Re: [RFC][PR82479] missing popcount builtin detection

[Kugan Vivekanandarajah <kugan dot vivekanandarajah at linaro dot org>]

Hi Bin,

Thanks for the review. Please find the revised patch based on the
review comments.

Thanks,
Kugan

On 17 May 2018 at 19:56, Bin.Cheng <amker.cheng@gmail.com> wrote:
> On Thu, May 17, 2018 at 2:39 AM, Kugan Vivekanandarajah
> <kugan.vivekanandarajah@linaro.org> wrote:
>> Hi Richard,
>>
>> On 6 March 2018 at 02:24, Richard Biener <richard.guenther@gmail.com> wrote:
>>> On Thu, Feb 8, 2018 at 1:41 AM, Kugan Vivekanandarajah
>>> <kugan.vivekanandarajah@linaro.org> wrote:
>>>> Hi Richard,
>>>>
>>>> On 1 February 2018 at 23:21, Richard Biener <richard.guenther@gmail.com> wrote:
>>>>> On Thu, Feb 1, 2018 at 5:07 AM, Kugan Vivekanandarajah
>>>>> <kugan.vivekanandarajah@linaro.org> wrote:
>>>>>> Hi Richard,
>>>>>>
>>>>>> On 31 January 2018 at 21:39, Richard Biener <richard.guenther@gmail.com> wrote:
>>>>>>> On Wed, Jan 31, 2018 at 11:28 AM, Kugan Vivekanandarajah
>>>>>>> <kugan.vivekanandarajah@linaro.org> wrote:
>>>>>>>> Hi Richard,
>>>>>>>>
>>>>>>>> Thanks for the review.
>>>>>>>> On 25 January 2018 at 20:04, Richard Biener <richard.guenther@gmail.com> wrote:
>>>>>>>>> On Wed, Jan 24, 2018 at 10:56 PM, Kugan Vivekanandarajah
>>>>>>>>> <kugan.vivekanandarajah@linaro.org> wrote:
>>>>>>>>>> Hi All,
>>>>>>>>>>
>>>>>>>>>> Here is a patch for popcount builtin detection similar to LLVM. I
>>>>>>>>>> would like to queue this for review for next stage 1.
>>>>>>>>>>
>>>>>>>>>> 1. This is done part of loop-distribution and effective for -O3 and above.
>>>>>>>>>> 2. This does not distribute loop to detect popcount (like
>>>>>>>>>> memcpy/memmove). I dont think that happens in practice. Please correct
>>>>>>>>>> me if I am wrong.
>>>>>>>>>
>>>>>>>>> But then it has no business inside loop distribution but instead is
>>>>>>>>> doing final value
>>>>>>>>> replacement, right?  You are pattern-matching the whole loop after all.  I think
>>>>>>>>> final value replacement would already do the correct thing if you
>>>>>>>>> teached number of
>>>>>>>>> iteration analysis that niter for
>>>>>>>>>
>>>>>>>>>   <bb 3> [local count: 955630224]:
>>>>>>>>>   # b_11 = PHI <b_5(5), b_8(6)>
>>>>>>>>>   _1 = b_11 + -1;
>>>>>>>>>   b_8 = _1 & b_11;
>>>>>>>>>   if (b_8 != 0)
>>>>>>>>>     goto <bb 6>; [89.00%]
>>>>>>>>>   else
>>>>>>>>>     goto <bb 8>; [11.00%]
>>>>>>>>>
>>>>>>>>>   <bb 6> [local count: 850510900]:
>>>>>>>>>   goto <bb 3>; [100.00%]
>>>>>>>>
>>>>>>>> I am looking into this approach. What should be the scalar evolution
>>>>>>>> for b_8 (i.e. b & (b -1) in a loop) should be? This is not clear to me
>>>>>>>> and can this be represented with the scev?
>>>>>>>
>>>>>>> No, it's not affine and thus cannot be represented.  You only need the
>>>>>>> scalar evolution of the counting IV which is already handled and
>>>>>>> the number of iteration analysis needs to handle the above IV - this
>>>>>>> is the missing part.
>>>>>> Thanks for the clarification. I am now matching this loop pattern in
>>>>>> number_of_iterations_exit when number_of_iterations_exit_assumptions
>>>>>> fails. If the pattern matches, I am inserting the _builtin_popcount in
>>>>>> the loop preheater and setting the loop niter with this. This will be
>>>>>> used by the final value replacement. Is this what you wanted?
>>>>>
>>>>> No, you shouldn't insert a popcount stmt but instead the niter
