Re: PING^1 [PATCH v7] tree-ssa-sink: Improve code sinking pass

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Jul 18, 2023 at 1:17 PM Ajit Agarwal <aagarwa1@linux.ibm.com> wrote:
>
>
>
> On 18/07/23 4:38 pm, Prathamesh Kulkarni wrote:
> > On Tue, 18 Jul 2023 at 13:26, Ajit Agarwal via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> >>
> >>
> >> Ping!
> >>
> >> please review.
> >>
> >> Thanks & Regards
> >> Ajit
> >>
> >>
> >> This patch improves code sinking pass to sink statements before call to reduce
> >> register pressure.
> >> Review comments are incorporated.
> >>
> >> For example :
> >>
> >> void bar();
> >> int j;
> >> void foo(int a, int b, int c, int d, int e, int f)
> >> {
> >>   int l;
> >>   l = a + b + c + d +e + f;
> >>   if (a != 5)
> >>     {
> >>       bar();
> >>       j = l;
> >>     }
> >> }
> >>
> >> Code Sinking does the following:
> >>
> >> void bar();
> >> int j;
> >> void foo(int a, int b, int c, int d, int e, int f)
> >> {
> >>   int l;
> >>
> >>   if (a != 5)
> >>     {
> >>       l = a + b + c + d +e + f;
> >>       bar();
> >>       j = l;
> >>     }
> >> }
> >>
> >> Bootstrapped regtested on powerpc64-linux-gnu.
> >>
> >> Thanks & Regards
> >> Ajit
> >>
> >>
> >> tree-ssa-sink: Improve code sinking pass
> >>
> >> Currently, code sinking will sink code after function calls.  This increases
> >> register pressure for callee-saved registers.  The following patch improves
> >> code sinking by placing the sunk code before calls in the use block or in
> >> the immediate dominator of the use blocks.
> >>
> >> 2023-06-01  Ajit Kumar Agarwal  <aagarwa1@linux.ibm.com>
> >>
> >> gcc/ChangeLog:
> >>
> >>         PR tree-optimization/81953
> >>         * tree-ssa-sink.cc (statement_sink_location): Move statements before
> >>         calls.
> >>         (def_use_same_block): New function.
> >>         (select_best_block): Add heuristics to select the best blocks in the
> >>         immediate post dominator.
> >>
> >> gcc/testsuite/ChangeLog:
> >>
> >>         PR tree-optimization/81953
> >>         * gcc.dg/tree-ssa/ssa-sink-20.c: New testcase.
> >>         * gcc.dg/tree-ssa/ssa-sink-21.c: New testcase.
> >> ---
> >>  gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-20.c | 15 ++++
> >>  gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c | 19 +++++
> >>  gcc/tree-ssa-sink.cc                        | 79 ++++++++++++++-------
> >>  3 files changed, 87 insertions(+), 26 deletions(-)
> >>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-20.c
> >>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
> >>
> >> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-20.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-20.c
> >> new file mode 100644
> >> index 00000000000..d3b79ca5803
> >> --- /dev/null
> >> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-20.c
> >> @@ -0,0 +1,15 @@
> >> +/* { dg-do compile } */
> >> +/* { dg-options "-O2 -fdump-tree-sink-stats" } */
> >> +void bar();
> >> +int j;
> >> +void foo(int a, int b, int c, int d, int e, int f)
> >> +{
> >> +  int l;
> >> +  l = a + b + c + d +e + f;
> >> +  if (a != 5)
> >> +    {
> >> +      bar();
> >> +      j = l;
> >> +    }
> >> +}
> >> +/* { dg-final { scan-tree-dump {l_12\s+=\s+_4\s+\+\s+f_11\(D\);\n\s+bar\s+\(\)} sink1 } } */
> >> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
> >> new file mode 100644
> >> index 00000000000..84e7938c54f
> >> --- /dev/null
> >> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
> >> @@ -0,0 +1,19 @@
> >> +/* { dg-do compile } */
