/* Array prefetching.
- Copyright (C) 2005 Free Software Foundation, Inc.
+ Copyright (C) 2005, 2007 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
-Free Software Foundation; either version 2, or (at your option) any
+Free Software Foundation; either version 3, or (at your option) any
later version.
GCC is distributed in the hope that it will be useful, but WITHOUT
for more details.
You should have received a copy of the GNU General Public License
-along with GCC; see the file COPYING. If not, write to the Free
-Software Foundation, 59 Temple Place - Suite 330, Boston, MA
-02111-1307, USA. */
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
#include "config.h"
#include "system.h"
#include "toplev.h"
#include "params.h"
#include "langhooks.h"
+#include "tree-inline.h"
+#include "tree-data-ref.h"
+#include "optabs.h"
/* This pass inserts prefetch instructions to optimize cache usage during
accesses to arrays in loops. It processes loops sequentially and:
7/32.
(5) has PREFETCH_MOD 1 as well.
+ Additionally, we use data dependence analysis to determine for each
+ reference the distance till the first reuse; this information is used
+ to determine the temporality of the issued prefetch instruction.
+
3) We determine how much ahead we need to prefetch. The number of
iterations needed is time to fetch / time spent in one iteration of
the loop. The problem is that we do not know either of these values,
/* Magic constants follow. These should be replaced by machine specific
numbers. */
-/* A number that should rouhgly correspond to the number of instructions
- executed before the prefetch is completed. */
-
-#ifndef PREFETCH_LATENCY
-#define PREFETCH_LATENCY 200
-#endif
-
-/* Number of prefetches that can run at the same time. */
-
-#ifndef SIMULTANEOUS_PREFETCHES
-#define SIMULTANEOUS_PREFETCHES 3
-#endif
-
/* True if write can be prefetched by a read prefetch. */
#ifndef WRITE_CAN_USE_READ_PREFETCH
#define READ_CAN_USE_WRITE_PREFETCH 0
#endif
-/* Cache line size. Assumed to be a power of two. */
+/* The size of the block loaded by a single prefetch. Usually, this is
+ the same as cache line size (at the moment, we only consider one level
+ of cache hierarchy). */
#ifndef PREFETCH_BLOCK
-#define PREFETCH_BLOCK 32
+#define PREFETCH_BLOCK L1_CACHE_LINE_SIZE
#endif
/* Do we have a forward hardware sequential prefetching? */
#define HAVE_prefetch 0
#endif
+#define L1_CACHE_SIZE_BYTES ((unsigned) (L1_CACHE_SIZE * 1024))
+#define L2_CACHE_SIZE_BYTES ((unsigned) (L2_CACHE_SIZE * 1024))
+
+/* We consider a memory access nontemporal if it is not reused sooner than
+ after L2_CACHE_SIZE_BYTES of memory are accessed. However, we ignore
+ accesses closer than L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION,
+ so that we use nontemporal prefetches e.g. if single memory location
+ is accessed several times in a single iteration of the loop. */
+#define NONTEMPORAL_FRACTION 16
+
+/* In case we have to emit a memory fence instruction after the loop that
+ uses nontemporal stores, this defines the builtin to use. */
+
+#ifndef FENCE_FOLLOWING_MOVNT
+#define FENCE_FOLLOWING_MOVNT NULL_TREE
+#endif
+
/* The group of references between that reuse may occur. */
struct mem_ref_group
tree stmt; /* Statement in that the reference appears. */
tree mem; /* The reference. */
HOST_WIDE_INT delta; /* Constant offset of the reference. */
- bool write_p; /* Is it a write? */
struct mem_ref_group *group; /* The group of references it belongs to. */
unsigned HOST_WIDE_INT prefetch_mod;
/* Prefetch only each PREFETCH_MOD-th
unsigned HOST_WIDE_INT prefetch_before;
/* Prefetch only first PREFETCH_BEFORE
iterations. */
- bool issue_prefetch_p; /* Should we really issue the prefetch? */
+ unsigned reuse_distance; /* The amount of data accessed before the first
+ reuse of this value. */
struct mem_ref *next; /* The next reference in the group. */
+ unsigned write_p : 1; /* Is it a write? */
+ unsigned independent_p : 1; /* True if the reference is independent on
+ all other references inside the loop. */
+ unsigned issue_prefetch_p : 1; /* Should we really issue the prefetch? */
+ unsigned storent_p : 1; /* True if we changed the store to a
+ nontemporal one. */
};
-/* Dumps information obout reference REF to FILE. */
+/* Dumps information about reference REF to FILE. */
static void
dump_mem_ref (FILE *file, struct mem_ref *ref)
fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->group->step);
fprintf (file, ")\n");
- fprintf (dump_file, " delta ");
+ fprintf (file, " delta ");
fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->delta);
fprintf (file, "\n");
break;
}
- group = xcalloc (1, sizeof (struct mem_ref_group));
+ group = XNEW (struct mem_ref_group);
group->base = base;
group->step = step;
group->refs = NULL;
return;
}
- (*aref) = xcalloc (1, sizeof (struct mem_ref));
+ (*aref) = XNEW (struct mem_ref);
(*aref)->stmt = stmt;
(*aref)->mem = mem;
(*aref)->delta = delta;
(*aref)->write_p = write_p;
(*aref)->prefetch_before = PREFETCH_ALL;
(*aref)->prefetch_mod = 1;
+ (*aref)->reuse_distance = 0;
(*aref)->issue_prefetch_p = false;
(*aref)->group = group;
(*aref)->next = NULL;
+ (*aref)->independent_p = false;
+ (*aref)->storent_p = false;
if (dump_file && (dump_flags & TDF_DETAILS))
dump_mem_ref (dump_file, *aref);
static bool
idx_analyze_ref (tree base, tree *index, void *data)
{
- struct ar_data *ar_data = data;
+ struct ar_data *ar_data = (struct ar_data *) data;
tree ibase, step, stepsize;
HOST_WIDE_INT istep, idelta = 0, imult = 1;
affine_iv iv;
ibase = iv.base;
step = iv.step;
- if (zero_p (step))
- istep = 0;
- else
- {
- if (!cst_and_fits_in_hwi (step))
- return false;
- istep = int_cst_value (step);
- }
+ if (!cst_and_fits_in_hwi (step))
+ return false;
+ istep = int_cst_value (step);
- if (TREE_CODE (ibase) == PLUS_EXPR
+ if (TREE_CODE (ibase) == POINTER_PLUS_EXPR
&& cst_and_fits_in_hwi (TREE_OPERAND (ibase, 1)))
{
idelta = int_cst_value (TREE_OPERAND (ibase, 1));
if (cst_and_fits_in_hwi (ibase))
{
idelta += int_cst_value (ibase);
- ibase = build_int_cst_type (TREE_TYPE (ibase), 0);
+ ibase = build_int_cst (TREE_TYPE (ibase), 0);
}
if (TREE_CODE (base) == ARRAY_REF)
return true;
}
-/* Tries to express REF in shape &BASE + STEP * iter + DELTA, where DELTA and
+/* Tries to express REF_P in shape &BASE + STEP * iter + DELTA, where DELTA and
STEP are integer constants and iter is number of iterations of LOOP. The
- reference occurs in statement STMT. */
+ reference occurs in statement STMT. Strips nonaddressable component
+ references from REF_P. */
static bool
-analyze_ref (struct loop *loop, tree ref, tree *base,
+analyze_ref (struct loop *loop, tree *ref_p, tree *base,
HOST_WIDE_INT *step, HOST_WIDE_INT *delta,
tree stmt)
{
struct ar_data ar_data;
tree off;
HOST_WIDE_INT bit_offset;
+ tree ref = *ref_p;
*step = 0;
*delta = 0;
&& DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1)))
ref = TREE_OPERAND (ref, 0);
+ *ref_p = ref;
+
for (; TREE_CODE (ref) == COMPONENT_REF; ref = TREE_OPERAND (ref, 0))
{
off = DECL_FIELD_BIT_OFFSET (TREE_OPERAND (ref, 1));
}
/* Record a memory reference REF to the list REFS. The reference occurs in
- LOOP in statement STMT and it is write if WRITE_P. */
+ LOOP in statement STMT and it is write if WRITE_P. Returns true if the
+ reference was recorded, false otherwise. */
-static void
+static bool
gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs,
tree ref, bool write_p, tree stmt)
{
HOST_WIDE_INT step, delta;
struct mem_ref_group *agrp;
- if (!analyze_ref (loop, ref, &base, &step, &delta, stmt))
- return;
+ if (!analyze_ref (loop, &ref, &base, &step, &delta, stmt))
+ return false;
/* Now we know that REF = &BASE + STEP * iter + DELTA, where DELTA and STEP
are integer constants. */
agrp = find_or_create_group (refs, base, step);
record_ref (agrp, stmt, ref, delta, write_p);
+
+ return true;
}
-/* Record the suitable memory references in LOOP. */
+/* Record the suitable memory references in LOOP. NO_OTHER_REFS is set to
+ true if there are no other memory references inside the loop. */
static struct mem_ref_group *
-gather_memory_references (struct loop *loop)
+gather_memory_references (struct loop *loop, bool *no_other_refs)
{
basic_block *body = get_loop_body_in_dom_order (loop);
basic_block bb;
unsigned i;
block_stmt_iterator bsi;
- tree stmt, lhs, rhs;
+ tree stmt, lhs, rhs, call;
struct mem_ref_group *refs = NULL;
+ *no_other_refs = true;
+
/* Scan the loop body in order, so that the former references precede the
later ones. */
for (i = 0; i < loop->num_nodes; i++)
for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
{
stmt = bsi_stmt (bsi);
- if (TREE_CODE (stmt) != MODIFY_EXPR)
- continue;
+ call = get_call_expr_in (stmt);
+ if (call && !(call_expr_flags (call) & ECF_CONST))
