[LLVMbugs] [Bug 12901] New: likely wrong code bug

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12901

             Bug #: 12901
           Summary: likely wrong code bug
           Product: new-bugs
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: regehr at cs.utah.edu
                CC: chenyang at cs.utah.edu, llvmbugs at cs.uiuc.edu
    Classification: Unclassified


No idea what's going on here but I think the code is legit and that LLVM should
not be changing its answer.

[regehr at dyson r55]$ clang -O0 small.c ; ./a.out
1
[regehr at dyson r55]$ clang -O1 small.c ; ./a.out
0
[regehr at dyson r55]$ current-gcc -O3 small.c ; ./a.out 
1
[regehr at dyson r55]$ cat small.c
int printf (const char *, ...);
int a, b = 1, c, e, f, h, i, j;
int *d = &c, *g = &c;

void fn1 (int *p1)
{
    *p1 = *d;
}

void fn2 (int *p1)
{
    f = *p1;
    *g = f;
}

int main ()
{
    int *k = &b, *l = &b;
    h = 1;
    for (; h; h--)
        for (; j <= 0; j++)
        {
            int **m = &l;
            for (; i <= 0; i++)
                *l = 0;
            *k ^= 1;
            *m = 0;
        }
    e = b;
    fn2 (&e);
    fn1 (&a);
    printf ("%d\n", a);
    return 0;
}
[regehr at dyson r55]$ clang -v
clang version 3.2 (trunk 157145)
Target: x86_64-unknown-linux-gnu
Thread model: posix

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