https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113395
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Because of
#0 adjust_address_1 (memref=0x7ffff71e8db0, mode=E_HImode, offset=...,
validate=1, adjust_address=1, adjust_object=1, size=...)
at /space/rguenther/src/gcc/gcc/emit-rtl.cc:2409
#1 0x00000000011459af in narrow_bit_field_mem (mem=0x7ffff71e8db0,
mode=HImode, bitsize=2, bitnum=7, new_bitnum=0x7fffffffc8c0)
at /space/rguenther/src/gcc/gcc/expmed.cc:453
#2 0x0000000001145d1c in adjust_bit_field_mem_for_reg (pattern=EP_insv,
op0=0x7ffff71e8db0, bitsize=2, bitnum=7, bitregion_start=...,
bitregion_end=..., fieldmode=E_VOIDmode, new_bitnum=0x7fffffffc8c0)
at /space/rguenther/src/gcc/gcc/expmed.cc:511
#3 0x00000000011483bb in store_integral_bit_field (op0=0x7ffff71e8db0,
op0_mode=SImode, bitsize=2, bitnum=7, bitregion_start=...,
bitregion_end=..., fieldmode=E_VOIDmode, value=0x7ffff70124a0,
reverse=false, fallback_p=true)
at /space/rguenther/src/gcc/gcc/expmed.cc:1086
#4 0x00000000011476a0 in store_bit_field_1 (str_rtx=0x7ffff71e8db0,
bitsize=..., bitnum=..., bitregion_start=..., bitregion_end=...,
fieldmode=E_VOIDmode, value=0x7ffff70124a0, reverse=false,
fallback_p=true, undefined_p=false)
at /space/rguenther/src/gcc/gcc/expmed.cc:887
#5 0x0000000001148c31 in store_bit_field (str_rtx=0x7ffff71e8db0,
bitsize=..., bitnum=..., bitregion_start=..., bitregion_end=...,
fieldmode=E_VOIDmode, value=0x7ffff70124a0, reverse=false,
--Type <RET> for more, q to quit, c to continue without paging--
) at /space/rguenther/src/gcc/gcc/expmed.cc:1194
#6 0x000000000117dde0 in store_field (target=0x7ffff71e8db0, bitsize=...,
bitpos=..., bitregion_start=..., bitregion_end=..., mode=E_VOIDmode,
exp=<integer_cst 0x7ffff71c4ca8>, alias_set=1, nontemporal=false,
reverse=false) at /space/rguenther/src/gcc/gcc/expr.cc:8245
#7 0x0000000001174b21 in expand_assignment (
to=<component_ref 0x7ffff71e07b0>, from=<integer_cst 0x7ffff71c4ca8>,
nontemporal=false) at /space/rguenther/src/gcc/gcc/expr.cc:6303
and we run into
if (maybe_ne (size, 0))
{
/* Drop the object if the new right end is not within its bounds. */
if (adjust_object && maybe_gt (offset + size, attrs.size))
{
attrs.expr = NULL_TREE;
attrs.alias = 0;
}
as attrs.size is originally 1 and we are creating a two byte HImode access.
IMHO it's the fault of how we set up the initial memory attributes which
come via expand_assignment doing
tem = get_inner_reference (to, &bitsize, &bitpos, &offset, &mode1,
&unsignedp, &reversep, &volatilep);
..
if (TREE_CODE (to) == COMPONENT_REF
&& DECL_BIT_FIELD_TYPE (TREE_OPERAND (to, 1)))
get_bit_range (&bitregion_start, &bitregion_end, to, &bitpos, &offset);
..
to_rtx = expand_expr (tem, NULL_RTX, VOIDmode, EXPAND_WRITE);
..
if (MEM_P (to_rtx))
{
/* If the field is at offset zero, we could have been given the
DECL_RTX of the parent struct. Don't munge it. */
to_rtx = shallow_copy_rtx (to_rtx);
set_mem_attributes_minus_bitpos (to_rtx, to, 0, bitpos);
if (volatilep)
MEM_VOLATILE_P (to_rtx) = 1;
that's an unfortunate setup to eventually widen the setup.
RTL alias analysis then has to rely on find_base_term to perform it's
bogus optimistic points-to analysis.
