[XRay][llvm] Load XRay Profiles

Summary:
This change implements the profile loading functionality in LLVM to
support XRay's profiling mode in compiler-rt.

We introduce a type named `llvm::xray::Profile` which allows building a
profile representation. We can load an XRay profile from a file to build
Profile instances, or do it manually through the Profile type's API.

The intent is to get the `llvm-xray` tool to generate `Profile`
instances and use that as the common abstraction through which all
conversion and analysis can be done. In the future we can generate
`Profile` instances from `Trace` instances as well, through conversion
functions.

Some of the key operations supported by the `Profile` API are:

- Path interning (`Profile::internPath(...)`) which returns a unique path
  identifier.

- Block appending (`Profile::addBlock(...)`) to add thread-associated
  profile information.

- Path ID to Path lookup (`Profile::expandPath(...)`) to look up a
  PathID and return the original interned path.

- Block iteration.

A 'Path' in this context represents the function call stack in
leaf-to-root order. This is represented as a path in an internally
managed prefix tree in the `Profile` instance. Having a handle (PathID)
to identify the unique Paths we encounter for a particular Profile
allows us to reduce the amount of memory required to associate profile
data to a particular Path.

This is the first of a series of patches to migrate the `llvm-stacks`
tool towards using a single profile representation.

Depends on D48653.

Reviewers: kpw, eizan

Reviewed By: kpw

Subscribers: mgorny, llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D48370

llvm-svn: 338825

llvm/include/llvm/XRay/Profile.h

@@ -0,0 +1,130 @@
+//===- Profile.h - XRay Profile Abstraction -------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Defines the XRay Profile class representing the latency profile generated by
+// XRay's profiling mode.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_XRAY_PROFILE_H
+#define LLVM_XRAY_PROFILE_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Error.h"
+#include <list>
+#include <utility>
+#include <vector>
+
+namespace llvm {
+namespace xray {
+
+class Profile;
+
+// We forward declare the Trace type for turning a Trace into a Profile.
+class Trace;
+
+/// This function will attempt to load an XRay Profiling Mode profile from the
+/// provided |Filename|.
+///
+/// For any errors encountered in the loading of the profile data from
+/// |Filename|, this function will return an Error condition appropriately.
+Expected<Profile> loadProfile(StringRef Filename);
+
+/// This algorithm will merge two Profile instances into a single Profile
+/// instance, aggregating blocks by Thread ID.
+Profile mergeProfilesByThread(const Profile &L, const Profile &R);
+
+/// This algorithm will merge two Profile instances into a single Profile
+/// instance, aggregating blocks by function call stack.
+Profile mergeProfilesByStack(const Profile &L, const Profile &R);
+
+/// This function takes a Trace and creates a Profile instance from it.
+Expected<Profile> profileFromTrace(const Trace &T);
+
+/// Profile instances are thread-compatible.
+class Profile {
+public:
+  using ThreadID = uint64_t;
+  using PathID = unsigned;
+  using FuncID = int32_t;
+
+  struct Data {
+    uint64_t CallCount;
+    uint64_t CumulativeLocalTime;
+  };
+
+  struct Block {
+    ThreadID Thread;
+    std::vector<std::pair<PathID, Data>> PathData;
+  };
+
+  /// Provides a sequence of function IDs from a previously interned PathID.
+  ///
+  /// Returns an error if |P| had not been interned before into the Profile.
+  ///
+  Expected<std::vector<FuncID>> expandPath(PathID P) const;
+
+  /// The stack represented in |P| must be in stack order (leaf to root). This
+  /// will always return the same PathID for |P| that has the same sequence.
+  PathID internPath(ArrayRef<FuncID> P);
+
+  /// Appends a fully-formed Block instance into the Profile.
+  ///
+  /// Returns an error condition in the following cases:
+  ///
+  ///    - The PathData component of the Block is empty
+  ///
+  Error addBlock(Block &&B);
+
+  Profile() = default;
+  ~Profile() = default;
+  Profile(Profile &&) noexcept = default;
+  Profile &operator=(Profile &&) noexcept = default;
+
+  // Disable copy construction and assignment.
+  Profile(const Profile &) = delete;
+  Profile &operator=(const Profile &) = delete;
+
+private:
+  using BlockList = std::list<Block>;
+
+  struct TrieNode {
+    FuncID Func = 0;
+    std::vector<TrieNode *> Callees{};
+    TrieNode *Caller = nullptr;
+    PathID ID = 0;
+  };
+
+  // List of blocks associated with a Profile.
+  BlockList Blocks;
+
+  // List of TrieNode elements we've seen.
+  std::list<TrieNode> NodeStorage;
+
+  // List of call stack roots.
+  SmallVector<TrieNode *, 4> Roots;
+
+  // Reverse mapping between a PathID to a TrieNode*.
+  DenseMap<PathID, TrieNode *> PathIDMap;
+
+  // Used to increment
+  PathID NextID = 1;
+
+public:
+  using const_iterator = BlockList::const_iterator;
+  const_iterator begin() const { return Blocks.begin(); }
+  const_iterator end() const { return Blocks.end(); }
+  bool empty() const { return Blocks.empty(); }
+};
+
+} // namespace xray
+} // namespace llvm
+
+#endif

