[LLVMbugs] [Bug 22173] New: wrong code at -Os and above on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=22173

            Bug ID: 22173
           Summary: wrong code at -Os and above on x86_64-linux-gnu
           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 current clang trunk miscompiles the following code at -Os and above on
x86_64-linux-gnu in both 32-bit and 64-bit modes.

This is a regression from 3.5.0.  


$ clang-trunk -v
clang version 3.6.0 (trunk 225511)
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-trunk -O1 small.c; a.out
$ clang-3.5.0 -Os small.c; a.out
$ 
$ clang-trunk -Os small.c
$ a.out
Aborted (core dumped)
$ 


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


int a, b = 1;
char c;

void
fn1 ()
{
  c = a - b;
  if (c)
    b = 0;
}

int
main ()
{
  for (a = 0; a < 1; a++)
    fn1 ();

  if (b != 0) 
    __builtin_abort (); 

  return 0;
}

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