2018-11-11 Sandra Loosemore <[email protected]>

PR c/26366 gcc/ * doc/extend.texi (Other Builtins): Document probability associated with __builtin_expect. git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@266017 138bc75d-0d04-0410-961f-82ee72b054a4
stffrdhrn · Nov 11, 2018 · faa4091 · faa4091
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diff --git a/gcc/ChangeLog b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2018-11-11  Sandra Loosemore  <[email protected]>
+
+	PR c/26366
+	* doc/extend.texi (Other Builtins): Document probability associated
+	with __builtin_expect.
+
 2018-11-11  Uros Bizjak  <[email protected]>
 
 	PR target/87928

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
@@ -12121,6 +12121,12 @@ if (__builtin_expect (ptr != NULL, 1))
 
 @noindent
 when testing pointer or floating-point values.
+
+For the purposes of branch prediction optimizations, the probability that
+a @code{__builtin_expect} expression is true is controlled by GCC's
+@code{builtin-expect-probability} parameter, which defaults to 90%.  
+You can also use @code{__builtin_expect_with_probability} to explicitly 
+assign a probability value to individual expressions.
 @end deftypefn
 
 @deftypefn {Built-in Function} long __builtin_expect_with_probability