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

1 files changed, 21 insertions, 0 deletions

diff --git a/absl/base/attributes.h b/absl/base/attributes.h
index faa5b27e..cf2cb550 100644
--- a/absl/base/attributes.h
+++ b/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_