#include "wide-int.h"
#include "inchash.h"
#include "tree.h"
+#include "stor-layout.h"
#include "fold-const.h"
#include "calls.h"
#include "hashtab.h"
niter->niter = delta;
niter->max = widest_int::from (wi::from_mpz (niter_type, bnds->up, false),
TYPE_SIGN (niter_type));
+ niter->control.no_overflow = true;
return true;
}
return false;
niter->assumptions = boolean_false_node;
+ niter->control.base = NULL_TREE;
+ niter->control.step = NULL_TREE;
+ niter->control.no_overflow = false;
last = last_stmt (exit->src);
if (!last)
return false;
record_niter_bound (loop, new_i_bound, realistic, upper);
}
+/* Records the control iv analyzed in NITER for LOOP if the iv is valid
+ and doesn't overflow. */
+
+static void
+record_control_iv (struct loop *loop, struct tree_niter_desc *niter)
+{
+ struct control_iv *iv;
+
+ if (!niter->control.base || !niter->control.step)
+ return;
+
+ if (!integer_onep (niter->assumptions) || !niter->control.no_overflow)
+ return;
+
+ iv = ggc_alloc<control_iv> ();
+ iv->base = niter->control.base;
+ iv->step = niter->control.step;
+ iv->next = loop->control_ivs;
+ loop->control_ivs = iv;
+
+ return;
+}
+
/* Record the estimate on number of iterations of LOOP based on the fact that
the induction variable BASE + STEP * i evaluated in STMT does not wrap and
its values belong to the range <LOW, HIGH>. REALISTIC is true if the
record_estimate (loop, niter, niter_desc.max,
last_stmt (ex->src),
true, ex == likely_exit, true);
+ record_control_iv (loop, &niter_desc);
}
exits.release ();
return false;
}
+/* Return true if we can prove LOOP is exited before evolution of induction
+ variabled {BASE, STEP} overflows with respect to its type bound. */
+
+static bool
+loop_exits_before_overflow (tree base, tree step,
+ gimple at_stmt, struct loop *loop)
+{
+ widest_int niter;
+ struct control_iv *civ;
+ struct nb_iter_bound *bound;
+ tree e, delta, step_abs, unsigned_base;
+ tree type = TREE_TYPE (step);
+ tree unsigned_type, valid_niter;
+
+ /* Don't issue signed overflow warnings. */
+ fold_defer_overflow_warnings ();
+
+ /* Compute the number of iterations before we reach the bound of the
+ type, and verify that the loop is exited before this occurs. */
+ unsigned_type = unsigned_type_for (type);
+ unsigned_base = fold_convert (unsigned_type, base);
+
+ if (tree_int_cst_sign_bit (step))
+ {
+ tree extreme = fold_convert (unsigned_type,
+ lower_bound_in_type (type, type));
+ delta = fold_build2 (MINUS_EXPR, unsigned_type, unsigned_base, extreme);
+ step_abs = fold_build1 (NEGATE_EXPR, unsigned_type,
+ fold_convert (unsigned_type, step));
+ }
+ else
+ {
+ tree extreme = fold_convert (unsigned_type,
+ upper_bound_in_type (type, type));
+ delta = fold_build2 (MINUS_EXPR, unsigned_type, extreme, unsigned_base);
+ step_abs = fold_convert (unsigned_type, step);
+ }
+
+ valid_niter = fold_build2 (FLOOR_DIV_EXPR, unsigned_type, delta, step_abs);
+
+ estimate_numbers_of_iterations_loop (loop);
+
+ if (max_loop_iterations (loop, &niter)
+ && wi::fits_to_tree_p (niter, TREE_TYPE (valid_niter))
+ && (e = fold_binary (GT_EXPR, boolean_type_node, valid_niter,
+ wide_int_to_tree (TREE_TYPE (valid_niter),
+ niter))) != NULL
+ && integer_nonzerop (e))
+ {
+ fold_undefer_and_ignore_overflow_warnings ();
+ return true;
+ }
+ if (at_stmt)
+ for (bound = loop->bounds; bound; bound = bound->next)
+ {
+ if (n_of_executions_at_most (at_stmt, bound, valid_niter))
+ {
+ fold_undefer_and_ignore_overflow_warnings ();
+ return true;
+ }
+ }
+ fold_undefer_and_ignore_overflow_warnings ();
+
+ /* Try to prove loop is exited before {base, step} overflows with the
+ help of analyzed loop control IV. This is done only for IVs with
+ constant step because otherwise we don't have the information. */
+ if (TREE_CODE (step) == INTEGER_CST)
+ for (civ = loop->control_ivs; civ; civ = civ->next)
