> On 23 Oct 2024, at 16:49, Richard Sandiford <richard.sandif...@arm.com> wrote:
>
> External email: Use caution opening links or attachments
>
>
> Jennifer Schmitz <jschm...@nvidia.com> writes:
>> This patch folds svindex with constant arguments into a vector series.
>> We implemented this in svindex_impl::fold using the function
>> build_vec_series.
>> For example,
>> svuint64_t f1 ()
>> {
>> return svindex_u642 (10, 3);
>> }
>> compiled with -O2 -march=armv8.2-a+sve, is folded to {10, 13, 16, ...}
>> in the gimple pass lower.
>> This optimization benefits cases where svindex is used in combination with
>> other gimple-level optimizations.
>> For example,
>> svuint64_t f2 ()
>> {
>> return svmul_x (svptrue_b64 (), svindex_u64 (10, 3), 5);
>> }
>> has previously been compiled to
>> f2:
>> index z0.d, #10, #3
>> mul z0.d, z0.d, #5
>> ret
>> Now, it is compiled to
>> f2:
>> mov x0, 50
>> index z0.d, x0, #15
>> ret
>
> Nice! Thanks for doing this.
>
>> For non-constant arguments, build_vec_series produces a VEC_SERIES_EXPR,
>> which is translated back at RTL level to an index instruction without codegen
>> changes.
>>
>> We added test cases checking
>> - the application of the transform during gimple for constant arguments,
>> - the interaction with another gimple-level optimization.
>>
>> The patch was bootstrapped and regtested on aarch64-linux-gnu, no regression.
>> OK for mainline?
>>
>> Signed-off-by: Jennifer Schmitz <jschm...@nvidia.com>
>>
>> gcc/
>> * config/aarch64/aarch64-sve-builtins-base.cc
>> (svindex_impl::fold): Add constant folding.
>>
>> gcc/testsuite/
>> * gcc.target/aarch64/sve/index_const_fold.c: New test.
>> ---
>> .../aarch64/aarch64-sve-builtins-base.cc | 12 +++++++
>> .../gcc.target/aarch64/sve/index_const_fold.c | 35 +++++++++++++++++++
>> 2 files changed, 47 insertions(+)
>> create mode 100644 gcc/testsuite/gcc.target/aarch64/sve/index_const_fold.c
>>
>> diff --git a/gcc/config/aarch64/aarch64-sve-builtins-base.cc
>> b/gcc/config/aarch64/aarch64-sve-builtins-base.cc
>> index 1c17149e1f0..f6b1657ecbb 100644
>> --- a/gcc/config/aarch64/aarch64-sve-builtins-base.cc
>> +++ b/gcc/config/aarch64/aarch64-sve-builtins-base.cc
>> @@ -1304,6 +1304,18 @@ public:
>>
>> class svindex_impl : public function_base
>> {
>> +public:
>> + gimple *
>> + fold (gimple_folder &f) const override
>> + {
>> + tree vec_type = TREE_TYPE (f.lhs);
>> + tree base = gimple_call_arg (f.call, 0);
>> + tree step = gimple_call_arg (f.call, 1);
>
> Could we restrict this to:
>
> if (TREE_CODE (base) != INTEGER_CST || TREE_CODE (step) != INTEGER_CST)
> return nullptr;
>
> for now? This goes back to the previous discussion about how "creative"
> the compiler is allowed to be in replacing the user's original instruction
> selection. IIRC, it'd also be somewhat novel to use VEC_SERIES_EXPR for
> constant-length vectors.
>
> We can always relax this later if we find a compelling use case.
> But it looks like the tests would still pass with the guard above.
>
> OK with that change, thanks.
Thanks for the review.
I added the guard you proposed and pushed to trunk:
90e38c4ffad086a82635e8ea9bf0e7e9e02f1ff7.
Best,
Jennifer
>
> Richard
>
>> +
>> + return gimple_build_assign (f.lhs,
>> + build_vec_series (vec_type, base, step));
>> + }
>> +
>> public:
>> rtx
>> expand (function_expander &e) const override
>> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/index_const_fold.c
>> b/gcc/testsuite/gcc.target/aarch64/sve/index_const_fold.c
>> new file mode 100644
>> index 00000000000..7abb803f58b
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/aarch64/sve/index_const_fold.c
>> @@ -0,0 +1,35 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -fdump-tree-optimized" } */
>> +
>> +#include <arm_sve.h>
>> +#include <stdint.h>
>> +
>> +#define INDEX_CONST(TYPE, TY) \
>> + sv##TYPE f_##TY##_index_const () \
>> + { \
>> + return svindex_##TY (10, 3); \
>> + }
>> +
>> +#define MULT_INDEX(TYPE, TY) \
>> + sv##TYPE f_##TY##_mult_index () \
>> + { \
>> + return svmul_x (svptrue_b8 (), \
>> + svindex_##TY (10, 3), \
>> + 5); \
>> + }
>> +
>> +#define ALL_TESTS(TYPE, TY) \
>> + INDEX_CONST (TYPE, TY) \
>> + MULT_INDEX (TYPE, TY)
>> +
>> +ALL_TESTS (uint8_t, u8)
>> +ALL_TESTS (uint16_t, u16)
>> +ALL_TESTS (uint32_t, u32)
>> +ALL_TESTS (uint64_t, u64)
>> +ALL_TESTS (int8_t, s8)
>> +ALL_TESTS (int16_t, s16)
>> +ALL_TESTS (int32_t, s32)
>> +ALL_TESTS (int64_t, s64)
>> +
>> +/* { dg-final { scan-tree-dump-times "return \\{ 10, 13, 16, ... \\}" 8
>> "optimized" } } */
>> +/* { dg-final { scan-tree-dump-times "return \\{ 50, 65, 80, ... \\}" 8
>> "optimized" } } */
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