llvm/lib/XRay/CMakeLists.txt

@@ -1,5 +1,6 @@
 add_llvm_library(LLVMXRay
   InstrumentationMap.cpp
+	Profile.cpp
   Trace.cpp
 
   ADDITIONAL_HEADER_DIRS

llvm/lib/XRay/Profile.cpp

@@ -0,0 +1,379 @@
+//===- Profile.cpp - XRay Profile Abstraction -----------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Defines the XRay Profile class representing the latency profile generated by
+// XRay's profiling mode.
+//
+//===----------------------------------------------------------------------===//
+#include "llvm/XRay/Profile.h"
+
+#include "llvm/Support/DataExtractor.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/XRay/Trace.h"
+#include <deque>
+#include <memory>
+
+namespace llvm {
+namespace xray {
+
+namespace {
+
+struct BlockHeader {
+  uint32_t Size;
+  uint32_t Number;
+  uint64_t Thread;
+};
+
+static Expected<BlockHeader> readBlockHeader(DataExtractor &Extractor,
+                                             uint32_t &Offset) {
+  BlockHeader H;
+  uint32_t CurrentOffset = Offset;
+  H.Size = Extractor.getU32(&Offset);
+  if (Offset == CurrentOffset)
+    return make_error<StringError>(
+        Twine("Error parsing block header size at offset '") +
+            Twine(CurrentOffset) + "'",
+        std::make_error_code(std::errc::invalid_argument));
+  CurrentOffset = Offset;
+  H.Number = Extractor.getU32(&Offset);
+  if (Offset == CurrentOffset)
+    return make_error<StringError>(
+        Twine("Error parsing block header number at offset '") +
+            Twine(CurrentOffset) + "'",
+        std::make_error_code(std::errc::invalid_argument));
+  CurrentOffset = Offset;
+  H.Thread = Extractor.getU64(&Offset);
+  if (Offset == CurrentOffset)
+    return make_error<StringError>(
+        Twine("Error parsing block header thread id at offset '") +
+            Twine(CurrentOffset) + "'",
+        std::make_error_code(std::errc::invalid_argument));
+  return H;
+}
+
+static Expected<std::vector<Profile::FuncID>> readPath(DataExtractor &Extractor,
+                                                       uint32_t &Offset) {
+  // We're reading a sequence of int32_t's until we find a 0.
+  std::vector<Profile::FuncID> Path;
+  auto CurrentOffset = Offset;
+  int32_t FuncId;
+  do {
+    FuncId = Extractor.getSigned(&Offset, 4);
+    if (CurrentOffset == Offset)
+      return make_error<StringError>(
+          Twine("Error parsing path at offset '") + Twine(CurrentOffset) + "'",
+          std::make_error_code(std::errc::invalid_argument));
+    CurrentOffset = Offset;
+    Path.push_back(FuncId);
+  } while (FuncId != 0);
+  return std::move(Path);
+}
+
+static Expected<Profile::Data> readData(DataExtractor &Extractor,
+                                        uint32_t &Offset) {
+  // We expect a certain number of elements for Data:
+  //   - A 64-bit CallCount
+  //   - A 64-bit CumulativeLocalTime counter
+  Profile::Data D;
+  auto CurrentOffset = Offset;
+  D.CallCount = Extractor.getU64(&Offset);
+  if (CurrentOffset == Offset)
+    return make_error<StringError>(
+        Twine("Error parsing call counts at offset '") + Twine(CurrentOffset) +
+            "'",
+        std::make_error_code(std::errc::invalid_argument));
+  CurrentOffset = Offset;
