Initial check-in of gcc 4.7.2.

Change-Id: I4a2f5a921c21741a0e18bda986d77e5f1bef0365

1 files changed, 1946 insertions, 0 deletions

diff --git a/gcc-4.7/gcc/tree-ssa-loop-prefetch.c b/gcc-4.7/gcc/tree-ssa-loop-prefetch.c
new file mode 100644
index 000000000..264d97bc1
--- /dev/null
+++ b/gcc-4.7/gcc/tree-ssa-loop-prefetch.c
@@ -0,0 +1,1946 @@
+/* Array prefetching.
+   Copyright (C) 2005, 2007, 2008, 2009, 2010, 2011
+   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 3, 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 COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "tree.h"
+#include "tm_p.h"
+#include "basic-block.h"
+#include "output.h"
+#include "tree-pretty-print.h"
+#include "tree-flow.h"
+#include "tree-dump.h"
+#include "timevar.h"
+#include "cfgloop.h"
+#include "tree-pass.h"
+#include "insn-config.h"
+#include "recog.h"
+#include "hashtab.h"
+#include "tree-chrec.h"
+#include "tree-scalar-evolution.h"
+#include "diagnostic-core.h"
+#include "params.h"
+#include "langhooks.h"
+#include "tree-inline.h"
+#include "tree-data-ref.h"
+
+
+/* FIXME: Needed for optabs, but this should all be moved to a TBD interface
+   between the GIMPLE and RTL worlds.  */
+#include "expr.h"
+#include "optabs.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 (5) is the same with probability only
+	   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,
+      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?
+
+   A cost model is implemented to determine whether or not prefetching is
+   profitable for a given loop.  The cost model has three heuristics:
+
+   1. Function trip_count_to_ahead_ratio_too_small_p implements a
+      heuristic that determines whether or not the loop has too few
+      iterations (compared to ahead).  Prefetching is not likely to be
+      beneficial if the trip count to ahead ratio is below a certain
+      minimum.
+
+   2. Function mem_ref_count_reasonable_p implements a heuristic that
+      determines whether the given loop has enough CPU ops that can be
+      overlapped with cache missing memory ops.  If not, the loop
+      won't benefit from prefetching.  In the implementation,
+      prefetching is not considered beneficial if the ratio between
+      the instruction count and the mem ref count is below a certain
+      minimum.
+
+   3. Function insn_to_prefetch_ratio_too_small_p implements a
+      heuristic that disables prefetching in a loop if the prefetching
+      cost is above a certain limit.  The relative prefetching cost is
+      estimated by taking the ratio between the prefetch count and the
+      total intruction count (this models the I-cache cost).
+
+   The limits used in these heuristics are defined as parameters with
+   reasonable default values. Machine-specific default values will be
+   added later.
+
+   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.  */
+
+/* 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
+
+/* 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 L1_CACHE_LINE_SIZE
+#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) per thousand.  */
+
+#ifndef ACCEPTABLE_MISS_RATE
+#define ACCEPTABLE_MISS_RATE 50
+#endif
+
+#ifndef HAVE_prefetch
+#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
+
+/* It is not profitable to prefetch when the trip count is not at
+   least TRIP_COUNT_TO_AHEAD_RATIO times the prefetch ahead distance.
