[LLVMdev] Eliminate PHI for non-copyable registers

[Chris Lattner]

On Feb 12, 2009, at 1:41 AM, [Alex] wrote:
> They "should" be non-allocatable if the hardware implements the same  
> number
> of these i32 registers as the "specification".  The input language  
> (which is
> converted to LLVM IR) may use up to 4 registers but the hardware  
> only has 2.
> So they must be allocatable, right?

To be allocatable, the code generator must be able to emit copies into  
and out of the registers and must be able to spill them, even if it  
means going through another temporary register class.

-Chris