Re: [patch] Optimize statements created by if-conversion

[Ira Rosen <IRAR at il dot ibm dot com>]

Richard Guenther <richard.guenther@gmail.com> wrote on 29/06/2010 12:46:52
PM:

> On Tue, Jun 29, 2010 at 10:03 AM, Ira Rosen <IRAR@il.ibm.com> wrote:
> >
> > Hi,
> >
> > For the following minloc loop (which I am trying to vectorize):
> >
> > ?for (i = 0; i < N; i++)
> > ? ?if (arr[i] < limit)
> > ? ? ?{
> > ? ? ? ?pos = i + 1;
> > ? ? ? ?limit = arr[i];
> > ? ? ?}
> >
> > if-conversion generates
> >
> > ?# pos_22 = PHI <pos_1(8), 1(3)>
> > ?# i_23 = PHI <prephitmp.8_2(8), 0(3)>
> > ?# limit_24 = PHI <limit_4(8), 1.28e+2(3)>
> > ?limit_10 = arr[i_23];
> > ?pos_11 = i_23 + 1;
> > ?pretmp.7_3 = i_23 + 1;
> > ?pos_1 = [cond_expr] limit_10 >= limit_24 ? pos_22 : pos_11;
> > ?limit_4 = [cond_expr] limit_10 >= limit_24 ? limit_24 : limit_10;
> > ?prephitmp.8_2 = [cond_expr] limit_10 >= limit_24 ? pretmp.7_3 :
pos_11;
> > ?if (prephitmp.8_2 < n_9(D))
> > ? ?goto <bb 8>;
> > ?else
> > ? ?goto <bb 9>;
> >
> >
> > For
> >
> > prephitmp.8_2 = [cond_expr] limit_10 >= limit_24 ? pretmp.7_3 : pos_11;
> >
> > then and else clauses are equivalent, so
> >
> > prephitmp.8_2 = pretmp.7_3;
> >
> > should be enough.
> >
> >
> > Does the following patch make sense? (Meanwhile, I only tested it with
> > vectorizer testsuite).
>
> Can you provide a complete testcase?  PRE should have recognized
> the equivalecy already.

(See attached file: test.c)

Thanks,
Ira

>
> Richard.
>
> > Thanks,
> > Ira
> >
> > ChangeLog:
> >
> > ? ? ?* tree-if-conv.c (replace_phi_with_cond_gimple_assign_stmt):
> > ? ? ?If then and else clauses are equivalent, use one of them as a
> > ? ? ?rhs.
> >
> > Index: tree-if-conv.c
> > ===================================================================
> > --- tree-if-conv.c ? ? ?(revision 161484)
> > +++ tree-if-conv.c ? ? ?(working copy)
> > @@ -925,6 +925,8 @@ replace_phi_with_cond_gimple_assign_stmt
> > ? basic_block bb;
> > ? tree rhs;
> > ? tree arg;
> > + ?gimple def_stmt0, def_stmt1;
> > + ?enum tree_code code;
> >
> > ? gcc_assert (gimple_code (phi) == GIMPLE_PHI
> > ? ? ? ? ? ? ?&& gimple_phi_num_args (phi) == 2);
> > @@ -949,9 +951,35 @@ replace_phi_with_cond_gimple_assign_stmt
> > ? ? ? ? ?arg_1 = gimple_phi_arg_def (phi, 1);
> > ? ? ? ?}
> >
> > - ? ? ?/* Build new RHS using selected condition and arguments. ?*/
> > - ? ? ?rhs = build3 (COND_EXPR, TREE_TYPE (PHI_RESULT (phi)),
> > - ? ? ? ? ? ? ? ? ? unshare_expr (cond), arg_0, arg_1);
> > + ? ? ?if (TREE_CODE (arg_0) == SSA_NAME && TREE_CODE (arg_1) ==
SSA_NAME
> > + ? ? ? ? ?&& (def_stmt0 = SSA_NAME_DEF_STMT (arg_0))
> > + ? ? ? ? ?&& (def_stmt1 = SSA_NAME_DEF_STMT (arg_1))
> > + ? ? ? ? ?&& is_gimple_assign (def_stmt0)
> > + ? ? ? ? ?&& is_gimple_assign (def_stmt1)
> > + ? ? ? ? ?&& (code = gimple_assign_rhs_code (def_stmt0))
> > + ? ? ? ? ? ? == gimple_assign_rhs_code (def_stmt1)
> > + ? ? ? ? ?&& ((get_gimple_rhs_class (code) == GIMPLE_UNARY_RHS
> > + ? ? ? ? ? ? ? && operand_equal_p (gimple_assign_rhs1 (def_stmt0),
> > + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? gimple_assign_rhs1 (def_stmt1), 0))
> > + ? ? ? ? ? ? ?|| (get_gimple_rhs_class (code) == GIMPLE_BINARY_RHS
> > + ? ? ? ? ? ? ? ? ?&& operand_equal_p (gimple_assign_rhs1 (def_stmt0),
> > + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?gimple_assign_rhs1 (def_stmt1),
0)
> > + ? ? ? ? ? ? ? ? ?&& operand_equal_p (gimple_assign_rhs2 (def_stmt0),
> > + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?gimple_assign_rhs2 (def_stmt1),
0))
> > + ? ? ? ? ? ? ?|| (get_gimple_rhs_class (code) == GIMPLE_TERNARY_RHS
> > + ? ? ? ? ? ? ? ? ?&& operand_equal_p (gimple_assign_rhs1 (def_stmt0),
> > + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?gimple_assign_rhs1 (def_stmt1),
0)
> > + ? ? ? ? ? ? ? ? ?&& operand_equal_p (gimple_assign_rhs2 (def_stmt0),
> > + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?gimple_assign_rhs2 (def_stmt1),
0)
> > + ? ? ? ? ? ? ? ? ?&& operand_equal_p (gimple_assign_rhs3 (def_stmt0),
> > + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?gimple_assign_rhs3 (def_stmt1),
> > 0))))
> > + ? ? ? ?/* Since then and else parts are equivalent, make RHS to be
one of
> > + ? ? ? ? ? them. ?*/
> > + ? ? ? ?rhs = arg_0;
> > + ? ? ?else
> > + ? ? ? ?/* Build new RHS using selected condition and arguments. ?*/
> > + ? ? ? ?rhs = build3 (COND_EXPR, TREE_TYPE (PHI_RESULT (phi)),
> > + ? ? ? ? ? ? ? ? ? ? unshare_expr (cond), arg_0, arg_1);
> > ? ? }
> >
> > ? new_stmt = gimple_build_assign (PHI_RESULT (phi), rhs);
> >
> >

Attachment: test.c
Description: Binary data