[clang][Interp] Handle CXXScalarValueInitExprs (#67147)

Handle those by just zero-initializing the result.

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -1531,6 +1531,12 @@ bool ByteCodeExprGen<Emitter>::VisitOffsetOfExpr(const OffsetOfExpr *E) {
   return this->emitOffsetOf(T, E, E);
 }
 
+template <class Emitter>
+bool ByteCodeExprGen<Emitter>::VisitCXXScalarValueInitExpr(
+    const CXXScalarValueInitExpr *E) {
+  return this->visitZeroInitializer(E->getType(), E);
+}
+
 template <class Emitter> bool ByteCodeExprGen<Emitter>::discard(const Expr *E) {
   if (E->containsErrors())
     return false;

clang/lib/AST/Interp/ByteCodeExprGen.h

@@ -106,6 +106,7 @@ class ByteCodeExprGen : public ConstStmtVisitor<ByteCodeExprGen<Emitter>, bool>,
   bool VisitCXXConstructExpr(const CXXConstructExpr *E);
   bool VisitSourceLocExpr(const SourceLocExpr *E);
   bool VisitOffsetOfExpr(const OffsetOfExpr *E);
+  bool VisitCXXScalarValueInitExpr(const CXXScalarValueInitExpr *E);
 
 protected:
   bool visitExpr(const Expr *E) override;

clang/test/AST/Interp/literals.cpp

@@ -31,6 +31,33 @@ static_assert(b, "");
 constexpr int one = true;
 static_assert(one == 1, "");
 
+constexpr bool b2 = bool();
+static_assert(!b2, "");
+
+namespace ScalarTypes {
+  constexpr int ScalarInitInt = int();
+  static_assert(ScalarInitInt == 0, "");
+  constexpr float ScalarInitFloat = float();
+  static_assert(ScalarInitFloat == 0.0f, "");
+
+  static_assert(decltype(nullptr)() == nullptr, "");
+
+  template<typename T>
+  constexpr T getScalar() { return T(); }
+
+  static_assert(getScalar<const int>() == 0, "");
+  static_assert(getScalar<const double>() == 0.0, "");
+
+  static_assert(getScalar<void*>() == nullptr, "");
+  static_assert(getScalar<void(*)(void)>() == nullptr, "");
+
+  enum E {
+    First = 0,
+  };
+  static_assert(getScalar<E>() == First, "");
+  /// FIXME: Member pointers.
+}
+
 namespace IntegralCasts {
   constexpr int i = 12;
   constexpr unsigned int ui = i;