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Use base inequality for some vector alias checks

Browse source 
This patch checks whether two data references x and y cannot
partially overlap and so are independent whenever &x != &y.
We can then use this in the vectoriser to optimise alias checks.

gcc/
2016-08-04  Richard Sandiford  <richard.sandiford@linaro.org>

	* hash-traits.h (pair_hash): New struct.
	* tree-data-ref.h (data_dependence_relation): Add object_a and
	object_b fields.
	(DDR_OBJECT_A, DDR_OBJECT_B): New macros.
	* tree-data-ref.c (initialize_data_dependence_relation): Initialize
	DDR_OBJECT_A and DDR_OBJECT_B.
	* tree-vectorizer.h (vec_object_pair): New type.
	(_loop_vec_info): Add a check_unequal_addrs field.
	(LOOP_VINFO_CHECK_UNEQUAL_ADDRS): New macro.
	(LOOP_REQUIRES_VERSIONING_FOR_ALIAS): Return true if there is an
	entry in check_unequal_addrs.  Check comp_alias_ddrs instead of
	may_alias_ddrs.
	* tree-vect-loop.c (destroy_loop_vec_info): Release
	LOOP_VINFO_CHECK_UNEQUAL_ADDRS.
	(vect_analyze_loop_2): Likewise, when restarting.
	(vect_estimate_min_profitable_iters): Estimate the cost of
	LOOP_VINFO_CHECK_UNEQUAL_ADDRS.
	* tree-vect-data-refs.c: Include tree-hash-traits.h.
	(vect_prune_runtime_alias_test_list): Try to handle conflicts
	using LOOP_VINFO_CHECK_UNEQUAL_ADDRS, if the data dependence allows.
	Count such tests in the final summary.
	* tree-vect-loop-manip.c (chain_cond_expr): New function.
	(vect_create_cond_for_align_checks): Use it.
	(vect_create_cond_for_unequal_addrs): New function.
	(vect_loop_versioning): Call it.

gcc/testsuite/
	* gcc.dg/vect/vect-alias-check-6.c: New test.

From-SVN: r250868
This commit is contained in:
Richard Sandiford 2017-08-04 10:40:35 +00:00
parent dfbddbeb1c
commit 9adee30521
8 changed files with 200 additions and 14 deletions
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70
gcc/hash-traits.h
View file

@ -301,6 +301,76 @@ struct ggc_cache_ptr_hash : pointer_hash <T>, ggc_cache_remove <T *> {};
struct nofree_string_hash : string_hash, typed_noop_remove <const char *> {};
/* Traits for pairs of values, using the first to record empty and
deleted slots. */
template <typename T1, typename T2>
struct pair_hash
{
typedef std::pair <typename T1::value_type,
typename T2::value_type> value_type;
typedef std::pair <typename T1::compare_type,
typename T2::compare_type> compare_type;
static inline hashval_t hash (const value_type &);
static inline bool equal (const value_type &, const compare_type &);
static inline void remove (value_type &);
static inline void mark_deleted (value_type &);
static inline void mark_empty (value_type &);
static inline bool is_deleted (const value_type &);
static inline bool is_empty (const value_type &);
};
template <typename T1, typename T2>
inline hashval_t
pair_hash <T1, T2>::hash (const value_type &x)
{
return iterative_hash_hashval_t (T1::hash (x.first), T2::hash (x.second));
}
template <typename T1, typename T2>
inline bool
pair_hash <T1, T2>::equal (const value_type &x, const compare_type &y)
{
return T1::equal (x.first, y.first) && T2::equal (x.second, y.second);
}
template <typename T1, typename T2>
inline void
pair_hash <T1, T2>::remove (value_type &x)
{
T1::remove (x.first);
T2::remove (x.second);
}
template <typename T1, typename T2>
inline void
pair_hash <T1, T2>::mark_deleted (value_type &x)
{
T1::mark_deleted (x.first);
}
template <typename T1, typename T2>
inline void
pair_hash <T1, T2>::mark_empty (value_type &x)
{
T1::mark_empty (x.first);
}
template <typename T1, typename T2>
inline bool
pair_hash <T1, T2>::is_deleted (const value_type &x)
{
return T1::is_deleted (x.first);
}
template <typename T1, typename T2>
inline bool
pair_hash <T1, T2>::is_empty (const value_type &x)
{
return T1::is_empty (x.first);
}
template <typename T> struct default_hash_traits : T {};
template <typename T>