+ *no_other_refs = false;
- lhs = TREE_OPERAND (stmt, 0);
- rhs = TREE_OPERAND (stmt, 1);
+ if (TREE_CODE (stmt) != GIMPLE_MODIFY_STMT)
+ {
+ if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS))
+ *no_other_refs = false;
+ continue;
+ }
+
+ lhs = GIMPLE_STMT_OPERAND (stmt, 0);
+ rhs = GIMPLE_STMT_OPERAND (stmt, 1);
if (REFERENCE_CLASS_P (rhs))
- gather_memory_references_ref (loop, &refs, rhs, false, stmt);
+ *no_other_refs &= gather_memory_references_ref (loop, &refs,
+ rhs, false, stmt);
if (REFERENCE_CLASS_P (lhs))
- gather_memory_references_ref (loop, &refs, lhs, true, stmt);
+ *no_other_refs &= gather_memory_references_ref (loop, &refs,
+ lhs, true, stmt);
}
}
free (body);
if (ref->prefetch_before != PREFETCH_ALL)
return false;
+ /* Do not prefetch nontemporal stores. */
+ if (ref->storent_p)
+ return false;
+
return true;
}
schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor,
unsigned ahead)
{
- unsigned max_prefetches, n_prefetches;
+ unsigned remaining_prefetch_slots, n_prefetches, prefetch_slots;
+ unsigned slots_per_prefetch;
struct mem_ref *ref;
bool any = false;
- max_prefetches = (SIMULTANEOUS_PREFETCHES * unroll_factor) / ahead;
- if (max_prefetches > (unsigned) SIMULTANEOUS_PREFETCHES)
- max_prefetches = SIMULTANEOUS_PREFETCHES;
+ /* At most SIMULTANEOUS_PREFETCHES should be running at the same time. */
+ remaining_prefetch_slots = SIMULTANEOUS_PREFETCHES;
+ /* The prefetch will run for AHEAD iterations of the original loop, i.e.,
+ AHEAD / UNROLL_FACTOR iterations of the unrolled loop. In each iteration,
+ it will need a prefetch slot. */
+ slots_per_prefetch = (ahead + unroll_factor / 2) / unroll_factor;
if (dump_file && (dump_flags & TDF_DETAILS))
- fprintf (dump_file, "Max prefetches to issue: %d.\n", max_prefetches);
-
- if (!max_prefetches)
- return false;
+ fprintf (dump_file, "Each prefetch instruction takes %u prefetch slots.\n",
+ slots_per_prefetch);
/* For now we just take memory references one by one and issue
prefetches for as many as possible. The groups are sorted
starting with the largest step, since the references with
- large step are more likely to cause many cache mises. */
+ large step are more likely to cause many cache misses. */
for (; groups; groups = groups->next)
for (ref = groups->refs; ref; ref = ref->next)
if (!should_issue_prefetch_p (ref))
continue;
- ref->issue_prefetch_p = true;
-
- /* If prefetch_mod is less then unroll_factor, we need to insert
- several prefetches for the reference. */
+ /* If we need to prefetch the reference each PREFETCH_MOD iterations,
+ and we unroll the loop UNROLL_FACTOR times, we need to insert
+ ceil (UNROLL_FACTOR / PREFETCH_MOD) instructions in each
+ iteration. */
n_prefetches = ((unroll_factor + ref->prefetch_mod - 1)
/ ref->prefetch_mod);
- if (max_prefetches <= n_prefetches)
- return true;
+ prefetch_slots = n_prefetches * slots_per_prefetch;
+
+ /* If more than half of the prefetches would be lost anyway, do not
+ issue the prefetch. */
+ if (2 * remaining_prefetch_slots < prefetch_slots)
+ continue;
- max_prefetches -= n_prefetches;
+ ref->issue_prefetch_p = true;
+
+ if (remaining_prefetch_slots <= prefetch_slots)
+ return true;
+ remaining_prefetch_slots -= prefetch_slots;
any = true;
}
/* Issue prefetches for the reference REF into loop as decided before.
HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR
- is the factor by thet LOOP was unrolled. */
+ is the factor by which LOOP was unrolled. */
static void
issue_prefetch_ref (struct mem_ref *ref, unsigned unroll_factor, unsigned ahead)
{
HOST_WIDE_INT delta;
- tree addr, addr_base, prefetch, params, write_p;
+ tree addr, addr_base, prefetch, write_p, local;
block_stmt_iterator bsi;
unsigned n_prefetches, ap;
+ bool nontemporal = ref->reuse_distance >= L2_CACHE_SIZE_BYTES;
if (dump_file && (dump_flags & TDF_DETAILS))
- fprintf (dump_file, "Issued prefetch for %p.\n", (void *) ref);
+ fprintf (dump_file, "Issued%s prefetch for %p.\n",
+ nontemporal ? " nontemporal" : "",
+ (void *) ref);
bsi = bsi_for_stmt (ref->stmt);
n_prefetches = ((unroll_factor + ref->prefetch_mod - 1)
/ ref->prefetch_mod);
addr_base = build_fold_addr_expr_with_type (ref->mem, ptr_type_node);
- addr_base = force_gimple_operand_bsi (&bsi, unshare_expr (addr_base), true, NULL);
+ addr_base = force_gimple_operand_bsi (&bsi, unshare_expr (addr_base),
+ true, NULL, true, BSI_SAME_STMT);
