[LLVMbugs] [Bug 19958] New: wrong code at -O1 and above on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19958

            Bug ID: 19958
           Summary: wrong code at -O1 and above on x86_64-linux-gnu
           Product: clang
           Version: unspecified
          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 current clang trunk miscompiles the following code at -O1 and above on
x86_64-linux-gnu (in both 32-bit and 64-bit modes). 

This is a regression from 3.4. 

$ clang-trunk -v
clang version 3.5.0 (trunk 210239)
Target: x86_64-unknown-linux-gnu
Thread model: posix
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 multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
$ 
$ clang-3.4 -O1 small.c; a.out; echo $?
0
$ clang-trunk -O0 small.c; a.out; echo $?
0
$     
$ clang-trunk -O1 small.c; a.out; echo $?
1
$ 


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


int a, c, d;
unsigned int b;
char e;

int
main ()
{
  for (; c < 1; c++)
    {
      for (b = 0; b < 2; b++)
    a = (d != 0); 
      e = a - 8;
      if ((unsigned int) e >= b)
    break;
    }

  return c; 
}

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