On Mon, Feb 26, 2018 at 3:37 PM, Richard Sandiford
<richard.sandif...@linaro.org> wrote:
> Richard Biener <richard.guent...@gmail.com> writes:
>> On Tue, Feb 20, 2018 at 5:53 PM, Richard Sandiford
>> <richard.sandif...@linaro.org> wrote:
>>> This patch prevents pattern-matching of fold-left SLP reduction chains,
>>> which the previous patch for 83965 didn't handle properly. It only
>>> stops the last statement in the group from being matched, but that's
>>> enough to cause the group to be dissolved later.
>>>
>>> A better fix would be to put all the information about the reduction
>>> on the the first statement in the reduction chain, so that every
>>> statement in the group can tell what the group is doing. That doesn't
>>> seem like stage 4 material though.
>>>
>>> As it stands, things seem to be a bit of a mess. In
>>> vect_force_simple_reduction we attach the reduction type and
>>> phi pointer to the last statement in a reduction chain:
>>>
>>> reduc_def_info = vinfo_for_stmt (def);
>>> STMT_VINFO_REDUC_TYPE (reduc_def_info) = v_reduc_type;
>>> STMT_VINFO_REDUC_DEF (reduc_def_info) = phi;
>>>
>>> and mark it as vect_reduction_type in vect_analyze_scalar_cycles_1:
>>>
>>> STMT_VINFO_DEF_TYPE (vinfo_for_stmt (reduc_stmt)) =
>>>
>>> vect_reduction_def;
>>>
>>> This code in vectorizable_reduction gave the impression that
>>> everything really is keyed off the last statement:
>>>
>>> /* In case of reduction chain we switch to the first stmt in the chain,
>>> but
>>> we don't update STMT_INFO, since only the last stmt is marked as
>>> reduction
>>> and has reduction properties. */
>>> if (GROUP_FIRST_ELEMENT (stmt_info)
>>> && GROUP_FIRST_ELEMENT (stmt_info) != stmt)
>>> {
>>> stmt = GROUP_FIRST_ELEMENT (stmt_info);
>>> first_p = false;
>>> }
>>>
>>> But this code is dead these days. GROUP_FIRST_ELEMENT is only nonnull
>>> for SLP reduction chains, since we dissolve the group if SLP fails.
>>> And SLP only analyses the first statement in the group, not the last:
>>>
>>> stmt = SLP_TREE_SCALAR_STMTS (node)[0];
>>> stmt_vec_info stmt_info = vinfo_for_stmt (stmt);
>>> [...]
>>> bool res = vect_analyze_stmt (stmt, &dummy, node, node_instance);
>>>
>>> So from that point of view the DEF_TYPE, REDUC_TYPE and REDUC_DEF
>>> are being attached to the wrong statement, since we only analyse
>>> the first one. But it turns out that REDUC_TYPE and REDUC_DEF
>>> don't matter for the first statement in the group, since that
>>> takes the phi as an input, and when the phi is a direct input,
>>> we use *its* REDUC_TYPE and REDUC_DEF instead of the statement's
>>> own info. The DEF_TYPE problem is handled by:
>>>
>>> /* Mark the first element of the reduction chain as reduction to
>>> properly
>>> transform the node. In the reduction analysis phase only the last
>>> element of the chain is marked as reduction. */
>>> if (!STMT_VINFO_GROUPED_ACCESS (vinfo_for_stmt (stmt)))
>>> STMT_VINFO_DEF_TYPE (vinfo_for_stmt (stmt)) = vect_reduction_def;
>>>
>>> in vect_analyze_slp_instance (cancelled by:
>>>
>>> STMT_VINFO_DEF_TYPE (vinfo_for_stmt (first_element))
>>> = vect_internal_def;
>>>
>>> in vect_analyze_slp on failure), with the operation being repeated
>>> in vect_schedule_slp_instance (redundantly AFAICT):
>>>
>>> /* Mark the first element of the reduction chain as reduction to properly
>>> transform the node. In the analysis phase only the last element of the
>>> chain is marked as reduction. */
>>> if (GROUP_FIRST_ELEMENT (stmt_info) && !STMT_VINFO_GROUPED_ACCESS
>>> (stmt_info)
>>> && GROUP_FIRST_ELEMENT (stmt_info) == stmt)
>>> {
>>> STMT_VINFO_DEF_TYPE (stmt_info) = vect_reduction_def;
>>> STMT_VINFO_TYPE (stmt_info) = reduc_vec_info_type;
>>> }
>>>
>>> Tested on aarch64-linux-gnu, x86_64-linux-gnu and powerpc64-linux-gnu.
>>> OK to install?
>>
>> Ok for stage1.
>
> It's a GCC 8 regression, so OK for stage4?
Oh, ok then.
Richard.
> Richard
>
>> Richard.