23
gcc/testsuite/gcc.dg/vect/vect-alias-check-6.c Normal file
View file

@ -0,0 +1,23 @@
/* { dg-do compile } */
/* { dg-require-effective-target vect_int } */
#define N 16
struct s { int x[N]; };
void
f1 (struct s *a, struct s *b)
{
for (int i = 0; i < N - 1; ++i)
a->x[i + 1] += b->x[i];
}
void
f2 (struct s *a, struct s *b)
{
for (int i = 0; i < N; ++i)
a->x[i] += b->x[N - i - 1];
}
/* { dg-final { scan-tree-dump-times {checking that [^\n]* and [^\n]* have different addresses} 2 "vect" } } */
/* { dg-final { scan-tree-dump-times "LOOP VECTORIZED" 2 "vect" } } */

9
gcc/tree-data-ref.c
View file

@ -2506,6 +2506,15 @@ initialize_data_dependence_relation (struct data_reference *a,
}
DDR_COULD_BE_INDEPENDENT_P (res) = true;
if (!loop_nest.exists ()
|| (object_address_invariant_in_loop_p (loop_nest[0],
full_seq.object_a)
&& object_address_invariant_in_loop_p (loop_nest[0],
full_seq.object_b)))
{
DDR_OBJECT_A (res) = full_seq.object_a;
DDR_OBJECT_B (res) = full_seq.object_b;
}
}
DDR_AFFINE_P (res) = true;

9
gcc/tree-data-ref.h
View file

@ -309,6 +309,13 @@ struct data_dependence_relation
but the analyzer cannot be more specific. */
tree are_dependent;
/* If nonnull, COULD_BE_INDEPENDENT_P is true and the accesses are
independent when the runtime addresses of OBJECT_A and OBJECT_B
are different. The addresses of both objects are invariant in the
loop nest. */
tree object_a;
tree object_b;
/* For each subscript in the dependence test, there is an element in
this array. This is the attribute that labels the edge A->B of
the data_dependence_relation. */
@ -372,6 +379,8 @@ typedef struct data_dependence_relation *ddr_p;
#define DDR_B(DDR) (DDR)->b
#define DDR_AFFINE_P(DDR) (DDR)->affine_p
#define DDR_ARE_DEPENDENT(DDR) (DDR)->are_dependent
#define DDR_OBJECT_A(DDR) (DDR)->object_a
#define DDR_OBJECT_B(DDR) (DDR)->object_b
#define DDR_SUBSCRIPTS(DDR) (DDR)->subscripts
#define DDR_SUBSCRIPT(DDR, I) DDR_SUBSCRIPTS (DDR)[I]
#define DDR_NUM_SUBSCRIPTS(DDR) DDR_SUBSCRIPTS (DDR).length ()