>>>>> GENERIC tree should be a CALL_EXPR to popcount with the
>>>>> appropriate argument.
>>>>
>>>> Thats what I tried earlier but ran into some ICEs. I wasn't sure if
>>>> niter in tree_niter_desc can take such.
>>>>
>>>> Attached patch now does this. Also had to add support for CALL_EXPR in
>>>> few places to handle niter with CALL_EXPR. Does this look OK?
>>>
>>> Overall this looks ok - the patch includes changes in places that I don't think
>>> need changes such as chrec_convert_1 or extract_ops_from_tree.
>>> The expression_expensive_p change should be more specific than making
>>> all calls inexpensive as well.
>>
>> Changed it.
>>
>>>
>>> The verify_ssa change looks bogus, you do
>>>
>>> +  dest = gimple_phi_result (count_phi);
>>> +  tree var = make_ssa_name (TREE_TYPE (dest), NULL);
>>> +  tree fn = builtin_decl_implicit (BUILT_IN_POPCOUNT);
>>> +
>>> +  var = build_call_expr (fn, 1, src);
>>> +  *niter = fold_build2 (MINUS_EXPR, TREE_TYPE (dest), var,
>>> +                       build_int_cst (TREE_TYPE (dest), 1));
>>>
>>> why do you allocate a new SSA name here?  It seems unused
>>> as you overwrive 'var' with the CALL_EXPR immediately.
>> Changed now.
>>
>>>
>>> I didn't review the pattern matching thoroughly nor the exact place you
>>> call it.  But
>>>
>>> +      if (check_popcount_pattern (loop, &count))
>>> +       {
>>> +         niter->assumptions = boolean_false_node;
>>> +         niter->control.base = NULL_TREE;
>>> +         niter->control.step = NULL_TREE;
>>> +         niter->control.no_overflow = false;
>>> +         niter->niter = count;
>>> +         niter->assumptions = boolean_true_node;
>>> +         niter->may_be_zero = boolean_false_node;
>>> +         niter->max = -1;
>>> +         niter->bound = NULL_TREE;
>>> +         niter->cmp = ERROR_MARK;
>>> +         return true;
>>> +       }
>>>
>>> simply setting may_be_zero to false looks fishy.
>> Should I set this to (argument to popcount == zero)?
> No, I think that's unnecessary.  The number of iterations is computed
> as: may_be_zero ? 0 : niter;
> Here niter is ZERO even when may_be_zero is set to false, and niters
> is computed correctly.
>
> I think the point is that may_be_zero is false doesn't imply that
> niters is non-zero.
>
>>
>>> Try with -fno-tree-loop-ch.
>> I changed the pattern matching to handle loop without header copying
>> too. Looks a bit complicated checking all the conditions. Wondering if
>> this can be done in a simpler and easier to read way.
>>
>>>  Also max should not be negative,
>>> it should be the number of bits in the IV type?
>>
>> Changed this too.
>>>
>>> A related testcase could be that we can completely peel
>>> a loop like the following which iterates at most 8 times:
>>>
>>> int a[8];
>>> void foo (unsigned char ctrl)
>>> {
>>>   int c = 0;
>>>   while (ctrl)
>>>     {
>>>        ctrl = ctrl & (ctrl - 1);
>>>        a[c++] = ctrl;
>>>     }
>>> }
>>
>> Hmm, this is an interesting test case but as I am now trying to match
>> a loop which does popcount, this is not handled.
>>
>>
>> Attaching the current version for review.
> Here are some comments.
>
>> diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
>> index 7a54c5f..f390321 100644
>> --- a/gcc/tree-ssa-loop-niter.c
>> +++ b/gcc/tree-ssa-loop-niter.c
>> @@ -2430,6 +2430,134 @@ number_of_iterations_exit_assumptions (struct loop *loop, edge exit,
