[LLVMdev] TargetRegisterClass for Physical Register

[Chris Lattner]

On Mon, 18 Jun 2007, David Greene wrote:
> So there are multiple ValueTypes here (the scalar registers each only have
> one corresponding to the bit size of the register).  But still, if I have
> physical register MM2, that completely determines its register class.

Right.

> Is there some other architecture where the physical register name/number
> does not completely determine its register class?

Yes, for example, X86.  On X86, we have XMM registers that can hold one of 
three things: an f32 value, a f64 value, or a vector value.  These are 
represented by different register classes containing the same registers.

Likewise, PPC has f32/f64 represented as two different register classes, 
but has all the F registers in both.

Ugly yes, but this does model the hardware more closely than artificially 
duplicating each register for each different value type it can hold...

-Chris

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