Re: SDCC porting feasibility study, part 1: the assembler

[David Given <dg@cowlark.com>]

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Brad Normand wrote:
[...]
> What scares me there is writing a whole toolchain isn't trivial.  In
> college, I took a class where we wrote the most basic of basic
> compilers in java (using a nice grammar parsing library), reading in a
> simplified ALGOL and targeting mips and doing no optimization or real
> register allocation at all.

I've been doing stuff with compilers for years (ask me about my C to
Perl compiler!), and this is so true. C compilation is painful. Doing C
compilation *well* is a life's work. You *seriously* don't want to write
one from scratch.

If you want to do an 8086 C compiler, I'd strongly recommend looking at
LLVM --- it's apparently got a really nice backend model, although the
documentation isn't brilliant. Better still, it may be possible to start
with the excellent 386 backend and cut it down, which should be a much
easier job than building one from scratch.

Other compiler backends I know about:

- gcc: unspeakable.

- Sparse: the engine behind the Linux kernel linter, which I used for
the above C to scripting engine compiler. It's not really intended as a
code generator but actually does a reasonable job.

- vbcc: I did a Z-machine backend for this; it's got a very nice
architecture, and is simple to work with and produces reasonable code,
but has a painful source-available-but-not-open-source license.

- the ACK: has the advantage of being a complete turnkey toolchain and
compiler, including assembler, linker, librarian, libc, etc, *and* it
already supports the 8086, but doesn't produce great code and is tough
to work on.

- tcc: very very very fast. Produces very very very crap code. It
started life as an IOCCC entry, and boy does it show.

Then there's TenDRA, which I've never had anything to do with but which
seems to have vanished. And there are C and C++ parsing libraries like
Elkhound which I've tried to look at but have been unable to get started
with.

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