This pass optimizes acc.firstprivate_map operations generated during
OpenACC recipe materialization when acc.firstprivate is materialized
into the mapping and a private allocation inside region. The
optimization applies to scalar variables of trivial types (integers,
reals, logicals) as long as they are not optional.
The pass hoists loads from the firstprivate variable to before the
compute region, converting the firstprivate copy to a pass-by-value
pattern. This eliminates the need for runtime copying the firstprivate
variable since only its value is needed for initializing private copies.
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