Re: Java virtual machine as target language for C/C++

khays@sequent.com (Kirk Hays) wrote:
>Remember, there is no problem in CS that can't be solved by another
>level of indirection.


dmoisan@shore.net wrote:
>True enough. Pascal for the CDC 170 did this too; the 170 has NO
>stack and no native recursion (fine for Fortran, bad for Pascal). I
>suspected that Pascal implementation (I can't remember whose it was,
>but I don't think it was CDC's) built a jump stack.


The run-time environment did not normally keep a run-time stack around,
as it wasn't required for Fortran or COBOL. Pity, as it would have saved
a lot of people a lot of work...


However ALGOL, PASCAL, LISP, and others all implemented dynamic memory
management. For an amusing anecdote, see Hennesy and Patterson's book
on Computer Architecture (1st edition). There is a chart on ALGOL
performance vs. Burroughs - a machine designed to run ALGOL. The 6600
creamed the Burroughs machine. Changed Patterson's whole outlook on
computer architecture.


>If I remember my COMPASS (CDC assembly), there wasn't indirect
>addressing so that programs that needed it actually built a jump
>instruction with the desired address and branched to that instruction.


You may be thinking of how the return jump instruction worked. It was
also possible to branch to a B register. In Fortran, for certain
known intrinsic functions, they avoided the normal RJ instruction
and simply stored the next instruction parcel address in a B register
and jumped. To return, they branched to the B register. FAST and
no memory access required.


And of course indirect addressing was easy for data. Stuff anything
you want in the appropriate A register.


>The 170 was an old archaic processor (no stack, but floating point!)
>but I loved it! (Within its limits, the orthogonality was quite good
>and code generation was relatively easy.)


It should be - it's roots lie in the famed CDC 6600 - the first
RISC machine. Seymour Cray knew what he was doing.


>Background: I'd used the Cyber in college and wrote a Pascal
>compiler--unheard-of for undergrads there--for my senior project. I'd
>planned on using the scheme I mentioned but I only got 70% finished by
>the end of the term. :(


Impressive!


Wirth's original PASCAL compiler was implemented on one of these machines.


Walt
--
Walt Spector
(wws@renaissance.cray.com)
Sunnyvale, California
_._ _._ _.... _. ._.


--

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