Export of internal Abseil changes.

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6258612abc571fa7f51f34046b410c73486505fe by Derek Mauro <dmauro@google.com>:

Rollback checking the return value of pthread functions in thread_identity.cc.

PiperOrigin-RevId: 248381230

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fda6acddab04fc53eeb84ec253de4a9655bf9a36 by CJ Johnson <johnsoncj@google.com>:

Removes too-restrictive benchmark abstraction in inlined_vector_benchmark

PiperOrigin-RevId: 248366325

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68674991e63c919de8a3eebced5adec6466ec8fe by Abseil Team <absl-team@google.com>:

Check for pthread_setmask() failure.

Log a fatal error message if pthread_setmask() fails.

PiperOrigin-RevId: 248347115

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45389e44c0d1badafb6b560cae3df99fc8bd16ac by Derek Mauro <dmauro@google.com>:

Fix a -Wredundant-move warning in GCC 9.

PiperOrigin-RevId: 248338682

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12cfbacf599084a8ac6bf4395026cbf193c85a26 by Derek Mauro <dmauro@google.com>:

Check the return value of pthread functions in thread_identity.cc.

PiperOrigin-RevId: 248327118

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2bc69998e68cfee96e812ce800e83cce7a715091 by Benjamin Barenblat <bbaren@google.com>:

Encourage judicious use of ABSL_PREDICT_{TRUE,FALSE}

Recommend that users use branch prediction annotations only on hot,
consistently mispredicted branches.

PiperOrigin-RevId: 248222450
GitOrigin-RevId: 6258612abc571fa7f51f34046b410c73486505fe
Change-Id: I09d409f9a3941ee926b8476b5473f9c4899cc3ff

1 files changed, 6 insertions, 0 deletions

diff --git a/absl/base/optimization.h b/absl/base/optimization.h
index 6974f1f60777..0dcbef32a3c5 100644
--- a/absl/base/optimization.h
+++ b/absl/base/optimization.h
@@ -163,6 +163,12 @@
 // Compilers can use the information that a certain branch is not likely to be
 // taken (for instance, a CHECK failure) to optimize for the common case in
 // the absence of better information (ie. compiling gcc with `-fprofile-arcs`).
+//
+// Recommendation: Modern CPUs dynamically predict branch execution paths,
+// typically with accuracy greater than 97%. As a result, annotating every
+// branch in a codebase is likely counterproductive; however, annotating
+// specific branches that are both hot and consistently mispredicted is likely
+// to yield performance improvements.
 #if ABSL_HAVE_BUILTIN(__builtin_expect) || \
     (defined(__GNUC__) && !defined(__clang__))
 #define ABSL_PREDICT_FALSE(x) (__builtin_expect(x, 0))