[Bug tree-optimization/19643] New: "0 % variable" isn't optimized to 0

[kazu at cs dot umass dot edu]

Consider the following testcase, reduced from cfgexpand.c:

int
foo (int align)
{
  int off = 0 % align;
  return off ? align - off : 0;
}

tree-level:

foo (align)
{
  int off;
  int D.1120;

<bb 0>:
  off = 0 % align;
  if (off != 0) goto <L0>; else goto <L5>;

<L5>:;
  D.1120 = 0;
  goto <bb 3> (<L2>);

<L0>:;
  D.1120 = align - off;

<L2>:;
  return D.1120;

}

RTL on i686-pc-linux-gnu after running the combiner

(insn 34 31 40 0 (set (reg/i:SI 0 ax [ <result> ])
        (const_int 0 [0x0])) 35 {*movsi_1} (nil)
    (nil))

(insn 40 34 0 0 (use (reg/i:SI 0 ax [ <result> ])) -1 (insn_list:REG_DEP_TRUE 34
(nil))
    (nil))

Notice that "0 % variable" is optimized to 0.

The simplification is performed in CSE.

-- 
           Summary: "0 % variable" isn't optimized to 0
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: missed-optimization, TREE
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at cs dot umass dot edu
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19643