https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98190
--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to rsand...@gcc.gnu.org from comment #10)
> If we can't assert, I guess the rule is that we need to extend
> whenever we're storing to the MSB of the inner register. We can
> do that either by extending the source value and the range to
> the outer register, or by assigning to the inner register and
> then extending it separately.
So perhaps:
--- gcc/expr.c.jj 2020-12-09 00:00:08.622548080 +0100
+++ gcc/expr.c 2020-12-09 10:36:12.198801940 +0100
@@ -5451,6 +5451,33 @@ expand_assignment (tree to, tree from, b
mode1, to_rtx, to, from,
reversep))
result = NULL;
+ else if (SUBREG_P (to_rtx)
+ && SUBREG_PROMOTED_VAR_P (to_rtx))
+ {
+ /* If to_rtx is a promoted subreg, this must be a store to the
+ whole variable, otherwise to_rtx would need to be MEM.
+ We need to zero or sign extend the value afterwards. */
+ gcc_assert (known_eq (bitpos, 0)
+ && known_eq (bitsize,
+ GET_MODE_BITSIZE (GET_MODE (to_rtx))));
+ if (TREE_CODE (to) == MEM_REF && !REF_REVERSE_STORAGE_ORDER (to))
+ result = store_expr (from, to_rtx, 0, nontemporal, false);
+ else
+ {
+ result = store_field (to_rtx, bitsize, bitpos,
+ bitregion_start, bitregion_end,
+ mode1, from, get_alias_set (to),
+ nontemporal, reversep);
+ rtx to_rtx1
+ = lowpart_subreg (subreg_unpromoted_mode (to_rtx),
+ SUBREG_REG (to_rtx),
+ subreg_promoted_mode (to_rtx));
+ to_rtx1 = convert_to_mode (subreg_promoted_mode (to_rtx),
+ to_rtx1,
+ SUBREG_PROMOTED_SIGN (to_rtx));
+ emit_move_insn (SUBREG_REG (to_rtx), to_rtx1);
+ }
+ }
else
result = store_field (to_rtx, bitsize, bitpos,
bitregion_start, bitregion_end,
then? As in, if store_expr can handle it, use that, otherwise perform the
extension at the end.
As for BIT_INSERT_EXPR, I'm not sure if SSA_NAMEs can get promoted SUBREGs or
not, but in any case it wouldn't be this code path, it would be store_expr
which handles the promoted SUBREGs already, because destination would not be a
MEM_REF with non-mem decl or reversed order, nor handled_component_p, nor
ARRAY_TYPE destination.
