> On Apr 10, 2025, at 11:12, Martin Uecker <[email protected]> wrote:
>
> Am Donnerstag, dem 10.04.2025 um 10:55 -0400 schrieb Siddhesh Poyarekar:
>> On 2025-04-10 10:50, Andrew MacLeod wrote:
>>> Its not clear to me exactly what is being asked, but I think the
>>> suggestion is that pointer references are being replaced with a builtin
>>> function called .ACCESS_WITH_SIZE ? and I presume that builtin
>>> function has some parameters that give you relevant range information of
>>> some sort?
>>
>> Added, not replaced, but yes, that's essentially it.
>>
>>> range-ops is setup to pull range information from builtin functions
>>> already in gimple-range-op.cc::
>>> gimple_range_op_handler::maybe_builtin_call (). We'd just need to write
>>> a handler for this new one. You can pull information from 2 operands
>>> under normal circumstances, but exceptions can be made. I'd need a
>>> description of what it looks like and how that translates to range info.
>>
>> That's perfect! It's probably redundant for cases where we end up with
>> both .ACCESS_WITH_SIZE and a __bos/__bdos call, but I don't remember if
>> that's the only place where .ACCESS_WITH_SIZE is generated today. Qing,
>> could you please work with Andrew on this?
>
> BTW, what I would find very interesting is inserting such information
> at the points where arrays decay to pointer.
Is the following the example?
1 #include <stdio.h>
2
3 void foo (int arr[]) {
4 // Inside the function, arr is treated as a pointer
5 arr[6] = 10;
6 }
7
8 int my_array[5] = {10, 20, 30, 40, 50};
9
10 int main() {
11 my_array[6] = 6;
12 int *ptr = my_array; // Array decays to pointer here
13 ptr[7] = 7;
14 foo (my_array);
15 16 return 0;
17 }
When I use the latest gcc to compile the above with -Warray-bounds:
[]$ gcc -O2 -Warray-bounds t.c
t.c: In function ‘main’:
t.c:13:6: warning: array subscript 7 is outside array bounds of ‘int[5]’
[-Warray-bounds=]
13 | ptr[7] = 7;
| ~~~^~~
t.c:8:5: note: at offset 28 into object ‘my_array’ of size 20
8 | int my_array[5] = {10, 20, 30, 40, 50};
| ^~~~~~~~
In function ‘foo’,
inlined from ‘main’ at t.c:14:3:
t.c:5:10: warning: array subscript 6 is outside array bounds of ‘int[5]’
[-Warray-bounds=]
5 | arr[6] = 10;
| ~~~~~~~^~~~
t.c: In function ‘main’:
t.c:8:5: note: at offset 24 into object ‘my_array’ of size 20
8 | int my_array[5] = {10, 20, 30, 40, 50};
| ^~~~~~~~
Looks like that even after the array decay to pointer, the bound information is
still carried
for the decayed pointer somehow (I guess that vrp did this?)
thanks.
Qing
>
> Martin