+   For example, in a loop with a prefetch ahead distance of 10,
+   supposing that TRIP_COUNT_TO_AHEAD_RATIO is equal to 4, it is
+   profitable to prefetch when the trip count is greater or equal to
+   40.  In that case, 30 out of the 40 iterations will benefit from
+   prefetching.  */
+
+#ifndef TRIP_COUNT_TO_AHEAD_RATIO
+#define TRIP_COUNT_TO_AHEAD_RATIO 4
+#endif
+
+/* The group of references between that reuse may occur.  */
+
+struct mem_ref_group
+{
+  tree base;			/* Base of the reference.  */
+  tree 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)
+
+/* Do not generate a prefetch if the unroll factor is significantly less
+   than what is required by the prefetch.  This is to avoid redundant
+   prefetches.  For example, when prefetch_mod is 16 and unroll_factor is
+   2, prefetching requires unrolling the loop 16 times, but
+   the loop is actually unrolled twice.  In this case (ratio = 8),
+   prefetching is not likely to be beneficial.  */
+
+#ifndef PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO
+#define PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO 4
+#endif
+
+/* Some of the prefetch computations have quadratic complexity.  We want to
+   avoid huge compile times and, therefore, want to limit the amount of
+   memory references per loop where we consider prefetching.  */
+
+#ifndef PREFETCH_MAX_MEM_REFS_PER_LOOP
+#define PREFETCH_MAX_MEM_REFS_PER_LOOP 200
+#endif
+
+/* The memory reference.  */
+
+struct mem_ref
+{
+  gimple stmt;			/* Statement in that the reference appears.  */
+  tree mem;			/* The reference.  */
+  HOST_WIDE_INT delta;		/* Constant offset of the reference.  */
+  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.  */
+  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 about 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 ");
+  if (cst_and_fits_in_hwi (ref->group->step))
+    fprintf (file, HOST_WIDE_INT_PRINT_DEC, int_cst_value (ref->group->step));
+  else
+    print_generic_expr (file, ref->group->step, TDF_TREE);
+  fprintf (file, ")\n");
+
+  fprintf (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, tree step)
+{
+  struct mem_ref_group *group;
+
+  for (; *groups; groups = &(*groups)->next)
+    {
+      if (operand_equal_p ((*groups)->step, step, 0)
+	  && operand_equal_p ((*groups)->base, base, 0))
+	return *groups;
+
+      /* If step is an integer constant, keep the list of groups sorted
+         by decreasing step.  */
+        if (cst_and_fits_in_hwi ((*groups)->step) && cst_and_fits_in_hwi (step)
+            && int_cst_value ((*groups)->step) < int_cst_value (step))
+	break;
+    }
+
+  group = XNEW (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, gimple 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) = 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);
+}
+
+/* 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.  */
+  gimple stmt;				/* Statement of the reference.  */
+  tree *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 = (struct ar_data *) data;
+  tree ibase, step, stepsize;
+  HOST_WIDE_INT idelta = 0, imult = 1;
+  affine_iv iv;
+
+  if (!simple_iv (ar_data->loop, loop_containing_stmt (ar_data->stmt),
+		  *index, &iv, true))
+    return false;
+  ibase = iv.base;
+  step = iv.step;
+
+  if (TREE_CODE (ibase) == POINTER_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 (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);
+      step = fold_build2 (MULT_EXPR, sizetype,
+			  fold_convert (sizetype, step),
+			  fold_convert (sizetype, stepsize));
+      idelta *= imult;
+    }
+
+  if (*ar_data->step == NULL_TREE)
+    *ar_data->step = step;
+  else
+    *ar_data->step = fold_build2 (PLUS_EXPR, sizetype,
+				  fold_convert (sizetype, *ar_data->step),
+				  fold_convert (sizetype, step));
+  *ar_data->delta += idelta;
+  *index = ibase;
+
+  return true;
+}
+
+/* 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.  Strips nonaddressable component
+   references from REF_P.  */
+
+static bool
+analyze_ref (struct loop *loop, tree *ref_p, tree *base,
+	     tree *step, HOST_WIDE_INT *delta,
+	     gimple stmt)
+{
+  struct ar_data ar_data;
+  tree off;
+  HOST_WIDE_INT bit_offset;
+  tree ref = *ref_p;
+
+  *step = NULL_TREE;
+  *delta = 0;
+
+  /* First strip off the component references.  Ignore bitfields.
+     Also strip off the real and imagine parts of a complex, so that
+     they can have the same base.  */
+  if (TREE_CODE (ref) == REALPART_EXPR
+      || TREE_CODE (ref) == IMAGPART_EXPR
+      || (TREE_CODE (ref) == COMPONENT_REF
+          && DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1))))
+    {
+      if (TREE_CODE (ref) == IMAGPART_EXPR)
+        *delta += int_size_in_bytes (TREE_TYPE (ref));
+      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));
+      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.  Returns true if the
+   reference was recorded, false otherwise.  */
+
+static bool
+gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs,
+			      tree ref, bool write_p, gimple stmt)
+{
+  tree base, step;
+  HOST_WIDE_INT delta;
+  struct mem_ref_group *agrp;
+
+  if (get_base_address (ref) == NULL)
+    return false;
+
+  if (!analyze_ref (loop, &ref, &base, &step, &delta, stmt))
+    return false;
+  /* If analyze_ref fails the default is a NULL_TREE.  We can stop here.  */
+  if (step == NULL_TREE)
+    return false;
+
+  /* Stop if the address of BASE could not be taken.  */
+  if (may_be_nonaddressable_p (base))
+    return false;
+
+  /* Limit non-constant step prefetching only to the innermost loops.  */
+  if (!cst_and_fits_in_hwi (step) && loop->inner != NULL)
+    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.  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, bool *no_other_refs, unsigned *ref_count)
+{
+  basic_block *body = get_loop_body_in_dom_order (loop);
+  basic_block bb;
+  unsigned i;
+  gimple_stmt_iterator bsi;
+  gimple stmt;
+  tree lhs, rhs;
+  struct mem_ref_group *refs = NULL;
+
+  *no_other_refs = true;
+  *ref_count = 0;
+
+  /* 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 = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi))
+	{
+	  stmt = gsi_stmt (bsi);
+
+	  if (gimple_code (stmt) != GIMPLE_ASSIGN)
+	    {
+	      if (gimple_vuse (stmt)
+		  || (is_gimple_call (stmt)
+		      && !(gimple_call_flags (stmt) & ECF_CONST)))
+		*no_other_refs = false;
+	      continue;
+	    }
+
+	  lhs = gimple_assign_lhs (stmt);
+	  rhs = gimple_assign_rhs1 (stmt);
+
+	  if (REFERENCE_CLASS_P (rhs))
+	    {
+	    *no_other_refs &= gather_memory_references_ref (loop, &refs,
+							    rhs, false, stmt);
+	    *ref_count += 1;
+	    }
+	  if (REFERENCE_CLASS_P (lhs))
+	    {
+	    *no_other_refs &= gather_memory_references_ref (loop, &refs,
+							    lhs, true, stmt);
+	    *ref_count += 1;
+	    }
+	}
+    }
+  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;
+  bool backward;
+
+  /* If the step size is non constant, we cannot calculate prefetch_mod.  */
+  if (!cst_and_fits_in_hwi (ref->group->step))
+    return;
+
+  step = int_cst_value (ref->group->step);
+
+  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;
+}
+
+/* Given a CACHE_LINE_SIZE and two inductive memory references
+   with a common STEP greater than CACHE_LINE_SIZE and an address
+   difference DELTA, compute the probability that they will fall
+   in different cache lines.  Return true if the computed miss rate
+   is not greater than the ACCEPTABLE_MISS_RATE.  DISTINCT_ITERS is the
+   number of distinct iterations after which the pattern repeats itself.
+   ALIGN_UNIT is the unit of alignment in bytes.  */
+
+static bool
+is_miss_rate_acceptable (unsigned HOST_WIDE_INT cache_line_size,
+		   HOST_WIDE_INT step, HOST_WIDE_INT delta,
+		   unsigned HOST_WIDE_INT distinct_iters,
+		   int align_unit)
+{
+  unsigned align, iter;
+  int total_positions, miss_positions, max_allowed_miss_positions;
+  int address1, address2, cache_line1, cache_line2;
+
+  /* It always misses if delta is greater than or equal to the cache
+     line size.  */
+  if (delta >= (HOST_WIDE_INT) cache_line_size)
+    return false;
+
+  miss_positions = 0;
+  total_positions = (cache_line_size / align_unit) * distinct_iters;
+  max_allowed_miss_positions = (ACCEPTABLE_MISS_RATE * total_positions) / 1000;
+
+  /* Iterate through all possible alignments of the first
+     memory reference within its cache line.  */
+  for (align = 0; align < cache_line_size; align += align_unit)
+
+    /* Iterate through all distinct iterations.  */
+    for (iter = 0; iter < distinct_iters; iter++)
+      {
+	address1 = align + step * iter;
+	address2 = address1 + delta;
+	cache_line1 = address1 / cache_line_size;
+	cache_line2 = address2 / cache_line_size;
+	if (cache_line1 != cache_line2)
+	  {
+	    miss_positions += 1;
+            if (miss_positions > max_allowed_miss_positions)
+	      return false;
+          }
+      }
+  return true;
+}
+
+/* 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;
+  bool backward;
+  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;
+  HOST_WIDE_INT reduced_step;
+  unsigned HOST_WIDE_INT reduced_prefetch_block;
+  tree ref_type;
+  int align_unit;
+
+  /* If the step is non constant we cannot calculate prefetch_before.  */
+  if (!cst_and_fits_in_hwi (ref->group->step)) {
+    return;
+  }
+
+  step = int_cst_value (ref->group->step);
+
+  backward = step < 0;
+
+
+  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;
+
+      /* Do not reduce prefetch_before if we meet beyond cache size.  */
+      if (prefetch_before > absu_hwi (L2_CACHE_SIZE_BYTES / step))
+        prefetch_before = PREFETCH_ALL;
+      if (prefetch_before < ref->prefetch_before)
+	ref->prefetch_before = prefetch_before;
+
+      return;
+    }
+
+  /* A more complicated case with step > prefetch_block.  First reduce
+     the ratio between the step and the cache line size to its simplest
+     terms.  The resulting denominator will then represent the number of
+     distinct iterations after which each address will go back to its
+     initial location within the cache line.  This computation assumes
+     that PREFETCH_BLOCK is a power of two.  */
+  prefetch_block = PREFETCH_BLOCK;
+  reduced_prefetch_block = prefetch_block;
+  reduced_step = step;
+  while ((reduced_step & 1) == 0
+	 && reduced_prefetch_block > 1)
+    {
+      reduced_step >>= 1;
+      reduced_prefetch_block >>= 1;
+    }
+
+  prefetch_before = delta / step;
+  delta %= step;
+  ref_type = TREE_TYPE (ref->mem);
+  align_unit = TYPE_ALIGN (ref_type) / 8;
+  if (is_miss_rate_acceptable (prefetch_block, step, delta,
+			       reduced_prefetch_block, align_unit))
+    {
+      /* Do not reduce prefetch_before if we meet beyond cache size.  */
+      if (prefetch_before > L2_CACHE_SIZE_BYTES / PREFETCH_BLOCK)
+        prefetch_before = PREFETCH_ALL;
+      if (prefetch_before < ref->prefetch_before)
+	ref->prefetch_before = prefetch_before;
+
+      return;
+    }
+
+  /* Try also the following iteration.  */
+  prefetch_before++;
+  delta = step - delta;
+  if (is_miss_rate_acceptable (prefetch_block, step, delta,
+			       reduced_prefetch_block, align_unit))
+    {
+      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)
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+        fprintf (dump_file, "Ignoring %p due to prefetch_before\n",
+		 (void *) ref);
+      return false;
+    }
+
+  /* Do not prefetch nontemporal stores.  */
+  if (ref->storent_p)
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+        fprintf (dump_file, "Ignoring nontemporal store %p\n", (void *) ref);
+      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 remaining_prefetch_slots, n_prefetches, prefetch_slots;
+  unsigned slots_per_prefetch;
+  struct mem_ref *ref;
+  bool any = false;
+
+  /* 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, "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 misses.  */
+
+  for (; groups; groups = groups->next)
+    for (ref = groups->refs; ref; ref = ref->next)
+      {
+	if (!should_issue_prefetch_p (ref))
+	  continue;
+
+        /* The loop is far from being sufficiently unrolled for this
+           prefetch.  Do not generate prefetch to avoid many redudant
+           prefetches.  */
+        if (ref->prefetch_mod / unroll_factor > PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO)
+          continue;
+
+	/* 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);
+	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;
+
+	ref->issue_prefetch_p = true;
+
+	if (remaining_prefetch_slots <= prefetch_slots)
+	  return true;
+	remaining_prefetch_slots -= prefetch_slots;
+	any = true;
+      }
+
+  return any;
+}
+
+/* Return TRUE if no prefetch is going to be generated in the given
+   GROUPS.  */
+
+static bool
+nothing_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 false;
+
+  return true;
+}
+
+/* Estimate the number of prefetches in the given GROUPS.
