[cfe-dev] ext_vector_type cg-gen crash on x86-64 and some questions on the ABI

[Mattias Holm]

I have some code that simplified is:

///////////////////////////////
#include <math.h>
#include <stdint.h>

#if __has_feature(attribute_ext_vector_type)
typedef float __attribute__((ext_vector_type (3))) float3;
typedef int32_t __attribute__((ext_vector_type (3))) int3;
typedef union float3_u {
   float3 v;
   float a[3];
} float3_u;
#endif

struct lwcoord {
   float3 offs;
   int3 seg;
};
static  float3
vf3_set(float x, float y, float z)
{
   float3_u uc = {.a = {x,y,z}};
   return uc.v;
}
static  int3
vi3_set(int32_t a, int32_t b, int32_t c)
{
   union {
     int3 v;
     struct {
       int32_t x, y, z;
     } s;
   } u;

   u.s.x = a;
   u.s.y = b;
   u.s.z = c;

   return u.v;
}

typedef struct lwcoord lwcoord;

void
lwc_set(lwcoord *coord, float x, float y, float z)
{
   coord->offs = vf3_set(x, y, z);
   coord->seg = vi3_set(0, 0, 0); // Remove this and it compiles
}

///////////////////////////////

Compiling this for x86-64 results in the following crash (using the 
clang version distributed with Snow Leopard).

1.	<eof> parser at end of file
2.	Code generation
3.	Running pass 'X86 DAG->DAG Instruction Selection' on function '@lwc_set'


It compiles fine with x86 (32 bit).

It also seems to be fine if you remove the vi3_set line, but not if you 
remove the vf3_set line.

Now some questions on the semantics of the ext_vector_type, since it is 
not that well documented in the clang extensions page.

1. What is the ABI for an ext_vector_type? Will the vectors be passed in 
SSE registers if they are passed as function arguments, or will they be 
passed by address?
2. Sizeof (float3) returns 12 and not 16 as I would have guessed for 
alignment reasons, why is this the case? Assuming you want to use SSE 
for computing with the vectors, they must be aligned IIRC.


Regards,
Mattias