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Avoid quadratic behaviour in prune_runtime_alias_test_list

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prune_runtime_alias_test_list used ordered_remove to remove a merged
alias pair, which made the function quadratic when many aliases could
be removed.

I had a testcase in which these memmoves accounted for an impressive
85% of compile time.  The fact that we had so many probably shows
a deeper problem, but still, it's easy to remove as we go.

2019-12-06  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-data-ref.c (prune_runtime_alias_test_list): Exit early
	for empty vectors.  Avoid using ordered_remove and instead
	shuffle the vector as we go.

From-SVN: r279038
This commit is contained in:
Richard Sandiford 2019-12-06 10:31:44 +00:00 committed by Richard Sandiford
parent 28fabd43d9
commit ea1ff9e46c
2 changed files with 19 additions and 4 deletions
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6
gcc/ChangeLog
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@ -1,3 +1,9 @@
2019-12-06 Richard Sandiford <richard.sandiford@arm.com>
* tree-data-ref.c (prune_runtime_alias_test_list): Exit early
for empty vectors. Avoid using ordered_remove and instead
shuffle the vector as we go.
2019-12-06 Richard Biener <rguenther@suse.de>
* genmatch.c (enum tree_code): Remove CONVERT{0,1,2} and

17
gcc/tree-data-ref.c
View File

@ -1535,6 +1535,9 @@ void
prune_runtime_alias_test_list (vec<dr_with_seg_len_pair_t> *alias_pairs,
poly_uint64)
{
if (alias_pairs->is_empty ())
return;
/* Canonicalize each pair so that the base components are ordered wrt
data_ref_compare_tree. This allows the loop below to merge more
cases. */
@ -1565,10 +1568,11 @@ prune_runtime_alias_test_list (vec<dr_with_seg_len_pair_t> *alias_pairs,
/* Scan the sorted dr pairs and check if we can combine alias checks
of two neighboring dr pairs. */
unsigned int last = 0;
for (i = 1; i < alias_pairs->length (); ++i)
{
/* Deal with two ddrs (dr_a1, dr_b1) and (dr_a2, dr_b2). */
dr_with_seg_len_pair_t *alias_pair1 = &(*alias_pairs)[i - 1];
dr_with_seg_len_pair_t *alias_pair1 = &(*alias_pairs)[last];
dr_with_seg_len_pair_t *alias_pair2 = &(*alias_pairs)[i];
dr_with_seg_len *dr_a1 = &alias_pair1->first;
@ -1584,10 +1588,15 @@ prune_runtime_alias_test_list (vec<dr_with_seg_len_pair_t> *alias_pairs,
DR_REF (dr_a1->dr), DR_REF (dr_b1->dr),
DR_REF (dr_a2->dr), DR_REF (dr_b2->dr));
alias_pair1->flags |= alias_pair2->flags;
alias_pairs->ordered_remove (i--);
continue;
}
/* Assume that we won't be able to merge the pairs, then correct
if we do. */
last += 1;
if (last != i)
(*alias_pairs)[last] = (*alias_pairs)[i];
if (*dr_a1 == *dr_a2 || *dr_b1 == *dr_b2)
{
/* We consider the case that DR_B1 and DR_B2 are same memrefs,
@ -1695,10 +1704,10 @@ prune_runtime_alias_test_list (vec<dr_with_seg_len_pair_t> *alias_pairs,
DR_REF (dr_a1->dr), DR_REF (dr_b1->dr),
DR_REF (dr_a2->dr), DR_REF (dr_b2->dr));
alias_pair1->flags |= alias_pair2->flags;
alias_pairs->ordered_remove (i);
i--;
last -= 1;
}
}
alias_pairs->truncate (last + 1);
/* Try to restore the original dr_with_seg_len order within each
dr_with_seg_len_pair_t. If we ended up combining swapped and