[M3devel] field accesses in m3cg?

[Jay K]

No luck. In a jam between bitfields and configure -enable-checking:
     error ("statement makes a memory store, but has no VDEFS");
   gimple_stmt (stderr, stmt, 0, TDF_VOPS);


the "failsafe" form doesn't hit that error, but crashes somewhere.
I'll probably have to debug said crash.

I wonder..maybe we can prototype/synthesize field accesses?
ie: without a frontend/m3cg change?

In parse.c given an offset load/store, we could look at the base,
and if it is a record just walk the fields linearly until the offset matches
and then generate a component/field reference?

Obviously it'd be better to do something without linear search.

Similarly but easier for arrays. Heck, I have to imagine that
arrays aren't a problem with the non-bitfield form.

This still leaves some missing parts, mainly type information
for other things, like packed and maybe opaque.
I have to understand packed better.

 - Jay

----------------------------------------
> From: jay.krell at cornell.edu
> To: hosking at cs.purdue.edu
> Date: Sun, 12 Sep 2010 23:53:18 +0000
> CC: m3devel at elegosoft.com
> Subject: Re: [M3devel] field accesses in m3cg?
>
>
> The more I look at this, the more I think we need to do it.
> If we want to stop hacking optimizations off, use -O3, use configure -enable-checking.
> The "failsafe" replacement for bitfields doesn't even work, though I'm trying to make it work.
>
> Inevitably, for now, we are trading one set of deoptimizations vs. another.
> For example, the heavy use of volatile was a big deoptimization that enabled
>   "all" the rest to be done..at least from parse.c's point of view, though presumably
>    volatile stopped a lot of code below.
>
> Now I'm trying throwing around TREE_ADDRESSABLE, which I'm sure will
>  also pessimize. We'll see. I'm not convinced that using ADDR_EXPR
>  is equivalent to TREE_ADDRESSABLE. We'll see.
>
> It wasn't enough to throw in TREE_ADDRESSABLE on load/store with offset != 0.
> I'm trying it on all load/store now.
>
>  - Jay
>
> ----------------------------------------
> > From: hosking at cs.purdue.edu
> > Date: Fri, 3 Sep 2010 09:34:29 -0400
> > To: jay.krell at cornell.edu
> > CC: m3devel at elegosoft.com
> > Subject: Re: [M3devel] field accesses in m3cg?
> >
> > On 3 Sep 2010, at 07:28, Jay K wrote:
> >
> > >
> > > Thoughts on exposing higher level "field load/store" in m3cg?
> > > I'm wary of it currently.
> > > Would rather do other stuff for now.
> > >
> > > It'd let the bitfield refs be replaced by something "proper".
> > >
> > > But it opens up more danger in terms of frontend/backend layout disagreement.
> >
> > I worry about this.
> >
> > >
> > > - Jay
> > >
> > >
> > >
> > >
> > >
> >
>