https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104914
--- Comment #17 from Roger Sayle <roger at nextmovesoftware dot com> ---
I think this patch might resolve the problem (or move it somewhere else):
diff --git a/gcc/expr.cc b/gcc/expr.cc
index 9fef2bf6585..218bca905f5 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -6274,10 +6274,7 @@ expand_assignment (tree to, tree from, bool nontemporal)
result = store_expr (from, to_rtx, 0, nontemporal, false);
else
{
- rtx to_rtx1
- = lowpart_subreg (subreg_unpromoted_mode (to_rtx),
- SUBREG_REG (to_rtx),
- subreg_promoted_mode (to_rtx));
+ rtx to_rtx1 = gen_reg_rtx (subreg_unpromoted_mode (to_rtx));
result = store_field (to_rtx1, bitsize, bitpos,
bitregion_start, bitregion_end,
mode1, from, get_alias_set (to),
The motivation/solution comes from a comment in expmed.cc:
/* If the destination is a paradoxical subreg such that we need a
truncate to the inner mode, perform the insertion on a temporary and
truncate the result to the original destination. Note that we can't
just truncate the paradoxical subreg as (truncate:N (subreg:W (reg:N
X) 0)) is (reg:N X). */
The same caveat applies to extensions on MIPS, so we should use a new
pseudo temporary register rather than update the SUBREG in place.
If someone could confirm this fixes the issue on MIPS, I'll try to come up
with a milder form of this fix that checks TARGET_MODE_REP_EXTENDED that'll
limit the churn/impact on other targets.
