* Re: [PATCH GCC]Improve overflow in scev by using information computed in loop niter, part II
2015-06-01 10:41 ` Richard Biener
@ 2015-06-01 10:46 ` Bin.Cheng
0 siblings, 0 replies; 3+ messages in thread
From: Bin.Cheng @ 2015-06-01 10:46 UTC (permalink / raw)
To: Richard Biener; +Cc: gcc-patches List
[-- Attachment #1: Type: text/plain, Size: 2330 bytes --]
On Mon, Jun 1, 2015 at 6:41 PM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Tue, May 26, 2015 at 1:13 PM, Bin.Cheng <amker.cheng@gmail.com> wrote:
>> Hi,
>> The first part patch improving how we handle overflow in scev is
>> posted at https://gcc.gnu.org/ml/gcc-patches/2015-05/msg01795.html .
>> Here comes the second part patch.
>>
>> This patch does below improvements:
>> 1) Computes and records control iv for each loop's exit edge. This
>> provides a way to compute overflow information in loop niter and use
>> it in different customers. It think it's useful, especially with
>> option -funsafe-loop-optimizers.
>> 2) Improve chrec_convert by adding new interface
>> loop_exits_before_overflow. It checks if a converted IV overflows
>> wrto its type and loop using overflow information of loop's control
>> iv. This basically propagates no-overflow information from control iv
>> to ivs converted from control iv. Moreover, we can further improve
>> the logic by using possible VRP information in the future.
>>
>> With this patch, cases like scev-9.c and scev-10.c in patch can be
>> handled now. Cases reported in PR48052 can be vectorized too.
>> Opinions?
>
> -ENOPATCH
Here comes the patch. Sorry for the inconvenience.
Thanks,
bin
>
>> Thanks,
>> bin
>>
>>
>> 2015-05-26 Bin Cheng <bin.cheng@arm.com>
>>
>> * cfgloop.h (struct control_iv): New.
>> (struct loop): New field control_ivs.
>> * tree-ssa-loop-niter.c : Include "stor-layout.h".
>> (number_of_iterations_lt): Set no_overflow information.
>> (number_of_iterations_exit): Init control iv in niter struct.
>> (record_control_iv): New.
>> (estimate_numbers_of_iterations_loop): Call record_control_iv.
>> (loop_exits_before_overflow): New. Interface factored out of
>> scev_probably_wraps_p.
>> (scev_probably_wraps_p): Factor loop niter related code into
>> loop_exits_before_overflow.
>> (free_numbers_of_iterations_estimates_loop): Free control ivs.
>> * tree-ssa-loop-niter.h (free_loop_control_ivs): New.
>>
>> gcc/testsuite/ChangeLog
>> 2015-05-26 Bin Cheng <bin.cheng@arm.com>
>>
>> PR tree-optimization/48052
>> * gcc.dg/tree-ssa/scev-8.c: New.
>> * gcc.dg/tree-ssa/scev-9.c: New.
>> * gcc.dg/tree-ssa/scev-10.c: New.
>> * gcc.dg/vect/pr48052.c: New.
[-- Attachment #2: improve-overlow-in-loop_niter-scev-20150526.txt --]
[-- Type: text/plain, Size: 16706 bytes --]
Index: gcc/tree-ssa-loop-niter.c
===================================================================
--- gcc/tree-ssa-loop-niter.c (revision 222758)
+++ gcc/tree-ssa-loop-niter.c (working copy)
@@ -31,6 +31,7 @@ along with GCC; see the file COPYING3. If not see
#include "wide-int.h"
#include "inchash.h"
#include "tree.h"
+#include "stor-layout.h"
#include "fold-const.h"
#include "calls.h"
#include "hashtab.h"
@@ -1184,6 +1185,7 @@ number_of_iterations_lt (tree type, affine_iv *iv0
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;
}
@@ -1965,6 +1967,9 @@ number_of_iterations_exit (struct loop *loop, edge
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;
@@ -2744,6 +2749,29 @@ record_estimate (struct loop *loop, tree bound, co
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
@@ -3467,6 +3495,7 @@ estimate_numbers_of_iterations_loop (struct loop *
record_estimate (loop, niter, niter_desc.max,
last_stmt (ex->src),
true, ex == likely_exit, true);
+ record_control_iv (loop, &niter_desc);
}
exits.release ();
@@ -3773,6 +3802,188 @@ nowrap_type_p (tree type)
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. This is done by proving
+ below conditions:
+
+ base <= UPPER_BOUND (type) - step ;;step > 0
+ base >= LOWER_BOUND (type) - step ;;step < 0
+
+ by 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
@@ -3788,13 +3999,6 @@ scev_probably_wraps_p (tree base, tree step,
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.
