[clang][Interp] Fix zero-init of float and pointer arrays

[tbaeder]

Summary

Our Zero opcode only exists for integer types. Use
visitZeroInitializer() here as well so it works for floats and pointers.

[aaron.ballman]

LGTM!

clang/lib/AST/Interp/ByteCodeExprGen.cpp

if (const auto *InitList = dyn_cast<InitListExpr>(Initializer)) {
     const auto *CAT = cast<ConstantArrayType>(AT);
     size_t NumElems = CAT->getSize().getZExtValue();
 
     if (std::optional<PrimType> ElemT = classify(CAT->getElementType())) {
       // TODO(perf): For int and bool types, we can probably just skip this
       //   since we memset our Block*s to 0 and so we have the desired value
       //   without this.
       for (size_t I = 0; I != NumElems; ++I) {
-        if (!this->emitZero(*ElemT, Initializer))
+        if (!this->visitZeroInitializer(CAT->getElementType(), Initializer))
           return false;
         if (!this->emitInitElem(*ElemT, I, Initializer))
           return false;
       }
     } else {
       assert(false && "default initializer for non-primitive type");
     }
 

clang/test/AST/Interp/arrays.cpp

e--; // expected-note 2{{cannot refer to element -1 of array of 4 elements}} \
          // ref-note 2{{cannot refer to element -1 of array of 4 elements}}
     return *e; // This is UB as well
   }
    static_assert(bad3() == 0, ""); // expected-error {{not an integral constant expression}} \
                                    // expected-note {{in call to}} \
                                    // ref-error {{not an integral constant expression}} \
                                   // ref-note {{in call to}}
 };
+
+namespace ZeroInit {
+  struct A {
+    int *p[2];
+  };
+  constexpr A a = {};
+  static_assert(a.p[0] == nullptr, "");
+  static_assert(a.p[1] == nullptr, "");
+
+  struct B {
+    double f[2];
+  };
+  constexpr B b = {};
+  static_assert(b.f[0] == 0.0, "");
+  static_assert(b.f[1] == 0.0, "");
+}