39
gcc/tree-vect-data-refs.c
View file

@ -51,6 +51,7 @@ along with GCC; see the file COPYING3. If not see
#include "builtins.h"
#include "params.h"
#include "tree-cfg.h"
#include "tree-hash-traits.h"
/* Return true if load- or store-lanes optab OPTAB is implemented for
COUNT vectors of type VECTYPE. NAME is the name of OPTAB. */
@ -2986,10 +2987,14 @@ dependence_distance_ge_vf (data_dependence_relation *ddr,
bool
vect_prune_runtime_alias_test_list (loop_vec_info loop_vinfo)
{
vec<ddr_p> may_alias_ddrs =
LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo);
vec<dr_with_seg_len_pair_t>& comp_alias_ddrs =
LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo);
typedef pair_hash <tree_operand_hash, tree_operand_hash> tree_pair_hash;
hash_set <tree_pair_hash> compared_objects;
vec<ddr_p> may_alias_ddrs = LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo);
vec<dr_with_seg_len_pair_t> &comp_alias_ddrs
= LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo);
vec<vec_object_pair> &check_unequal_addrs
= LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo);
int vect_factor = LOOP_VINFO_VECT_FACTOR (loop_vinfo);
tree scalar_loop_iters = LOOP_VINFO_NITERS (loop_vinfo);
@ -3024,6 +3029,24 @@ vect_prune_runtime_alias_test_list (loop_vec_info loop_vinfo)
if (dependence_distance_ge_vf (ddr, loop_depth, vect_factor))
continue;
if (DDR_OBJECT_A (ddr))
{
vec_object_pair new_pair (DDR_OBJECT_A (ddr), DDR_OBJECT_B (ddr));
if (!compared_objects.add (new_pair))
{
if (dump_enabled_p ())
{
dump_printf_loc (MSG_NOTE, vect_location, "checking that ");
dump_generic_expr (MSG_NOTE, TDF_SLIM, new_pair.first);
dump_printf (MSG_NOTE, " and ");
dump_generic_expr (MSG_NOTE, TDF_SLIM, new_pair.second);
dump_printf (MSG_NOTE, " have different addresses\n");
}
LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo).safe_push (new_pair);
}
continue;
}
dr_a = DDR_A (ddr);
stmt_a = DR_STMT (DDR_A (ddr));
dr_group_first_a = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_a));
@ -3085,11 +3108,13 @@ vect_prune_runtime_alias_test_list (loop_vec_info loop_vinfo)
prune_runtime_alias_test_list (&comp_alias_ddrs,
(unsigned HOST_WIDE_INT) vect_factor);
unsigned int count = (comp_alias_ddrs.length ()
+ check_unequal_addrs.length ());
dump_printf_loc (MSG_NOTE, vect_location,
"improved number of alias checks from %d to %d\n",
may_alias_ddrs.length (), comp_alias_ddrs.length ());
if ((int) comp_alias_ddrs.length () >
PARAM_VALUE (PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS))
may_alias_ddrs.length (), count);
if ((int) count > PARAM_VALUE (PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS))
{
if (dump_enabled_p ())
dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,

45
gcc/tree-vect-loop-manip.c
View file

@ -1944,6 +1944,19 @@ vect_create_cond_for_niters_checks (loop_vec_info loop_vinfo, tree *cond_expr)
*cond_expr = part_cond_expr;
}
/* Set *COND_EXPR to a tree that is true when both the original *COND_EXPR
and PART_COND_EXPR are true. Treat a null *COND_EXPR as "true". */
static void
chain_cond_expr (tree *cond_expr, tree part_cond_expr)
{
if (*cond_expr)
*cond_expr = fold_build2 (TRUTH_AND_EXPR, boolean_type_node,
*cond_expr, part_cond_expr);
else
*cond_expr = part_cond_expr;
}
/* Function vect_create_cond_for_align_checks.
Create a conditional expression that represents the alignment checks for
@ -2054,11 +2067,28 @@ vect_create_cond_for_align_checks (loop_vec_info loop_vinfo,
ptrsize_zero = build_int_cst (int_ptrsize_type, 0);
part_cond_expr = fold_build2 (EQ_EXPR, boolean_type_node,
and_tmp_name, ptrsize_zero);
if (*cond_expr)
*cond_expr = fold_build2 (TRUTH_AND_EXPR, boolean_type_node,
*cond_expr, part_cond_expr);
else
*cond_expr = part_cond_expr;
chain_cond_expr (cond_expr, part_cond_expr);
}
/* If LOOP_VINFO_CHECK_UNEQUAL_ADDRS contains <A1, B1>, ..., <An, Bn>,
create a tree representation of: (&A1 != &B1) && ... && (&An != &Bn).
Set *COND_EXPR to a tree that is true when both the original *COND_EXPR
and this new condition are true. Treat a null *COND_EXPR as "true". */
static void
vect_create_cond_for_unequal_addrs (loop_vec_info loop_vinfo, tree *cond_expr)
{
vec<vec_object_pair> pairs = LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo);
unsigned int i;
vec_object_pair *pair;
FOR_EACH_VEC_ELT (pairs, i, pair)
{
tree addr1 = build_fold_addr_expr (pair->first);
tree addr2 = build_fold_addr_expr (pair->second);
tree part_cond_expr = fold_build2 (NE_EXPR, boolean_type_node,
addr1, addr2);
chain_cond_expr (cond_expr, part_cond_expr);
}
}
/* Function vect_create_cond_for_alias_checks.
@ -2158,7 +2188,10 @@ vect_loop_versioning (loop_vec_info loop_vinfo,
&cond_expr_stmt_list);
if (version_alias)
vect_create_cond_for_alias_checks (loop_vinfo, &cond_expr);
{
vect_create_cond_for_unequal_addrs (loop_vinfo, &cond_expr);
vect_create_cond_for_alias_checks (loop_vinfo, &cond_expr);
}
cond_expr = force_gimple_operand_1 (cond_expr, &gimplify_stmt_list,
is_gimple_condexpr, NULL_TREE);

