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

[tbaeder]

Ping

[tbaeder]

Ping

[cor3ntin]

LGTM

clang/lib/AST/Interp/ByteCodeExprGen.cpp

for (const Expr *Init : E->inits()) {
       if (!this->discard(Init))
         return false;
     }
     return true;
   }
 
   // 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]);
   }
 
   QualType T = E->getType();
   if (T->isRecordType())
     return this->visitInitList(E->inits(), E);
 
   if (T->isArrayType()) {

clang/test/AST/Interp/literals.cpp

 static_assert(~INT_MIN == INT_MAX, "");
 static_assert(~INT_MAX == INT_MIN, "");
 
 static_assert(-(1 << 31), ""); // expected-error {{not an integral constant expression}} \
                                // expected-note {{outside the range of representable values}} \
                                // 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);
 static_assert(~e == -1, "");
 
 
 constexpr int m = 10;
 constexpr const int *p = &m;