Looking at the PSoC 4 TCPWM datasheet the maximum operating frequency of the counter block is 48MHz, with a counter resolution of 21ns.
Assuming that you have a high resolution incremental rotary encoder with 10,000 counts per revolution, and spin the rotor at 15,000 rpm, that's 2,500,000 counts per second (2.5MHz), comfortably less than the 48MHz max. sampling rate.
Sadly, it is not clear if the PSoC 4 TCPWM suffers the same 10x sampling requirement as the PSoC QuadDec mentioned in Simon Jenkins' answer. I suspect not, as the datasheet doesn't include the clock signals on the timing diagrams. This implies that PSoC 4 TCPWM is edge driven (limited by the counter clock), while PSoC QuadDec is driven by level at each clock edge and thus limited by the sampling at the clock frequency.
Even if the PSoC 4 TCPWM does require over sampling, then the max 2.5MHz pulse train is still less than both 10x at 48MHz for the PSoC 4 TCPWM and 28MHz for the PSoC QuadDec.
If you only need 2000 PPR at 6000 RPM (as suggested in your comment), then you only need to support 200 KHz (2000*6000/60), so a 2MHz clock should be sufficient.
Another concern is whether the CPU will be able to cope with the interrupts this could generate.
If we assume that you are running the quadrature right at the limit of the decoder block, i.e. 48MHz with a 16bit counter you will be getting 1465 overflow interrupts per second, so unless you can service your interrupt (including any context switching required) in less than 682 micro seconds, then you are going to struggle.
Luckily, it looks like the the Cortex-M0 processors have very efficient ISR handling (See A Beginner’s Guide on Interrupt Latency - and Interrupt Latency of the ARM® Cortex®-M processors) so unless your ISR is very inefficient, it should be able to handle this.
Incidentally, it looks like you will need to use X4 mode if you want to count individual quadrature state transitions. If you use X1 then you only see whole quadrature cycles (4 states), while if you use X2 then you only see half of the states.