[Courgette] Initial Implementation of LabelManager

This is part of the effort to reduce Courgette's peak memory. Main changes:
- Moving Label to image_utils.h, and change Label::count_ from int to int32.
- Adding utility class ConsecutiveRangeVisitor, with tests.
- Adding LabelManager, with tests.
The new code is not yet used in production.

Review URL: https://codereview.chromium.org/1491703003

Cr-Commit-Position: refs/heads/master@{#363688}

courgette/BUILD.gn

@@ -11,6 +11,7 @@ static_library("courgette_lib") {
     "adjustment_method_2.cc",
     "assembly_program.cc",
     "assembly_program.h",
+    "consecutive_range_visitor.h",
     "courgette.h",
     "crc.cc",
     "crc.h",
@@ -35,6 +36,8 @@ static_library("courgette_lib") {
     "ensemble_apply.cc",
     "ensemble_create.cc",
     "image_utils.h",
+    "label_manager.cc",
+    "label_manager.h",
     "memory_allocator.cc",
     "memory_allocator.h",
     "patch_generator_x86_32.h",
@@ -100,6 +103,7 @@ test("courgette_unittests") {
     "base_test_unittest.cc",
     "base_test_unittest.h",
     "bsdiff_memory_unittest.cc",
+    "consecutive_range_visitor_unittest.cc",
     "difference_estimator_unittest.cc",
     "disassembler_elf_32_x86_unittest.cc",
     "disassembler_win32_x64_unittest.cc",
@@ -108,6 +112,7 @@ test("courgette_unittests") {
     "encoded_program_unittest.cc",
     "ensemble_unittest.cc",
     "image_utils_unittest.cc",
+    "label_manager_unittest.cc",
     "memory_allocator_unittest.cc",
     "rel32_finder_win32_x86_unittest.cc",
     "streams_unittest.cc",

courgette/assembly_program.h

@@ -13,29 +13,13 @@
 #include "base/memory/scoped_ptr.h"
 
 #include "courgette/disassembler.h"
+#include "courgette/image_utils.h"
 #include "courgette/memory_allocator.h"
 
 namespace courgette {
 
 class EncodedProgram;
 
-// A Label is a symbolic reference to an address.  Unlike a conventional
-// assembly language, we always know the address.  The address will later be
-// stored in a table and the Label will be replaced with the index into the
-// table.
-//
-// TODO(sra): Make fields private and add setters and getters.
-class Label {
- public:
-  static const int kNoIndex = -1;
-  Label() : rva_(0), index_(kNoIndex), count_(0) {}
-  explicit Label(RVA rva) : rva_(rva), index_(kNoIndex), count_(0) {}
-
-  RVA rva_;    // Address referred to by the label.
-  int index_;  // Index of address in address table, kNoIndex until assigned.
-  int count_;
-};
-
 typedef std::map<RVA, Label*> RVAToLabel;
 
 // Opcodes of simple assembly language

courgette/consecutive_range_visitor.h

@@ -0,0 +1,57 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COURGETTE_CONSECUTIVE_RANGE_VISITOR_H_
+#define COURGETTE_CONSECUTIVE_RANGE_VISITOR_H_
+
+#include <iterator>
+
+#include "base/macros.h"
+
+namespace courgette {
+
+// Usage note: First check whether std::unique() would suffice.
+//
+// ConsecutiveRangeVisitor is a visitor to read equal consecutive items
+// ("ranges") between two iterators. The base value of InputIterator must
+// implement the == operator.
+//
+// Example: "AAAAABZZZZOO" consists of ranges ["AAAAA", "B", "ZZZZ", "OO"]. The
+// visitor provides accessors to iterate through the ranges, and to access each
+// range's value and repeat, i.e., [('A', 5), ('B', 1), ('Z', 4), ('O', 2)].
+template <class InputIterator>
+class ConsecutiveRangeVisitor {
+ public:
+  ConsecutiveRangeVisitor(InputIterator begin, InputIterator end)
+      : head_(begin), end_(end) {
+    advance();
+  }
+
+  // Returns whether there are more ranges to traverse.
+  bool has_more() const { return tail_ != end_; }
+
+  // Returns an iterator to an element in the current range.
+  InputIterator cur() const { return tail_; }
+
+  // Returns the number of repeated elements in the current range.
+  size_t repeat() const { return std::distance(tail_, head_); }
+
+  // Advances to the next range.
+  void advance() {
+    tail_ = head_;
+    if (head_ != end_)
+      while (++head_ != end_ && *head_ == *tail_) {}
+  }
+
+ private:
+  InputIterator tail_;  // The trailing pionter of a range (inclusive).
+  InputIterator head_;  // The leading pointer of a range (exclusive).
+  InputIterator end_;   // Store the end pointer so we know when to stop.
+
+  DISALLOW_COPY_AND_ASSIGN(ConsecutiveRangeVisitor);
+};
+
+}  // namespace courgette
+
+#endif  // COURGETTE_CONSECUTIVE_RANGE_VISITOR_H_

