/* 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 roughly 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));
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
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_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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