IAS is actually a measure of ram-air pressure, not speed directly. All it measures is the ram-air pressure captured in the pitot tube. Which is then displayed as an effective aerodynamic speed on the IAS gauge.
Since lift is related to the aerodynamic speed or IAS, it is
roughly true that a wing that stalls at, for example, 175 kts
indicated at sea level will also stall at about 175 kts
indicated in the thinner air at higher altitudes. This is why IAS is still a useful measure of performance and for "situational awareness," even if it is grossly "wrong" for estimating time-of-arrival when flying at 35000 feet.
However, there are other effects, such as Mach effects (incipient shock wave formation, buffet) or compressibility/calibration effects (CAS = calibrated airspeed, EAS = equivalent airspeed). All of which can change with altitude and air density and TRUE airspeed.
And of course we know that what
really causes a stall is angle-of-attack - a wing can stall at any IAS if the AoA is high enough.
The relatively high speed envelopes, Mach envelopes and altitude envelopes of jets thus complicate what is a simpler and more direct calculation with a C172.
An electronic "glass" speed tape/barber pole will (or should) include computed corrections for those effects. In much the same way that the Vmo barber pole at the
top end of the speed range will slowly
decrease with increased altitude.
See also "Coffin corner" - the place where the Mach limit and the stall limit (
both barber-poles) are only a few knots apart.
https://en.wikipedia.org/wiki/Coffin..._(aerodynamics)