On 2025-04-28 02:43, Bruno Haible wrote:
Paul Eggert wrote:
Remove -Wdisabled-optimization, as this is a warning about the
compiler not the program.
Does gcc's warning message give a hint how the compiler options could
be adjusted, so as to enable the optimization?
Unfortunately not, at least not to me. Here's the diagnostic:
bytecode.c: In function ‘exec_byte_code’:
bytecode.c:1792:1: error: fold-mem-offsets: 419 basic blocks and 52
edges/basic block [-Werror=disabled-optimization]
1792 | }
| ^
cc1: all warnings being treated as errors
make[2]: *** [Makefile:444: bytecode.o] Error 1
This is with gcc-15 (Ubuntu 15-20250404-0ubuntu1) 15.0.1 20250404
(experimental) [master r15-9193-g08e803aa9be] on Ubuntu 25.04 with Emacs
master commit b06046edcfceb6ba426880444894373f21ea4a79 configured via
"./configure --enable-gcc-warnings 'CC=gcc-15 -Wdisabled-optimization'".
I do not get the diagnostic with gcc (GCC) 15.1.1 20250425 (Red Hat
15.1.1-1) on Fedora 42 with the same Emacs commit configured via
"./configure --enable-gcc-warnings 'CC=gcc -Wdisabled-optimization'".
Since the Ubuntu failure is with an experimental compiler, if it were
the only issue I suppose we could enable -Wdisabled-optimization for now
and see whether there are problems on non-experimental GCCs. However, if
the -Wdisabled-optimization diagnostics are useless in practice, this
kind of experimentation won't be worth the hassle.
For what it's worth, in 2017 libvirt ran into the same problem I did in
Emacs, and disabled the warning for the same reason[1].
My impression from looking at Google hits is that the warning is more
useful in C++ which has more of a code-bloat problem, and where one can
use the diagnostic as an idiot light meaning "overuse of templates". So
it might make sense to omit it for C but enable it for C++. I'm no C++
expert though.
Also there is precedent for for not enabling this sort of warning, as we
don't enable -Wanalyzer-symbol-too-complex either.
[1]:
https://lists.libvirt.org/archives/list/[email protected]/message/PJZ52SOEHXF3RULW26BKDIGJNXTCDRFP/
