Re: [patch] expr.c: Fix PR middle-end/18008.

[Jason Merrill <jason at redhat dot com>]

>> After the tree optimizers run, I get
>> 
>>   b->b = (<unnamed type>) (unsigned char) v;
>> 
>> where <unnamed type> is a 2-bit integer type.  The problem is that we
>> get ANDs from two places.  The first one is generated by the cast to
>> (<unnamed type>).  The second one is from the assignment, more
>> specifically store_bit_field.
>> 
>> The patch fixes the problem by stripping a narrowing conversion.

It seems to me that the right fix is to avoid generating an AND in
store_bit_field if the value assigned is already appropriately narrow.

Jason