>>    return (!integer_zerop (niter->assumptions));
>>  }
>>
>> +/* See if LOOP is a popcout implementation of the form
>> +
>> +    int c = 0;
>> +    while (b) {
>> +    b = b & (b - 1);
>> +    c++;
>> +    }
>> +
>> +    If so, Set NITER to  __builtin_popcount (b) - 1
>> +    return true if we did, false otherwise.  */
>> +
>> +static bool
>> +check_popcount_pattern (loop_p loop, tree *niter, HOST_WIDE_INT *max)
>> +{
>> +  tree lhs, rhs;
>> +  tree dest;
>> +  gimple *and_minus_one;
>> +  gimple *phi;
>> +  int count = 0;
>> +  gimple *count_stmt = NULL;
>> +  bool adjust = true;
>> +
>> +  if (!single_exit (loop))
>> +    return false;
>> +
>> +  /* Check loop terminating branch is like
>> +     if (b != 0).  */
>> +  gimple *stmt = last_stmt (loop->header);
>> +  if (!stmt
>> +      || gimple_code (stmt) != GIMPLE_COND
>> +      || !zerop (gimple_cond_rhs (stmt)))
> The check doesn't fully match the comment.  NE is not checked here.
> Also can move below "(TREE_CODE (lhs) != SSA_NAME)" check up to this
> point, making simple checks earlier.
>
>> +    return false;
>> +
>> +  /* Check the loop closed SSA definition for just the variable c defined in
>> +     loop.  */
>> +  basic_block bb = single_exit (loop)->dest;
> single_exit is repeatedly called various times, call it once and use
> the returning edge instead?  I am not sure GCC is smart enough
> removing repeated call instances.  Same to loop_latch_edge.
>
>> +  for (gphi_iterator gpi = gsi_start_phis (bb);
>> +       !gsi_end_p (gpi); gsi_next (&gpi))
>> +    {
>> +      phi = gpi.phi ();
>> +      count++;
>> +    }
>> +
>> +  if (count != 1)
>> +    return false;
>> +
>> +  rhs = gimple_phi_arg_def (phi, single_exit (loop)->dest_idx);
>> +  if (TREE_CODE (rhs) != SSA_NAME)
>> +    return false;
>> +  count_stmt = SSA_NAME_DEF_STMT (rhs);
>> +  lhs = gimple_cond_lhs (stmt);
>> +  if (TREE_CODE (lhs) != SSA_NAME)
>> +    return false;
>> +  gimple *and_stmt = SSA_NAME_DEF_STMT (lhs);
>> +
>> +  /* Depending on copy-header is performed, feeding PHI stmts might be in
>> +     the loop header or loop exit, handle this.  */
>> +  if (gimple_code (count_stmt) == GIMPLE_PHI)
>> +    {
>> +      tree t;
>> +      if (gimple_code (and_stmt) != GIMPLE_PHI
>> +      || gimple_bb (and_stmt) != single_exit (loop)->src
>> +      || gimple_bb (count_stmt) != single_exit (loop)->src)
>> +    return false;
>> +      t = gimple_phi_arg_def (count_stmt, loop_latch_edge (loop)->dest_idx);
>> +      if (TREE_CODE (t) != SSA_NAME)
>> +    return false;
>> +      count_stmt = SSA_NAME_DEF_STMT (t);
>> +      t = gimple_phi_arg_def (and_stmt, loop_latch_edge (loop)->dest_idx);
>> +      if (TREE_CODE (t) != SSA_NAME)
>> +    return false;
>> +      and_stmt = SSA_NAME_DEF_STMT (t);
>> +      adjust = false;
>> +    }
>> +
>> +  /* Make sure we have a count by one.  */
>> +  if (!is_gimple_assign (count_stmt)
>> +      || (gimple_assign_rhs_code (count_stmt) != PLUS_EXPR)
>> +      || !integer_onep (gimple_assign_rhs2 (count_stmt)))
>> +    return false;
>> +
>> +  /* Cheeck "b = b & (b - 1)" is calculated.  */
> Typo.
>
>> +  if (!is_gimple_assign (and_stmt)
>> +      || gimple_assign_rhs_code (and_stmt) != BIT_AND_EXPR)
>> +    return false;
>> +
>> +  lhs = gimple_assign_rhs1 (and_stmt);
>> +  rhs = gimple_assign_rhs2 (and_stmt);
>> +  if (TREE_CODE (lhs) == SSA_NAME
