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From: "su at cs dot ucdavis.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/61434] New: wrong code at -O3 on x86_64-linux
Date: Fri, 06 Jun 2014 22:24:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61434

            Bug ID: 61434
           Summary: wrong code at -O3 on x86_64-linux
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

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

This is a regression from 4.9.x. The issue seems to be in the tree vectorizer
as the reported test does not fail with -fno-tree-vectorize. 

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/4.10.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 4.10.0 20140606 (experimental) [trunk revision 211299] (GCC) 
$ 
$ gcc-trunk -O2 small.c; a.out
$ gcc-trunk -fno-tree-vectorize -O3 small.c; a.out
$ gcc-4.9.0 -O3 small.c; a.out
$ 
$ gcc-trunk -O3 small.c  
$ a.out
Aborted (core dumped)
$ 


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


int a, b[2], c, d, e, f, g;

struct
{
  int f1:1;
  int f2:1;
} w;

void
fn1 (int p1, int p2)
{
  // does nothing 
}

int
main ()
{
  b[1] = 1;
  for (; f < 1; f++)
    {
      w.f2 = 0;
      if (w.f1)
        fn1 (e++, a++ && d++);
    }
  for (; g < 1; g++)
    c = b[a];

  if (c != 0) 
    __builtin_abort (); 

  return 0;
}