[llvm-dev] Allowing virtual registers after register allocation

Derek Schuff via llvm-dev llvm-dev at lists.llvm.org
Thu Dec 10 11:21:52 PST 2015

On Thu, Dec 10, 2015 at 11:13 AM Hal Finkel <hfinkel at anl.gov> wrote:

> > I don’t know for the other passes, but I don’t think it makes sense
> > to teach PrologEpilogInserter to work on virtual registers, since
> > part of its job is to get rid of any virtual registers created when
> > lowering the frame.
> > I.e., that would indirectly mean that we would need to teach the
> > scavenger how to recycle virtual registers!
> >
> I think this is exactly the part of PEI that they disable.

Yes; see  http://reviews.llvm.org/D15394
If the target has no callee-saved registers and you disable scavenging,
you're basically left with.... prolog/epilog insertion and FrameIndex
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