[LLVMbugs] [Bug 20079] New: clang hangs on valid code at -O1 and above on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20079

            Bug ID: 20079
           Summary: clang hangs on valid code at -O1 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 following testcase causes the current clang trunk to hang when compiling 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 3.5.0 (trunk 211159)
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 multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
$ 
$ time clang-trunk -O0 -c small.c
0.00user 0.00system 0:00.07elapsed 17%CPU (0avgtext+0avgdata 41840maxresident)k
0inputs+8outputs (0major+3835minor)pagefaults 0swaps
$ time clang-3.4 -O1 -c small.c
0.01user 0.00system 0:00.06elapsed 23%CPU (0avgtext+0avgdata 47680maxresident)k
0inputs+8outputs (0major+4053minor)pagefaults 0swaps
$ time clang-3.4 -O3 -c small.c
0.00user 0.01system 0:00.09elapsed 17%CPU (0avgtext+0avgdata 48192maxresident)k
0inputs+8outputs (0major+4085minor)pagefaults 0swaps
$ 
$ timeout -s 9 60 clang-trunk -O1 -c small.c
Killed
$ 


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


int a, b[1], c, *d, e, f, g, *h;

void
fn1 ()
{
  d = h = &b[0];
  f = -a;
  g = -1;
  e = (g ^ f) * (d == &c);
}

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