--- /dev/null
+/* Array prefetching.
+ Copyright (C) 2005 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
+later version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+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. */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "tree.h"
+#include "rtl.h"
+#include "tm_p.h"
+#include "hard-reg-set.h"
+#include "basic-block.h"
+#include "output.h"
+#include "diagnostic.h"
+#include "tree-flow.h"
+#include "tree-dump.h"
+#include "timevar.h"
+#include "cfgloop.h"
+#include "varray.h"
+#include "expr.h"
+#include "tree-pass.h"
+#include "ggc.h"
+#include "insn-config.h"
+#include "recog.h"
+#include "hashtab.h"
+#include "tree-chrec.h"
+#include "tree-scalar-evolution.h"
+#include "toplev.h"
+#include "params.h"
+#include "langhooks.h"
+
+/* This pass inserts prefetch instructions to optimize cache usage during
+ accesses to arrays in loops. It processes loops sequentially and:
+
+ 1) Gathers all memory references in the single loop.
+ 2) For each of the references it decides when it is profitable to prefetch
+ it. To do it, we evaluate the reuse among the accesses, and determines
+ two values: PREFETCH_BEFORE (meaning that it only makes sense to do
+ prefetching in the first PREFETCH_BEFORE iterations of the loop) and
+ PREFETCH_MOD (meaning that it only makes sense to prefetch in the
+ iterations of the loop that are zero modulo PREFETCH_MOD). For example
+ (assuming cache line size is 64 bytes, char has size 1 byte and there
+ is no hardware sequential prefetch):
+
+ char *a;
+ for (i = 0; i < max; i++)
+ {
+ a[255] = ...; (0)
+ a[i] = ...; (1)
+ a[i + 64] = ...; (2)
+ a[16*i] = ...; (3)
+ a[187*i] = ...; (4)
+ a[187*i + 50] = ...; (5)
+ }
+
+ (0) obviously has PREFETCH_BEFORE 1
+ (1) has PREFETCH_BEFORE 64, since (2) accesses the same memory
+ location 64 iterations before it, and PREFETCH_MOD 64 (since
+ it hits the same cache line otherwise).
+ (2) has PREFETCH_MOD 64
+ (3) has PREFETCH_MOD 4
+ (4) has PREFETCH_MOD 1. We do not set PREFETCH_BEFORE here, since
+ the cache line accessed by (4) is the same with probability only
+ 7/32.
+ (5) has PREFETCH_MOD 1 as well.
+
+ 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,
+ so we just make a heuristic guess based on a magic (possibly)
+ target-specific constant and size of the loop.
+
+ 4) Determine which of the references we prefetch. We take into account
+ that there is a maximum number of simultaneous prefetches (provided
+ by machine description). We prefetch as many prefetches as possible
+ while still within this bound (starting with those with lowest
+ prefetch_mod, since they are responsible for most of the cache
+ misses).
+
+ 5) We unroll and peel loops so that we are able to satisfy PREFETCH_MOD
+ and PREFETCH_BEFORE requirements (within some bounds), and to avoid
+ prefetching nonaccessed memory.
+ TODO -- actually implement peeling.
+
+ 6) We actually emit the prefetch instructions. ??? Perhaps emit the
+ prefetch instructions with guards in cases where 5) was not sufficient
+ to satisfy the constraints?
