https://gcc.gnu.org/g:8daae81113eeff37b4ae2e08a9797295fbc8b81e
commit r15-2234-g8daae81113eeff37b4ae2e08a9797295fbc8b81e
Author: Andi Kleen <a...@linux.intel.com>
Date: Tue Jan 23 23:38:23 2024 -0800
Add documentation for musttail attribute
gcc/ChangeLog:
PR c/83324
* doc/extend.texi: Document [[musttail]]
Diff:
---
gcc/doc/extend.texi | 25 +++++++++++++++++++++++--
1 file changed, 23 insertions(+), 2 deletions(-)
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 4b77599380b5..b0273927b256 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -9921,7 +9921,7 @@ 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
@@ -9978,6 +9978,25 @@ 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, so it is safe to use tail recursion
+to implement long running loops.
+
+@smallexample
+[[gnu::musttail]] return foo();
+@end smallexample
+
+If the compiler cannot generate a @code{musttail} tail call it will report
+an error. On some targets tail calls may never be supported.
+Tail calls cannot reference locals in memory, which may affect
+builds without optimization when passing small structures, or passing
+or returning large structures. Enabling -O1 or -O2 can improve
+the success of tail calls.
@end table
@node Attribute Syntax
@@ -10101,7 +10120,9 @@ 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
