Genmatch: Refine the gen_phi_on_cond by match_cond_with_binary_phi

Genmatch: Refine the gen_phi_on_cond by match_cond_with_binary_phi

This patch would like to leverage the match_cond_with_binary_phi to
match the phi on cond, and get the true/false arg if matched.  This
helps a lot to simplify the implementation of gen_phi_on_cond.

Before this patch:
basic_block _b1 = gimple_bb (_a1);
if (gimple_phi_num_args (_a1) == 2)
  {
    basic_block _pb_0_1 = EDGE_PRED (_b1, 0)->src;
    basic_block _pb_1_1 = EDGE_PRED (_b1, 1)->src;
    basic_block _db_1 = safe_dyn_cast <gcond *> (*gsi_last_bb (_pb_0_1)) ? _pb_0_1 : _pb_1_1;
    basic_block _other_db_1 = safe_dyn_cast <gcond *> (*gsi_last_bb (_pb_0_1)) ? _pb_1_1 : _pb_0_1;
    gcond *_ct_1 = safe_dyn_cast <gcond *> (*gsi_last_bb (_db_1));
    if (_ct_1 && EDGE_COUNT (_other_db_1->preds) == 1
        && EDGE_COUNT (_other_db_1->succs) == 1
        && EDGE_PRED (_other_db_1, 0)->src == _db_1)
        {
          tree _cond_lhs_1 = gimple_cond_lhs (_ct_1);
          tree _cond_rhs_1 = gimple_cond_rhs (_ct_1);
          tree _p0 = build2 (gimple_cond_code (_ct_1), boolean_type_node, _cond_lhs_1, _cond_rhs_1);
          bool _arg_0_is_true_1 = gimple_phi_arg_edge (_a1, 0)->flags & EDGE_TRUE_VALUE;
          tree _p1 = gimple_phi_arg_def (_a1, _arg_0_is_true_1 ? 0 : 1);
          tree _p2 = gimple_phi_arg_def (_a1, _arg_0_is_true_1 ? 1 : 0);
...

After this patch:
basic_block _b1 = gimple_bb (_a1);
tree _p1, _p2;
gcond *_cond_1 = match_cond_with_binary_phi (_a1, &_p1, &_p2);
if (_cond_1)
  {
    tree _cond_lhs_1 = gimple_cond_lhs (_cond_1);
    tree _cond_rhs_1 = gimple_cond_rhs (_cond_1);
    tree _p0 = build2 (gimple_cond_code (_cond_1), boolean_type_node, _cond_lhs_1, _cond_rhs_1);
...

The below test suites are passed for this patch.
* The rv64gcv fully regression test.
* The x86 bootstrap test.
* The x86 fully regression test.

gcc/ChangeLog:

	* genmatch.cc (dt_operand::gen_phi_on_cond): Leverage the
	match_cond_with_binary_phi API to get cond gimple, true and
	false TREE arg.

Signed-off-by: Pan Li <pan2.li@intel.com>