>> +      && (and_minus_one = SSA_NAME_DEF_STMT (lhs))
>> +      && is_gimple_assign (and_minus_one)
>> +      && (gimple_assign_rhs_code (and_minus_one) == PLUS_EXPR)
>> +      && integer_minus_onep (gimple_assign_rhs2 (and_minus_one)))
>> +      lhs = rhs;
>> +  else if (TREE_CODE (rhs) == SSA_NAME
>> +      && (and_minus_one = SSA_NAME_DEF_STMT (rhs))
>> +      && is_gimple_assign (and_minus_one)
>> +      && (gimple_assign_rhs_code (and_minus_one) == PLUS_EXPR)
>> +      && integer_minus_onep (gimple_assign_rhs2 (and_minus_one)))
> Could you avoid duplication by factoring the condition into an inline
> function?  They are exactly the same for lhs/rhs.
>
>> +      ;
>> +  else
>> +    return false;
>> +
>> +  if ((gimple_assign_rhs1 (and_stmt) != gimple_assign_rhs1 (and_minus_one))
>> +      && (gimple_assign_rhs2 (and_stmt) != gimple_assign_rhs1 (and_minus_one)))
> Here you already got lhs correctly, so don't need to check on and_stmt
> rhs directly.  You can even merge this check into above one.
>
>> +    return false;
>> +
>> +  /* Check the recurrence.  */
>> +  phi = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (and_minus_one));
>> +  gimple *src_phi = SSA_NAME_DEF_STMT (lhs);
>> +  if (gimple_code (phi) != GIMPLE_PHI
>> +      || gimple_code (src_phi) != GIMPLE_PHI)
> I think this is redundant since you have lhs equals to
> gimple_assign_rhs1 (and_minus_one).  So phi == src_phi is always true?
>
>> +    return false;
>> +
>> +  dest = gimple_assign_lhs (count_stmt);
>> +  tree fn = builtin_decl_implicit (BUILT_IN_POPCOUNT);
>> +  tree src = gimple_phi_arg_def (src_phi, loop_preheader_edge (loop)->dest_idx);
>> +  if (adjust)
>> +    *niter = fold_build2 (MINUS_EXPR, TREE_TYPE (dest),
>> +              build_call_expr (fn, 1, src),
>> +              build_int_cst (TREE_TYPE (dest), 1));
>> +  else
>> +    *niter = build_call_expr (fn, 1, src);
>> +  *max = int_cst_value (TYPE_MAX_VALUE (TREE_TYPE (dest)));
>> +  return true;
>> +}
>> +
>> +
>>  /* Like number_of_iterations_exit_assumptions, but return TRUE only if
>>     the niter information holds unconditionally.  */
>>
>> @@ -2441,7 +2569,25 @@ number_of_iterations_exit (struct loop *loop, edge exit,
>>    gcond *stmt;
>>    if (!number_of_iterations_exit_assumptions (loop, exit, niter,
>>                            &stmt, every_iteration))
>> -    return false;
>> +    {
>> +      tree count;
>> +      HOST_WIDE_INT max;
>> +      if (check_popcount_pattern (loop, &count, &max))
>> +    {
>> +      niter->assumptions = boolean_false_node;
>> +      niter->control.base = NULL_TREE;
>> +      niter->control.step = NULL_TREE;
>> +      niter->control.no_overflow = false;
>> +      niter->niter = count;
>> +      niter->assumptions = boolean_true_node;
>> +      niter->may_be_zero = boolean_false_node;
>> +      niter->max = max;
>> +      niter->bound = NULL_TREE;
>> +      niter->cmp = ERROR_MARK;
>> +      return true;
>> +    }
> Better to merge these compound statement into check_popcount_pattern
> and rename it into something like number_of_iterations_popcount.
>
> I wondered if the more inefficient version popcount should be checked, like:
>
> int count = 0;
> while (x)
> {
>   count += x & 1;
>   x = x >> 1;
> }
>
> Thanks,
> bin
>
>> +      return false;
>> +    }
>>
>>    if (integer_nonzerop (niter->assumptions))
>>      return true;
>> --
>> 2.7.4
>>

