* [Bug c/97100] -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings
2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
@ 2023-07-17 12:11 ` Hi-Angel at yandex dot ru
2023-08-04 6:06 ` muecker at gwdg dot de
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From: Hi-Angel at yandex dot ru @ 2023-07-17 12:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
Konstantin Kharlamov <Hi-Angel at yandex dot ru> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |Hi-Angel at yandex dot ru
--- Comment #1 from Konstantin Kharlamov <Hi-Angel at yandex dot ru> ---
Still relevant. Just stumbled upon it in 13.1.1, was about to report a bug.
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2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
2023-07-17 12:11 ` [Bug c/97100] " Hi-Angel at yandex dot ru
@ 2023-08-04 6:06 ` muecker at gwdg dot de
2023-08-05 8:40 ` cvs-commit at gcc dot gnu.org
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From: muecker at gwdg dot de @ 2023-08-04 6:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
Martin Uecker <muecker at gwdg dot de> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |muecker at gwdg dot de
--- Comment #2 from Martin Uecker <muecker at gwdg dot de> ---
PATCH: https://gcc.gnu.org/pipermail/gcc-patches/2023-August/626319.html
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2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
2023-07-17 12:11 ` [Bug c/97100] " Hi-Angel at yandex dot ru
2023-08-04 6:06 ` muecker at gwdg dot de
@ 2023-08-05 8:40 ` cvs-commit at gcc dot gnu.org
2023-11-03 19:26 ` uecker at gcc dot gnu.org
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From: cvs-commit at gcc dot gnu.org @ 2023-08-05 8:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Uecker <uecker@gcc.gnu.org>:
https://gcc.gnu.org/g:54be338589ea93ad4ff53d22adde476a0582537b
commit r14-3004-g54be338589ea93ad4ff53d22adde476a0582537b
Author: Martin Uecker <uecker@tugraz.at>
Date: Fri Aug 4 07:48:21 2023 +0200
c: _Generic should not warn in non-active branches
[PR68193,PR97100,PR110703]
To avoid false diagnostics, use c_inhibit_evaluation_warnings when
a generic association is known to not match during parsing. We may
still generate false positives if the default branch comes earler than
a specific association that matches.
PR c/68193
PR c/97100
PR c/110703
gcc/c/:
* c-parser.cc (c_parser_generic_selection): Inhibit evaluation
warnings branches that are known not be taken during parsing.
gcc/testsuite/ChangeLog:
* gcc.dg/pr68193.c: New test.
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2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
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From: uecker at gcc dot gnu.org @ 2023-11-03 19:26 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
uecker at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |14.0
Known to fail| |4.9.0
CC| |uecker at gcc dot gnu.org
Status|UNCONFIRMED |RESOLVED
Resolution|--- |FIXED
--- Comment #4 from uecker at gcc dot gnu.org ---
Fixed on trunk.
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@ 2024-04-16 3:07 ` alx at kernel dot org
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From: alx at kernel dot org @ 2024-04-16 3:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
Alejandro Colomar <alx at kernel dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |alx at kernel dot org
--- Comment #5 from Alejandro Colomar <alx at kernel dot org> ---
I can still reproduce it, using gcc-14 from Debian RC-Buggy.
alx@debian:~/tmp/c$ gcc-14 -Wall -Wextra g.c -S
g.c: In function ‘main’:
g.c:96:21: error: passing argument 1 of ‘a2si_c’ from incompatible pointer type
[-Wincompatible-pointer-types]
96 | a2i(time_t, &t, "42", NULL, 0, 0, 10);
| ^~
| |
| time_t * {aka long int *}
g.c:30:11: note: in definition of macro ‘a2si’
30 | )(n, s, endp, base, min, max)
\
| ^
g.c:96:9: note: in expansion of macro ‘a2i’
96 | a2i(time_t, &t, "42", NULL, 0, 0, 10);
| ^~~
g.c:54:22: note: expected ‘int * restrict’ but argument is of type ‘time_t *’
{aka ‘long int *’}
54 | a2si_c(int *restrict n, const char *s,
| ~~~~~~~~~~~~~~^
alx@debian:~/tmp/c$ gcc-14 --version
gcc-14 (Debian 14-20240330-1) 14.0.1 20240330 (experimental) [master
r14-9728-g6fc84f680d0]
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
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@ 2024-04-16 3:08 ` alx at kernel dot org
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From: alx at kernel dot org @ 2024-04-16 3:08 UTC (permalink / raw)
To: gcc-bugs
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--- Comment #6 from Alejandro Colomar <alx at kernel dot org> ---
Oh well, in my case it is -Wincompatible-pointer-types. Maybe the fix was only
for -Wformat.
