Re: register variables in C.

Is it not true that good register allocators treat live ranges (even of
the same variable) separately in the cost function? Even split live
ranges at e.g. loop boundaries?


In this context, it seems more appropriate to have programmers tag uses of
variables rather than declarations. With apologies for the syntax:


    for (i = 0; f(i); ++i) {
          a[ i:reg ] = .... < executes a million times >
    }


    < hairy code that needs a lot of regs's >


      z = i:noreg * 5; < executes once >


The meaning of i:reg is that the compiler should try to make the defs of i
for this use into a register. Conversely i:noreg means that if the
upstream defs are into a register, and other live ranges overlapping this
one need a register, the live range of i should be split and i spilled to
permit it.


Gene
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