On Sun, May 5, 2024 at 8:16 PM Andi Kleen <a...@linux.intel.com> wrote:
>
> gcc/ChangeLog:
>
> * doc/extend.texi: Document [[musttail]]
> ---
> gcc/doc/extend.texi | 22 ++++++++++++++++++++--
> 1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index e290265d68d3..deb100ad93b6 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -9839,7 +9839,7 @@ same manner as the @code{deprecated} attribute.
> @section Statement Attributes
> @cindex Statement Attributes
>
> -GCC allows attributes to be set on null statements. @xref{Attribute Syntax},
> +GCC allows attributes to be set on statements. @xref{Attribute Syntax},
> for details of the exact syntax for using attributes. Other attributes are
> available for functions (@pxref{Function Attributes}), variables
> (@pxref{Variable Attributes}), labels (@pxref{Label Attributes}), enumerators
> @@ -9896,6 +9896,22 @@ foo (int x, int y)
> @code{y} is not actually incremented and the compiler can but does not
> have to optimize it to just @code{return 42 + 42;}.
>
> +@cindex @code{musttail} statement attribute
> +@item musttail
> +
> +The @code{gnu::musttail} or @code{clang::musttail} attribute
> +can be applied to a @code{return} statement with a return-value expression
> +that is a function call. It asserts that the call must be a tail call that
> +does not allocate extra stack space.
> +
> +@smallexample
> +[[gnu::musttail]] return foo();
> +@end smallexample
> +
> +If the compiler cannot generate a tail call it generates
> +an error. Tail calls generally require enabling optimization.
> +On some targets they may not be supported.
Looks generally OK though does this mean people can debug
programs using [[gnu::musttail]] only with optimized builds? It
seems to me we should try harder to make [[gnu::musttail]] work
at -O0 and generally behave the same at all optimization levels?
> +
> @end table
>
> @node Attribute Syntax
> @@ -10019,7 +10035,9 @@ the constant expression, if present.
>
> @subsubheading Statement Attributes
> In GNU C, an attribute specifier list may appear as part of a null
> -statement. The attribute goes before the semicolon.
> +statement. The attribute goes before the semicolon.
> +Some attributes in new style syntax are also supported
> +on non-null statements.
>
> @subsubheading Type Attributes
>
> --
> 2.44.0
>
