llvm dev - Sep 2010 - [LLVMdev] [LLVMDev] [Question] How do I get the number of machine registers.

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
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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
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

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.

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
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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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?
Registers are numbered from 1 to TRI::getNumRegs()-1. Reg 0 is not a register,
but it is counted by getNumRegs.

They are currently sorted by name by StringRef::compare_numeric(), but try to
avoid depending on that. It could easily change, I have been experimenting with
the performance impact of a topological order.

/jakob

Jacob, have you completed the topological sorting or the registers? It
seems I iterate through sub/alias-registers quite often, and I think a
performance gain might occur if the sub-registers were grouped better.

Thanks,
Jeff Kunkel