[LLVMbugs] [Bug 18886] New: wrong code (hangs) at -O1 and above on x86_64-linux-gnu (in both 32-bit and 64-bit modes)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18886

            Bug ID: 18886
           Summary: wrong code (hangs) at -O1 and above on
                    x86_64-linux-gnu (in both 32-bit and 64-bit modes)
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: su at cs.ucdavis.edu
                CC: llvmbugs at cs.uiuc.edu
    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 3.4. 


$ clang-trunk -v
clang version 3.5 (trunk 201573)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.8.1
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.6
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/4.8.1
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Candidate multiilb: .;@m64
Candidate multiilb: 32;@m32
Selected multilib: .;@m64
$ 
$ clang-trunk -O0 small.c; a.out
$ clang-3.4 -O1 small.c; a.out
$ 
$ clang-trunk -O1 small.c
$ a.out
^C
$ 


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


long long a;

void __assert_fail () __attribute__ ((__noreturn__));

int
main ()
{
  for (a = -21; a < 9; a += 8) 
    if (!a)
      __assert_fail ();
  return 0;
}

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