[LLVMdev] [LLVMDev] [Question] How do I get the number of machine registers.

[Jeff Kunkel]

I am using allocation_order_begin() and allocation_order_end(). Thank you
about the caveat about reserved registers.


On Fri, Sep 3, 2010 at 2:54 PM, Jim Grosbach <grosbach at apple.com> wrote:

>
> On Sep 3, 2010, at 10:46 AM, Jeff Kunkel wrote:
>
> > It's not too much of a problem then. I can make a DenseMap between the
> registers and my registers. It's just one more intermediate step for a
> lookup.
> >
> > I wish to mimic all the of the registers on the machine with my
> std::vector<RegisterInfo> RegisterIndexes; vector. Then when a register is
> used I can assign it easily. I know about alias register and those are taken
> care of ever so cleverly.
>
> Is this because you want to control the order in which the physical
> registers are allocated? If so, it'll normally  be better to use the
> TargetRegisterClass::allocation_order_begin() and allocation_order_end()
> functions to control that. These can be overridden directly in the .td file
> (see the ARMRegisterInfo.td file for examples) if you want. Other pieces of
> the compiler also use those iterators to walk the available registers in a
> register class for local allocation needs, so it's best to keep that logic
> together (the register scavenger and the anti-dependency breaker, in
> particular, use them).
>
> Within a register class, the registers will be sorted by name, so if
> they're named generically ("R0, R1, R2..."), they'll be ordered as you'd
> expect (including knowing that R10 > R1, I believe). The default allocation
> order just has begin() be the first register of the class and end() be one
> past the last register in the class (i.e., it's all the registers in the
> register class, in order).
>
> One thing to keep in mind is that the an allocator should explicitly check
> for reserved registers and avoid allocating them. Allocation orders are not
> required to omit reserved registers (although some do). See the recent
> series of patches the RegAlloc*.cpp for reference.
>
> Regards,
>   Jim
>
> >
> > If this can be done without an extra lookup, it would improve
> performance. I have one too many as is in some parts.
> >
> > Thanks,
> > Jeff Kunkel
> >
> > On Fri, Sep 3, 2010 at 12:57 PM, Jim Grosbach <grosbach at apple.com>
> wrote:
> > TargetRegisterInfo::getNumRegs().
> >
> > Generally, it's best not to make any assumptions about the internal
> ordering or numbering if you can avoid it. What are you looking to do?
> >
> > -Jim
> >
> > On Sep 3, 2010, at 9:37 AM, Jeff Kunkel wrote:
> >
> > > How do I get the total number of machine registers? I have currently a
> MachineFunction and some derivatives.
> > >
> > > How are the machine registers ordered internally? Can I index them off
> of a zero based array or do I have to create a map to have them be zero
> based?
> > >
> > > Thanks,
> > > Jeff Kunkel
> > > _______________________________________________
> > > LLVM Developers mailing list
> > > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
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> >
> >
>
>
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