[NFC] Add filters to hasNItems and hasNItemsOrMore

[jdoerfert]

llvm/include/llvm/ADT/STLExtras.h

1515

Do we need to provide a default for Pred (aka. PredTy)? If so, is a function pointer really what we want?

[Tyker]

llvm/include/llvm/ADT/STLExtras.h

1515

sadly Pred can't be deduced from a default argument, so we need to specify a default template argument as well.

do you see any particular issues or limitation with Pred being a function pointer when no Predicate is provided ?

[jdoerfert]

Assuming we inline (=eliminate) the default value properly, LGTM.

[Tyker]

In D74967#1918323, @jdoerfert wrote:

Assuming we inline (=eliminate) the default value properly, LGTM.

gcc and clang generate exactly the same code before and after the patch https://godbolt.org/z/Zv4-Dg

llvm/include/llvm/ADT/STLExtras.h

using Indices = std::make_index_sequence<
       std::tuple_size<typename std::decay<Tuple>::type>::value>;
 
   return detail::apply_tuple_impl(std::forward<F>(f), std::forward<Tuple>(t),
                                   Indices{});
 }
 
 /// Return true if the sequence [Begin, End) has exactly N items. Runs in O(N)
 /// time. Not meant for use with random-access iterators.
-template <typename IterTy>
+/// Can optionally take a predicate to filter lazily some items.
+template <typename IterTy,
+          typename Pred = bool (*)(const decltype(*std::declval<IterTy>()) &)>
 bool hasNItems(
     IterTy &&Begin, IterTy &&End, unsigned N,
+    Pred &&ShouldBeCounted =
+        [](const decltype(*std::declval<IterTy>()) &) { return true; },
     std::enable_if_t<
         !std::is_same<typename std::iterator_traits<std::remove_reference_t<
                           decltype(Begin)>>::iterator_category,
                       std::random_access_iterator_tag>::value,
         void> * = nullptr) {
-  for (; N; --N, ++Begin)
+  for (; N; ++Begin) {
     if (Begin == End)
       return false; // Too few.
+    N -= ShouldBeCounted(*Begin);
+  }
   return Begin == End;
 }
 
 /// Return true if the sequence [Begin, End) has N or more items. Runs in O(N)
 /// time. Not meant for use with random-access iterators.
-template <typename IterTy>
+/// Can optionally take a predicate to filter lazily some items.
+template <typename IterTy,
+          typename Pred = bool (*)(const decltype(*std::declval<IterTy>()) &)>
 bool hasNItemsOrMore(
     IterTy &&Begin, IterTy &&End, unsigned N,
+    Pred &&ShouldBeCounted =
+        [](const decltype(*std::declval<IterTy>()) &) { return true; },
     std::enable_if_t<
         !std::is_same<typename std::iterator_traits<std::remove_reference_t<
                           decltype(Begin)>>::iterator_category,
                       std::random_access_iterator_tag>::value,
         void> * = nullptr) {
-  for (; N; --N, ++Begin)
+  for (; N; ++Begin) {
     if (Begin == End)
       return false; // Too few.
+    N -= ShouldBeCounted(*Begin);
+  }
   return true;
 }
 
 /// Returns a raw pointer that represents the same address as the argument.
 ///
 /// This implementation can be removed once we move to C++20 where it's defined
 /// as std::to_addres().
 ///
 /// The std::pointer_traits<>::to_address(p) variations of these overloads has
 /// not been implemented.
 template <class Ptr> auto to_address(const Ptr &P) { return P.operator->(); }
 template <class T> constexpr T *to_address(T *P) { return P; }
 
 } // end namespace llvm
 
 #endif // LLVM_ADT_STLEXTRAS_H