Revert "Implement nullPointerConstant() using a better API."

This reverts commit 9148302 (2019-08-22) which broke the pre-existing
unit test for the matcher.  Also revert commit 518b226 (Fix the
nullPointerConstant() test to get bots back to green., 2019-08-22) which
incorrectly changed the test to expect the broken behavior.

Differential Revision: https://reviews.llvm.org/D96665

Author: steveire

clang/include/clang/ASTMatchers/ASTMatchers.h

@@ -7384,9 +7384,10 @@ extern const internal::VariadicDynCastAllOfMatcher<Stmt, CUDAKernelCallExpr>
 /// expr(nullPointerConstant())
 ///   matches the initializer for v1, v2, v3, cp, and ip. Does not match the
 ///   initializer for i.
-AST_MATCHER(Expr, nullPointerConstant) {
-  return Node.isNullPointerConstant(Finder->getASTContext(),
-                                    Expr::NPC_ValueDependentIsNull);
+AST_MATCHER_FUNCTION(internal::Matcher<Expr>, nullPointerConstant) {
+  return anyOf(
+      gnuNullExpr(), cxxNullPtrLiteralExpr(),
+      integerLiteral(equals(0), hasParent(expr(hasType(pointerType())))));
 }
 
 /// Matches the DecompositionDecl the binding belongs to.

clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp

@@ -3663,7 +3663,7 @@ TEST_P(ASTMatchersTest, NullPointerConstant) {
                       expr(nullPointerConstant())));
   EXPECT_TRUE(matches("char *cp = (char *)0;", expr(nullPointerConstant())));
   EXPECT_TRUE(matches("int *ip = 0;", expr(nullPointerConstant())));
-  EXPECT_TRUE(matches("int i = 0;", expr(nullPointerConstant())));
+  EXPECT_FALSE(matches("int i = 0;", expr(nullPointerConstant())));
 }
 
 TEST_P(ASTMatchersTest, NullPointerConstant_GNUNull) {