On Fri, Nov 3, 2023 at 11:20 AM Ajit Agarwal <aagar...@linux.ibm.com> wrote:
>
> Hello Richard:
>
> On 03/11/23 12:51 pm, Richard Biener wrote:
> > On Thu, Nov 2, 2023 at 9:50 PM Ajit Agarwal <aagar...@linux.ibm.com> wrote:
> >>
> >> Hello All:
> >>
[...]
> >>
> >> High register pressure region is the region where there are live-in of
> >> early blocks that has been modified by the early block. If there are
> >> modification of the variables in best block that are live-in in early
> >> block that are live-out of best block.
> >
> > ?! Parse error.
> >
>
> I didnt understand what you meant here. Please suggest.
I can't even guess what that paragraph means. It fails at a
parsing level already, I can't even start to reason about what
the sentences mean.
> >> Bootstrapped and regtested on powerpc64-linux-gnu.
> >
> > What's the effect on code generation?
> >
> > Note that live is a quadratic problem while sinking was not. You
> > are effectively making the pass unfit for -O1.
> >
> > You are computing "liveness" on GIMPLE where within EBBs there
> > isn't really any particular order of stmts, so it's kind of a garbage
> > heuristic. Likewise you are not computing the effect that moving
> > a stmt has on liveness as far as I can see but you are just identifying
> > some odd metrics (I don't really understand them) to rank blocks,
> > not even taking the register file size into account.
>
>
> if the live out of best_bb <= live out of early_bb, that shows
> that there are modification in best_bb.
Hm? Do you maybe want to say that if live_out (bb) < live_in (bb)
then some variables die during the execution of bb? Otherwise,
if live_out (early) > live_out (best) then somewhere on the path
from early to best some variables die.
> Then it's
> safer to move statements in best_bb as there are lesser interfering
> live variables in best_bb.
consider a stmt
a = b + c;
where b and c die at the definition of a. Then moving the stmt
down from early_bb means you increase live_out (early_bb) by
one. So why's that "safer" then? Of course live_out (best_bb)
also increases by two then.
> if there are lesser live out in best_bb, there is lesser chance
> of interfering live ranges and hence moving statements in best_bb
> will not increase register pressure.
>
> If the liveout of best_bb is greater than live-out of early_bb,
> moving statements in best_bb will increase chances of more interfering
> live ranges and hence increase in register pressure.
>
> This is how the heuristics is defined.
I don't think they will work. Do you have any numbers?
>
> >
> > You are replacing the hot/cold heuristic.
>
> >
> > IMHO the sinking pass is the totally wrong place to do anything
> > about register pressure. You are trying to solve a scheduling
> > problem by just looking at a single stmt.
> >
>
> bb->count from profile.cc are prone to errors as you have
> mentioned in previous mails. Main bottlenecks with code
> motion is increase in register pressure as that counts to
> spills in later phases of the compiler backend.
>
> Calculation of best_bb based of immediate dominator should
> consider register pressure instead of hold cold regions as that
> would effect code generation.
>
> If there is increase in register pressure with code motion and if
> we are moving into colder regions, that wont improve code generations.
>
> Hold/cold should be criteria but not the improved criteria with
> code motion.
>
> We should consider register pressure with code motion than hot/cold
> regions.
>
> Thanks & Regards
> Ajit
>
> > Richard.
> >
> >> Thanks & Regards
>
>
> >> Ajit
> >>
> >> tree-optimization: Add register pressure heuristics
> >>
> >> Currently code sinking heuristics are based on profile data like
> >> basic block count and sink frequency threshold. We have removed
> >> such heuristics to add register pressure heuristics based on
> >> live-in and live-out of early blocks and immediate dominator of
> >> use blocks.
> >>
> >> High register pressure region is the region where there are live-in of
> >> early blocks that has been modified by the early block. If there are
> >> modification of the variables in best block that are live-in in early
> >> block that are live-out of best block.
> >>
> >> 2023-11-03 Ajit Kumar Agarwal <aagar...@linux.ibm.com>
> >>
> >> gcc/ChangeLog:
> >>
> >> * tree-ssa-sink.cc (statement_sink_location): Add tree_live_info_p
> >> as paramters.
> >> (sink_code_in_bb): Ditto.
> >> (select_best_block): Add register pressure heuristics to select
> >> the best blocks in the immediate dominator for same loop nest
> >> depth.
> >> (execute): Add live range analysis.
> >> (additional_var_map): New function.
> >> * tree-ssa-live.cc (set_var_live_on_entry): Add virtual operand
> >> tests on ssa_names.
> >> (verify_live_on_entry): Ditto.
> >>
> >> gcc/testsuite/ChangeLog:
> >>
> >> * gcc.dg/tree-ssa/ssa-sink-21.c: New test.