+  D.CumulativeLocalTime = Extractor.getU64(&Offset);
+  if (CurrentOffset == Offset)
+    return make_error<StringError>(
+        Twine("Error parsing cumulative local time at offset '") +
+            Twine(CurrentOffset) + "'",
+        std::make_error_code(std::errc::invalid_argument));
+  return D;
+}
+
+} // namespace
+
+Error Profile::addBlock(Block &&B) {
+  if (B.PathData.empty())
+    return make_error<StringError>(
+        "Block may not have empty path data.",
+        std::make_error_code(std::errc::invalid_argument));
+
+  Blocks.emplace_back(std::move(B));
+  return Error::success();
+}
+
+Expected<std::vector<Profile::FuncID>> Profile::expandPath(PathID P) const {
+  auto It = PathIDMap.find(P);
+  if (It == PathIDMap.end())
+    return make_error<StringError>(
+        Twine("PathID not found: ") + Twine(P),
+        std::make_error_code(std::errc::invalid_argument));
+  std::vector<Profile::FuncID> Path;
+  for (auto Node = It->second; Node; Node = Node->Caller)
+    Path.push_back(Node->Func);
+  return std::move(Path);
+}
+
+Profile::PathID Profile::internPath(ArrayRef<FuncID> P) {
+  if (P.empty())
+    return 0;
+
+  auto RootToLeafPath = reverse(P);
+
+  // Find the root.
+  auto It = RootToLeafPath.begin();
+  auto PathRoot = *It++;
+  auto RootIt =
+      find_if(Roots, [PathRoot](TrieNode *N) { return N->Func == PathRoot; });
+
+  // If we've not seen this root before, remember it.
+  TrieNode *Node = nullptr;
+  if (RootIt == Roots.end()) {
+    NodeStorage.emplace_back();
+    Node = &NodeStorage.back();
+    Node->Func = PathRoot;
+    Roots.push_back(Node);
+  } else {
+    Node = *RootIt;
+  }
+
+  // Now traverse the path, re-creating if necessary.
+  while (It != RootToLeafPath.end()) {
+    auto NodeFuncID = *It++;
+    auto CalleeIt = find_if(Node->Callees, [NodeFuncID](TrieNode *N) {
+      return N->Func == NodeFuncID;
+    });
+    if (CalleeIt == Node->Callees.end()) {
+      NodeStorage.emplace_back();
+      auto NewNode = &NodeStorage.back();
+      NewNode->Func = NodeFuncID;
+      NewNode->Caller = Node;
+      Node->Callees.push_back(NewNode);
+      Node = NewNode;
+    } else {
+      Node = *CalleeIt;
+    }
+  }
+
+  // At this point, Node *must* be pointing at the leaf.
+  assert(Node->Func == P.front());
+  if (Node->ID == 0) {
+    Node->ID = NextID++;
+    PathIDMap.insert({Node->ID, Node});
+  }
+  return Node->ID;
+}
+
+Profile mergeProfilesByThread(const Profile &L, const Profile &R) {
+  Profile Merged;
+  using PathDataMap = DenseMap<Profile::PathID, Profile::Data>;
+  using PathDataMapPtr = std::unique_ptr<PathDataMap>;
+  using PathDataVector = decltype(Profile::Block::PathData);
+  using ThreadProfileIndexMap = DenseMap<Profile::ThreadID, PathDataMapPtr>;
+  ThreadProfileIndexMap ThreadProfileIndex;
+
+  for (const auto &P : {std::ref(L), std::ref(R)})
+    for (const auto &Block : P.get()) {
+      ThreadProfileIndexMap::iterator It;
+      std::tie(It, std::ignore) = ThreadProfileIndex.insert(
+          {Block.Thread, PathDataMapPtr{new PathDataMap()}});
+      for (const auto &PathAndData : Block.PathData) {
+        auto &PathID = PathAndData.first;
+        auto &Data = PathAndData.second;
