Eval expression R/O once time (src/backend/executor/execExpr.c)

Hi,

Currently when determining where CoerceToDomainValue can be read,
it evaluates every step in a loop.
But, I think that the expression is immutable and should be solved only
once.

Otherwise the logic is wrong since by the rules of C, even though the
variable is
being initialized in the declaration, it still receives initialization at
each repetition.
What causes palloc running multiple times.

In other words:
Datum *domainval = NULL;

is the same:
Datum *domainval;
domainval = NULL;

Once there, reduce the scope for save_innermost_domainval and
save_innermost_domainnull.

Thoughts?

regards,
Ranier Vilela