Re: Small memory compilers - was SmartPort remapping

["William Garber" <willy46pa@garberstreet.com>]

It's very interesting, but doesn't belong
in this group. Am I wrong? If I was involved,
I'd have been reprimanded way before this.

William Garber
Email Address - willy46pa@garberstreet.com
Alt. Email - willy46pa@comcast.net
Web address - http://www.garberstreet.com


"David Schmenk" <dschmenk@YUCH.gmail.com> wrote in message news:gc27j.6355$4q5.4475@nlpi069.nbdc.sbc.com...
: Or just change the subject.  I find it rather interesting.
:
: Dave...
:
: William Garber wrote:
: > This has gotten a bit OT, don't you think?
: >
: > Maybe the two of you can continue this
: > topic in private emails. Thank you.
: >
: > William Garber
: > Email Address - willy46pa@garberstreet.com
: > Alt. Email - willy46pa@comcast.net
: > Web address - http://www.garberstreet.com
: >
: >
: > "glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message 8rSdnb9dx6HeA8HanZ2dnUVZ_oimnZ2d@comcast.com">news:8rSdnb9dx6HeA8HanZ2dnUVZ_oimnZ2d@comcast.com...
: > : Michael J. Mahon wrote:
: > :
: > : > glen herrmannsfeldt wrote:
: > :
: > : (snip)
: > :
: > : >> And written in some special language (like P-code or JVM code) and
: > : >> interpreted.  The operations are all generated by macros for the
: > : >> OS/360 assembler.
: > :
: > : > It was a requirement imposed by IBM that the standard IBM tools
: > : > be used to create the compiler, hence OS/360 assembler.
: > :
: > : > All of Digitek's compilers were produced using the same approach--
: > : > they were written on a virtual machine with multiple (32? 64?) stacks
: > : > as operands, and the input stream and output (code) stream.
: > :
: > : > After the compiler was running interpretively, the interpreter
: > : > profiled the interpreted code (in the other half of memory), then
: > : > the macros were tagged to generate either 1) the interpreted op,
: > : > 2) a quick linkage to the "execute routine" of the interpreter,
: > : > thus saving the fetch and decode overhead, or 3) an in-line
: > : > expansion of the execute routine, saving all interpretive
: > : > overhead.
: > :
: > : Hmm, a little like what IBM did with VM and microcode assist.
: > :
: > : > Normally, expanding just a few percent of the code resulted in
: > : > near native code performance, leading to the smallest, fastest
: > : > compilers extant, particularly on small memory machines.
: > :
: > : And the problem of writing compilers for small memory
: > : machines makes this relevant to this newsgroup.
: > :
: > : > The FORTRAN G (128KB) compiler has a special history.  It was
: > : > commissioned as FORTRAN E (32KB)(or F (64KB), I forget), but it
: > : > ran faster in less memory than the IBM-produced FORTRAN G, so it
: > : > was "promoted" to be FORTRAN G--making it the smallest G-level
: > : > compiler, by far!
: > :
: > : The memory needed depends on the size of the program.
: > : The PL/I (F) compiler was supposed to be able to compile in 44K
: > : (That is, 64K machine minus 20K for OS).  To do that it might
: > : have to keep the symbol table on disk.  (The one thing you would
: > : expect a compiler to always keep in core.)  At the end of compilation
: > : it tells the minimum region size needed to keep the symbol table
: > : in core.
: > :
: > : > IBM also had a religious committment to the use of the peculiar
: > : > 3-register setup BXLE op for closing DO loops (which is what it
: > : > was designed for).  The Digitek compiler used normal ops for DO
: > : > loops, usually resulting in smaller, faster code.  But, under
: > : > contractual pressure, they relented, and every DO loop closing
: > : > was replace by a LM (Load Multiple) of the usual 3 registers,
: > : > followed by the BXLE--one of the few cases I recall of "protest"
: > : > code generation!  ;-)
: > :
: > : I do remember that IBM preferred the end test DO loop, such
: > : that many believe that Fortran 66 requires it.  It doesn't,
: > : but it does allow it.  (Technically, a loop with the end
: > : value less than the start value is not legal.)
: > :
: > : > Digitek compilers were very portable, requiring only three
: > : > interfaces to the OS:  read a line, print a line, and write
: > : > a buffer of code.
: > :
: > : Both G and H use the same runtime library.  The G compiler
: > : has an interesting debug feature that H doesn't have, that allows
: > : putting debug statements at the end, in a debug packet, but
: > : to have the effect of inserting them into other parts of the
: > : program.
: > :
: > : -- glen
: > :
: >
: >