Thank you for your comments. I have a few questions.
I don't think this specific case qualifies for -Wdisabled-optimization.
The diagnostic is for cases the user can control and was invented
for limits we put up for compile-time and memory-usage issues
where there exist --param XYZ to adjust limits.
It would be more appropriate to change this to
dump_printf_loc (MSG_MISSED_OPTIMIZATION, ...)
where this was designe to diagnose cases the compiler failed to
optimize for other reasons than running into some --param.
I'm sorry, I don't understand what dump_printf_loc does, where does it
dump this information? What is the form of information that is usually
dumped, and for which purpose?
So, NAK.
What does "NAK" mean?
When I added the -Wdisabled-optimization warning to gcc in 2000, I was
trying to give the user information about when the compiler may not do
an optimization that the user asks for. And yes, my idea was that the
user can either ignore the warning or do something to the code or change
a --param to allow the optimization to succeed.
Whether gcc actually optimizes tail or sibling calls that appear in the
Gambit source code has been a point of discussion among the Gambit
Scheme community for years; sometimes that discussion has bled into the
GCC mail lists, there's a fairly long thread here:
https://gcc.gnu.org/pipermail/gcc-help/2021-December/140957.html
I actually built a profiled gcc to see whether
maybe_complain_about_tail_call was called when compiling the output of
Gambit's Scheme->C compiler; afterwards I reported to the Gambit mail
list that it had not, all sibling calls were optimized.
To me, -Wdisabled-optimization seems very appropriate when the user asks
explicitly for -foptimize-sibling-calls (which the Gambit makefile does,
because it doesn't want all -O2 optimizations) and a sibling call can't
be optimized.
maybe_complain_about_tail_call is even passed a helpful message that
explains *why* the call can't be optimized. With this information, the
user can actually do something, rewrite the code to remove the obstacle,
or decide that optimizing that particular call isn't important (which
sometimes it isn't, if it's in the handwritten C support library instead
of the C code generated by the Scheme->C compiler).
So I'm really hoping that some kind of information can be sent back to
the user in this situation.
Brad
