[Bug tree-optimization/71438] New: wrong code at -O3 on x86_64-linux-gnu (by tree vectorizer)

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71438

            Bug ID: 71438
           Summary: wrong code at -O3 on x86_64-linux-gnu (by tree
                    vectorizer)
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

The current gcc trunk miscompiles the following testcase on x86_64-linux at -O3
in both 32-bit and 64-bit modes.  

This appears to be a tree vectorizer bug as it goes away with
-fno-tree-vectorize. 

This is a regression from 6.1.x.  


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/usr/local/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 7.0.0 20160606 (experimental) [trunk revision 237117] (GCC) 
$ 
$ gcc-trunk -O2 small.c; ./a.out
$ gcc-6.1 -O3 small.c; ./a.out
$ 
$ gcc-trunk -O3 small.c; ./a.out
Aborted (core dumped)
$          
$ gcc-trunk -O3 -fno-tree-vectorize small.c; ./a.out
$ 


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


int a, b, c, d;

int
main ()
{
  int e = d = 3;
  for (; d >= 0; d--)
    {
      c = e;
      e = a ^ (a && b) && 1;
    }

  if (c != 0) 
    __builtin_abort (); 

  return 0; 
}