> >> * gcc.dg/tree-ssa/ssa-sink-22.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-live.cc | 11 ++-
> >> gcc/tree-ssa-sink.cc | 93 ++++++++++++++-------
> >> 4 files changed, 104 insertions(+), 34 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-live.cc b/gcc/tree-ssa-live.cc
> >> index f06daf23035..998fe588278 100644
> >> --- a/gcc/tree-ssa-live.cc
> >> +++ b/gcc/tree-ssa-live.cc
> >> @@ -1141,7 +1141,8 @@ set_var_live_on_entry (tree ssa_name,
> >> tree_live_info_p live)
> >> def_bb = ENTRY_BLOCK_PTR_FOR_FN (cfun);
> >>
> >> /* An undefined local variable does not need to be very alive. */
> >> - if (ssa_undefined_value_p (ssa_name, false))
> >> + if (virtual_operand_p (ssa_name)
> >> + || ssa_undefined_value_p (ssa_name, false))
> >> return;
> >>
> >> /* Visit each use of SSA_NAME and if it isn't in the same block as the
> >> def,
> >> @@ -1540,7 +1541,6 @@ debug (tree_live_info_d *ptr)
> >>
> >>
> >> /* Verify that the info in LIVE matches the current cfg. */
> >> -
> >> static void
> >> verify_live_on_entry (tree_live_info_p live)
> >> {
> >> @@ -1569,11 +1569,13 @@ verify_live_on_entry (tree_live_info_p live)
> >> tree d = NULL_TREE;
> >> bitmap loe;
> >> var = partition_to_var (map, i);
> >> + if (var == NULL_TREE)
> >> + continue;
> >> stmt = SSA_NAME_DEF_STMT (var);
> >> tmp = gimple_bb (stmt);
> >> +
> >> if (SSA_NAME_VAR (var))
> >> d = ssa_default_def (cfun, SSA_NAME_VAR (var));
> >> -
> >> loe = live_on_entry (live, e->dest);
> >> if (loe && bitmap_bit_p (loe, i))
> >> {
> >> @@ -1614,7 +1616,8 @@ verify_live_on_entry (tree_live_info_p live)
> >> {
> >> /* An undefined local variable does not need to be very
> >> alive. */
> >> - if (ssa_undefined_value_p (var, false))
> >> + if (virtual_operand_p (var)
> >> + || ssa_undefined_value_p (var, false))
> >> continue;
> >>
> >> /* The only way this var shouldn't be marked live on entry
> >> is
> >> diff --git a/gcc/tree-ssa-sink.cc b/gcc/tree-ssa-sink.cc
> >> index a360c5cdd6e..d0c9ef1ab86 100644
> >> --- a/gcc/tree-ssa-sink.cc
> >> +++ b/gcc/tree-ssa-sink.cc
> >> @@ -176,6 +176,9 @@ nearest_common_dominator_of_uses (def_operand_p def_p,
> >> bool *debug_stmts)
> >> tree, return the best basic block between them (inclusive) to place
> >> statements.
> >>
> >> + The best basic block should be an immediate dominator of
> >> + best basic block if we've moved to same loop nest.
> >> +
> >> We want the most control dependent block in the shallowest loop nest.
> >>
> >> If the resulting block is in a shallower loop nest, then use it. Else
> >> @@ -191,24 +194,23 @@ 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,
> >> + tree_live_info_p &live)
> >> {
> >> basic_block best_bb = late_bb;
> >> basic_block temp_bb = late_bb;
> >> - int threshold;
> >>
> >> while (temp_bb != early_bb)
> >> {
> >> /* If we've moved into a lower loop nest, then that becomes
> >> our best block. */
> >> - 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;
> >>
> >> /* 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. */
> >> @@ -233,24 +235,36 @@ 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;
> >> - }
> >> + int best_bb_liveout_cnt
> >> + = bitmap_count_bits (&live->liveout[best_bb->index]);
> >> + int early_bb_liveout_cnt
> >> + = bitmap_count_bits (&live->liveout[early_bb->index]);
> >> + int early_livein_cnt
> >> + = bitmap_count_bits (&live->livein[early_bb->index]);
> >> +
> >> + /* High register pressure region is the region where there are live-in
> >> of
> >> + early blocks that has been modified by the early block. If there are
> >> + modification of the variables in best block that are live-in in early
> >> + block that are live-out of best block. */
> >> + bool live_in_rgn = (early_livein_cnt != 0
> >> + && early_bb_liveout_cnt <= early_livein_cnt);
> >> +
> >> + bool high_reg_pressure_rgn
> >> + = ((best_bb_liveout_cnt != 0 || live_in_rgn)
> >> + && best_bb_liveout_cnt <= early_bb_liveout_cnt);
> >>
> >> /* If BEST_BB is at the same nesting level, then require it to have
> >> - significantly lower execution frequency to avoid gratuitous
> >> movement. */
> >> + significantly high register pressure region to avoid gratuitous
> >> + movement. */
> >> if (bb_loop_depth (best_bb) == bb_loop_depth (early_bb)
> >> - /* If result of comparsion is unknown, prefer EARLY_BB.
