Richard Biener <richard.guent...@gmail.com> writes:
> On Wed, Jul 26, 2023 at 4:02 AM Hao Liu OS via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> > When was STMT_VINFO_REDUC_DEF empty? I just want to make sure that we're
>> > not papering over an issue elsewhere.
>>
>> Yes, I also wonder if this is an issue in vectorizable_reduction. Below is
>> the the gimple of "gcc.target/aarch64/sve/cost_model_13.c":
>>
>> <bb 3>:
>> # res_18 = PHI <res_15(7), 0(6)>
>> # i_20 = PHI <i_16(7), 0(6)>
>> _1 = (long unsigned int) i_20;
>> _2 = _1 * 2;
>> _3 = x_14(D) + _2;
>> _4 = *_3;
>> _5 = (unsigned short) _4;
>> res.0_6 = (unsigned short) res_18;
>> _7 = _5 + res.0_6; <-- The current stmt_info
>> res_15 = (short int) _7;
>> i_16 = i_20 + 1;
>> if (n_11(D) > i_16)
>> goto <bb 7>;
>> else
>> goto <bb 4>;
>>
>> <bb 7>:
>> goto <bb 3>;
>>
>> It looks like that STMT_VINFO_REDUC_DEF should be "res_18 = PHI <res_15(7),
>> 0(6)>"?
>> The status here is:
>> STMT_VINFO_REDUC_IDX (stmt_info): 1
>> STMT_VINFO_REDUC_TYPE (stmt_info): TREE_CODE_REDUCTION
>> STMT_VINFO_REDUC_VECTYPE (stmt_info): 0x0
>
> Not all stmts in the SSA cycle forming the reduction have
> STMT_VINFO_REDUC_DEF set,
> only the last (latch def) and live stmts have at the moment.
Ah, thanks. In that case, Hao, I think we can avoid the ICE by changing:
if ((kind == scalar_stmt || kind == vector_stmt || kind == vec_to_scalar)
&& vect_is_reduction (stmt_info))
to:
if ((kind == scalar_stmt || kind == vector_stmt || kind == vec_to_scalar)
&& STMT_VINFO_LIVE_P (stmt_info)
&& vect_is_reduction (stmt_info))
instead of using a null check.
I see that vectorizable_reduction calculates a reduc_chain_length.
Would it be OK to store that in the stmt_vec_info? I suppose the
AArch64 code should be multiplying by that as well. (It would be a
separate patch from this one though.)
Richard
>
> Richard.
>
>> Thanks,
>> Hao
>>
>> ________________________________________
>> From: Richard Sandiford <richard.sandif...@arm.com>
>> Sent: Tuesday, July 25, 2023 17:44
>> To: Hao Liu OS
>> Cc: GCC-patches@gcc.gnu.org
>> Subject: Re: [PATCH] AArch64: Do not increase the vect reduction latency by
>> multiplying count [PR110625]
>>
>> Hao Liu OS <h...@os.amperecomputing.com> writes:
>> > Hi,
>> >
>> > Thanks for the suggestion. I tested it and found a gcc_assert failure:
>> > gcc.target/aarch64/sve/cost_model_13.c (internal compiler error: in
>> > info_for_reduction, at tree-vect-loop.cc:5473)
>> >
>> > It is caused by empty STMT_VINFO_REDUC_DEF.
>>
>> When was STMT_VINFO_REDUC_DEF empty? I just want to make sure that
>> we're not papering over an issue elsewhere.
>>
>> Thanks,
>> Richard
>>
>> So, I added an extra check before checking single_defuse_cycle. The
>> updated patch is below. Is it OK for trunk?
>> >
>> > ---
>> >
>> > The new costs should only count reduction latency by multiplying count for
>> > single_defuse_cycle. For other situations, this will increase the
>> > reduction
>> > latency a lot and miss vectorization opportunities.
>> >
>> > Tested on aarch64-linux-gnu.
>> >
>> > gcc/ChangeLog:
>> >
>> > PR target/110625
>> > * config/aarch64/aarch64.cc (count_ops): Only '* count' for
>> > single_defuse_cycle while counting reduction_latency.
>> >
>> > gcc/testsuite/ChangeLog:
>> >
>> > * gcc.target/aarch64/pr110625_1.c: New testcase.
>> > * gcc.target/aarch64/pr110625_2.c: New testcase.