+ write_p = ref->write_p ? integer_one_node : integer_zero_node;
+ local = build_int_cst (integer_type_node, nontemporal ? 0 : 3);
for (ap = 0; ap < n_prefetches; ap++)
{
/* Determine the address to prefetch. */
delta = (ahead + ap * ref->prefetch_mod) * ref->group->step;
- addr = fold_build2 (PLUS_EXPR, ptr_type_node,
- addr_base, build_int_cst (ptr_type_node, delta));
- addr = force_gimple_operand_bsi (&bsi, unshare_expr (addr), true, NULL);
+ addr = fold_build2 (POINTER_PLUS_EXPR, ptr_type_node,
+ addr_base, size_int (delta));
+ addr = force_gimple_operand_bsi (&bsi, unshare_expr (addr), true, NULL,
+ true, BSI_SAME_STMT);
/* Create the prefetch instruction. */
- write_p = ref->write_p ? integer_one_node : integer_zero_node;
- params = tree_cons (NULL_TREE, addr,
- tree_cons (NULL_TREE, write_p, NULL_TREE));
-
- prefetch = build_function_call_expr (built_in_decls[BUILT_IN_PREFETCH],
- params);
+ prefetch = build_call_expr (built_in_decls[BUILT_IN_PREFETCH],
+ 3, addr, write_p, local);
bsi_insert_before (&bsi, prefetch, BSI_SAME_STMT);
}
}
issue_prefetch_ref (ref, unroll_factor, ahead);
}
+/* Returns true if REF is a memory write for that a nontemporal store insn
+ can be used. */
+
+static bool
+nontemporal_store_p (struct mem_ref *ref)
+{
+ enum machine_mode mode;
+ enum insn_code code;
+
+ /* REF must be a write that is not reused. We require it to be independent
+ on all other memory references in the loop, as the nontemporal stores may
+ be reordered with respect to other memory references. */
+ if (!ref->write_p
+ || !ref->independent_p
+ || ref->reuse_distance < L2_CACHE_SIZE_BYTES)
+ return false;
+
+ /* Check that we have the storent instruction for the mode. */
+ mode = TYPE_MODE (TREE_TYPE (ref->mem));
+ if (mode == BLKmode)
+ return false;
+
+ code = optab_handler (storent_optab, mode)->insn_code;
+ return code != CODE_FOR_nothing;
+}
+
+/* If REF is a nontemporal store, we mark the corresponding modify statement
+ and return true. Otherwise, we return false. */
+
+static bool
+mark_nontemporal_store (struct mem_ref *ref)
+{
+ if (!nontemporal_store_p (ref))
+ return false;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, "Marked reference %p as a nontemporal store.\n",
+ (void *) ref);
+
+ MOVE_NONTEMPORAL (ref->stmt) = true;
+ ref->storent_p = true;
+
+ return true;
+}
+
+/* Issue a memory fence instruction after LOOP. */
+
+static void
+emit_mfence_after_loop (struct loop *loop)
+{
+ VEC (edge, heap) *exits = get_loop_exit_edges (loop);
+ edge exit;
+ tree call;
+ block_stmt_iterator bsi;
+ unsigned i;
+
+ for (i = 0; VEC_iterate (edge, exits, i, exit); i++)
+ {
+ call = build_function_call_expr (FENCE_FOLLOWING_MOVNT, NULL_TREE);
+
+ if (!single_pred_p (exit->dest)
+ /* If possible, we prefer not to insert the fence on other paths
+ in cfg. */
+ && !(exit->flags & EDGE_ABNORMAL))
+ split_loop_exit_edge (exit);
+ bsi = bsi_after_labels (exit->dest);
+
+ bsi_insert_before (&bsi, call, BSI_NEW_STMT);
+ mark_virtual_ops_for_renaming (call);
+ }
+
+ VEC_free (edge, heap, exits);
+ update_ssa (TODO_update_ssa_only_virtuals);
+}
+
+/* Returns true if we can use storent in loop, false otherwise. */
+
+static bool
+may_use_storent_in_loop_p (struct loop *loop)
+{
+ bool ret = true;
+
+ if (loop->inner != NULL)
+ return false;
+
+ /* If we must issue a mfence insn after using storent, check that there
+ is a suitable place for it at each of the loop exits. */
+ if (FENCE_FOLLOWING_MOVNT != NULL_TREE)
+ {
+ VEC (edge, heap) *exits = get_loop_exit_edges (loop);
+ unsigned i;
+ edge exit;
+
+ for (i = 0; VEC_iterate (edge, exits, i, exit); i++)
+ if ((exit->flags & EDGE_ABNORMAL)
+ && exit->dest == EXIT_BLOCK_PTR)
+ ret = false;
+
+ VEC_free (edge, heap, exits);
+ }
+
+ return ret;
+}
+
+/* Marks nontemporal stores in LOOP. GROUPS contains the description of memory
+ references in the loop. */
+
+static void
+mark_nontemporal_stores (struct loop *loop, struct mem_ref_group *groups)
+{
+ struct mem_ref *ref;
+ bool any = false;
+
+ if (!may_use_storent_in_loop_p (loop))
+ return;
+
+ for (; groups; groups = groups->next)
+ for (ref = groups->refs; ref; ref = ref->next)
+ any |= mark_nontemporal_store (ref);
+
+ if (any && FENCE_FOLLOWING_MOVNT != NULL_TREE)
+ emit_mfence_after_loop (loop);
+}
+
/* Determines whether we can profitably unroll LOOP FACTOR times, and if
this is the case, fill in DESC by the description of number of