+
+ Some other TODO:
+ -- write and use more general reuse analysis (that could be also used
+ in other cache aimed loop optimizations)
+ -- make it behave sanely together with the prefetches given by user
+ (now we just ignore them; at the very least we should avoid
+ optimizing loops in that user put his own prefetches)
+ -- we assume cache line size alignment of arrays; this could be
+ improved. */
+
+/* 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 WRITE_CAN_USE_READ_PREFETCH 1
+#endif
+
+/* True if read can be prefetched by a write prefetch. */
+
+#ifndef READ_CAN_USE_WRITE_PREFETCH
+#define READ_CAN_USE_WRITE_PREFETCH 0
+#endif
+
+/* Cache line size. Assumed to be a power of two. */
+
+#ifndef PREFETCH_BLOCK
+#define PREFETCH_BLOCK 32
+#endif
+
+/* Do we have a forward hardware sequential prefetching? */
+
+#ifndef HAVE_FORWARD_PREFETCH
+#define HAVE_FORWARD_PREFETCH 0
+#endif
+
+/* Do we have a backward hardware sequential prefetching? */
+
+#ifndef HAVE_BACKWARD_PREFETCH
+#define HAVE_BACKWARD_PREFETCH 0
+#endif
+
+/* In some cases we are only able to determine that there is a certain
+ probability that the two accesses hit the same cache line. In this
+ case, we issue the prefetches for both of them if this probability
+ is less then (1000 - ACCEPTABLE_MISS_RATE) promile. */
+
+#ifndef ACCEPTABLE_MISS_RATE
+#define ACCEPTABLE_MISS_RATE 50
+#endif
+
+#ifndef HAVE_prefetch
+#define HAVE_prefetch 0
+#endif
+
+/* The group of references between that reuse may occur. */
+
+struct mem_ref_group
+{
+ tree base; /* Base of the reference. */
+ HOST_WIDE_INT step; /* Step of the reference. */
+ struct mem_ref *refs; /* References in the group. */
+ struct mem_ref_group *next; /* Next group of references. */
+};
+
+/* Assigned to PREFETCH_BEFORE when all iterations are to be prefetched. */
+
+#define PREFETCH_ALL (~(unsigned HOST_WIDE_INT) 0)
+
+/* The memory reference. */
+
+struct mem_ref
+{
+ 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
+ iteration. */
+ unsigned HOST_WIDE_INT prefetch_before;
+ /* Prefetch only first PREFETCH_BEFORE
+ iterations. */
+ bool issue_prefetch_p; /* Should we really issue the prefetch? */
+ struct mem_ref *next; /* The next reference in the group. */
+};
+
+/* Dumps information obout reference REF to FILE. */
+
+static void
+dump_mem_ref (FILE *file, struct mem_ref *ref)
+{
+ fprintf (file, "Reference %p:\n", (void *) ref);
+
+ fprintf (file, " group %p (base ", (void *) ref->group);
+ print_generic_expr (file, ref->group->base, TDF_SLIM);
+ fprintf (file, ", step ");
+ fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->group->step);
+ fprintf (file, ")\n");
+
+ fprintf (dump_file, " delta ");
+ fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->delta);
+ fprintf (file, "\n");
+
+ fprintf (file, " %s\n", ref->write_p ? "write" : "read");
+
+ fprintf (file, "\n");
+}
+
+/* Finds a group with BASE and STEP in GROUPS, or creates one if it does not
+ exist. */
+
+static struct mem_ref_group *
+find_or_create_group (struct mem_ref_group **groups, tree base,
+ HOST_WIDE_INT step)
+{
+ struct mem_ref_group *group;
+
+ for (; *groups; groups = &(*groups)->next)
+ {
+ if ((*groups)->step == step
