Agner`s CPU blog

I have designed a consistent code structure where everything fits nicely. All instruction forms and addressing modes fit into the same template. All immediate constants and address offsets have power-of-2 sizes and proper alignment. The code word size is 32 bits, and each instruction can use one, two or three words. Each instruction can be coded in many different versions with different operand types, addressing modes, options and features. Simple common instructions can be packed in a tiny format with two tiny instructions stuffed into one 32-bit code word, but the 4-byte alignment of the code is maintained.

The idea of variable-length vector registers fits excellently with the design goals. The same executable program can run optimally on different microprocessors from small office computers and tablets to large scientific supercomputers with very long vector registers, without the need for separate compilation for each platform.

The instruction set has no name yet. I have considered calling it CRISC, because it combines the best from RISC and CISC. The modular format with easy detection of instruction length makes decoding simple and fast. Instructions have a moderate degree of complexity. An instruction can do multiple things, but only if it fits into the pipeline structure so that it does one thing at each pipeline stage. This will assure a throughput of one instruction per clock cycle per pipeline lane (except for division and cache misses). There is no need to split instructions into micro-operations or to use microcode. My ambition is to design a system that can outperform the best existing microprocessor designs.

My proposal includes standardization of the entire ecosystem of ABI standard, binary file format, function libraries, compiler support and OS support. With open standards for the entire ecosystem we would be able to combine different programming languages in the same program and use the same function libraries with all compilers.

Isn't that a nice vision? I am looking forward to your intelligent comments.