patch: remove PseudoSourceValue from Value.

[Nick Lewycky]

On 24 February 2014 16:20, Hal Finkel <hfinkel at anl.gov> wrote:

> What is the underlying motivation for doing this?
>

The proximate cause is that I'm trying to remove the vtable from
llvm::Value, and in order to do that I'm going to write dispatch functions
that switch on the ValueID and call the appropriate function from the
most-derived-type. If I do that, then we have lib/IR placing calls to
lib/CodeGen, which is a layering violation.

At a higher level, PSV does not belong there. It is not part of the IR. No
IR passes use or understand it. It's not documented in the LangRef.
Frankly, it's a hack -- and it's a great hack that and I understand its
utility for lib/CodeGen -- but that doesn't change the fact that it's not
part of llvm's IR. I've just never been motivated to do something about it
until now.

Nick


> ----- Original Message -----
> > From: "Nick Lewycky" <nlewycky at google.com>
> > To: "Commit Messages and Patches for LLVM" <llvm-commits at cs.uiuc.edu>
> > Sent: Monday, February 24, 2014 6:13:30 PM
> > Subject: patch: remove PseudoSourceValue from Value.
> >
> >
> >
> > The attached patch removes PseudoSourceValue from the Value
> > hierarchy. No functionality change intended, but I had to make a
> > number of assumptions in order to make that claim. I assume nobody
> > ever assigned names to PSV's. I assume nobody has an AliasAnalysis
> > that is smart about PSV's (it's not in tree). That sort of thing.
> >
> >
> > I'm going to say up front, this patch isn't entirely pretty. There's
> > some PointerUnions involved. Some code did get nicer, there were
> > users that had tests for Value* then if isa<PseudoSourceValue> do
> > something that would end in an unconditional return or continue,
> > then afterwards handle non-PSV Value's. These are now sensible
> > conditions for the two cases. Some code got worse. Target/Mips wins
> > the contest for actually having code that treated PSV's and Value's
> > through the same code paths, good job guys! Sorry that I'm doing
> > this to you.
> >
> >
> > At its core, this patch makes PseudoSourceValue the root of its own
> > hierarchy with just itself and FixedPseudoSourceValue in it, then
> > updated MachinePointerInfo to store a pointer-union of the PSV and
> > Value*. Various bits of code throughout lib/CodeGen and lib/Target
> > are updated to pass MPI's around instead of extracting the Value*
> > from an MPI, passing that, then rebuilding the MPI on the other end.
> > Such code was silly anyways.
> >
> >
> > Please review. Before we get a low-level code review, I'm expecting
> > to be told that I've violated some design criteria of the backend
> > that I wasn't aware of. I mean, I moved a method from private to
> > public, so that's a pretty big sign. Please feel free to tell me how
> > things ought to be layered.
> >
> >
> > Nick
> >
> >
> > _______________________________________________
> > llvm-commits mailing list
> > llvm-commits at cs.uiuc.edu
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> >
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
>
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