Loop_Statement_to_gnu (Node_Id gnat_node)
{
const Node_Id gnat_iter_scheme = Iteration_Scheme (gnat_node);
- tree gnu_loop_stmt = build5 (LOOP_STMT, void_type_node, NULL_TREE,
- NULL_TREE, NULL_TREE, NULL_TREE, NULL_TREE);
+ tree gnu_loop_stmt = build4 (LOOP_STMT, void_type_node, NULL_TREE,
+ NULL_TREE, NULL_TREE, NULL_TREE);
tree gnu_loop_label = create_artificial_label (input_location);
tree gnu_loop_var = NULL_TREE, gnu_cond_expr = NULL_TREE;
tree gnu_result;
tree gnu_low = TYPE_MIN_VALUE (gnu_type);
tree gnu_high = TYPE_MAX_VALUE (gnu_type);
tree gnu_base_type = get_base_type (gnu_type);
- tree gnu_first, gnu_last, gnu_limit, gnu_test;
- enum tree_code update_code, test_code;
+ tree gnu_one_node = convert (gnu_base_type, integer_one_node);
+ tree gnu_first, gnu_last;
+ enum tree_code update_code, test_code, shift_code;
+ bool reverse = Reverse_Present (gnat_loop_spec), fallback = false;
/* We must disable modulo reduction for the iteration variable, if any,
in order for the loop comparison to be effective. */
gnu_last = gnu_low;
update_code = MINUS_NOMOD_EXPR;
test_code = GE_EXPR;
- gnu_limit = TYPE_MIN_VALUE (gnu_base_type);
+ shift_code = PLUS_NOMOD_EXPR;
}
else
{
gnu_last = gnu_high;
update_code = PLUS_NOMOD_EXPR;
test_code = LE_EXPR;
- gnu_limit = TYPE_MAX_VALUE (gnu_base_type);
+ shift_code = MINUS_NOMOD_EXPR;
}
- /* We know that the iteration variable will not overflow if GNU_LAST is
- a constant and is not equal to GNU_LIMIT. If it might overflow, we
- have to turn the limit test into an inequality test and move it to
- the end of the loop; as a consequence, we also have to test for an
- empty loop before entering it. */
- if (TREE_CODE (gnu_last) != INTEGER_CST
- || TREE_CODE (gnu_limit) != INTEGER_CST
- || tree_int_cst_equal (gnu_last, gnu_limit))
+ /* We use two different strategies to translate the loop, depending on
+ whether optimization is enabled.
+
+ If it is, we try to generate the canonical form of loop expected by
+ the loop optimizer, which is the do-while form:
+
+ ENTRY_COND
+ loop:
+ TOP_UPDATE
+ BODY
+ BOTTOM_COND
+ GOTO loop
+
+ This makes it possible to bypass loop header copying and to turn the
+ BOTTOM_COND into an inequality test. This should catch (almost) all
+ loops with constant starting point. If we cannot, we try to generate
+ the default form, which is:
+
+ loop:
+ TOP_COND
+ BODY
+ BOTTOM_UPDATE
+ GOTO loop
+
+ It will be rotated during loop header copying and an entry test added
+ to yield the do-while form. This should catch (almost) all loops with
+ constant ending point. If we cannot, we generate the fallback form:
+
+ ENTRY_COND
+ loop:
+ BODY
+ BOTTOM_COND
+ BOTTOM_UPDATE
+ GOTO loop
+
+ which works in all cases but for which loop header copying will copy
+ the BOTTOM_COND, thus adding a third conditional branch.
+
+ If optimization is disabled, loop header copying doesn't come into
+ play and we try to generate the loop forms with the less conditional
+ branches directly. First, the default form, it should catch (almost)
+ all loops with constant ending point. Then, if we cannot, we try to
+ generate the shifted form:
+
+ loop:
+ TOP_COND
+ TOP_UPDATE
+ BODY
+ GOTO loop
+
+ which should catch loops with constant starting point. Otherwise, if
+ we cannot, we generate the fallback form. */
+
+ if (optimize)
+ {
+ /* We can use the do-while form if GNU_FIRST-1 doesn't overflow. */
+ if (!can_equal_min_val_p (gnu_first, gnu_base_type, reverse))
+ {
+ gnu_first = build_binary_op (shift_code, gnu_base_type,
+ gnu_first, gnu_one_node);
+ LOOP_STMT_TOP_UPDATE_P (gnu_loop_stmt) = 1;
+ LOOP_STMT_BOTTOM_COND_P (gnu_loop_stmt) = 1;
+ }
+
+ /* Otherwise, we can use the default form if GNU_LAST+1 doesn't. */
+ else if (!can_equal_max_val_p (gnu_last, gnu_base_type, reverse))
+ ;
+
+ /* Otherwise, use the fallback form. */
+ else
+ fallback = true;
+ }
+ else
+ {
+ /* We can use the default form if GNU_LAST+1 doesn't overflow. */
+ if (!can_equal_max_val_p (gnu_last, gnu_base_type, reverse))
+ ;
+
+ /* Otherwise, we can use the shifted form if neither GNU_FIRST-1 nor
+ GNU_LAST-1 does. */
+ else if (!can_equal_min_val_p (gnu_first, gnu_base_type, reverse)
+ && !can_equal_min_val_p (gnu_last, gnu_base_type, reverse))
+ {
+ gnu_first = build_binary_op (shift_code, gnu_base_type,
+ gnu_first, gnu_one_node);
+ gnu_last = build_binary_op (shift_code, gnu_base_type,
+ gnu_last, gnu_one_node);
+ LOOP_STMT_TOP_UPDATE_P (gnu_loop_stmt) = 1;
+ }
+
+ /* Otherwise, use the fallback form. */
+ else
+ fallback = true;
+ }
+
+ if (fallback)
+ LOOP_STMT_BOTTOM_COND_P (gnu_loop_stmt) = 1;
+
+ /* If we use the BOTTOM_COND, we can turn the test into an inequality
+ test but we have to add an ENTRY_COND to protect the empty loop. */
+ if (LOOP_STMT_BOTTOM_COND_P (gnu_loop_stmt))
{
test_code = NE_EXPR;
gnu_cond_expr
gnu_low, gnu_high),
NULL_TREE, alloc_stmt_list ());
set_expr_location_from_node (gnu_cond_expr, gnat_loop_spec);
- test_code = NE_EXPR;
}
/* Open a new nesting level that will surround the loop to declare the
/* Do all the arithmetics in the base type. */
gnu_loop_var = convert (gnu_base_type, gnu_loop_var);
- /* Set either the top or bottom exit condition as appropriate depending
- on whether or not we know an overflow cannot occur. */
- gnu_test = build_binary_op (test_code, integer_type_node, gnu_loop_var,
- gnu_last);
- if (gnu_cond_expr)
- LOOP_STMT_BOT_COND (gnu_loop_stmt) = gnu_test;
- else
- LOOP_STMT_TOP_COND (gnu_loop_stmt) = gnu_test;
+ /* Set either the top or bottom exit condition. */
+ LOOP_STMT_COND (gnu_loop_stmt)
+ = build_binary_op (test_code, integer_type_node, gnu_loop_var,
+ gnu_last);
/* Set either the top or bottom update statement and give it the source
location of the iteration for better coverage info. */
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