diff options
Diffstat (limited to 'gcc/doc/extend.texi')
| -rw-r--r-- | gcc/doc/extend.texi | 38 |
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 |