>>
>>> Richard
>>>
>>>
>>> 2018-02-20 Richard Sandiford <richard.sandif...@linaro.org>
>>>
>>> gcc/
>>> PR tree-optimization/83965
>>> * tree-vect-patterns.c (vect_reassociating_reduction_p): Assume
>>> that grouped statements are part of a reduction chain. Return
>>> true if the statement is not marked as a reduction itself but
>>> is part of a group.
>>> (vect_recog_dot_prod_pattern): Don't check whether the statement
>>> is part of a group here.
>>> (vect_recog_sad_pattern): Likewise.
>>> (vect_recog_widen_sum_pattern): Likewise.
>>>
>>> gcc/testsuite/
>>> PR tree-optimization/83965
>>> * gcc.dg/vect/pr83965-2.c: New test.
>>>
>>> Index: gcc/tree-vect-patterns.c
>>> ===================================================================
>>> --- gcc/tree-vect-patterns.c 2018-02-20 09:40:41.843451227 +0000
>>> +++ gcc/tree-vect-patterns.c 2018-02-20 16:28:55.636762056 +0000
>>> @@ -222,13 +222,16 @@ vect_recog_temp_ssa_var (tree type, gimp
>>> }
>>>
>>> /* Return true if STMT_VINFO describes a reduction for which reassociation
>>> - is allowed. */
>>> + is allowed. If STMT_INFO is part of a group, assume that it's part of
>>> + a reduction chain and optimistically assume that all statements
>>> + except the last allow reassociation. */
>>>
>>> static bool
>>> vect_reassociating_reduction_p (stmt_vec_info stmt_vinfo)
>>> {
>>> return (STMT_VINFO_DEF_TYPE (stmt_vinfo) == vect_reduction_def
>>> - && STMT_VINFO_REDUC_TYPE (stmt_vinfo) != FOLD_LEFT_REDUCTION);
>>> + ? STMT_VINFO_REDUC_TYPE (stmt_vinfo) != FOLD_LEFT_REDUCTION
>>> + : GROUP_FIRST_ELEMENT (stmt_vinfo) != NULL);
>>> }
>>>
>>> /* Function vect_recog_dot_prod_pattern
>>> @@ -350,8 +353,7 @@ vect_recog_dot_prod_pattern (vec<gimple
>>> {
>>> gimple *def_stmt;
>>>
>>> - if (!vect_reassociating_reduction_p (stmt_vinfo)
>>> - && ! STMT_VINFO_GROUP_FIRST_ELEMENT (stmt_vinfo))
>>> + if (!vect_reassociating_reduction_p (stmt_vinfo))
>>> return NULL;
>>> oprnd0 = gimple_assign_rhs1 (last_stmt);
>>> oprnd1 = gimple_assign_rhs2 (last_stmt);
>>> @@ -571,8 +573,7 @@ vect_recog_sad_pattern (vec<gimple *> *s
>>> {
>>> gimple *def_stmt;
>>>
>>> - if (!vect_reassociating_reduction_p (stmt_vinfo)
>>> - && ! STMT_VINFO_GROUP_FIRST_ELEMENT (stmt_vinfo))
>>> + if (!vect_reassociating_reduction_p (stmt_vinfo))
>>> return NULL;
>>> plus_oprnd0 = gimple_assign_rhs1 (last_stmt);
>>> plus_oprnd1 = gimple_assign_rhs2 (last_stmt);
>>> @@ -1256,8 +1257,7 @@ vect_recog_widen_sum_pattern (vec<gimple
>>> if (gimple_assign_rhs_code (last_stmt) != PLUS_EXPR)
>>> return NULL;
>>>
>>> - if (!vect_reassociating_reduction_p (stmt_vinfo)
>>> - && ! STMT_VINFO_GROUP_FIRST_ELEMENT (stmt_vinfo))
>>> + if (!vect_reassociating_reduction_p (stmt_vinfo))
>>> return NULL;
>>>
>>> oprnd0 = gimple_assign_rhs1 (last_stmt);
>>> Index: gcc/testsuite/gcc.dg/vect/pr83965-2.c
>>> ===================================================================
>>> --- /dev/null 2018-02-19 19:34:42.906488063 +0000
>>> +++ gcc/testsuite/gcc.dg/vect/pr83965-2.c 2018-02-20
>>> 16:28:55.635762095 +0000
>>> @@ -0,0 +1,16 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-additional-options "-Ofast -ftrapv" } */
>>> +
>>> +int c;
>>> +unsigned char d;
>>> +int e (unsigned char *f)
>>> +{
>>> + int g;
>>> + for (int a; a; a++)
>>> + {
>>> + for (int b = 0; b < 6; b++)
>>> + g += __builtin_abs (f[b] - d);
>>> + f += c;
>>> + }
>>> + return g;
>>> +}
