[llvm-bugs] [Bug 33246] New: wrong code at -O0 only in 32-bit mode on x86_64-linux-gnu

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=33246

            Bug ID: 33246
           Summary: wrong code at -O0 only in 32-bit mode on
                    x86_64-linux-gnu
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: chengniansun at gmail.com
                CC: llvm-bugs at lists.llvm.org

$ clang-trunk -v
clang version 5.0.0 (trunk 304216)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/i686-linux-gnu/5
Found candidate GCC installation: /usr/bin/../lib/gcc/i686-linux-gnu/5.3.0
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8.5
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.9.3
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.3.0
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$ clang-trunk -m32 -O0 small.c ; ./a.out
0
0
0
0
0
0
0
5
$ clang-trunk -m32 -O1 small.c ; ./a.out
0
0
0
0
0
0
0
0
$ cat small.c
int printf(const char *, ...);
int a[6];
int crc32_context, crc32_gentab_i, j, i, k;
char ga[8][30];
int main() {
  for (; crc32_gentab_i < 6; crc32_gentab_i++)
    a[0] = crc32_gentab_i;
  for (; i < 8; i++) {
    j = 0;
    for (; j < 5; j++) {
      k = 0;
      for (; k < 6; k++) {
        long long val = ga[i][j * 5];
        crc32_context = a[crc32_context ^ val];
      }
    }
    printf("%X\n", crc32_context);
  }
  return 0;
}
$

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