Juzhe-Zhong <juzhe.zh...@rivai.ai> writes:
> hen doing fortran test with 'V' extension enabled on RISC-V port.
> I saw multiple ICE: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111590
>
> The root cause is on DSE:
>
> internal compiler error: in smallest_mode_for_size, at stor-layout.cc:356
> 0x1918f70 smallest_mode_for_size(poly_int<2u, unsigned long>, mode_class)
> ../../../../gcc/gcc/stor-layout.cc:356
> 0x11f75bb smallest_int_mode_for_size(poly_int<2u, unsigned long>)
> ../../../../gcc/gcc/machmode.h:916
> 0x3304141 find_shift_sequence
> ../../../../gcc/gcc/dse.cc:1738
> 0x3304f1a get_stored_val
> ../../../../gcc/gcc/dse.cc:1906
> 0x3305377 replace_read
> ../../../../gcc/gcc/dse.cc:2010
> 0x3306226 check_mem_read_rtx
> ../../../../gcc/gcc/dse.cc:2310
> 0x330667b check_mem_read_use
> ../../../../gcc/gcc/dse.cc:2415
>
> After investigations, DSE is trying to do optimization like this following
> codes:
>
> (insn 86 85 87 9 (set (reg:V4DI 168)
> (mem/u/c:V4DI (reg/f:DI 171) [0 S32 A128])) "bug.f90":6:18 discrim 6
> 1167 {*movv4di}
> (expr_list:REG_EQUAL (const_vector:V4DI [
> (const_int 4 [0x4])
> (const_int 1 [0x1]) repeated x2
> (const_int 3 [0x3])
> ])
> (nil)))
>
> (set (mem) (reg:V4DI 168))
>
> Then it ICE on: auto new_mode = smallest_int_mode_for_size (access_size *
> BITS_PER_UNIT);
>
> The access_size may be 24 or 32. We don't have such integer modes with these
> size so it ICE.
>
> TODO: The better way maybe make DSE use native_encode_rtx/native_decode_rtx
> but I don't know how to do that. So let's quickly fix this issue, we
> can improve the fix later.
>
> gcc/ChangeLog:
>
> * dse.cc (find_shift_sequence): Check the mode with access_size exist
> on the target.
OK, thanks, but...
> Authored-By: Richard Sandiford <richard.sandif...@arm.com>
...it was just a review comment. I didn't write the patch.
Richard
>
> ---
> gcc/dse.cc | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/dse.cc b/gcc/dse.cc
> index 8b07be17674..1a85dae1f8c 100644
> --- a/gcc/dse.cc
> +++ b/gcc/dse.cc
> @@ -1733,7 +1733,8 @@ 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. */
> - if (store_info->const_rhs)
> + if (store_info->const_rhs
> + && known_le (access_size, GET_MODE_SIZE (MAX_MODE_INT)))
> {
> auto new_mode = smallest_int_mode_for_size (access_size *
> BITS_PER_UNIT);
> auto byte = subreg_lowpart_offset (new_mode, store_mode);
