Is the compiler "smart enough" to know that I exited the loop and therefore the memory allocated to $j can now be reclaimed?

Perl doesn't reclaim lexicals, it just clears them. And yes, $j gets cleared.

sub DESTROY { print("DESTROYED\n"); }

for ( my $i = 0; $i < 10; $i++ ) {
    my $j = bless({});
    if ( $i == 0 ) { goto newlocation; }
}
newlocation:
  print( "jumped out" );
[download]

DESTROYED
jumped out
[download]