From 37dfff057418e02f8e5322da12684dd927e3d881 Mon Sep 17 00:00:00 2001
From: Andrew Turner <andrew@FreeBSD.org>
Date: Mon, 30 Jul 2012 10:58:13 +0000
Subject: Import compiler-rt r160957.

---
 lib/tsan/rtl/tsan_clock.cc | 118 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 118 insertions(+)
 create mode 100644 lib/tsan/rtl/tsan_clock.cc

(limited to 'lib/tsan/rtl/tsan_clock.cc')

diff --git a/lib/tsan/rtl/tsan_clock.cc b/lib/tsan/rtl/tsan_clock.cc
new file mode 100644
index 000000000000..32ed91dc2103
--- /dev/null
+++ b/lib/tsan/rtl/tsan_clock.cc
@@ -0,0 +1,118 @@
+//===-- tsan_clock.cc -----------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of ThreadSanitizer (TSan), a race detector.
+//
+//===----------------------------------------------------------------------===//
+#include "tsan_clock.h"
+#include "tsan_rtl.h"
+
+// It's possible to optimize clock operations for some important cases
+// so that they are O(1). The cases include singletons, once's, local mutexes.
+// First, SyncClock must be re-implemented to allow indexing by tid.
+// It must not necessarily be a full vector clock, though. For example it may
+// be a multi-level table.
+// Then, each slot in SyncClock must contain a dirty bit (it's united with
+// the clock value, so no space increase). The acquire algorithm looks
+// as follows:
+// void acquire(thr, tid, thr_clock, sync_clock) {
+//   if (!sync_clock[tid].dirty)
+//     return;  // No new info to acquire.
+//              // This handles constant reads of singleton pointers and
+//              // stop-flags.
+//   acquire_impl(thr_clock, sync_clock);  // As usual, O(N).
+//   sync_clock[tid].dirty = false;
+//   sync_clock.dirty_count--;
+// }
+// The release operation looks as follows:
+// void release(thr, tid, thr_clock, sync_clock) {
+//   // thr->sync_cache is a simple fixed-size hash-based cache that holds
+//   // several previous sync_clock's.
+//   if (thr->sync_cache[sync_clock] >= thr->last_acquire_epoch) {
+//     // The thread did no acquire operations since last release on this clock.
+//     // So update only the thread's slot (other slots can't possibly change).
+//     sync_clock[tid].clock = thr->epoch;
+//     if (sync_clock.dirty_count == sync_clock.cnt
+//         || (sync_clock.dirty_count == sync_clock.cnt - 1
+//           && sync_clock[tid].dirty == false))
+//       // All dirty flags are set, bail out.
+//       return;
+//     set all dirty bits, but preserve the thread's bit.  // O(N)
+//     update sync_clock.dirty_count;
+//     return;
+//   }
+//   release_impl(thr_clock, sync_clock);  // As usual, O(N).
+//   set all dirty bits, but preserve the thread's bit.
+//   // The previous step is combined with release_impl(), so that
+//   // we scan the arrays only once.
+//   update sync_clock.dirty_count;
+// }
+
+namespace __tsan {
+
+ThreadClock::ThreadClock() {
+  nclk_ = 0;
+  for (uptr i = 0; i < (uptr)kMaxTidInClock; i++)
+    clk_[i] = 0;
+}
+
+void ThreadClock::acquire(const SyncClock *src) {
+  DCHECK(nclk_ <= kMaxTid);
+  DCHECK(src->clk_.Size() <= kMaxTid);
+
+  const uptr nclk = src->clk_.Size();
+  if (nclk == 0)
+    return;
+  nclk_ = max(nclk_, nclk);
+  for (uptr i = 0; i < nclk; i++) {
+    if (clk_[i] < src->clk_[i])
+      clk_[i] = src->clk_[i];
+  }
+}
+
+void ThreadClock::release(SyncClock *dst) const {
+  DCHECK(nclk_ <= kMaxTid);
+  DCHECK(dst->clk_.Size() <= kMaxTid);
+
+  if (dst->clk_.Size() < nclk_)
+    dst->clk_.Resize(nclk_);
+  for (uptr i = 0; i < nclk_; i++) {
+    if (dst->clk_[i] < clk_[i])
+      dst->clk_[i] = clk_[i];
+  }
+}
+
+void ThreadClock::ReleaseStore(SyncClock *dst) const {
+  DCHECK(nclk_ <= kMaxTid);
+  DCHECK(dst->clk_.Size() <= kMaxTid);
+
+  if (dst->clk_.Size() < nclk_)
+    dst->clk_.Resize(nclk_);
+  for (uptr i = 0; i < nclk_; i++)
+    dst->clk_[i] = clk_[i];
+  for (uptr i = nclk_; i < dst->clk_.Size(); i++)
+    dst->clk_[i] = 0;
+}
+
+void ThreadClock::acq_rel(SyncClock *dst) {
+  acquire(dst);
+  release(dst);
+}
+
+void ThreadClock::Disable(unsigned tid) {
+  u64 c0 = clk_[tid];
+  for (uptr i = 0; i < kMaxTidInClock; i++)
+    clk_[i] = (u64)-1;
+  clk_[tid] = c0;
+}
+
+SyncClock::SyncClock()
+  : clk_(MBlockClock) {
+}
+}  // namespace __tsan
-- 
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