Merge pull request #17202 from ziglang/llvm17

Update to LLVM 17

1 files changed, 72 insertions, 0 deletions

diff --git a/lib/libcxx/src/pstl/libdispatch.cpp b/lib/libcxx/src/pstl/libdispatch.cpp
new file mode 100644
index 0000000000..b3a9559d08
--- /dev/null
+++ b/lib/libcxx/src/pstl/libdispatch.cpp
@@ -0,0 +1,72 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <__algorithm/min.h>
+#include <__algorithm/pstl_backends/cpu_backends/libdispatch.h>
+#include <__config>
+#include <dispatch/dispatch.h>
+#include <thread>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace __par_backend::inline __libdispatch {
+
+
+void __dispatch_apply(size_t chunk_count, void* context, void (*func)(void* context, size_t chunk)) noexcept {
+  ::dispatch_apply_f(chunk_count, DISPATCH_APPLY_AUTO, context, func);
+}
+
+__chunk_partitions __partition_chunks(ptrdiff_t element_count) {
+  if (element_count == 0) {
+    return __chunk_partitions{1, 0, 0};
+  } else if (element_count == 1) {
+    return __chunk_partitions{1, 0, 1};
+  }
+
+  __chunk_partitions partitions;
+  partitions.__chunk_count_ = [&] {
+    ptrdiff_t cores = std::max(1u, thread::hardware_concurrency());
+
+    auto medium = [&](ptrdiff_t n) { return cores + ((n - cores) / cores); };
+
+    // This is an approximation of `log(1.01, sqrt(n))` which seemes to be reasonable for `n` larger than 500 and tops
+    // at 800 tasks for n ~ 8 million
+    auto large = [](ptrdiff_t n) { return static_cast<ptrdiff_t>(100.499 * std::log(std::sqrt(n))); };
+
+    if (element_count < cores)
+      return element_count;
+    else if (element_count < 500)
+      return medium(element_count);
+    else
+      return std::min(medium(element_count), large(element_count)); // provide a "smooth" transition
+  }();
+  partitions.__chunk_size_       = element_count / partitions.__chunk_count_;
+  partitions.__first_chunk_size_ = partitions.__chunk_size_;
+
+  const ptrdiff_t leftover_item_count = element_count - (partitions.__chunk_count_ * partitions.__chunk_size_);
+
+  if (leftover_item_count == 0)
+    return partitions;
+
+  if (leftover_item_count == partitions.__chunk_size_) {
+    partitions.__chunk_count_ += 1;
+    return partitions;
+  }
+
+  const ptrdiff_t n_extra_items_per_chunk = leftover_item_count / partitions.__chunk_count_;
+  const ptrdiff_t n_final_leftover_items  = leftover_item_count - (n_extra_items_per_chunk * partitions.__chunk_count_);
+
+  partitions.__chunk_size_ += n_extra_items_per_chunk;
+  partitions.__first_chunk_size_ = partitions.__chunk_size_ + n_final_leftover_items;
+  return partitions;
+}
+
+// NOLINTNEXTLINE(llvm-namespace-comment) // This is https://llvm.org/PR56804
+} // namespace __par_backend::inline __libdispatch
+
+_LIBCPP_END_NAMESPACE_STD