- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Hi,
I noticed a strange problem. If I give structs and unions without tag-names, I get no issues but if I specify tag-names, I get static_assert.
Here is the code:
typedef struct KernelLightDistribution {
float totarea;
int prim;
union dpct_type_be6907 {
struct dpct_type_12c54e {
int shader_flag;
int object_id;
} mesh_light;
struct dpct_type_ff924c {
float pad;
float size;
} lamp;
};
} KernelLightDistribution;
static_assert_align(KernelLightDistribution, 16);
where static_assert_align is:
#define static_assert_align(st, align) \
static_assert((sizeof(st) % (align) == 0), "Structure must be strictly aligned") // NOLINT
When I compile using dpcpp (with -std=c++17), I get static_assert
../kernel/kernel_types.h:1553:1: error: static_assert failed due to requirement 'sizeof(ccl::KernelLightDistribution) % (16) == 0' "Structure must be strictly aligned"
static_assert_align(KernelLightDistribution, 16);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../util/util_static_assert.h:32:3: note: expanded from macro 'static_assert_align'
static_assert((sizeof(st) % (align) == 0), "Structure must be strictly aligned") // NOLINT
But If I comment out the tag-names and use anonymous union and structs, static_assert disappears and code compiles without error.
Code with tag-names commented out:
typedef struct KernelLightDistribution {
float totarea;
int prim;
union /* dpct_type_be6907 */ {
struct /* dpct_type_12c54e */ {
int shader_flag;
int object_id;
} mesh_light;
struct /* dpct_type_ff924c */ {
float pad;
float size;
} lamp;
};
} KernelLightDistribution;
static_assert_align(KernelLightDistribution, 16);
Now the file compiles without any error.
Should struct or union tag-names affect its size or alignment?
static_assert comes back if I uncomment union tag name or struct tag-names ie if I uncomment any of the three tag-names, problem comes back.
Regards,
Gagan
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Hi,
There is a small bug in your code. You have not initialized the union dpct_type_be6907. As a result, memory is not getting created for that particular data structure. Anonymous structs/unions are a bit lenient when it comes to initialization since they can be accessed right way and they are guaranteed to be present within a struct/union. (Memory always gets created for anonymous structs/unions)
Refer to the modified code snippet below.
#include <CL/sycl.hpp>
#include <iostream>
#define static_assert_align(st, align) \
static_assert((sizeof(st) % (align) == 0), "Structure must be strictly aligned") // NOLINT
typedef struct KernelLightDistribution {
float totarea;
int prim;
union dpct_type_be6907 {
struct dpct_type_12c54e {
int shader_flag;
int object_id;
} mesh_light;
struct dpct_type_ff924c {
float pad;
float size;
} lamp;
} union_name; //Note the inialization here
} KernelLightDistribution;
int main() {
std::cout << sizeof(KernelLightDistribution) << "\n";
static_assert_align(KernelLightDistribution, 16);
return 0;
}
Regards,
Rahul
Link Copied
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Hi,
There is a small bug in your code. You have not initialized the union dpct_type_be6907. As a result, memory is not getting created for that particular data structure. Anonymous structs/unions are a bit lenient when it comes to initialization since they can be accessed right way and they are guaranteed to be present within a struct/union. (Memory always gets created for anonymous structs/unions)
Refer to the modified code snippet below.
#include <CL/sycl.hpp>
#include <iostream>
#define static_assert_align(st, align) \
static_assert((sizeof(st) % (align) == 0), "Structure must be strictly aligned") // NOLINT
typedef struct KernelLightDistribution {
float totarea;
int prim;
union dpct_type_be6907 {
struct dpct_type_12c54e {
int shader_flag;
int object_id;
} mesh_light;
struct dpct_type_ff924c {
float pad;
float size;
} lamp;
} union_name; //Note the inialization here
} KernelLightDistribution;
int main() {
std::cout << sizeof(KernelLightDistribution) << "\n";
static_assert_align(KernelLightDistribution, 16);
return 0;
}
Regards,
Rahul
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Hi Gagan,
Could you let me know if the solution provided helped?
Thanks,
Rahul
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Hi Rahul,
Yes, that issue got solved. And yeah, once you pointed out, the mistake became quite clear.
But to match ported code with actual code, I went ahead with using anonymous structs/unions. Thanks for your help.
Regards,
Gagan
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Thanks for the confirmation.
Intel will no longer monitor this thread. However, it will remain open for community discussion.
![](/skins/images/45C6C2D737ED71F4C51F0145C8CB1E9C/responsive_peak/images/icon_anonymous_message.png)
- Subscribe to RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Printer Friendly Page