Index: tools/CMakeLists.txt
===================================================================
--- tools/CMakeLists.txt
+++ tools/CMakeLists.txt
@@ -39,6 +39,7 @@
 add_llvm_tool_subdirectory(llvm-config)
 add_llvm_tool_subdirectory(llvm-lto)
 add_llvm_tool_subdirectory(llvm-profdata)
+add_llvm_tool_subdirectory(xray)
 
 # Projects supported via LLVM_EXTERNAL_*_SOURCE_DIR need to be explicitly
 # specified.
Index: tools/xray/CMakeLists.txt
===================================================================
--- /dev/null
+++ tools/xray/CMakeLists.txt
@@ -0,0 +1,6 @@
+set(LLVM_LINK_COMPONENTS
+    ${LLVM_TARGETS_TO_BUILD}
+    Support)
+
+add_llvm_tool(xray-fc-account
+    xray-fc-account.cc)
Index: tools/xray/xray-fc-account.cc
===================================================================
--- /dev/null
+++ tools/xray/xray-fc-account.cc
@@ -0,0 +1,161 @@
+//===- xray-fc-account.cc - XRay Function Call Accounting Tool ------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the Function Call Accounting tool that takes an XRay
+// trace and generates function call accounting statistics for that given trace.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <fcntl.h>
+#include <map>
+#include <stack>
+#include <unistd.h>
+#include <utility>
+
+using namespace llvm;
+
+static StringRef ToolName;
+
+static cl::opt<std::string> Input(cl::Positional, cl::desc("<input file>"),
+                                  cl::Required);
+
+static cl::opt<std::string> BinaryInstrMap(
+    "instr_map",
+    cl::desc("binary or file containing an xray instrumentation map"),
+    cl::value_desc("filename"), cl::Optional);
+
+LLVM_ATTRIBUTE_NORETURN static void fail(Twine Error) {
+  outs() << ToolName << ": " << Error << ".\n";
+  exit(1);
+}
+
+class FileCloser {
+  int Fd;
+
+public:
+  explicit FileCloser(int Fd) : Fd(Fd) {}
+
+  ~FileCloser() noexcept {
+    if (Fd != -1)
+      close(Fd);
+  }
+};
+
+namespace __xray {
+
+// FIXME: Make this available in a common header between compiler-rt and this
+// tool.
+struct alignas(32) XRayRecord {
+  // Get the full 8 bytes of the TSC when we get the log record.
+  uint64_t TSC = 0;
+
+  // The thread ID for the currently running thread.
+  pid_t TId = 0;
+
+  // The CPU where the thread is running. We assume number of CPUs <= 256.
+  uint8_t CPU = 0;
+
+  // The type of the event. Usually either ENTER = 0 or EXIT = 1.
+  uint8_t Type = 0;
+
+  // The function ID for the record.
+  int32_t FuncId = 0;
+};
+}
+
+int main(int argc, char *argv[]) {
+  ToolName = argv[0];
+  cl::ParseCommandLineOptions(
+      argc, argv, "XRay Function Call Accounting (xray-fc-account)\n\n"
+                  "  This program takes an XRay trace file and does some basic "
+                  "function call accounting statistics.\n");
+
+  if (BinaryInstrMap.empty()) {
+    errs() << ToolName << ": instrumentation map not provided, using raw "
+                          "function IDs in output.\n";
+  }
+
+  if (Input.empty())
+    fail("No input file provided.");
+
+  // FIXME: Load the instrumentation map as the runtime would, but generate the
+  // function IDs in a similar manner then create a mapping to a function
+  // pointer as well as the symbol associated with that funciton.
+
+  int Fd = open(Input.c_str(), O_RDONLY);
+  while (Fd == -1 && errno == EINTR) {
+    Fd = open(Input.c_str(), O_RDONLY);
+  }
+  if (Fd == -1)
+    fail(Twine("Failed to open file '") + Input + "'; errno=" + Twine(errno));
+  FileCloser FC(Fd);
+
+  __xray::XRayRecord Record;
+  std::stack<std::pair<int32_t, uint64_t>> FunctionStack;
+  std::map<int32_t, std::vector<int64_t>> FunctionTimings;
+  while (auto ReadBytes = read(Fd, &Record, sizeof(__xray::XRayRecord))) {
+    if (ReadBytes == -1) {
+      if (errno == EINTR)
+        continue;
+      fail(Twine("Failed to read file '") + Input + "'; errno=" + Twine(errno));
+    }
+    if (Record.Type == 0) {
+      FunctionStack.push({Record.FuncId, Record.TSC});
+    }
+    if (Record.Type == 1) {
+      if (FunctionStack.top().first != Record.FuncId) {
+        errs() << ToolName << ": Encountered X" << Record.FuncId
+               << " not matching E" << FunctionStack.top().first;
+        fail("Corrupted input file found.");
+      } else {
+        const auto &Top = FunctionStack.top();
+        int64_t Timing =
+            std::max(Top.second, Record.TSC) - std::min(Top.second, Record.TSC);
+        auto &Timings = FunctionTimings[Record.FuncId];
+        Timings.push_back(Timing);
+        FunctionStack.pop();
+      }
+    }
+  }
+
+  // We then want to generate the output such that we show:
+  // Function ID          min, median,90pct, 99pct, max
+  outs() << "FuncId\tmin,median,90pct,99pct,max\n";
+  for (auto &FT : FunctionTimings) {
+    const auto &FuncId = FT.first;
+    auto &Timings = FT.second;
+    outs() << FuncId << "\t";
+    std::nth_element(Timings.begin(), Timings.begin(), Timings.end());
+    auto Min = Timings.front();
+    auto MedianOff = std::distance(Timings.begin(), Timings.end()) / 2;
+    std::nth_element(Timings.begin(), Timings.begin() + (MedianOff),
+                     Timings.end());
+    auto Median = Timings[MedianOff];
+    auto Pct90Off =
+        std::floor(std::distance(Timings.begin(), Timings.end()) * 0.9);
+    std::nth_element(Timings.begin(), Timings.begin() + Pct90Off,
+                     Timings.end());
+    auto Pct90 = Timings[Pct90Off];
+    auto Pct99Off =
+        std::floor(std::distance(Timings.begin(), Timings.end()) * 0.99);
+    std::nth_element(Timings.begin(), Timings.begin() + Pct99Off,
+                     Timings.end());
+    auto Pct99 = Timings[Pct99Off];
+    std::nth_element(Timings.begin(),
+                     Timings.begin() +
+                         std::distance(Timings.begin(), Timings.end()),
+                     Timings.end());
+    auto Max = Timings.back();
+    outs() << Min << "," << Median << "," << Pct90 << "," << Pct99 << "," << Max
+           << "\n";
+  }
+}