[clang][Interp] Fix ImplicitValueInitExprs for pointer types

[tbaeder]

Summary

This previously ran into an "unknown type" assertion when trying to emit
a 'Zero' op for a pointer type. Emit a NullPtr op instead.

[tbaeder]

Ping

[tbaeder]

Ping

[tbaeder]

Ping

[aaron.ballman]

LGTM!

[shafik]

LGTM

clang/lib/AST/Interp/ByteCodeExprGen.cpp

bool ByteCodeExprGen<Emitter>::VisitPointerArithBinOp(const BinaryOperator *E) {
   else if (Op == BO_Sub)
     return this->emitSubOffset(OffsetType, E);
 
   return this->bail(E);
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitImplicitValueInitExpr(const ImplicitValueInitExpr *E) {
-  if (std::optional<PrimType> T = classify(E))
-    return this->emitZero(*T, E);
+  std::optional<PrimType> T = classify(E);
 
+  if (!T)
     return false;
+
+  if (E->getType()->isPointerType())
+    return this->emitNullPtr(E);
+
+  return this->emitZero(*T, E);
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitArraySubscriptExpr(
     const ArraySubscriptExpr *E) {
   const Expr *Base = E->getBase();
   const Expr *Index = E->getIdx();
   PrimType IndexT = classifyPrim(Index->getType());

clang/test/AST/Interp/literals.cpp

namespace IntegralCasts {
   constexpr bool bu = ui;
   static_assert(bu, "");
   constexpr bool ns = zero;
   static_assert(!ns, "");
   constexpr bool nu = uzero;
   static_assert(!nu, "");
 };
 
-
+constexpr int UninitI; // expected-error {{must be initialized by a constant expression}} \
+                       // ref-error {{must be initialized by a constant expression}}
+constexpr int *UninitPtr; // expected-error {{must be initialized by a constant expression}} \
+                          // ref-error {{must be initialized by a constant expression}}
 
 constexpr bool getTrue() { return true; }
 constexpr bool getFalse() { return false; }
 constexpr void* getNull() { return nullptr; }
 
 constexpr int neg(int m) { return -m; }
 constexpr bool inv(bool b) { return !b; }