llvm dev - Jan 2011 - [LLVMdev] Increasing TargetRegisterInfo::FirstVirtualRegister?

On 01/07/2011 02:07 AM, Chris Lattner wrote:
>
> Unless your goal is to merge this work onto LLVM mainline, the best thing
to do is a local hack in your tree.
>
> -Chris
Yes, I will create a patch for my tree to increase 
FirstVirtualRegister.  Would this be a good change to include in 2.9?

We might want to make physical registers negative and virtuals positive, or vice
versa.   Then FirstVirtualRegister is 0 or 1, and we could get rid of those
annoying subtractions of FirstVirtualRegister all over the
virtual-register-handling passes.  Since 0 is used all over the place as
"invalid register" it is probably best to leave this alone, let
FirstVirtualRegister be 1, and simply ignore (i.e. treat as erroneous) the 0th
element of anything keyed off FirstVirtualRegister.

On Jan 7, 2011, at 11:08 AMPST, Andrew Clinton wrote:
> On 01/07/2011 02:07 AM, Chris Lattner wrote:
>> 
>> Unless your goal is to merge this work onto LLVM mainline, the best
thing to do is a local hack in your tree.
>> 
>> -Chris
> 
> Yes, I will create a patch for my tree to increase 
> FirstVirtualRegister.  Would this be a good change to include in 2.9?
> _______________________________________________
> 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 Jan 7, 2011, at 11:08 AM, Andrew Clinton wrote:
> On 01/07/2011 02:07 AM, Chris Lattner wrote:
>> 
>> Unless your goal is to merge this work onto LLVM mainline, the best
thing to do is a local hack in your tree.
>> 
>> -Chris
> 
> Yes, I will create a patch for my tree to increase 
> FirstVirtualRegister.  Would this be a good change to include in 2.9?
I think it makes the most sense to discuss that when you're interested in
merging the dependent work onto mainline.  Dales's idea of using
positive/negative numbers makes sense to me.

-Chris

On Jan 7, 2011, at 11:25 AM, Dale Johannesen wrote:
> We might want to make physical registers negative and virtuals positive, or
vice versa.   Then FirstVirtualRegister is 0 or 1, and we could get rid of those
annoying subtractions of FirstVirtualRegister all over the
virtual-register-handling passes.  Since 0 is used all over the place as
"invalid register" it is probably best to leave this alone, let
FirstVirtualRegister be 1, and simply ignore (i.e. treat as erroneous) the 0th
element of anything keyed off FirstVirtualRegister.
Fixed in r123137.

I decided to move the virtual register numbers because there is so much code
already using physical register numbers as direct indices.

My first attempt was to let the virtuals run from -1 downwards, but it turns out
that we have code in isel depending on createVirtualRegister() returning
increasing numbers. DenseMap<unsigned> also complained because it uses -1u
and -2u as sentinels.

So I moved the virtual register range to 2^31 growing upwards.

The range from 2^30 to 2^31 is reserved for representing stack slots.

Physical registers get 1 .. 2^30-1.

/jakob

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