4 ms·

Have you ever seen the jiter use SIMD? Having written some test code that was the simplest use case (multiply an array of floats by a float constant iirc) I hav

by yaur 11y ago

Have you ever seen the jiter use SIMD? Having written some test code that was the simplest use case (multiply an array of floats by a float constant iirc) I have not. C# is a great language, but not for compute bound problems.

ChrisLomont 11y ago
Yes, I have seen that. Of course the JITer will not perform the same level of optimizations as the fullblown code generator, but then you can just call that if you like. The new JIT engine does support SIMD [1]. And C# can generate SIMD code using various libraries (I think MS has one, and I know Mono does). And various people have shown how to do fullblown x86 assembly code generation and execution from within C#, but it's fragile. [1] http://blogs.msdn.com/b/dotnet/archive/2014/04/07/the-jit-finally-proposed-jit-and-simd-are-getting-married.aspx http://blogs.msdn.com/b/dotnet/archive/2014/04/07/the-jit-fi...
jj10 11y ago
Actually, I just tried it: float[] floats = new float[1000]; float factor = 1.01f; int index = 0; while (index < 1000) { floats[index++] *= factor; } ...becomes... 00007ff8`80a804a9 488d549010 lea rdx,[rax+rdx*4+10h] 00007ff8`80a804ae c4e17a1002 vmovss xmm0,dword ptr [rdx] 00007ff8`80a804b3 c4e17a590524000000 vmulss xmm0,xmm0,dword ptr [00007ff8`80a804e0] 00007ff8`80a804bc c4e17a1102 vmovss dword ptr [rdx],xmm0 This is in VS 2013, compiled with DEBUG off, prefer x86 off, and 'any cpu' as the target.
- tbirdz 11y ago
  Those are scalar instructions, not the SIMD instructions. With x86_64 the fpu stack operations are basically for legacy purposes only, and normal floating point operations are expected to be done with the SSE/AVX scalar instructions. SIMD instruction used the packed variants of the commands allowing you to multiple say 4 floats in a single instruction.
pjmlp 11y ago
Yes, you just need to fulfil three conditions: - Use the new RyuJIT - Make use of 64 bits CPU - Use the vector and matrix classes from System.Numerics

by yaur 11y ago

ChrisLomont 11y ago

Yes, I have seen that. Of course the JITer will not perform the same level of optimizations as the fullblown code generator, but then you can just call that if you like. The new JIT engine does support SIMD [1]. And C# can generate SIMD code using various libraries (I think MS has one, and I know Mono does). And various people have shown how to do fullblown x86 assembly code generation and execution from within C#, but it's fragile. [1] http://blogs.msdn.com/b/dotnet/archive/2014/04/07/the-jit-finally-proposed-jit-and-simd-are-getting-married.aspx http://blogs.msdn.com/b/dotnet/archive/2014/04/07/the-jit-fi...

jj10 11y ago

Actually, I just tried it: float[] floats = new float[1000]; float factor = 1.01f; int index = 0; while (index < 1000) { floats[index++] *= factor; } ...becomes... 00007ff8`80a804a9 488d549010 lea rdx,[rax+rdx*4+10h] 00007ff8`80a804ae c4e17a1002 vmovss xmm0,dword ptr [rdx] 00007ff8`80a804b3 c4e17a590524000000 vmulss xmm0,xmm0,dword ptr [00007ff8`80a804e0] 00007ff8`80a804bc c4e17a1102 vmovss dword ptr [rdx],xmm0 This is in VS 2013, compiled with DEBUG off, prefer x86 off, and 'any cpu' as the target.

tbirdz 11y ago
Those are scalar instructions, not the SIMD instructions. With x86_64 the fpu stack operations are basically for legacy purposes only, and normal floating point operations are expected to be done with the SSE/AVX scalar instructions. SIMD instruction used the packed variants of the commands allowing you to multiple say 4 floats in a single instruction.

pjmlp 11y ago

Yes, you just need to fulfil three conditions: - Use the new RyuJIT - Make use of 64 bits CPU - Use the vector and matrix classes from System.Numerics