https://gcc.gnu.org/g:a3e790a9c9fbb84c103c1407d9afd4beae10d512
commit r15-9147-ga3e790a9c9fbb84c103c1407d9afd4beae10d512
Author: Jakub Jelinek <ja...@redhat.com>
Date: Wed Apr 2 12:36:29 2025 +0200
doc: Extend musttail attribute docs
On Wed, Apr 02, 2025 at 10:32:20AM +0200, Richard Biener wrote:
> I wonder if we can amend the documentation to suggest to end lifetime
> of variables explicitly by proper scoping?
In the -Wmaybe-musttail-local-addr attribute description I've already
tried to show that in the example, but if you think something like
the following would make it clearer.
2025-04-02 Jakub Jelinek <ja...@redhat.com>
* doc/extend.texi (musttail statement attribute): Hint how
to avoid -Wmaybe-musttail-local-addr warnings.
Diff:
---
gcc/doc/extend.texi | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 9bf401b18a4d..109c7d26ea28 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -9368,6 +9368,31 @@ baz (int *x)
@}
@}
@end smallexample
+
+To avoid the @option{-Wmaybe-musttail-local-addr} warning in the
+above @code{*x == 2} case and similar code, consider defining the
+maybe escaped variables in a separate scope which will end before the
+return statement if possible to make it clear that the variable is not
+live during the call. So
+
+@smallexample
+ else if (*x == 2)
+ @{
+ @{
+ int a = 42;
+ bar (&a);
+ @}
+ /* The call will be tail called (would not be without the
+ attribute), if bar stores the pointer anywhere, dereferencing
+ it in foo will be undefined behavior and there will be a warning
+ emitted for this with @option{-Wextra}, which implies
+ @option{-Wmaybe-musttail-local-addr}. */
+ [[gnu::musttail]] return foo (nullptr);
+ @}
+@end smallexample
+
+in this case. That is not possible if it is function argument which
+is address taken because those are in scope for the whole function.
@end table
@node Attribute Syntax
