public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
* [Bug c/111730] New: erroneous alloc-size-larger-than warning with -O1 @ 2023-10-09 1:12 xavier.cooney03 at gmail dot com 2023-10-09 1:36 ` [Bug c/111730] " pinskia at gcc dot gnu.org ` (3 more replies) 0 siblings, 4 replies; 5+ messages in thread From: xavier.cooney03 at gmail dot com @ 2023-10-09 1:12 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111730 Bug ID: 111730 Summary: erroneous alloc-size-larger-than warning with -O1 Product: gcc Version: 13.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: xavier.cooney03 at gmail dot com Target Milestone: --- Created attachment 56076 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56076&action=edit bug.c Hi, in some circumstances gcc incorrectly emits the alloc-size-larger-than warning: $ gcc -O1 -Wall -c bug.c bug.c: In function ‘foo’: bug.c:9:15: warning: argument 1 range [18446744071562067968, 18446744073709551615] exceeds maximum object size 9223372036854775807 [-Walloc-size-larger-than=] 9 | char *a = malloc(x); | ^~~~~~~~~ bug.c:4:14: note: in a call to allocation function ‘malloc’ declared here 4 | extern void *malloc (size_t size) __attribute__ ((__malloc__)); | ^~~~~~ This only seems to occur when using -O1, other optimisation levels (-O0, -O2, -O3, -Os) don't result in the warning. The 'useless' loops are necessary to reproduce, removing the first or last loop causes the warning to disappear. 18446744071562067968 = 0xffffffff80000000 18446744073709551615 = 0xffffffffffffffff It seems as if gcc is incorrectly deducing that `x` must be negative. $ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/13.2.1/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /build/gcc/src/gcc/configure --enable-languages=ada,c,c++,d,fortran,go,lto,objc,obj-c++ --enable-bootstrap --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --with-build-config=bootstrap-lto --with-linker-hash-style=gnu --with-system-zlib --enable-__cxa_atexit --enable-cet=auto --enable-checking=release --enable-clocale=gnu --enable-default-pie --enable-default-ssp --enable-gnu-indirect-function --enable-gnu-unique-object --enable-libstdcxx-backtrace --enable-link-serialization=1 --enable-linker-build-id --enable-lto --enable-multilib --enable-plugin --enable-shared --enable-threads=posix --disable-libssp --disable-libstdcxx-pch --disable-werror Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 13.2.1 20230801 (GCC) ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/111730] erroneous alloc-size-larger-than warning with -O1 2023-10-09 1:12 [Bug c/111730] New: erroneous alloc-size-larger-than warning with -O1 xavier.cooney03 at gmail dot com @ 2023-10-09 1:36 ` pinskia at gcc dot gnu.org 2023-10-09 2:08 ` [Bug tree-optimization/111730] " pinskia at gcc dot gnu.org ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-10-09 1:36 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111730 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- You might want to add a check that x is not negative and I suspect that will fix the warning. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/111730] erroneous alloc-size-larger-than warning with -O1 2023-10-09 1:12 [Bug c/111730] New: erroneous alloc-size-larger-than warning with -O1 xavier.cooney03 at gmail dot com 2023-10-09 1:36 ` [Bug c/111730] " pinskia at gcc dot gnu.org @ 2023-10-09 2:08 ` pinskia at gcc dot gnu.org 2023-10-09 2:15 ` pinskia at gcc dot gnu.org 2023-10-09 2:38 ` xavier.cooney03 at gmail dot com 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-10-09 2:08 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111730 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- The difference between -O1 and -O2 is -O2 removes the empty loops. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/111730] erroneous alloc-size-larger-than warning with -O1 2023-10-09 1:12 [Bug c/111730] New: erroneous alloc-size-larger-than warning with -O1 xavier.cooney03 at gmail dot com 2023-10-09 1:36 ` [Bug c/111730] " pinskia at gcc dot gnu.org 2023-10-09 2:08 ` [Bug tree-optimization/111730] " pinskia at gcc dot gnu.org @ 2023-10-09 2:15 ` pinskia at gcc dot gnu.org 2023-10-09 2:38 ` xavier.cooney03 at gmail dot com 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-10-09 2:15 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111730 --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Note you can reproduce the same warning with ( -O2 -fno-code-hoisting -fno-tree-loop-im -fno-tree-pre): ``` // #include <stdlib.h> typedef long unsigned int size_t; extern void *malloc (size_t size) __attribute__ ((__malloc__)); int *t; void foo(int x) { // if (x < 1) return; for (int i = 0; i < x; i++) {*t = i;} char *a = malloc(x); for (int i = 0; i < x; i++) a[i] = 0; while (a[x - 1]) {*t++;} } ``` I still think you should add a check for x being negative to fix the code/warning. Unless you have a unreduced testcase which has the test before and still able to produce the warning, this will most likely be closed as invalid. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/111730] erroneous alloc-size-larger-than warning with -O1 2023-10-09 1:12 [Bug c/111730] New: erroneous alloc-size-larger-than warning with -O1 xavier.cooney03 at gmail dot com ` (2 preceding siblings ...) 2023-10-09 2:15 ` pinskia at gcc dot gnu.org @ 2023-10-09 2:38 ` xavier.cooney03 at gmail dot com 3 siblings, 0 replies; 5+ messages in thread From: xavier.cooney03 at gmail dot com @ 2023-10-09 2:38 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111730 --- Comment #4 from Xavier Cooney <xavier.cooney03 at gmail dot com> --- I see, thanks for looking into this. The unreduced test case (which was from a student confused about the error message) was still passing a value to `malloc` which from the context which gcc could see wasn't /necessarily/ non-negative. But the code ``` void foo2(int x) { char *a = malloc(x); (void) a; } ``` doesn't trigger the warning, even though `x` could also be negative. I'm not sure why the extra loops are necessary for the warning to be emitted if the compiler is trying to warn about any time a potentially negative value might be passed to `malloc`. Also the error message reads to me as saying that argument 1 must be in the range [18446744071562067968, 18446744073709551615] (in which case it would be incorrect), rather than saying the argument could be in the range (in which case it would be correct). Thanks again for look into this :) ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2023-10-09 2:38 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2023-10-09 1:12 [Bug c/111730] New: erroneous alloc-size-larger-than warning with -O1 xavier.cooney03 at gmail dot com 2023-10-09 1:36 ` [Bug c/111730] " pinskia at gcc dot gnu.org 2023-10-09 2:08 ` [Bug tree-optimization/111730] " pinskia at gcc dot gnu.org 2023-10-09 2:15 ` pinskia at gcc dot gnu.org 2023-10-09 2:38 ` xavier.cooney03 at gmail dot com
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).