Richard Biener <richard.guent...@gmail.com> writes:
> On Thu, Jul 8, 2021 at 2:45 PM Richard Sandiford via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> This patch adds a helper function called vect_phi_initial_value
>> for returning the incoming value of a given loop phi. The main
>> reason for adding it is to ensure that the right preheader edge
>> is used when vectorising nested loops. (PHI_ARG_DEF_FROM_EDGE
>> itself doesn't assert that the given edge is for the right block,
>> although I guess that would be good to add separately.)
>
> We were sometimes (most of the time?) using an explicit
> loop where you now get it from the PHI - that makes the
> assert somewhat pointless to some extent - of course it
> makes sense on its own that the loop is the same as that
> of the PHI def. I just wonder if you think any of the existing
> code might have been wrong? If so the new assert doesn't
> catch all originally wrong cases.
I don't remember seeing a case where the existing code got it wrong,
but I think one of the patches in the series did initially use the
wrong loop's preheader.
But yeah, the function and assert only help to avoid using
PHI_ARG_DEF_FROM_EDGE with the wrong edge. If the problem was instead
passing the wrong phi then the patch doesn't help to catch that.
The edge mistake is more likely to be a silent failure though,
since the edge indices for both loops might happen to be the same
(but might not).
Thanks,
Richard
>
> Otherwise OK,
> Richard.
>
>> gcc/
>> * tree-vectorizer.h: Include tree-ssa-operands.h.
>> (vect_phi_initial_value): New function.
>> * tree-vect-loop.c (neutral_op_for_slp_reduction): Use it.
>> (get_initial_defs_for_reduction, info_for_reduction): Likewise.
>> (vect_create_epilog_for_reduction, vectorizable_reduction): Likewise.
>> (vect_transform_cycle_phi, vectorizable_induction): Likewise.
>> ---
>> gcc/tree-vect-loop.c | 29 +++++++++--------------------
>> gcc/tree-vectorizer.h | 21 ++++++++++++++++++++-
>> 2 files changed, 29 insertions(+), 21 deletions(-)
>>
>> diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
>> index 1bd9a6ea52c..a31d7621c3b 100644
>> --- a/gcc/tree-vect-loop.c
>> +++ b/gcc/tree-vect-loop.c
>> @@ -3288,8 +3288,7 @@ neutral_op_for_slp_reduction (slp_tree slp_node, tree
>> vector_type,
>> has only a single initial value, so that value is neutral for
>> all statements. */
>> if (reduc_chain)
>> - return PHI_ARG_DEF_FROM_EDGE (stmt_vinfo->stmt,
>> - loop_preheader_edge (loop));
>> + return vect_phi_initial_value (stmt_vinfo);
>> return NULL_TREE;
>>
>> default:
>> @@ -4829,13 +4828,13 @@ get_initial_defs_for_reduction (vec_info *vinfo,
>> /* Get the def before the loop. In reduction chain we have only
>> one initial value. Else we have as many as PHIs in the group. */
>> if (reduc_chain)
>> - op = j != 0 ? neutral_op : PHI_ARG_DEF_FROM_EDGE (stmt_vinfo->stmt,
>> pe);
>> + op = j != 0 ? neutral_op : vect_phi_initial_value (stmt_vinfo);
>> else if (((vec_oprnds->length () + 1) * nunits
>> - number_of_places_left_in_vector >= group_size)
>> && neutral_op)
>> op = neutral_op;
>> else
>> - op = PHI_ARG_DEF_FROM_EDGE (stmt_vinfo->stmt, pe);
>> + op = vect_phi_initial_value (stmt_vinfo);
>>
>> /* Create 'vect_ = {op0,op1,...,opn}'. */
>> number_of_places_left_in_vector--;
>> @@ -4906,9 +4905,7 @@ info_for_reduction (vec_info *vinfo, stmt_vec_info
>> stmt_info)
>> }
>> else if (STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle)
>> {
>> - edge pe = loop_preheader_edge (gimple_bb (phi)->loop_father);
>> - stmt_vec_info info
>> - = vinfo->lookup_def (PHI_ARG_DEF_FROM_EDGE (phi, pe));
>> + stmt_vec_info info = vinfo->lookup_def (vect_phi_initial_value (phi));
>> if (info && STMT_VINFO_DEF_TYPE (info) == vect_double_reduction_def)
