On 30/10/23 5:51 pm, Ajit Agarwal wrote:
> Hello Richard:
>
> On 17/10/23 2:47 pm, Richard Biener wrote:
>> On Tue, Oct 17, 2023 at 10:53 AM Ajit Agarwal <aagar...@linux.ibm.com> wrote:
>>>
>>> Hello Richard:
>>>
>>> On 17/10/23 2:03 pm, Richard Biener wrote:
>>>> On Thu, Oct 12, 2023 at 10:42 AM Ajit Agarwal <aagar...@linux.ibm.com>
>>>> wrote:
>>>>>
>>>>> This patch improves code sinking pass to sink statements before call to
>>>>> reduce
>>>>> register pressure.
>>>>> Review comments are incorporated. Synced and modified with latest trunk
>>>>> sources.
>>>>>
>>>>> 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.
>>>>
>>>> The patch no longer does what the description above says.
>>> Why you think so. Please let me know.
>>
>> You talk about calls above but the patch doesn't do anything about calls.
>> You
>> also don't do anything about register pressure, rather the effect of
>> your changes
>> are to move some stmts by a smaller "distance", whatever effect that has.
>>
>>>>
>
> I have incorporated the changes in version 11 of the patch.
>>>> More comments below.
>>>>
>>>>> 2023-10-12 Ajit Kumar Agarwal <aagar...@linux.ibm.com>
>>>>>
>>>>> gcc/ChangeLog:
>>>>>
>>>>> PR tree-optimization/81953
>>>>> * tree-ssa-sink.cc (statement_sink_location): Move statements
>>>>> before
>>>>> calls.
>>>>> (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 test.
>>>>> * gcc.dg/tree-ssa/ssa-sink-21.c: New test.
>>>>> ---
>>>>> gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c | 15 ++++++++
>>>>> gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c | 19 ++++++++++
>>>>> gcc/tree-ssa-sink.cc | 39 ++++++++++++---------
>>>>> 3 files changed, 56 insertions(+), 17 deletions(-)
>>>>> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
>>>>> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c
>>>>>
>>>>> 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..d3b79ca5803
>>>>> --- /dev/null
>>>>> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.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-22.c
>>>>> b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c
>>>>> new file mode 100644
>>>>> index 00000000000..84e7938c54f
>>>>> --- /dev/null
>>>>> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.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 a360c5cdd6e..95298bc8402 100644
>>>>> --- a/gcc/tree-ssa-sink.cc
>>>>> +++ b/gcc/tree-ssa-sink.cc
>>>>> @@ -174,7 +174,8 @@ nearest_common_dominator_of_uses (def_operand_p
>>>>> def_p, bool *debug_stmts)
>>>>>
>>>>> /* 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.
>>>>>
>>>>> @@ -196,6 +197,16 @@ select_best_block (basic_block early_bb,
>>>>> 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)
>>>>> {
>>>>> @@ -204,6 +215,14 @@ select_best_block (basic_block early_bb,
>>>>> if (bb_loop_depth (temp_bb) < bb_loop_depth (best_bb))
>>>>> best_bb = temp_bb;
>>>>>
>>>>> + /* if we have temp_bb post dominated by use block block then
>>>>> immediate
>>>>> + * dominator would be our best block. */
>>>>> + if (!gimple_vuse (stmt)
>>>>> + && bb_loop_depth (temp_bb) == bb_loop_depth (early_bb)
>>>>> + && !(temp_bb->count * 100 >= early_bb->count * threshold)
>>>>> + && dominated_by_p (CDI_DOMINATORS, late_bb, temp_bb))
>>>>
>>>> this isn't a post-dominance check, in fact this always returns true. This
>>>> also overrides the best found loop depth which probably means finding
>>>> both inside the same loop doesn't work.
>>>
>>> I can remove dominated check. You would like me to do in different loop
>>> than doing inside the same
>>> loop. Please let me know.
>>>
>>>
>>>> What's the intent of the change?
>>>
>>> The purpose of this change is to assign best_bb the immediate dominator if
>>> both early_bb and temp_bb have same loop depth.
>>
>> So why is the change then not simply
>>
>> - if (bb_loop_depth (temp_bb) < bb_loop_depth (best_bb))
>> + if (bb_loop_depth (temp_bb) <= bb_loop_depth (best_bb))
>> best_bb = temp_bb;
>
> I have made changes in version 10 of the patch with additional check of
> avoiding
> memory operand statements to move immediate dominator. I have not heard from
> you.
> I was wondering what wrong with my changes.
>
> I have made changes in the version 11 of the patch as you have suggested
> above with later avoid sinking to immediate
> dominator with memory operands.
>
> Please let me know if this is okay for trunk.
For gimple_vuse (stmt) true we do code sinking in nearest common dominator
with same nesting loop depth
and moving to domoinator of commondom breaks the code in gcc testsuite. Thats
why I have made additional
checks of gimple_vuse (stmt) to place in common dominator instead of moving to
dominator of commondom.
Thanks & Regards
Ajit
>> ? Not that I think this is desirable. We want to sink to the least
>> executed place which
>> doesn't map 1:1 to loop depth but control flow forks. The heuristic using
>> basic-block counts is prone to profile errors (but otherwise should cover the
>> general idea of the existing code).
>>
>
> I have been looking at better heuristics on top of basic block count changes
> in original code, but that
> will come in later patches after I commit the version 10/11 of the patch.
>
> Thanks & Regards
> Ajit
>>> Thanks & Regards
>>> Ajit
>>>>
>>>>> + 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);
>>>>> @@ -233,17 +252,6 @@ select_best_block (basic_block early_bb,
>>>>> && !dominated_by_p (CDI_DOMINATORS, best_bb->loop_father->latch,
>>>>> best_bb))
>>>>> return early_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)
>>>>> @@ -430,6 +438,7 @@ statement_sink_location (gimple *stmt, basic_block
>>>>> frombb,
>>>>> continue;
>>>>> break;
>>>>> }
>>>>> +
>>>>> use = USE_STMT (one_use);
>>>>>
>>>>> if (gimple_code (use) != GIMPLE_PHI)
>>>>> @@ -439,10 +448,7 @@ statement_sink_location (gimple *stmt, basic_block
>>>>> frombb,
>>>>> 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;
>>>>> }
>>>>> @@ -825,7 +831,6 @@ pass_sink_code::execute (function *fun)
>>>>> mark_dfs_back_edges (fun);
>>>>> memset (&sink_stats, 0, sizeof (sink_stats));
>>>>> calculate_dominance_info (CDI_DOMINATORS);
>>>>> -
>>>>> virtual_operand_live vop_live;
>>>>>
>>>>> int *rpo = XNEWVEC (int, n_basic_blocks_for_fn (cfun));
>>>>> --
>>>>> 2.39.3
>>>>>