> >> +/* { dg-options "-O2 -fdump-tree-sink-stats" } */
> >> +void bar();
> >> +int j, x;
> >> +void foo(int a, int b, int c, int d, int e, int f)
> >> +{
> >> +  int l;
> >> +  l = a + b + c + d +e + f;
> >> +  if (a != 5)
> >> +    {
> >> +      bar();
> >> +      if (b != 3)
> >> +        x = 3;
> >> +      else
> >> +        x = 5;
> >> +      j = l;
> >> +    }
> >> +}
> >> +/* { dg-final { scan-tree-dump {l_13\s+=\s+_4\s+\+\s+f_12\(D\);\n\s+bar\s+\(\)} sink1 } } */
> >> diff --git a/gcc/tree-ssa-sink.cc b/gcc/tree-ssa-sink.cc
> >> index b1ba7a2ad6c..113c89d0967 100644
> >> --- a/gcc/tree-ssa-sink.cc
> >> +++ b/gcc/tree-ssa-sink.cc
> >> @@ -171,9 +171,28 @@ nearest_common_dominator_of_uses (def_operand_p def_p, bool *debug_stmts)
> >>    return commondom;
> >>  }
> >>
> >> +/* Return TRUE if immediate defs of STMT and STMT are in same
> >> + * block, FALSE otherwise.  */
> >> +
> >> +static bool
> >> +def_use_same_block (gimple *stmt)
> >> +{
> >> +  def_operand_p def;
> >> +  ssa_op_iter iter;
> >> +
> >> +  FOR_EACH_SSA_DEF_OPERAND (def, stmt, iter, SSA_OP_DEF)
> >> +    {
> >> +      gimple *def_stmt = SSA_NAME_DEF_STMT (DEF_FROM_PTR (def));
> >> +      if ((gimple_bb (def_stmt) == gimple_bb (stmt)))
> >> +       return true;
> > Hi Ajit,
> > Just wondering, won't this always return true since you're iterating over defs,
> > and def_stmt == stmt ? Sorry, if I misunderstood.
>
>
> Hello Prathamesh:
>
> In this passing we are passing use and in this function we are iterating over defs
> for the use and we are checking block of use (which is stmt) and def are in the same
> block or not. I dont think its always true.

The function still always returns true and I've pointe this out
repeatedly before.

Richard.

> Thanks & Regards
> Ajit
> >
> > Thanks,
> > Prathamesh
> >> +     }
> >> +  return false;
> >> +}
> >> +
> >>  /* Given EARLY_BB and LATE_BB, two blocks in a path through the dominator
> >>     tree, return the best basic block between them (inclusive) to place
> >> -   statements.
> >> +   statements. The best basic block should be an immediate dominator of
> >> +   best basic block if the use stmt is after the call.
> >>
> >>     We want the most control dependent block in the shallowest loop nest.
> >>
> >> @@ -190,11 +209,22 @@ nearest_common_dominator_of_uses (def_operand_p def_p, bool *debug_stmts)
> >>  static basic_block
> >>  select_best_block (basic_block early_bb,
> >>                    basic_block late_bb,
> >> -                  gimple *stmt)
> >> +                  gimple *stmt,
> >> +                  gimple *use)
> >>  {
> >>    basic_block best_bb = late_bb;
> >>    basic_block temp_bb = late_bb;
> >>    int threshold;
> >> +  /* Get the sinking threshold.  If the statement to be moved has memory
> >> +     operands, then increase the threshold by 7% as those are even more
> >> +     profitable to avoid, clamping at 100%.  */
> >> +  threshold = param_sink_frequency_threshold;
> >> +  if (gimple_vuse (stmt) || gimple_vdef (stmt))
> >> +    {
> >> +      threshold += 7;
> >> +      if (threshold > 100)
> >> +       threshold = 100;
> >> +    }
> >>
> >>    while (temp_bb != early_bb)
> >>      {
> >> @@ -203,34 +233,33 @@ select_best_block (basic_block early_bb,
> >>        if (bb_loop_depth (temp_bb) < bb_loop_depth (best_bb))
> >>         best_bb = temp_bb;
> >>
> >> +      /* Placing a statement before a setjmp-like function would be invalid
> >> +        (it cannot be reevaluated when execution follows an abnormal edge).
> >> +        If we selected a block with abnormal predecessors, just punt.  */
> >> +      if (bb_has_abnormal_pred (temp_bb))
> >> +       return early_bb;
> >> +
> >> +      /* if we have temp_bb post dominated by use block and def
> >> +        and use are not in same block then immediate dominator
> >> +        would be our best block.  */
> >> +      if (use
> >> +         && bb_loop_depth(temp_bb) == bb_loop_depth (early_bb)
> >> +         && !(temp_bb->count * 100 >= early_bb->count * threshold)
> >> +         && dominated_by_p (CDI_POST_DOMINATORS, temp_bb, gimple_bb (use))
> >> +         && !def_use_same_block (use))
> >> +       best_bb = temp_bb;
> >> +
> >>        /* Walk up the dominator tree, hopefully we'll find a shallower
> >>          loop nest.  */
> >>        temp_bb = get_immediate_dominator (CDI_DOMINATORS, temp_bb);
> >>      }
> >>
> >> -  /* Placing a statement before a setjmp-like function would be invalid
> >> -     (it cannot be reevaluated when execution follows an abnormal edge).
> >> -     If we selected a block with abnormal predecessors, just punt.  */
> >> -  if (bb_has_abnormal_pred (best_bb))
> >> -    return early_bb;
> >> -
> >>    /* If we found a shallower loop nest, then we always consider that
> >>       a win.  This will always give us the most control dependent block
> >>       within that loop nest.  */
> >>    if (bb_loop_depth (best_bb) < bb_loop_depth (early_bb))
> >>      return best_bb;
> >>
> >> -  /* Get the sinking threshold.  If the statement to be moved has memory
> >> -     operands, then increase the threshold by 7% as those are even more
> >> -     profitable to avoid, clamping at 100%.  */
> >> -  threshold = param_sink_frequency_threshold;
> >> -  if (gimple_vuse (stmt) || gimple_vdef (stmt))
> >> -    {
> >> -      threshold += 7;
> >> -      if (threshold > 100)
> >> -       threshold = 100;
> >> -    }
> >> -
> >>    /* If BEST_BB is at the same nesting level, then require it to have
> >>       significantly lower execution frequency to avoid gratuitous movement.  */
> >>    if (bb_loop_depth (best_bb) == bb_loop_depth (early_bb)
> >> @@ -439,7 +468,7 @@ statement_sink_location (gimple *stmt, basic_block frombb,
> >>        if (!dominated_by_p (CDI_DOMINATORS, commondom, frombb))
> >>         return false;
> >>
> >> -      commondom = select_best_block (frombb, commondom, stmt);
> >> +      commondom = select_best_block (frombb, commondom, stmt, NULL);
> >>
> >>        if (commondom == frombb)
> >>         return false;
> >> @@ -456,19 +485,17 @@ statement_sink_location (gimple *stmt, basic_block frombb,
> >>             continue;
> >>           break;
> >>         }
> >> +
> >>        use = USE_STMT (one_use);
> >>
> >>        if (gimple_code (use) != GIMPLE_PHI)
> >>         {
> >> -         sinkbb = select_best_block (frombb, gimple_bb (use), stmt);
> >> +         sinkbb = select_best_block (frombb, gimple_bb (use), stmt, use);
> >>
> >>           if (sinkbb == frombb)
> >>             return false;
> >>
> >> -         if (sinkbb == gimple_bb (use))
> >> -           *togsi = gsi_for_stmt (use);
> >> -         else
> >> -           *togsi = gsi_after_labels (sinkbb);
> >> +         *togsi = gsi_after_labels (sinkbb);
> >>
> >>           return true;
> >>         }
> >> @@ -480,7 +507,7 @@ statement_sink_location (gimple *stmt, basic_block frombb,
> >>    if (!sinkbb)
> >>      return false;
> >>
> >> -  sinkbb = select_best_block (frombb, sinkbb, stmt);
> >> +  sinkbb = select_best_block (frombb, sinkbb, stmt, NULL);
> >>    if (!sinkbb || sinkbb == frombb)
> >>      return false;
> >>
> >> --
> >> 2.39.3
> >>