> >> - Thus use !(...>=..) rather than (...<...) */
> >> - && !(best_bb->count * 100 >= early_bb->count * threshold))
> >> - return best_bb;
> >> + && high_reg_pressure_rgn)
> >> + {
> >> + /* Avoid sinking to immediate dominator if the statement to be moved
> >> + has memory operand and same loop nest. */
> >> + if (best_bb != late_bb && gimple_vuse (stmt))
> >> + return late_bb;
> >> + return best_bb;
> >> + }
> >>
> >> /* No better block found, so return EARLY_BB, which happens to be the
> >> statement's original block. */
> >> @@ -265,7 +279,8 @@ select_best_block (basic_block early_bb,
> >> static bool
> >> statement_sink_location (gimple *stmt, basic_block frombb,
> >> gimple_stmt_iterator *togsi, bool *zero_uses_p,
> >> - virtual_operand_live &vop_live)
> >> + virtual_operand_live &vop_live,
> >> + tree_live_info_p &live)
> >> {
> >> gimple *use;
> >> use_operand_p one_use = NULL_USE_OPERAND_P;
> >> @@ -413,7 +428,7 @@ 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, live);
> >>
> >> if (commondom == frombb)
> >> return false;
> >> @@ -430,19 +445,17 @@ 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, live);
> >>
> >> 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;
> >> }
> >> @@ -454,7 +467,7 @@ 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, live);
> >> if (!sinkbb || sinkbb == frombb)
> >> return false;
> >>
> >> @@ -643,7 +656,8 @@ sink_common_stores_to_bb (basic_block bb)
> >> /* Perform code sinking on BB */
> >>
> >> static unsigned
> >> -sink_code_in_bb (basic_block bb, virtual_operand_live &vop_live)
> >> +sink_code_in_bb (basic_block bb, virtual_operand_live &vop_live,
> >> + tree_live_info_p &live)
> >> {
> >> gimple_stmt_iterator gsi;
> >> edge_iterator ei;
> >> @@ -670,7 +684,8 @@ sink_code_in_bb (basic_block bb, virtual_operand_live
> >> &vop_live)
> >> gimple_stmt_iterator togsi;
> >> bool zero_uses_p;
> >>
> >> - if (!statement_sink_location (stmt, bb, &togsi, &zero_uses_p,
> >> vop_live))
> >> + if (!statement_sink_location (stmt, bb, &togsi, &zero_uses_p,
> >> + vop_live, live))
> >> {
> >> gimple_stmt_iterator saved = gsi;
> >> if (!gsi_end_p (gsi))
> >> @@ -814,6 +829,15 @@ private:
> >> bool unsplit_edges;
> >> }; // class pass_sink_code
> >>
> >> +void additional_var_map (var_map &map)
> >> +{
> >> + map->bmp_bbs = BITMAP_ALLOC (NULL);
> >> + map->outofssa_p = false;
> >> + basic_block bb;
> >> + FOR_EACH_BB_FN (bb, cfun)
> >> + bitmap_set_bit (map->bmp_bbs, bb->index);
> >> +}
> >> +
> >> unsigned int
> >> pass_sink_code::execute (function *fun)
> >> {
> >> @@ -827,12 +851,21 @@ pass_sink_code::execute (function *fun)
> >> calculate_dominance_info (CDI_DOMINATORS);
> >>
> >> virtual_operand_live vop_live;
> >> + var_map map = init_var_map (num_ssa_names);
> >> + additional_var_map (map);
> >> + tree_live_info_p live = calculate_live_ranges (map, true);
> >>
> >> int *rpo = XNEWVEC (int, n_basic_blocks_for_fn (cfun));
> >> int n = inverted_rev_post_order_compute (fun, rpo);
> >> +
> >> for (int i = 0; i < n; ++i)
> >> - todo |= sink_code_in_bb (BASIC_BLOCK_FOR_FN (fun, rpo[i]), vop_live);
> >> + todo |= sink_code_in_bb (BASIC_BLOCK_FOR_FN (fun, rpo[i]), vop_live,
> >> live);
> >> free (rpo);
> >> + if (live)
> >> + delete_tree_live_info (live);
> >> +
> >> + if (map)
> >> + delete_var_map (map);
> >>
> >> statistics_counter_event (fun, "Sunk statements", sink_stats.sunk);
> >> statistics_counter_event (fun, "Commoned stores", sink_stats.commoned);
> >> --
> >> 2.39.3
> >>
> >>
