patch: remove PseudoSourceValue from Value.

[Hal Finkel]

What is the underlying motivation for doing this?

 -Hal

----- 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
> 
> 
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-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory