diff --git a/gcc/cfgloop.h b/gcc/cfgloop.h
index 11378ca..c5bcca7 100644
--- a/gcc/cfgloop.h
+++ b/gcc/cfgloop.h
@@ -232,6 +232,9 @@ public:
      Other values means unroll with the given unrolling factor.  */
   unsigned short unroll;
 
+  /* Like unroll field above, but it's estimated in middle-end.  */
+  unsigned short estimated_unroll;
+
   /* If this loop was inlined the main clique of the callee which does
      not need remapping when copying the loop body.  */
   unsigned short owned_clique;
diff --git a/gcc/tree-ssa-loop-manip.c b/gcc/tree-ssa-loop-manip.c
index 120b35b..8a5a1a9 100644
--- a/gcc/tree-ssa-loop-manip.c
+++ b/gcc/tree-ssa-loop-manip.c
@@ -21,6 +21,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "system.h"
 #include "coretypes.h"
 #include "backend.h"
+#include "target.h"
 #include "tree.h"
 #include "gimple.h"
 #include "cfghooks.h"
@@ -42,6 +43,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "cfgloop.h"
 #include "tree-scalar-evolution.h"
 #include "tree-inline.h"
+#include "wide-int.h"
 
 /* All bitmaps for rewriting into loop-closed SSA go on this obstack,
    so that we can free them all at once.  */
@@ -1592,3 +1594,254 @@ canonicalize_loop_ivs (class loop *loop, tree *nit, bool bump_in_latch)
 
   return var_before;
 }
+
+/* Try to determine estimated unroll factor for given LOOP with constant number
+   of iterations, mainly refer to decide_unroll_constant_iterations.
+    - NITER_DESC holds number of iteration description if it isn't NULL.
+    - NUNROLL holds a unroll factor value computed with instruction numbers.
+    - ITER holds estimated or likely max loop iterations.
+   Return true if it succeeds, also update estimated_unroll.  */
+
+static bool
+decide_unroll_const_iter (class loop *loop, const tree_niter_desc *niter_desc,
+		      unsigned nunroll, const widest_int *iter)
+{
+  /* Skip big loops.  */
+  if (nunroll <= 1)
+    return false;
+
+  gcc_assert (niter_desc && niter_desc->assumptions);
+
+  /* Check number of iterations is constant, return false if no.  */
+  if ((niter_desc->may_be_zero && !integer_zerop (niter_desc->may_be_zero))
+      || !tree_fits_uhwi_p (niter_desc->niter))
+    return false;
+
+  unsigned HOST_WIDE_INT const_niter = tree_to_uhwi (niter_desc->niter);
+
+  /* If unroll factor is set explicitly, use it as estimated_unroll.  */
+  if (loop->unroll > 0 && loop->unroll < USHRT_MAX)
+    {
+      /* It should have been peeled instead.  */
+      if (const_niter == 0 || (unsigned) loop->unroll > const_niter - 1)
+	loop->estimated_unroll = 1;
+      else
+	loop->estimated_unroll = loop->unroll;
+      return true;
+    }
+
+  /* Check whether the loop rolls enough to consider.  */
+  if (const_niter < 2 * nunroll || wi::ltu_p (*iter, 2 * nunroll))
+    return false;
+
+  /* Success; now compute number of iterations to unroll.  */
+  unsigned best_unroll = 0, n_copies = 0;
+  unsigned best_copies = 2 * nunroll + 10;
+  unsigned i = 2 * nunroll + 2;
+
+  if (i > const_niter - 2)
+    i = const_niter - 2;
+
+  for (; i >= nunroll - 1; i--)
+    {
+      unsigned exit_mod = const_niter % (i + 1);
+
+      if (!empty_block_p (loop->latch))
+	n_copies = exit_mod + i + 1;
+      else if (exit_mod != i)
+	n_copies = exit_mod + i + 2;
+      else
+	n_copies = i + 1;
+
+      if (n_copies < best_copies)
+	{
+	  best_copies = n_copies;
+	  best_unroll = i;
+	}
+    }
+
+  loop->estimated_unroll = best_unroll + 1;
+  return true;
+}
+
+/* Try to determine estimated unroll factor for given LOOP with countable but
+   non-constant number of iterations, mainly refer to
+   decide_unroll_runtime_iterations.
+    - NITER_DESC holds number of iteration description if it isn't NULL.
+    - NUNROLL_IN holds a unroll factor value computed with instruction numbers.
+    - ITER holds estimated or likely max loop iterations.
+   Return true if it succeeds, also update estimated_unroll.  */
+
+static bool
+decide_unroll_runtime_iter (class loop *loop, const tree_niter_desc *niter_desc,
+			unsigned nunroll_in, const widest_int *iter)
+{
+  unsigned nunroll = nunroll_in;
+  if (loop->unroll > 0 && loop->unroll < USHRT_MAX)
+    nunroll = loop->unroll;
+
+  /* Skip big loops.  */
+  if (nunroll <= 1)
+    return false;
+
+  gcc_assert (niter_desc && niter_desc->assumptions);
+
+  /* Skip constant number of iterations.  */
+  if ((!niter_desc->may_be_zero || !integer_zerop (niter_desc->may_be_zero))
+      && tree_fits_uhwi_p (niter_desc->niter))
+    return false;
+
+  /* Check whether the loop rolls.  */
+  if (wi::ltu_p (*iter, 2 * nunroll))
+    return false;
+
+  /* Success; now force nunroll to be power of 2.  */
+  unsigned i;
+  for (i = 1; 2 * i <= nunroll; i *= 2)
+    continue;
+
+  loop->estimated_unroll = i;
+  return true;
+}
+
+/* Try to determine estimated unroll factor for given LOOP with uncountable
+   number of iterations, mainly refer to decide_unroll_stupid.
+    - NITER_DESC holds number of iteration description if it isn't NULL.
+    - NUNROLL_IN holds a unroll factor value computed with instruction numbers.
+    - ITER holds estimated or likely max loop iterations.
+   Return true if it succeeds, also update estimated_unroll.  */
+
+static bool
+decide_unroll_stupid (class loop *loop, const tree_niter_desc *niter_desc,
+		  unsigned nunroll_in, const widest_int *iter)
+{
+  if (!flag_unroll_all_loops && !loop->unroll)
+    return false;
+
+  unsigned nunroll = nunroll_in;
+  if (loop->unroll > 0 && loop->unroll < USHRT_MAX)
+    nunroll = loop->unroll;
+
+  /* Skip big loops.  */
+  if (nunroll <= 1)
+    return false;
+
+  gcc_assert (!niter_desc || !niter_desc->assumptions);
+
+  /* Skip loop with multiple branches for now.  */
+  if (num_loop_branches (loop) > 1)
+    return false;
+
+  /* Check whether the loop rolls.  */
+  if (wi::ltu_p (*iter, 2 * nunroll))
+    return false;
+
+  /* Success; now force nunroll to be power of 2.  */
+  unsigned i;
+  for (i = 1; 2 * i <= nunroll; i *= 2)
+    continue;
+
+  loop->estimated_unroll = i;
+  return true;
+}
+
+/* Try to estimate whether this given LOOP can be unrolled or not, and compute
+   its estimated unroll factor if it can.  To avoid duplicated computation, you
+   can pass number of iterations information by DESC.  The heuristics mainly
+   refer to decide_unrolling in loop-unroll.c.  */
+
+void
+estimate_unroll_factor (class loop *loop, tree_niter_desc *desc)
+{
+  /* Return the existing estimated unroll factor.  */
+  if (loop->estimated_unroll)
+    return;
+
+  /* Don't unroll explicitly.  */
+  if (loop->unroll == 1)
+    {
+      loop->estimated_unroll = loop->unroll;
+      return;
+    }
+
+  /* Like decide_unrolling, don't unroll if:
+     1) the loop is cold.
+     2) the loop can't be manipulated.
+     3) the loop isn't innermost.  */
+  if (optimize_loop_for_size_p (loop) || !can_duplicate_loop_p (loop)
+      || loop->inner != NULL)
+    {
+      loop->estimated_unroll = 1;
+      return;
+    }
+
+  /* Don't unroll without explicit information.  */
+  if (!loop->unroll && !flag_unroll_loops && !flag_unroll_all_loops)
+    {
+      loop->estimated_unroll = 1;
+      return;
+    }
+
+  /* Check for instruction number and average instruction number.  */
+  loop->ninsns = tree_num_loop_insns (loop, &eni_size_weights);
+  loop->av_ninsns = tree_average_num_loop_insns (loop, &eni_size_weights);
+  unsigned nunroll = param_max_unrolled_insns / loop->ninsns;
+  unsigned nunroll_by_av = param_max_average_unrolled_insns / loop->av_ninsns;
+
+  if (nunroll > nunroll_by_av)
+    nunroll = nunroll_by_av;
+  if (nunroll > (unsigned) param_max_unroll_times)
+    nunroll = param_max_unroll_times;
+
+  if (targetm.loop_unroll_adjust)
+    nunroll = targetm.loop_unroll_adjust (nunroll, loop);
+
+  tree_niter_desc *niter_desc = NULL;
+  bool desc_need_delete = false;
+
+  /* Compute number of iterations if need.  */
+  if (!desc)
+    {
+      /* For now, use single_dom_exit for simplicity. TODO: Support multiple
+	 exits like find_simple_exit if we finds some profitable cases.  */
+      niter_desc = XNEW (class tree_niter_desc);
+      gcc_assert (niter_desc);
+      edge exit = single_dom_exit (loop);
+      if (!exit || !number_of_iterations_exit (loop, exit, niter_desc, true))
+	{
+	  XDELETE (niter_desc);
+	  niter_desc = NULL;
+	}
+      else
+	desc_need_delete = true;
+    }
+  else
+    niter_desc = desc;
+
+  /* For checking the loop rolls enough to consider, also consult loop bounds
+     and profile.  */
+  widest_int iterations;
+  if (!get_estimated_loop_iterations (loop, &iterations)
+      && !get_likely_max_loop_iterations (loop, &iterations))
+    iterations = 0;
+
+  if (niter_desc && niter_desc->assumptions)
+    {
+      /* For countable loops.  */
+      if (!decide_unroll_const_iter (loop, niter_desc, nunroll, &iterations)
+	  && !decide_unroll_runtime_iter (loop, niter_desc, nunroll, &iterations))
+	loop->estimated_unroll = 1;
+    }
+  else
+    {
+      if (!decide_unroll_stupid (loop, niter_desc, nunroll, &iterations))
+	loop->estimated_unroll = 1;
+    }
+
+  if (desc_need_delete)
+    {
+      XDELETE (niter_desc);
+      niter_desc = NULL;
+    }
+}
+
diff --git a/gcc/tree-ssa-loop-manip.h b/gcc/tree-ssa-loop-manip.h
index e789e4f..773a2b3 100644
--- a/gcc/tree-ssa-loop-manip.h
+++ b/gcc/tree-ssa-loop-manip.h
@@ -55,7 +55,6 @@ extern void tree_transform_and_unroll_loop (class loop *, unsigned,
 extern void tree_unroll_loop (class loop *, unsigned,
 			      edge, class tree_niter_desc *);
 extern tree canonicalize_loop_ivs (class loop *, tree *, bool);
-
-
+extern void estimate_unroll_factor (class loop *, tree_niter_desc *);
 
