Export of internal Abseil changes

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77e710b0ced5792a328e88bcb938a41484bf4cdc by Saleem Abdulrasool <abdulras@google.com>:

absl: add an implementation for UnscaledCycleClock on RISCV

Add an implementation for UnscaledCycleClock on RISC-V targets.

PiperOrigin-RevId: 395982312

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84430fce6760c488ca36401cd530f44268ac710d by Martijn Vels <mvels@google.com>:

Harden CordRepBtreeReader against reading up to or beyond EOF

This change hardens the reader to Next() calls on EOF situations. It changes the 'consumed()' property inside CordRepBtreeReader into a 'remaining()' property which is easier to understand and use than the 'consumed()' property QED the function documentation and use in cord.cc

This change also adds the CharIterator test to the CordTest fixture enabling them to be run with btree cords.

PiperOrigin-RevId: 395971732

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6557e628f2613169da8f693189223acb30e07833 by Martijn Vels <mvels@google.com>:

Add AdvanceAndRead() test addressing the edge case surfaced in b/197776822

This adds a test explicitly exercising all possible AdvanceAndRead() calls on CharIterator. As per the linked bug, a partial or full small read ending exactly at the end of the last edge of a btree cord results in an attempt to read beyond that last edge and subsequent failure. We will fix the bug and enable these tests for btree in a subsequent change.

PiperOrigin-RevId: 395958317
GitOrigin-RevId: 77e710b0ced5792a328e88bcb938a41484bf4cdc
Change-Id: Ie6e21ce36980515165af7cf046cf199ecbe0ddb0

1 files changed, 12 insertions, 0 deletions

diff --git a/absl/base/internal/unscaledcycleclock.cc b/absl/base/internal/unscaledcycleclock.cc
index 1545288c..fc07e300 100644
--- a/absl/base/internal/unscaledcycleclock.cc
+++ b/absl/base/internal/unscaledcycleclock.cc
@@ -119,6 +119,18 @@ double UnscaledCycleClock::Frequency() {
   return aarch64_timer_frequency;
 }
 
+#elif defined(__riscv)
+
+int64_t UnscaledCycleClock::Now() {
+  int64_t virtual_timer_value;
+  asm volatile("rdcycle %0" : "=r"(virtual_timer_value));
+  return virtual_timer_value;
+}
+
+double UnscaledCycleClock::Frequency() {
+  return base_internal::NominalCPUFrequency();
+}
+
 #elif defined(_M_IX86) || defined(_M_X64)
 
 #pragma intrinsic(__rdtsc)