[Bug tree-optimization/83569] New: Wrong constant folding

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83569

            Bug ID: 83569
           Summary: Wrong constant folding
           Product: gcc
           Version: 8.0
            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 8.0 for x86_64 miscompiles the following code.

% cat test.c
int a[2] =  {0,1};
int x =  129;
int main (void)
{
  volatile int v = 0;
  int t = x;
  for (int i = 0; i < (1+v+v+v+v+v+v+v+v+a[a[0]]); i++) {
    t = a[(signed char)(130-x)];
  }
  if (t != 1) __builtin_abort();
  return 0;
}

% gcc-8.0.0 test.c
% ./a.out

% gcc-8.0.0 test.c -O3
% ./a.out
zsh: abort (core dumped)  ./a.out

% gcc-8.0.0 -v
Using built-in specs.
COLLECT_GCC=gcc-8.0.0
COLLECT_LTO_WRAPPER=/home/cappie/opt/gcc-8.0.0/libexec/gcc/x86_64-pc-linux-gnu/8.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/home/cappie/opt/gcc-8.0.0 --disable-nls
--disable-multilib --program-suffix=-8.0.0 --enable-languages=c
Thread model: posix
gcc version 8.0.0 20171215 (experimental) (GCC)

--- Comment #1 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
*** Bug 83579 has been marked as a duplicate of this bug. ***