+        auto NewPathID =
+            Merged.internPath(cantFail(P.get().expandPath(PathID)));
+        PathDataMap::iterator PathDataIt;
+        bool Inserted;
+        std::tie(PathDataIt, Inserted) = It->second->insert({NewPathID, Data});
+        if (!Inserted) {
+          auto &ExistingData = PathDataIt->second;
+          ExistingData.CallCount += Data.CallCount;
+          ExistingData.CumulativeLocalTime += Data.CumulativeLocalTime;
+        }
+      }
+    }
+
+  for (const auto &IndexedThreadBlock : ThreadProfileIndex) {
+    PathDataVector PathAndData;
+    PathAndData.reserve(IndexedThreadBlock.second->size());
+    copy(*IndexedThreadBlock.second, std::back_inserter(PathAndData));
+    cantFail(
+        Merged.addBlock({IndexedThreadBlock.first, std::move(PathAndData)}));
+  }
+  return Merged;
+}
+
+Profile mergeProfilesByStack(const Profile &L, const Profile &R) {
+  Profile Merged;
+  using PathDataMap = DenseMap<Profile::PathID, Profile::Data>;
+  PathDataMap PathData;
+  using PathDataVector = decltype(Profile::Block::PathData);
+  for (const auto &P : {std::ref(L), std::ref(R)})
+    for (const auto &Block : P.get())
+      for (const auto &PathAndData : Block.PathData) {
+        auto &PathId = PathAndData.first;
+        auto &Data = PathAndData.second;
+        auto NewPathID =
+            Merged.internPath(cantFail(P.get().expandPath(PathId)));
+        PathDataMap::iterator PathDataIt;
+        bool Inserted;
+        std::tie(PathDataIt, Inserted) = PathData.insert({NewPathID, Data});
+        if (!Inserted) {
+          auto &ExistingData = PathDataIt->second;
+          ExistingData.CallCount += Data.CallCount;
+          ExistingData.CumulativeLocalTime += Data.CumulativeLocalTime;
+        }
+      }
+
+  // In the end there's a single Block, for thread 0.
+  PathDataVector Block;
+  Block.reserve(PathData.size());
+  copy(PathData, std::back_inserter(Block));
+  cantFail(Merged.addBlock({0, std::move(Block)}));
+  return Merged;
+}
+
+Expected<Profile> loadProfile(StringRef Filename) {
+  int Fd;
+  if (auto EC = sys::fs::openFileForRead(Filename, Fd))
+    return make_error<StringError>(
+        Twine("Cannot read profile from '") + Filename + "'", EC);
+
+  uint64_t FileSize;
+  if (auto EC = sys::fs::file_size(Filename, FileSize))
+    return make_error<StringError>(
+        Twine("Cannot get filesize of '") + Filename + "'", EC);
+
+  std::error_code EC;
+  sys::fs::mapped_file_region MappedFile(
+      Fd, sys::fs::mapped_file_region::mapmode::readonly, FileSize, 0, EC);
+  if (EC)
+    return make_error<StringError>(
+        Twine("Cannot mmap profile '") + Filename + "'", EC);
+  StringRef Data(MappedFile.data(), MappedFile.size());
+
+  Profile P;
+  uint32_t Offset = 0;
+  DataExtractor Extractor(Data, true, 8);
+
+  // For each block we get from the file:
+  while (Offset != MappedFile.size()) {
+    auto HeaderOrError = readBlockHeader(Extractor, Offset);
+    if (!HeaderOrError)
+      return HeaderOrError.takeError();
+
+    // TODO: Maybe store this header information for each block, even just for
+    // debugging?
+    const auto &Header = HeaderOrError.get();
+
+    // Read in the path data.
