[Bug tree-optimization/67781] Wrong code generated on mips32 with -O1 -fexpensive-optimizations

[sje at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67781

Steve Ellcey <sje at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-12-08
                 CC|                            |sje at gcc dot gnu.org
          Component|rtl-optimization            |tree-optimization
     Ever confirmed|0                           |1

--- Comment #2 from Steve Ellcey <sje at gcc dot gnu.org> ---
It looks like this is going wrong in the bswap pass (tree-ssa-math-opts.c) that
is only done with expensive optimizations.  It also looks like it only affects
big-endian targets, but I think it affects all big-endian targets.

If I compile the test program with -O1 -fdump-tree-all
-fexpensive-optimizations

I get this code before the bswap pass:

main ()
{
  uint32_t c;
  unsigned int _2;
  unsigned int _3;
  unsigned char _4;
  unsigned int _5;

  <bb 2>:
  _2 = s.a;
  _3 = _2 << 8;
  _4 = s.b;
  _5 = (unsigned int) _4;
  c_6 = _3 | _5;
  printf ("%x\n", c_6);
  return 0;

}

And this code after the bswap pass:

main ()
{
  uint32_t c;
  unsigned int _2;
  unsigned int _3;
  unsigned char _4;
  unsigned int _5;
  uint32_t * load_src_8;

  <bb 2>:
  load_src_8 = &s.a;
  c_6 = MEM[(void *)load_src_8];
  _2 = s.a;
  _3 = _2 << 8;
  _4 = s.b;
  _5 = (unsigned int) _4;
  printf ("%x\n", c_6);
  return 0;

}