Hello Richard:
Below review comments are incorporated in version 10 of the patch,
Please review and let me know if its okay for trunk.
Thanks & Regards
Ajit
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.
>
>>>
>>> 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;
>
> ? 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).
>
>> 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
>>>>