>> > ---
>> > gcc/config/aarch64/aarch64.cc | 13 ++++--
>> > gcc/testsuite/gcc.target/aarch64/pr110625_1.c | 46 +++++++++++++++++++
>> > gcc/testsuite/gcc.target/aarch64/pr110625_2.c | 14 ++++++
>> > 3 files changed, 69 insertions(+), 4 deletions(-)
>> > create mode 100644 gcc/testsuite/gcc.target/aarch64/pr110625_1.c
>> > create mode 100644 gcc/testsuite/gcc.target/aarch64/pr110625_2.c
>> >
>> > diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
>> > index 560e5431636..478a4e00110 100644
>> > --- a/gcc/config/aarch64/aarch64.cc
>> > +++ b/gcc/config/aarch64/aarch64.cc
>> > @@ -16788,10 +16788,15 @@ aarch64_vector_costs::count_ops (unsigned int
>> > count, vect_cost_for_stmt kind,
>> > {
>> > unsigned int base
>> > = aarch64_in_loop_reduction_latency (m_vinfo, stmt_info,
>> > m_vec_flags);
>> > -
>> > - /* ??? Ideally we'd do COUNT reductions in parallel, but
>> > unfortunately
>> > - that's not yet the case. */
>> > - ops->reduction_latency = MAX (ops->reduction_latency, base * count);
>> > + if (STMT_VINFO_REDUC_DEF (stmt_info)
>> > + && STMT_VINFO_FORCE_SINGLE_CYCLE (
>> > + info_for_reduction (m_vinfo, stmt_info)))
>> > + /* ??? Ideally we'd use a tree to reduce the copies down to 1 vector,
>> > + and then accumulate that, but at the moment the loop-carried
>> > + dependency includes all copies. */
>> > + ops->reduction_latency = MAX (ops->reduction_latency, base * count);
>> > + else
>> > + ops->reduction_latency = MAX (ops->reduction_latency, base);
>> > }
>> >
>> > /* Assume that multiply-adds will become a single operation. */
>> > diff --git a/gcc/testsuite/gcc.target/aarch64/pr110625_1.c
>> > b/gcc/testsuite/gcc.target/aarch64/pr110625_1.c
>> > new file mode 100644
>> > index 00000000000..0965cac33a0
>> > --- /dev/null
>> > +++ b/gcc/testsuite/gcc.target/aarch64/pr110625_1.c
>> > @@ -0,0 +1,46 @@
>> > +/* { dg-do compile } */
>> > +/* { dg-options "-Ofast -mcpu=neoverse-n2 -fdump-tree-vect-details
>> > -fno-tree-slp-vectorize" } */
>> > +/* { dg-final { scan-tree-dump-not "reduction latency = 8" "vect" } } */
>> > +
>> > +/* Do not increase the vector body cost due to the incorrect reduction
>> > latency
>> > + Original vector body cost = 51
>> > + Scalar issue estimate:
>> > + ...
>> > + reduction latency = 2
>> > + estimated min cycles per iteration = 2.000000
>> > + estimated cycles per vector iteration (for VF 2) = 4.000000
>> > + Vector issue estimate:
>> > + ...
>> > + reduction latency = 8 <-- Too large
>> > + estimated min cycles per iteration = 8.000000
>> > + Increasing body cost to 102 because scalar code would issue more
>> > quickly
>> > + ...
>> > + missed: cost model: the vector iteration cost = 102 divided by the
>> > scalar iteration cost = 44 is greater or equal to the vectorization factor
>> > = 2.
>> > + missed: not vectorized: vectorization not profitable. */
>> > +
>> > +typedef struct
>> > +{
>> > + unsigned short m1, m2, m3, m4;
>> > +} the_struct_t;
>> > +typedef struct
>> > +{
>> > + double m1, m2, m3, m4, m5;
>> > +} the_struct2_t;
>> > +
>> > +double
>> > +bar (the_struct2_t *);
>> > +
>> > +double
>> > +foo (double *k, unsigned int n, the_struct_t *the_struct)
>> > +{
>> > + unsigned int u;
>> > + the_struct2_t result;
>> > + for (u = 0; u < n; u++, k--)
>> > + {
>> > + result.m1 += (*k) * the_struct[u].m1;
>> > + result.m2 += (*k) * the_struct[u].m2;
>> > + result.m3 += (*k) * the_struct[u].m3;
>> > + result.m4 += (*k) * the_struct[u].m4;
>> > + }
>> > + return bar (&result);
>> > +}
>> > diff --git a/gcc/testsuite/gcc.target/aarch64/pr110625_2.c
>> > b/gcc/testsuite/gcc.target/aarch64/pr110625_2.c
>> > new file mode 100644
>> > index 00000000000..7a84aa8355e
>> > --- /dev/null
>> > +++ b/gcc/testsuite/gcc.target/aarch64/pr110625_2.c
>> > @@ -0,0 +1,14 @@
>> > +/* { dg-do compile } */
>> > +/* { dg-options "-Ofast -mcpu=neoverse-n2 -fdump-tree-vect-details
>> > -fno-tree-slp-vectorize" } */
>> > +/* { dg-final { scan-tree-dump "reduction latency = 8" "vect" } } */
>> > +
>> > +/* The reduction latency should be multiplied by the count for
>> > + single_defuse_cycle. */
>> > +
>> > +long
>> > +f (long res, short *ptr1, short *ptr2, int n)
>> > +{
>> > + for (int i = 0; i < n; ++i)
>> > + res += (long) ptr1[i] << ptr2[i];
>> > + return res;
>> > +}
