Assigning multiple contiguous registers to a virtual register

Hi
          I have seen this being done in multiple compilers. However, am
not sure abt why the compilers choose to do this way.
                  Usually the register allocation does a one to one mapping
between virtual registers and physical registers. If you have virtual
registers that needs multiple physical registers, then you define new
pseudo-names that represent a set of physical registers. Now, you
assign this new pseudo-physical register instead.


My question is what is the motivation here ?


1. Is it that there is no need to do it otherwise? Most program dont
see virtual registers of very different sizes ?


2. Makes it easier. If this is the case, I am curious abt how ? Is it
that dependency information is likely to be too cluttered if there are
no pseudo names ?


thanks
shrey
[I expect this is for architectures where some of the instructions need
register pairs. -John]

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