[clang][Interp] Allow zero-init of primitives with an empty init list

Differential Revision: https://reviews.llvm.org/D158595

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -571,8 +571,10 @@ bool ByteCodeExprGen<Emitter>::VisitInitListExpr(const InitListExpr *E) {
 
   // Primitive values.
   if (std::optional<PrimType> T = classify(E->getType())) {
-    assert(E->getNumInits() == 1);
     assert(!DiscardResult);
+    if (E->getNumInits() == 0)
+      return this->visitZeroInitializer(E->getType(), E);
+    assert(E->getNumInits() == 1);
     return this->delegate(E->inits()[0]);
   }
 

clang/test/AST/Interp/literals.cpp

@@ -91,6 +91,15 @@ static_assert(-(1 << 31), ""); // expected-error {{not an integral constant expr
                                // ref-error {{not an integral constant expression}} \
                                // ref-note {{outside the range of representable values}} \
 
+namespace PrimitiveEmptyInitList {
+  constexpr int a = {};
+  static_assert(a == 0, "");
+  constexpr bool b = {};
+  static_assert(!b, "");
+  constexpr double d = {};
+  static_assert(d == 0.0, "");
+}
+
 
 enum E {};
 constexpr E e = static_cast<E>(0);