On Sat, Dec 9, 2023 at 3:25 AM Alexandre Oliva <ol...@adacore.com> wrote:
>
>
> smallest_int_mode_for_size may abort when the requested mode is not
> available. Call int_mode_for_size instead, that signals the
> unsatisfiable request in a more graceful way.
>
> Regstrapped on x86_64-linux-gnu. Ok to install?
>
>
> for gcc/ChangeLog
>
> PR middle-end/112784
> * expr.cc (emit_block_move_via_loop): Call int_mode_for_size
> for maybe-too-wide sizes.
> (emit_block_cmp_via_loop): Likewise.
>
> for gcc/testsuite/ChangeLog
>
> PR middle-end/112784
> * gcc.target/i386/avx512cd-inline-stringops-pr112784.c: New.
> ---
> gcc/expr.cc | 22
> ++++++++++++--------
> .../i386/avx512cd-inline-stringops-pr112784.c | 12 +++++++++++
> 2 files changed, 25 insertions(+), 9 deletions(-)
> create mode 100644
> gcc/testsuite/gcc.target/i386/avx512cd-inline-stringops-pr112784.c
>
> diff --git a/gcc/expr.cc b/gcc/expr.cc
> index 6da51f2aca296..178b3ec6d5adb 100644
> --- a/gcc/expr.cc
> +++ b/gcc/expr.cc
> @@ -2449,15 +2449,17 @@ emit_block_move_via_loop (rtx x, rtx y, rtx size,
> }
> emit_move_insn (iter, iter_init);
>
> - scalar_int_mode int_move_mode
> - = smallest_int_mode_for_size (incr * BITS_PER_UNIT);
> - if (GET_MODE_BITSIZE (int_move_mode) != incr * BITS_PER_UNIT)
> + opt_scalar_int_mode int_move_mode
> + = int_mode_for_size (incr * BITS_PER_UNIT, 1);
> + if (!int_move_mode.exists ()
you can use .exists (&move_mode) here to ...
> + || (GET_MODE_BITSIZE (as_a <scalar_int_mode> (int_move_mode))
> + != incr * BITS_PER_UNIT))
> {
> move_mode = BLKmode;
> gcc_checking_assert (can_move_by_pieces (incr, align));
> }
> else
> - move_mode = int_move_mode;
> + move_mode = as_a <scalar_int_mode> (int_move_mode);
... elide this else IIRC.
>
> x_addr = force_operand (XEXP (x, 0), NULL_RTX);
> y_addr = force_operand (XEXP (y, 0), NULL_RTX);
> @@ -2701,16 +2703,18 @@ emit_block_cmp_via_loop (rtx x, rtx y, rtx len, tree
> len_type, rtx target,
> iter = gen_reg_rtx (iter_mode);
> emit_move_insn (iter, iter_init);
>
> - scalar_int_mode int_cmp_mode
> - = smallest_int_mode_for_size (incr * BITS_PER_UNIT);
> - if (GET_MODE_BITSIZE (int_cmp_mode) != incr * BITS_PER_UNIT
> - || !can_compare_p (NE, int_cmp_mode, ccp_jump))
> + opt_scalar_int_mode int_cmp_mode
> + = int_mode_for_size (incr * BITS_PER_UNIT, 1);
> + if (!int_cmp_mode.exists ()
> + || (GET_MODE_BITSIZE (as_a <scalar_int_mode> (int_cmp_mode))
> + != incr * BITS_PER_UNIT)
> + || !can_compare_p (NE, as_a <scalar_int_mode> (int_cmp_mode),
> ccp_jump))
> {
> cmp_mode = BLKmode;
> gcc_checking_assert (incr != 1);
> }
> else
> - cmp_mode = int_cmp_mode;
> + cmp_mode = as_a <scalar_int_mode> (int_cmp_mode);
Likewise.
I'll note that int_mode_for_size and smallest_int_mode_for_size
are not semantically equivalent in what they can return. In
particular it seems you are incrementing by iter_incr even when
formerly smallest_int_mode_for_size would have returned a
larger than necessary mode, resulting in at least inefficient
code, copying/comparing pieces multiple times.
So int_mode_for_size looks more correct.
OK with the above change.
Richard.
> /* Save the base addresses. */
> x_addr = force_operand (XEXP (x, 0), NULL_RTX);
> diff --git
> a/gcc/testsuite/gcc.target/i386/avx512cd-inline-stringops-pr112784.c
> b/gcc/testsuite/gcc.target/i386/avx512cd-inline-stringops-pr112784.c
> new file mode 100644
> index 0000000000000..c81f99c693c24
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/avx512cd-inline-stringops-pr112784.c
> @@ -0,0 +1,12 @@
> +/* { dg-do compile } */
> +/* { dg-options "-mavx512cd -finline-stringops" } */
> +
> +struct S {
> + int e;
> +} __attribute__((aligned(128)));
> +
> +int main() {
> + struct S s1;
> + struct S s2;
> + int v = __builtin_memcmp(&s1, &s2, sizeof(s1));
> +}
>
> --
> Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
> Free Software Activist GNU Toolchain Engineer
> More tolerance and less prejudice are key for inclusion and diversity
> Excluding neuro-others for not behaving ""normal"" is *not* inclusive