+ {
+ enum tree_code code;
+ tree stepped, extreme, civ_type = TREE_TYPE (civ->step);
+
+ /* Have to consider type difference because operand_equal_p ignores
+ that for constants. */
+ if (TYPE_UNSIGNED (type) != TYPE_UNSIGNED (civ_type)
+ || element_precision (type) != element_precision (civ_type))
+ continue;
+
+ /* Only consider control IV with same step. */
+ if (!operand_equal_p (step, civ->step, 0))
+ continue;
+
+ /* Done proving if this is a no-overflow control IV. */
+ if (operand_equal_p (base, civ->base, 0))
+ return true;
+
+ /* If this is a before stepping control IV, in other words, we have
+
+ {civ_base, step} = {base + step, step}
+
+ Because civ {base + step, step} doesn't overflow during loop
+ iterations, {base, step} will not overflow if we can prove the
+ operation "base + step" does not overflow. Specifically, we try
+ to prove below conditions are satisfied:
+
+ base <= UPPER_BOUND (type) - step ;;step > 0
+ base >= LOWER_BOUND (type) - step ;;step < 0
+
+ by proving the reverse conditions are false using loop's initial
+ condition. */
+ stepped = fold_build2 (PLUS_EXPR, TREE_TYPE (base), base, step);
+ if (operand_equal_p (stepped, civ->base, 0))
+ {
+ if (tree_int_cst_sign_bit (step))
+ {
+ code = LT_EXPR;
+ extreme = lower_bound_in_type (type, type);
+ }
+ else
+ {
+ code = GT_EXPR;
+ extreme = upper_bound_in_type (type, type);
+ }
+ extreme = fold_build2 (MINUS_EXPR, type, extreme, step);
+ e = fold_build2 (code, boolean_type_node, base, extreme);
+ e = simplify_using_initial_conditions (loop, e);
+ if (integer_zerop (e))
+ return true;
+
+ continue;
+ }
+
+ /* Similar to above, only in this case we have:
+
+ {civ_base, step} = {(signed T)((unsigned T)base + step), step}
+ && TREE_TYPE (civ_base) = signed T.
+
+ We prove that below condition is satisfied:
+
+ (signed T)((unsigned T)base + step)
+ == (signed T)(unsigned T)base + step
+ == base + step
+
+ because of exact the same reason as above. This also proves
+ there is no overflow in the operation "base + step", thus the
+ induction variable {base, step} during loop iterations.
+
+ This is necessary to handle cases as below:
+
+ int foo (int *a, signed char s, signed char l)
+ {
+ signed char i;
+ for (i = s; i < l; i++)
+ a[i] = 0;
+ return 0;
+ }
+
+ The variable I is firstly converted to type unsigned char,
+ incremented, then converted back to type signed char. */
+ if (!CONVERT_EXPR_P (civ->base) || TREE_TYPE (civ->base) != type)
+ continue;
+ e = TREE_OPERAND (civ->base, 0);
+ if (TREE_CODE (e) != PLUS_EXPR
+ || TREE_CODE (TREE_OPERAND (e, 1)) != INTEGER_CST
+ || !operand_equal_p (step,
+ fold_convert (type,
+ TREE_OPERAND (e, 1)), 0))
+ continue;
+ e = TREE_OPERAND (e, 0);
+ if (!CONVERT_EXPR_P (e) || !operand_equal_p (e, unsigned_base, 0))
+ continue;
+ e = TREE_OPERAND (e, 0);
+ gcc_assert (operand_equal_p (e, base, 0));
+ if (tree_int_cst_sign_bit (step))
+ {
+ code = LT_EXPR;
+ extreme = lower_bound_in_type (type, type);
+ }
+ else
+ {
+ code = GT_EXPR;
+ extreme = upper_bound_in_type (type, type);
+ }
+ extreme = fold_build2 (MINUS_EXPR, type, extreme, step);
+ e = fold_build2 (code, boolean_type_node, base, extreme);
+ e = simplify_using_initial_conditions (loop, e);
+ if (integer_zerop (e))
+ return true;
+ }
+
+ return false;
+}
+
/* Return false only when the induction variable BASE + STEP * I is
known to not overflow: i.e. when the number of iterations is small
enough with respect to the step and initial condition in order to
gimple at_stmt, struct loop *loop,
bool use_overflow_semantics)
{
- tree delta, step_abs;
- tree unsigned_type, valid_niter;
- tree type = TREE_TYPE (step);
- tree e;
- widest_int niter;
- struct nb_iter_bound *bound;
-
/* FIXME: We really need something like
http://gcc.gnu.org/ml/gcc-patches/2005-06/msg02025.html.
