diff options
Diffstat (limited to 'gcc/tree-ssa-dse.c')
| -rw-r--r-- | gcc/tree-ssa-dse.c | 72 |
1 files changed, 70 insertions, 2 deletions
diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c index 7087018..fa3ba96 100644 --- a/gcc/tree-ssa-dse.c +++ b/gcc/tree-ssa-dse.c @@ -83,6 +83,13 @@ struct dse_block_local_data bitmap stores; }; +/* Basic blocks of the potentially dead store and the following + store, for memory_address_same. */ +struct address_walk_data +{ + basic_block store1_bb, store2_bb; +}; + static bool gate_dse (void); static void tree_ssa_dse (void); static void dse_initialize_block_local_data (struct dom_walk_data *, @@ -145,6 +152,64 @@ dse_initialize_block_local_data (struct dom_walk_data *walk_data, } } +/* Helper function for memory_address_same via walk_tree. Returns + non-NULL if it finds an SSA_NAME which is part of the address, + such that the definition of the SSA_NAME post-dominates the store + we want to delete but not the store that we believe makes it + redundant. This indicates that the address may change between + the two stores. */ + +static tree +memory_ssa_name_same (tree *expr_p, int *walk_subtrees ATTRIBUTE_UNUSED, + void *data) +{ + struct address_walk_data *walk_data = data; + tree expr = *expr_p; + tree def_stmt; + basic_block def_bb; + + if (TREE_CODE (expr) != SSA_NAME) + return NULL_TREE; + + /* If we've found a default definition, then there's no problem. Both + stores will post-dominate it. And def_bb will be NULL. */ + if (expr == default_def (SSA_NAME_VAR (expr))) + return NULL_TREE; + + def_stmt = SSA_NAME_DEF_STMT (expr); + def_bb = bb_for_stmt (def_stmt); + + /* DEF_STMT must dominate both stores. So if it is in the same + basic block as one, it does not post-dominate that store. */ + if (walk_data->store1_bb != def_bb + && dominated_by_p (CDI_POST_DOMINATORS, walk_data->store1_bb, def_bb)) + { + if (walk_data->store2_bb == def_bb + || !dominated_by_p (CDI_POST_DOMINATORS, walk_data->store2_bb, + def_bb)) + /* Return non-NULL to stop the walk. */ + return def_stmt; + } + + return NULL_TREE; +} + +/* Return TRUE if the destination memory address in STORE1 and STORE2 + might be modified after STORE1, before control reaches STORE2. */ + +static bool +memory_address_same (tree store1, tree store2) +{ + struct address_walk_data walk_data; + + walk_data.store1_bb = bb_for_stmt (store1); + walk_data.store2_bb = bb_for_stmt (store2); + + return (walk_tree (&TREE_OPERAND (store1, 0), memory_ssa_name_same, + &walk_data, NULL) + == NULL); +} + /* Attempt to eliminate dead stores in the statement referenced by BSI. A dead store is a store into a memory location which will later be @@ -251,11 +316,14 @@ dse_optimize_stmt (struct dom_walk_data *walk_data, } /* If we have precisely one immediate use at this point, then we may - have found redundant store. */ + have found redundant store. Make sure that the stores are to + the same memory location. This includes checking that any + SSA-form variables in the address will have the same values. */ if (use_p != NULL_USE_OPERAND_P && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt)) && operand_equal_p (TREE_OPERAND (stmt, 0), - TREE_OPERAND (use_stmt, 0), 0)) + TREE_OPERAND (use_stmt, 0), 0) + && memory_address_same (stmt, use_stmt)) { /* Make sure we propagate the ABNORMAL bit setting. */ if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (USE_FROM_PTR (first_use_p))) |