1 //===-- runtime/time-intrinsic.cpp ----------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 // Implements time-related intrinsic subroutines.
10
11 #include "time-intrinsic.h"
12
13 #include <ctime>
14
15 // CPU_TIME (Fortran 2018 16.9.57)
16 // We can use std::clock() from the <ctime> header as a fallback implementation
17 // that should be available everywhere. This may not provide the best resolution
18 // and is particularly troublesome on (some?) POSIX systems where CLOCKS_PER_SEC
19 // is defined as 10^6 regardless of the actual precision of std::clock().
20 // Therefore, we will usually prefer platform-specific alternatives when they
21 // are available.
22 //
23 // We can use SFINAE to choose a platform-specific alternative. To do so, we
24 // introduce a helper function template, whose overload set will contain only
25 // implementations relying on interfaces which are actually available. Each
26 // overload will have a dummy parameter whose type indicates whether or not it
27 // should be preferred. Any other parameters required for SFINAE should have
28 // default values provided.
29 namespace {
30 // Types for the dummy parameter indicating the priority of a given overload.
31 // We will invoke our helper with an integer literal argument, so the overload
32 // with the highest priority should have the type int.
33 using fallback_implementation = double;
34 using preferred_implementation = int;
35
36 // This is the fallback implementation, which should work everywhere.
GetCpuTime(fallback_implementation)37 template <typename Unused = void> double GetCpuTime(fallback_implementation) {
38 std::clock_t timestamp{std::clock()};
39 if (timestamp != static_cast<std::clock_t>(-1)) {
40 return static_cast<double>(timestamp) / CLOCKS_PER_SEC;
41 }
42
43 // Return some negative value to represent failure.
44 return -1.0;
45 }
46
47 // POSIX implementation using clock_gettime. This is only enabled if
48 // clock_gettime is available.
49 template <typename T = int, typename U = struct timespec>
GetCpuTime(preferred_implementation,T ClockId=0,U * Timespec=nullptr,decltype(clock_gettime (ClockId,Timespec))* Enabled=nullptr)50 double GetCpuTime(preferred_implementation,
51 // We need some dummy parameters to pass to decltype(clock_gettime).
52 T ClockId = 0, U *Timespec = nullptr,
53 decltype(clock_gettime(ClockId, Timespec)) *Enabled = nullptr) {
54 #if defined CLOCK_THREAD_CPUTIME_ID
55 #define CLOCKID CLOCK_THREAD_CPUTIME_ID
56 #elif defined CLOCK_PROCESS_CPUTIME_ID
57 #define CLOCKID CLOCK_PROCESS_CPUTIME_ID
58 #elif defined CLOCK_MONOTONIC
59 #define CLOCKID CLOCK_MONOTONIC
60 #else
61 #define CLOCKID CLOCK_REALTIME
62 #endif
63 struct timespec tspec;
64 if (clock_gettime(CLOCKID, &tspec) == 0) {
65 return tspec.tv_nsec * 1.0e-9 + tspec.tv_sec;
66 }
67
68 // Return some negative value to represent failure.
69 return -1.0;
70 }
71 } // anonymous namespace
72
73 namespace Fortran::runtime {
74 extern "C" {
75
RTNAME(CpuTime)76 double RTNAME(CpuTime)() { return GetCpuTime(0); }
77 } // extern "C"
78 } // namespace Fortran::runtime
79