> The effect is demonstrated by a new test case that shows
that the by-pieces framework now emits `sb` instructions
instead of triggering an ICE
So these small memset() now don't use RVV at all if xtheadvector is enabled?
I don't have evidence whether the use of RVV (whether V or
xtheadvector) for these memsets is a win or not, but the treatment
should probably be consistent.
I don't know why RVV 1.0 uses a fractional LMUL at all here. It would
work perfectly well with LMUL=1 and just setting vl to the appropriate
length (which is always less than 16 bytes). Use of fractional LMUL
doesn't save any resources.
On Fri, Mar 22, 2024 at 12:46 PM Christoph Müllner
<christoph.muell...@vrull.eu> wrote:
>
> The expansion of `memset` (via expand_builtin_memset_args())
> uses clear_by_pieces() and store_by_pieces() to avoid calls
> to the C runtime. To check if a type can be used for that purpose
> the function by_pieces_mode_supported_p() tests if a `mov` and
> a `vec_duplicate` INSN can be expaned by the backend.
>
> The `vec_duplicate` expansion takes arguments of type `V_VLS`.
> The `mov` expansions take arguments of type `V`, `VB`, `VT`,
> `VLS_AVL_IMM`, and `VLS_AVL_REG`. Some of these types (in fact
> not types but type iterators) include fractional LMUL types.
> E.g. `V_VLS` includes `V`, which includes `VI`, which includes
> `RVVMF2QI`.
>
> This results in an attempt to use fractional LMUL-types for
> the `memset` expansion resulting in an ICE for XTheadVector,
> because that extension cannot handle fractional LMULs.
>
> This patch addresses this issue by splitting the definition
> of the `VI` mode itereator into `VI_NOFRAC` (without fractional
> LMUL types) and `VI_FRAC` (only fractional LMUL types).
> Further, it defines `V_VLS` such, that `VI_FRAC` types are only
> included if XTheadVector is not enabled.
>
> The effect is demonstrated by a new test case that shows
> that the by-pieces framework now emits `sb` instructions
> instead of triggering an ICE.
>
> Signed-off-by: Christoph Müllner <christoph.muell...@vrull.eu>
>
> PR 114194
>
> gcc/ChangeLog:
>
> * config/riscv/vector-iterators.md: Split VI into VI_FRAC and
> VI_NOFRAC.
> Only include VI_NOFRAC in V_VLS without TARGET_XTHEADVECTOR.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/riscv/rvv/xtheadvector/pr114194.c: New test.
>
> Signed-off-by: Christoph Müllner <christoph.muell...@vrull.eu>
> ---
> gcc/config/riscv/vector-iterators.md | 19 +++++--
> .../riscv/rvv/xtheadvector/pr114194.c | 56 +++++++++++++++++++
> 2 files changed, 69 insertions(+), 6 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/xtheadvector/pr114194.c
>
> diff --git a/gcc/config/riscv/vector-iterators.md
> b/gcc/config/riscv/vector-iterators.md
> index c2ea7e8b10a..a24e1bf078f 100644
> --- a/gcc/config/riscv/vector-iterators.md
> +++ b/gcc/config/riscv/vector-iterators.md
> @@ -108,17 +108,24 @@ (define_c_enum "unspecv" [
> UNSPECV_FRM_RESTORE_EXIT
> ])
>
> -(define_mode_iterator VI [
> - RVVM8QI RVVM4QI RVVM2QI RVVM1QI RVVMF2QI RVVMF4QI (RVVMF8QI
> "TARGET_MIN_VLEN > 32")
> -
> - RVVM8HI RVVM4HI RVVM2HI RVVM1HI RVVMF2HI (RVVMF4HI "TARGET_MIN_VLEN > 32")
> -
> - RVVM8SI RVVM4SI RVVM2SI RVVM1SI (RVVMF2SI "TARGET_MIN_VLEN > 32")
> +;; Subset of VI with fractional LMUL types
> +(define_mode_iterator VI_FRAC [
> + RVVMF2QI RVVMF4QI (RVVMF8QI "TARGET_MIN_VLEN > 32")
> + RVVMF2HI (RVVMF4HI "TARGET_MIN_VLEN > 32")
> + (RVVMF2SI "TARGET_MIN_VLEN > 32")
> +])
>
> +;; Subset of VI with non-fractional LMUL types
> +(define_mode_iterator VI_NOFRAC [
> + RVVM8QI RVVM4QI RVVM2QI RVVM1QI
> + RVVM8HI RVVM4HI RVVM2HI RVVM1HI
> + RVVM8SI RVVM4SI RVVM2SI RVVM1SI
> (RVVM8DI "TARGET_VECTOR_ELEN_64") (RVVM4DI "TARGET_VECTOR_ELEN_64")
> (RVVM2DI "TARGET_VECTOR_ELEN_64") (RVVM1DI "TARGET_VECTOR_ELEN_64")
> ])
>
> +(define_mode_iterator VI [ VI_NOFRAC (VI_FRAC "!TARGET_XTHEADVECTOR") ])
> +
> ;; This iterator is the same as above but with TARGET_VECTOR_ELEN_FP_16
> ;; changed to TARGET_ZVFH. TARGET_VECTOR_ELEN_FP_16 is also true for
> ;; TARGET_ZVFHMIN while we actually want to disable all instructions apart
> diff --git a/gcc/testsuite/gcc.target/riscv/rvv/xtheadvector/pr114194.c
> b/gcc/testsuite/gcc.target/riscv/rvv/xtheadvector/pr114194.c
> new file mode 100644
> index 00000000000..fc2d1349425
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/rvv/xtheadvector/pr114194.c
> @@ -0,0 +1,56 @@
> +/* { dg-do compile } */
> +/* { dg-options "-march=rv32gc_xtheadvector" { target { rv32 } } } */
> +/* { dg-options "-march=rv64gc_xtheadvector" { target { rv64 } } } */
> +/* { dg-final { check-function-bodies "**" "" } } */
> +
> +/*
> +** foo0_1:
> +** sb\tzero,0([a-x0-9]+)
> +** ret
> +*/
> +void foo0_1 (void *p)
> +{
> + __builtin_memset (p, 0, 1);
> +}
> +
> +/*
> +** foo0_7:
> +** sb\tzero,0([a-x0-9]+)
> +** sb\tzero,1([a-x0-9]+)
> +** sb\tzero,2([a-x0-9]+)
> +** sb\tzero,3([a-x0-9]+)
> +** sb\tzero,4([a-x0-9]+)
> +** sb\tzero,5([a-x0-9]+)
> +** sb\tzero,6([a-x0-9]+)
> +** ret
> +*/
> +void foo0_7 (void *p)
> +{
> + __builtin_memset (p, 0, 7);
> +}
> +
> +/*
> +** foo1_1:
> +** li\t[a-x0-9]+,1
> +** sb\t[a-x0-9]+,0([a-x0-9]+)
> +** ret
> +*/
> +void foo1_1 (void *p)
> +{
> + __builtin_memset (p, 1, 1);
> +}
> +
> +/*
> +** foo1_5:
> +** li\t[a-x0-9]+,1
> +** sb\t[a-x0-9]+,0([a-x0-9]+)
> +** sb\t[a-x0-9]+,1([a-x0-9]+)
> +** sb\t[a-x0-9]+,2([a-x0-9]+)
> +** sb\t[a-x0-9]+,3([a-x0-9]+)
> +** sb\t[a-x0-9]+,4([a-x0-9]+)
> +** ret
> +*/
> +void foo1_5 (void *p)
> +{
> + __builtin_memset (p, 1, 5);
> +}
> --
> 2.44.0
>
>
