[Bug tree-optimization/70600] New: Missed tree optimization with multiple additions in different types.

["bernds at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70600

            Bug ID: 70600
           Summary: Missed tree optimization with multiple additions in
                    different types.
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bernds at gcc dot gnu.org
  Target Milestone: ---
            Target: x86_64-pc-linux-gnu

The following is a testcase reduced from a Linux kernel file. Compile with -O2
on x86_64-linux.

There are two additions, the first in type unsigned long, the second one after
casting the first result to unsigned int. Together, they end up as a no-op, but
this is not caught during tree optimization. The combiner finally manages to
eliminate them, with the help of a note added by fwprop.

(I was looking at whether we could eliminate the creation of REG_EQUAL notes
from fwprop, and found only three cases out of a set of 4492 source files where
they changed code generation; this was one of them.)

int p (long mem_map, long page, unsigned int *p, unsigned int *frag)
{

  unsigned int _83 = *p;
  long _142 = page - mem_map;
  long _143 = _142 / 56;
  unsigned long _144 = _143;
  unsigned long _145 = _144 << 12;
  unsigned long _146 = _145 + 0xc0000000;
  unsigned int _147 = _146;
  unsigned int _190 = _83 + 0x40000000;
  unsigned int _149 = _147 + _190;
  return _149;
}