Add llvm-exegesis tool.

Summary:
[llvm-exegesis][RFC] Automatic Measurement of Instruction Latency/Uops

This is the code corresponding to the RFC "llvm-exegesis Automatic Measurement of Instruction Latency/Uops".

The RFC is available on the LLVM mailing lists as well as the following document
for easier reading:
https://docs.google.com/document/d/1QidaJMJUyQdRrFKD66vE1_N55whe0coQ3h1GpFzz27M/edit?usp=sharing

Subscribers: mgorny, gchatelet, orwant, llvm-commits

Differential Revision: https://reviews.llvm.org/D44519

llvm-svn: 329156

1 files changed, 103 insertions, 0 deletions

diff --git a/llvm/tools/llvm-exegesis/lib/PerfHelper.h b/llvm/tools/llvm-exegesis/lib/PerfHelper.h
new file mode 100644
index 00000000000..22da2061c52
--- /dev/null
+++ b/llvm/tools/llvm-exegesis/lib/PerfHelper.h
@@ -0,0 +1,103 @@
+//===-- PerfHelper.h ------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Helpers for measuring perf events.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H
+#define LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
+#include <functional>
+#include <memory>
+
+struct perf_event_attr;
+
+namespace exegesis {
+namespace pfm {
+
+// Returns true on error.
+bool pfmInitialize();
+void pfmTerminate();
+
+// Retrieves the encoding for the event described by pfm_event_string.
+// NOTE: pfm_initialize() must be called before creating PerfEvent objects.
+class PerfEvent {
+public:
+  // http://perfmon2.sourceforge.net/manv4/libpfm.html
+  // Events are expressed as strings. e.g. "INSTRUCTION_RETIRED"
+  explicit PerfEvent(llvm::StringRef pfm_event_string);
+
+  PerfEvent(const PerfEvent &) = delete;
+  PerfEvent(PerfEvent &&other);
+  ~PerfEvent();
+
+  // The pfm_event_string passed at construction time.
+  llvm::StringRef name() const;
+
+  // Whether the event was successfully created.
+  bool valid() const;
+
+  // The encoded event to be passed to the Kernel.
+  const perf_event_attr *attribute() const;
+
+  // The fully qualified name for the event.
+  // e.g. "snb_ep::INSTRUCTION_RETIRED:e=0:i=0:c=0:t=0:u=1:k=0:mg=0:mh=1"
+  llvm::StringRef getPfmEventString() const;
+
+private:
+  const std::string EventString;
+  std::string FullQualifiedEventString;
+  perf_event_attr *Attr;
+};
+
+// Uses a valid PerfEvent to configure the Kernel so we can measure the
+// underlying event.
+struct Counter {
+  // event: the PerfEvent to measure.
+  explicit Counter(const PerfEvent &event);
+
+  Counter(const Counter &) = delete;
+  Counter(Counter &&other) = default;
+
+  ~Counter();
+
+  void start();         // Starts the measurement of the event.
+  void stop();          // Stops the measurement of the event.
+  int64_t read() const; // Return the current value of the counter.
+
+private:
+  int FileDescriptor = -1;
+};
+
+// Helper to measure a list of PerfEvent for a particular function.
+// callback is called for each successful measure (PerfEvent needs to be valid).
+template <typename Function>
+void Measure(
+    llvm::ArrayRef<PerfEvent> Events,
+    const std::function<void(const PerfEvent &Event, int64_t Value)> &Callback,
+    Function Fn) {
+  for (const auto &Event : Events) {
+    if (!Event.valid())
+      continue;
+    Counter Cnt(Event);
+    Cnt.start();
+    Fn();
+    Cnt.stop();
+    Callback(Event, Cnt.read());
+  }
+}
+
+} // namespace pfm
+} // namespace exegesis
+
+#endif // LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H