@@ -3828,57 +4032,9 @@ scev_probably_wraps_p (tree base, tree step,
if (TREE_CODE (step) != INTEGER_CST)
return true;
- /* Don't issue signed overflow warnings. */
- fold_defer_overflow_warnings ();
+ if (loop_exits_before_overflow (base, step, at_stmt, loop))
+ return false;
- /* 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 ();
-
/* At this point we still don't have a proof that the iv does not
overflow: give up. */
return true;
@@ -3889,17 +4045,26 @@ scev_probably_wraps_p (tree base, tree step,
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;
- 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. */
Index: gcc/tree-ssa-loop-niter.h
===================================================================
--- gcc/tree-ssa-loop-niter.h (revision 222758)
+++ gcc/tree-ssa-loop-niter.h (working copy)
@@ -41,6 +41,7 @@ extern void estimate_numbers_of_iterations (void);
extern bool stmt_dominates_stmt_p (gimple, gimple);
extern bool nowrap_type_p (tree);
extern bool scev_probably_wraps_p (tree, tree, gimple, struct loop *, bool);
+extern void free_loop_control_ivs (struct loop *);
extern void free_numbers_of_iterations_estimates_loop (struct loop *);
extern void free_numbers_of_iterations_estimates (void);
extern void substitute_in_loop_info (struct loop *, tree, tree);
Index: gcc/testsuite/gcc.dg/vect/pr48052.c
===================================================================
--- gcc/testsuite/gcc.dg/vect/pr48052.c (revision 0)
+++ gcc/testsuite/gcc.dg/vect/pr48052.c (revision 0)
@@ -0,0 +1,27 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-O3" } */
+
+int foo(int* A, int* B, unsigned start, unsigned BS)
+{
+ int s;
+ for (unsigned k = start; k < start + BS; k++)
+ {
+ s += A[k] * B[k];
+ }
+
+ return s;
+}
+
+int bar(int* A, int* B, unsigned BS)
+{
+ int s;
+ for (unsigned k = 0; k < BS; k++)
+ {
+ s += A[k] * B[k];
+ }
+
+ return s;
+}
+
+/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 2 "vect" } } */
+/* { dg-final { cleanup-tree-dump "vect" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/scev-8.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/scev-8.c (revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/scev-8.c (revision 0)
@@ -0,0 +1,63 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-ivopts-details" } */
+
+int *a;
+
+int
+foo1 (long long s, long long l)
+{
+ long long i;
+
+ for (i = s; i < l; i++)
+ {
+ a[(short)i] = 0;
+ }
+ return 0;
+}
+
+int
+foo2 (unsigned char s, unsigned char l, unsigned char c)
+{
+ unsigned char i, step = 1;
+ int sum = 0;
+
+ for (i = s; i < l; i++)
+ {
+ sum += a[c];
+ c += step;
+ }
+
+ return sum;
+}
+
+int
+foo3 (unsigned char s, unsigned char l, unsigned char c)
+{
+ unsigned char i;
+ int sum = 0;
+
+ for (i = s; i != l; i += c)
+ {
+ sum += a[i];
+ }
+
+ return sum;
+}
+
+int
+foo4 (unsigned char s, unsigned char l)
+{
+ unsigned char i;
+ int sum = 0;
+
+ for (i = s; i != l; i++)
+ {
+ sum += a[i];
+ }
+
+ return sum;
+}
+
+/* Address of array references are not scevs. */
+/* { dg-final { scan-tree-dump-not "use \[0-9\]\n address" "ivopts" } } */
+/* { dg-final { cleanup-tree-dump "ivopts" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/scev-10.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/scev-10.c (revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/scev-10.c (revision 0)
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-ivopts-details" } */
+
+int *a;
+
+int
+foo (signed char s, signed char l)
+{
+ signed char i;
+ int sum = 0;
+
+ for (i = s; i < l; i++)
+ {
+ sum += a[i];
+ }
+
+ return sum;
+}
+
+/* Address of array references are not scevs. */
+/* { dg-final { scan-tree-dump-times "use \[0-9\]\n address" 1 "ivopts" } } */
+/* { dg-final { cleanup-tree-dump "ivopts" } } */
+
+
Index: gcc/testsuite/gcc.dg/tree-ssa/scev-9.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/scev-9.c (revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/scev-9.c (revision 0)
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-ivopts-details" } */
+
+int *a;
+
+int
+foo (unsigned char s, unsigned char l)
+{
+ unsigned char i;
+ int sum = 0;
+
+ for (i = s; i < l; i += 1)
+ {
+ sum += a[i];
+ }
+
+ return sum;
+}
+
+/* Address of array references are not scevs. */
+/* { dg-final { scan-tree-dump-times "use \[0-9\]\n address" 1 "ivopts" } } */
+/* { dg-final { cleanup-tree-dump "ivopts" } } */
+
Index: gcc/cfgloop.h
===================================================================
--- gcc/cfgloop.h (revision 222758)
+++ gcc/cfgloop.h (working copy)
@@ -116,6 +116,14 @@ enum loop_estimation
EST_LAST
};
+/* The structure describing a non-overflow control induction variable
+ of loop's exit edge. */
+struct GTY ((chain_next ("%h.next"))) control_iv {
+ tree base;
+ tree step;
+ struct control_iv *next;
+};
+
/* Structure to hold information for each natural loop. */
struct GTY ((chain_next ("%h.next"))) loop {
/* Index into loops array. */
@@ -203,6 +211,9 @@ struct GTY ((chain_next ("%h.next"))) loop {
/* Upper bound on number of iterations of a loop. */
struct nb_iter_bound *bounds;
+ /* Non-overflow control ivs of a loop. */
+ struct control_iv *control_ivs;
+
/* Head of the cyclic list of the exits of the loop. */
struct loop_exit *exits;
^ permalink raw reply [flat|nested] 3+ messages in thread