errors.h (warning, [...]): Mark as cold.

	* errors.h (warning, error, fatal, internal_error): Mark as cold.
	* predict.c (maybe_hot_bb): Cold functions are never hot; hot functions
	are hot.
	(probably_cold_bb_p): Cold functions are cold.
	(probably_never_executed_bb_p): Cold functions are cold.
	(tree_bb_level_predictions): Predict calls to cold functions as not
	taken.
	(compute_function_frequency): Check hot/cold attributes.
	* function.h (function_frequency): Update comments.
	* predict.def (PRED_COLD_FUNCTION): Predict cold function.
	* c-common.c (handle_hot_attribute, handle_cold_attribute): New.
	(c_common_att): Add cold and hot.

	* doc/extend.texi (hot,cold attributes): Document.
	
	* ansidecl.h (ATTRIBUTE_COLD, ATTRIBUTE_HOT): New.

From-SVN: r122632

1 files changed, 34 insertions, 4 deletions

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index dfa4f5d..788cbfc 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -1578,10 +1578,11 @@ attributes are currently defined for functions on all targets:
 @code{section}, @code{constructor}, @code{destructor}, @code{used},
 @code{unused}, @code{deprecated}, @code{weak}, @code{malloc},
 @code{alias}, @code{warn_unused_result}, @code{nonnull},
-@code{gnu_inline} and @code{externally_visible}.  Several other
-attributes are defined for functions on particular target systems.  Other
-attributes, including @code{section} are supported for variables declarations
-(@pxref{Variable Attributes}) and for types (@pxref{Type Attributes}).
+@code{gnu_inline} and @code{externally_visible}, @code{hot}, @code{cold}.
+Several other attributes are defined for functions on particular target
+systems.  Other attributes, including @code{section} are supported for
+variables declarations (@pxref{Variable Attributes}) and for types (@pxref{Type
+Attributes}).
 
 You may also specify attributes with @samp{__} preceding and following
 each keyword.  This allows you to use them in header files without
@@ -2242,6 +2243,35 @@ two consecutive calls (such as @code{feof} in a multithreading environment).
 The attribute @code{pure} is not implemented in GCC versions earlier
 than 2.96.
 
+@item hot
+@cindex @code{hot} function attribute
+The @code{hot} attribute is used to inform the compiler that a function is a
+hot spot of the compiled program.  The function is optimized more aggressively
+and on many target it is placed into special subsection of the text section so
+all hot functions appears close together improving locality.
+
+When profile feedback is available, via @option{-fprofile-use}, hot functions
+are automatically detected and this attribute is ignored.
+
+The @code{hot} attribute is not implemented in GCC versions earlier than 4.3.
+
+@item cold
+@cindex @code{cold} function attribute
+The @code{cold} attribute is used to inform the compiler that a function is
+unlikely executed.  The function is optimized for size rather than speed and on
+many targets it is placed into special subsection of the text section so all
+cold functions appears close together improving code locality of non-cold parts
+of program.  The paths leading to call of cold functions within code are marked
+as unlikely by the branch prediction mechanizm. It is thus useful to mark
+functions used to handle unlikely conditions, such as @code{perror}, as cold to
+improve optimization of hot functions that do call marked functions in rare
+occasions.
+
+When profile feedback is available, via @option{-fprofile-use}, hot functions
+are automatically detected and this attribute is ignored.
+
+The @code{hot} attribute is not implemented in GCC versions earlier than 4.3.
+
 @item regparm (@var{number})
 @cindex @code{regparm} attribute
 @cindex functions that are passed arguments in registers on the 386