+ && operand_equal_p ((*groups)->base, base, 0))
+ return *groups;
+
+ /* Keep the list of groups sorted by decreasing step. */
+ if ((*groups)->step < step)
+ break;
+ }
+
+ group = xcalloc (1, sizeof (struct mem_ref_group));
+ group->base = base;
+ group->step = step;
+ group->refs = NULL;
+ group->next = *groups;
+ *groups = group;
+
+ return group;
+}
+
+/* Records a memory reference MEM in GROUP with offset DELTA and write status
+ WRITE_P. The reference occurs in statement STMT. */
+
+static void
+record_ref (struct mem_ref_group *group, tree stmt, tree mem,
+ HOST_WIDE_INT delta, bool write_p)
+{
+ struct mem_ref **aref;
+
+ /* Do not record the same address twice. */
+ for (aref = &group->refs; *aref; aref = &(*aref)->next)
+ {
+ /* It does not have to be possible for write reference to reuse the read
+ prefetch, or vice versa. */
+ if (!WRITE_CAN_USE_READ_PREFETCH
+ && write_p
+ && !(*aref)->write_p)
+ continue;
+ if (!READ_CAN_USE_WRITE_PREFETCH
+ && !write_p
+ && (*aref)->write_p)
+ continue;
+
+ if ((*aref)->delta == delta)
+ return;
+ }
+
+ (*aref) = xcalloc (1, sizeof (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)->issue_prefetch_p = false;
+ (*aref)->group = group;
+ (*aref)->next = NULL;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ dump_mem_ref (dump_file, *aref);
+}
+
+/* Release memory references in GROUPS. */
+
+static void
+release_mem_refs (struct mem_ref_group *groups)
+{
+ struct mem_ref_group *next_g;
+ struct mem_ref *ref, *next_r;
+
+ for (; groups; groups = next_g)
+ {
+ next_g = groups->next;
+ for (ref = groups->refs; ref; ref = next_r)
+ {
+ next_r = ref->next;
+ free (ref);
+ }
+ free (groups);
+ }
+}
+
+/* A structure used to pass arguments to idx_analyze_ref. */
+
+struct ar_data
+{
+ struct loop *loop; /* Loop of the reference. */
+ tree stmt; /* Statement of the reference. */
+ HOST_WIDE_INT *step; /* Step of the memory reference. */
+ HOST_WIDE_INT *delta; /* Offset of the memory reference. */
+};
+
+/* Analyzes a single INDEX of a memory reference to obtain information
+ described at analyze_ref. Callback for for_each_index. */
+
+static bool
+idx_analyze_ref (tree base, tree *index, void *data)
+{
+ struct ar_data *ar_data = data;
+ tree ibase, step, stepsize;
+ HOST_WIDE_INT istep, idelta = 0, imult = 1;
+ affine_iv iv;
+
+ if (TREE_CODE (base) == MISALIGNED_INDIRECT_REF
+ || TREE_CODE (base) == ALIGN_INDIRECT_REF)
+ return false;
+
+ if (!simple_iv (ar_data->loop, ar_data->stmt, *index, &iv, false))
+ return false;
+ 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 (TREE_CODE (ibase) == PLUS_EXPR
+ && cst_and_fits_in_hwi (TREE_OPERAND (ibase, 1)))
+ {
+ idelta = int_cst_value (TREE_OPERAND (ibase, 1));
+ ibase = TREE_OPERAND (ibase, 0);
+ }
+ if (cst_and_fits_in_hwi (ibase))
+ {
+ idelta += int_cst_value (ibase);
+ ibase = build_int_cst_type (TREE_TYPE (ibase), 0);
+ }
+
+ if (TREE_CODE (base) == ARRAY_REF)
+ {
+ stepsize = array_ref_element_size (base);
+ if (!cst_and_fits_in_hwi (stepsize))
+ return false;
+ imult = int_cst_value (stepsize);
+
+ istep *= imult;
+ idelta *= imult;
+ }
+
+ *ar_data->step += istep;
+ *ar_data->delta += idelta;
+ *index = ibase;
+
+ return true;
+}
+