 #endif /* GCC_TREE_SSA_LOOP_MANIP_H */
diff --git a/gcc/tree-ssa-loop.c b/gcc/tree-ssa-loop.c
index 5e8365d..25320fb 100644
--- a/gcc/tree-ssa-loop.c
+++ b/gcc/tree-ssa-loop.c
@@ -40,6 +40,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "diagnostic-core.h"
 #include "stringpool.h"
 #include "attribs.h"
+#include "sreal.h"
 
 
 /* A pass making sure loops are fixed up.  */
@@ -790,5 +791,37 @@ tree_num_loop_insns (class loop *loop, eni_weights *weights)
   return size;
 }
 
+/* Computes an estimated number of insns on average per iteration in LOOP,
+   weighted by WEIGHTS.  Refer to function average_num_loop_insns.  */
 
+unsigned
+tree_average_num_loop_insns (class loop *loop, eni_weights *weights)
+{
+  basic_block *body = get_loop_body (loop);
+  gimple_stmt_iterator gsi;
+  unsigned bb_size, i;
+  sreal nsize = 0;
+
+  for (i = 0; i < loop->num_nodes; i++)
+    {
+      bb_size = 0;
+      for (gsi = gsi_start_bb (body[i]); !gsi_end_p (gsi); gsi_next (&gsi))
+	bb_size += estimate_num_insns (gsi_stmt (gsi), weights);
+      nsize += (sreal) bb_size
+	       * body[i]->count.to_sreal_scale (loop->header->count);
+      /* Avoid overflows.   */
+      if (nsize > 1000000)
+	{
+	  free (body);
+	  return 1000000;
+	}
+    }
+  free (body);
+
+  unsigned ret = nsize.to_int ();
+  if (!ret)
+    ret = 1; /* To avoid division by zero.  */
+
+  return ret;
+}
 
diff --git a/gcc/tree-ssa-loop.h b/gcc/tree-ssa-loop.h
index 9e35125..af36177 100644
--- a/gcc/tree-ssa-loop.h
+++ b/gcc/tree-ssa-loop.h
@@ -67,6 +67,8 @@ public:
 extern bool for_each_index (tree *, bool (*) (tree, tree *, void *), void *);
 extern char *get_lsm_tmp_name (tree ref, unsigned n, const char *suffix = NULL);
 extern unsigned tree_num_loop_insns (class loop *, struct eni_weights *);
+extern unsigned tree_average_num_loop_insns (class loop *,
+					     struct eni_weights *);
 
 /* Returns the loop of the statement STMT.  */
 
