How does one determine the instruction set for a particular application?

When processor is designed specifically for lets say graphics application and I am sure there are other examples, the instruction set of the processor is designed to contain specific instructions that help to carry out the tasks in that application. My question is, how does one determine what type and complexity instructions be included in the ISA?

Note that this question has been inspired by the TMS34010 ISA which contains instructions for graphic operations.

The complexity of ISA comes from complexity of the application that processor will be used for. A simple 8-bit MCU does simple control task, no processing, so a simple RISC architecture with few instructions are enough to make it.

For graphics processing, the input data is always a matrix or pixels or vertices. So, u need matrix math which can be easily implemented with SIMD instructions, where a single instruction does matrix multiplication and addition in single cycle for DSP math on an image. This implementation of instruction is quite complex.

Graphics display is another different application where, u get the 2D matrix of image that goes to LED duty cycle for different colors of each pixel in OLED display. Here, acquiring data and generating PWM or DAC output on color filters is required.