I have but that was not the point? My first point was exactly that there are more ISA registers and not only 8, and therefore the question mark. My second point was about register renaming which, contrary what you say, does mitigate the artifacts of running out of registers by spilling the variables to the stack memory. It does it by eliminating the false dependencies between variables/registers and xor eax, eax is a great candidate for that.
Ok, it obviously doesn't increase the number of ISA registers. What I am suggesting is something else - imagine a situation in which the compiler understands that the spill over will take place, and therefore rearranges the code such that it reduces the pressure on the registers. It can do that if it can break the data dependencies between the variables for instance. Or it can do that by unrolling the loops or by moving the initialization closer to where the variable is being used, no? I am pretty certain that compilers are already doing these kind of transformations, and in a sense this is taking advantage of register renaming but indirectly.
Register renaming allows the CPU to execute in parallel instructions it might otherwise need to serialize.
But it does nothing to help you, the programmer, when your algorithm really needs to have 9 registers worth of data in registers and your CPU only has 8 architectural registers available to you. At that point, you either spill manually, or you take the performance hit from keeping the ninth value in memory instead of a register.