[flang] [llvm] [flang][flang-rt] Add support for non-standard TIMEF intrinsic (PR #185377)

[Eugene Epshteyn via llvm-commits]

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@@ -413,6 +416,54 @@ double RTNAME(Dsecnds)(double *refTime, const char *sourceFile, int line) {
 // GNU extension function TIME()
 std::int64_t RTNAME(time)() { return time(nullptr); }
 
+/*
+ * Extension function TIMEF().
+ * By default, it returns number of seconds that have
+ * elapsed since the first time TIMEF was called.
+ * For the first call, it returns 0.
+ *
+ * FLANG_TIMEF_IN_MILLISECONDS=1 sets the resolution to
+ * milliseconds
+ */
+double RTNAME(Timef)() {
+#ifndef _WIN32
+  // posix-compliant
+  static clock_t start = (clock_t)-1;
+  static long ticks_per_sec = 0;
+  struct tms b;
+  clock_t current;
+  double duration;
+  {
+    CriticalSection critical{timef_lock};
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eugeneepshteyn wrote:

It seems that `timef_lock` is only used here. Could its declaration be moved to this function, like `ticks_per_sec` above?

https://github.com/llvm/llvm-project/pull/185377