[Bug tree-optimization/78305] New: Wrong constant folding

["ishiura-compiler at ml dot kwansei.ac.jp" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78305

            Bug ID: 78305
           Summary: Wrong constant folding
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ishiura-compiler at ml dot kwansei.ac.jp
  Target Milestone: ---

GCC 7.0.0 for x86_64 miscompiles the following code.


% cat test.c
int main (void)
{
        int a = 2;
        int b = 1;

        int t = -1 * ( -0x40000000 * a / ( -0x20000000 + b ) )  / -1;

        if (t != 4) __builtin_abort();

        return 0;
}
% gcc-7.0 test.c
% ./a.out
zsh: abort (core dumped)  ./a.out
% gcc-7.0 -v
Using built-in specs.
COLLECT_GCC=gcc-7.0
COLLECT_LTO_WRAPPER=/home/cappie/opt/gcc-7.0.0/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/home/cappie/opt/gcc-7.0.0 --disable-nls
--disable-multilib --program-suffix=-7.0 --enable-languages=c
Thread model: posix
gcc version 7.0.0 20161108 (experimental) (GCC)