[Bug c/102661] New: signed integer overflow not detected in comparison since gcc-8

[lrspam at sfr dot fr via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102661

            Bug ID: 102661
           Summary: signed integer overflow not detected in comparison
                    since gcc-8
           Product: gcc
           Version: 9.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lrspam at sfr dot fr
  Target Milestone: ---

$ uname -srmpio
Linux 5.4.0-88-generic x86_64 x86_64 x86_64 GNU/Linux

$ cat ioverflow.c
#include <stdio.h>
#include <limits.h>

int
main (void)
{
  int ia, ib, one;
  one = 1;
  ia = INT_MAX;
  ib = ia;
  printf ("%i %i %i\n", ia, ia + one, ia < ia + one);
  ia += one;
  printf ("%i %i %i\n", ib, ia, ib < ia);
}

$ gcc-8 -v
Using built-in specs.
COLLECT_GCC=gcc-8
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 8.4.0-3ubuntu2'
--with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-8
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib=auto --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 8.4.0 (Ubuntu 8.4.0-3ubuntu2) 

RESULT observed:
$ gcc-8 ioverflow.c -o ioverflow
$ ./ioverflow
2147483647 -2147483648 1
2147483647 -2147483648 0

RESULT expected (as for gcc-7):
$ gcc-7 ioverflow.c -o ioverflow
$ ./ioverflow
2147483647 -2147483648 0
2147483647 -2147483648 0