return false;
}
+/* Given a statement STMT and its right hand side which is a load, try
+ to look for the expression stored in the location for the load, and
+ return true if a useful equivalence was recorded for LHS. */
+
+static bool
+try_look_through_load (tree lhs, tree mem_ref, tree stmt, basic_block block)
+{
+ tree store_stmt = NULL;
+ tree rhs;
+ ssa_op_iter i;
+ tree vuse;
+
+ FOR_EACH_SSA_TREE_OPERAND (vuse, stmt, i, SSA_OP_VIRTUAL_USES)
+ {
+ tree def_stmt;
+
+ gcc_assert (TREE_CODE (vuse) == SSA_NAME);
+ def_stmt = SSA_NAME_DEF_STMT (vuse);
+
+ /* If there is no useful statement for this VUSE, we'll not find a
+ useful expression to return either. Likewise, if there is a
+ statement but it is not a simple assignment or it has virtual
+ uses, we can stop right here. Note that this means we do
+ not look through PHI nodes, which is intentional. */
+ if (!def_stmt
+ || TREE_CODE (def_stmt) != MODIFY_EXPR
+ || !ZERO_SSA_OPERANDS (def_stmt, SSA_OP_VIRTUAL_USES))
+ return false;
+
+ /* If this is not the same statement as one we have looked at for
+ another VUSE of STMT already, we have two statements producing
+ something that reaches our STMT. */
+ if (store_stmt && store_stmt != def_stmt)
+ return false;
+ else
+ {
+ /* Is this a store to the exact same location as the one we are
+ loading from in STMT? */
+ if (!operand_equal_p (TREE_OPERAND (def_stmt, 0), mem_ref, 0))
+ return false;
+
+ /* Otherwise remember this statement and see if all other VUSEs
+ come from the same statement. */
+ store_stmt = def_stmt;
+ }
+ }
+
+ /* Alright then, we have visited all VUSEs of STMT and we've determined
+ that all of them come from the same statement STORE_STMT. See if there
+ is a useful expression we can deduce from STORE_STMT. */
+ rhs = TREE_OPERAND (store_stmt, 1);
+ if (TREE_CODE (rhs) == SSA_NAME
+ || is_gimple_min_invariant (rhs)
+ || TREE_CODE (rhs) == ADDR_EXPR
+ || TREE_INVARIANT (rhs))
+ {
+ /* Yay! Compute a value number for the RHS of the statement and
+ add its value to the AVAIL_OUT set for the block. Add the LHS
+ to TMP_GEN. */
+ add_to_sets (lhs, rhs, store_stmt, TMP_GEN (block), AVAIL_OUT (block));
+ if (TREE_CODE (rhs) == SSA_NAME
+ && !is_undefined_value (rhs))
+ value_insert_into_set (EXP_GEN (block), rhs);
+ return true;
+ }
+
+ return false;
+}
+
/* Compute the AVAIL set for all basic blocks.
This function performs value numbering of the statements in each basic
tree lhs = TREE_OPERAND (stmt, 0);
tree rhs = TREE_OPERAND (stmt, 1);
+ /* Try to look through loads. */
+ if (TREE_CODE (lhs) == SSA_NAME
+ && !ZERO_SSA_OPERANDS (stmt, SSA_OP_VIRTUAL_USES)
+ && try_look_through_load (lhs, rhs, stmt, block))
+ continue;
+
STRIP_USELESS_TYPE_CONVERSION (rhs);
if (UNARY_CLASS_P (rhs)
|| BINARY_CLASS_P (rhs)
fprintf (dump_file, " in ");
print_generic_stmt (dump_file, stmt, 0);
}
+
if (TREE_CODE (sprime) == SSA_NAME)
NECESSARY (SSA_NAME_DEF_STMT (sprime)) = 1;
+ /* We need to make sure the new and old types actually match,
+ which may require adding a simple cast, which fold_convert
+ will do for us. */
+ if (TREE_CODE (*rhs_p) != SSA_NAME
+ && !tree_ssa_useless_type_conversion_1 (TREE_TYPE (*rhs_p),
+ TREE_TYPE (sprime)))
+ sprime = fold_convert (TREE_TYPE (*rhs_p), sprime);
+
pre_stats.eliminations++;
propagate_tree_value (rhs_p, sprime);
update_stmt (stmt);
TODO_dump_func | TODO_ggc_collect | TODO_verify_ssa, /* todo_flags_finish */
0 /* letter */
};
+
+/* Return true if T is a copy statement between two ssa names. */
+
+static bool
+is_copy_stmt (tree t)
+{
+ if (!t || TREE_CODE (t) != MODIFY_EXPR)
+ return false;
+ if (TREE_CODE (TREE_OPERAND (t, 0)) == SSA_NAME
+ && TREE_CODE (TREE_OPERAND (t, 1)) == SSA_NAME)
+ return true;
+ return false;
+}
+
+/* Starting from START, walk copy statements till we hit a statement with a
+ VUSE or a non-copy statement. */
+
+static tree
+follow_copies_till_vuse (tree start)
+{
+ if (is_copy_stmt (start) && ZERO_SSA_OPERANDS (start, SSA_OP_VIRTUAL_USES))
+ {
+ tree rhs, defstmt;
+
+ rhs = TREE_OPERAND (start, 1);
+ defstmt = SSA_NAME_DEF_STMT (rhs);
+ return follow_copies_till_vuse (defstmt);
+ }
+ return start;
+}
+
+/* Gate and execute functions for eliminate useless stores.
