Re: Writing compilers, and example.c vs compile-i386.c

[David Given <dg@cowlark.com>]

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Mike Frysinger wrote:
> this may be worth investigating as well:
> http://pcc.ludd.ltu.se/

That was actually where I started; it works pretty well, though after a
couple of hours of examining the code I realised that there was a good
reason why it looked like code that had been written 25 years ago and
then randomly hacked ever since. It's a little opaque, which is why I
ended up here.

Christopher Li wrote:
[...]
> I would strongly recommend using the example.c rather than compile-i386.c.
> If you want to do any thing interesting with the back end at all, using
> the linearize byte code is the way to go.

Yes, that's what I suspected --- being the more complicated file! Oh,
well, I've been examining it, and it's slow beginning to make sense.

However: I notice that the code seems to make use of OP_DEATHNOTE
instructions to mark hardregs as being dead. However, these are only
generated if track_pseudo_death(ep) is called --- and example.c never
calls this. It *is*, however, called if -vdead is specified on the
command line. Is this a bug in example.c or am I just misunderstanding
things?

(Also, the OP_DEATHNOTE instructions appear to occur *before* the
instruction that uses them last --- is this so that the instruction can
reuse the register is the code generator sees fit to do so?)

(In addition, I notice that once liveness tracking has been done phisrc
nodes get annotated with the desired shared register that the phi should
occupy; suddenly, the phi stuff all makes sense.)



(PS. Please don't cc me if you're also mailing the list --- I only need
one copy!)

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