+    auto PathOrError = readPath(Extractor, Offset);
+    if (!PathOrError)
+      return PathOrError.takeError();
+    const auto &Path = PathOrError.get();
+
+    // For each path we encounter, we should intern it to get a PathID.
+    auto DataOrError = readData(Extractor, Offset);
+    if (!DataOrError)
+      return DataOrError.takeError();
+    auto &Data = DataOrError.get();
+
+    if (auto E =
+            P.addBlock(Profile::Block{Profile::ThreadID{Header.Thread},
+                                      {{P.internPath(Path), std::move(Data)}}}))
+      return std::move(E);
+  }
+
+  return P;
+}
+
+namespace {
+
+struct StackEntry {
+  uint64_t Timestamp;
+  Profile::FuncID FuncId;
+};
+
+} // namespace
+
+Expected<Profile> profileFromTrace(const Trace &T) {
+  Profile P;
+
+  // The implementation of the algorithm re-creates the execution of
+  // the functions based on the trace data. To do this, we set up a number of
+  // data structures to track the execution context of every thread in the
+  // Trace.
+  DenseMap<Profile::ThreadID, std::vector<StackEntry>> ThreadStacks;
+  DenseMap<Profile::ThreadID, DenseMap<Profile::PathID, Profile::Data>>
+      ThreadPathData;
+
+  //  We then do a pass through the Trace to account data on a per-thread-basis.
+  for (const auto &E : T) {
+    auto &TSD = ThreadStacks[E.TId];
+    switch (E.Type) {
+    case RecordTypes::ENTER:
+    case RecordTypes::ENTER_ARG:
+
+      // Push entries into the function call stack.
+      TSD.push_back({E.TSC, E.FuncId});
+      break;
+
+    case RecordTypes::EXIT:
+    case RecordTypes::TAIL_EXIT:
+
+      // Exits cause some accounting to happen, based on the state of the stack.
+      // For each function we pop off the stack, we take note of the path and
+      // record the cumulative state for this path. As we're doing this, we
+      // intern the path into the Profile.
+      while (!TSD.empty()) {
+        auto Top = TSD.back();
+        auto FunctionLocalTime = AbsoluteDifference(Top.Timestamp, E.TSC);
+        SmallVector<Profile::FuncID, 16> Path;
+        transform(reverse(TSD), std::back_inserter(Path),
+                  std::mem_fn(&StackEntry::FuncId));
+        auto InternedPath = P.internPath(Path);
+        auto &TPD = ThreadPathData[E.TId][InternedPath];
+        ++TPD.CallCount;
+        TPD.CumulativeLocalTime += FunctionLocalTime;
+        TSD.pop_back();
+
+        // If we've matched the corresponding entry event for this function,
+        // then we exit the loop.
+        if (Top.FuncId == E.FuncId)
+          break;
+
+        // FIXME: Consider the intermediate times and the cumulative tree time
+        // as well.
+      }
+
+      break;
+    }
+  }
+
+  // Once we've gone through the Trace, we now create one Block per thread in
+  // the Profile.
+  for (const auto &ThreadPaths : ThreadPathData) {
+    const auto &TID = ThreadPaths.first;
+    const auto &PathsData = ThreadPaths.second;
+    if (auto E = P.addBlock({
+            TID,
+            std::vector<std::pair<Profile::PathID, Profile::Data>>(
+                PathsData.begin(), PathsData.end()),
+        }))
+      return std::move(E);
+  }
+
+  return P;
+}
+
+} // namespace xray
+} // namespace llvm

