Re: How about VLIW used as RISC?

Alex Colvin <alexc@std.com>
2 May 2004 21:48:52 -0400

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From: Alex Colvin <alexc@std.com>
Newsgroups: comp.arch,comp.compilers
Date: 2 May 2004 21:48:52 -0400
Organization: The World : www.TheWorld.com : Since 1989
References: 04-04-088
Keywords: architecture
Posted-Date: 02 May 2004 21:48:52 EDT

>We have simple scalar RISC and superscalar RISC but why there is few
>or no VLIW used as an RISC for general application? There is criticism
>about code density. However, as many has pointed out, modern VLIW has
>already used compression to remove NOOP instruction in the instruction
>packet. I guess 40-bit instruction is enough hold the additional
>control information, such as predicate bits, p bits(for indicating the
>last instruction of the instruction packet).


You might find the old (circa 1990) WM design relevant.
http://www.cs.virginia.edu/~wm/wm.html
sort of a narrow VLIW/RISC with two operations, three operands and one
result.


ANother answer might be that VLIW is hard to run out-of-order
--
mac the naf


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