iterations. */
/* Determine the coefficient by that unroll LOOP, from the information
contained in the list of memory references REFS. Description of
- umber of iterations of LOOP is stored to DESC. AHEAD is the number
- of iterations ahead that we need to prefetch. NINSNS is number of
- insns of the LOOP. */
+ umber of iterations of LOOP is stored to DESC. NINSNS is the number of
+ insns of the LOOP. EST_NITER is the estimated number of iterations of
+ the loop, or -1 if no estimate is available. */
static unsigned
determine_unroll_factor (struct loop *loop, struct mem_ref_group *refs,
- unsigned ahead, unsigned ninsns,
- struct tree_niter_desc *desc)
+ unsigned ninsns, struct tree_niter_desc *desc,
+ HOST_WIDE_INT est_niter)
{
- unsigned upper_bound, size_factor, constraint_factor;
- unsigned factor, max_mod_constraint, ahead_factor;
+ unsigned upper_bound;
+ unsigned nfactor, factor, mod_constraint;
struct mem_ref_group *agp;
struct mem_ref *ref;
- upper_bound = PARAM_VALUE (PARAM_MAX_UNROLL_TIMES);
-
- /* First check whether the loop is not too large to unroll. */
- size_factor = PARAM_VALUE (PARAM_MAX_UNROLLED_INSNS) / ninsns;
- if (size_factor <= 1)
+ /* First check whether the loop is not too large to unroll. We ignore
+ PARAM_MAX_UNROLL_TIMES, because for small loops, it prevented us
+ from unrolling them enough to make exactly one cache line covered by each
+ iteration. Also, the goal of PARAM_MAX_UNROLL_TIMES is to prevent
+ us from unrolling the loops too many times in cases where we only expect
+ gains from better scheduling and decreasing loop overhead, which is not
+ the case here. */
+ upper_bound = PARAM_VALUE (PARAM_MAX_UNROLLED_INSNS) / ninsns;
+
+ /* If we unrolled the loop more times than it iterates, the unrolled version
+ of the loop would be never entered. */
+ if (est_niter >= 0 && est_niter < (HOST_WIDE_INT) upper_bound)
+ upper_bound = est_niter;
+
+ if (upper_bound <= 1)
return 1;
- if (size_factor < upper_bound)
- upper_bound = size_factor;
-
- max_mod_constraint = 1;
+ /* Choose the factor so that we may prefetch each cache just once,
+ but bound the unrolling by UPPER_BOUND. */
+ factor = 1;
for (agp = refs; agp; agp = agp->next)
for (ref = agp->refs; ref; ref = ref->next)
- if (should_issue_prefetch_p (ref)
- && ref->prefetch_mod > max_mod_constraint)
- max_mod_constraint = ref->prefetch_mod;
-
- /* Set constraint_factor as large as needed to be able to satisfy the
- largest modulo constraint. */
- constraint_factor = max_mod_constraint;
-
- /* If ahead is too large in comparison with the number of available
- prefetches, unroll the loop as much as needed to be able to prefetch
- at least partially some of the references in the loop. */
- ahead_factor = ((ahead + SIMULTANEOUS_PREFETCHES - 1)
- / SIMULTANEOUS_PREFETCHES);
-
- /* Unroll as much as useful, but bound the code size growth. */
- if (constraint_factor < ahead_factor)
- factor = ahead_factor;
- else
- factor = constraint_factor;
- if (factor > upper_bound)
- factor = upper_bound;
+ if (should_issue_prefetch_p (ref))
+ {
+ mod_constraint = ref->prefetch_mod;
+ nfactor = least_common_multiple (mod_constraint, factor);
+ if (nfactor <= upper_bound)
+ factor = nfactor;
+ }
if (!should_unroll_loop_p (loop, desc, factor))
return 1;
return factor;
}
+/* Returns the total volume of the memory references REFS, taking into account
+ reuses in the innermost loop and cache line size. TODO -- we should also
+ take into account reuses across the iterations of the loops in the loop
+ nest. */
+
+static unsigned
+volume_of_references (struct mem_ref_group *refs)
+{
+ unsigned volume = 0;
+ struct mem_ref_group *gr;
+ struct mem_ref *ref;
+
+ for (gr = refs; gr; gr = gr->next)
+ for (ref = gr->refs; ref; ref = ref->next)
+ {
+ /* Almost always reuses another value? */
+ if (ref->prefetch_before != PREFETCH_ALL)
+ continue;
+
+ /* If several iterations access the same cache line, use the size of
+ the line divided by this number. Otherwise, a cache line is
+ accessed in each iteration. TODO -- in the latter case, we should
+ take the size of the reference into account, rounding it up on cache
+ line size multiple. */
+ volume += L1_CACHE_LINE_SIZE / ref->prefetch_mod;
+ }
+ return volume;
+}
+
+/* Returns the volume of memory references accessed across VEC iterations of
+ loops, whose sizes are described in the LOOP_SIZES array. N is the number
