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Re: [PATCH] Reducing number of alias checks in vectorization.


On Wed, Oct 23, 2013 at 5:53 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Tue, Oct 22, 2013 at 11:12 PM, Cong Hou <congh@google.com> wrote:
>> On Fri, Oct 18, 2013 at 6:09 AM, Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>> On Tue, Oct 15, 2013 at 12:43 AM, Cong Hou <congh@google.com> wrote:
>>>> Sorry for forgetting using plain-text mode. Resend it.
>>>>
>>>>
>>>> ---------- Forwarded message ----------
>>>> From: Cong Hou <congh@google.com>
>>>> Date: Mon, Oct 14, 2013 at 3:29 PM
>>>> Subject: Re: [PATCH] Reducing number of alias checks in vectorization.
>>>> To: Richard Biener <rguenther@suse.de>, GCC Patches <gcc-patches@gcc.gnu.org>
>>>> Cc: Jakub Jelinek <jakub@redhat.com>
>>>>
>>>>
>>>> I have made a new patch for this issue according to your comments.
>>>>
>>>> There are several modifications to my previous patch:
>>>>
>>>>
>>>> 1. Remove the use of STL features such as vector and sort. Use GCC's
>>>> vec and qsort instead.
>>>
>>> I think that using <utility> and thus std::pair and std::swap is ok.  Including
>>> of <utility> should be done via system.h though.
>>>
>>
>>
>> Unfortunately, std::swap is defined in <algorithm>. Can I still use it?
>
> Hmm, let's defer this issue for now, adding swap and pair templates
> locally in GCC is better for now.  That is, I don't want a discussion of
> what parts of the standard library to use inside this thread.  You may
> want to rise the this issue in a new thread on gcc@gcc.gnu.org.
>
>>>> 2. Comparisons between tree nodes are not based on their addresses any
>>>> more. Use compare_tree() function instead.
>>>
>>> Ok.
>>>
>>>> 3. The function vect_create_cond_for_alias_checks() now returns the
>>>> number of alias checks. If its second parameter cond_expr is NULL,
>>>> then this function only calculate the number of alias checks after the
>>>> merging and won't generate comparison expressions.
>>>
>>> We now perform the merging twice - that's easily avoided by recording
>>> the merge result in loop_vinfo alongside may_alias_ddrs (which you
>>> should be able to drop as they are already contained in the data
>>> structures you build).
>>>
>>> Which means you can split the function and move the merging
>>> part to vect_prune_runtime_alias_test_list.
>>
>>
>> I have added one more field to loop_vec_info to store the dr pairs
>> from which alias checks are built. And I also split the functionality
>> of vect_create_cond_for_alias_checks() into two functions, so that we
>> now perform the merging once instead of twice.
>>
>>
>>>
>>>> 4. The function vect_prune_runtime_alias_test_list() now uses
>>>> vect_create_cond_for_alias_checks() to get the number of alias checks.
>>>>
>>>>
>>>> The patch is attached as a text file.
>>>>
>>>> Please give me your comment on this patch. Thank you!
>>>
>>> +  if (!operand_equal_p (dr_a1->basic_addr, dr_a2->basic_addr, 0)
>>> +      || TREE_CODE (dr_a1->offset) != INTEGER_CST
>>> +      || TREE_CODE (dr_a2->offset) != INTEGER_CST)
>>> +    continue;
>>> +
>>> +  HOST_WIDEST_INT diff = widest_int_cst_value (dr_a2->offset) -
>>> + widest_int_cst_value (dr_a1->offset);
>>>
>>> use !host_integerp (dr_a1->offset) as check and then int_cst_value.
>>
>>
>> Done.
>>
>>
>>>
>>> +  if (diff <= vect_factor
>>> +      || (TREE_CODE (dr_a1->seg_len) == INTEGER_CST
>>> +  && diff - widest_int_cst_value (dr_a1->seg_len) < vect_factor)
>>> +      || (TREE_CODE (dr_a1->seg_len) == INTEGER_CST
>>> +  && TREE_CODE (dr_b1->seg_len) == INTEGER_CST
>>> +  && diff - widest_int_cst_value (dr_a1->seg_len) <
>>> +     widest_int_cst_value (dr_b1->seg_len)))
>>>
>>> can you add a comment above this why it is safe to combine under
>>> this condition?  You seem to combine offsets but not data-ref steps
>>> for example.  The segment length is computed quite optimistically
>>> and you don't seem to adjust that.  That is, generally the alias
>>> check, if implemented as simple overlap, would need to intersect
>>> [init, init + niter * step]  intervals, losing some non-aliasing cases.
>>> The current segment length is optimistically computed and thus
>>> can recover some more cases, but you have to be careful with
>>> merging to not break its implicit assumptions.
>>
>>
>> I have changed the code and made it more clear as shown below. I still
>> use the condition
>>
>>
>> DR_A2->OFFSET - DR_A1->OFFSET - SEGMENT_LENGTH_A < SEGMENT_LENGTH_B
>>
>>
>> But in case that SEGMENT_LENGTH_A or SEGMENT_LENGTH_B is not constant,
>> we can still check the following two conditions:
>>
>>
>> DR_A2->OFFSET - DR_A1->OFFSET  < SEGMENT_LENGTH_B
>> (if SEGMENT_LENGTH_A is not a constant).
>>
>>
>> DR_A2->OFFSET - DR_A1->OFFSET - SEGMENT_LENGTH_A < VECT_FACTOR
>> (if SEGMENT_LENGTH_B is not a constant, then its minimum value should
>> be VECT_FACTOR).
>>
>>
>>
>> The corresponding code is:
>>
>>
>>  /* Now we check if the following condition is satisfied:
>>
>>     DIFF - SEGMENT_LENGTH_A < SEGMENT_LENGTH_B
>>
>>     where DIFF = DR_A2->OFFSET - DR_A1->OFFSET.  However,
>>     SEGMENT_LENGTH_A or SEGMENT_LENGTH_B may not be constant so we
>>     have to make a best estimation.  We can get the minimum value
>>     of SEGMENT_LENGTH_B as a constant, represented by MIN_SEG_LEN_B,
>>     then either of the following two conditions can guarantee the
>>     one above:
>>
>>     1: DIFF <= MIN_SEG_LEN_B
>>     2: DIFF - SEGMENT_LENGTH_A < MIN_SEG_LEN_B
>>
>>     */
>>
>>  HOST_WIDEST_INT
>>  min_seg_len_b = (TREE_CODE (dr_b1->seg_len) == INTEGER_CST) ?
>>      widest_int_cst_value (dr_b1->seg_len) :
>>      vect_factor;
>>
>>  if (diff <= min_seg_len_b
>>      || (TREE_CODE (dr_a1->seg_len) == INTEGER_CST
>>  && diff - widest_int_cst_value (dr_a1->seg_len) <
>>     min_seg_len_b))
>>    { ... }
>>
>>
>>
>> The new patch is pasted here again. Bootstrapping and regression tests
>> are passed.
>>
>>
>> thanks,
>> Cong
>>
>>
>>
>> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
>> index 8a38316..7333f6a 100644
>> --- a/gcc/ChangeLog
>> +++ b/gcc/ChangeLog
>> @@ -1,3 +1,12 @@
>> +2013-10-14  Cong Hou  <congh@google.com>
>> +
>> + * tree-vect-loop-manip.c (vect_create_cond_for_alias_checks):
>> + Combine alias checks if it is possible to amortize the runtime
>> + overhead.  Return the number of alias checks after merging.
>> + * tree-vect-data-refs.c (vect_prune_runtime_alias_test_list):
>> + Use the function vect_create_cond_for_alias_checks () to check
>> + the number of alias checks.
>> +
>
> Your MUA eats tabs ... ;)


That is why I attached a text file ;)


