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middle-end/114480 - IDF compute is slow

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The testcase in this PR shows very slow IDF compute:

  tree SSA rewrite                   :  76.99 ( 31%)
  24.78%        243663  cc1plus  cc1plus             [.] compute_idf

which can be mitigated to some extent by refactoring the bitmap
operations to simpler variants.  With the patch below this becomes

  tree SSA rewrite                   :  15.23 (  8%)

when not optimizing and in addition to that

  tree SSA incremental               : 181.52 ( 30%)

to

  tree SSA incremental               :  24.09 (  6%)

when optimizing.

	PR middle-end/114480
	* cfganal.cc (compute_idf): Use simpler bitmap iteration,
	touch work_set only when phi_insertion_points changed.
This commit is contained in:
Richard Biener 2024-03-27 16:19:01 +01:00
parent f6d7ff4796
commit 0bad303944
1 changed files with 8 additions and 7 deletions
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15
gcc/cfganal.cc
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@ -1701,8 +1701,7 @@ compute_idf (bitmap def_blocks, bitmap_head *dfs)
on earlier blocks first is better. on earlier blocks first is better.
??? Basic blocks are by no means guaranteed to be ordered in ??? Basic blocks are by no means guaranteed to be ordered in
optimal order for this iteration. */ optimal order for this iteration. */
bb_index = bitmap_first_set_bit (work_set); bb_index = bitmap_clear_first_set_bit (work_set);
bitmap_clear_bit (work_set, bb_index);
/* Since the registration of NEW -> OLD name mappings is done /* Since the registration of NEW -> OLD name mappings is done
separately from the call to update_ssa, when updating the SSA separately from the call to update_ssa, when updating the SSA
@ -1712,12 +1711,14 @@ compute_idf (bitmap def_blocks, bitmap_head *dfs)
gcc_checking_assert (bb_index gcc_checking_assert (bb_index
< (unsigned) last_basic_block_for_fn (cfun)); < (unsigned) last_basic_block_for_fn (cfun));
EXECUTE_IF_AND_COMPL_IN_BITMAP (&dfs[bb_index], phi_insertion_points, /* The population counts of the dominance frontiers is low
0, i, bi) compared to that of phi_insertion_points which approaches
{ the IDF and of work_set which is at most that of the IDF
as well. That makes iterating over the DFS bitmap preferential
to whole bitmap operations involving also phi_insertion_points. */
EXECUTE_IF_SET_IN_BITMAP (&dfs[bb_index], 0, i, bi)
if (bitmap_set_bit (phi_insertion_points, i))
bitmap_set_bit (work_set, i); bitmap_set_bit (work_set, i);
bitmap_set_bit (phi_insertion_points, i);
}
} }
return phi_insertion_points; return phi_insertion_points;