Comment by lowbloodsugar
1 day ago
Executing the instruction after the jump seemed mental, but after a few days it was second nature. N64 had related issue: had to find an instruction to put between two multiplies. If the first multiple multiplied by zero or otherwise finished in two cycles, the CPU would freeze if the next instruction was also a multiply.
Another weird corner case is that COP2 (GTE) instructions actually start executing one instruction early with respect to where the program counter is. As a result when an exception happens the kernel interrupt handler checks to see if the next instruction is COP2 and has to add 4 to the program counter in order to not execute it twice.
Also COP2 instructions were not allowed in branch delay slots (presumably for similar reasons), however some games (from memory Tekken3) do actually do this. I always wondered if it was a sneaky anti-emulation thing :) (because many emulators had issues with this, or needed special handling).