>
>>  2013-10-14  David Malcolm  <dmalcolm@redhat.com>
>>
>>   * dumpfile.h (gcc::dump_manager): New class, to hold state
>> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
>> index 075d071..ea2782f 100644
>> --- a/gcc/testsuite/ChangeLog
>> +++ b/gcc/testsuite/ChangeLog
>> @@ -1,3 +1,7 @@
>> +2013-10-14  Cong Hou  <congh@google.com>
>> +
>> + * gcc.dg/vect/vect-alias-check.c: New.
>> +
>>  2013-10-14  Tobias Burnus  <burnus@net-b.de>
>>
>>   PR fortran/58658
>> diff --git a/gcc/testsuite/gcc.dg/vect/vect-alias-check.c
>> b/gcc/testsuite/gcc.dg/vect/vect-alias-check.c
>> new file mode 100644
>> index 0000000..bf9eb6b
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/vect/vect-alias-check.c
>> @@ -0,0 +1,19 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -ftree-vectorize
>> +     --param=vect-max-version-for-alias-checks=2
>> +     -fdump-tree-vect-details" } */
>> +
>> +/* A test case showing three potential alias checks between
>> +   a[i] and b[i], b[i+7], b[i+14]. With alias checks merging
>> +   enabled, those tree checks can be merged into one, and the
>> +   loop will be vectorized with vect-max-version-for-alias-checks=2.  */
>> +
>> +void foo (int *a, int *b)
>> +{
>> +  int i;
>> +  for (i = 0; i < 1000; ++i)
>> +    a[i] = b[i] + b[i+7] + b[i+14];
>> +}
>> +
>> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
>> +/* { dg-final { cleanup-tree-dump "vect" } } */
>> diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
>> index e7b2f33..5f70d58 100644
>> --- a/gcc/tree-vect-data-refs.c
>> +++ b/gcc/tree-vect-data-refs.c
>> @@ -128,41 +128,6 @@ vect_get_smallest_scalar_type (gimple stmt,
>> HOST_WIDE_INT *lhs_size_unit,
>>  }
>>
>>
>> -/* Check if data references pointed by DR_I and DR_J are same or
>> -   belong to same interleaving group.  Return FALSE if drs are
>> -   different, otherwise return TRUE.  */
>> -
>> -static bool
>> -vect_same_range_drs (data_reference_p dr_i, data_reference_p dr_j)
>> -{
>> -  gimple stmt_i = DR_STMT (dr_i);
>> -  gimple stmt_j = DR_STMT (dr_j);
>> -
>> -  if (operand_equal_p (DR_REF (dr_i), DR_REF (dr_j), 0)
>> -      || (GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_i))
>> -    && GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_j))
>> -    && (GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_i))
>> - == GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_j)))))
>> -    return true;
>> -  else
>> -    return false;
>> -}
>> -
>> -/* If address ranges represented by DDR_I and DDR_J are equal,
>> -   return TRUE, otherwise return FALSE.  */
>> -
>> -static bool
>> -vect_vfa_range_equal (ddr_p ddr_i, ddr_p ddr_j)
>> -{
>> -  if ((vect_same_range_drs (DDR_A (ddr_i), DDR_A (ddr_j))
>> -       && vect_same_range_drs (DDR_B (ddr_i), DDR_B (ddr_j)))
>> -      || (vect_same_range_drs (DDR_A (ddr_i), DDR_B (ddr_j))
>> -  && vect_same_range_drs (DDR_B (ddr_i), DDR_A (ddr_j))))
>> -    return true;
>> -  else
>> -    return false;
>> -}
>> -
>>  /* Insert DDR into LOOP_VINFO list of ddrs that may alias and need to be
>>     tested at run-time.  Return TRUE if DDR was successfully inserted.
>>     Return false if versioning is not supported.  */
>> @@ -2647,69 +2612,331 @@ vect_analyze_data_ref_accesses (loop_vec_info
>> loop_vinfo, bb_vec_info bb_vinfo)
>>    return true;
>>  }
>>
>> +
>> +/* Operator == between two dr_addr_with_seg_len objects.
>> +
>> +   This equality operator is used to make sure two data refs
>> +   are the same one so that we will consider to combine the
>> +   aliasing checks of those two pairs of data dependent data
>> +   refs.  */
>> +
>> +static bool
>> +operator == (const dr_addr_with_seg_len& d1,
>> +     const dr_addr_with_seg_len& d2)
>> +{
>> +  return operand_equal_p (d1.basic_addr, d2.basic_addr, 0)
>> + && compare_tree (d1.offset, d2.offset) == 0
>> + && compare_tree (d1.seg_len, d2.seg_len) == 0;
>> +}
>> +
>> +/* Function comp_dr_addr_with_seg_len_pair.
>> +
>> +   Comparison function for sorting objects of dr_addr_with_seg_len_pair_t
>> +   so that we can combine aliasing checks in one scan.  */
>> +
>> +static int
>> +comp_dr_addr_with_seg_len_pair (const void *p1_, const void *p2_)
>> +{
>> +  const dr_addr_with_seg_len_pair_t* p1 =
>> +    (const dr_addr_with_seg_len_pair_t *) p1_;
>> +  const dr_addr_with_seg_len_pair_t* p2 =
>> +    (const dr_addr_with_seg_len_pair_t *) p2_;
>> +
>> +  const dr_addr_with_seg_len &p11 = p1->first,
>> +     &p12 = p1->second,
>> +     &p21 = p2->first,
>> +     &p22 = p2->second;
>> +
>> +  int comp_res = compare_tree (p11.basic_addr, p21.basic_addr);
>> +  if (comp_res != 0)
>> +    return comp_res;
>> +
>> +  comp_res = compare_tree (p12.basic_addr, p22.basic_addr);
>> +  if (comp_res != 0)
>> +    return comp_res;
>> +
>> +  if (TREE_CODE (p11.offset) != INTEGER_CST
>> +      || TREE_CODE (p21.offset) != INTEGER_CST)
>> +    {
>> +      comp_res = compare_tree (p11.offset, p21.offset);
>> +      if (comp_res != 0)
>> + return comp_res;
>> +    }
>> +  if (tree_int_cst_compare (p11.offset, p21.offset) < 0)
>> +    return -1;
>> +  if (tree_int_cst_compare (p11.offset, p21.offset) > 0)
>> +    return 1;
>> +  if (TREE_CODE (p12.offset) != INTEGER_CST
>> +      || TREE_CODE (p22.offset) != INTEGER_CST)
>> +    {
>> +      comp_res = compare_tree (p12.offset, p22.offset);
>> +      if (comp_res != 0)
>> + return comp_res;
>> +    }
>> +  if (tree_int_cst_compare (p12.offset, p22.offset) < 0)
>> +    return -1;
>> +  if (tree_int_cst_compare (p12.offset, p22.offset) > 0)
>> +    return 1;
>> +
>> +  return 0;
>> +}
>> +
>> +template <class T> static void
>> +swap (T& a, T& b)
>> +{
>> +  T c (a);
>> +  a = b;
>> +  b = c;
>> +}
>> +
>> +/* Function vect_vfa_segment_size.
>> +
>> +   Create an expression that computes the size of segment
>> +   that will be accessed for a data reference.  The functions takes into
>> +   account that realignment loads may access one more vector.
>> +
>> +   Input:
>> +     DR: The data reference.
>> +     LENGTH_FACTOR: segment length to consider.
>> +
>> +   Return an expression whose value is the size of segment which will be
>> +   accessed by DR.  */
>> +
>> +static tree
>> +vect_vfa_segment_size (struct data_reference *dr, tree length_factor)
>> +{
>> +  tree segment_length;
>> +
>> +  if (integer_zerop (DR_STEP (dr)))
>> +    segment_length = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (dr)));
>> +  else
>> +    segment_length = size_binop (MULT_EXPR,
>> +                                 fold_convert (sizetype, DR_STEP (dr)),
>> +                                 fold_convert (sizetype, length_factor));
>> +
>> +  if (vect_supportable_dr_alignment (dr, false)
>> +        == dr_explicit_realign_optimized)
>> +    {
>> +      tree vector_size = TYPE_SIZE_UNIT
>> +  (STMT_VINFO_VECTYPE (vinfo_for_stmt (DR_STMT (dr))));
>> +
>> +      segment_length = size_binop (PLUS_EXPR, segment_length, vector_size);
>> +    }
>> +  return segment_length;
>> +}
>> +
>>  /* Function vect_prune_runtime_alias_test_list.
>>
>>     Prune a list of ddrs to be tested at run-time by versioning for alias.
>> +   Merge several alias checks into one if possible.
>>     Return FALSE if resulting list of ddrs is longer then allowed by
>>     PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS, otherwise return TRUE.  */
>>
>>  bool
>>  vect_prune_runtime_alias_test_list (loop_vec_info loop_vinfo)
>>  {
>> -  vec<ddr_p>  ddrs =
>> +  vec<ddr_p> may_alias_ddrs =
>>      LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo);
>> -  unsigned i, j;
>> +  vec<dr_addr_with_seg_len_pair_t>& comp_alias_ddrs =
>> +    LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo);
>> +  int vect_factor = LOOP_VINFO_VECT_FACTOR (loop_vinfo);
>> +  tree scalar_loop_iters = LOOP_VINFO_NITERS (loop_vinfo);
>> +
>> +  ddr_p ddr;
>> +  unsigned int i;
>> +  tree length_factor;
>>
>>    if (dump_enabled_p ())
>>      dump_printf_loc (MSG_NOTE, vect_location,
>>                       "=== vect_prune_runtime_alias_test_list ===\n");
>>
>> -  for (i = 0; i < ddrs.length (); )
>> +  if (may_alias_ddrs.is_empty ())
>> +    return true;
>> +
>> +  /* Basically, for each pair of dependent data refs store_ptr_0
>> +     and load_ptr_0, we create an expression:
>> +
>> +     ((store_ptr_0 + store_segment_length_0) <= load_ptr_0)
>> +     || (load_ptr_0 + load_segment_length_0) <= store_ptr_0))
>> +
>> +     for aliasing checks.  However, in some cases we can decrease
>> +     the number of checks by combining two checks into one.  For
>> +     example, suppose we have another pair of data refs store_ptr_0
>> +     and load_ptr_1, and if the following condition is satisfied:
>> +
>> +     load_ptr_0 < load_ptr_1  &&
>> +     load_ptr_1 - load_ptr_0 - load_segment_length_0 < store_segment_length_0
>> +
>> +     (this condition means, in each iteration of vectorized loop,
>> +     the accessed memory of store_ptr_0 cannot be between the memory
>> +     of load_ptr_0 and load_ptr_1.)
>> +
>> +     we then can use only the following expression to finish the
>> +     alising checks between store_ptr_0 & load_ptr_0 and
>> +     store_ptr_0 & load_ptr_1:
>> +
>> +     ((store_ptr_0 + store_segment_length_0) <= load_ptr_0)
>> +     || (load_ptr_1 + load_segment_length_1 <= store_ptr_0))
>> +
>> +     Note that we only consider that load_ptr_0 and load_ptr_1 have the
>> +     same basic address.  */
>> +
>> +  comp_alias_ddrs.create (may_alias_ddrs.length ());
>> +
>> +  /* First, we collect all data ref pairs for aliasing checks.  */
>> +  FOR_EACH_VEC_ELT (may_alias_ddrs, i, ddr)
>>      {
>> -      bool found;
>> -      ddr_p ddr_i;
>> +      struct data_reference *dr_a, *dr_b;
>> +      gimple dr_group_first_a, dr_group_first_b;
>> +      tree segment_length_a, segment_length_b;
>> +      gimple stmt_a, stmt_b;
>> +
>> +      dr_a = DDR_A (ddr);
>> +      stmt_a = DR_STMT (DDR_A (ddr));
>> +      dr_group_first_a = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_a));
>> +      if (dr_group_first_a)
>> + {
>> +  stmt_a = dr_group_first_a;
>> +  dr_a = STMT_VINFO_DATA_REF (vinfo_for_stmt (stmt_a));
>> + }
>>
>> -      ddr_i = ddrs[i];
>> -      found = false;
>> +      dr_b = DDR_B (ddr);
>> +      stmt_b = DR_STMT (DDR_B (ddr));
>> +      dr_group_first_b = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_b));
>> +      if (dr_group_first_b)
>> + {
>> +  stmt_b = dr_group_first_b;
>> +  dr_b = STMT_VINFO_DATA_REF (vinfo_for_stmt (stmt_b));
>> + }
>>
>> -      for (j = 0; j < i; j++)
>> -        {
>> -  ddr_p ddr_j = ddrs[j];
>> +      if (!operand_equal_p (DR_STEP (dr_a), DR_STEP (dr_b), 0))
>> + length_factor = scalar_loop_iters;
>> +      else
>> + length_factor = size_int (vect_factor);
>
> ^^^^
>
> this is the thing I am worried about.  When the steps are equal we
> build reduced size segments to handle overlaps with a dependence
> distance bigger than vect_factor.


I don't quite understand here. Could you give me an example?


>
>> +      segment_length_a = vect_vfa_segment_size (dr_a, length_factor);
>> +      segment_length_b = vect_vfa_segment_size (dr_b, length_factor);
>> +
>> +      dr_addr_with_seg_len_pair_t dr_with_seg_len_pair
>> +  (dr_addr_with_seg_len
>> +       (dr_a, DR_BASE_ADDRESS (dr_a),
>> + size_binop (PLUS_EXPR, DR_OFFSET (dr_a), DR_INIT (dr_a)),
>> + segment_length_a),
>> +   dr_addr_with_seg_len
>> +       (dr_b, DR_BASE_ADDRESS (dr_b),
>> + size_binop (PLUS_EXPR, DR_OFFSET (dr_b), DR_INIT (dr_b)),
>> + segment_length_b));
>> +
>> +      if (compare_tree (dr_with_seg_len_pair.first.basic_addr,
>> + dr_with_seg_len_pair.second.basic_addr) > 0)
>> + swap (dr_with_seg_len_pair.first, dr_with_seg_len_pair.second);
>> +
>> +      comp_alias_ddrs.safe_push (dr_with_seg_len_pair);
>> +    }
>>
>> -  if (vect_vfa_range_equal (ddr_i, ddr_j))
>> +  /* Second, we sort the collected data ref pairs so that we can scan
>> +     them once to combine all possible aliasing checks.  */
>> +  comp_alias_ddrs.qsort (comp_dr_addr_with_seg_len_pair);
>> +
>> +  /* Third, we scan the sorted dr pairs and check if we can combine
>> +     alias checks of two neighbouring dr pairs.  */
>> +  for (size_t i = 1; i < comp_alias_ddrs.length (); ++i)
>> +    {
>> +      /* Deal with two ddrs (dr_a1, dr_b1) and (dr_a2, dr_b2).  */
>> +      dr_addr_with_seg_len *dr_a1 = &comp_alias_ddrs[i-1].first,
>> +   *dr_b1 = &comp_alias_ddrs[i-1].second,
>> +   *dr_a2 = &comp_alias_ddrs[i].first,
>> +   *dr_b2 = &comp_alias_ddrs[i].second;
>> +
>> +      /* Remove duplicate data ref pairs.  */
>> +      if (*dr_a1 == *dr_a2 && *dr_b1 == *dr_b2)
>> + {
>> +  if (dump_enabled_p ())
>> +    {
>> +      dump_printf_loc (MSG_NOTE, vect_location,
>> +       "found equal ranges ");
>> +      dump_generic_expr (MSG_NOTE, TDF_SLIM,
>> + DR_REF (dr_a1->dr));
>> +      dump_printf (MSG_NOTE,  ", ");
>> +      dump_generic_expr (MSG_NOTE, TDF_SLIM,
>> + DR_REF (dr_b1->dr));
>> +      dump_printf (MSG_NOTE,  " and ");
>> +      dump_generic_expr (MSG_NOTE, TDF_SLIM,
>> + DR_REF (dr_a2->dr));
>> +      dump_printf (MSG_NOTE,  ", ");
>> +      dump_generic_expr (MSG_NOTE, TDF_SLIM,
>> + DR_REF (dr_b2->dr));
>> +      dump_printf (MSG_NOTE, "\n");
>> +    }
>> +
>> +  comp_alias_ddrs.ordered_remove (i--);
>> +  continue;
>> + }
>> +
>> +      if (*dr_a1 == *dr_a2 || *dr_b1 == *dr_b2)
>> + {
>> +  /* We consider the case that DR_B1 and DR_B2 are same memrefs,
>> +     and DR_A1 and DR_A2 are two consecutive memrefs.  */
>> +  if (*dr_a1 == *dr_a2)
>> +    {
>> +      swap (dr_a1, dr_b1);
>> +      swap (dr_a2, dr_b2);
>> +    }
>> +
>> +  if (!operand_equal_p (dr_a1->basic_addr, dr_a2->basic_addr, 0)
>> +      || !host_integerp (dr_a1->offset, 0)
>> +      || !host_integerp (dr_a2->offset, 0))
>> +    continue;
>> +
>> +  HOST_WIDEST_INT diff = widest_int_cst_value (dr_a2->offset) -
>> + widest_int_cst_value (dr_a1->offset);
>> +
>> +
>> +  /* Now we check if the following condition is satisfied:
>> +
>> +     DIFF - SEGMENT_LENGTH_A < SEGMENT_LENGTH_B
>> +
>> +     where DIFF = DR_A2->OFFSET - DR_A1->OFFSET.  However,
>> +     SEGMENT_LENGTH_A or SEGMENT_LENGTH_B may not be constant so we
>> +     have to make a best estimation.  We can get the minimum value
>> +     of SEGMENT_LENGTH_B as a constant, represented by MIN_SEG_LEN_B,
>> +     then either of the following two conditions can guarantee the
>> +     one above:
>> +
>> +     1: DIFF <= MIN_SEG_LEN_B
>> +     2: DIFF - SEGMENT_LENGTH_A < MIN_SEG_LEN_B
>> +
>> +     */
>> +
>> +  HOST_WIDEST_INT
>> +  min_seg_len_b = (TREE_CODE (dr_b1->seg_len) == INTEGER_CST) ?
>> +      widest_int_cst_value (dr_b1->seg_len) :
>
> don't use widest_int_cst_value but tree_int_cst_low () if you previously
> checked host_integerp.


OK. Done.