+/* Tries to express REF 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. */
+
+static bool
+analyze_ref (struct loop *loop, tree ref, tree *base,
+ HOST_WIDE_INT *step, HOST_WIDE_INT *delta,
+ tree stmt)
+{
+ struct ar_data ar_data;
+ tree off;
+ HOST_WIDE_INT bit_offset;
+
+ *step = 0;
+ *delta = 0;
+
+ /* First strip off the component references. Ignore bitfields. */
+ if (TREE_CODE (ref) == COMPONENT_REF
+ && DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1)))
+ ref = TREE_OPERAND (ref, 0);
+
+ for (; TREE_CODE (ref) == COMPONENT_REF; ref = TREE_OPERAND (ref, 0))
+ {
+ off = DECL_FIELD_BIT_OFFSET (TREE_OPERAND (ref, 1));
+ bit_offset = TREE_INT_CST_LOW (off);
+ gcc_assert (bit_offset % BITS_PER_UNIT == 0);
+
+ *delta += bit_offset / BITS_PER_UNIT;
+ }
+
+ *base = unshare_expr (ref);
+ ar_data.loop = loop;
+ ar_data.stmt = stmt;
+ ar_data.step = step;
+ ar_data.delta = delta;
+ return for_each_index (base, idx_analyze_ref, &ar_data);
+}
+
+/* Record a memory reference REF to the list REFS. The reference occurs in
+ LOOP in statement STMT and it is write if WRITE_P. */
+
+static void
+gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs,
+ tree ref, bool write_p, tree stmt)
+{
+ tree base;
+ HOST_WIDE_INT step, delta;
+ struct mem_ref_group *agrp;
+
+ if (!analyze_ref (loop, ref, &base, &step, &delta, stmt))
+ return;
+
+ /* 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);
+}
+
+/* Record the suitable memory references in LOOP. */
+
+static struct mem_ref_group *
+gather_memory_references (struct loop *loop)
+{
+ basic_block *body = get_loop_body_in_dom_order (loop);
+ basic_block bb;
+ unsigned i;
+ block_stmt_iterator bsi;
+ tree stmt, lhs, rhs;
+ struct mem_ref_group *refs = NULL;
+
+ /* Scan the loop body in order, so that the former references precede the
+ later ones. */
+ for (i = 0; i < loop->num_nodes; i++)
+ {
+ bb = body[i];
+ if (bb->loop_father != loop)
+ continue;
+
+ for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
+ {
+ stmt = bsi_stmt (bsi);
+ if (TREE_CODE (stmt) != MODIFY_EXPR)
+ continue;
+
+ lhs = TREE_OPERAND (stmt, 0);
+ rhs = TREE_OPERAND (stmt, 1);
+
+ if (REFERENCE_CLASS_P (rhs))
+ gather_memory_references_ref (loop, &refs, rhs, false, stmt);
+ if (REFERENCE_CLASS_P (lhs))
+ gather_memory_references_ref (loop, &refs, lhs, true, stmt);
+ }
+ }
+ free (body);
+
+ return refs;
+}
+
+/* Prune the prefetch candidate REF using the self-reuse. */
+
+static void
+prune_ref_by_self_reuse (struct mem_ref *ref)
+{
+ HOST_WIDE_INT step = ref->group->step;
+ bool backward = step < 0;
+
+ if (step == 0)
+ {
+ /* Prefetch references to invariant address just once. */
+ ref->prefetch_before = 1;
+ return;
+ }
+
+ if (backward)
+ step = -step;
+
+ if (step > PREFETCH_BLOCK)
+ return;
+
+ if ((backward && HAVE_BACKWARD_PREFETCH)
+ || (!backward && HAVE_FORWARD_PREFETCH))
+ {
+ ref->prefetch_before = 1;
+ return;
+ }
+
+ ref->prefetch_mod = PREFETCH_BLOCK / step;
+}
+
+/* Divides X by BY, rounding down. */
+
+static HOST_WIDE_INT
+ddown (HOST_WIDE_INT x, unsigned HOST_WIDE_INT by)
+{
+ gcc_assert (by > 0);
+
+ if (x >= 0)
+ return x / by;
+ else
+ return (x + by - 1) / by;
+}
+
+/* Prune the prefetch candidate REF using the reuse with BY.
