One instruction, no zero needed
A lot of ISAs negate a number by subtracting it from zero. PowerPC skips all that. There is neg rD, rA, which is rD = -rA, one instruction that flips the sign without ever touching a zero register.
Two int arguments, negation of the second:
neg r3, r4
blr
rA is r4, the second argument, and rD = -rA settles into r3, ready to hand back.
You'll meet this habit again and again. Where a dedicated instruction exists, MWCC grabs it rather than building the operation out of smaller pieces, and learning to recognize those idioms is most of the work.
The target gives you rD = -rA; the C expression follows.
Your task
Write negate, taking an int x, to match the target assembly.