[esan] Add circular buffer data structure

Summary:
Adds a new class, CircularBuffer, for holding a wrap-around fixed-size
sequence of a primitive data type.  This will be used initially by the
working set tool.

Adds a unit test for CircularBuffer, including infrastructure support to
include esan headers and to link with the esan library by pretending to
want the working set tool.

Reviewers: aizatsky, filcab

Subscribers: vitalybuka, zhaoqin, kcc, eugenis, llvm-commits, kubabrecka

Differential Revision: http://reviews.llvm.org/D20579

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@271286 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 92 insertions, 0 deletions

diff --git a/lib/esan/esan_circular_buffer.h b/lib/esan/esan_circular_buffer.h
new file mode 100644
index 000000000..98891109c
--- /dev/null
+++ b/lib/esan/esan_circular_buffer.h
@@ -0,0 +1,92 @@
+//===-- esan_circular_buffer.h ----------------------------------*- C++ -*-===//
+//
+//                     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 EfficiencySanitizer, a family of performance tuners.
+//
+// Circular buffer data structure.
+//===----------------------------------------------------------------------===//
+
+#include "sanitizer_common/sanitizer_common.h"
+
+namespace __esan {
+
+// A circular buffer for POD data whose memory is allocated using mmap.
+// There are two usage models: one is to use initialize/free (for global
+// instances) and the other is to use placement new with the
+// constructor and to call the destructor or free (they are equivalent).
+template<typename T>
+class CircularBuffer {
+ public:
+  // To support global instances we cannot initialize any field in the
+  // default constructor.
+  explicit CircularBuffer() {}
+  CircularBuffer(uptr BufferCapacity) {
+    initialize(BufferCapacity);
+  }
+  ~CircularBuffer() {
+    free();
+  }
+  void initialize(uptr BufferCapacity) {
+    Capacity = BufferCapacity;
+    // MmapOrDie rounds up to the page size for us.
+    Data = (T *)MmapOrDie(Capacity * sizeof(T), "CircularBuffer");
+    StartIdx = 0;
+    Count = 0;
+  }
+  void free() {
+    UnmapOrDie(Data, Capacity * sizeof(T));
+  }
+  T &operator[](uptr Idx) {
+    CHECK_LT(Idx, Count);
+    uptr ArrayIdx = (StartIdx + Idx) % Capacity;
+    return Data[ArrayIdx];
+  }
+  const T &operator[](uptr Idx) const {
+    CHECK_LT(Idx, Count);
+    uptr ArrayIdx = (StartIdx + Idx) % Capacity;
+    return Data[ArrayIdx];
+  }
+  void push_back(const T &Item) {
+    CHECK_GT(Capacity, 0);
+    uptr ArrayIdx = (StartIdx + Count) % Capacity;
+    Data[ArrayIdx] = Item;
+    if (Count < Capacity)
+      ++Count;
+    else
+      StartIdx = (StartIdx + 1) % Capacity;
+  }
+  T &back() {
+    CHECK_GT(Count, 0);
+    uptr ArrayIdx = (StartIdx + Count - 1) % Capacity;
+    return Data[ArrayIdx];
+  }
+  void pop_back() {
+    CHECK_GT(Count, 0);
+    --Count;
+  }
+  uptr size() const {
+    return Count;
+  }
+  void clear() {
+    StartIdx = 0;
+    Count = 0;
+  }
+  bool empty() const { return size() == 0; }
+
+ private:
+  CircularBuffer(const CircularBuffer&);
+  void operator=(const CircularBuffer&);
+
+  T *Data;
+  uptr Capacity;
+  uptr StartIdx;
+  uptr Count;
+};
+
+} // namespace __esan