+ If BY_IS_BEFORE is true, BY is before REF in the loop. */
+
+static void
+prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by,
+ bool by_is_before)
+{
+ HOST_WIDE_INT step = ref->group->step;
+ bool backward = step < 0;
+ HOST_WIDE_INT delta_r = ref->delta, delta_b = by->delta;
+ HOST_WIDE_INT delta = delta_b - delta_r;
+ HOST_WIDE_INT hit_from;
+ unsigned HOST_WIDE_INT prefetch_before, prefetch_block;
+
+ if (delta == 0)
+ {
+ /* If the references has the same address, only prefetch the
+ former. */
+ if (by_is_before)
+ ref->prefetch_before = 0;
+
+ return;
+ }
+
+ if (!step)
+ {
+ /* If the reference addresses are invariant and fall into the
+ same cache line, prefetch just the first one. */
+ if (!by_is_before)
+ return;
+
+ if (ddown (ref->delta, PREFETCH_BLOCK)
+ != ddown (by->delta, PREFETCH_BLOCK))
+ return;
+
+ ref->prefetch_before = 0;
+ return;
+ }
+
+ /* Only prune the reference that is behind in the array. */
+ if (backward)
+ {
+ if (delta > 0)
+ return;
+
+ /* Transform the data so that we may assume that the accesses
+ are forward. */
+ delta = - delta;
+ step = -step;
+ delta_r = PREFETCH_BLOCK - 1 - delta_r;
+ delta_b = PREFETCH_BLOCK - 1 - delta_b;
+ }
+ else
+ {
+ if (delta < 0)
+ return;
+ }
+
+ /* Check whether the two references are likely to hit the same cache
+ line, and how distant the iterations in that it occurs are from
+ each other. */
+
+ if (step <= PREFETCH_BLOCK)
+ {
+ /* The accesses are sure to meet. Let us check when. */
+ hit_from = ddown (delta_b, PREFETCH_BLOCK) * PREFETCH_BLOCK;
+ prefetch_before = (hit_from - delta_r + step - 1) / step;
+
+ if (prefetch_before < ref->prefetch_before)
+ ref->prefetch_before = prefetch_before;
+
+ return;
+ }
+
+ /* A more complicated case. First let us ensure that size of cache line
+ and step are coprime (here we assume that PREFETCH_BLOCK is a power
+ of two. */
+ prefetch_block = PREFETCH_BLOCK;
+ while ((step & 1) == 0
+ && prefetch_block > 1)
+ {
+ step >>= 1;
+ prefetch_block >>= 1;
+ delta >>= 1;
+ }
+
+ /* Now step > prefetch_block, and step and prefetch_block are coprime.
+ Determine the probability that the accesses hit the same cache line. */
+
+ prefetch_before = delta / step;
+ delta %= step;
+ if ((unsigned HOST_WIDE_INT) delta
+ <= (prefetch_block * ACCEPTABLE_MISS_RATE / 1000))
+ {
+ if (prefetch_before < ref->prefetch_before)
+ ref->prefetch_before = prefetch_before;
+
+ return;
+ }
+
+ /* Try also the following iteration. */
+ prefetch_before++;
+ delta = step - delta;
+ if ((unsigned HOST_WIDE_INT) delta
+ <= (prefetch_block * ACCEPTABLE_MISS_RATE / 1000))
+ {
+ if (prefetch_before < ref->prefetch_before)
+ ref->prefetch_before = prefetch_before;
+
+ return;
+ }
+
+ /* The ref probably does not reuse by. */
+ return;
+}
+
+/* Prune the prefetch candidate REF using the reuses with other references
+ in REFS. */
+
+static void
+prune_ref_by_reuse (struct mem_ref *ref, struct mem_ref *refs)
+{
+ struct mem_ref *prune_by;
+ bool before = true;
+
+ prune_ref_by_self_reuse (ref);
+
+ for (prune_by = refs; prune_by; prune_by = prune_by->next)
+ {
+ if (prune_by == ref)
+ {
+ before = false;
+ continue;
+ }
+
+ if (!WRITE_CAN_USE_READ_PREFETCH
+ && ref->write_p
+ && !prune_by->write_p)
+ continue;
+ if (!READ_CAN_USE_WRITE_PREFETCH
+ && !ref->write_p
+ && prune_by->write_p)
+ continue;
+
+ prune_ref_by_group_reuse (ref, prune_by, before);
+ }
+}
+
+/* Prune the prefetch candidates in GROUP using the reuse analysis. */
+
+static void
+prune_group_by_reuse (struct mem_ref_group *group)
+{
+ struct mem_ref *ref_pruned;
+
