http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58970
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |jakub at gcc dot gnu.org
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Bernd Edlinger from comment #4)
> Created attachment 31145 [details]
> For a possible patch.
>
> This patch is assuming that a statement like "s->mode[-1].b = 0;"
> is basically invoking undefined behaviour, so it should not matter
> if we have correct bitregion_start/end values or just set them to zero
> in this case.
That doesn't look safe, negative rbitpos is not necessarily undefined behavior.
Can't you get the same with say
struct S { unsigned char s : 1; };
...
void function(struct S *p)
{
p[-1].s = 0;
}
Apparently get_inner_reference only gives negative bitpos if offset is
NULL_TREE, otherwise it adjusts offset such that the bitpos is positive.
I wonder if get_bit_range shouldn't do the same thing if it detects *bitpos
is negative and *offset is NULL_TREE before doing the bitoffset > *bitpos
comparison. It might be as easy as replacing the
gcc_assert (*offset != NULL_TREE);
with if (*offset == NULL_TREE) *offset = size_int (0);
Of course, the comment would need to be adjusted.
