[LLVMbugs] [Bug 16058] New: incorrect loop optimization at -O3

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16058

            Bug ID: 16058
           Summary: incorrect loop optimization at -O3
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: dhazeghi at yahoo.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The following testcase is miscompiled by clang trunk at -O3 optimization level
on x86_64-linux-gnu, producing an executable that hangs.  This occurs in both
32-bit and 64-bit mode.

$ clang-trunk -v
clang version 3.4 (trunk 182084)
Target: x86_64-pc-linux-gnu
Thread model: posix
$ clang-trunk -O2 hang.c 
$ ./a.out 
$ clang-trunk -O3 hang.c 
$ ./a.out 
<hangs>

--------------------------------

int a, b, c, *p = &a;

static void
foo(int *l)
{
    for (b = -28; b < 4; b++)
    {
        *l = 1;
        for (c = 0; c; --c)
            *l = 0;
    }
label:
    for (b = 0; b >= 0; --b)
    {
        if (*p)
            continue;
        goto label;
    }
    return;
}

int
main()
{
    int *q = &a;
    foo(q);
    return 0;
}

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