>
>> +      vect_factor;
>> +
>> +  if (diff <= min_seg_len_b
>> +      || (TREE_CODE (dr_a1->seg_len) == INTEGER_CST
>> +  && diff - widest_int_cst_value (dr_a1->seg_len) <
>> +     min_seg_len_b))
>>      {
>>        if (dump_enabled_p ())
>>   {
>> -  dump_printf_loc (MSG_NOTE, vect_location,
>> -                   "found equal ranges ");
>> -  dump_generic_expr (MSG_NOTE, TDF_SLIM,
>> -                     DR_REF (DDR_A (ddr_i)));
>> -  dump_printf (MSG_NOTE,  ", ");
>> -  dump_generic_expr (MSG_NOTE, TDF_SLIM,
>> -                     DR_REF (DDR_B (ddr_i)));
>> -  dump_printf (MSG_NOTE,  " and ");
>> -  dump_generic_expr (MSG_NOTE, TDF_SLIM,
>> -                     DR_REF (DDR_A (ddr_j)));
>> -  dump_printf (MSG_NOTE,  ", ");
>> -  dump_generic_expr (MSG_NOTE, TDF_SLIM,
>> -                     DR_REF (DDR_B (ddr_j)));
>> +  dump_printf_loc
>> +      (MSG_NOTE, vect_location,
>> +       "merging two runtime checks for data references ");
>> +  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_a1->dr));
>> +  dump_printf (MSG_NOTE, " and ");
>> +  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_a2->dr));
>>    dump_printf (MSG_NOTE, "\n");
>>   }
>> -      found = true;
>> -      break;
>> +
>> +      dr_a1->seg_len = size_binop (PLUS_EXPR,
>> +   dr_a2->seg_len, size_int (diff));
>> +      comp_alias_ddrs.ordered_remove (i--);
>>      }
>>   }
>> -
>> -      if (found)
>> -      {
>> - ddrs.ordered_remove (i);
>> - continue;
>> -      }
>> -      i++;
>>      }
>>
>> -  if (ddrs.length () >
>> -       (unsigned) PARAM_VALUE (PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS))
>> +  if ((int) comp_alias_ddrs.length () >
>> +      PARAM_VALUE (PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS))
>>      {
>>        if (dump_enabled_p ())
>>   {
>> @@ -2718,8 +2945,6 @@ vect_prune_runtime_alias_test_list
>> (loop_vec_info loop_vinfo)
>>                     "generated checks exceeded.\n");
>>   }
>>
>> -      LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo).truncate (0);
>> -
>>        return false;
>>      }
>>
>> diff --git a/gcc/tree-vect-loop-manip.c b/gcc/tree-vect-loop-manip.c
>> index 574446a..1e03853 100644
>> --- a/gcc/tree-vect-loop-manip.c
>> +++ b/gcc/tree-vect-loop-manip.c
>> @@ -2211,44 +2211,6 @@ vect_create_cond_for_align_checks
>> (loop_vec_info loop_vinfo,
>>      *cond_expr = part_cond_expr;
>>  }
>>
>> -
>> -/* Function vect_vfa_segment_size.
>> -
>> -   Create an expression that computes the size of segment
>> -   that will be accessed for a data reference.  The functions takes into
>> -   account that realignment loads may access one more vector.
>> -
>> -   Input:
>> -     DR: The data reference.
>> -     LENGTH_FACTOR: segment length to consider.
>> -
>> -   Return an expression whose value is the size of segment which will be
>> -   accessed by DR.  */
>> -
>> -static tree
>> -vect_vfa_segment_size (struct data_reference *dr, tree length_factor)
>> -{
>> -  tree segment_length;
>> -
>> -  if (integer_zerop (DR_STEP (dr)))
>> -    segment_length = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (dr)));
>> -  else
>> -    segment_length = size_binop (MULT_EXPR,
>> -                                 fold_convert (sizetype, DR_STEP (dr)),
>> -                                 fold_convert (sizetype, length_factor));
>> -
>> -  if (vect_supportable_dr_alignment (dr, false)
>> -        == dr_explicit_realign_optimized)
>> -    {
>> -      tree vector_size = TYPE_SIZE_UNIT
>> -  (STMT_VINFO_VECTYPE (vinfo_for_stmt (DR_STMT (dr))));
>> -
>> -      segment_length = size_binop (PLUS_EXPR, segment_length, vector_size);
>> -    }
>> -  return segment_length;
>> -}
>> -
>> -
>>  /* Function vect_create_cond_for_alias_checks.
>>
>>     Create a conditional expression that represents the run-time checks for
>> @@ -2257,28 +2219,24 @@ vect_vfa_segment_size (struct data_reference
>> *dr, tree length_factor)
>>
>>     Input:
>>     COND_EXPR  - input conditional expression.  New conditions will be chained
>> -                with logical AND operation.
>> +                with logical AND operation.  If it is NULL, then the function
>> +                is used to return the number of alias checks.
>>     LOOP_VINFO - field LOOP_VINFO_MAY_ALIAS_STMTS contains the list of ddrs
>>          to be checked.
>>
>>     Output:
>>     COND_EXPR - conditional expression.
>>
>> -   The returned value is the conditional expression to be used in the if
>> +   The returned COND_EXPR is the conditional expression to be used in the if
>>     statement that controls which version of the loop gets executed at runtime.
>>  */
>>
>> -static void
>> +void
>>  vect_create_cond_for_alias_checks (loop_vec_info loop_vinfo, tree * cond_expr)
>>  {
>> -  vec<ddr_p>  may_alias_ddrs =
>> -    LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo);
>> -  int vect_factor = LOOP_VINFO_VECT_FACTOR (loop_vinfo);
>> -  tree scalar_loop_iters = LOOP_VINFO_NITERS (loop_vinfo);
>> -
>> -  ddr_p ddr;
>> -  unsigned int i;
>> -  tree part_cond_expr, length_factor;
>> +  vec<dr_addr_with_seg_len_pair_t> comp_alias_ddrs =
>> +    LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo);
>> +  tree part_cond_expr;
>>
>>    /* Create expression
>>       ((store_ptr_0 + store_segment_length_0) <= load_ptr_0)
>> @@ -2289,70 +2247,39 @@ vect_create_cond_for_alias_checks
>> (loop_vec_info loop_vinfo, tree * cond_expr)
>>       ((store_ptr_n + store_segment_length_n) <= load_ptr_n)
>>       || (load_ptr_n + load_segment_length_n) <= store_ptr_n))  */
>>
>> -  if (may_alias_ddrs.is_empty ())
>> +  if (comp_alias_ddrs.is_empty ())
>>      return;
>>
>> -  FOR_EACH_VEC_ELT (may_alias_ddrs, i, ddr)
>> +  for (size_t i = 0, s = comp_alias_ddrs.length (); i < s; ++i)
>>      {
>> -      struct data_reference *dr_a, *dr_b;
>> -      gimple dr_group_first_a, dr_group_first_b;
>> -      tree addr_base_a, addr_base_b;
>> -      tree segment_length_a, segment_length_b;
>> -      gimple stmt_a, stmt_b;
>> -      tree seg_a_min, seg_a_max, seg_b_min, seg_b_max;
>> -
>> -      dr_a = DDR_A (ddr);
>> -      stmt_a = DR_STMT (DDR_A (ddr));
>> -      dr_group_first_a = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_a));
>> -      if (dr_group_first_a)
>> -        {
>> -  stmt_a = dr_group_first_a;
>> -  dr_a = STMT_VINFO_DATA_REF (vinfo_for_stmt (stmt_a));
>> - }
>> -
>> -      dr_b = DDR_B (ddr);
>> -      stmt_b = DR_STMT (DDR_B (ddr));
>> -      dr_group_first_b = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_b));
>> -      if (dr_group_first_b)
>> -        {
>> -  stmt_b = dr_group_first_b;
>> -  dr_b = STMT_VINFO_DATA_REF (vinfo_for_stmt (stmt_b));
>> - }
>> +      const dr_addr_with_seg_len& dr_a = comp_alias_ddrs[i].first;
>> +      const dr_addr_with_seg_len& dr_b = comp_alias_ddrs[i].second;
>> +      tree segment_length_a = dr_a.seg_len;
>> +      tree segment_length_b = dr_b.seg_len;
>>
>> -      addr_base_a
>> - = fold_build_pointer_plus (DR_BASE_ADDRESS (dr_a),
>> -   size_binop (PLUS_EXPR, DR_OFFSET (dr_a),
>> -       DR_INIT (dr_a)));
>> -      addr_base_b
>> - = fold_build_pointer_plus (DR_BASE_ADDRESS (dr_b),
>> -   size_binop (PLUS_EXPR, DR_OFFSET (dr_b),
>> -       DR_INIT (dr_b)));
>> -
>> -      if (!operand_equal_p (DR_STEP (dr_a), DR_STEP (dr_b), 0))
>> - length_factor = scalar_loop_iters;
>> -      else
>> - length_factor = size_int (vect_factor);
>> -      segment_length_a = vect_vfa_segment_size (dr_a, length_factor);
>> -      segment_length_b = vect_vfa_segment_size (dr_b, length_factor);
>> +      tree addr_base_a
>> + = fold_build_pointer_plus (dr_a.basic_addr, dr_a.offset);
>> +      tree addr_base_b
>> + = fold_build_pointer_plus (dr_b.basic_addr, dr_b.offset);
>>
>>        if (dump_enabled_p ())
>>   {
>>    dump_printf_loc (MSG_NOTE, vect_location,
>> -                           "create runtime check for data references ");
>> -  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_a));
>> +   "create runtime check for data references ");
>> +  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_a.dr));
>>    dump_printf (MSG_NOTE, " and ");
>> -  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_b));
>> -          dump_printf (MSG_NOTE, "\n");
>> +  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_b.dr));
>> +  dump_printf (MSG_NOTE, "\n");
>>   }
>>
>> -      seg_a_min = addr_base_a;
>> -      seg_a_max = fold_build_pointer_plus (addr_base_a, segment_length_a);
>> -      if (tree_int_cst_compare (DR_STEP (dr_a), size_zero_node) < 0)
>> +      tree seg_a_min = addr_base_a;
>> +      tree seg_a_max = fold_build_pointer_plus (addr_base_a, segment_length_a);
>> +      if (tree_int_cst_compare (DR_STEP (dr_a.dr), size_zero_node) < 0)
>>   seg_a_min = seg_a_max, seg_a_max = addr_base_a;
>>
>> -      seg_b_min = addr_base_b;
>> -      seg_b_max = fold_build_pointer_plus (addr_base_b, segment_length_b);
>> -      if (tree_int_cst_compare (DR_STEP (dr_b), size_zero_node) < 0)
>> +      tree seg_b_min = addr_base_b;
>> +      tree seg_b_max = fold_build_pointer_plus (addr_base_b, segment_length_b);
>> +      if (tree_int_cst_compare (DR_STEP (dr_b.dr), size_zero_node) < 0)
>>   seg_b_min = seg_b_max, seg_b_max = addr_base_b;
>>
>>        part_cond_expr =
>> @@ -2370,7 +2297,9 @@ vect_create_cond_for_alias_checks (loop_vec_info
>> loop_vinfo, tree * cond_expr)
>>    if (dump_enabled_p ())
>>      dump_printf_loc (MSG_NOTE, vect_location,
>>       "created %u versioning for alias checks.\n",
>> -     may_alias_ddrs.length ());
>> +     comp_alias_ddrs.length ());
>> +
>> +  comp_alias_ddrs.release ();
>>  }
>>
>>
>> diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
>> index 8b7b345..f231b62 100644
>> --- a/gcc/tree-vectorizer.h
>> +++ b/gcc/tree-vectorizer.h
>> @@ -175,6 +175,36 @@ typedef struct _slp_oprnd_info
>>
>>
>>
>> +/* This struct is used to store the information of a data reference,
>> +   including the data ref itself, its basic address, the access offset
>> +   and the segment length for aliasing checks.  This is used to generate
>> +   alias checks.  */
>> +
>> +struct dr_addr_with_seg_len
>> +{
>> +  dr_addr_with_seg_len (data_reference* d, tree addr, tree off, tree len)
>> +    : dr (d), basic_addr (addr), offset (off), seg_len (len) {}
>> +
>> +  data_reference *dr;
>> +  tree basic_addr;
>> +  tree offset;
>> +  tree seg_len;
>> +};
>> +
>> +/* This struct contains two dr_addr_with_seg_len objects with aliasing data
>> +   refs.  Two comparisons are generated from them.  */
>> +
>> +struct dr_addr_with_seg_len_pair_t
>> +{
>> +  dr_addr_with_seg_len_pair_t (const dr_addr_with_seg_len& d1,
>> +       const dr_addr_with_seg_len& d2)
>> +    : first (d1), second (d2) {}
>> +
>> +  dr_addr_with_seg_len first;
>> +  dr_addr_with_seg_len second;
>> +};
>> +
>> +
>>  typedef struct _vect_peel_info
>>  {
>>    int npeel;
>> @@ -274,6 +304,10 @@ typedef struct _loop_vec_info {
>>       for a run-time aliasing check.  */
>>    vec<ddr_p> may_alias_ddrs;
>>
>> +  /* Data Dependence Relations defining address ranges together with segment
>> +     lengths from which the run-time aliasing check is built.  */
>> +  vec<dr_addr_with_seg_len_pair_t> comp_alias_ddrs;
>> +
>
> Are you sure you release those on all paths that exit the vectorizer?


You are right. This may not a good idea. I have removed this dump info.