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2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
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From: uecker at gcc dot gnu.org @ 2024-04-16 5:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
--- Comment #7 from uecker at gcc dot gnu.org ---
The fix suppresses certain warnings which are guarded by a flag, but it is not
always clear whether a specific warning should be suppressed or not in dead
code.
You could also always add a cast.
Fundamentally, the program is that _Generic is not ideally designed for this
use case. One could consider an extension
_Generic(x, int i: f(i), long l: g(l));
that allows referring to the first argument with the type it would have in each
branch.
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2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
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From: Hi-Angel at yandex dot ru @ 2024-04-16 5:58 UTC (permalink / raw)
To: gcc-bugs
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--- Comment #8 from Konstantin Kharlamov <Hi-Angel at yandex dot ru> ---
(In reply to uecker from comment #7)
> Fundamentally, the program is that _Generic is not ideally designed for this
> use case.
Why?
> One could consider an extension
>
> _Generic(x, int i: f(i), long l: g(l));
>
> that allows referring to the first argument with the type it would have in
> each branch.
Unless I'm missing something, a compiler already knows if `x` is an `int` or
`long`. I see no benefit in devising such extension.
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2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
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From: uecker at gcc dot gnu.org @ 2024-04-16 6:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
--- Comment #9 from uecker at gcc dot gnu.org ---
x is - according to the C standard - always whatever it is in the controlling
expression. Some warnings are then even required to be standard compliant.
Note that this also does not have to be an identifier, but could be a complex
expression. So there seems no simply algorithm for a compiler to do the right
thing in general regarding warnings.
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2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
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@ 2024-04-16 6:27 ` Hi-Angel at yandex dot ru
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From: Hi-Angel at yandex dot ru @ 2024-04-16 6:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
--- Comment #10 from Konstantin Kharlamov <Hi-Angel at yandex dot ru> ---
(In reply to uecker from comment #9)
> Some warnings are then even required to be standard compliant.
I just searched through the C standard and no warnings seem to be required by
it. The only place where word "warning" is mentioned is in the Annex Ⅰ, which
tilted as "informative" and only serves as an example of where warnings might
be useful.
> x is - according to the C standard - always whatever it is in the controlling
> expression.
With the prev. paragraph in mind, compiler is free to warn or not to about
anything. The only (arguable) limitation is being useful. So nothing holds a
compiler off from considering for the warning purposes the `x` to have
different types on the outside of _Generic() compared to the inside.
> Note that this also does not have to be an identifier, but could be a complex
> expression. So there seems no simply algorithm for a compiler to do the right thing
> in general regarding warnings.
Idk why complexity matters, it's not like `x` is dynamically typed, so no
solving halting problem requried. For me it looks simple: if `x` entered either
branch of _Generic, just consider it to have a type different from what it was
and produce correct warnings 😊
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2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
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From: muecker at gwdg dot de @ 2024-04-16 7:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
--- Comment #11 from Martin Uecker <muecker at gwdg dot de> ---
A conforming C compiler has to diagnose all violations of constraints with the
same correct type of x in all branches (not the type it would have in another
context where a different is taken).
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2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
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From: Hi-Angel at yandex dot ru @ 2024-04-16 7:33 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
--- Comment #12 from Konstantin Kharlamov <Hi-Angel at yandex dot ru> ---
(In reply to Martin Uecker from comment #11)
> A conforming C compiler has to diagnose all violations of constraints with
> the same correct type of x in all branches (not the type it would have in
> another context where a different is taken).
As mentioned in my prev. comment, a conforming C compiler don't have to
diagnose anything at all. And in fact, GCC doesn't even diagnose anything, well
not unless you explicitly pass a -Wfoo. Which doesn't make GCC any less
conforming. Thus, I see no constraints to printing warnings that are useful.
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@ 2024-04-16 8:23 ` muecker at gwdg dot de
2024-04-16 9:55 ` alx at kernel dot org
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From: muecker at gwdg dot de @ 2024-04-16 8:23 UTC (permalink / raw)
To: gcc-bugs
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--- Comment #13 from Martin Uecker <muecker at gwdg dot de> ---
A C compiler has to diagnose all constraint violations. Alternatively, it could
also reject the program with an error.
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2020-09-18 0:56 [Bug c/97100] New: -Wformat checks all arms of _Generic leading to irrelevant type expectation warnings sherzberg+gcc at freeshell dot org
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@ 2024-04-16 9:55 ` alx at kernel dot org
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From: alx at kernel dot org @ 2024-04-16 9:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
--- Comment #14 from Alejandro Colomar <alx at kernel dot org> ---
Hi Martin,
For the discussion of my -Wincompatible-pointer-types reproducer, please visit
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114731>. I'll reply to you
there, since it's more on-topic, and also, I posted there the full reproducer.
Have a lovely day!
Alex
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