topic Re:assert failes if struct tag-name is given in Intel® oneAPI DPC++/C++ Compiler

assert failes if struct tag-name is given

Shukla__Gagandeep — Fri, 04 Sep 2020 14:59:37 GMT

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

Re: assert failes if struct tag-name is given

RahulV_intel — Mon, 07 Sep 2020 09:23:00 GMT

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

Re:assert failes if struct tag-name is given

RahulV_intel — Mon, 14 Sep 2020 07:15:55 GMT

Hi Gagan,

Could you let me know if the solution provided helped?

Thanks,

Rahul

Re: Re:assert failes if struct tag-name is given

Shukla__Gagandeep — Tue, 15 Sep 2020 13:35:43 GMT

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

Re:assert failes if struct tag-name is given

RahulV_intel — Wed, 16 Sep 2020 06:01:16 GMT

Thanks for the confirmation.

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