I resubmitted an corrected version of this patch in https://gcc.gnu.org/pipermail/gcc-patches/2024-October/665648.html
> On 16 Oct 2024, at 10:32, Jennifer Schmitz <jschm...@nvidia.com> wrote:
>
> 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
>
> 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);
> +
> + 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..f5e6c0f7a85
> --- /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 "return \\{ 10, 13, 16, ... \\}" 8
> "optimized" } } */
> +/* { dg-final { scan-tree-dump "return \\{ 50, 65, 80, ... \\}" 8
> "optimized" } } */
> --
> 2.44.0
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