Thank you for you patient comment again! The updated patch is pasted below.


thanks,
Cong




diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 8a38316..7333f6a 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2013-10-14  Cong Hou  <congh@google.com>
+
+ * tree-vect-loop-manip.c (vect_create_cond_for_alias_checks):
+ Combine alias checks if it is possible to amortize the runtime
+ overhead.  Return the number of alias checks after merging.
+ * tree-vect-data-refs.c (vect_prune_runtime_alias_test_list):
+ Use the function vect_create_cond_for_alias_checks () to check
+ the number of alias checks.
+
 2013-10-14  David Malcolm  <dmalcolm@redhat.com>

  * dumpfile.h (gcc::dump_manager): New class, to hold state
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 075d071..ea2782f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2013-10-14  Cong Hou  <congh@google.com>
+
+ * gcc.dg/vect/vect-alias-check.c: New.
+
 2013-10-14  Tobias Burnus  <burnus@net-b.de>

  PR fortran/58658
diff --git a/gcc/testsuite/gcc.dg/vect/vect-alias-check.c
b/gcc/testsuite/gcc.dg/vect/vect-alias-check.c
new file mode 100644
index 0000000..bf9eb6b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-alias-check.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-vectorize
+     --param=vect-max-version-for-alias-checks=2
+     -fdump-tree-vect-details" } */
+
+/* A test case showing three potential alias checks between
+   a[i] and b[i], b[i+7], b[i+14]. With alias checks merging
+   enabled, those tree checks can be merged into one, and the
+   loop will be vectorized with vect-max-version-for-alias-checks=2.  */
+
+void foo (int *a, int *b)
+{
+  int i;
+  for (i = 0; i < 1000; ++i)
+    a[i] = b[i] + b[i+7] + b[i+14];
+}
+
+/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
+/* { dg-final { cleanup-tree-dump "vect" } } */
diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
index e7b2f33..ee6e6d0 100644
--- a/gcc/tree-vect-data-refs.c
+++ b/gcc/tree-vect-data-refs.c
@@ -128,41 +128,6 @@ vect_get_smallest_scalar_type (gimple stmt,
HOST_WIDE_INT *lhs_size_unit,
 }


-/* Check if data references pointed by DR_I and DR_J are same or
-   belong to same interleaving group.  Return FALSE if drs are
-   different, otherwise return TRUE.  */
-
-static bool
-vect_same_range_drs (data_reference_p dr_i, data_reference_p dr_j)
-{
-  gimple stmt_i = DR_STMT (dr_i);
-  gimple stmt_j = DR_STMT (dr_j);
-
-  if (operand_equal_p (DR_REF (dr_i), DR_REF (dr_j), 0)
-      || (GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_i))
-    && GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_j))
-    && (GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_i))
- == GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_j)))))
-    return true;
-  else
-    return false;
-}
-
-/* If address ranges represented by DDR_I and DDR_J are equal,
-   return TRUE, otherwise return FALSE.  */
-
-static bool
-vect_vfa_range_equal (ddr_p ddr_i, ddr_p ddr_j)
-{
-  if ((vect_same_range_drs (DDR_A (ddr_i), DDR_A (ddr_j))
-       && vect_same_range_drs (DDR_B (ddr_i), DDR_B (ddr_j)))
-      || (vect_same_range_drs (DDR_A (ddr_i), DDR_B (ddr_j))
-  && vect_same_range_drs (DDR_B (ddr_i), DDR_A (ddr_j))))
-    return true;
-  else
-    return false;
-}
-
 /* Insert DDR into LOOP_VINFO list of ddrs that may alias and need to be
    tested at run-time.  Return TRUE if DDR was successfully inserted.
    Return false if versioning is not supported.  */
@@ -2647,69 +2612,320 @@ vect_analyze_data_ref_accesses (loop_vec_info
loop_vinfo, bb_vec_info bb_vinfo)
   return true;
 }

+
+/* Operator == between two dr_addr_with_seg_len objects.
+
+   This equality operator is used to make sure two data refs
+   are the same one so that we will consider to combine the
+   aliasing checks of those two pairs of data dependent data
+   refs.  */
+
+static bool
+operator == (const dr_addr_with_seg_len& d1,
+     const dr_addr_with_seg_len& d2)
+{
+  return operand_equal_p (d1.basic_addr, d2.basic_addr, 0)
+ && compare_tree (d1.offset, d2.offset) == 0
+ && compare_tree (d1.seg_len, d2.seg_len) == 0;
+}
+
+/* Function comp_dr_addr_with_seg_len_pair.
+
+   Comparison function for sorting objects of dr_addr_with_seg_len_pair_t
+   so that we can combine aliasing checks in one scan.  */
+
+static int
+comp_dr_addr_with_seg_len_pair (const void *p1_, const void *p2_)
+{
+  const dr_addr_with_seg_len_pair_t* p1 =
+    (const dr_addr_with_seg_len_pair_t *) p1_;
+  const dr_addr_with_seg_len_pair_t* p2 =
+    (const dr_addr_with_seg_len_pair_t *) p2_;
+
+  const dr_addr_with_seg_len &p11 = p1->first,
+     &p12 = p1->second,
+     &p21 = p2->first,
+     &p22 = p2->second;
+
+  int comp_res = compare_tree (p11.basic_addr, p21.basic_addr);
+  if (comp_res != 0)
+    return comp_res;
+
+  comp_res = compare_tree (p12.basic_addr, p22.basic_addr);
+  if (comp_res != 0)
+    return comp_res;
+
+  if (TREE_CODE (p11.offset) != INTEGER_CST
+      || TREE_CODE (p21.offset) != INTEGER_CST)
+    {
+      comp_res = compare_tree (p11.offset, p21.offset);
+      if (comp_res != 0)
+ return comp_res;
+    }
+  if (tree_int_cst_compare (p11.offset, p21.offset) < 0)
+    return -1;
+  if (tree_int_cst_compare (p11.offset, p21.offset) > 0)
+    return 1;
+  if (TREE_CODE (p12.offset) != INTEGER_CST
+      || TREE_CODE (p22.offset) != INTEGER_CST)
+    {
+      comp_res = compare_tree (p12.offset, p22.offset);
+      if (comp_res != 0)
+ return comp_res;
+    }
+  if (tree_int_cst_compare (p12.offset, p22.offset) < 0)
+    return -1;
+  if (tree_int_cst_compare (p12.offset, p22.offset) > 0)
+    return 1;
+
+  return 0;
+}
+
+template <class T> static void
+swap (T& a, T& b)
+{
+  T c (a);
+  a = b;
+  b = c;
+}
+
+/* Function vect_vfa_segment_size.
+
+   Create an expression that computes the size of segment
+   that will be accessed for a data reference.  The functions takes into
+   account that realignment loads may access one more vector.
+
+   Input:
+     DR: The data reference.
+     LENGTH_FACTOR: segment length to consider.
+
+   Return an expression whose value is the size of segment which will be
+   accessed by DR.  */
+
+static tree
+vect_vfa_segment_size (struct data_reference *dr, tree length_factor)
+{
+  tree segment_length;
+
+  if (integer_zerop (DR_STEP (dr)))
+    segment_length = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (dr)));
+  else
+    segment_length = size_binop (MULT_EXPR,
+                                 fold_convert (sizetype, DR_STEP (dr)),
+                                 fold_convert (sizetype, length_factor));
+
+  if (vect_supportable_dr_alignment (dr, false)
+        == dr_explicit_realign_optimized)
+    {
+      tree vector_size = TYPE_SIZE_UNIT
+  (STMT_VINFO_VECTYPE (vinfo_for_stmt (DR_STMT (dr))));
+
+      segment_length = size_binop (PLUS_EXPR, segment_length, vector_size);
+    }
+  return segment_length;
+}
+
 /* Function vect_prune_runtime_alias_test_list.

    Prune a list of ddrs to be tested at run-time by versioning for alias.
+   Merge several alias checks into one if possible.
    Return FALSE if resulting list of ddrs is longer then allowed by
    PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS, otherwise return TRUE.  */

 bool
 vect_prune_runtime_alias_test_list (loop_vec_info loop_vinfo)
 {
-  vec<ddr_p>  ddrs =
+  vec<ddr_p> may_alias_ddrs =
     LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo);
-  unsigned i, j;
+  vec<dr_addr_with_seg_len_pair_t>& comp_alias_ddrs =
+    LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo);
+  int vect_factor = LOOP_VINFO_VECT_FACTOR (loop_vinfo);
+  tree scalar_loop_iters = LOOP_VINFO_NITERS (loop_vinfo);
+
+  ddr_p ddr;
+  unsigned int i;
+  tree length_factor;

   if (dump_enabled_p ())
     dump_printf_loc (MSG_NOTE, vect_location,
                      "=== vect_prune_runtime_alias_test_list ===\n");

-  for (i = 0; i < ddrs.length (); )
+  if (may_alias_ddrs.is_empty ())
+    return true;
+
+  /* Basically, for each pair of dependent data refs store_ptr_0
+     and load_ptr_0, we create an expression:
+
+     ((store_ptr_0 + store_segment_length_0) <= load_ptr_0)
+     || (load_ptr_0 + load_segment_length_0) <= store_ptr_0))
+
+     for aliasing checks.  However, in some cases we can decrease
+     the number of checks by combining two checks into one.  For
+     example, suppose we have another pair of data refs store_ptr_0
+     and load_ptr_1, and if the following condition is satisfied:
+
+     load_ptr_0 < load_ptr_1  &&
+     load_ptr_1 - load_ptr_0 - load_segment_length_0 < store_segment_length_0
+
+     (this condition means, in each iteration of vectorized loop,
+     the accessed memory of store_ptr_0 cannot be between the memory
+     of load_ptr_0 and load_ptr_1.)
+
+     we then can use only the following expression to finish the
+     alising checks between store_ptr_0 & load_ptr_0 and
+     store_ptr_0 & load_ptr_1:
+
+     ((store_ptr_0 + store_segment_length_0) <= load_ptr_0)
+     || (load_ptr_1 + load_segment_length_1 <= store_ptr_0))
+
+     Note that we only consider that load_ptr_0 and load_ptr_1 have the
+     same basic address.  */
+
+  comp_alias_ddrs.create (may_alias_ddrs.length ());
+
+  /* First, we collect all data ref pairs for aliasing checks.  */
+  FOR_EACH_VEC_ELT (may_alias_ddrs, i, ddr)
     {
-      bool found;
-      ddr_p ddr_i;
+      struct data_reference *dr_a, *dr_b;
+      gimple dr_group_first_a, dr_group_first_b;
+      tree segment_length_a, segment_length_b;
+      gimple stmt_a, stmt_b;
+
+      dr_a = DDR_A (ddr);
+      stmt_a = DR_STMT (DDR_A (ddr));
+      dr_group_first_a = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_a));
+      if (dr_group_first_a)
+ {
+  stmt_a = dr_group_first_a;
+  dr_a = STMT_VINFO_DATA_REF (vinfo_for_stmt (stmt_a));
+ }

-      ddr_i = ddrs[i];
-      found = false;
+      dr_b = DDR_B (ddr);
+      stmt_b = DR_STMT (DDR_B (ddr));
+      dr_group_first_b = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_b));
+      if (dr_group_first_b)
+ {
+  stmt_b = dr_group_first_b;
+  dr_b = STMT_VINFO_DATA_REF (vinfo_for_stmt (stmt_b));
+ }

-      for (j = 0; j < i; j++)
-        {
-  ddr_p ddr_j = ddrs[j];
+      if (!operand_equal_p (DR_STEP (dr_a), DR_STEP (dr_b), 0))
+ length_factor = scalar_loop_iters;
+      else
+ length_factor = size_int (vect_factor);
+      segment_length_a = vect_vfa_segment_size (dr_a, length_factor);
+      segment_length_b = vect_vfa_segment_size (dr_b, length_factor);
+
+      dr_addr_with_seg_len_pair_t dr_with_seg_len_pair
+  (dr_addr_with_seg_len
+       (dr_a, DR_BASE_ADDRESS (dr_a),
+ size_binop (PLUS_EXPR, DR_OFFSET (dr_a), DR_INIT (dr_a)),
+ segment_length_a),
+   dr_addr_with_seg_len
+       (dr_b, DR_BASE_ADDRESS (dr_b),
+ size_binop (PLUS_EXPR, DR_OFFSET (dr_b), DR_INIT (dr_b)),
+ segment_length_b));
+
+      if (compare_tree (dr_with_seg_len_pair.first.basic_addr,
+ dr_with_seg_len_pair.second.basic_addr) > 0)
+ swap (dr_with_seg_len_pair.first, dr_with_seg_len_pair.second);
+
+      comp_alias_ddrs.safe_push (dr_with_seg_len_pair);
+    }

