There is no NOT instruction
C's ~x flips every bit. MIPS has no instruction for it — and by now you can guess the compiler's move: lean on zero. The instruction it leans with is nor — NOT-OR: OR the two operands, then invert all 32 bits of the result. Here's plain ~x:
nor v0, a0, zero # ~(x | 0) = ~x
jr ra
nop
OR-ing with zero changes nothing, so all that's left is the inversion: nor rd, rs, zero reads as rd = ~rs. File it next to or rd, rs, zero as "the copy" — this is "the NOT", one more zero-register idiom for your collection. Some disassemblers print it as a friendly not; ours shows you the real nor, so learn the raw spelling.
But nor isn't only a crutch for NOT — it's a real three-operand instruction, and IDO exploits that. When the C inverts the result of an OR, the compiler doesn't need an or followed by a nor-with-zero. The nor does both jobs in one go: OR the two values, invert, done. One instruction, two C operators.
So when you meet a nor whose second operand isn't zero, don't read it as a copy-shaped NOT — read the OR that's built into it, then wrap the whole thing in ~. The target below is exactly that shape.
Your task
Write func_80060484 to reproduce the target assembly.