[libcxx-commits] [libcxx] [libc++] `std::ranges::advance`: avoid unneeded bounds checks when advancing iterator (PR #84126)

[Konstantin Varlamov via libcxx-commits]

Jan =?utf-8?q?Kokemüller?= <jan.kokemueller at gmail.com>,
Jan =?utf-8?q?Kokemüller?= <jan.kokemueller at gmail.com>,
Jan =?utf-8?q?Kokemüller?= <jan.kokemueller at gmail.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/84126 at github.com>


================
@@ -42,6 +42,13 @@ constexpr void check_forward(int* first, int* last, std::iter_difference_t<It> n
     // regardless of the iterator category.
     assert(it.stride_count() == M);
     assert(it.stride_displacement() == M);
+    if (n == 0) {
+      assert(it.equals_count() == 0);
+    } else {
+      assert(it.equals_count() > 0);
+      assert(it.equals_count() == M || it.equals_count() == M + 1);
----------------
var-const wrote:

Thanks for explaining! In that case, we should either pass the expected number of comparisons as a parameter to this function, or pass a boolean parameter to indicate whether we expect the algorithm to hit the sentinel or not. Test cases should be simple so that we can be sure exactly what we're testing.

https://github.com/llvm/llvm-project/pull/84126