-  if (vect_vfa_range_equal (ddr_i, ddr_j))
+  /* Second, we sort the collected data ref pairs so that we can scan
+     them once to combine all possible aliasing checks.  */
+  comp_alias_ddrs.qsort (comp_dr_addr_with_seg_len_pair);
+
+  /* Third, we scan the sorted dr pairs and check if we can combine
+     alias checks of two neighbouring dr pairs.  */
+  for (size_t i = 1; i < comp_alias_ddrs.length (); ++i)
+    {
+      /* Deal with two ddrs (dr_a1, dr_b1) and (dr_a2, dr_b2).  */
+      dr_addr_with_seg_len *dr_a1 = &comp_alias_ddrs[i-1].first,
+   *dr_b1 = &comp_alias_ddrs[i-1].second,
+   *dr_a2 = &comp_alias_ddrs[i].first,
+   *dr_b2 = &comp_alias_ddrs[i].second;
+
+      /* Remove duplicate data ref pairs.  */
+      if (*dr_a1 == *dr_a2 && *dr_b1 == *dr_b2)
+ {
+  if (dump_enabled_p ())
     {
-      if (dump_enabled_p ())
- {
-  dump_printf_loc (MSG_NOTE, vect_location,
-                   "found equal ranges ");
-  dump_generic_expr (MSG_NOTE, TDF_SLIM,
-                     DR_REF (DDR_A (ddr_i)));
-  dump_printf (MSG_NOTE,  ", ");
-  dump_generic_expr (MSG_NOTE, TDF_SLIM,
-                     DR_REF (DDR_B (ddr_i)));
-  dump_printf (MSG_NOTE,  " and ");
-  dump_generic_expr (MSG_NOTE, TDF_SLIM,
-                     DR_REF (DDR_A (ddr_j)));
-  dump_printf (MSG_NOTE,  ", ");
-  dump_generic_expr (MSG_NOTE, TDF_SLIM,
-                     DR_REF (DDR_B (ddr_j)));
-  dump_printf (MSG_NOTE, "\n");
- }
-      found = true;
-      break;
+      dump_printf_loc (MSG_NOTE, vect_location,
+       "found equal ranges ");
+      dump_generic_expr (MSG_NOTE, TDF_SLIM,
+ DR_REF (dr_a1->dr));
+      dump_printf (MSG_NOTE,  ", ");
+      dump_generic_expr (MSG_NOTE, TDF_SLIM,
+ DR_REF (dr_b1->dr));
+      dump_printf (MSG_NOTE,  " and ");
+      dump_generic_expr (MSG_NOTE, TDF_SLIM,
+ DR_REF (dr_a2->dr));
+      dump_printf (MSG_NOTE,  ", ");
+      dump_generic_expr (MSG_NOTE, TDF_SLIM,
+ DR_REF (dr_b2->dr));
+      dump_printf (MSG_NOTE, "\n");
     }
+
+  comp_alias_ddrs.ordered_remove (i--);
+  continue;
  }

-      if (found)
-      {
- ddrs.ordered_remove (i);
- continue;
-      }
-      i++;
+      if (*dr_a1 == *dr_a2 || *dr_b1 == *dr_b2)
+ {
+  /* We consider the case that DR_B1 and DR_B2 are same memrefs,
+     and DR_A1 and DR_A2 are two consecutive memrefs.  */
+  if (*dr_a1 == *dr_a2)
+    {
+      swap (dr_a1, dr_b1);
+      swap (dr_a2, dr_b2);
+    }
+
+  if (!operand_equal_p (dr_a1->basic_addr, dr_a2->basic_addr, 0)
+      || !host_integerp (dr_a1->offset, 0)
+      || !host_integerp (dr_a2->offset, 0))
+    continue;
+
+  HOST_WIDE_INT diff = TREE_INT_CST_LOW (dr_a2->offset) -
+       TREE_INT_CST_LOW (dr_a1->offset);
+
+
+  /* Now we check if the following condition is satisfied:
+
+     DIFF - SEGMENT_LENGTH_A < SEGMENT_LENGTH_B
+
+     where DIFF = DR_A2->OFFSET - DR_A1->OFFSET.  However,
+     SEGMENT_LENGTH_A or SEGMENT_LENGTH_B may not be constant so we
+     have to make a best estimation.  We can get the minimum value
+     of SEGMENT_LENGTH_B as a constant, represented by MIN_SEG_LEN_B,
+     then either of the following two conditions can guarantee the
+     one above:
+
+     1: DIFF <= MIN_SEG_LEN_B
+     2: DIFF - SEGMENT_LENGTH_A < MIN_SEG_LEN_B
+
+     */
+
+  HOST_WIDE_INT
+  min_seg_len_b = (TREE_CODE (dr_b1->seg_len) == INTEGER_CST) ?
+      TREE_INT_CST_LOW (dr_b1->seg_len) :
+      vect_factor;
+
+  if (diff <= min_seg_len_b
+      || (TREE_CODE (dr_a1->seg_len) == INTEGER_CST
+  && diff - TREE_INT_CST_LOW (dr_a1->seg_len) <
+     min_seg_len_b))
+    {
+      dr_a1->seg_len = size_binop (PLUS_EXPR,
+   dr_a2->seg_len, size_int (diff));
+      comp_alias_ddrs.ordered_remove (i--);
+    }
+ }
     }

-  if (ddrs.length () >
-       (unsigned) PARAM_VALUE (PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS))
+  if ((int) comp_alias_ddrs.length () >
+      PARAM_VALUE (PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS))
     {
       if (dump_enabled_p ())
  {
@@ -2718,8 +2934,6 @@ vect_prune_runtime_alias_test_list
(loop_vec_info loop_vinfo)
                    "generated checks exceeded.\n");
  }

-      LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo).truncate (0);
-
       return false;
     }

diff --git a/gcc/tree-vect-loop-manip.c b/gcc/tree-vect-loop-manip.c
index 574446a..1e03853 100644
--- a/gcc/tree-vect-loop-manip.c
+++ b/gcc/tree-vect-loop-manip.c
@@ -2211,44 +2211,6 @@ vect_create_cond_for_align_checks
(loop_vec_info loop_vinfo,
     *cond_expr = part_cond_expr;
 }

-
-/* Function vect_vfa_segment_size.
-
-   Create an expression that computes the size of segment
-   that will be accessed for a data reference.  The functions takes into
-   account that realignment loads may access one more vector.
-
-   Input:
-     DR: The data reference.
-     LENGTH_FACTOR: segment length to consider.
-
-   Return an expression whose value is the size of segment which will be
-   accessed by DR.  */
-
-static tree
-vect_vfa_segment_size (struct data_reference *dr, tree length_factor)
-{
-  tree segment_length;
-
-  if (integer_zerop (DR_STEP (dr)))
-    segment_length = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (dr)));
-  else
-    segment_length = size_binop (MULT_EXPR,
-                                 fold_convert (sizetype, DR_STEP (dr)),
-                                 fold_convert (sizetype, length_factor));
-
-  if (vect_supportable_dr_alignment (dr, false)
-        == dr_explicit_realign_optimized)
-    {
-      tree vector_size = TYPE_SIZE_UNIT
-  (STMT_VINFO_VECTYPE (vinfo_for_stmt (DR_STMT (dr))));
-
-      segment_length = size_binop (PLUS_EXPR, segment_length, vector_size);
-    }
-  return segment_length;
-}
-
-
 /* Function vect_create_cond_for_alias_checks.

    Create a conditional expression that represents the run-time checks for
@@ -2257,28 +2219,24 @@ vect_vfa_segment_size (struct data_reference
*dr, tree length_factor)

    Input:
    COND_EXPR  - input conditional expression.  New conditions will be chained
-                with logical AND operation.
+                with logical AND operation.  If it is NULL, then the function
+                is used to return the number of alias checks.
    LOOP_VINFO - field LOOP_VINFO_MAY_ALIAS_STMTS contains the list of ddrs
         to be checked.

    Output:
    COND_EXPR - conditional expression.

-   The returned value is the conditional expression to be used in the if
+   The returned COND_EXPR is the conditional expression to be used in the if
    statement that controls which version of the loop gets executed at runtime.
 */

-static void
+void
 vect_create_cond_for_alias_checks (loop_vec_info loop_vinfo, tree * cond_expr)
 {
-  vec<ddr_p>  may_alias_ddrs =
-    LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo);
-  int vect_factor = LOOP_VINFO_VECT_FACTOR (loop_vinfo);
-  tree scalar_loop_iters = LOOP_VINFO_NITERS (loop_vinfo);
-
-  ddr_p ddr;
-  unsigned int i;
-  tree part_cond_expr, length_factor;
+  vec<dr_addr_with_seg_len_pair_t> comp_alias_ddrs =
+    LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo);
+  tree part_cond_expr;

   /* Create expression
      ((store_ptr_0 + store_segment_length_0) <= load_ptr_0)
@@ -2289,70 +2247,39 @@ vect_create_cond_for_alias_checks
(loop_vec_info loop_vinfo, tree * cond_expr)
      ((store_ptr_n + store_segment_length_n) <= load_ptr_n)
      || (load_ptr_n + load_segment_length_n) <= store_ptr_n))  */

-  if (may_alias_ddrs.is_empty ())
+  if (comp_alias_ddrs.is_empty ())
     return;

-  FOR_EACH_VEC_ELT (may_alias_ddrs, i, ddr)
+  for (size_t i = 0, s = comp_alias_ddrs.length (); i < s; ++i)
     {
-      struct data_reference *dr_a, *dr_b;
-      gimple dr_group_first_a, dr_group_first_b;
-      tree addr_base_a, addr_base_b;
-      tree segment_length_a, segment_length_b;
-      gimple stmt_a, stmt_b;
-      tree seg_a_min, seg_a_max, seg_b_min, seg_b_max;
-
-      dr_a = DDR_A (ddr);
-      stmt_a = DR_STMT (DDR_A (ddr));
-      dr_group_first_a = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_a));
-      if (dr_group_first_a)
-        {
-  stmt_a = dr_group_first_a;
-  dr_a = STMT_VINFO_DATA_REF (vinfo_for_stmt (stmt_a));
- }
-
-      dr_b = DDR_B (ddr);
-      stmt_b = DR_STMT (DDR_B (ddr));
-      dr_group_first_b = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_b));
-      if (dr_group_first_b)
-        {
-  stmt_b = dr_group_first_b;
-  dr_b = STMT_VINFO_DATA_REF (vinfo_for_stmt (stmt_b));
- }
+      const dr_addr_with_seg_len& dr_a = comp_alias_ddrs[i].first;
+      const dr_addr_with_seg_len& dr_b = comp_alias_ddrs[i].second;
+      tree segment_length_a = dr_a.seg_len;
+      tree segment_length_b = dr_b.seg_len;

-      addr_base_a
- = fold_build_pointer_plus (DR_BASE_ADDRESS (dr_a),
-   size_binop (PLUS_EXPR, DR_OFFSET (dr_a),
-       DR_INIT (dr_a)));
-      addr_base_b
- = fold_build_pointer_plus (DR_BASE_ADDRESS (dr_b),
-   size_binop (PLUS_EXPR, DR_OFFSET (dr_b),
-       DR_INIT (dr_b)));
-
-      if (!operand_equal_p (DR_STEP (dr_a), DR_STEP (dr_b), 0))
- length_factor = scalar_loop_iters;
-      else
- length_factor = size_int (vect_factor);
-      segment_length_a = vect_vfa_segment_size (dr_a, length_factor);
-      segment_length_b = vect_vfa_segment_size (dr_b, length_factor);
+      tree addr_base_a
+ = fold_build_pointer_plus (dr_a.basic_addr, dr_a.offset);
+      tree addr_base_b
+ = fold_build_pointer_plus (dr_b.basic_addr, dr_b.offset);

       if (dump_enabled_p ())
  {
   dump_printf_loc (MSG_NOTE, vect_location,
-                           "create runtime check for data references ");
-  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_a));
+   "create runtime check for data references ");
+  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_a.dr));
   dump_printf (MSG_NOTE, " and ");
-  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_b));
-          dump_printf (MSG_NOTE, "\n");
+  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_b.dr));
+  dump_printf (MSG_NOTE, "\n");
  }

-      seg_a_min = addr_base_a;
-      seg_a_max = fold_build_pointer_plus (addr_base_a, segment_length_a);
-      if (tree_int_cst_compare (DR_STEP (dr_a), size_zero_node) < 0)
+      tree seg_a_min = addr_base_a;
+      tree seg_a_max = fold_build_pointer_plus (addr_base_a, segment_length_a);
+      if (tree_int_cst_compare (DR_STEP (dr_a.dr), size_zero_node) < 0)
  seg_a_min = seg_a_max, seg_a_max = addr_base_a;

-      seg_b_min = addr_base_b;
-      seg_b_max = fold_build_pointer_plus (addr_base_b, segment_length_b);
-      if (tree_int_cst_compare (DR_STEP (dr_b), size_zero_node) < 0)
+      tree seg_b_min = addr_base_b;
+      tree seg_b_max = fold_build_pointer_plus (addr_base_b, segment_length_b);
+      if (tree_int_cst_compare (DR_STEP (dr_b.dr), size_zero_node) < 0)
  seg_b_min = seg_b_max, seg_b_max = addr_base_b;

       part_cond_expr =
@@ -2370,7 +2297,9 @@ vect_create_cond_for_alias_checks (loop_vec_info
loop_vinfo, tree * cond_expr)
   if (dump_enabled_p ())
     dump_printf_loc (MSG_NOTE, vect_location,
      "created %u versioning for alias checks.\n",
-     may_alias_ddrs.length ());
+     comp_alias_ddrs.length ());
+
+  comp_alias_ddrs.release ();
 }


diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index 8b7b345..f231b62 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -175,6 +175,36 @@ typedef struct _slp_oprnd_info



