[llvm] [RISCV] Remove interrupt handler special case from RISCVFrameLowering::determineCalleeSaves. (PR #88069)

[Kito Cheng via llvm-commits]

kito-cheng wrote:

> Should we standardize this behavior in psabi? cc @kito-cheng

psABI may not best place, but I think we should document this more clear in https://github.com/riscv-non-isa/riscv-c-api-doc/blob/master/riscv-c-api.md

https://github.com/llvm/llvm-project/pull/88069