That is what the Constitution is for. If framed right from the start, there wouldn't have been any gerrymandering in the first place, because it would have been against the Constitution and therefore illegal.
Gerrymandering has always been about giving an unfair advantage to the PAP by redrawing borders, absorbing opposition strongholds into GRCs and pushing areas with strong support of the PAP into 'weaker areas' to improve results.
Of course, gerrymandering also results in geographical silliness (Bedok belongs to East Coast GRC? Telok Blangah is part of West Coast GRC?), but who cares about historical/geographical borders as long as the Lightning Clan is in power, right?
redistricting is needed to reflect population changes since the last census. gerrymandering is when those in charge of redistricting deliberately divide the precincts to favor one party. the constitution can't really prevent gerrymandering.