+/* This struct is used to store the information of a data reference,
+   including the data ref itself, its basic address, the access offset
+   and the segment length for aliasing checks.  This is used to generate
+   alias checks.  */
+
+struct dr_addr_with_seg_len
+{
+  dr_addr_with_seg_len (data_reference* d, tree addr, tree off, tree len)
+    : dr (d), basic_addr (addr), offset (off), seg_len (len) {}
+
+  data_reference *dr;
+  tree basic_addr;
+  tree offset;
+  tree seg_len;
+};
+
+/* This struct contains two dr_addr_with_seg_len objects with aliasing data
+   refs.  Two comparisons are generated from them.  */
+
+struct dr_addr_with_seg_len_pair_t
+{
+  dr_addr_with_seg_len_pair_t (const dr_addr_with_seg_len& d1,
+       const dr_addr_with_seg_len& d2)
+    : first (d1), second (d2) {}
+
+  dr_addr_with_seg_len first;
+  dr_addr_with_seg_len second;
+};
+
+
 typedef struct _vect_peel_info
 {
   int npeel;
@@ -274,6 +304,10 @@ typedef struct _loop_vec_info {
      for a run-time aliasing check.  */
   vec<ddr_p> may_alias_ddrs;

+  /* Data Dependence Relations defining address ranges together with segment
+     lengths from which the run-time aliasing check is built.  */
+  vec<dr_addr_with_seg_len_pair_t> comp_alias_ddrs;
+
   /* Statements in the loop that have data references that are candidates for a
      runtime (loop versioning) misalignment check.  */
   vec<gimple> may_misalign_stmts;
@@ -336,6 +370,7 @@ typedef struct _loop_vec_info {
 #define LOOP_VINFO_MAY_MISALIGN_STMTS(L)   (L)->may_misalign_stmts
 #define LOOP_VINFO_LOC(L)                  (L)->loop_line_number
 #define LOOP_VINFO_MAY_ALIAS_DDRS(L)       (L)->may_alias_ddrs
+#define LOOP_VINFO_COMP_ALIAS_DDRS(L)      (L)->comp_alias_ddrs
 #define LOOP_VINFO_GROUPED_STORES(L)       (L)->grouped_stores
 #define LOOP_VINFO_SLP_INSTANCES(L)        (L)->slp_instances
 #define LOOP_VINFO_SLP_UNROLLING_FACTOR(L) (L)->slp_unrolling_factor







