When is the intrinsic instruction in codegen_arm.cc generated?

I use armv7a as the target target. When debugging in codegen_arm.cc, I found that I didn’t do anything in the CreateIntrinsic function. I added vectorize to the schedule, but I found no difference.
I have two questions, the first one, tvm will call llvm intrinsic under what conditions. Second, how does tvm relate llvm’s intrinsic to tvm ir?