base: Add generic Memoizer class

This class implements a generic memoization object:

It takes a function as a constructor argument and memoizes
it. Every time the function gets invoked through the Memoizer object
the result gets saved in the internal cache, ready
to be retrieved next time an invokation is made with the same
arguments.

Example usage:

int fibonacci(int n);

Memoizer fibonacci_memo(fibonacci);
fibonacci_memo(5);

There are two ways to discard a memoization

1) Delete the Memoizer object
2) Use the Memoizer::flush method

In some cases there is little or no reason to discard a memoization
(like in the fibonacci example, where fibonacci(k) always returns
the same value for the same input k)
The memoizer could be used in more complex cases, where a change in
the global state affects the output of the function, which
effectively invalidates the cached results.
It is up to the client to understand when memoization is no longer
valid and to flush the result cache as a consequence.

Change-Id: I6cf496b2aef5a66f5375a627165b2cb2e3a1bfc2
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/59149
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
3 files changed