Export of internal Abseil changes

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f27dbf50d5db12279ab018f11c93ad1704043006 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 358298501

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864c141a59e20e96234c06700d7519d43bc73d71 by Derek Mauro <dmauro@google.com>:

Annotates the duration-to-int64 and duration-to-double conversion
functions as "pure" to potentially optimize out repeated calls with
the same argument

This adds an ABSL_ATTRIBUTE_PURE_FUNCTION macro for this purpose.

PiperOrigin-RevId: 358247225
GitOrigin-RevId: f27dbf50d5db12279ab018f11c93ad1704043006
Change-Id: I5c2238911711b15d9d3ae53da44db788f20b402b

absl/base/attributes.h

@@ -678,4 +678,25 @@
 #define ABSL_CONST_INIT
 #endif  // ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization)
 
+// ABSL_ATTRIBUTE_PURE_FUNCTION
+//
+// ABSL_ATTRIBUTE_PURE_FUNCTION is used to annotate declarations of "pure"
+// functions. A function is pure if its return value is only a function of its
+// arguments. The pure attribute prohibits a function from modifying the state
+// of the program that is observable by means other than inspecting the
+// function's return value. Declaring such functions with the pure attribute
+// allows the compiler to avoid emitting some calls in repeated invocations of
+// the function with the same argument values.
+//
+// Example:
+//
+//  ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Milliseconds(Duration d);
+#if ABSL_HAVE_CPP_ATTRIBUTE(gnu::pure)
+#define ABSL_ATTRIBUTE_PURE_FUNCTION [[gnu::pure]]
+#elif ABSL_HAVE_ATTRIBUTE(pure)
+#define ABSL_ATTRIBUTE_PURE_FUNCTION __attribute__((pure))
+#else
+#define ABSL_ATTRIBUTE_PURE_FUNCTION
+#endif
+
 #endif  // ABSL_BASE_ATTRIBUTES_H_

absl/debugging/internal/stacktrace_powerpc-inl.inc

@@ -132,9 +132,10 @@ static void **NextStackFrame(void **old_sp, const void *uc) {
           reinterpret_cast<const ucontext_t*>(uc);
       void **const sp_before_signal =
 #if defined(__PPC64__)
-          reinterpret_cast<void**>(signal_context->uc_mcontext.gp_regs[PT_R1]);
+          reinterpret_cast<void **>(signal_context->uc_mcontext.gp_regs[PT_R1]);
 #else
-          reinterpret_cast<void**>(signal_context->uc_mcontext.uc_regs->gregs[PT_R1]);
+          reinterpret_cast<void **>(
+              signal_context->uc_mcontext.uc_regs->gregs[PT_R1]);
 #endif
       // Check that alleged sp before signal is nonnull and is reasonably
       // aligned.

absl/time/time.h

@@ -458,12 +458,12 @@ Duration Hours(T n) {
 //
 //   absl::Duration d = absl::Milliseconds(1500);
 //   int64_t isec = absl::ToInt64Seconds(d);  // isec == 1
-int64_t ToInt64Nanoseconds(Duration d);
-int64_t ToInt64Microseconds(Duration d);
-int64_t ToInt64Milliseconds(Duration d);
-int64_t ToInt64Seconds(Duration d);
-int64_t ToInt64Minutes(Duration d);
-int64_t ToInt64Hours(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Nanoseconds(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Microseconds(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Milliseconds(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Seconds(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Minutes(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Hours(Duration d);
 
 // ToDoubleNanoSeconds()
 // ToDoubleMicroseconds()
@@ -480,12 +480,12 @@ int64_t ToInt64Hours(Duration d);
 //
 //   absl::Duration d = absl::Milliseconds(1500);
 //   double dsec = absl::ToDoubleSeconds(d);  // dsec == 1.5
-double ToDoubleNanoseconds(Duration d);
-double ToDoubleMicroseconds(Duration d);
-double ToDoubleMilliseconds(Duration d);
-double ToDoubleSeconds(Duration d);
-double ToDoubleMinutes(Duration d);
-double ToDoubleHours(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleNanoseconds(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleMicroseconds(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleMilliseconds(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleSeconds(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleMinutes(Duration d);
+ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleHours(Duration d);
 
 // FromChrono()
 //