gcc: Explicit Register Variables

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1 6.45.5 Variables in Specified Registers
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1 GNU C allows you to associate specific hardware registers with C
1 variables.  In almost all cases, allowing the compiler to assign
1 registers produces the best code.  However under certain unusual
1 circumstances, more precise control over the variable storage is
1 required.
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1  Both global and local variables can be associated with a register.  The
1 consequences of performing this association are very different between
1 the two, as explained in the sections below.
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· Global Register Variables   Variables declared at global scope.
· Local Register Variables    Variables declared within a function.
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