llvm/unittests/XRay/CMakeLists.txt

@@ -1,9 +1,11 @@
 set(LLVM_LINK_COMPONENTS
   Support
+	XRay
   )
 
 add_llvm_unittest(XRayTests
   GraphTest.cpp
+	ProfileTest.cpp
   )
 
 add_dependencies(XRayTests intrinsics_gen)

llvm/unittests/XRay/ProfileTest.cpp

@@ -0,0 +1,218 @@
+//===- ProfileTest.cpp - XRay Profile unit tests ----------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+#include "llvm/XRay/Profile.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+#include <numeric>
+
+namespace llvm {
+namespace xray {
+namespace {
+
+using ::testing::AllOf;
+using ::testing::ElementsAre;
+using ::testing::Eq;
+using ::testing::Field;
+using ::testing::Not;
+using ::testing::Pair;
+using ::testing::UnorderedElementsAre;
+
+TEST(ProfileTest, CreateProfile) { Profile P; }
+
+TEST(ProfileTest, InternPath) {
+  Profile P;
+  auto Path0 = P.internPath({3, 2, 1});
+  auto Path1 = P.internPath({3, 2, 1});
+  auto Path2 = P.internPath({2, 1});
+  EXPECT_THAT(Path0, Eq(Path1));
+  EXPECT_THAT(Path0, Not(Eq(Path2)));
+}
+
+TEST(ProfileTest, ExpandPath) {
+  Profile P;
+  auto PathID = P.internPath({3, 2, 1});
+  auto PathOrError = P.expandPath(PathID);
+  if (!PathOrError)
+    FAIL() << "Error: " << PathOrError.takeError();
+  EXPECT_THAT(PathOrError.get(), ElementsAre(3, 2, 1));
+}
+
+TEST(ProfileTest, AddBlocks) {
+  Profile P;
+  // Expect an error on adding empty blocks.
+  EXPECT_TRUE(errorToBool(P.addBlock({})));
+
+  // Thread blocks may not be empty.
+  EXPECT_TRUE(errorToBool(P.addBlock({1, {}})));
+
+  // Thread blocks with data must succeed.
+  EXPECT_FALSE(errorToBool(P.addBlock(
+      Profile::Block{Profile::ThreadID{1},
+                     {
+                         {P.internPath({2, 1}), Profile::Data{1, 1000}},
+                         {P.internPath({3, 2, 1}), Profile::Data{10, 100}},
+                     }})));
+}
+
+TEST(ProfileTest, MergeProfilesByThread) {
+  Profile P0, P1;
+
+  // Set up the blocks for two different threads in P0.
+  EXPECT_FALSE(errorToBool(P0.addBlock(
+      Profile::Block{Profile::ThreadID{1},
+                     {{P0.internPath({2, 1}), Profile::Data{1, 1000}},
+                      {P0.internPath({4, 1}), Profile::Data{1, 1000}}}})));
+  EXPECT_FALSE(errorToBool(P0.addBlock(
+      Profile::Block{Profile::ThreadID{2},
+                     {{P0.internPath({3, 1}), Profile::Data{1, 1000}}}})));
+
+  // Set up the blocks for two different threads in P1.
+  EXPECT_FALSE(errorToBool(P1.addBlock(
+      Profile::Block{Profile::ThreadID{1},
+                     {{P1.internPath({2, 1}), Profile::Data{1, 1000}}}})));
+  EXPECT_FALSE(errorToBool(P1.addBlock(
+      Profile::Block{Profile::ThreadID{2},
+                     {{P1.internPath({3, 1}), Profile::Data{1, 1000}},
+                      {P1.internPath({4, 1}), Profile::Data{1, 1000}}}})));
+
+  Profile Merged = mergeProfilesByThread(P0, P1);
+  EXPECT_THAT(
+      Merged,
+      UnorderedElementsAre(
+          // We want to see two threads after the merge.
+          AllOf(Field(&Profile::Block::Thread, Eq(Profile::ThreadID{1})),
+                Field(&Profile::Block::PathData,
+                      UnorderedElementsAre(
+                          Pair(Merged.internPath({2, 1}),
