microcode, compilers, and supercomputer architecture

From: Eric Smith <eric_at_brouhaha.com>
Date: Sun Apr 4 22:04:52 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.
Received on Sun Apr 04 1999 - 22:04:52 BST

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