[Bug tree-optimization/54733] New: Missing opportunity to optimize endian independent load/store

["joey.ye at arm dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54733

             Bug #: 54733
           Summary: Missing opportunity to optimize endian independent
                    load/store
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: joey.ye@arm.com


This case tries to load from memory in little-endian way, no matter what
endianess current target is.

On trunk 4.8 little-endian target, two byte loads should be able to combined
into a single 16-byte load.

int read_aux(void *, int);

int read_le()
{ 
    unsigned char data[2]; 
    read_aux(data, 2); 
    return data[0] | (data[1]<<8);
}

Current Tree (optimized):
  unsigned char data[2];

  read_aux (&data, 2);
  D.4064_1 = data[0];
  D.4065_2 = (int) D.4064_1;
  D.4066_3 = data[1];
  D.4067_4 = (int) D.4066_3;
  D.4068_5 = D.4067_4 << 8;
  D.4063_6 = D.4068_5 | D.4065_2;
  data ={v} {CLOBBER};
  return D.4063_6;

Expected Tree (optimized):
  unsigned char data[2];
  unsigned short *temp;
  unsigned in D.4064;

  read_aux (&data, 2);
  temp=&data;
  D.4064_1 = *temp;
  return D.4064_1;