+   UNROLL_FACTOR is the factor by which LOOP was unrolled.  */
+
+static int
+estimate_prefetch_count (struct mem_ref_group *groups, unsigned unroll_factor)
+{
+  struct mem_ref *ref;
+  unsigned n_prefetches;
+  int prefetch_count = 0;
+
+  for (; groups; groups = groups->next)
+    for (ref = groups->refs; ref; ref = ref->next)
+      if (should_issue_prefetch_p (ref))
+	{
+	  n_prefetches = ((unroll_factor + ref->prefetch_mod - 1)
+			  / ref->prefetch_mod);
+	  prefetch_count += n_prefetches;
+	}
+
+  return prefetch_count;
+}
+
+/* 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 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, write_p, local, forward;
+  gimple prefetch;
+  gimple_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%s prefetch for %p.\n",
+	     nontemporal ? " nontemporal" : "",
+	     (void *) ref);
+
+  bsi = gsi_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_gsi (&bsi, unshare_expr (addr_base),
+					true, NULL, true, GSI_SAME_STMT);
+  write_p = ref->write_p ? integer_one_node : integer_zero_node;
+  local = nontemporal ? integer_zero_node : integer_three_node;
+
+  for (ap = 0; ap < n_prefetches; ap++)
+    {
+      if (cst_and_fits_in_hwi (ref->group->step))
+        {
+          /* Determine the address to prefetch.  */
+          delta = (ahead + ap * ref->prefetch_mod) *
+		   int_cst_value (ref->group->step);
+          addr = fold_build_pointer_plus_hwi (addr_base, delta);
+          addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, NULL,
+                                           true, GSI_SAME_STMT);
+        }
+      else
+        {
+          /* The step size is non-constant but loop-invariant.  We use the
+             heuristic to simply prefetch ahead iterations ahead.  */
+          forward = fold_build2 (MULT_EXPR, sizetype,
+                                 fold_convert (sizetype, ref->group->step),
+                                 fold_convert (sizetype, size_int (ahead)));
+          addr = fold_build_pointer_plus (addr_base, forward);
+          addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true,
+					   NULL, true, GSI_SAME_STMT);
+      }
+      /* Create the prefetch instruction.  */
+      prefetch = gimple_build_call (builtin_decl_explicit (BUILT_IN_PREFETCH),
+				    3, addr, write_p, local);
+      gsi_insert_before (&bsi, prefetch, GSI_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);
+}
+
+/* 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);
+  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);
+
+  gimple_assign_set_nontemporal_move (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;
+  gimple call;
+  gimple_stmt_iterator bsi;
+  unsigned i;
+
+  FOR_EACH_VEC_ELT (edge, exits, i, exit)
+    {
+      call = gimple_build_call (FENCE_FOLLOWING_MOVNT, 0);
+
+      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 = gsi_after_labels (exit->dest);
+
+      gsi_insert_before (&bsi, call, GSI_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_EACH_VEC_ELT (edge, exits, i, exit)
+	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.  */
+
+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.  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 ninsns, struct tree_niter_desc *desc,
+			 HOST_WIDE_INT est_niter)
+{
+  unsigned upper_bound;
+  unsigned nfactor, factor, mod_constraint;
+  struct mem_ref_group *agp;
+  struct mem_ref *ref;
+
+  /* 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;
+
+  /* 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))
+	{
+	  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_EACH_VEC_ELT (tree, access_fns, i, access_fn)
+    {
+      /* 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 = max_stmt_executions_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, loop_containing_stmt (ref->stmt),
+			      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_EACH_VEC_ELT (data_reference_p, datarefs, i, dr)
+    {
+      dist = self_reuse_distance (dr, loop_data_size, n, loop);
+      ref = (struct mem_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_EACH_VEC_ELT (ddr_p, dependences, i, dep)
+    {
+      if (DDR_ARE_DEPENDENT (dep) == chrec_known)
+	continue;
+
+      ref = (struct mem_ref *) DDR_A (dep)->aux;
+      refb = (struct mem_ref *) 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);
+    }
+}
+
+/* Determine whether or not the trip count to ahead ratio is too small based
+   on prefitablility consideration.
