The issue fixes itself if I wrap the int in a struct.
#ifdef USE_STRUCT
struct Point {
int x;
};
#endif
export void
run()
{
#ifdef USE_STRUCT
varying Point p[programCount];
for (uniform int i = 0; i < programCount; ++i) {
p[i].x = i * programCount + programIndex;
print("% --> %, %\n", &p[i], p[i].x);
}
varying Point * varying a = &p[0];
print("%\n", a);
varying Point * varying av = a;
print("%\n", av);
varying Point aDeref = *a;
varying Point avDeref = *av;
print("%\n", aDeref.x);
print("%\n", avDeref.x);
#else
varying int p[programCount];
for (uniform int i = 0; i < programCount; ++i) {
p[i] = i * programCount + programIndex;
print("%\n", p[i]);
}
varying int * uniform a = &p[0];
print("%\n", a);
varying int * varying av = a;
print("%\n", av);
varying int aDeref = *a;
varying int avDeref = *av;
print("%\n", aDeref);
print("%\n", avDeref);
#endif
}
ispc test.ispc --target=sse2-i32x4 -o test_ispc.o -h test_ispc.h
-DUSE_STRUCT
0x7fff144ab7c0 --> [0,1,2,3],
0x7fff144ab7d0 --> [4,5,6,7],
0x7fff144ab7e0 --> [8,9,10,11],
0x7fff144ab7f0 --> [12,13,14,15],
[0x7fff144ab7c0,0x7fff144ab7c0,0x7fff144ab7c0,0x7fff144ab7c0]
[0x7fff144ab7c0,0x7fff144ab7c0,0x7fff144ab7c0,0x7fff144ab7c0]
[0,1,2,3]
[0,1,2,3]
vs
ispc test.ispc --target=sse2-i32x4 -o test_ispc.o -h test_ispc.h
[0,1,2,3]
[4,5,6,7]
[8,9,10,11]
[12,13,14,15]
0x7ffc84759520
[0x7ffc84759520,0x7ffc84759520,0x7ffc84759520,0x7ffc84759520]
[0,1,2,3]
[0,0,0,0]
That may explain why I haven't encountered this issue in the past. Usually
our varying types are wrapped in some sort of struct. I don't have
immediate access to one of the newer versions of ISPC, but I will try with
an updated ISPC version at some point.
-Brian
On Friday, April 26, 2019 at 6:44:46 AM UTC-7, Matt Pharr wrote:
>
> Hmmm.. As far as I can tell, that's a bug in ispc.
>
> To summarize: a uniform pointer to varying data is a single scalar
> pointer, but when it's dereferenced, because it's pointing to varying data,
> there's an implicit indexing by programIndex. (Alternatively, it's a vector
> load.) A varying pointer to varying data is a per-program instance pointer
> that, when dereferenced, should also have that implicit indexing applied.
> (In a sense, each program instance only sees its own instance of the
> varying data.)
>
> I *think* that it's intended for a varying pointer to varying data to have
> the same address value, as you're seeing here, and that then the bug is in
> the code emitted to dereference *av. I am a little surprised that that
> would be broken, though (surely that's in the test suite), so there may be
> something wrong in the analysis above.
>
> Thanks,
> Matt
>
>
> On Thu, Apr 25, 2019 at 12:10 PM Brian Green <[email protected]
> <javascript:>> wrote:
>
>> I'm running a simple test case that makes me question my understanding of
>> how varying types are created when varying pointers to varying types are
>> dereferenced. My understanding was that each pointer would be dereferenced
>> with the appropriate lane. But this appears to not be the case.
>>
>> Consider:
>>
>> export void
>> run()
>> {
>> varying int p[programCount];
>> for (uniform int i = 0; i < programCount; ++i) {
>> p[i] = i * programCount + programIndex;
>> print("%\n", p[i]);
>> }
>>
>> varying int * uniform a = &p[0];
>> print("%\n", a);
>> varying int * varying av = a;
>> print("%\n", av);
>> varying int aDeref = *a;
>> varying int avDeref = *av;
>> print("%\n", aDeref);
>> print("%\n", avDeref);
>> }
>>
>>
>> Compiled with ispc-1.9.2 as:
>> ispc test.ispc --target=sse2-i32x4 -o test_ispc.o -h test_ispc.h
>>
>> The following output is produced:
>> [0,1,2,3]
>> [4,5,6,7]
>> [8,9,10,11]
>> [12,13,14,15]
>> 0x7ffd8568d240
>> [0x7ffd8568d240,0x7ffd8568d240,0x7ffd8568d240,0x7ffd8568d240]
>> [0,1,2,3]
>> [0,0,0,0]
>>
>> The avDeref value suprises me. I was expecting [0,1,2,3]. In other
>> words, the pointer in lane 0 would be dereferenced for lane 0, the pointer
>> in lane 1 would be dereferenced at lane 1, etc... But instead all of them
>> seem to be dereferenced for lane 0. I've tested this with avx1-i32x8 and
>> avx2-i32x8 and seen similar results. So, what am I misunderstanding about
>> varying pointers to varying types?
>>
>> Thanks,
>> -Brian
>>
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