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author | Andi Kleen <ak@linux.intel.com> | 2024-01-23 23:38:23 -0800 |
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committer | Andi Kleen <ak@gcc.gnu.org> | 2024-07-23 13:27:12 -0700 |
commit | 8daae81113eeff37b4ae2e08a9797295fbc8b81e (patch) | |
tree | 9274f79406f551b0d96d6b02ca140067bacde4e0 | |
parent | 8d1af8f904a0c08656d976cbf8ca56dba35197b0 (diff) | |
download | gcc-8daae81113eeff37b4ae2e08a9797295fbc8b81e.zip gcc-8daae81113eeff37b4ae2e08a9797295fbc8b81e.tar.gz gcc-8daae81113eeff37b4ae2e08a9797295fbc8b81e.tar.bz2 |
Add documentation for musttail attribute
gcc/ChangeLog:
PR c/83324
* doc/extend.texi: Document [[musttail]]
-rw-r--r-- | gcc/doc/extend.texi | 25 |
1 files changed, 23 insertions, 2 deletions
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index 4b77599..b027392 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 |