+   AHEAD: the iteration ahead distance,
+   EST_NITER: the estimated trip count.  */
+
+static bool
+trip_count_to_ahead_ratio_too_small_p (unsigned ahead, HOST_WIDE_INT est_niter)
+{
+  /* Assume trip count to ahead ratio is big enough if the trip count could not
+     be estimated at compile time.  */
+  if (est_niter < 0)
+    return false;
+
+  if (est_niter < (HOST_WIDE_INT) (TRIP_COUNT_TO_AHEAD_RATIO * ahead))
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file,
+		 "Not prefetching -- loop estimated to roll only %d times\n",
+		 (int) est_niter);
+      return true;
+    }
+
+  return false;
+}
+
+/* Determine whether or not the number of memory references in the loop is
+   reasonable based on the profitablity and compilation time considerations.
+   NINSNS: estimated number of instructions in the loop,
+   MEM_REF_COUNT: total number of memory references in the loop.  */
+
+static bool
+mem_ref_count_reasonable_p (unsigned ninsns, unsigned mem_ref_count)
+{
+  int insn_to_mem_ratio;
+
+  if (mem_ref_count == 0)
+    return false;
+
+  /* Miss rate computation (is_miss_rate_acceptable) and dependence analysis
+     (compute_all_dependences) have high costs based on quadratic complexity.
+     To avoid huge compilation time, we give up prefetching if mem_ref_count
+     is too large.  */
+  if (mem_ref_count > PREFETCH_MAX_MEM_REFS_PER_LOOP)
+    return false;
+
+  /* Prefetching improves performance by overlapping cache missing
+     memory accesses with CPU operations.  If the loop does not have
+     enough CPU operations to overlap with memory operations, prefetching
+     won't give a significant benefit.  One approximate way of checking
+     this is to require the ratio of instructions to memory references to
+     be above a certain limit.  This approximation works well in practice.
+     TODO: Implement a more precise computation by estimating the time
+     for each CPU or memory op in the loop. Time estimates for memory ops
+     should account for cache misses.  */
+  insn_to_mem_ratio = ninsns / mem_ref_count;
+
+  if (insn_to_mem_ratio < PREFETCH_MIN_INSN_TO_MEM_RATIO)
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+        fprintf (dump_file,
+		 "Not prefetching -- instruction to memory reference ratio (%d) too small\n",
+		 insn_to_mem_ratio);
+      return false;
+    }
+
+  return true;
+}
+
+/* Determine whether or not the instruction to prefetch ratio in the loop is
+   too small based on the profitablity consideration.
+   NINSNS: estimated number of instructions in the loop,
+   PREFETCH_COUNT: an estimate of the number of prefetches,
+   UNROLL_FACTOR:  the factor to unroll the loop if prefetching.  */
+
+static bool
+insn_to_prefetch_ratio_too_small_p (unsigned ninsns, unsigned prefetch_count,
+                                     unsigned unroll_factor)
+{
+  int insn_to_prefetch_ratio;
+
+  /* Prefetching most likely causes performance degradation when the instruction
+     to prefetch ratio is too small.  Too many prefetch instructions in a loop
+     may reduce the I-cache performance.