courgette/consecutive_range_visitor_unittest.cc

@@ -0,0 +1,70 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "courgette/consecutive_range_visitor.h"
+
+#include <string>
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace courgette {
+
+TEST(ConsecutiveRangeVisitorTest, Basic) {
+  std::string s = "AAAAABZZZZOO";
+  ConsecutiveRangeVisitor<std::string::iterator> vis(s.begin(), s.end());
+  EXPECT_TRUE(vis.has_more());
+  EXPECT_EQ('A', *vis.cur());
+  EXPECT_EQ(5U, vis.repeat());
+  vis.advance();
+
+  EXPECT_TRUE(vis.has_more());
+  EXPECT_EQ('B', *vis.cur());
+  EXPECT_EQ(1U, vis.repeat());
+  vis.advance();
+
+  EXPECT_TRUE(vis.has_more());
+  EXPECT_EQ('Z', *vis.cur());
+  EXPECT_EQ(4U, vis.repeat());
+  vis.advance();
+
+  EXPECT_TRUE(vis.has_more());
+  EXPECT_EQ('O', *vis.cur());
+  EXPECT_EQ(2U, vis.repeat());
+  vis.advance();
+
+  EXPECT_FALSE(vis.has_more());
+}
+
+TEST(ConsecutiveRangeVisitorTest, UnitRanges) {
+  // Unsorted, no consecutive characters.
+  const char s[] = "elephant elephant";
+  ConsecutiveRangeVisitor<const char*> vis(std::begin(s), std::end(s) - 1);
+  for (const char* scan = &s[0]; *scan; ++scan) {
+    EXPECT_TRUE(vis.has_more());
+    EXPECT_EQ(*scan, *vis.cur());
+    EXPECT_EQ(1U, vis.repeat());
+    vis.advance();
+  }
+  EXPECT_FALSE(vis.has_more());
+}
+
+TEST(ConsecutiveRangeVisitorTest, SingleRange) {
+  for (size_t len = 1U; len < 10U; ++len) {
+    std::vector<int> v(len, 137);
+    ConsecutiveRangeVisitor<std::vector<int>::iterator> vis(v.begin(), v.end());
+    EXPECT_TRUE(vis.has_more());
+    EXPECT_EQ(137, *vis.cur());
+    EXPECT_EQ(len, vis.repeat());
+    vis.advance();
+    EXPECT_FALSE(vis.has_more());
+  }
+}
+
+TEST(ConsecutiveRangeVisitorTest, Empty) {
+  std::string s;
+  ConsecutiveRangeVisitor<std::string::iterator> vis(s.begin(), s.end());
+  EXPECT_FALSE(vis.has_more());
+}
+
+}  // namespace courgette

courgette/courgette.gyp

@@ -11,6 +11,7 @@
       'adjustment_method.h',
       'assembly_program.cc',
       'assembly_program.h',
+      'consecutive_range_visitor.h',
       'courgette.h',
       'crc.cc',
       'crc.h',
@@ -35,6 +36,8 @@
       'ensemble_apply.cc',
       'ensemble_create.cc',
       'image_utils.h',
+      'label_manager.cc',
+      'label_manager.h',
       'memory_allocator.cc',
       'memory_allocator.h',
       'region.h',
@@ -102,6 +105,7 @@
         'bsdiff_memory_unittest.cc',
         'base_test_unittest.cc',
         'base_test_unittest.h',
+        'consecutive_range_visitor_unittest.cc',
         'difference_estimator_unittest.cc',
         'disassembler_elf_32_x86_unittest.cc',
         'disassembler_win32_x86_unittest.cc',
@@ -110,6 +114,7 @@
         'encode_decode_unittest.cc',
         'ensemble_unittest.cc',
         'image_utils_unittest.cc',
+        'label_manager_unittest.cc',
         'memory_allocator_unittest.cc',
         'rel32_finder_win32_x86_unittest.cc',
         'streams_unittest.cc',

courgette/image_utils.h

@@ -15,6 +15,26 @@ namespace courgette {
 
 typedef uint32 RVA;
 
+// A Label is a symbolic reference to an address.  Unlike a conventional
+// assembly language, we always know the address.  The address will later be
+// stored in a table and the Label will be replaced with the index into the
+// table.
+// TODO(huangs): Make this a struct, and remove "_" from member names.
+class Label {
+ public:
+  enum : int { kNoIndex = -1 };
+  explicit Label(RVA rva) : rva_(rva) {}
+
+  bool operator==(const Label& other) const {
+    return rva_ == other.rva_ && index_ == other.index_ &&
+           count_ == other.count_;
+  }
+
+  RVA rva_ = 0;           // Address referred to by the label.
+  int index_ = kNoIndex;  // Index of address in address table.
+  int32 count_ = 0;
+};
+
 // These helper functions avoid the need for casts in the main code.
 inline uint16 ReadU16(const uint8* address, size_t offset) {
   return *reinterpret_cast<const uint16*>(address + offset);

