On Tue, 2020-08-25 at 02:16 -0300, Alexandre Oliva wrote: > On Aug 24, 2020, Richard Biener <rguent...@suse.de> wrote: > > > since the option is quite elaborate on what (sub-)set of regs is > > supposed to be cleared I'm not sure an implementation not involving > > any target hook is possible? > > I don't think this follows. Machine-independent code has a pretty good > notion of what registers are call-saved or call-clobbered, which ones > could be changed in this regard for function-specific calling > conventions, which ones may be used by a function to hold its return > value, which ones are used within a function... > > It *should* be possible to introduce this in machine-independent code, > emitting insns to set registers to zero and regarding them as holding > values to be returned from the function. Machine-specific code could > use more efficient insns to get the same result, but I can't see good > reason to not have a generic fallback implementation with at least a > best-effort attempt to offer the desired feature. I think part of the problem here is you have to worry about stubs which can change caller-saved registers. Return path stubs aren't particularly common, but they do exist -- 32 bit hpux for example :(
Jeff
