[llvm-bugs] [Bug 25831] New: wrong code at -O1 and above

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=25831

            Bug ID: 25831
           Summary: wrong code at -O1 and above
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: chengniansun at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

The following code is miscompiled by the current clang trunk at -O1 and above
in both 32-bit and 64-bit modes on x86_64-linux-gnu.

This is a regression from 3.7. 

$: clang-trunk -v
clang version 3.8.0 (trunk 255518)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.2.1
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.4
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/5.2.1
Found candidate GCC installation:
/usr/local/bin/../lib/gcc/x86_64-unknown-linux-gnu/4.6.3
Found candidate GCC installation:
/usr/local/bin/../lib/gcc/x86_64-unknown-linux-gnu/4.7.4
Found candidate GCC installation:
/usr/local/bin/../lib/gcc/x86_64-unknown-linux-gnu/4.8.2
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$: 
$: clang-trunk -O1 -w small.c ; ./a.out
l_282=0
g_9=6
-1
$: clang-trunk -O2 -w small.c ; ./a.out
l_282=0
g_9=6
-1
$: clang-trunk -O3 -w small.c ; ./a.out
l_282=0
g_9=6
-1
$: clang-trunk -O0 -w small.c ; ./a.out
l_282=0
g_9=6
0
$: clang-3.7 -O3 -w small.c ; ./a.out
l_282=0
g_9=6
0
$: 
$: cat small.c
static short a = 7;
int b = 1, c, d, e, f;
void fn1(short *p1) {
  b = 4 % a & a / b;
  d = f && 1 / d;
  a = f | a ^ 1;
  if (a || a)
    printf("l_282=%lld\n", (long long)f);
  printf("g_9=%lld\n", (long long)a);
  d = a;
  *p1 = e;
  if (a && f < 4)
    c--;
}

int main() {
  fn1(&a);
  printf("%d\n", c);
  return 0;
}
$:

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