[PATCH] Improve match_simplify_replacement in phi-opt

Andrew Pinski pinskia@gmail.com
Wed Jun 2 07:16:06 GMT 2021


On Tue, Jun 1, 2021 at 11:46 PM Richard Biener via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Tue, Jun 1, 2021 at 9:07 PM apinski--- via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > From: Andrew Pinski <apinski@marvell.com>
> >
> > This improves match_simplify_replace in phi-opt to handle the
> > case where there is one cheap preparation statement in the
> > middle basic block similar to xor_replacement and others.
> > This allows to remove xor_replacement too.
> >
> > OK?  Bootstrapped and tested on x86_64-linux-gnu with no regressions.
> >
> > gcc/ChangeLog:
> >
> >         PR tree-optimization/25290
> >         * tree-ssa-phiopt.c (xor_replacement): Delete.
> >         (tree_ssa_phiopt_worker): Delete use of xor_replacement.
> >         (match_simplify_replacement): Allow one cheap preparation
> >         statement that can be moved to before the if.
> >
> > gcc/testsuite/ChangeLog:
> >
> >         * gcc.dg/tree-ssa/pr96928-1.c: Fix testcase for now that ~
> >         happens on the outside of the bit_xor.
> > ---
> >  gcc/testsuite/gcc.dg/tree-ssa/pr96928-1.c |   4 +-
> >  gcc/tree-ssa-phiopt.c                     | 136 +++++-----------------
> >  2 files changed, 28 insertions(+), 112 deletions(-)
> >
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr96928-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr96928-1.c
> > index a2770e5e896..2e86620da11 100644
> > --- a/gcc/testsuite/gcc.dg/tree-ssa/pr96928-1.c
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr96928-1.c
> > @@ -1,9 +1,9 @@
> >  /* PR tree-optimization/96928 */
> >  /* { dg-do compile } */
> > -/* { dg-options "-O2 -fdump-tree-phiopt2" } */
> > +/* { dg-options "-O2 -fdump-tree-phiopt2 -fdump-tree-optimized" } */
> >  /* { dg-final { scan-tree-dump-times " = a_\[0-9]*\\\(D\\\) >> " 5 "phiopt2" } } */
> >  /* { dg-final { scan-tree-dump-times " = ~c_\[0-9]*\\\(D\\\);" 1 "phiopt2" } } */
> > -/* { dg-final { scan-tree-dump-times " = ~" 1 "phiopt2" } } */
> > +/* { dg-final { scan-tree-dump-times " = ~" 1 "optimized" } } */
> >  /* { dg-final { scan-tree-dump-times " = \[abc_0-9\\\(\\\)D]* \\\^ " 5 "phiopt2" } } */
> >  /* { dg-final { scan-tree-dump-not "a < 0" "phiopt2" } } */
> >
> > diff --git a/gcc/tree-ssa-phiopt.c b/gcc/tree-ssa-phiopt.c
> > index 969b868397e..4f98e505029 100644
> > --- a/gcc/tree-ssa-phiopt.c
> > +++ b/gcc/tree-ssa-phiopt.c
> > @@ -63,8 +63,6 @@ static bool minmax_replacement (basic_block, basic_block,
> >                                 edge, edge, gphi *, tree, tree);
> >  static bool abs_replacement (basic_block, basic_block,
> >                              edge, edge, gphi *, tree, tree);
> > -static bool xor_replacement (basic_block, basic_block,
> > -                            edge, edge, gphi *, tree, tree);
> >  static bool spaceship_replacement (basic_block, basic_block,
> >                                    edge, edge, gphi *, tree, tree);
> >  static bool cond_removal_in_popcount_clz_ctz_pattern (basic_block, basic_block,
> > @@ -352,9 +350,6 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
> >             cfgchanged = true;
> >           else if (abs_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
> >             cfgchanged = true;
> > -         else if (!early_p
> > -                  && xor_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
> > -           cfgchanged = true;
> >           else if (!early_p
> >                    && cond_removal_in_popcount_clz_ctz_pattern (bb, bb1, e1,
> >                                                                 e2, phi, arg0,
> > @@ -801,9 +796,23 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
> >    edge true_edge, false_edge;
> >    gimple_seq seq = NULL;
> >    tree result;
> > +  gimple *stmt_to_move = NULL;
> >
> > +  /* If the basic block only has a cheap preparation statement. */
> >    if (!empty_block_p (middle_bb))
> > -    return false;
> > +    {
> > +      stmt_to_move = last_and_only_stmt (middle_bb);
> > +      if (!stmt_to_move)
> > +       return false;
> > +      if (gimple_could_trap_p (stmt_to_move)
> > +         || gimple_has_side_effects (stmt_to_move))
> > +       return false;
>
> In tree-ssa-ifcombine we in addition check gimple_uses_undefined_value_p ()
>
> > +      if ((!is_gimple_assign (stmt_to_move)
> > +          || TREE_CODE (gimple_assign_lhs (stmt_to_move)) != SSA_NAME)
> > +         && (!is_gimple_call (stmt_to_move)
> > +             || !gimple_inexpensive_call_p (as_a <gcall *>  (stmt_to_move))))
>
> any reason to allow calls at this point?  ifcombine has
>
>           /* const calls don't match any of the above, yet they could
>              still have some side-effects - they could contain
>              gimple_could_trap_p statements, like floating point
>              exceptions or integer division by zero.  See PR70586.
>              FIXME: perhaps gimple_has_side_effects or gimple_could_trap_p
>              should handle this.  */
>
> and disallows any calls.  Not sure if any gimple_inexpensive_call_p could
> trap for example, at least we don't document that it doesn't (just thinking
> of IFN_SQRT for example).