+                               AllOf(Field(&Profile::Data::CallCount, Eq(2u)),
+                                     Field(&Profile::Data::CumulativeLocalTime,
+                                           Eq(2000u)))),
+                          Pair(Merged.internPath({4, 1}),
+                               AllOf(Field(&Profile::Data::CallCount, Eq(1u)),
+                                     Field(&Profile::Data::CumulativeLocalTime,
+                                           Eq(1000u))))))),
+          AllOf(Field(&Profile::Block::Thread, Eq(Profile::ThreadID{2})),
+                Field(&Profile::Block::PathData,
+                      UnorderedElementsAre(
+                          Pair(Merged.internPath({3, 1}),
+                               AllOf(Field(&Profile::Data::CallCount, Eq(2u)),
+                                     Field(&Profile::Data::CumulativeLocalTime,
+                                           Eq(2000u)))),
+                          Pair(Merged.internPath({4, 1}),
+                               AllOf(Field(&Profile::Data::CallCount, Eq(1u)),
+                                     Field(&Profile::Data::CumulativeLocalTime,
+                                           Eq(1000u)))))))));
+}
+
+TEST(ProfileTest, MergeProfilesByStack) {
+  Profile P0, P1;
+  EXPECT_FALSE(errorToBool(P0.addBlock(
+      Profile::Block{Profile::ThreadID{1},
+                     {{P0.internPath({2, 1}), Profile::Data{1, 1000}}}})));
+  EXPECT_FALSE(errorToBool(P1.addBlock(
+      Profile::Block{Profile::ThreadID{2},
+                     {{P1.internPath({2, 1}), Profile::Data{1, 1000}}}})));
+
+  Profile Merged = mergeProfilesByStack(P0, P1);
+  EXPECT_THAT(Merged,
+              ElementsAre(AllOf(
+                  // We expect that we lose the ThreadID dimension in this
+                  // algorithm.
+                  Field(&Profile::Block::Thread, Eq(Profile::ThreadID{0})),
+                  Field(&Profile::Block::PathData,
+                        ElementsAre(Pair(
+                            Merged.internPath({2, 1}),
+                            AllOf(Field(&Profile::Data::CallCount, Eq(2u)),
+                                  Field(&Profile::Data::CumulativeLocalTime,
+                                        Eq(2000u)))))))));
+}
+
+TEST(ProfileTest, MergeProfilesByStackAccumulate) {
+  std::vector<Profile> Profiles(3);
+  EXPECT_FALSE(errorToBool(Profiles[0].addBlock(Profile::Block{
+      Profile::ThreadID{1},
+      {{Profiles[0].internPath({2, 1}), Profile::Data{1, 1000}}}})));
+  EXPECT_FALSE(errorToBool(Profiles[1].addBlock(Profile::Block{
+      Profile::ThreadID{2},
+      {{Profiles[1].internPath({2, 1}), Profile::Data{1, 1000}}}})));
+  EXPECT_FALSE(errorToBool(Profiles[2].addBlock(Profile::Block{
+      Profile::ThreadID{3},
+      {{Profiles[2].internPath({2, 1}), Profile::Data{1, 1000}}}})));
+  Profile Merged = std::accumulate(Profiles.begin(), Profiles.end(), Profile(),
+                                   mergeProfilesByStack);
+  EXPECT_THAT(Merged,
+              ElementsAre(AllOf(
+                  // We expect that we lose the ThreadID dimension in this
+                  // algorithm.
+                  Field(&Profile::Block::Thread, Eq(Profile::ThreadID{0})),
+                  Field(&Profile::Block::PathData,
