Re: sparse-llvm array size computation issue

[Dibyendu Majumdar <mobile@majumdar.org.uk>]

Hi Luc,

On 28 March 2017 at 22:06, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
> On 28 March 2017 at 21:49, Luc Van Oostenryck
> <luc.vanoostenryck@gmail.com> wrote:
>> On Tue, Mar 28, 2017 at 10:41 PM, Dibyendu Majumdar
>> <mobile@majumdar.org.uk> wrote:
>>> On 28 March 2017 at 21:25, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
>>>> I am investigating an issue with following test case:
>>>>
>>>> int main(void)
>>>> {
>>>> const char *names[] = {
>>>> "dibyendu",
>>>> "majumdar",
>>>> NULL,
>>>> };
>>>> return 0;
>>>> }
>>>>
>>>> The issue here is that sparse-llvm thinks the array size is zero:
>>>>
>>>> define i32 @main() {
>>>> L0:
>>>>   %names_0000026DE9D2DDA8. = alloca [0 x i8*]
>>>>
>>>> It appears that sparse is correctly calculating the size of the array
>>>> in examine_node_type() in symbol.c, but by the time the symbol gets to
>>>> sparse-llvm the bit_size is somehow changed to -1. I haven't yet
>>>> tracked down where this is happening.
>>>>
>>>
>>> Looks like the computed bit_size is being held on the SYM_NODE but
>>> sparse-llvm looks as the bit_size field in the SYM_ARRAY node. Does
>>> this sound like a problem - i.e. somehow the SYM_ARRAY is not getting
>>> its size set?
>>

I think that there is a bug in examine_node_type() in symbol.c - it
should set the base_type's bit_size perhaps? See the line marked as
FIX below,

/* Unsized array? The size might come from the initializer.. */
if (bit_size < 0 && base_type->type == SYM_ARRAY) {
struct expression *initializer = get_symbol_initializer(sym);
if (initializer) {
struct symbol *node_type = base_type->ctype.base_type;
int count = count_array_initializer(S, node_type, initializer);

if (node_type && node_type->bit_size >= 0)
bit_size = array_element_offset(S->C->target, node_type->bit_size, count);
base_type->bit_size = bit_size;   /*** FIX set base_type->bit_size ***/
}
}

Thanks and Regards
Dibyendu