https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115326
Bug ID: 115326
Summary: __builtin_sub_overflow reports incorrect overflow
value
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: cody at tapscott dot me
Target Milestone: ---
Created attachment 58334
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58334&action=edit
reduced test case
The `__builtin_sub_overflow` intrinsic appears to report an incorrect overflow
value, in a specific case when it is used with pointers to the field of a
union.
I would expect the two evaluations in the attached test program to be
identical, but instead on my machine the abort() is triggered:
$ gcc test2.c -O0 -fno-strict-aliasing
$ ./a.out
[1] 1099972 IOT instruction ./a.out
$ gcc -v:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/opt/gcc-latest/libexec/gcc/x86_64-pc-linux-gnu/13.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/opt/gcc-latest --enable-languages=c,c++
--enable-libstdcxx-debug --enable-libstdcxx-backtrace --disable-bootstrap
--disable-multilib --disable-libvtv --with-system-zlib --without-isl
--enable-multiarch
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.0.1 20230416 (experimental) (GCC)
