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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.
??? Basic blocks are by no means guaranteed to be ordered in
optimal order for this iteration. */
bb_index = bitmap_first_set_bit (work_set);
bitmap_clear_bit (work_set, bb_index);
bb_index = bitmap_clear_first_set_bit (work_set);
/* Since the registration of NEW -> OLD name mappings is done
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
< (unsigned) last_basic_block_for_fn (cfun));
EXECUTE_IF_AND_COMPL_IN_BITMAP (&dfs[bb_index], phi_insertion_points,
0, i, bi)
{
/* The population counts of the dominance frontiers is low
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 (phi_insertion_points, i);
}
}
return phi_insertion_points;