search for: zero_caller_saved_regs

...or each target. Targets that don't support the flag should probably emit a warning or error. Our proposal for the feature is modeled off of H. J. Lu's description[1] (copied with some modifications): ``` Add -mzero-caller-saved-regs=[skip|used-gpr|all-gpr|used|all] command-line option and zero_caller_saved_regs function attributes: * Don't zero caller-saved registers upon function return (default): -mzero-caller-saved-regs=skip zero_caller_saved_regs("skip") * Zero used caller-saved integer registers upon function return: -mzero-caller-saved-regs=used-gpr zero_caller_save...