> Yes, convert_modes does this, on the other side e.g. convert_move a few
> hundred lines above it doesn't:
> if (GET_CODE (from) == SUBREG
> && SUBREG_PROMOTED_VAR_P (from)
> && is_a <scalar_int_mode> (to_mode, &to_int_mode)
> && (GET_MODE_PRECISION (subreg_promoted_mode (from))
>
> >= GET_MODE_PRECISION (to_int_mode))
>
> && SUBREG_CHECK_PROMOTED_SIGN (from, unsignedp))
> from = gen_lowpart (to_int_mode, from), from_mode = to_int_mode;
Right, they were originally alike, but someone you know very well changed it:
2013-12-17 Jakub Jelinek <ja...@redhat.com>
* expr.c (convert_modes): For SUBREG_PROMOTED_VAR_P use SUBREG_REG (x)
instead of x as last gen_lowpart argument.
> 2018-04-17 Jakub Jelinek <ja...@redhat.com>
>
> PR middle-end/85414
> * simplify-rtx.c (simplify_unary_operation_1) <case SIGN_EXTEND,
> case ZERO_EXTEND>: Pass SUBREG_REG (op) rather than op to
> gen_lowpart_no_emit.
> * rtlhooks.c (gen_lowpart_if_possible): Don't call gen_lowpart_SUBREG
> on a SUBREG.
>
> * gcc.dg/pr85414.c: New test.
I'd say, either we change both convert_move and simplify-rtx.c for GCC 8 or we
change none of them. You're the RM so it's more of your call than mine.
--
Eric Botcazou
