Ignore implicity casts for zero-as-null-pointer-constant warning

The repro in https://bugs.llvm.org/show_bug.cgi?id=34362
caused the left nullptr to be cast to a int* implicitly, which
resulted diagnosing this falsely.

Differential Revision: https://reviews.llvm.org/D39301

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@316605 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 1c6ec39fd744fa88b373ec68d31a5ddb43cf932f)
diff --git a/lib/Sema/Sema.cpp b/lib/Sema/Sema.cpp
index 6f22620..6417b44 100644
--- a/lib/Sema/Sema.cpp
+++ b/lib/Sema/Sema.cpp
@@ -391,7 +391,7 @@
 void Sema::diagnoseZeroToNullptrConversion(CastKind Kind, const Expr* E) {
   if (Kind != CK_NullToPointer && Kind != CK_NullToMemberPointer)
     return;
-  if (E->getType()->isNullPtrType())
+  if (E->IgnoreParenImpCasts()->getType()->isNullPtrType())
     return;
   // nullptr only exists from C++11 on, so don't warn on its absence earlier.
   if (!getLangOpts().CPlusPlus11)
diff --git a/test/SemaCXX/warn-zero-nullptr.cpp b/test/SemaCXX/warn-zero-nullptr.cpp
index edd2a75..7228040 100644
--- a/test/SemaCXX/warn-zero-nullptr.cpp
+++ b/test/SemaCXX/warn-zero-nullptr.cpp
@@ -25,3 +25,10 @@
 // Warn on these too. Matches gcc and arguably makes sense.
 void* pp = (decltype(nullptr))0; // expected-warning{{zero as null pointer constant}}
 void* pp2 = static_cast<decltype(nullptr)>(0); // expected-warning{{zero as null pointer constant}}
+
+// Shouldn't warn.
+namespace pr34362 {
+struct A { operator int*() { return nullptr; } };
+void func() { if (nullptr == A()) {} }
+void func2() { if ((nullptr) == A()) {} }
+}