+ The goal here is to recognize the pattern *x = ... *x, and eliminate the
+ store because the value hasn't changed. Store copy/const prop won't
+ do this because making *more* loads (IE propagating *x) is not a win, so it
+ ignores them.
+ This pass is currently geared completely towards static variable store
+ elimination. */
+
+static void
+do_eustores (void)
+{
+ basic_block bb;
+ /* For each basic block
+ For each statement (STMT) in the block
+ if STMT is a stores of the pattern *x = y
+ follow the chain of definitions for y, until we hit a non-copy
+ statement or a statement with a vuse.
+ if the statement we arrive at is a vuse of the operand we killed,
+ accessed through the same memory operation, then we have a
+ useless store (because it is *x = ... = *x). */
+
+ FOR_EACH_BB (bb)
+ {
+ block_stmt_iterator bsi;
+
+ for (bsi = bsi_start (bb);
+ !bsi_end_p (bsi);)
+ {
+ tree stmt = bsi_stmt (bsi);
+ tree startat;
+ tree kill;
+ tree found;
+
+ if (NUM_SSA_OPERANDS (stmt, SSA_OP_VMUSTDEF) != 1
+ || TREE_CODE (stmt) != MODIFY_EXPR
+ || TREE_CODE (TREE_OPERAND (stmt, 1)) != SSA_NAME)
+ {
+ bsi_next (&bsi);
+ continue;
+ }
+
+ kill = MUSTDEF_KILL (MUSTDEF_OPS (stmt));
+ startat = TREE_OPERAND (stmt, 1);
+ startat = SSA_NAME_DEF_STMT (startat);
+ found = follow_copies_till_vuse (startat);
+
+ if (found && TREE_CODE (found) == MODIFY_EXPR)
+ {
+
+ /* We want exactly one virtual use, and it should match up with
+ the use being killed. */
+
+ if (NUM_SSA_OPERANDS (found, SSA_OP_VUSE) != 1
+ || VUSE_OP (VUSE_OPS (found)) != kill
+ || !DECL_P (TREE_OPERAND (stmt, 0))
+ || !operand_equal_p (TREE_OPERAND (found, 1),
+ TREE_OPERAND (stmt, 0), 0))
+ {
+ bsi_next (&bsi);
+ continue;
+ }
+
+ if (dump_file)
+ {
+ fprintf (dump_file, "Eliminating useless store ");
+ print_generic_stmt (dump_file, stmt, 0);
+ }
+ mark_sym_for_renaming (TREE_OPERAND (stmt, 0));
+ bsi_remove (&bsi);
+ }
+ else
+ {
+ bsi_next (&bsi);
+ continue;
+ }
+ }
+ }
+}
+
+static bool
+gate_eustores(void)
+{
+ return flag_unit_at_a_time != 0;
+}
+
+struct tree_opt_pass pass_eliminate_useless_stores =
+{
+ "eustores", /* name */
+ gate_eustores, /* gate */
+ do_eustores, /* execute */
+ NULL, /* sub */
+ NULL, /* next */
+ 0, /* static_pass_number */
+ 0, /* tv_id */
+ PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */
+ 0, /* properties_provided */
+ 0, /* properties_destroyed */
+ 0, /* todo_flags_start */
+ TODO_update_ssa | TODO_dump_func
+ | TODO_ggc_collect | TODO_verify_ssa, /* todo_flags_finish */
+ 0 /* letter */
+};
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