar() {}
+};
+class Foo : public Bar {};
+
+// CHECK-LABEL: @_Z7checkmev
+void checkme() {
+  // CHECK: [[CMP_RES:%.*]] = icmp ne %class.Foo* %{{[0-9]+}}, null
+  // CHECK: br {{.*}} [[CMP_RES]], label %[[NOT_NULLBB:.*]], label %[[NULLBB:.*]]
+  // CHECK: br label %[[NULLBB]]
+  Bar *bar = 0;
+  Foo* foo = static_cast<Foo*>(bar); // static_cast on the null pointer value.
+  return;
+}
Index: lib/CodeGen/CGExpr.cpp
===================================================================
--- lib/CodeGen/CGExpr.cpp
+++ lib/CodeGen/CGExpr.cpp
@@ -461,7 +461,7 @@
   llvm::Value *Cond = nullptr;
   llvm::BasicBlock *Done = nullptr;
 
-  if (SanOpts->Null) {
+  if (SanOpts->Null || TCK == TCK_DowncastPointer) {
     // The glvalue must not be an empty glvalue.
     Cond = Builder.CreateICmpNE(
         Address, llvm::Constant::getNullValue(Address->getType()));
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