From: Richard Biener <rguenther@suse.de>
To: Richard Sandiford <richard.sandiford@arm.com>
Cc: Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] tree-optimization/110742 - fix latent issue with permuting existing vectors
Date: Thu, 20 Jul 2023 19:10:49 +0200 [thread overview]
Message-ID: <39395404-A479-4451-A2E8-2BF46AE766C0@suse.de> (raw)
In-Reply-To: <mptpm4mikod.fsf@arm.com>
> Am 20.07.2023 um 18:59 schrieb Richard Sandiford <richard.sandiford@arm.com>:
>
> Richard Biener <rguenther@suse.de> writes:
>>>> Am 20.07.2023 um 16:09 schrieb Richard Sandiford <richard.sandiford@arm.com>:
>>>
>>> Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
>>>> When we materialize a layout we push edge permutes to constant/external
>>>> defs without checking we can actually do so. For externals defined
>>>> by vector stmts rather than scalar components we can't.
>>>>
>>>> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>>>>
>>>> OK?
>>>>
>>>> Thanks,
>>>> Richard.
>>>>
>>>> PR tree-optimization/110742
>>>> * tree-vect-slp.cc (vect_optimize_slp_pass::get_result_with_layout):
>>>> Do not materialize an edge permutation in an external node with
>>>> vector defs.
>>>> (vect_slp_analyze_node_operations_1): Guard purely internal
>>>> nodes better.
>>>>
>>>> * g++.dg/torture/pr110742.C: New testcase.
>>>> ---
>>>> gcc/testsuite/g++.dg/torture/pr110742.C | 47 +++++++++++++++++++++++++
>>>> gcc/tree-vect-slp.cc | 8 +++--
>>>> 2 files changed, 53 insertions(+), 2 deletions(-)
>>>> create mode 100644 gcc/testsuite/g++.dg/torture/pr110742.C
>>>>
>>>> diff --git a/gcc/testsuite/g++.dg/torture/pr110742.C b/gcc/testsuite/g++.dg/torture/pr110742.C
>>>> new file mode 100644
>>>> index 00000000000..d41ac0479d2
>>>> --- /dev/null
>>>> +++ b/gcc/testsuite/g++.dg/torture/pr110742.C
>>>> @@ -0,0 +1,47 @@
>>>> +// { dg-do compile }
>>>> +
>>>> +struct HARD_REG_SET {
>>>> + HARD_REG_SET operator~() const {
>>>> + HARD_REG_SET res;
>>>> + for (unsigned int i = 0; i < (sizeof(elts) / sizeof((elts)[0])); ++i)
>>>> + res.elts[i] = ~elts[i];
>>>> + return res;
>>>> + }
>>>> + HARD_REG_SET operator&(const HARD_REG_SET &other) const {
>>>> + HARD_REG_SET res;
>>>> + for (unsigned int i = 0; i < (sizeof(elts) / sizeof((elts)[0])); ++i)
>>>> + res.elts[i] = elts[i] & other.elts[i];
>>>> + return res;
>>>> + }
>>>> + unsigned long elts[4];
>>>> +};
>>>> +typedef const HARD_REG_SET &const_hard_reg_set;
>>>> +inline bool hard_reg_set_subset_p(const_hard_reg_set x, const_hard_reg_set y) {
>>>> + unsigned long bad = 0;
>>>> + for (unsigned int i = 0; i < (sizeof(x.elts) / sizeof((x.elts)[0])); ++i)
>>>> + bad |= (x.elts[i] & ~y.elts[i]);
>>>> + return bad == 0;
>>>> +}
>>>> +inline bool hard_reg_set_empty_p(const_hard_reg_set x) {
>>>> + unsigned long bad = 0;
>>>> + for (unsigned int i = 0; i < (sizeof(x.elts) / sizeof((x.elts)[0])); ++i)
>>>> + bad |= x.elts[i];
>>>> + return bad == 0;
>>>> +}
>>>> +extern HARD_REG_SET rr[2];
>>>> +extern int t[2];
>>>> +extern HARD_REG_SET nn;
>>>> +static HARD_REG_SET mm;
>>>> +void setup_reg_class_relations(void) {
>>>> + HARD_REG_SET intersection_set, union_set, temp_set2;
>>>> + for (int cl2 = 0; cl2 < 2; cl2++) {
>>>> + temp_set2 = rr[cl2] & ~nn;
