D45837.diff
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	diff --git a/share/man/man9/style.9 b/share/man/man9/style.9
	--- a/share/man/man9/style.9
	+++ b/share/man/man9/style.9
	@@ -897,6 +897,22 @@
	.Fn _Static_assert
	instead of the older
	.Fn CTASSERT .
	+.Pp
	+.Fn __predict_true
	+and
	+.Fn __predict_false
	+should only be used in frequently executed code when it makes the code
	+measurably faster.
	+It is wasteful to make predictions for infrequently run code, like subsystem
	+initialization.
	+When using branch prediction hints, atypical error conditions should use
	+.Fn __predict_false
	+(document the exceptions).
	+Operations that almost always succeed use
	+.Fn __predict_true .
	+Only use the annotation for the entire if statement, rather than individual clauses.
	+Do not add these annotations without empirical evidence of the likelihood of the
	+branch.
	.Sh FILES
	.Bl -tag -width indent
	.It Pa /usr/src/tools/build/checkstyle9.pl
	diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
	--- a/sys/sys/cdefs.h
	+++ b/sys/sys/cdefs.h
	@@ -321,6 +321,13 @@
	#define __restrict restrict
	#endif

	+/*
	+ * All modern compilers have explicit branch prediction so that the CPU back-end
	+ * can hint to the processor and also so that code blocks can be reordered such
	+ * that the predicted path sees a more linear flow, thus improving cache
	+ * behavior, etc. Use sparingly, except in performance critical code where
	+ * they make things measurably faster.
	+ */
	#define __predict_true(exp) __builtin_expect((exp), 1)
	#define __predict_false(exp) __builtin_expect((exp), 0)