+ of the loops in the nest (length of VEC and LOOP_SIZES vectors). */
+
+static unsigned
+volume_of_dist_vector (lambda_vector vec, unsigned *loop_sizes, unsigned n)
+{
+ unsigned i;
+
+ for (i = 0; i < n; i++)
+ if (vec[i] != 0)
+ break;
+
+ if (i == n)
+ return 0;
+
+ gcc_assert (vec[i] > 0);
+
+ /* We ignore the parts of the distance vector in subloops, since usually
+ the numbers of iterations are much smaller. */
+ return loop_sizes[i] * vec[i];
+}
+
+/* Add the steps of ACCESS_FN multiplied by STRIDE to the array STRIDE
+ at the position corresponding to the loop of the step. N is the depth
+ of the considered loop nest, and, LOOP is its innermost loop. */
+
+static void
+add_subscript_strides (tree access_fn, unsigned stride,
+ HOST_WIDE_INT *strides, unsigned n, struct loop *loop)
+{
+ struct loop *aloop;
+ tree step;
+ HOST_WIDE_INT astep;
+ unsigned min_depth = loop_depth (loop) - n;
+
+ while (TREE_CODE (access_fn) == POLYNOMIAL_CHREC)
+ {
+ aloop = get_chrec_loop (access_fn);
+ step = CHREC_RIGHT (access_fn);
+ access_fn = CHREC_LEFT (access_fn);
+
+ if ((unsigned) loop_depth (aloop) <= min_depth)
+ continue;
+
+ if (host_integerp (step, 0))
+ astep = tree_low_cst (step, 0);
+ else
+ astep = L1_CACHE_LINE_SIZE;
+
+ strides[n - 1 - loop_depth (loop) + loop_depth (aloop)] += astep * stride;
+
+ }
+}
+
+/* Returns the volume of memory references accessed between two consecutive
+ self-reuses of the reference DR. We consider the subscripts of DR in N
+ loops, and LOOP_SIZES contains the volumes of accesses in each of the
+ loops. LOOP is the innermost loop of the current loop nest. */
+
+static unsigned
+self_reuse_distance (data_reference_p dr, unsigned *loop_sizes, unsigned n,
+ struct loop *loop)
+{
+ tree stride, access_fn;
+ HOST_WIDE_INT *strides, astride;
+ VEC (tree, heap) *access_fns;
+ tree ref = DR_REF (dr);
+ unsigned i, ret = ~0u;
+
+ /* In the following example:
+
+ for (i = 0; i < N; i++)
+ for (j = 0; j < N; j++)
+ use (a[j][i]);
+ the same cache line is accessed each N steps (except if the change from
+ i to i + 1 crosses the boundary of the cache line). Thus, for self-reuse,
+ we cannot rely purely on the results of the data dependence analysis.
+
+ Instead, we compute the stride of the reference in each loop, and consider
+ the innermost loop in that the stride is less than cache size. */
+
+ strides = XCNEWVEC (HOST_WIDE_INT, n);
+ access_fns = DR_ACCESS_FNS (dr);
+
+ for (i = 0; VEC_iterate (tree, access_fns, i, access_fn); i++)
+ {
+ /* Keep track of the reference corresponding to the subscript, so that we
+ know its stride. */
+ while (handled_component_p (ref) && TREE_CODE (ref) != ARRAY_REF)
+ ref = TREE_OPERAND (ref, 0);
+
+ if (TREE_CODE (ref) == ARRAY_REF)
+ {
+ stride = TYPE_SIZE_UNIT (TREE_TYPE (ref));
+ if (host_integerp (stride, 1))
+ astride = tree_low_cst (stride, 1);
+ else
+ astride = L1_CACHE_LINE_SIZE;
+
+ ref = TREE_OPERAND (ref, 0);
+ }
+ else
+ astride = 1;
+
+ add_subscript_strides (access_fn, astride, strides, n, loop);
+ }
+
+ for (i = n; i-- > 0; )
+ {
+ unsigned HOST_WIDE_INT s;
+
+ s = strides[i] < 0 ? -strides[i] : strides[i];
+
+ if (s < (unsigned) L1_CACHE_LINE_SIZE
+ && (loop_sizes[i]
+ > (unsigned) (L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION)))
+ {
+ ret = loop_sizes[i];
+ break;
+ }
+ }
+
+ free (strides);
+ return ret;
+}
+
+/* Determines the distance till the first reuse of each reference in REFS
+ in the loop nest of LOOP. NO_OTHER_REFS is true if there are no other
+ memory references in the loop. */
+
+static void
+determine_loop_nest_reuse (struct loop *loop, struct mem_ref_group *refs,
+ bool no_other_refs)
+{
+ struct loop *nest, *aloop;
+ VEC (data_reference_p, heap) *datarefs = NULL;
+ VEC (ddr_p, heap) *dependences = NULL;
+ struct mem_ref_group *gr;
+ struct mem_ref *ref, *refb;
+ VEC (loop_p, heap) *vloops = NULL;
+ unsigned *loop_data_size;
+ unsigned i, j, n;
+ unsigned volume, dist, adist;
+ HOST_WIDE_INT vol;
+ data_reference_p dr;
+ ddr_p dep;
+
+ if (loop->inner)
+ return;
+
+ /* Find the outermost loop of the loop nest of loop (we require that
+ there are no sibling loops inside the nest). */
+ nest = loop;
+ while (1)
+ {
+ aloop = loop_outer (nest);
+
+ if (aloop == current_loops->tree_root
+ || aloop->inner->next)
+ break;
+
+ nest = aloop;
+ }
+
+ /* For each loop, determine the amount of data accessed in each iteration.
