Detailed explanation for instructions

[Ming Wei]

Hi Scott,

I am trying to use MaxAs to write highly optimized kernels for CUDA. MaxAs is a fascinating tool, but I fail to find a detailed "instruction reference manual" for it. For example, what does "XMAD.PSL.CBCC" mean? Skimming through CUDA Binary Utilities Document, I can only find XMAD means Integer Short Multiply Add, but no knowledge about "PSL.CBCC".

Could you help me with that? Where can I find the information that I need?

Thanks in advance.

Best Regards,

Ming

[Scott Gray]

Maxas is designed for experienced cuda programmers who aren't shy about examining compiled sass.  With enough of this you're already a good ways towards understanding the ISA.

XMAD is one of the more complicated instructions.  It's a 16 bit multiply 32 bit accumulate which has several modes to let you combine instructions to achieve wider bit multiplication.

I typically use 3 sequences:

A single unsigned 16bit mad (flags for signed mode are available):

XMAD d, a, b, c;

A 16 bit times a 32 bit:

XMAD d, a, b, c;

XMAD.PSL d, a.H1, b, d;

or

XMAD d, a, b, c;

XMAD.PSL d, a, b.H1, d;

A 32 bit times a 32 bit and just keeping the lower 32 bits of result:

XMAD.MRG x, a, b.H1, RZ;

XMAD d, a, b, c;

XMAD.PSL.CBCC d, a.H1, x.H1, d;

But there are many other modes to explore, and VMAD is also a similar instruction but lets you add sign operations.

Basically you'll need to study the MaxasGrammar file.  I look at that file pretty frequently to find instructions and their flags.

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[Ming Wei]

Sorry for the late response. I'll try to figure it out from looking into MaxasGrammar file and the compiled sass, thanks :)