On Oct 6, 2005, at 12:00 PM, Olivier Hainque wrote:
Hello,
The Ada testcase below, compiled with -O2 on x86-linux, triggers a
SEGV in the current mainline compiler, there:
do_simple_structure_copy
{ ...
for (; p && p->offset < last; p = p->next)
{ ...
q = first_vi_for_offset (q, q->offset + fieldoffset);
==> temprhs.var = q->id;
Below is a description of what is going on, plus suggestions on how to
address the problem. I'd welcome feedback before submitting a patch
with all the required testing process.
The test basically constructs a record type with two 6bits long
components, each of a record type also, and the two components (called
key1 and key2) are tighly packed with a representation clause (no
hole between the two components). Something like:
6bits 6bits
|.......|.......|
key1 key2
Eventhough the field *decls* specify a 6bits length, the *type* of
each is actually QI integer (8bits long).
IOW, you are lying to the middle-end about the size of the fields.
Why is the type not a 6 bit integer?
A very simple way to deal with this is to just 'break' out of the loop
when 'q' happens to be null, with an appropriate comment briefly
explaining how this could happen.
Except that it should never happen.
We should never have a case where we've computed the sizes wrong,
such that a simple structure copy fails.
Simply breaking out of this loop will cause you erorrs later.
Another way would be to compute the incoming 'size' argument from decl
information when appropriate. This seems more involved at first sight.
This is the correct fix, however, if you are going to lie to the
middle end about TYPE_SIZE so that the TYPE_SIZE and DECL_SIZE do not
match.