courgette/label_manager.cc

@@ -0,0 +1,74 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "courgette/label_manager.h"
+
+#include <algorithm>
+
+#include "base/logging.h"
+#include "base/numerics/safe_math.h"
+#include "courgette/consecutive_range_visitor.h"
+
+namespace courgette {
+
+LabelManager::RvaVisitor::~RvaVisitor() {}
+
+LabelManager::LabelManager() {}
+
+LabelManager::~LabelManager() {}
+
+// We wish to minimize peak memory usage here. Analysis: Let
+//   m = number of (RVA) elements in |rva_visitor|,
+//   n = number of distinct (RVA) elements in |rva_visitor|.
+// The final storage is n * sizeof(Label) bytes. During computation we uniquify
+// m RVAs, and count repeats. Taking sizeof(RVA) = 4, an implementation using
+// std::map or std::unordered_map would consume additionally 32 * n bytes.
+// Meanwhile, our std::vector implementation consumes additionally 4 * m bytes
+// For our typical usage (i.e. Chrome) we see m = ~4n, so we use 16 * n bytes of
+// extra contiguous memory during computation. Assuming memory fragmentation
+// would not be an issue, this is much better than using std::map.
+void LabelManager::Read(RvaVisitor* rva_visitor) {
+  // Write all values in |rva_visitor| to |rvas|.
+  size_t num_rva = rva_visitor->Remaining();
+  std::vector<RVA> rvas(num_rva);
+  for (size_t i = 0; i < num_rva; ++i, rva_visitor->Next())
+    rvas[i] = rva_visitor->Get();
+
+  // Sort |rvas|, then count the number of distinct values.
+  using CRV = ConsecutiveRangeVisitor<std::vector<RVA>::iterator>;
+  std::sort(rvas.begin(), rvas.end());
+  size_t num_distinct_rva = 0;
+  for (CRV it(rvas.begin(), rvas.end()); it.has_more(); it.advance())
+    ++num_distinct_rva;
+
+  // Reserve space for |labels_|, populate with sorted RVA and repeats.
+  DCHECK(labels_.empty());
+  labels_.reserve(num_distinct_rva);
+  for (CRV it(rvas.begin(), rvas.end()); it.has_more(); it.advance()) {
+    labels_.push_back(Label(*it.cur()));
+    base::CheckedNumeric<uint32> count = it.repeat();
+    labels_.back().count_ = count.ValueOrDie();
+  }
+}
+
+void LabelManager::RemoveUnderusedLabels(int32 count_threshold) {
+  if (count_threshold <= 0)
+    return;
+  labels_.erase(std::remove_if(labels_.begin(), labels_.end(),
+                               [count_threshold](const Label& label) {
+                                 return label.count_ < count_threshold;
+                               }),
+                labels_.end());
+  // Not shrinking |labels_|, since this may cause reallocation.
+}
+
+// Uses binary search to find |rva|.
+Label* LabelManager::Find(RVA rva) {
+  auto it = std::lower_bound(
+      labels_.begin(), labels_.end(), Label(rva),
+      [](const Label& l1, const Label& l2) { return l1.rva_ < l2.rva_; });
+  return it == labels_.end() || it->rva_ != rva ? nullptr : &(*it);
+}
+
+}  // namespace courgette

courgette/label_manager.h

@@ -0,0 +1,64 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COURGETTE_LABEL_MANAGER_H_
+#define COURGETTE_LABEL_MANAGER_H_
+
+#include <vector>
+
+#include "base/macros.h"
+#include "courgette/image_utils.h"
+
+namespace courgette {
+
+// A container to store and manage Label instances. A key consideration is peak
+// memory usage reduction. To this end we preallocate Label instances in bulk,
+// and carefully control transient memory usage when initializing Labels.
+class LabelManager {
+ public:
+  // An adaptor to sequentially traverse multiple RVAs. This is useful for RVA
+  // translation without extra storage. For example, we might have a stored list
+  // of RVA locations, but we want to traverse the matching RVA targets.
+  class RvaVisitor {
+   public:
+    virtual ~RvaVisitor();
+
+    // Returns the number of remaining RVAs to visit.
+    virtual size_t Remaining() const = 0;
+
+    // Returns the current RVA.
+    virtual RVA Get() const = 0;
+
+    // Advances to the next RVA.
+    virtual void Next() = 0;
+  };
+
+  LabelManager();
+  virtual ~LabelManager();
+
+  // Initializes |labels_| using RVAs from |rva_visitor|. Each distinct RVA from
+  // |rva_visitor| yields a Label with |rva_| assigned as the RVA, and |count_|
+  // assigned as the repeat.
+  void Read(RvaVisitor* rva_visitor);
+
+  // Removes |labels_| elements whose |count_| is less than |count_threshold|.
+  void RemoveUnderusedLabels(int32 count_threshold);
+
+  // Efficiently searches for a Label that targets |rva|. Returns the pointer to
+  // the stored Label instance if found, or null otherwise.
+  Label* Find(RVA rva);
+
+  // TODO(huangs): Move AssignRemainingIndexes() here.
+
+ protected:
+  // The main list of Label instances, sorted by the |rva_| member.
+  std::vector<Label> labels_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(LabelManager);
+};
+
+}  // namespace courgette
+
+#endif  // COURGETTE_LABEL_MANAGER_H_