Add a Chrono.h header to libSupport

[mehdi_amini]

Summary

The intent is to add helpers (utility functions or wrapper)
to manipulate std::chrono types.

[mehdi_amini]

Fix typo in doxygen comment

[mehdi_amini]

It should be worth noting that this is a straw man proposal to start a utility header to support the use of std::chrono in LLDB.
Also with the drop of MSVC2013, we should be table to slowly move away from TimeValue, unless it provides some other benefits that I missed?

[labath]

After studying the chrono library a bit more, I've learned of an easier way to do this, one that renders this function redundant (it's std::chrono::duration<double, std::milli (or whatever)>(value) if anyone wonders). Thank you for testing out the waters for me though :).

I'll soon come up with a proposal for adding conversions from/to the legacy types that we need to this header.

[mehdi_amini]

Superseded by: D25416: Add Chrono.h - std::chrono support header

include/llvm/Support/Chrono.h

+//===- llvm/Support/Chrono.h - Utilities for Timing Manipulation-*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_CHRONO_H
+#define LLVM_SUPPORT_CHRONO_H
+
+#include <chrono>
+
+namespace llvm {
+
+/// Return duration \p Dur as a floating point value, after conversion in the
+/// unit passed in as a template parameter. For example:
+///
+/// std::chrono::duration<std::chrono::microsecond> MillionMicros(1000000);
+/// errs() << floatDuration<std::chrono::milliseconds>(MillionMicros) << "\n"
+/// /* Print '1000.0' on the output */
+template <typename DurOut, typename DurIn>
+static double floatDuration(DurIn Dur) {
+  return std::chrono::duration_cast<
+             std::chrono::duration<double, typename DurOut::period>>(Dur)
+      .count();
+}
+
+} // namespace llvm
+
+#endif // LLVM_SUPPORT_CHRONO_H

unittests/Support/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
   Support
   )
 
 add_llvm_unittest(SupportTests
   AlignOfTest.cpp
   AllocatorTest.cpp
   ArrayRecyclerTest.cpp
   BlockFrequencyTest.cpp
   BranchProbabilityTest.cpp
   Casting.cpp
   CommandLineTest.cpp
   CompressionTest.cpp
   ConvertUTFTest.cpp
+  Chrono.cpp
   DataExtractorTest.cpp
   DwarfTest.cpp
   EndianStreamTest.cpp
   EndianTest.cpp
   ErrorTest.cpp
   ErrorOrTest.cpp
   FileOutputBufferTest.cpp
   LEB128Test.cpp

unittests/Support/Chrono.cpp

+//===- llvm/unittest/Support/Chrono.cpp - Time utilities tests ------------===//
+//
+//           The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Chrono.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(Chrono, FloatConversion) {
+  std::chrono::microseconds MillionMicros(1000000);
+  ASSERT_EQ(1000., floatDuration<std::chrono::milliseconds>(MillionMicros));
+  ASSERT_EQ(1., floatDuration<std::chrono::seconds>(MillionMicros));
+
+  std::chrono::seconds TenSeconds(10);
+  ASSERT_EQ(10000., floatDuration<std::chrono::milliseconds>(TenSeconds));
+  ASSERT_EQ(10000000., floatDuration<std::chrono::microseconds>(TenSeconds));
+
+  // Check that floatDuration accepts a non-float based duration
+  std::chrono::duration<int, std::ratio<1, 1>> TenSecondsInt(10);
+  ASSERT_EQ(10000., floatDuration<std::chrono::milliseconds>(TenSecondsInt));
+  ASSERT_EQ(10000000., floatDuration<std::chrono::microseconds>(TenSecondsInt));
+}
+
+} // anonymous namespace