[libcxx-commits] [libcxx] [libc++] Remove unused _LIBCPP_HAS_NO_TREE_BARRIER macro and associated dead code (PR #122769)
Louis Dionne via libcxx-commits
libcxx-commits at lists.llvm.org
Mon Jan 13 11:11:50 PST 2025
https://github.com/ldionne created https://github.com/llvm/llvm-project/pull/122769
That macro was present in the original implementation of the synchronization library, but it was never defined and so it's effectively unused.
>From 684ae2d737de6f0028778c48056e4141007f3473 Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionne.2 at gmail.com>
Date: Mon, 13 Jan 2025 14:06:14 -0500
Subject: [PATCH] [libc++] Remove unused _LIBCPP_HAS_NO_TREE_BARRIER macro and
associated dead code
That macro was present in the original implementation of the synchronization
library, but it was never defined and so it's effectively unused.
---
libcxx/include/barrier | 105 ------------------
libcxx/src/barrier.cpp | 4 -
.../clang_tidy_checks/internal_ftm_use.cpp | 3 -
3 files changed, 112 deletions(-)
diff --git a/libcxx/include/barrier b/libcxx/include/barrier
index 91dfa9720a376c..7237847505b8db 100644
--- a/libcxx/include/barrier
+++ b/libcxx/include/barrier
@@ -79,8 +79,6 @@ struct __empty_completion {
inline _LIBCPP_HIDE_FROM_ABI void operator()() noexcept {}
};
-# ifndef _LIBCPP_HAS_NO_TREE_BARRIER
-
/*
The default implementation of __barrier_base is a classic tree barrier.
@@ -153,109 +151,6 @@ public:
}
};
-# else
-
-/*
-
-The alternative implementation of __barrier_base is a central barrier.
-
-Two versions of this algorithm are provided:
- 1. A fairly straightforward implementation of the litterature for the
- general case where the completion function is not empty.
- 2. An optimized implementation that exploits 2's complement arithmetic
- and well-defined overflow in atomic arithmetic, to handle the phase
- roll-over for free.
-
-*/
-
-template <class _CompletionF>
-class __barrier_base {
- atomic<ptrdiff_t> __expected;
- atomic<ptrdiff_t> __arrived;
- _CompletionF __completion;
- atomic<bool> __phase;
-
-public:
- using arrival_token = bool;
-
- static constexpr ptrdiff_t max() noexcept { return numeric_limits<ptrdiff_t>::max(); }
-
- _LIBCPP_HIDE_FROM_ABI __barrier_base(ptrdiff_t __expected, _CompletionF __completion = _CompletionF())
- : __expected(__expected), __arrived(__expected), __completion(std::move(__completion)), __phase(false) {}
- [[nodiscard]] _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI arrival_token arrive(ptrdiff_t update) {
- auto const __old_phase = __phase.load(memory_order_relaxed);
- auto const __result = __arrived.fetch_sub(update, memory_order_acq_rel) - update;
- auto const new_expected = __expected.load(memory_order_relaxed);
-
- _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
- update <= new_expected, "update is greater than the expected count for the current barrier phase");
-
- if (0 == __result) {
- __completion();
- __arrived.store(new_expected, memory_order_relaxed);
- __phase.store(!__old_phase, memory_order_release);
- __phase.notify_all();
- }
- return __old_phase;
- }
- _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void wait(arrival_token&& __old_phase) const {
- __phase.wait(__old_phase, memory_order_acquire);
- }
- _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void arrive_and_drop() {
- __expected.fetch_sub(1, memory_order_relaxed);
- (void)arrive(1);
- }
-};
-
-template <>
-class __barrier_base<__empty_completion> {
- static constexpr uint64_t __expected_unit = 1ull;
- static constexpr uint64_t __arrived_unit = 1ull << 32;
- static constexpr uint64_t __expected_mask = __arrived_unit - 1;
- static constexpr uint64_t __phase_bit = 1ull << 63;
- static constexpr uint64_t __arrived_mask = (__phase_bit - 1) & ~__expected_mask;
-
- atomic<uint64_t> __phase_arrived_expected;
-
- static _LIBCPP_HIDE_FROM_ABI constexpr uint64_t __init(ptrdiff_t __count) _NOEXCEPT {
- return ((uint64_t(1u << 31) - __count) << 32) | (uint64_t(1u << 31) - __count);
- }
-
-public:
- using arrival_token = uint64_t;
-
- static constexpr ptrdiff_t max() noexcept { return ptrdiff_t(1u << 31) - 1; }
-
- _LIBCPP_HIDE_FROM_ABI explicit inline __barrier_base(ptrdiff_t __count, __empty_completion = __empty_completion())
- : __phase_arrived_expected(__init(__count)) {}
- [[nodiscard]] inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI arrival_token arrive(ptrdiff_t update) {
- auto const __inc = __arrived_unit * update;
- auto const __old = __phase_arrived_expected.fetch_add(__inc, memory_order_acq_rel);
-
- _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
- update <= __old, "update is greater than the expected count for the current barrier phase");
-
- if ((__old ^ (__old + __inc)) & __phase_bit) {
- __phase_arrived_expected.fetch_add((__old & __expected_mask) << 32, memory_order_relaxed);
- __phase_arrived_expected.notify_all();
- }
- return __old & __phase_bit;
- }
- inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void wait(arrival_token&& __phase) const {
- auto const __test_fn = [=]() -> bool {
- uint64_t const __current = __phase_arrived_expected.load(memory_order_acquire);
- return ((__current & __phase_bit) != __phase);
- };
- __libcpp_thread_poll_with_backoff(__test_fn, __libcpp_timed_backoff_policy());
- }
- inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void arrive_and_drop() {
- __phase_arrived_expected.fetch_add(__expected_unit, memory_order_relaxed);
- (void)arrive(1);
- }
-};
-
-# endif // !_LIBCPP_HAS_NO_TREE_BARRIER
-
template <class _CompletionF = __empty_completion>
class barrier {
__barrier_base<_CompletionF> __b_;
diff --git a/libcxx/src/barrier.cpp b/libcxx/src/barrier.cpp
index b97c7bd73b74cd..868f1bfbaffc22 100644
--- a/libcxx/src/barrier.cpp
+++ b/libcxx/src/barrier.cpp
@@ -11,8 +11,6 @@
_LIBCPP_BEGIN_NAMESPACE_STD
-#if !defined(_LIBCPP_HAS_NO_TREE_BARRIER)
-
class __barrier_algorithm_base {
public:
struct alignas(64) /* naturally-align the heap state */ __state_t {
@@ -70,6 +68,4 @@ _LIBCPP_EXPORTED_FROM_ABI void __destroy_barrier_algorithm_base(__barrier_algori
delete __barrier;
}
-#endif // !defined(_LIBCPP_HAS_NO_TREE_BARRIER)
-
_LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/test/tools/clang_tidy_checks/internal_ftm_use.cpp b/libcxx/test/tools/clang_tidy_checks/internal_ftm_use.cpp
index 173762e5602a71..ade82b6ac9f77d 100644
--- a/libcxx/test/tools/clang_tidy_checks/internal_ftm_use.cpp
+++ b/libcxx/test/tools/clang_tidy_checks/internal_ftm_use.cpp
@@ -26,9 +26,6 @@ std::array valid_macros{
// Testing macros
"_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER",
- // TODO: Why does this macro even exist?
- "_LIBCPP_HAS_NO_TREE_BARRIER",
-
// Experimental features
"_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB",
"_LIBCPP_HAS_NO_EXPERIMENTAL_SYNCSTREAM",
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