Support CPU cycle counter on ARM64

ARM64 CPUs don't use __rdtsc to get the CPU cycle counter because that
is an x86/x64 specific instruction. This change updates ThreadTicks to
use the appropriate counter on ARM64 builds on Win32.

Bug: 893460
Change-Id: Ia9679aa8d560f887c5a787b9e6f333ceed9d1192
Reviewed-on: https://chromium-review.googlesource.com/c/1301577Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609467}

AUTHORS

@@ -277,6 +277,7 @@ Gajendra Singh <wxjg68@motorola.com>
 Ganesh Borle <ganesh.borle@samsung.com>
 Gao Chun <chun.gao@intel.com>
 Gao Chun <gaochun.dev@gmail.com>
+Gaurav Dhol <gaurav.dhol@einfochips.com>
 Gautham Banasandra <gautham.bangalore@gmail.com>
 George Adams <geoada@amazon.com>
 George Joseph <kottackal.george@gmail.com>
@@ -980,8 +981,7 @@ Zsolt Borbely <zsborbely.u-szeged@partner.samsung.com>
 Rajesh Mahindra <rmahindra@uber.com>
 Yuan-Pin Yu <yjames@uber.com>
 Vinoth Chandar <vinoth@uber.com>
-Zheng Xu <zxu@kobo.com>
-Gaurav Dhol <gaurav.dhol@einfochips.com>
+Zheng Xu <zxu@kobo.com>
 
 ACCESS CO., LTD. <*@access-company.com>
 Akamai Inc. <*@akamai.com>

base/time/time_win.cc

@@ -650,6 +650,12 @@ void ThreadTicks::WaitUntilInitializedWin() {
     ::Sleep(10);
 }
 
+#if defined(_M_ARM64) && defined(__clang__)
+#define ReadCycleCounter() _ReadStatusReg(ARM64_PMCCNTR_EL0)
+#else
+#define ReadCycleCounter() __rdtsc()
+#endif
+
 double ThreadTicks::TSCTicksPerSecond() {
   DCHECK(IsSupported());
 
@@ -670,12 +676,13 @@ double ThreadTicks::TSCTicksPerSecond() {
 
   // The first time that this function is called, make an initial reading of the
   // TSC and the performance counter.
-  static const uint64_t tsc_initial = __rdtsc();
+
+  static const uint64_t tsc_initial = ReadCycleCounter();
   static const uint64_t perf_counter_initial = QPCNowRaw();
 
   // Make a another reading of the TSC and the performance counter every time
   // that this function is called.
-  uint64_t tsc_now = __rdtsc();
+  uint64_t tsc_now = ReadCycleCounter();
   uint64_t perf_counter_now = QPCNowRaw();
 
   // Reset the thread priority.
@@ -709,6 +716,7 @@ double ThreadTicks::TSCTicksPerSecond() {
   return tsc_ticks_per_second;
 }
 
+#undef ReadCycleCounter
 // static
 TimeTicks TimeTicks::FromQPCValue(LONGLONG qpc_value) {
   return TimeTicks() + QPCValueToTimeDelta(qpc_value);