+                        ElementsAre(Pair(
+                            Merged.internPath({2, 1}),
+                            AllOf(Field(&Profile::Data::CallCount, Eq(3u)),
+                                  Field(&Profile::Data::CumulativeLocalTime,
+                                        Eq(3000u)))))))));
+}
+
+TEST(ProfileTest, MergeProfilesByThreadAccumulate) {
+  std::vector<Profile> Profiles(2);
+
+  // Set up the blocks for two different threads in Profiles[0].
+  EXPECT_FALSE(errorToBool(Profiles[0].addBlock(Profile::Block{
+      Profile::ThreadID{1},
+      {{Profiles[0].internPath({2, 1}), Profile::Data{1, 1000}},
+       {Profiles[0].internPath({4, 1}), Profile::Data{1, 1000}}}})));
+  EXPECT_FALSE(errorToBool(Profiles[0].addBlock(Profile::Block{
+      Profile::ThreadID{2},
+      {{Profiles[0].internPath({3, 1}), Profile::Data{1, 1000}}}})));
+
+  // Set up the blocks for two different threads in Profiles[1].
+  EXPECT_FALSE(errorToBool(Profiles[1].addBlock(Profile::Block{
+      Profile::ThreadID{1},
+      {{Profiles[1].internPath({2, 1}), Profile::Data{1, 1000}}}})));
+  EXPECT_FALSE(errorToBool(Profiles[1].addBlock(Profile::Block{
+      Profile::ThreadID{2},
+      {{Profiles[1].internPath({3, 1}), Profile::Data{1, 1000}},
+       {Profiles[1].internPath({4, 1}), Profile::Data{1, 1000}}}})));
+
+  Profile Merged = std::accumulate(Profiles.begin(), Profiles.end(), Profile(),
+                                   mergeProfilesByThread);
+  EXPECT_THAT(
+      Merged,
+      UnorderedElementsAre(
+          // We want to see two threads after the merge.
+          AllOf(Field(&Profile::Block::Thread, Eq(Profile::ThreadID{1})),
+                Field(&Profile::Block::PathData,
+                      UnorderedElementsAre(
+                          Pair(Merged.internPath({2, 1}),
+                               AllOf(Field(&Profile::Data::CallCount, Eq(2u)),
+                                     Field(&Profile::Data::CumulativeLocalTime,
+                                           Eq(2000u)))),
+                          Pair(Merged.internPath({4, 1}),
+                               AllOf(Field(&Profile::Data::CallCount, Eq(1u)),
+                                     Field(&Profile::Data::CumulativeLocalTime,
+                                           Eq(1000u))))))),
+          AllOf(Field(&Profile::Block::Thread, Eq(Profile::ThreadID{2})),
+                Field(&Profile::Block::PathData,
+                      UnorderedElementsAre(
+                          Pair(Merged.internPath({3, 1}),
+                               AllOf(Field(&Profile::Data::CallCount, Eq(2u)),
+                                     Field(&Profile::Data::CumulativeLocalTime,
+                                           Eq(2000u)))),
+                          Pair(Merged.internPath({4, 1}),
+                               AllOf(Field(&Profile::Data::CallCount, Eq(1u)),
+                                     Field(&Profile::Data::CumulativeLocalTime,
+                                           Eq(1000u)))))))));
+}
+// FIXME: Add a test creating a Trace and generating a Profile
+// FIXME: Add tests for ranking/sorting profile blocks by dimension
+
+} // namespace
+} // namespace xray
+} // namespace llvm