+     (unroll_factor * ninsns) is used to estimate the number of instructions in
+     the unrolled loop.  This implementation is a bit simplistic -- the number
+     of issued prefetch instructions is also affected by unrolling.  So,
+     prefetch_mod and the unroll factor should be taken into account when
+     determining prefetch_count.  Also, the number of insns of the unrolled
+     loop will usually be significantly smaller than the number of insns of the
+     original loop * unroll_factor (at least the induction variable increases
+     and the exit branches will get eliminated), so it might be better to use
+     tree_estimate_loop_size + estimated_unrolled_size.  */
+  insn_to_prefetch_ratio = (unroll_factor * ninsns) / prefetch_count;
+  if (insn_to_prefetch_ratio < MIN_INSN_TO_PREFETCH_RATIO)
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+        fprintf (dump_file,
+		 "Not prefetching -- instruction to prefetch ratio (%d) too small\n",
+		 insn_to_prefetch_ratio);
+      return true;
+    }
+
+  return false;
+}
+
+
+/* Issue prefetch instructions for array references in LOOP.  Returns
+   true if the LOOP was unrolled.  */
+
+static bool
+loop_prefetch_arrays (struct loop *loop)
+{
+  struct mem_ref_group *refs;
+  unsigned ahead, ninsns, time, unroll_factor;
+  HOST_WIDE_INT est_niter;
+  struct tree_niter_desc desc;
+  bool unrolled = false, no_other_refs;
+  unsigned prefetch_count;
+  unsigned mem_ref_count;
+
+  if (optimize_loop_nest_for_size_p (loop))
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file, "  ignored (cold area)\n");
+      return false;
+    }
+
+  /* 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);
+  if (time == 0)
+    return false;
+
+  ahead = (PREFETCH_LATENCY + time - 1) / time;
+  est_niter = max_stmt_executions_int (loop, false);
+
+  /* Prefetching is not likely to be profitable if the trip count to ahead
+     ratio is too small.  */
+  if (trip_count_to_ahead_ratio_too_small_p (ahead, est_niter))
+    return false;
+
+  ninsns = tree_num_loop_insns (loop, &eni_size_weights);
+
+  /* Step 1: gather the memory references.  */
+  refs = gather_memory_references (loop, &no_other_refs, &mem_ref_count);
+
+  /* Give up prefetching if the number of memory references in the
+     loop is not reasonable based on profitablity and compilation time
+     considerations.  */
+  if (!mem_ref_count_reasonable_p (ninsns, mem_ref_count))
+    goto fail;
+
+  /* Step 2: estimate the reuse effects.  */
+  prune_by_reuse (refs);
+
+  if (nothing_to_prefetch_p (refs))
+    goto fail;
+
+  determine_loop_nest_reuse (loop, refs, no_other_refs);
+
+  /* Step 3: determine unroll factor.  */
+  unroll_factor = determine_unroll_factor (loop, refs, ninsns, &desc,
+					   est_niter);
+
+  /* Estimate prefetch count for the unrolled loop.  */
+  prefetch_count = estimate_prefetch_count (refs, unroll_factor);
+  if (prefetch_count == 0)
+    goto fail;
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    fprintf (dump_file, "Ahead %d, unroll factor %d, trip count "
+	     HOST_WIDE_INT_PRINT_DEC "\n"
+	     "insn count %d, mem ref count %d, prefetch count %d\n",
+	     ahead, unroll_factor, est_niter,
+	     ninsns, mem_ref_count, prefetch_count);
+
+  /* Prefetching is not likely to be profitable if the instruction to prefetch
+     ratio is too small.  */
+  if (insn_to_prefetch_ratio_too_small_p (ninsns, prefetch_count,
+					  unroll_factor))
+    goto fail;
+
+  mark_nontemporal_stores (loop, refs);
+
+  /* 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 (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.  */
+
+unsigned int
+tree_ssa_prefetch_arrays (void)
+{
+  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.
+	 -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 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, "    min insn-to-prefetch ratio: %d \n",
+	       MIN_INSN_TO_PREFETCH_RATIO);
+      fprintf (dump_file, "    min insn-to-mem ratio: %d \n",
+	       PREFETCH_MIN_INSN_TO_MEM_RATIO);
+      fprintf (dump_file, "\n");
+    }
+
+  initialize_original_copy_tables ();
+
+  if (!builtin_decl_explicit_p (BUILT_IN_PREFETCH))
+    {
+      tree type = build_function_type_list (void_type_node,
+					    const_ptr_type_node, NULL_TREE);
+      tree decl = add_builtin_function ("__builtin_prefetch", type,
+					BUILT_IN_PREFETCH, BUILT_IN_NORMAL,
+					NULL, NULL_TREE);
+      DECL_IS_NOVOPS (decl) = true;
+      set_builtin_decl (BUILT_IN_PREFETCH, decl, false);
+    }
+
+  /* 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_EACH_LOOP (li, loop, LI_FROM_INNERMOST)
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file, "Processing loop %d:\n", loop->num);
+
+      unrolled |= loop_prefetch_arrays (loop);
+
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file, "\n\n");
+    }
+
+  if (unrolled)
+    {
+      scev_reset ();
+      todo_flags |= TODO_cleanup_cfg;
+    }
+
+  free_original_copy_tables ();
+  return todo_flags;
+}