Forget to mention that the alias check merger can reduce the number of
checks from 7 to 2 for this example:
struct A {
int *base;
int offset;
int offset2;
int offset3;
int offset4;
int offset5;
int offset6;
int offset7;
int offset8;
};
void foo (struct A * ar1, struct A* ar2)
{
int i;
for (i = 0; i < 10000; i++)
{
ar1->base[i] = 2*ar2->base[i] + ar2->offset + ar2->offset2
+ ar2->offset3 + ar2->offset4 + ar2->offset5 + ar2->offset6; /* +
ar2->offset7 + ar2->offset8;*/
}
}
thanks,
Cong
On Wed, Oct 2, 2013 at 2:18 PM, Xinliang David Li <davi...@google.com> wrote:
> On Wed, Oct 2, 2013 at 4:24 AM, Richard Biener <rguent...@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).
>
> yes.
>
>>
>> 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
>
> Yes. The handling of this should be moved to
> 'vect_prune_runtime_alias_test_list' to avoid premature decisions.
>
>
>
>>which currently inhibits
>> vectorization of the HIMENO benchmark by default (and make us look bad
>> compared to LLVM).
>
> Here is a small reproducible:
>
> struct A {
> int *base;
> int offset;
> int offset2;
> int offset3;
> int offset4;
> int offset5;
> int offset6;
> int offset7;
> int offset8;
> };
>
> void foo (struct A * ar1, struct A* ar2)
> {
> int i;
> for (i = 0; i < 10000; i++)
> {
> ar1->base[i] = 2*ar2->base[i] + ar2->offset + ar2->offset2
> + ar2->offset3 + ar2->offset4 + ar2->offset5 + ar2->offset6; /* +
> ar2->offset7 + ar2->offset8;*/
> }
> }
>
> GCC trunk won't vectorize it at O2 due to the limit.
>
>
> There is another problem we should be tracking: GCC no longer
> vectorize the loop (with large
> --param=vect-max-version-for-alias-checks=40) when -fno-strict-alias
> is specified. However with additional runtime alias check, the loop
> should be vectorizable.
>
> David
>
>
>>
>> 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.
>>
>> 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 <co...@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 <rguent...@suse.de>
>> SUSE / SUSE Labs
>> SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
>> GF: Jeff Hawn, Jennifer Guild, Felix Imend
