> 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
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;
> +}