+ We use this to estimate whether the reference is evicted from the
+ cache before its reuse. */
+ find_loop_nest (nest, &vloops);
+ n = VEC_length (loop_p, vloops);
+ loop_data_size = XNEWVEC (unsigned, n);
+ volume = volume_of_references (refs);
+ i = n;
+ while (i-- != 0)
+ {
+ loop_data_size[i] = volume;
+ /* Bound the volume by the L2 cache size, since above this bound,
+ all dependence distances are equivalent. */
+ if (volume > L2_CACHE_SIZE_BYTES)
+ continue;
+
+ aloop = VEC_index (loop_p, vloops, i);
+ vol = estimated_loop_iterations_int (aloop, false);
+ if (vol < 0)
+ vol = expected_loop_iterations (aloop);
+ volume *= vol;
+ }
+
+ /* Prepare the references in the form suitable for data dependence
+ analysis. We ignore unanalyzable data references (the results
+ are used just as a heuristics to estimate temporality of the
+ references, hence we do not need to worry about correctness). */
+ for (gr = refs; gr; gr = gr->next)
+ for (ref = gr->refs; ref; ref = ref->next)
+ {
+ dr = create_data_ref (nest, ref->mem, ref->stmt, !ref->write_p);
+
+ if (dr)
+ {
+ ref->reuse_distance = volume;
+ dr->aux = ref;
+ VEC_safe_push (data_reference_p, heap, datarefs, dr);
+ }
+ else
+ no_other_refs = false;
+ }
+
+ for (i = 0; VEC_iterate (data_reference_p, datarefs, i, dr); i++)
+ {
+ dist = self_reuse_distance (dr, loop_data_size, n, loop);
+ ref = dr->aux;
+ if (ref->reuse_distance > dist)
+ ref->reuse_distance = dist;
+
+ if (no_other_refs)
+ ref->independent_p = true;
+ }
+
+ compute_all_dependences (datarefs, &dependences, vloops, true);
+
+ for (i = 0; VEC_iterate (ddr_p, dependences, i, dep); i++)
+ {
+ if (DDR_ARE_DEPENDENT (dep) == chrec_known)
+ continue;
+
+ ref = DDR_A (dep)->aux;
+ refb = DDR_B (dep)->aux;
+
+ if (DDR_ARE_DEPENDENT (dep) == chrec_dont_know
+ || DDR_NUM_DIST_VECTS (dep) == 0)
+ {
+ /* If the dependence cannot be analyzed, assume that there might be
+ a reuse. */
+ dist = 0;
+
+ ref->independent_p = false;
+ refb->independent_p = false;
+ }
+ else
+ {
+ /* The distance vectors are normalized to be always lexicographically
+ positive, hence we cannot tell just from them whether DDR_A comes
+ before DDR_B or vice versa. However, it is not important,
+ anyway -- if DDR_A is close to DDR_B, then it is either reused in
+ DDR_B (and it is not nontemporal), or it reuses the value of DDR_B
+ in cache (and marking it as nontemporal would not affect
+ anything). */
+
+ dist = volume;
+ for (j = 0; j < DDR_NUM_DIST_VECTS (dep); j++)
+ {
+ adist = volume_of_dist_vector (DDR_DIST_VECT (dep, j),
+ loop_data_size, n);
+
+ /* If this is a dependence in the innermost loop (i.e., the
+ distances in all superloops are zero) and it is not
+ the trivial self-dependence with distance zero, record that
+ the references are not completely independent. */
+ if (lambda_vector_zerop (DDR_DIST_VECT (dep, j), n - 1)
+ && (ref != refb
+ || DDR_DIST_VECT (dep, j)[n-1] != 0))
+ {
+ ref->independent_p = false;
+ refb->independent_p = false;
+ }
+
+ /* Ignore accesses closer than
+ L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION,
+ so that we use nontemporal prefetches e.g. if single memory
+ location is accessed several times in a single iteration of
+ the loop. */
+ if (adist < L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION)
+ continue;
+
+ if (adist < dist)
+ dist = adist;
+ }
+ }
+
+ if (ref->reuse_distance > dist)
+ ref->reuse_distance = dist;
+ if (refb->reuse_distance > dist)
+ refb->reuse_distance = dist;
+ }
+
+ free_dependence_relations (dependences);
+ free_data_refs (datarefs);
+ free (loop_data_size);
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Reuse distances:\n");
+ for (gr = refs; gr; gr = gr->next)
+ for (ref = gr->refs; ref; ref = ref->next)
+ fprintf (dump_file, " ref %p distance %u\n",
+ (void *) ref, ref->reuse_distance);
+ }
+}
+
/* Issue prefetch instructions for array references in LOOP. Returns
- true if the LOOP was unrolled. LOOPS is the array containing all
- loops. */
+ true if the LOOP was unrolled. */
static bool
-loop_prefetch_arrays (struct loops *loops, struct loop *loop)
+loop_prefetch_arrays (struct loop *loop)
{
struct mem_ref_group *refs;
- unsigned ahead, ninsns, unroll_factor;
+ unsigned ahead, ninsns, time, unroll_factor;
+ HOST_WIDE_INT est_niter;
struct tree_niter_desc desc;
- bool unrolled = false;
+ bool unrolled = false, no_other_refs;
+
+ if (!maybe_hot_bb_p (loop->header))
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, " ignored (cold area)\n");
