https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118549
Sam James <sjames at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
CC| |bruno at clisp dot org
Assignee|unassigned at gcc dot gnu.org |sjames at gcc dot
gnu.org
--- Comment #9 from Sam James <sjames at gcc dot gnu.org> ---
This came up in
https://lists.gnu.org/archive/html/bug-gnulib/2025-02/msg00024.html too:
"""
[...]
1) ISO C 23 ยง 7.21.1.(3) is clear that it's undefined behaviour.
This is also what gcc does with the usual optimization options:
It produces no instruction at all, leaving the CPU to execute
whatever instruction may follow.
It's documented in
<https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html>
but you can see it directly: compile this code with "gcc -m32 -O2 -S":
-----------------------------------------------------
void foo (void) { __builtin_unreachable(); }
-----------------------------------------------------
Even with the option -funreachable-traps of GCC >= 13, documented in
<https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html>,
it produces zero instructions, not even a trap. (See:
compile the code above with "gcc -m64 -funreachable-traps -S").
[...]
"""
so I think there's a clear case for refining the documentation. I'll put it on
my list.
