Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx> writes:
> On Mon, Jan 25, 2016 at 04:00:48PM +0100, Nicolai Stange wrote:
>> Currently, the determination of a __builtin_offsetof() expressions'
>> constness flags is done in two steps:
>> - Several flags are speculatively set at expression parsing time
>> - and possibly cleared again at evaluation if the member expression
>> includes a non-const array index like in
>> __builtin_offsetof(struct A, a.b[non_const_foo])
>>
>> For consistency with other expression types' evaluation, defer the
>> determination of a __builtin_offsetof() expression's constness to
>> evaluation time, too.
>>
>> Furthermore, carry an array index expression's constness flags
>> through the implicit cast to size_t type.
>
> Better to split this into two patches.
>
>> @@ -3028,13 +3026,18 @@ static struct symbol *evaluate_offsetof(struct expression *expr)
>> } else {
>> struct expression *idx = expr->index, *m;
>> struct symbol *i_type = evaluate_expression(idx);
>> + unsigned old_idx_flags;
>> int i_class = classify_type(i_type, &i_type);
>> +
>> if (!is_int(i_class)) {
>> expression_error(expr, "non-integer index");
>> return NULL;
>> }
>> unrestrict(idx, i_class, &i_type);
>> + old_idx_flags = idx->flags;
>> idx = cast_to(idx, size_t_ctype);
>> + idx->flags |= old_idx_flags;
>> + expr_flags_decay_consts(&idx->flags);
>> m = alloc_const_expression(expr->pos,
>> bits_to_bytes(ctype->bit_size));
>> m->ctype = size_t_ctype;
>
> It's not clear at all to me why this is needed.
> Why cast_to() can't set itself the right value for idx->flags?
cast_to() is for implicit casts and to be honest, I don't know what the
->flags should be set to.
Also, this is the only place in the whole code where preserving the
flags over a cast_to() call is needed.
Furthermore, we could get rid of the flags' save and restore by moving
the calculation of expr->flags in front of the cast_to() invocation --
all other cast_to() actually do it this way.
However, I think, it's better to have the assignment to expr->flags
grouped with the rest of the assignments to expr's members.
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