+ return false;
+ }
/* Step 1: gather the memory references. */
- refs = gather_memory_references (loop);
+ refs = gather_memory_references (loop, &no_other_refs);
/* Step 2: estimate the reuse effects. */
prune_by_reuse (refs);
if (!anything_to_prefetch_p (refs))
goto fail;
+ determine_loop_nest_reuse (loop, refs, no_other_refs);
+
/* Step 3: determine the ahead and unroll factor. */
- /* FIXME: We should use not size of the loop, but the average number of
- instructions executed per iteration of the loop. */
- ninsns = tree_num_loop_insns (loop);
- ahead = (PREFETCH_LATENCY + ninsns - 1) / ninsns;
- unroll_factor = determine_unroll_factor (loop, refs, ahead, ninsns,
- &desc);
+ /* FIXME: the time should be weighted by the probabilities of the blocks in
+ the loop body. */
+ time = tree_num_loop_insns (loop, &eni_time_weights);
+ ahead = (PREFETCH_LATENCY + time - 1) / time;
+ est_niter = estimated_loop_iterations_int (loop, false);
+
+ /* The prefetches will run for AHEAD iterations of the original loop. Unless
+ the loop rolls at least AHEAD times, prefetching the references does not
+ make sense. */
+ if (est_niter >= 0 && est_niter <= (HOST_WIDE_INT) ahead)
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file,
+ "Not prefetching -- loop estimated to roll only %d times\n",
+ (int) est_niter);
+ goto fail;
+ }
+
+ mark_nontemporal_stores (loop, refs);
+
+ ninsns = tree_num_loop_insns (loop, &eni_size_weights);
+ unroll_factor = determine_unroll_factor (loop, refs, ninsns, &desc,
+ est_niter);
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "Ahead %d, unroll factor %d\n", ahead, unroll_factor);
- /* If the loop rolls less than the required unroll factor, prefetching
- is useless. */
- if (unroll_factor > 1
- && cst_and_fits_in_hwi (desc.niter)
- && (unsigned HOST_WIDE_INT) int_cst_value (desc.niter) < unroll_factor)
- goto fail;
-
/* Step 4: what to prefetch? */
if (!schedule_prefetches (refs, unroll_factor, ahead))
goto fail;
iterations so that we do not issue superfluous prefetches. */
if (unroll_factor != 1)
{
- tree_unroll_loop (loops, loop, unroll_factor,
+ tree_unroll_loop (loop, unroll_factor,
single_dom_exit (loop), &desc);
unrolled = true;
}
return unrolled;
}
-/* Issue prefetch instructions for array references in LOOPS. */
+/* Issue prefetch instructions for array references in loops. */
-void
-tree_ssa_prefetch_arrays (struct loops *loops)
+unsigned int
+tree_ssa_prefetch_arrays (void)
{
- unsigned i;
+ loop_iterator li;
struct loop *loop;
bool unrolled = false;
+ int todo_flags = 0;
if (!HAVE_prefetch
/* It is possible to ask compiler for say -mtune=i486 -march=pentium4.
of processor costs and i486 does not have prefetch, but
-march=pentium4 causes HAVE_prefetch to be true. Ugh. */
|| PREFETCH_BLOCK == 0)
- return;
+ return 0;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Prefetching parameters:\n");
+ fprintf (dump_file, " simultaneous prefetches: %d\n",
+ SIMULTANEOUS_PREFETCHES);
+ fprintf (dump_file, " prefetch latency: %d\n", PREFETCH_LATENCY);
+ fprintf (dump_file, " prefetch block size: %d\n", PREFETCH_BLOCK);
+ fprintf (dump_file, " L1 cache size: %d lines, %d kB\n",
+ L1_CACHE_SIZE_BYTES / L1_CACHE_LINE_SIZE, L1_CACHE_SIZE);
+ fprintf (dump_file, " L1 cache line size: %d\n", L1_CACHE_LINE_SIZE);
+ fprintf (dump_file, " L2 cache size: %d kB\n", L2_CACHE_SIZE);
+ fprintf (dump_file, "\n");
+ }
initialize_original_copy_tables ();
tree_cons (NULL_TREE,
const_ptr_type_node,
NULL_TREE));
- tree decl = lang_hooks.builtin_function ("__builtin_prefetch", type,
- BUILT_IN_PREFETCH, BUILT_IN_NORMAL,
- NULL, NULL_TREE);
+ tree decl = add_builtin_function ("__builtin_prefetch", type,
+ BUILT_IN_PREFETCH, BUILT_IN_NORMAL,
+ NULL, NULL_TREE);
DECL_IS_NOVOPS (decl) = true;
built_in_decls[BUILT_IN_PREFETCH] = decl;
}
here. */
gcc_assert ((PREFETCH_BLOCK & (PREFETCH_BLOCK - 1)) == 0);
- for (i = loops->num - 1; i > 0; i--)
+ FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST)
{
- loop = loops->parray[i];
-
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "Processing loop %d:\n", loop->num);
- if (loop)
- unrolled |= loop_prefetch_arrays (loops, loop);
+ unrolled |= loop_prefetch_arrays (loop);
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "\n\n");
if (unrolled)
{
scev_reset ();
- cleanup_tree_cfg_loop ();
+ todo_flags |= TODO_cleanup_cfg;
}
free_original_copy_tables ();
+ return todo_flags;
}
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