I will disallow them then.

>
> I think we also want to restrict the intermediate stmts to those feeding the
> PHI in the CFG merge and not allow arbitrary random stmts?  Thus sth
> like
>
>       tree lhs = gimple_get_lhs (stmt_to_move);
>       if (!lhs || TREE_CODE (lhs) != SSA_NAME || !single_imm_use (...)
> || use_stmt != phi)
>         return false;

Since this will only be allowing one (assignment) statement, the use
statement needs to be that phi node at this point due to being used
with single_non_singleton_phi_for_edges; otherwise you have some kind
of SSA violation unless there is no usage but that should have already
been taken care of due to gimple_has_side_effects/gimple_could_trap_p
I think.
I will still add the check just in case.

Thanks,
Andrew Pinski

>
> Richard.
>
> > +       return false;
> > +    }
> >
> >    /* Special case A ? B : B as this will always simplify to B. */
> >    if (operand_equal_for_phi_arg_p (arg0, arg1))
> > @@ -844,7 +853,17 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
> >      return false;
> >
> >    gsi = gsi_last_bb (cond_bb);
> > -
> > +  if (stmt_to_move)
> > +    {
> > +      if (dump_file && (dump_flags & TDF_DETAILS))
> > +       {
> > +         fprintf (dump_file, "statement un-sinked:\n");
> > +         print_gimple_stmt (dump_file, stmt_to_move, 0,
> > +                          TDF_VOPS|TDF_MEMSYMS);
> > +       }
> > +      gimple_stmt_iterator gsi1 = gsi_for_stmt (stmt_to_move);
> > +      gsi_move_before (&gsi1, &gsi);
> > +    }
> >    if (seq)
> >      gsi_insert_seq_before (&gsi, seq, GSI_SAME_STMT);
> >
> > @@ -2592,109 +2611,6 @@ abs_replacement (basic_block cond_bb, basic_block middle_bb,
> >    return true;
> >  }
> >
> > -/* Optimize x < 0 ? ~y : y into (x >> (prec-1)) ^ y.  */
> > -
> > -static bool
> > -xor_replacement (basic_block cond_bb, basic_block middle_bb,
> > -                edge e0 ATTRIBUTE_UNUSED, edge e1,
> > -                gphi *phi, tree arg0, tree arg1)
> > -{
> > -  if (!INTEGRAL_TYPE_P (TREE_TYPE (arg1)))
> > -    return false;
> > -
> > -  /* OTHER_BLOCK must have only one executable statement which must have the
> > -     form arg0 = ~arg1 or arg1 = ~arg0.  */
> > -
> > -  gimple *assign = last_and_only_stmt (middle_bb);
> > -  /* If we did not find the proper one's complement assignment, then we cannot
> > -     optimize.  */
> > -  if (assign == NULL)
> > -    return false;
> > -
> > -  /* If we got here, then we have found the only executable statement
> > -     in OTHER_BLOCK.  If it is anything other than arg = ~arg1 or
> > -     arg1 = ~arg0, then we cannot optimize.  */
> > -  if (!is_gimple_assign (assign))
> > -    return false;
> > -
> > -  if (gimple_assign_rhs_code (assign) != BIT_NOT_EXPR)
> > -    return false;
> > -
> > -  tree lhs = gimple_assign_lhs (assign);
> > -  tree rhs = gimple_assign_rhs1 (assign);
> > -
> > -  /* The assignment has to be arg0 = -arg1 or arg1 = -arg0.  */
> > -  if (!(lhs == arg0 && rhs == arg1) && !(lhs == arg1 && rhs == arg0))
