[clang][Interp] Support __null

[cor3ntin]

clang/test/AST/Interp/literals.cpp

16

Can you add a test along the lines of

constexpr void* v = nullptr;
static_assert(__null == v);

clang/lib/AST/Interp/ByteCodeExprGen.h

public:
   bool VisitPointerArithBinOp(const BinaryOperator *E);
   bool VisitCXXDefaultArgExpr(const CXXDefaultArgExpr *E);
   bool VisitCallExpr(const CallExpr *E);
   bool VisitBuiltinCallExpr(const CallExpr *E);
   bool VisitCXXMemberCallExpr(const CXXMemberCallExpr *E);
   bool VisitCXXDefaultInitExpr(const CXXDefaultInitExpr *E);
   bool VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *E);
   bool VisitCXXNullPtrLiteralExpr(const CXXNullPtrLiteralExpr *E);
+  bool VisitGNUNullExpr(const GNUNullExpr *E);
   bool VisitCXXThisExpr(const CXXThisExpr *E);
   bool VisitUnaryOperator(const UnaryOperator *E);
   bool VisitDeclRefExpr(const DeclRefExpr *E);
   bool VisitImplicitValueInitExpr(const ImplicitValueInitExpr *E);
   bool VisitSubstNonTypeTemplateParmExpr(const SubstNonTypeTemplateParmExpr *E);
   bool VisitArraySubscriptExpr(const ArraySubscriptExpr *E);
   bool VisitInitListExpr(const InitListExpr *E);
   bool VisitConstantExpr(const ConstantExpr *E);

clang/lib/AST/Interp/ByteCodeExprGen.cpp

bool ByteCodeExprGen<Emitter>::VisitCXXNullPtrLiteralExpr(
     const CXXNullPtrLiteralExpr *E) {
   if (DiscardResult)
     return true;
 
   return this->emitNullPtr(E);
 }
 
 template <class Emitter>
+bool ByteCodeExprGen<Emitter>::VisitGNUNullExpr(const GNUNullExpr *E) {
+  if (DiscardResult)
+    return true;
+
+  assert(E->getType()->isIntegerType());
+
+  PrimType T = classifyPrim(E->getType());
+  return this->emitZero(T, E);
+}
+
+template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitCXXThisExpr(const CXXThisExpr *E) {
   if (DiscardResult)
     return true;
   return this->emitThis(E);
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitUnaryOperator(const UnaryOperator *E) {

clang/test/AST/Interp/literals.cpp

 // RUN: %clang_cc1 -fexperimental-new-constant-interpreter -fms-extensions -std=c++11 -verify %s
 // RUN: %clang_cc1 -fexperimental-new-constant-interpreter -fms-extensions -std=c++20 -verify %s
 // RUN: %clang_cc1 -std=c++11 -fms-extensions -verify=ref %s
 // RUN: %clang_cc1 -std=c++20 -fms-extensions -verify=ref %s
 
 #define INT_MIN (~__INT_MAX__)
 #define INT_MAX __INT_MAX__
 
 typedef __INTPTR_TYPE__ intptr_t;
 
 
 static_assert(true, "");
 static_assert(false, ""); // expected-error{{failed}} ref-error{{failed}}
 static_assert(nullptr == nullptr, "");
+static_assert(__null == __null, "");
 static_assert(1 == 1, "");
 static_assert(1 == 3, ""); // expected-error{{failed}} ref-error{{failed}}
 
+constexpr void* v = nullptr;
+static_assert(__null == v, "");
+
 constexpr int number = 10;
 static_assert(number == 10, "");
 static_assert(number != 10, ""); // expected-error{{failed}} \
                                  // ref-error{{failed}} \
                                  // expected-note{{evaluates to}} \
                                  // ref-note{{evaluates to}}
 
 constexpr bool b = number;
constexpr int ignoredExprs() {
     arr[0];
     "a";
     'b';
     sizeof(int);
     alignof(int);
 
     (short)5;
     (bool)1;
+    __null;
 
     return 0;
   }
   static_assert(ignoredExprs() == 0, "");
 
   constexpr int oh_my(int x) {
     (int){ x++ };
     return x;