[libcxx-commits] [libcxx] [libc++] Optimize ranges::{for_each, for_each_n} for segmented iterators (PR #132896)

[A. Jiang via libcxx-commits]

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@@ -13,69 +13,113 @@
 //    constexpr InputIterator      // constexpr after C++17
 //    for_each_n(InputIterator first, Size n, Function f);
 
-
 #include <algorithm>
 #include <cassert>
+#include <deque>
 #include <functional>
+#include <iterator>
+#include <ranges>
+#include <vector>
 
 #include "test_macros.h"
 #include "test_iterators.h"
 
-#if TEST_STD_VER > 17
-TEST_CONSTEXPR bool test_constexpr() {
-    int ia[] = {1, 3, 6, 7};
-    int expected[] = {3, 5, 8, 9};
-    const std::size_t N = 4;
+struct for_each_test {
+  TEST_CONSTEXPR for_each_test(int c) : count(c) {}
+  int count;
+  TEST_CONSTEXPR_CXX14 void operator()(int& i) {
+    ++i;
+    ++count;
+  }
+};
 
-    auto it = std::for_each_n(std::begin(ia), N, [](int &a) { a += 2; });
-    return it == (std::begin(ia) + N)
-        && std::equal(std::begin(ia), std::end(ia), std::begin(expected))
-        ;
-    }
-#endif
+struct deque_test {
+  std::deque<int>* d_;
+  int* i_;
+
+  deque_test(std::deque<int>& d, int& i) : d_(&d), i_(&i) {}
 
-struct for_each_test
-{
-    for_each_test(int c) : count(c) {}
-    int count;
-    void operator()(int& i) {++i; ++count;}
+  void operator()(int& v) {
+    assert(&(*d_)[*i_] == &v);
+    ++*i_;
+  }
 };
 
-int main(int, char**)
-{
+/*TEST_CONSTEXPR_CXX23*/
+void test_segmented_deque_iterator() { // TODO: Mark as TEST_CONSTEXPR_CXX23 once std::deque is constexpr
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frederick-vs-ja wrote:

The macro should be `TEST_CONSTEXPR_CXX26`.

https://github.com/llvm/llvm-project/pull/132896