Re: __simd_sto confusion

[Benjamin Thaut via Digitalmars-d-learn]

On Saturday, 3 October 2015 at 14:47:02 UTC, Nachtraaf wrote:
I'm trying to create some linear algebra functions using simd 
intrinsics. I watched the dconf 2013 presentation by Manu Evans 
but i'm still confused about some aspects and the following 
piece of code doesn't work. I'm trying to copy the result of a 
dot product from the register to memory but dmd fails with an 
overload resolution error, which i guess is due some implicit 
conversion?


dmd error:

simd1.d(34): Error: core.simd.__simd_sto called with argument 
types (XMM, float, __vector(float[4])) matches both:
/usr/include/dlang/dmd/core/simd.d(434): 
core.simd.__simd_sto(XMM opcode, double op1, __vector(void[16]) 
op2)

and:
/usr/include/dlang/dmd/core/simd.d(435): 
core.simd.__simd_sto(XMM opcode, float op1, __vector(void[16]) 
op2)


from the following piece of code:

float dot_simd1(float4  a, float4 b)
{
float4 result = __simd(XMM.DPPS, a, b, 0xFF);
float value;
__simd_sto(XMM.STOSS, value, result);
return value;
}

What am I doing wrong here?


core.simd is horribly broken. I recommend that you avoid it for 
any serious work. If you want to do simd programming with D get 
LDC or GDC and use their simd intrinsics instead of core.simd.

If you have to do simd with dmd write inline assembly.

Re: __simd_sto confusion

[Nachtraaf via Digitalmars-d-learn]

That's a shame. I've read that each compiler has his own quirks 
and not support everything dmd supports. I do want to keep the 
code as portable as possible. Guess I'll try using inline 
assembler and runtime checks for the right cpu architecture.


Thanks for the help people.

Re: __simd_sto confusion

[Marco Leise via Digitalmars-d-learn]

This is a bug in overload resolution when __vector(void[16])
is involved. You can go around it by changing float4 to void16,
only to run into an internal compiler error:
  backend/gother.c 988
So file a bug for both @ issues.dlang.org
Also it looks like DMD wants you to use the return value of
the intrinsic, is that expected?

-- 
Marco

Re: __simd_sto confusion

[Nachtraaf via Digitalmars-d-learn]

On Saturday, 3 October 2015 at 15:39:33 UTC, Marco Leise wrote:

This is a bug in overload resolution when __vector(void[16])
is involved. You can go around it by changing float4 to void16,
only to run into an internal compiler error:
  backend/gother.c 988
So file a bug for both @ issues.dlang.org
Also it looks like DMD wants you to use the return value of
the intrinsic, is that expected?


I guessed I wouldn't need the return value as the intel C 
intrinsic for this opcode has a void return type. I did try 
supplying a return type but I couldn't circumvent the overload 
error so I had no clue if it would make any difference.


I changed the type of result to void16 like this:

float dot_simd1(float4  a, float4 b)
{
void16 result = __simd(XMM.DPPS, a, b, 0xFF);
float value;
__simd_sto(XMM.STOSS, value, result);
return value;
}

and for me this code compiles and runs without any errors now.
I'm using DMD64 D Compiler v2.068 on Linux. If you got an 
internal compiler error that means that it's a compiler bug 
though I have no clue what. Did you try the same thing I did or 
casting the variable?
I guess I should file a bugreport for overload resolution if it's 
not a duplicate for now?

Re: __simd_sto confusion

[Marco Leise via Digitalmars-d-learn]

Am Sat, 03 Oct 2015 23:42:22 +
schrieb Nachtraaf :

> I changed the type of result to void16 like this:
> 
> float dot_simd1(float4  a, float4 b)
> {
>  void16 result = __simd(XMM.DPPS, a, b, 0xFF);
>  float value;
>  __simd_sto(XMM.STOSS, value, result);
>  return value;
> }
> 
> and for me this code compiles and runs without any errors now.
> I'm using DMD64 D Compiler v2.068 on Linux. If you got an 
> internal compiler error that means that it's a compiler bug 
> though I have no clue what. Did you try the same thing I did or 
> casting the variable?
> I guess I should file a bugreport for overload resolution if it's 
> not a duplicate for now?

Yes. At some point the intrinsics will need a more thorough
rework. Currently none of those that return void, int or set
flags work as they should.

-- 
Marco