microcode, compilers, and supercomputer architecture

From: Buck Savage <hhacker_at_home.com>
Date: Sun Apr 4 22:26:46 1999

>Megan wrote:
>> well put... I've yet to find a compiler which can produce code which
>> could not then be further optimized in some way by a person well
>> versed in that machine's architecture...
>
>Yes, but if you paid attention to the original claim, you would see that
>I asserted that it was true for horizontal microcode with large amounts
>of data dependency. This is *very* different than trying to compile C
>(or Pascal, or Bliss, or whatever) for a typical architecture (which more
>closely resembles vertical microcode).
>
>One of the systems I microcoded had 512 words of control store (of about
>72 bits each), and running my microprogram source code through the compiler
>produced 514 words of microinstructions. With about two weeks of
>concentrated effort, I was able to eventually squeeze out two
>microinstructions. Total development time: 6 weeks.
>
>If I had tried to write all of the microcode in "assembly", it would have
taken
>me longer to write, and it probably would have been *bigger* on the first
>pass. And I still would have had to spend a lot of time on hand
optimization.
>I think this would have taken at least 12 weeks of development time,
although
>since I didn't do it that way I'll never know.

Your argument, Eric, was that the microcode compiler generated code
that is equally as efficient as that you, or someone else, could have
constructed by hand. Megan in no way implies the use of assembly code.
The microcode compiler would generate an object file, which by your
own admission above, generated more code than could fit in the
memory space available. You accepted her argument that the human
was required to generate code more efficient than that produced by
the microcode compiler. You protest _too loudly_ my friend.

William R. Buckley
Received on Sun Apr 04 1999 - 22:26:46 BST