From 413aafbb5d53812546c4af5f556f362aafdb32d4 Mon Sep 17 00:00:00 2001
From: Kugan Vivekanandarajah <kugan.vivekanandarajah@linaro.org>
Date: Thu, 10 May 2018 21:41:53 +1000
Subject: [PATCH] popcount

Change-Id: I2f796dd4518937495cc1855852b0dfa5c4ff1143
---
 gcc/ipa-fnsummary.c                       |   4 +
 gcc/testsuite/gcc.dg/tree-ssa/popcount.c  |  41 ++++++++
 gcc/testsuite/gcc.dg/tree-ssa/popcount2.c |  29 ++++++
 gcc/testsuite/gcc.dg/tree-ssa/popcount3.c |  28 ++++++
 gcc/tree-scalar-evolution.c               |   7 ++
 gcc/tree-ssa-loop-ivopts.c                |  10 ++
 gcc/tree-ssa-loop-niter.c                 | 156 +++++++++++++++++++++++++++++-
 7 files changed, 274 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/popcount.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/popcount2.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/popcount3.c

diff --git a/gcc/ipa-fnsummary.c b/gcc/ipa-fnsummary.c
index bdf9ba1..4dc156a 100644
--- a/gcc/ipa-fnsummary.c
+++ b/gcc/ipa-fnsummary.c
@@ -1485,6 +1485,10 @@ will_be_nonconstant_expr_predicate (struct ipa_node_params *info,
 					       nonconstant_names);
       return p2.or_with (summary->conds, p1);
     }
+  else if (TREE_CODE (expr) == CALL_EXPR)
+    {
+      return false;
+    }
   else
     {
       debug_tree (expr);
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/popcount.c b/gcc/testsuite/gcc.dg/tree-ssa/popcount.c
new file mode 100644
index 0000000..86a66cb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/popcount.c
@@ -0,0 +1,41 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-optimized" } */
+
+extern int foo (int);
+
+int PopCount (long b) {
+    int c = 0;
+    b++;
+
+    while (b) {
+	b &= b - 1;
+	c++;
+    }
+    return c;
+}
+int PopCount2 (long b) {
+    int c = 0;
+
+    while (b) {
+	b &= b - 1;
+	c++;
+    }
+    foo (c);
+    return foo (c);
+}
+
+void PopCount3 (long b1) {
+
+    for (long i = 0; i < b1; ++i)
+      {
+	long b = i;
+	int c = 0;
+	while (b) {
+	    b &= b - 1;
+	    c++;
+	}
+	foo (c);
+      }
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin_popcount" 3 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/popcount2.c b/gcc/testsuite/gcc.dg/tree-ssa/popcount2.c
new file mode 100644
index 0000000..52afc2d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/popcount2.c
@@ -0,0 +1,29 @@
+/* { dg-do execute } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int
+__attribute__ ((noinline, noclone))
+foo (int i, long b)
+{
+    int c = i;
+
+    while (b) {
+	b &= b - 1;
+	c++;
+    }
+    return c;
+}
+
+int main()
+{
+
+  if (foo (1, 7) != 4)
+   __builtin_abort ();
+  if (foo (0, 0) != 0)
+   __builtin_abort ();
+  if (foo (8, 0xff) != 16)
+   __builtin_abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin_popcount" 1 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/popcount3.c b/gcc/testsuite/gcc.dg/tree-ssa/popcount3.c
new file mode 100644
index 0000000..0c69d97
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/popcount3.c
@@ -0,0 +1,28 @@
+/* { dg-do execute } */
+/* { dg-options "-O2 -fno-tree-ch -fdump-tree-optimized" } */
+
+int
+__attribute__ ((noinline, noclone))
+foo (long b)
+{
+    int c = i;
+
+    while (b) {
+	b &= b - 1;
+	c++;
+    }
+    return c;
+}
+
+int main()
+{
+  if (foo (7) != 3)
+   __builtin_abort ();
+  if (foo (0) != 0)
+   __builtin_abort ();
+  if (foo (0xff) != 8)
+   __builtin_abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin_popcount" 1 "optimized" } } */
diff --git a/gcc/tree-scalar-evolution.c b/gcc/tree-scalar-evolution.c
index fefc9de..967b154 100644
--- a/gcc/tree-scalar-evolution.c
+++ b/gcc/tree-scalar-evolution.c
@@ -1984,6 +1984,7 @@ interpret_expr (struct loop *loop, gimple *at_stmt, tree expr)
     return expr;
 
   if (TREE_CODE (expr) == POLYNOMIAL_CHREC
+      || TREE_CODE (expr) == CALL_EXPR
       || get_gimple_rhs_class (TREE_CODE (expr)) == GIMPLE_TERNARY_RHS)
     return chrec_dont_know;
 