8
gcc/tree-vect-loop.c
View file

@ -1275,6 +1275,8 @@ destroy_loop_vec_info (loop_vec_info loop_vinfo, bool clean_stmts)
destroy_cost_data (LOOP_VINFO_TARGET_COST_DATA (loop_vinfo));
loop_vinfo->scalar_cost_vec.release ();
LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo).release ();
free (loop_vinfo);
loop->aux = NULL;
}
@ -2343,6 +2345,7 @@ again:
}
/* Free optimized alias test DDRS. */
LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo).release ();
LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo).release ();
/* Reset target cost data. */
destroy_cost_data (LOOP_VINFO_TARGET_COST_DATA (loop_vinfo));
LOOP_VINFO_TARGET_COST_DATA (loop_vinfo)
@ -3434,6 +3437,11 @@ vect_estimate_min_profitable_iters (loop_vec_info loop_vinfo,
unsigned len = LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo).length ();
(void) add_stmt_cost (target_cost_data, len, vector_stmt, NULL, 0,
vect_prologue);
len = LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo).length ();
if (len)
/* Count LEN - 1 ANDs and LEN comparisons. */
(void) add_stmt_cost (target_cost_data, len * 2 - 1, scalar_stmt,
NULL, 0, vect_prologue);
dump_printf (MSG_NOTE,
"cost model: Adding cost of checks for loop "
"versioning aliasing.\n");

11
gcc/tree-vectorizer.h
View file

@ -149,6 +149,10 @@ typedef struct _slp_instance {
/* Describes two objects whose addresses must be unequal for the vectorized
loop to be valid. */
typedef std::pair<tree, tree> vec_object_pair;
/* Vectorizer state common between loop and basic-block vectorization. */
struct vec_info {
enum { bb, loop } kind;
@ -245,6 +249,9 @@ typedef struct _loop_vec_info : public vec_info {
lengths from which the run-time aliasing check is built. */
vec<dr_with_seg_len_pair_t> comp_alias_ddrs;
/* Check that the addresses of each pair of objects is unequal. */
vec<vec_object_pair> check_unequal_addrs;
/* Statements in the loop that have data references that are candidates for a
runtime (loop versioning) misalignment check. */
vec<gimple *> may_misalign_stmts;
@ -339,6 +346,7 @@ typedef struct _loop_vec_info : public vec_info {
#define LOOP_VINFO_MAY_MISALIGN_STMTS(L) (L)->may_misalign_stmts
#define LOOP_VINFO_MAY_ALIAS_DDRS(L) (L)->may_alias_ddrs
#define LOOP_VINFO_COMP_ALIAS_DDRS(L) (L)->comp_alias_ddrs
#define LOOP_VINFO_CHECK_UNEQUAL_ADDRS(L) (L)->check_unequal_addrs
#define LOOP_VINFO_GROUPED_STORES(L) (L)->grouped_stores
#define LOOP_VINFO_SLP_INSTANCES(L) (L)->slp_instances
#define LOOP_VINFO_SLP_UNROLLING_FACTOR(L) (L)->slp_unrolling_factor
@ -358,7 +366,8 @@ typedef struct _loop_vec_info : public vec_info {
#define LOOP_REQUIRES_VERSIONING_FOR_ALIGNMENT(L) \
((L)->may_misalign_stmts.length () > 0)
#define LOOP_REQUIRES_VERSIONING_FOR_ALIAS(L) \
((L)->comp_alias_ddrs.length () > 0)
((L)->comp_alias_ddrs.length () > 0 \
|| (L)->check_unequal_addrs.length () > 0)
#define LOOP_REQUIRES_VERSIONING_FOR_NITERS(L) \
(LOOP_VINFO_NITERS_ASSUMPTIONS (L))
#define LOOP_REQUIRES_VERSIONING(L) \