local-alloc update_equiv_regs and moving register initialization

[John Wehle]

>> Why isn't desirable to move the register initialization just before the
>> use when both are within the same loop?
>
> Because then you might change the semantics of the program.

That's a good reason, however I'm feeling a bit dense.  How could it
change the semantics of the program?  If it's safe to change:

  a = 3;
  ...
  c = a + b;

to

  ...
  a = 3;
  c = a + b;

when a = 3 and c = a + b are outside a loop, why isn't it safe to make
the same change when both are inside the same loop?

-- John
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