>
> Thanks,
> Richard.
>
>>    /* Statements in the loop that have data references that are candidates for a
>>       runtime (loop versioning) misalignment check.  */
>>    vec<gimple> may_misalign_stmts;
>> @@ -336,6 +370,7 @@ typedef struct _loop_vec_info {
>>  #define LOOP_VINFO_MAY_MISALIGN_STMTS(L)   (L)->may_misalign_stmts
>>  #define LOOP_VINFO_LOC(L)                  (L)->loop_line_number
>>  #define LOOP_VINFO_MAY_ALIAS_DDRS(L)       (L)->may_alias_ddrs
>> +#define LOOP_VINFO_COMP_ALIAS_DDRS(L)      (L)->comp_alias_ddrs
>>  #define LOOP_VINFO_GROUPED_STORES(L)       (L)->grouped_stores
>>  #define LOOP_VINFO_SLP_INSTANCES(L)        (L)->slp_instances
>>  #define LOOP_VINFO_SLP_UNROLLING_FACTOR(L) (L)->slp_unrolling_factor
>>
>>
>>
>>
>>
>>>
>>> Thanks,
>>> Richard.
>>>
>>>>
>>>> Cong
>>>>
>>>>
>>>> On Thu, Oct 3, 2013 at 2:35 PM, Cong Hou <congh@google.com> wrote:
>>>>>
>>>>> Forget about this "aux" idea as the segment length for one data ref
>>>>> can be different in different dr pairs.
>>>>>
>>>>> In my patch I created a struct as shown below:
>>>>>
>>>>> struct dr_addr_with_seg_len
>>>>> {
>>>>>   data_reference *dr;
>>>>>   tree basic_addr;
>>>>>   tree offset;
>>>>>   tree seg_len;
>>>>> };
>>>>>
>>>>>
>>>>> Note that basic_addr and offset can always obtained from dr, but we
>>>>> need to store two segment lengths for each dr pair. It is improper to
>>>>> add a field to data_dependence_relation as it is defined outside of
>>>>> vectorizer. We can change the type (a new one combining
>>>>> data_dependence_relation and segment length) of may_alias_ddrs in
>>>>> loop_vec_info to include such information, but we have to add a new
>>>>> type to tree-vectorizer.h which is only used in two places - still too
>>>>> much.
>>>>>
>>>>> One possible solution is that we create a local struct as shown above
>>>>> and a new function which returns the merged alias check information.
>>>>> This function will be called twice: once during analysis phase and
>>>>> once in transformation phase. Then we don't have to store the merged
>>>>> alias check information during those two phases. The additional time
>>>>> cost is minimal as there will not be too many data dependent dr pairs
>>>>> in a loop.
>>>>>
>>>>> Any comment?
>>>>>
>>>>>
>>>>> thanks,
>>>>> Cong
>>>>>
>>>>>
>>>>> On Thu, Oct 3, 2013 at 10:57 AM, Cong Hou <congh@google.com> wrote:
>>>>> > I noticed that there is a "struct dataref_aux" defined in
>>>>> > tree-vectorizer.h which is specific to the vectorizer pass and is
>>>>> > stored in (void*)aux in "struct data_reference". Can we add one more
>>>>> > field "segment_length" to dataref_aux so that we can pass this
>>>>> > information for merging alias checks? Then we can avoid to modify or
>>>>> > create other structures.
>>>>> >
>>>>> >
>>>>> > thanks,
>>>>> > Cong
>>>>> >
>>>>> >
>>>>> > On Wed, Oct 2, 2013 at 2:34 PM, Cong Hou <congh@google.com> wrote:
>>>>> >> On Wed, Oct 2, 2013 at 4:24 AM, Richard Biener <rguenther@suse.de> wrote:
>>>>> >>> On Tue, 1 Oct 2013, Cong Hou wrote:
>>>>> >>>
>>>>> >>>> When alias exists between data refs in a loop, to vectorize it GCC
>>>>> >>>> does loop versioning and adds runtime alias checks. Basically for each
>>>>> >>>> pair of data refs with possible data dependence, there will be two
>>>>> >>>> comparisons generated to make sure there is no aliasing between them
>>>>> >>>> in each iteration of the vectorized loop. If there are many such data
>>>>> >>>> refs pairs, the number of comparisons can be very large, which is a
>>>>> >>>> big overhead.
>>>>> >>>>
>>>>> >>>> However, in some cases it is possible to reduce the number of those
>>>>> >>>> comparisons. For example, for the following loop, we can detect that
>>>>> >>>> b[0] and b[1] are two consecutive member accesses so that we can
>>>>> >>>> combine the alias check between a[0:100]&b[0] and a[0:100]&b[1] into
>>>>> >>>> checking a[0:100]&b[0:2]:
>>>>> >>>>
>>>>> >>>> void foo(int*a, int* b)
>>>>> >>>> {
>>>>> >>>>    for (int i = 0; i < 100; ++i)
>>>>> >>>>     a[i] = b[0] + b[1];
>>>>> >>>> }
>>>>> >>>>
>>>>> >>>> Actually, the requirement of consecutive memory accesses is too
>>>>> >>>> strict. For the following loop, we can still combine the alias checks
>>>>> >>>> between a[0:100]&b[0] and a[0:100]&b[100]:
>>>>> >>>>
>>>>> >>>> void foo(int*a, int* b)
>>>>> >>>> {
>>>>> >>>>    for (int i = 0; i < 100; ++i)
>>>>> >>>>     a[i] = b[0] + b[100];
>>>>> >>>> }
>>>>> >>>>
>>>>> >>>> This is because if b[0] is not in a[0:100] and b[100] is not in
>>>>> >>>> a[0:100] then a[0:100] cannot be between b[0] and b[100]. We only need
>>>>> >>>> to check a[0:100] and b[0:101] don't overlap.
>>>>> >>>>
>>>>> >>>> More generally, consider two pairs of data refs (a, b1) and (a, b2).
>>>>> >>>> Suppose addr_b1 and addr_b2 are basic addresses of data ref b1 and b2;
>>>>> >>>> offset_b1 and offset_b2 (offset_b1 < offset_b2) are offsets of b1 and
>>>>> >>>> b2, and segment_length_a, segment_length_b1, and segment_length_b2 are
>>>>> >>>> segment length of a, b1, and b2. Then we can combine the two
>>>>> >>>> comparisons into one if the following condition is satisfied:
>>>>> >>>>
>>>>> >>>> offset_b2- offset_b1 - segment_length_b1 < segment_length_a
>>>>> >>>>
>>>>> >>>>
>>>>> >>>> This patch detects those combination opportunities to reduce the
>>>>> >>>> number of alias checks. It is tested on an x86-64 machine.
>>>>> >>>
>>>>> >>> Apart from the other comments you got (to which I agree) the patch
>>>>> >>> seems to do two things, namely also:
>>>>> >>>
>>>>> >>> +  /* Extract load and store statements on pointers with zero-stride
>>>>> >>> +     accesses.  */
>>>>> >>> +  if (LOOP_REQUIRES_VERSIONING_FOR_ALIAS (loop_vinfo))
>>>>> >>> +    {
>>>>> >>>
>>>>> >>> which I'd rather see in a separate patch (and done also when
>>>>> >>> the loop doesn't require versioning for alias).
>>>>> >>>
>>>>> >>
>>>>> >>
>>>>> >> My mistake.. I am working on those two patches at the same time and
>>>>> >> pasted that one also here by mistake. I will send another patch about
>>>>> >> the "hoist" topic.
>>>>> >>
>>>>> >>
>>>>> >>> Also combining the alias checks in vect_create_cond_for_alias_checks
>>>>> >>> is nice but doesn't properly fix the use of the
>>>>> >>> vect-max-version-for-alias-checks param which currently inhibits
>>>>> >>> vectorization of the HIMENO benchmark by default (and make us look bad
>>>>> >>> compared to LLVM).
>>>>> >>>
>>>>> >>> So I believe this merging should be done incrementally when
>>>>> >>> we collect the DDRs we need to test in vect_mark_for_runtime_alias_test.
>>>>> >>>
>>>>> >>
>>>>> >>
>>>>> >> I agree that vect-max-version-for-alias-checks param should count the
>>>>> >> number of checks after the merge. However, the struct
>>>>> >> data_dependence_relation could not record the new information produced
>>>>> >> by the merge. The new information I mentioned contains the new segment
>>>>> >> length for comparisons. This length is calculated right in
>>>>> >> vect_create_cond_for_alias_checks() function. Since
>>>>> >> vect-max-version-for-alias-checks is used during analysis phase, shall
>>>>> >> we move all those (get segment length for each data ref and merge
>>>>> >> alias checks) from transformation to analysis phase? If we cannot
>>>>> >> store the result properly (data_dependence_relation is not enough),
>>>>> >> shall we do it twice in both phases?
>>>>> >>
>>>>> >> I also noticed a possible bug in the function vect_same_range_drs()
>>>>> >> called by vect_prune_runtime_alias_test_list(). For the following code
>>>>> >> I get two pairs of data refs after
>>>>> >> vect_prune_runtime_alias_test_list(), but in
>>>>> >> vect_create_cond_for_alias_checks() after detecting grouped accesses I
>>>>> >> got two identical pairs of data refs. The consequence is two identical
>>>>> >> alias checks are produced.
>>>>> >>
>>>>> >>
>>>>> >> void yuv2yuyv_ref (int *d, int *src, int n)
>>>>> >> {
>>>>> >>   char *dest = (char *)d;
>>>>> >>   int i;
>>>>> >>
>>>>> >>   for(i=0;i<n/2;i++){
>>>>> >>     dest[i*4 + 0] = (src[i*2 + 0])>>16;
>>>>> >>     dest[i*4 + 1] = (src[i*2 + 1])>>8;
>>>>> >>     dest[i*4 + 2] = (src[i*2 + 0])>>16;
>>>>> >>     dest[i*4 + 3] = (src[i*2 + 0])>>0;
>>>>> >>   }
>>>>> >> }
>>>>> >>
>>>>> >>
>>>>> >> I think the solution to this problem is changing
>>>>> >>
>>>>> >> GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_i))
>>>>> >> == GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_j)
>>>>> >>
>>>>> >> into
>>>>> >>
>>>>> >> STMT_VINFO_DATA_REF (vinfo_for_stmt (GROUP_FIRST_ELEMENT
>>>>> >> (vinfo_for_stmt (stmt_i))))
>>>>> >> == STMT_VINFO_DATA_REF (vinfo_for_stmt (GROUP_FIRST_ELEMENT
>>>>> >> (vinfo_for_stmt (stmt_j)))
>>>>> >>
>>>>> >>
>>>>> >> in function vect_same_range_drs(). What do you think about it?
>>>>> >>
>>>>> >>
>>>>> >> thanks,
>>>>> >> Cong
>>>>> >>
>>>>> >>
>>>>> >>
>>>>> >>> Thanks for working on this,
>>>>> >>> Richard.
>>>>> >>>
>>>>> >>>>
>>>>> >>>> thanks,
>>>>> >>>> Cong
>>>>> >>>>
>>>>> >>>>
>>>>> >>>>
>>>>> >>>> Index: gcc/tree-vect-loop-manip.c
>>>>> >>>> ===================================================================
>>>>> >>>> --- gcc/tree-vect-loop-manip.c (revision 202662)
>>>>> >>>> +++ gcc/tree-vect-loop-manip.c (working copy)
>>>>> >>>> @@ -19,6 +19,10 @@ You should have received a copy of the G
>>>>> >>>>  along with GCC; see the file COPYING3.  If not see
>>>>> >>>>  <http://www.gnu.org/licenses/>.  */
>>>>> >>>>
>>>>> >>>> +#include <vector>
>>>>> >>>> +#include <utility>
>>>>> >>>> +#include <algorithm>
>>>>> >>>> +
>>>>> >>>>  #include "config.h"
>>>>> >>>>  #include "system.h"
>>>>> >>>>  #include "coretypes.h"
>>>>> >>>> @@ -2248,6 +2252,74 @@ vect_vfa_segment_size (struct data_refer
>>>>> >>>>    return segment_length;
>>>>> >>>>  }
>>>>> >>>>
>>>>> >>>> +namespace
>>>>> >>>> +{
>>>>> >>>> +
>>>>> >>>> +/* struct dr_addr_with_seg_len
>>>>> >>>> +
>>>>> >>>> +   A struct storing information of a data reference, including the data
>>>>> >>>> +   ref itself, its basic address, the access offset and the segment length
>>>>> >>>> +   for aliasing checks.  */
>>>>> >>>> +
>>>>> >>>> +struct dr_addr_with_seg_len
>>>>> >>>> +{
>>>>> >>>> +  dr_addr_with_seg_len (data_reference* d, tree addr, tree off, tree len)
>>>>> >>>> +    : dr (d), basic_addr (addr), offset (off), seg_len (len) {}
>>>>> >>>> +
>>>>> >>>> +  data_reference* dr;
>>>>> >>>> +  tree basic_addr;
>>>>> >>>> +  tree offset;
>>>>> >>>> +  tree seg_len;
>>>>> >>>> +};
>>>>> >>>> +
>>>>> >>>> +/* Operator == between two dr_addr_with_seg_len objects.
>>>>> >>>> +
>>>>> >>>> +   This equality operator is used to make sure two data refs
>>>>> >>>> +   are the same one so that we will consider to combine the
>>>>> >>>> +   aliasing checks of those two pairs of data dependent data
>>>>> >>>> +   refs.  */
>>>>> >>>> +
>>>>> >>>> +bool operator == (const dr_addr_with_seg_len& d1,
>>>>> >>>> +  const dr_addr_with_seg_len& d2)
>>>>> >>>> +{
>>>>> >>>> +  return operand_equal_p (d1.basic_addr, d2.basic_addr, 0)
>>>>> >>>> + && operand_equal_p (d1.offset, d2.offset, 0)
>>>>> >>>> + && operand_equal_p (d1.seg_len, d2.seg_len, 0);
>>>>> >>>> +}
>>>>> >>>> +
>>>>> >>>> +typedef std::pair <dr_addr_with_seg_len, dr_addr_with_seg_len>
>>>>> >>>> + dr_addr_with_seg_len_pair_t;
>>>>> >>>> +
>>>>> >>>> +
>>>>> >>>> +/* Operator < between two dr_addr_with_seg_len_pair_t objects.
>>>>> >>>> +
>>>>> >>>> +   This operator is used to sort objects of dr_addr_with_seg_len_pair_t
>>>>> >>>> +   so that we can combine aliasing checks during one scan.  */
>>>>> >>>> +
>>>>> >>>> +bool operator < (const dr_addr_with_seg_len_pair_t& p1,
>>>>> >>>> + const dr_addr_with_seg_len_pair_t& p2)
>>>>> >>>> +{
>>>>> >>>> +  const dr_addr_with_seg_len& p11 = p1.first;
>>>>> >>>> +  const dr_addr_with_seg_len& p12 = p1.second;
>>>>> >>>> +  const dr_addr_with_seg_len& p21 = p2.first;
>>>>> >>>> +  const dr_addr_with_seg_len& p22 = p2.second;
>>>>> >>>> +
>>>>> >>>> +  if (p11.basic_addr != p21.basic_addr)
>>>>> >>>> +    return p11.basic_addr < p21.basic_addr;
>>>>> >>>> +  if (p12.basic_addr != p22.basic_addr)
>>>>> >>>> +    return p12.basic_addr < p22.basic_addr;
>>>>> >>>> +  if (TREE_CODE (p11.offset) != INTEGER_CST
>>>>> >>>> +      || TREE_CODE (p21.offset) != INTEGER_CST)
>>>>> >>>> +    return p11.offset < p21.offset;
>>>>> >>>> +  if (int_cst_value (p11.offset) != int_cst_value (p21.offset))
>>>>> >>>> +    return int_cst_value (p11.offset) < int_cst_value (p21.offset);
>>>>> >>>> +  if (TREE_CODE (p12.offset) != INTEGER_CST
>>>>> >>>> +      || TREE_CODE (p22.offset) != INTEGER_CST)
>>>>> >>>> +    return p12.offset < p22.offset;
>>>>> >>>> +  return int_cst_value (p12.offset) < int_cst_value (p22.offset);
>>>>> >>>> +}
>>>>> >>>> +
>>>>> >>>> +}
>>>>> >>>>
>>>>> >>>>  /* Function vect_create_cond_for_alias_checks.
>>>>> >>>>
>>>>> >>>> @@ -2292,20 +2364,51 @@ vect_create_cond_for_alias_checks (loop_
>>>>> >>>>    if (may_alias_ddrs.is_empty ())
>>>>> >>>>      return;
>>>>> >>>>
>>>>> >>>> +
>>>>> >>>> +  /* Basically, for each pair of dependent data refs store_ptr_0
>>>>> >>>> +     and load_ptr_0, we create an expression:
>>>>> >>>> +
>>>>> >>>> +     ((store_ptr_0 + store_segment_length_0) <= load_ptr_0)
>>>>> >>>> +     || (load_ptr_0 + load_segment_length_0) <= store_ptr_0))
>>>>> >>>> +
>>>>> >>>> +     for aliasing checks. However, in some cases we can decrease
>>>>> >>>> +     the number of checks by combining two checks into one. For
>>>>> >>>> +     example, suppose we have another pair of data refs store_ptr_0
>>>>> >>>> +     and load_ptr_1, and if the following condition is satisfied:
>>>>> >>>> +
>>>>> >>>> +     load_ptr_0 < load_ptr_1  &&
>>>>> >>>> +     load_ptr_1 - load_ptr_0 - load_segment_length_0 < store_segment_length_0
>>>>> >>>> +
>>>>> >>>> +     (this condition means, in each iteration of vectorized loop,
>>>>> >>>> +     the accessed memory of store_ptr_0 cannot be between the memory
>>>>> >>>> +     of load_ptr_0 and load_ptr_1.)
>>>>> >>>> +
>>>>> >>>> +     we then can use only the following expression to finish the
>>>>> >>>> +     alising checks between store_ptr_0 & load_ptr_0 and