@@ -3472,6 +3473,7 @@ bool
 expression_expensive_p (tree expr)
 {
   enum tree_code code;
+  tree fndecl;
 
   if (is_gimple_val (expr))
     return false;
@@ -3492,6 +3494,11 @@ expression_expensive_p (tree expr)
       if (!integer_pow2p (TREE_OPERAND (expr, 1)))
 	return true;
     }
+  if (code == CALL_EXPR
+      && (fndecl = get_callee_fndecl (expr))
+      && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL
+      && (BUILT_IN_POPCOUNT == DECL_FUNCTION_CODE (fndecl)))
+    return false;
 
   switch (TREE_CODE_CLASS (code))
     {
diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index b313571..519649a 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -985,6 +985,16 @@ contains_abnormal_ssa_name_p (tree expr)
   code = TREE_CODE (expr);
   codeclass = TREE_CODE_CLASS (code);
 
+  if (code == CALL_EXPR)
+    {
+      tree arg;
+      call_expr_arg_iterator iter;
+      FOR_EACH_CALL_EXPR_ARG (arg, iter, expr)
+	if (contains_abnormal_ssa_name_p (arg))
+	  return true;
+      return false;
+    }
+
   if (code == SSA_NAME)
     return SSA_NAME_OCCURS_IN_ABNORMAL_PHI (expr) != 0;
 
diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
index 7a54c5f..66f9b4f 100644
--- a/gcc/tree-ssa-loop-niter.c
+++ b/gcc/tree-ssa-loop-niter.c
@@ -2430,6 +2430,156 @@ number_of_iterations_exit_assumptions (struct loop *loop, edge exit,
   return (!integer_zerop (niter->assumptions));
 }
 
