expmed: Fix store_bit_field_1 subreg offset

store_bit_field_1 tries to convert a field assignment into a subreg
assignment.  Normally it must check that the field occupies a full
word (or more specifically, a full REGMODE_NATURAL_SIZE chunk),
so that writing to the subreg doesn't clobber any other fields.
But it can skip that check if the structure is known to be in
an undefined state.

The idea was that, in the undefined case, we could rely on
simplify_gen_subreg to do the check for a valid subreg, rather
than having to repeat the required endianness logic in the caller.

Before the addition of the undefined case, the code could use
regnum * regsize to get the byte offset, where regnum came from
checking that the start was word-aligned.  In the undefined case
we need to calculate the byte offset explicitly.

gcc/
	* expmed.cc (store_bit_field_1): Fix byte offset calculation
	for undefined structures.

0 files changed, 0 insertions, 0 deletions