>>>>> >>>> +     store_ptr_0 & load_ptr_1:
>>>>> >>>> +
>>>>> >>>> +     ((store_ptr_0 + store_segment_length_0) <= load_ptr_0)
>>>>> >>>> +     || (load_ptr_1 + load_segment_length_1 <= store_ptr_0))
>>>>> >>>> +
>>>>> >>>> +     Note that we only consider that load_ptr_0 and load_ptr_1 have the
>>>>> >>>> +     same basic address.  */
>>>>> >>>> +
>>>>> >>>> +  std::vector<dr_addr_with_seg_len_pair_t> ddrs_with_seg_len;
>>>>> >>>> +
>>>>> >>>> +  /* First, we collect all data ref pairs for aliasing checks.  */
>>>>> >>>> +
>>>>> >>>>    FOR_EACH_VEC_ELT (may_alias_ddrs, i, ddr)
>>>>> >>>>      {
>>>>> >>>>        struct data_reference *dr_a, *dr_b;
>>>>> >>>>        gimple dr_group_first_a, dr_group_first_b;
>>>>> >>>> -      tree addr_base_a, addr_base_b;
>>>>> >>>>        tree segment_length_a, segment_length_b;
>>>>> >>>>        gimple stmt_a, stmt_b;
>>>>> >>>> -      tree seg_a_min, seg_a_max, seg_b_min, seg_b_max;
>>>>> >>>>
>>>>> >>>>        dr_a = DDR_A (ddr);
>>>>> >>>>        stmt_a = DR_STMT (DDR_A (ddr));
>>>>> >>>>        dr_group_first_a = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_a));
>>>>> >>>>        if (dr_group_first_a)
>>>>> >>>> -        {
>>>>> >>>> + {
>>>>> >>>>    stmt_a = dr_group_first_a;
>>>>> >>>>    dr_a = STMT_VINFO_DATA_REF (vinfo_for_stmt (stmt_a));
>>>>> >>>>   }
>>>>> >>>> @@ -2314,20 +2417,11 @@ vect_create_cond_for_alias_checks (loop_
>>>>> >>>>        stmt_b = DR_STMT (DDR_B (ddr));
>>>>> >>>>        dr_group_first_b = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_b));
>>>>> >>>>        if (dr_group_first_b)
>>>>> >>>> -        {
>>>>> >>>> + {
>>>>> >>>>    stmt_b = dr_group_first_b;
>>>>> >>>>    dr_b = STMT_VINFO_DATA_REF (vinfo_for_stmt (stmt_b));
>>>>> >>>>   }
>>>>> >>>>
>>>>> >>>> -      addr_base_a
>>>>> >>>> - = fold_build_pointer_plus (DR_BASE_ADDRESS (dr_a),
>>>>> >>>> -   size_binop (PLUS_EXPR, DR_OFFSET (dr_a),
>>>>> >>>> -       DR_INIT (dr_a)));
>>>>> >>>> -      addr_base_b
>>>>> >>>> - = fold_build_pointer_plus (DR_BASE_ADDRESS (dr_b),
>>>>> >>>> -   size_binop (PLUS_EXPR, DR_OFFSET (dr_b),
>>>>> >>>> -       DR_INIT (dr_b)));
>>>>> >>>> -
>>>>> >>>>        if (!operand_equal_p (DR_STEP (dr_a), DR_STEP (dr_b), 0))
>>>>> >>>>   length_factor = scalar_loop_iters;
>>>>> >>>>        else
>>>>> >>>> @@ -2335,24 +2429,149 @@ vect_create_cond_for_alias_checks (loop_
>>>>> >>>>        segment_length_a = vect_vfa_segment_size (dr_a, length_factor);
>>>>> >>>>        segment_length_b = vect_vfa_segment_size (dr_b, length_factor);
>>>>> >>>>
>>>>> >>>> +      dr_addr_with_seg_len_pair_t dr_with_seg_len_pair
>>>>> >>>> +  (dr_addr_with_seg_len
>>>>> >>>> +       (dr_a, DR_BASE_ADDRESS (dr_a),
>>>>> >>>> + size_binop (PLUS_EXPR, DR_OFFSET (dr_a), DR_INIT (dr_a)),
>>>>> >>>> + segment_length_a),
>>>>> >>>> +   dr_addr_with_seg_len
>>>>> >>>> +       (dr_b, DR_BASE_ADDRESS (dr_b),
>>>>> >>>> + size_binop (PLUS_EXPR, DR_OFFSET (dr_b), DR_INIT (dr_b)),
>>>>> >>>> + segment_length_b));
>>>>> >>>> +
>>>>> >>>> +      if (dr_with_seg_len_pair.first.basic_addr >
>>>>> >>>> +  dr_with_seg_len_pair.second.basic_addr)
>>>>> >>>> + std::swap (dr_with_seg_len_pair.first, dr_with_seg_len_pair.second);
>>>>> >>>> +
>>>>> >>>> +      ddrs_with_seg_len.push_back (dr_with_seg_len_pair);
>>>>> >>>> +    }
>>>>> >>>> +
>>>>> >>>> +  /* Second, we sort the collected data ref pairs so that we can scan
>>>>> >>>> +     them once to combine all possible aliasing checks.  */
>>>>> >>>> +
>>>>> >>>> +  std::sort (ddrs_with_seg_len.begin(), ddrs_with_seg_len.end());
>>>>> >>>> +
>>>>> >>>> +  /* Remove duplicate data ref pairs.  */
>>>>> >>>> +  ddrs_with_seg_len.erase (std::unique (ddrs_with_seg_len.begin(),
>>>>> >>>> + ddrs_with_seg_len.end()),
>>>>> >>>> +   ddrs_with_seg_len.end());
>>>>> >>>> +
>>>>> >>>> +  /* We then scan the sorted dr pairs and check if we can combine
>>>>> >>>> +     alias checks of two neighbouring dr pairs.  */
>>>>> >>>> +
>>>>> >>>> +  for (size_t i = 1; i < ddrs_with_seg_len.size (); ++i)
>>>>> >>>> +    {
>>>>> >>>> +      dr_addr_with_seg_len& dr_a1 = ddrs_with_seg_len[i-1].first;
>>>>> >>>> +      dr_addr_with_seg_len& dr_b1 = ddrs_with_seg_len[i-1].second;
>>>>> >>>> +      dr_addr_with_seg_len& dr_a2 = ddrs_with_seg_len[i].first;
>>>>> >>>> +      dr_addr_with_seg_len& dr_b2 = ddrs_with_seg_len[i].second;
>>>>> >>>> +
>>>>> >>>> +      if (dr_a1 == dr_a2)
>>>>> >>>> + {
>>>>> >>>> +  if (dr_b1.basic_addr != dr_b2.basic_addr
>>>>> >>>> +      || TREE_CODE (dr_b1.offset) != INTEGER_CST
>>>>> >>>> +      || TREE_CODE (dr_b2.offset) != INTEGER_CST)
>>>>> >>>> +    continue;
>>>>> >>>> +
>>>>> >>>> +  int diff = int_cst_value (dr_b2.offset) -
>>>>> >>>> +     int_cst_value (dr_b1.offset);
>>>>> >>>> +
>>>>> >>>> +  gcc_assert (diff > 0);
>>>>> >>>> +
>>>>> >>>> +  if (diff <= vect_factor
>>>>> >>>> +      || (TREE_CODE (dr_b1.seg_len) == INTEGER_CST
>>>>> >>>> +  && diff - int_cst_value (dr_b1.seg_len) < vect_factor)
>>>>> >>>> +      || (TREE_CODE (dr_b1.seg_len) == INTEGER_CST
>>>>> >>>> +  && TREE_CODE (dr_a1.seg_len) == INTEGER_CST
>>>>> >>>> +  && diff - int_cst_value (dr_b1.seg_len) <
>>>>> >>>> +     int_cst_value (dr_a1.seg_len)))
>>>>> >>>> +    {
>>>>> >>>> +      if (dump_enabled_p ())
>>>>> >>>> + {
>>>>> >>>> +  dump_printf_loc
>>>>> >>>> +      (MSG_NOTE, vect_location,
>>>>> >>>> +       "combining two runtime checks for data references ");
>>>>> >>>> +  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_b1.dr));
>>>>> >>>> +  dump_printf (MSG_NOTE, " and ");
>>>>> >>>> +  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_b2.dr));
>>>>> >>>> +  dump_printf (MSG_NOTE, "\n");
>>>>> >>>> + }
>>>>> >>>> +
>>>>> >>>> +      dr_b1.seg_len = size_binop (PLUS_EXPR,
>>>>> >>>> +  dr_b2.seg_len, size_int (diff));
>>>>> >>>> +      ddrs_with_seg_len.erase (ddrs_with_seg_len.begin () + i);
>>>>> >>>> +      --i;
>>>>> >>>> +    }
>>>>> >>>> + }
>>>>> >>>> +      else if (dr_b1 == dr_b2)
>>>>> >>>> + {
>>>>> >>>> +  if (dr_a1.basic_addr != dr_a2.basic_addr
>>>>> >>>> +      || TREE_CODE (dr_a1.offset) != INTEGER_CST
>>>>> >>>> +      || TREE_CODE (dr_a2.offset) != INTEGER_CST)
>>>>> >>>> +    continue;
>>>>> >>>> +
>>>>> >>>> +  int diff = int_cst_value (dr_a2.offset) -
>>>>> >>>> +     int_cst_value (dr_a1.offset);
>>>>> >>>> +
>>>>> >>>> +  gcc_assert (diff > 0);
>>>>> >>>> +
>>>>> >>>> +  if (diff <= vect_factor
>>>>> >>>> +      || (TREE_CODE (dr_a1.seg_len) == INTEGER_CST
>>>>> >>>> +  && diff - int_cst_value (dr_a1.seg_len) < vect_factor)
>>>>> >>>> +      || (TREE_CODE (dr_a1.seg_len) == INTEGER_CST
>>>>> >>>> +  && TREE_CODE (dr_b1.seg_len) == INTEGER_CST
>>>>> >>>> +  && diff - int_cst_value (dr_a1.seg_len) <
>>>>> >>>> +     int_cst_value (dr_b1.seg_len)))
>>>>> >>>> +    {
>>>>> >>>> +      if (dump_enabled_p ())
>>>>> >>>> + {
>>>>> >>>> +  dump_printf_loc
>>>>> >>>> +      (MSG_NOTE, vect_location,
>>>>> >>>> +       "combining two runtime checks for data references ");
>>>>> >>>> +  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_a1.dr));
>>>>> >>>> +  dump_printf (MSG_NOTE, " and ");
>>>>> >>>> +  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_a2.dr));
>>>>> >>>> +  dump_printf (MSG_NOTE, "\n");
>>>>> >>>> + }
>>>>> >>>> +
>>>>> >>>> +      dr_a1.seg_len = size_binop (PLUS_EXPR,
>>>>> >>>> +  dr_a2.seg_len, size_int (diff));
>>>>> >>>> +      ddrs_with_seg_len.erase (ddrs_with_seg_len.begin () + i);
>>>>> >>>> +      --i;
>>>>> >>>> +    }
>>>>> >>>> + }
>>>>> >>>> +    }
>>>>> >>>> +
>>>>> >>>> +  for (size_t i = 0, s = ddrs_with_seg_len.size (); i < s; ++i)
>>>>> >>>> +    {
>>>>> >>>> +      const dr_addr_with_seg_len& dr_a = ddrs_with_seg_len[i].first;
>>>>> >>>> +      const dr_addr_with_seg_len& dr_b = ddrs_with_seg_len[i].second;
>>>>> >>>> +      tree segment_length_a = dr_a.seg_len;
>>>>> >>>> +      tree segment_length_b = dr_b.seg_len;
>>>>> >>>> +
>>>>> >>>> +      tree addr_base_a
>>>>> >>>> + = fold_build_pointer_plus (dr_a.basic_addr, dr_a.offset);
>>>>> >>>> +      tree addr_base_b
>>>>> >>>> + = fold_build_pointer_plus (dr_b.basic_addr, dr_b.offset);
>>>>> >>>> +
>>>>> >>>>        if (dump_enabled_p ())
>>>>> >>>>   {
>>>>> >>>>    dump_printf_loc (MSG_NOTE, vect_location,
>>>>> >>>> -                           "create runtime check for data references ");
>>>>> >>>> -  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_a));
>>>>> >>>> +   "create runtime check for data references ");
>>>>> >>>> +  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_a.dr));
>>>>> >>>>    dump_printf (MSG_NOTE, " and ");
>>>>> >>>> -  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_b));
>>>>> >>>> -          dump_printf (MSG_NOTE, "\n");
>>>>> >>>> +  dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dr_b.dr));
>>>>> >>>> +  dump_printf (MSG_NOTE, "\n");
>>>>> >>>>   }
>>>>> >>>>
>>>>> >>>> -      seg_a_min = addr_base_a;
>>>>> >>>> -      seg_a_max = fold_build_pointer_plus (addr_base_a, segment_length_a);
>>>>> >>>> -      if (tree_int_cst_compare (DR_STEP (dr_a), size_zero_node) < 0)
>>>>> >>>> +      tree seg_a_min = addr_base_a;
>>>>> >>>> +      tree seg_a_max = fold_build_pointer_plus (addr_base_a, segment_length_a);
>>>>> >>>> +      if (tree_int_cst_compare (DR_STEP (dr_a.dr), size_zero_node) < 0)
>>>>> >>>>   seg_a_min = seg_a_max, seg_a_max = addr_base_a;
>>>>> >>>>
>>>>> >>>> -      seg_b_min = addr_base_b;
>>>>> >>>> -      seg_b_max = fold_build_pointer_plus (addr_base_b, segment_length_b);
>>>>> >>>> -      if (tree_int_cst_compare (DR_STEP (dr_b), size_zero_node) < 0)
>>>>> >>>> +      tree seg_b_min = addr_base_b;
>>>>> >>>> +      tree seg_b_max = fold_build_pointer_plus (addr_base_b, segment_length_b);
>>>>> >>>> +      if (tree_int_cst_compare (DR_STEP (dr_b.dr), size_zero_node) < 0)
>>>>> >>>>   seg_b_min = seg_b_max, seg_b_max = addr_base_b;
>>>>> >>>>
>>>>> >>>>        part_cond_expr =
>>>>> >>>> @@ -2477,6 +2696,81 @@ vect_loop_versioning (loop_vec_info loop
>>>>> >>>>        adjust_phi_and_debug_stmts (orig_phi, e, PHI_RESULT (new_phi));
>>>>> >>>>      }
>>>>> >>>>
>>>>> >>>> +  /* Extract load and store statements on pointers with zero-stride
>>>>> >>>> +     accesses.  */
>>>>> >>>> +  if (LOOP_REQUIRES_VERSIONING_FOR_ALIAS (loop_vinfo))
>>>>> >>>> +    {
>>>>> >>>> +
>>>>> >>>> +      /* In the loop body, we iterate each statement to check if it is a load
>>>>> >>>> + or store. Then we check the DR_STEP of the data reference.  If
>>>>> >>>> + DR_STEP is zero, then we will hoist the load statement to the loop
>>>>> >>>> + preheader, and move the store statement to the loop exit.  */
>>>>> >>>> +
>>>>> >>>> +      for (gimple_stmt_iterator si = gsi_start_bb (loop->header);
>>>>> >>>> +   !gsi_end_p (si); )
>>>>> >>>> + {
>>>>> >>>> +  gimple stmt = gsi_stmt (si);
>>>>> >>>> +  stmt_vec_info stmt_info = vinfo_for_stmt (stmt);
>>>>> >>>> +  struct data_reference *dr = STMT_VINFO_DATA_REF (stmt_info);
>>>>> >>>> +
>>>>> >>>> +
>>>>> >>>> +  if (dr && integer_zerop (DR_STEP (dr)))
>>>>> >>>> +    {
>>>>> >>>> +      if (DR_IS_READ (dr))
>>>>> >>>> + {
>>>>> >>>> +  if (dump_file)
>>>>> >>>> +    {
>>>>> >>>> +      fprintf (dump_file,
>>>>> >>>> +       "Hoist the load to outside of the loop:\n");
>>>>> >>>> +      print_gimple_stmt (dump_file, stmt, 0,
>>>>> >>>> + TDF_VOPS|TDF_MEMSYMS);
>>>>> >>>> +    }
>>>>> >>>> +
>>>>> >>>> +  basic_block preheader = loop_preheader_edge (loop)->src;
>>>>> >>>> +  gimple_stmt_iterator si_dst = gsi_last_bb (preheader);
>>>>> >>>> +  gsi_move_after (&si, &si_dst);
>>>>> >>>> + }
>>>>> >>>> +      else
>>>>> >>>> + {
>>>>> >>>> +  gimple_stmt_iterator si_dst =
>>>>> >>>> +      gsi_last_bb (single_exit (loop)->dest);
>>>>> >>>> +  gsi_move_after (&si, &si_dst);
>>>>> >>>> + }
>>>>> >>>> +              continue;
>>>>> >>>> +    }
>>>>> >>>> +  else if (!dr)
>>>>> >>>> +          {
>>>>> >>>> +            bool hoist = true;
>>>>> >>>> +            for (size_t i = 0; i < gimple_num_ops (stmt); i++)
>>>>> >>>> +            {
>>>>> >>>> +              tree op = gimple_op (stmt, i);
>>>>> >>>> +              if (TREE_CODE (op) == INTEGER_CST
>>>>> >>>> +                  || TREE_CODE (op) == REAL_CST)
>>>>> >>>> +                continue;
>>>>> >>>> +              if (TREE_CODE (op) == SSA_NAME)
>>>>> >>>> +              {
>>>>> >>>> +                gimple def = SSA_NAME_DEF_STMT (op);
>>>>> >>>> +                if (def == stmt
>>>>> >>>> +                    || gimple_nop_p (def)
>>>>> >>>> +                    || !flow_bb_inside_loop_p (loop, gimple_bb (def)))
>>>>> >>>> +                  continue;
>>>>> >>>> +              }
>>>>> >>>> +              hoist = false;
>>>>> >>>> +              break;
>>>>> >>>> +            }
>>>>> >>>> +
>>>>> >>>> +            if (hoist)
>>>>> >>>> +            {
>>>>> >>>> +              basic_block preheader = loop_preheader_edge (loop)->src;
>>>>> >>>> +              gimple_stmt_iterator si_dst = gsi_last_bb (preheader);
>>>>> >>>> +              gsi_move_after (&si, &si_dst);
>>>>> >>>> +              continue;
>>>>> >>>> +            }
>>>>> >>>> +          }
>>>>> >>>> +          gsi_next (&si);
>>>>> >>>> + }
>>>>> >>>> +    }
>>>>> >>>> +
>>>>> >>>>    /* End loop-exit-fixes after versioning.  */
>>>>> >>>>
>>>>> >>>>    if (cond_expr_stmt_list)
>>>>> >>>> Index: gcc/ChangeLog
>>>>> >>>> ===================================================================
>>>>> >>>> --- gcc/ChangeLog (revision 202663)
>>>>> >>>> +++ gcc/ChangeLog (working copy)
>>>>> >>>> @@ -1,3 +1,8 @@
>>>>> >>>> +2013-10-01  Cong Hou  <congh@google.com>
>>>>> >>>> +
>>>>> >>>> + * tree-vect-loop-manip.c (vect_create_cond_for_alias_checks): Combine
>>>>> >>>> + alias checks if it is possible to amortize the runtime overhead.
>>>>> >>>> +
>>>>> >>>>
>>>>> >>>>
>>>>> >>>
>>>>> >>> --
>>>>> >>> Richard Biener <rguenther@suse.de>
>>>>> >>> SUSE / SUSE Labs
>>>>> >>> SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
>>>>> >>> GF: Jeff Hawn, Jennifer Guild, Felix Imend

Attachment: patch-alias.txt
Description: Text document


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