[Bug c/97261] New: gcc-10 produces invalid -Warray-bounds warning
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97261 Bug ID: 97261 Summary: gcc-10 produces invalid -Warray-bounds warning Product: gcc Version: 10.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: gccbugs at dima dot secretsauce.net Target Milestone: --- Hi. I'm seeing gcc-10 flag a warning that I'm pretty sure is incorrect. gcc-9 and older did not warn about this (although that's probably because they weren't looking for these kinds of problems). Recipe: 1. save the attached as tst.c 2. gcc-10 -Wall -Wextra -Wno-unused-variable -fPIC -O3 -c -o tst.o tst.c I see this: tst.c: In function 'f': tst.c:21:17: warning: array subscript -1 is outside array bounds of 'double[1]' [-Warray-bounds] 21 | const ab_t* ab = (ab_t*)(pb - 1); | ^~ tst.c:16:13: note: while referencing 'b' 16 | double b = 4.; | ^ I believe this is false. Inside g(), ab->a is indeed out-of-bounds, but ab->b is not. And I only use ab->b. Taking away -fPIC or -O3 makes the warning go away. Making g() static makes it go away also. I'm using gcc-10 from Debian. Package version 10.1.0-5. Thanks!
[Bug c/97261] gcc-10 produces invalid -Warray-bounds warning
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97261 --- Comment #1 from Dima Kogan --- Created attachment 49294 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49294&action=edit Code to demo the issue
[Bug c/97261] gcc-10 produces invalid -Warray-bounds warning
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97261 --- Comment #3 from Dima Kogan --- Hi. Thanks for replying. I don't the warning that I'm claiming is bogus is complaining about the points you raised. If it did, then making g() static or building without -fPIC or -O3 wouldn't make the warning go away. I have some questions about your analysis, if that's ok. g() doesn't know where its ab argument came from, so how can the strict aliasing rules be violated? The only reason the compiler knows anything at all here is that with -O3 it's tracing the flow. With -O0, there's no warning. And g() may as well be in an entirely different compilation unit, in which case it'd compile that unit with no complaint at any optimization level. Similarly, for the undefined behavior. If I have a function that takes some double* x, then is it undefined behavior to refer to x[-1]? If not, then how is this different? Thanks.
[Bug c/114509] New: Infinite loop with openmp
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114509 Bug ID: 114509 Summary: Infinite loop with openmp Product: gcc Version: 13.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: gccbugs at dima dot secretsauce.net Target Milestone: --- Created attachment 57827 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57827&action=edit Reduced reproducer I git a bug in gcc 13.2 where an openmp loop causes he compiler to spin the cpu, and never finish. I used creduce to minimize the test case, and the reduced source is attached. I'm running Debian GNU/Linux with gcc=4:13.2.0-1. I get an infinite loop with gcc-13 -fopenmp -c -o /dev/null /tmp/infinite-openmp.c I happen to also have gcc-10 and gcc-11 installed, and they both produce an infinite loop with that input as well. Thanks
[Bug c/115379] New: -Wformat warning reports the wrong floating-point type
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115379
Bug ID: 115379
Summary: -Wformat warning reports the wrong floating-point type
Product: gcc
Version: 14.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: gccbugs at dima dot secretsauce.net
Target Milestone: ---
Hi. I have this program:
#include
void tst(void)
{
float x;
scanf("%f", x);
}
I compile and I see this:
$ gcc-14 -Wall -Wextra -c -o tst2 tst2.c
tst2.c: In function 'tst':
tst2.c:5:13: warning: format '%f' expects argument of type 'float *', but
argument 2 has type 'double' [-Wformat=]
5 | scanf("%f", x);
|~^ ~
| | |
| | double
| float *
...
Note that argument 2 has type "float", but the warning message says that it has
type "double". This is confusing. The actual bug is that it should be a
pointer, but it isn't.
This is gcc 14.1 from Debian version 14.1.0-1
Thanks
[Bug debug/78100] DWARF symbols for an array sometimes missing the array length
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78100 --- Comment #4 from Dima Kogan --- I just tried again, and I see that this bug has been fixed. I'm using gcc (Debian 13.2.0-2) 13.2.0 Should we close this report?