+/* Utility function to check if OP is defined by a stmt
+   that is a val - 1.  If that is the case, set it to STMT.  */
+
+static bool
+ssa_defined_by_and_minus_one_stmt_p (tree op, tree val, gimple **stmt)
+{
+  if (TREE_CODE (op) == SSA_NAME
+      && (*stmt = SSA_NAME_DEF_STMT (op))
+      && is_gimple_assign (*stmt)
+      && (gimple_assign_rhs_code (*stmt) == PLUS_EXPR)
+      && val == gimple_assign_rhs1 (*stmt)
+      && integer_minus_onep (gimple_assign_rhs2 (*stmt)))
+    return true;
+  else
+    return false;
+}
+
+/* See if LOOP is a popcout implementation of the form
+
+    int c = 0;
+    while (b) {
+	b = b & (b - 1);
+	c++;
+    }
+
+    If popcount pattern, update NITER accordingly.
+    i.e., set NITER to  __builtin_popcount (b)
+    return true if we did, false otherwise.
+
+ */
+
+static bool
+number_of_iterations_popcount (loop_p loop, struct tree_niter_desc *niter)
+{
+  tree rhs1, rhs2;
+  tree dest;
+  gimple *and_minus_one;
+  gimple *phi;
+  int count = 0;
+  gimple *count_stmt = NULL;
+  bool adjust = true;
+  edge exit;
+  tree iter;
+  HOST_WIDE_INT max;
+
+  if (!(exit = single_exit (loop)))
+    return false;
+
+  /* Check loop terminating branch is like
+     if (b != 0).  */
+  gimple *stmt = last_stmt (loop->header);
+  if (!stmt
+      || gimple_code (stmt) != GIMPLE_COND
+      || gimple_cond_code (stmt) != NE_EXPR
+      || !zerop (gimple_cond_rhs (stmt))
+      || TREE_CODE (gimple_cond_lhs (stmt)) != SSA_NAME)
+    return false;
+
+  /* Check the loop closed SSA definition for just the variable c defined in
+     loop.  */
+  basic_block bb = exit->dest;
+  for (gphi_iterator gpi = gsi_start_phis (bb);
+       !gsi_end_p (gpi); gsi_next (&gpi))
+    {
+      phi = gpi.phi ();
+      count++;
+    }
+
+  if (count != 1)
+    return false;
+
+  rhs1 = gimple_phi_arg_def (phi, exit->dest_idx);
+  if (TREE_CODE (rhs1) != SSA_NAME)
+    return false;
+  count_stmt = SSA_NAME_DEF_STMT (rhs1);
+  gimple *and_stmt = SSA_NAME_DEF_STMT (gimple_cond_lhs (stmt));
+
+  /* Depending on copy-header is performed, feeding PHI stmts might be in
+     the loop header or loop exit, handle this.  */
+  if (gimple_code (count_stmt) == GIMPLE_PHI)
+    {
+      tree t;
+      if (gimple_code (and_stmt) != GIMPLE_PHI
+	  || gimple_bb (and_stmt) != exit->src
+	  || gimple_bb (count_stmt) != exit->src)
+	return false;
+      t = gimple_phi_arg_def (count_stmt, loop_latch_edge (loop)->dest_idx);
+      if (TREE_CODE (t) != SSA_NAME)
+	return false;
+      count_stmt = SSA_NAME_DEF_STMT (t);
+      t = gimple_phi_arg_def (and_stmt, loop_latch_edge (loop)->dest_idx);
+      if (TREE_CODE (t) != SSA_NAME)
+	return false;
+      and_stmt = SSA_NAME_DEF_STMT (t);
+      adjust = false;
+    }
+
+  /* Make sure we have a count by one.  */
+  if (!is_gimple_assign (count_stmt)
+      || (gimple_assign_rhs_code (count_stmt) != PLUS_EXPR)
+      || !integer_onep (gimple_assign_rhs2 (count_stmt)))
+    return false;
+
+  /* Check "b = b & (b - 1)" is calculated.  */
+  if (!is_gimple_assign (and_stmt)
+      || gimple_assign_rhs_code (and_stmt) != BIT_AND_EXPR)
+    return false;
+
+  rhs1 = gimple_assign_rhs1 (and_stmt);
+  rhs2 = gimple_assign_rhs2 (and_stmt);
+
+  if (ssa_defined_by_and_minus_one_stmt_p (rhs1, rhs2, &and_minus_one))
+    rhs1 = rhs2;
+  else if (ssa_defined_by_and_minus_one_stmt_p (rhs2, rhs1, &and_minus_one))
+    ;
+  else
+    return false;
+
+  /* Check the recurrence.  */
+  phi = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (and_minus_one));
+  gimple *src_phi = SSA_NAME_DEF_STMT (rhs2);
+  if (gimple_code (phi) != GIMPLE_PHI
+      || gimple_code (src_phi) != GIMPLE_PHI)
+    return false;
+
+  dest = gimple_assign_lhs (count_stmt);
+  tree fn = builtin_decl_implicit (BUILT_IN_POPCOUNT);
+  tree src = gimple_phi_arg_def (src_phi, loop_preheader_edge (loop)->dest_idx);
+  if (adjust)
+    iter = fold_build2 (MINUS_EXPR, TREE_TYPE (dest),
+			build_call_expr (fn, 1, src),
+			build_int_cst (TREE_TYPE (dest), 1));
+  else
+    iter = build_call_expr (fn, 1, src);
+  max = int_cst_value (TYPE_MAX_VALUE (TREE_TYPE (dest)));
+
+  niter->assumptions = boolean_false_node;
+  niter->control.base = NULL_TREE;
+  niter->control.step = NULL_TREE;
+  niter->control.no_overflow = false;
+  niter->niter = iter;
+  niter->assumptions = boolean_true_node;
+  niter->may_be_zero = boolean_false_node;
+  niter->max = max;
+  niter->bound = NULL_TREE;
+  niter->cmp = ERROR_MARK;
+  return true;
+}
+
+
 /* Like number_of_iterations_exit_assumptions, but return TRUE only if
    the niter information holds unconditionally.  */
 
@@ -2441,7 +2591,11 @@ number_of_iterations_exit (struct loop *loop, edge exit,
   gcond *stmt;
   if (!number_of_iterations_exit_assumptions (loop, exit, niter,
 					      &stmt, every_iteration))
-    return false;
+    {
+      if (number_of_iterations_popcount (loop, niter))
+	return true;
+      return false;
+    }
 
   if (integer_nonzerop (niter->assumptions))
     return true;
-- 
2.7.4