On Wed, Aug 28, 2024 at 4:35 PM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> smallest_int_mode_for_size now returns an optional mode rather
> than aborting on failure. This patch adjusts a couple of callers
> so that they fail gracefully when no mode exists.
>
> There should be no behavioural change, since anything that triggers
> the new return paths would previously have aborted. I just think
> this is how the code would have been written if the option had been
> available earlier.
>
> Tested on aarch64-linux-gnu. OK to install?
OK.
Thanks,
Richard.
> Richard
>
>
> gcc/
> * dse.cc (find_shift_sequence): Allow smallest_int_mode_for_size
> to failure.
> * optabs.cc (expand_twoval_binop_libfunc): Likewise.
> ---
> gcc/dse.cc | 16 ++++++++--------
> gcc/optabs.cc | 6 ++++--
> 2 files changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/gcc/dse.cc b/gcc/dse.cc
> index c3feff06f86..75825a44cb9 100644
> --- a/gcc/dse.cc
> +++ b/gcc/dse.cc
> @@ -1717,12 +1717,12 @@ dump_insn_info (const char * start, insn_info_t
> insn_info)
> line up, we need to extract the value from lower part of the rhs of
> the store, shift it, and then put it into a form that can be shoved
> into the read_insn. This function generates a right SHIFT of a
> - value that is at least ACCESS_SIZE bytes wide of READ_MODE. The
> + value that is at least ACCESS_BYTES bytes wide of READ_MODE. The
> shift sequence is returned or NULL if we failed to find a
> shift. */
>
> static rtx
> -find_shift_sequence (poly_int64 access_size,
> +find_shift_sequence (poly_int64 access_bytes,
> store_info *store_info,
> machine_mode read_mode,
> poly_int64 shift, bool speed, bool require_cst)
> @@ -1734,11 +1734,11 @@ find_shift_sequence (poly_int64 access_size,
> /* If a constant was stored into memory, try to simplify it here,
> otherwise the cost of the shift might preclude this optimization
> e.g. at -Os, even when no actual shift will be needed. */
> + auto access_bits = access_bytes * BITS_PER_UNIT;
> if (store_info->const_rhs
> - && known_le (access_size, GET_MODE_SIZE (MAX_MODE_INT)))
> + && known_le (access_bytes, GET_MODE_SIZE (MAX_MODE_INT))
> + && smallest_int_mode_for_size (access_bits).exists (&new_mode))
> {
> - auto new_mode = smallest_int_mode_for_size
> - (access_size * BITS_PER_UNIT).require ();
> auto byte = subreg_lowpart_offset (new_mode, store_mode);
> rtx ret
> = simplify_subreg (new_mode, store_info->const_rhs, store_mode, byte);
> @@ -1810,7 +1810,7 @@ find_shift_sequence (poly_int64 access_size,
> }
> }
>
> - if (maybe_lt (GET_MODE_SIZE (new_mode), access_size))
> + if (maybe_lt (GET_MODE_SIZE (new_mode), access_bytes))
> continue;
>
> new_reg = gen_reg_rtx (new_mode);
> @@ -1839,8 +1839,8 @@ find_shift_sequence (poly_int64 access_size,
> of the arguments and could be precomputed. It may
> not be worth doing so. We could precompute if
> worthwhile or at least cache the results. The result
> - technically depends on both SHIFT and ACCESS_SIZE,
> - but in practice the answer will depend only on ACCESS_SIZE. */
> + technically depends on both SHIFT and ACCESS_BYTES,
> + but in practice the answer will depend only on ACCESS_BYTES. */
>
> if (cost > COSTS_N_INSNS (1))
> continue;
> diff --git a/gcc/optabs.cc b/gcc/optabs.cc
> index ded9cc3d947..2bcb3f7b47a 100644
> --- a/gcc/optabs.cc
> +++ b/gcc/optabs.cc
> @@ -2551,8 +2551,10 @@ expand_twoval_binop_libfunc (optab binoptab, rtx op0,
> rtx op1,
>
> /* The value returned by the library function will have twice as
> many bits as the nominal MODE. */
> - libval_mode
> - = smallest_int_mode_for_size (2 * GET_MODE_BITSIZE (mode)).require ();
> + auto return_size = 2 * GET_MODE_BITSIZE (mode);
> + if (!smallest_int_mode_for_size (return_size).exists (&libval_mode))
> + return false;
> +
> start_sequence ();
> libval = emit_library_call_value (libfunc, NULL_RTX, LCT_CONST,
> libval_mode,
> --
> 2.25.1
>
