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.
Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
Richard
2019-12-06 Richard Sandiford <richard.sandif...@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.
Index: gcc/tree-data-ref.c
===================================================================
--- gcc/tree-data-ref.c 2019-11-18 15:36:04.873884873 +0000
+++ gcc/tree-data-ref.c 2019-12-06 08:35:38.153410087 +0000
@@ -1535,6 +1535,9 @@ dump_alias_pair (dr_with_seg_len_pair_t
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_wi
/* 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_wi
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_wi
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