>> stmt_info = info;
>> }
>> @@ -5042,8 +5039,7 @@ vect_create_epilog_for_reduction (loop_vec_info
>> loop_vinfo,
>> {
>> /* Get at the scalar def before the loop, that defines the initial
>> value
>> of the reduction variable. */
>> - initial_def = PHI_ARG_DEF_FROM_EDGE (reduc_def_stmt,
>> - loop_preheader_edge (loop));
>> + initial_def = vect_phi_initial_value (reduc_def_stmt);
>> /* Optimize: for induction condition reduction, if we can't use zero
>> for induc_val, use initial_def. */
>> if (STMT_VINFO_REDUC_TYPE (reduc_info) ==
>> INTEGER_INDUC_COND_REDUCTION)
>> @@ -5558,9 +5554,7 @@ vect_create_epilog_for_reduction (loop_vec_info
>> loop_vinfo,
>> for MIN and MAX reduction, for example. */
>> if (!neutral_op)
>> {
>> - tree scalar_value
>> - = PHI_ARG_DEF_FROM_EDGE (orig_phis[i]->stmt,
>> - loop_preheader_edge (loop));
>> + tree scalar_value = vect_phi_initial_value (orig_phis[i]);
>> scalar_value = gimple_convert (&seq, TREE_TYPE (vectype),
>> scalar_value);
>> vector_identity = gimple_build_vector_from_val (&seq, vectype,
>> @@ -6752,10 +6746,7 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
>> else if (cond_reduc_dt == vect_constant_def)
>> {
>> enum vect_def_type cond_initial_dt;
>> - tree cond_initial_val
>> - = PHI_ARG_DEF_FROM_EDGE (reduc_def_phi, loop_preheader_edge
>> (loop));
>> -
>> - gcc_assert (cond_reduc_val != NULL_TREE);
>> + tree cond_initial_val = vect_phi_initial_value (reduc_def_phi);
>> vect_is_simple_use (cond_initial_val, loop_vinfo,
>> &cond_initial_dt);
>> if (cond_initial_dt == vect_constant_def
>> && types_compatible_p (TREE_TYPE (cond_initial_val),
>> @@ -7528,8 +7519,7 @@ vect_transform_cycle_phi (loop_vec_info loop_vinfo,
>> {
>> /* Get at the scalar def before the loop, that defines the initial
>> value of the reduction variable. */
>> - tree initial_def = PHI_ARG_DEF_FROM_EDGE (phi,
>> - loop_preheader_edge (loop));
>> + tree initial_def = vect_phi_initial_value (phi);
>> /* Optimize: if initial_def is for REDUC_MAX smaller than the base
>> and we can't use zero for induc_val, use initial_def. Similarly
>> for REDUC_MIN and initial_def larger than the base. */
>> @@ -8175,8 +8165,7 @@ vectorizable_induction (loop_vec_info loop_vinfo,
>> return true;
>> }
>>
>> - init_expr = PHI_ARG_DEF_FROM_EDGE (phi,
>> - loop_preheader_edge (iv_loop));
>> + init_expr = vect_phi_initial_value (phi);
>>
>> gimple_seq stmts = NULL;
>> if (!nested_in_vect_loop)
>> diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
>> index fa28336d429..e2fd3609fee 100644
>> --- a/gcc/tree-vectorizer.h
>> +++ b/gcc/tree-vectorizer.h
>> @@ -27,7 +27,7 @@ typedef class _stmt_vec_info *stmt_vec_info;
>> #include "tree-hash-traits.h"
>> #include "target.h"
>> #include "internal-fn.h"
>> -
>> +#include "tree-ssa-operands.h"
>>
>> /* Used for naming of new temporaries. */
>> enum vect_var_kind {
>> @@ -1369,6 +1369,25 @@ nested_in_vect_loop_p (class loop *loop,
>> stmt_vec_info stmt_info)
>> && (loop->inner == (gimple_bb (stmt_info->stmt))->loop_father));
>> }
>>
>> +/* PHI is either a scalar reduction phi or a scalar induction phi.
>> + Return the initial value of the variable on entry to the containing
>> + loop. */
>> +
>> +static inline tree
>> +vect_phi_initial_value (gphi *phi)
>> +{
>> + basic_block bb = gimple_bb (phi);
>> + edge pe = loop_preheader_edge (bb->loop_father);
>> + gcc_assert (pe->dest == bb);
>> + return PHI_ARG_DEF_FROM_EDGE (phi, pe);
>> +}
>> +
>> +static inline tree
>> +vect_phi_initial_value (stmt_vec_info stmt_info)
>> +{
>> + return vect_phi_initial_value (as_a <gphi *> (stmt_info->stmt));
>> +}
>> +
>> /* Return true if STMT_INFO should produce a vector mask type rather than
>> a normal nonmask type. */
>>
