[Bug tree-optimization/103237] New: wrong code with -ftree-vectorize at -O1 on x86_64-linux-gnu

[haoxintu at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103237

            Bug ID: 103237
           Summary: wrong code with -ftree-vectorize at -O1 on
                    x86_64-linux-gnu
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: haoxintu at gmail dot com
  Target Milestone: ---

Hi all.

This seems a long latent bug existed after GCC-10.1.

$cat small.c
#include <stdint.h>
#include <stdio.h>
struct S0 {
  uint16_t a;
};
union U1 {
  struct S0 b;
};
int32_t g1[1] = {0};
uint32_t g2[][10][1] = {
    {}, {}, {}, {}, {}, {}, {{}, {}, {}, {}, {}, {}, {4294967295UL}}};
union U1 g3;
static int32_t func_1() {
  int32_t *l_1 = &g1[0];
  uint32_t l_2 ;
  for (g3.b.a = (27); (g3.b.a != 45);
       g3.b.a = g3.b.a + 9) {
    for (l_2 = 0; (l_2 <= 3); l_2 += 1) {
      uint32_t *l_3 = &g2[6][6][0];
      *l_1 = *l_3 ^= ((0 == 0) << 0);
    }
  }
  return 0;
}
int main() {
  func_1();
  for (int i = 0; i < 1; i++)
    printf("%d\n", g1[i]);
  return 0;
}


$gcc -O2 -ftree-vectorize small.c ; ./a.out
-1

$gcc -O1 -ftree-vectorize small.c ; ./a.out
0

$gcc -O1 small.c ; ./a.out
-1

$gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/home/haoxin/haoxin-data/compilers/gcc/build/libexec/gcc/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with:../configure
--prefix=/home/haoxin/haoxin-data/compilers/gcc/build/ --enable-bootstrap
--enable-checking=release --enable-multilib --enable-languages=c,c++,lto
--no-create --no-recursion
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20211114 (experimental) (GCC) 

Can also check here: https://godbolt.org/z/ncar1aWYM

Thanks,
Haoxin