>>>> + if (hard_reg_set_empty_p(mm) && hard_reg_set_empty_p(temp_set2)) {
>>>> + mm = rr[0] & nn;
>>>> + if (hard_reg_set_subset_p(mm, intersection_set))
>>>> + if (!hard_reg_set_subset_p(mm, temp_set2) ||
>>>> + hard_reg_set_subset_p(rr[0], rr[t[cl2]]))
>>>> + t[cl2] = 0;
>>>> + }
>>>> + }
>>>> +}
>>>> diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
>>>> index 693621ca990..1d79c77e8ce 100644
>>>> --- a/gcc/tree-vect-slp.cc
>>>> +++ b/gcc/tree-vect-slp.cc
>>>> @@ -5198,7 +5198,10 @@ vect_optimize_slp_pass::get_result_with_layout (slp_tree node,
>>>> return result;
>>>>
>>>> if (SLP_TREE_DEF_TYPE (node) == vect_constant_def
>>>> - || SLP_TREE_DEF_TYPE (node) == vect_external_def)
>>>> + || (SLP_TREE_DEF_TYPE (node) == vect_external_def
>>>> + && (to_layout_i == 0
>>>> + /* We can't permute vector defs. */
>>>> + || SLP_TREE_VEC_DEFS (node).is_empty ())))
>>>
>>> Guess it's personal preference, but IMO it's easier to follow without the
>>> to_layout_i condition, so that it ties directly to the create_partitions
>>> test.
>>
>> I don’t understand- in the code guarding this we seem to expect to_layout_i == 0 and that’s the case we can handle as noop. I didn’t understand why the function doesn’t always just do nothing in this case though, so I must have missed something.
>
> OK, so I guess that disproves that my way is easier to understand :)
>
> I think logically, the code is doing the equivalent of:
>
> int partition_i = m_vertices[node->vertex].partition;
> if (partition < 0)
> {
> /* If the vector is uniform or unchanged, there's nothing to do. */
> ...
> }
> else
> {
> ... Return node if to_layout_i matches this partition's chosen layout...
> }
>
> And I guess I should have written it that way.
>
> So when there is no partition, we have a constant or external def
> built from individual scalars. We can use the node as-is if the
> caller wants an unpermuted node or if all elements are equal
> (so that the permutation doesn't matter). Otherwise we need
> to permute the scalars.
>
> When there is a partition, we can use the node as-is if the caller
> wants the layout that was chosen for that partition. Otherwise we
> need a new VEC_PERM_EXPR node.
>
> In the particular case of external defs built from vectors, we're
> guaranteed that the node's chosen layout is 0 (i.e. the original layout),
> and so both ways work.
Hmm, but I arrived here with that not being the case … (the chosen Lay-out not zero)
> But in principle this case fits the "else" arm
> better than the "then" arm, because we're dealing with a node that is in
> a partition, and that is not built from scalars.
>
> Thanks,
> Richard
next prev parent reply other threads:[~2023-07-20 17:11 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20230720123855.334A4385AF91@sourceware.org>
2023-07-20 14:08 ` Richard Sandiford
2023-07-20 14:57 ` Richard Biener
2023-07-20 16:58 ` Richard Sandiford
2023-07-20 17:10 ` Richard Biener [this message]
2023-07-20 17:40 ` Richard Sandiford
2023-07-21 6:12 ` Richard Biener
[not found] <20230720123851.61BA33857711@sourceware.org>
2023-07-20 21:31 ` Jeff Law
2023-07-20 12:38 Richard Biener
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