> > -    return false;
> > -
> > -  gimple *cond = last_stmt (cond_bb);
> > -  tree result = PHI_RESULT (phi);
> > -
> > -  /* Only relationals comparing arg[01] against zero are interesting.  */
> > -  enum tree_code cond_code = gimple_cond_code (cond);
> > -  if (cond_code != LT_EXPR && cond_code != GE_EXPR)
> > -    return false;
> > -
> > -  /* Make sure the conditional is x OP 0.  */
> > -  tree clhs = gimple_cond_lhs (cond);
> > -  if (TREE_CODE (clhs) != SSA_NAME
> > -      || !INTEGRAL_TYPE_P (TREE_TYPE (clhs))
> > -      || TYPE_UNSIGNED (TREE_TYPE (clhs))
> > -      || TYPE_PRECISION (TREE_TYPE (clhs)) != TYPE_PRECISION (TREE_TYPE (arg1))
> > -      || !integer_zerop (gimple_cond_rhs (cond)))
> > -    return false;
> > -
> > -  /* We need to know which is the true edge and which is the false
> > -     edge so that we know if have xor or inverted xor.  */
> > -  edge true_edge, false_edge;
> > -  extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);
> > -
> > -  /* For GE_EXPR, if the true edge goes to OTHER_BLOCK, then we
> > -     will need to invert the result.  Similarly for LT_EXPR if
> > -     the false edge goes to OTHER_BLOCK.  */
> > -  edge e;
> > -  if (cond_code == GE_EXPR)
> > -    e = true_edge;
> > -  else
> > -    e = false_edge;
> > -
> > -  bool invert = e->dest == middle_bb;
> > -
> > -  result = duplicate_ssa_name (result, NULL);
> > -
> > -  gimple_stmt_iterator gsi = gsi_last_bb (cond_bb);
> > -
> > -  int prec = TYPE_PRECISION (TREE_TYPE (clhs));
> > -  gimple *new_stmt
> > -    = gimple_build_assign (make_ssa_name (TREE_TYPE (clhs)), RSHIFT_EXPR, clhs,
> > -                          build_int_cst (integer_type_node, prec - 1));
> > -  gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
> > -
> > -  if (!useless_type_conversion_p (TREE_TYPE (result), TREE_TYPE (clhs)))
> > -    {
> > -      new_stmt = gimple_build_assign (make_ssa_name (TREE_TYPE (result)),
> > -                                     NOP_EXPR, gimple_assign_lhs (new_stmt));
> > -      gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
> > -    }
> > -  lhs = gimple_assign_lhs (new_stmt);
> > -
> > -  if (invert)
> > -    {
> > -      new_stmt = gimple_build_assign (make_ssa_name (TREE_TYPE (result)),
> > -                                     BIT_NOT_EXPR, rhs);
> > -      gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
> > -      rhs = gimple_assign_lhs (new_stmt);
> > -    }
> > -
> > -  new_stmt = gimple_build_assign (result, BIT_XOR_EXPR, lhs, rhs);
> > -  gsi_insert_before (&gsi, new_stmt, GSI_NEW_STMT);
> > -
> > -  replace_phi_edge_with_variable (cond_bb, e1, phi, result);
> > -
> > -  /* Note that we optimized this PHI.  */
> > -  return true;
> > -}
> > -
> >  /* Auxiliary functions to determine the set of memory accesses which
> >     can't trap because they are preceded by accesses to the same memory
> >     portion.  We do that for MEM_REFs, so we only need to track
> > --
> > 2.17.1
> >


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