[nhc-users] Native code generation

[Malcolm Wallace]

Arunkumar S Jadhav <arunk at it.iitb.ac.in> writes:

> > About 8-9 years ago, David Wakeling wrote a native code-generator
> > for nhc13
> 
> Is it publically available somewhere ? 

Not as far as I am aware.  You could ask him:  D.Wakeling at exeter.ac.uk

> I've built a native code generator that takes G-code straight out of SPJ's 
> book. The way I'm doing it is to represent each g-instruction as a sequence
> of subject trees each typically performing a memory operation (like
> overwrite root of the redex etc) and then use burg tree pattern matcher to
> generate i386 code. How feasible it would be to do something along similar
> lines for Gcode generated by nhc. 

I'm sure that is a reasonable approach.  nhc98's G-code is not very
complex.  Many of the bytecodes are just variations of a single
instruction, designed to use the minimum amount of storage where
possible.  For instance,

    PUSH_CVAL_P1 i
    PUSH_CVAL_P2 i j
    PUSH_CVAL_N1 i 
    PUSH_CVAL_N2 i j

... these all push a value read from the constant table (there is
one constant table per function) onto the stack; the only difference
is the calculation of the offset from the beginning of the table -
is it positive or negative (P or N), and is the offset represented
as one byte or two?

You may prefer to eliminate the constant tables altogether, and
instead do the table-lookup at compile-time.  The main reason why
there are constant tables in nhc98 is to reduce the size of the
generated bytecode by sharing the constants.  For a native-code
backend, reducing code-size is less important, and you will gain
speed by removing the extra indirect step.

> And BTW, the __ctype_b still persists :(....I tried all the ways (well
> most); linked using the code I got from bugzilla (which Malcolm had also
> sent), tried adding that object to Runtime.a with no luck. Will see it
> later; I'm surprized that no one reported this problem till now.

Perhaps not many people use RedHat 9.  Here, I have Slackware 10,
RedHat 7.2, and Knoppix.

Regards,
    Malcolm