if (TREE_CODE (step) != INTEGER_CST)
return true;
- /* Don't issue signed overflow warnings. */
- fold_defer_overflow_warnings ();
-
- /* Otherwise, compute the number of iterations before we reach the
- bound of the type, and verify that the loop is exited before this
- occurs. */
- unsigned_type = unsigned_type_for (type);
- base = fold_convert (unsigned_type, base);
-
- if (tree_int_cst_sign_bit (step))
- {
- tree extreme = fold_convert (unsigned_type,
- lower_bound_in_type (type, type));
- delta = fold_build2 (MINUS_EXPR, unsigned_type, base, extreme);
- step_abs = fold_build1 (NEGATE_EXPR, unsigned_type,
- fold_convert (unsigned_type, step));
- }
- else
- {
- tree extreme = fold_convert (unsigned_type,
- upper_bound_in_type (type, type));
- delta = fold_build2 (MINUS_EXPR, unsigned_type, extreme, base);
- step_abs = fold_convert (unsigned_type, step);
- }
-
- valid_niter = fold_build2 (FLOOR_DIV_EXPR, unsigned_type, delta, step_abs);
-
- estimate_numbers_of_iterations_loop (loop);
-
- if (max_loop_iterations (loop, &niter)
- && wi::fits_to_tree_p (niter, TREE_TYPE (valid_niter))
- && (e = fold_binary (GT_EXPR, boolean_type_node, valid_niter,
- wide_int_to_tree (TREE_TYPE (valid_niter),
- niter))) != NULL
- && integer_nonzerop (e))
- {
- fold_undefer_and_ignore_overflow_warnings ();
- return false;
- }
- if (at_stmt)
- for (bound = loop->bounds; bound; bound = bound->next)
- {
- if (n_of_executions_at_most (at_stmt, bound, valid_niter))
- {
- fold_undefer_and_ignore_overflow_warnings ();
- return false;
- }
- }
-
- fold_undefer_and_ignore_overflow_warnings ();
+ if (loop_exits_before_overflow (base, step, at_stmt, loop))
+ return false;
/* At this point we still don't have a proof that the iv does not
overflow: give up. */
void
free_numbers_of_iterations_estimates_loop (struct loop *loop)
{
- struct nb_iter_bound *bound, *next;
+ struct control_iv *civ;
+ struct nb_iter_bound *bound;
loop->nb_iterations = NULL;
loop->estimate_state = EST_NOT_COMPUTED;
- for (bound = loop->bounds; bound; bound = next)
+ for (bound = loop->bounds; bound;)
{
- next = bound->next;
+ struct nb_iter_bound *next = bound->next;
ggc_free (bound);
+ bound = next;
}
-
loop->bounds = NULL;
+
+ for (civ = loop->control_ivs; civ;)
+ {
+ struct control_iv *next = civ->next;
+ ggc_free (civ);
+ civ = next;
+ }
+ loop->control_ivs = NULL;
}
/* Frees the information on upper bounds on numbers of iterations of loops. */
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