use strict;

open( FILE, '<', "whatever.filename' ) or die "whatever... $!\n";

my $container;
my ( %SIR, %SFR );

while (<FILE>){
    chomp;
    if ( /SPECint_base/ ) {
        $container = \%SIR;
    }
    elsif ( /SPECfp_base/ ) {
        $container = \%SFR ;
    }
    elsif ( $container ) {
        $container->{$_} = undef;  # no need to repeat hash key as hash value
    }
}