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