+ for (ref_pruned = group->refs; ref_pruned; ref_pruned = ref_pruned->next)
+ {
+ prune_ref_by_reuse (ref_pruned, group->refs);
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Reference %p:", (void *) ref_pruned);
+
+ if (ref_pruned->prefetch_before == PREFETCH_ALL
+ && ref_pruned->prefetch_mod == 1)
+ fprintf (dump_file, " no restrictions");
+ else if (ref_pruned->prefetch_before == 0)
+ fprintf (dump_file, " do not prefetch");
+ else if (ref_pruned->prefetch_before <= ref_pruned->prefetch_mod)
+ fprintf (dump_file, " prefetch once");
+ else
+ {
+ if (ref_pruned->prefetch_before != PREFETCH_ALL)
+ {
+ fprintf (dump_file, " prefetch before ");
+ fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC,
+ ref_pruned->prefetch_before);
+ }
+ if (ref_pruned->prefetch_mod != 1)
+ {
+ fprintf (dump_file, " prefetch mod ");
+ fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC,
+ ref_pruned->prefetch_mod);
+ }
+ }
+ fprintf (dump_file, "\n");
+ }
+ }
+}
+
+/* Prune the list of prefetch candidates GROUPS using the reuse analysis. */
+
+static void
+prune_by_reuse (struct mem_ref_group *groups)
+{
+ for (; groups; groups = groups->next)
+ prune_group_by_reuse (groups);
+}
+
+/* Returns true if we should issue prefetch for REF. */
+
+static bool
+should_issue_prefetch_p (struct mem_ref *ref)
+{
+ /* For now do not issue prefetches for only first few of the
+ iterations. */
+ if (ref->prefetch_before != PREFETCH_ALL)
+ return false;
+
+ return true;
+}
+
+/* Decide which of the prefetch candidates in GROUPS to prefetch.
+ AHEAD is the number of iterations to prefetch ahead (which corresponds
+ to the number of simultaneous instances of one prefetch running at a
+ time). UNROLL_FACTOR is the factor by that the loop is going to be
+ unrolled. Returns true if there is anything to prefetch. */
+
+static bool
+schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor,
+ unsigned ahead)
+{
+ unsigned max_prefetches, n_prefetches;
+ struct mem_ref *ref;
+ bool any = false;
+
+ max_prefetches = (SIMULTANEOUS_PREFETCHES * unroll_factor) / ahead;
+ if (max_prefetches > (unsigned) SIMULTANEOUS_PREFETCHES)
+ max_prefetches = SIMULTANEOUS_PREFETCHES;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, "Max prefetches to issue: %d.\n", max_prefetches);
+
+ if (!max_prefetches)
+ return false;
+
+ /* 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. */
+
+ 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. */
+ n_prefetches = ((unroll_factor + ref->prefetch_mod - 1)
+ / ref->prefetch_mod);
+ if (max_prefetches <= n_prefetches)
+ return true;
+
+ max_prefetches -= n_prefetches;
+ any = true;
+ }
+
+ return any;
+}
+
+/* Determine whether there is any reference suitable for prefetching
+ in GROUPS. */
+
+static bool
+anything_to_prefetch_p (struct mem_ref_group *groups)
+{
+ struct mem_ref *ref;
+
+ for (; groups; groups = groups->next)
+ for (ref = groups->refs; ref; ref = ref->next)
+ if (should_issue_prefetch_p (ref))
+ return true;
+
+ return false;
+}
+
+/* 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. */
+
+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;
+ block_stmt_iterator bsi;
+ unsigned n_prefetches, ap;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, "Issued prefetch for %p.\n", (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);
+
+ 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);
+
+ /* 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);
+ bsi_insert_before (&bsi, prefetch, BSI_SAME_STMT);
+ }
+}
+
+/* Issue prefetches for the references in GROUPS into loop as decided before.
+ HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR is the
+ factor by that LOOP was unrolled. */
+
+static void
+issue_prefetches (struct mem_ref_group *groups,
+ unsigned unroll_factor, unsigned ahead)
+{
+ struct mem_ref *ref;
+
+ for (; groups; groups = groups->next)
+ for (ref = groups->refs; ref; ref = ref->next)
+ if (ref->issue_prefetch_p)
+ issue_prefetch_ref (ref, unroll_factor, ahead);
+}
+
+/* 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. */
+
+static bool
+should_unroll_loop_p (struct loop *loop, struct tree_niter_desc *desc,
+ unsigned factor)
+{
+ if (!can_unroll_loop_p (loop, factor, desc))
+ return false;
+
+ /* We only consider loops without control flow for unrolling. This is not
+ a hard restriction -- tree_unroll_loop works with arbitrary loops
+ as well; but the unrolling/prefetching is usually more profitable for
+ loops consisting of a single basic block, and we want to limit the
+ code growth. */
+ if (loop->num_nodes > 2)
+ return false;
+
+ return true;
+}
+
+/* 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. */
+
+static unsigned
+determine_unroll_factor (struct loop *loop, struct mem_ref_group *refs,
+ unsigned ahead, unsigned ninsns,
+ struct tree_niter_desc *desc)
+{
+ unsigned upper_bound, size_factor, constraint_factor;
+ unsigned factor, max_mod_constraint, ahead_factor;
+ 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)
+ return 1;
+
+ if (size_factor < upper_bound)
+ upper_bound = size_factor;
+
+ max_mod_constraint = 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_unroll_loop_p (loop, desc, factor))
+ return 1;
+
+ return factor;
+}
+
+/* Issue prefetch instructions for array references in LOOP. Returns
+ true if the LOOP was unrolled. LOOPS is the array containing all
+ loops. */
+
+static bool
+loop_prefetch_arrays (struct loops *loops, struct loop *loop)
+{
+ struct mem_ref_group *refs;
+ unsigned ahead, ninsns, unroll_factor;
+ struct tree_niter_desc desc;
+ bool unrolled = false;
+
+ /* Step 1: gather the memory references. */
+ refs = gather_memory_references (loop);
+
+ /* Step 2: estimate the reuse effects. */
+ prune_by_reuse (refs);
+
+ if (!anything_to_prefetch_p (refs))
+ goto fail;
+
+ /* 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);
+ 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;
+
+ /* Step 5: unroll the loop. TODO -- peeling of first and last few
+ iterations so that we do not issue superfluous prefetches. */
+ if (unroll_factor != 1)
+ {
+ tree_unroll_loop (loops, loop, unroll_factor,
+ single_dom_exit (loop), &desc);
+ unrolled = true;
+ }
+
+ /* Step 6: issue the prefetches. */
+ issue_prefetches (refs, unroll_factor, ahead);
+
+fail:
+ release_mem_refs (refs);
+ return unrolled;
+}
+
+/* Issue prefetch instructions for array references in LOOPS. */
+
+void
+tree_ssa_prefetch_arrays (struct loops *loops)
+{
+ unsigned i;
+ struct loop *loop;
+ bool unrolled = false;
+
+ if (!HAVE_prefetch
+ /* It is possible to ask compiler for say -mtune=i486 -march=pentium4.
+ -mtune=i486 causes us having PREFETCH_BLOCK 0, since this is part
+ of processor costs and i486 does not have prefetch, but
+ -march=pentium4 causes HAVE_prefetch to be true. Ugh. */
+ || PREFETCH_BLOCK == 0)
+ return;
+
+ initialize_original_copy_tables ();
+
+ if (!built_in_decls[BUILT_IN_PREFETCH])
+ {
+ tree type = build_function_type (void_type_node,
+ 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);
+ DECL_IS_NOVOPS (decl) = true;
+ built_in_decls[BUILT_IN_PREFETCH] = decl;
+ }
+
+ /* We assume that size of cache line is a power of two, so verify this
+ here. */
+ gcc_assert ((PREFETCH_BLOCK & (PREFETCH_BLOCK - 1)) == 0);
+
+ for (i = loops->num - 1; i > 0; i--)
+ {
+ 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);
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, "\n\n");
+ }
+
+ if (unrolled)
+ {
+ scev_reset ();
+ cleanup_tree_cfg_loop ();
+ }
+
+ free_original_copy_tables ();
+}
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