On Mon, 2 Mar 2020, Richard Biener wrote: > PR90348 is certainly entertaining. But I guess for a GSoC project > we need a more elaborate implementation plan. The above suggesting > of a "lifetime start" is IMHO a no-go btw. Instead I think the > only feasible way is to make all references indirect and thus > make both "allocation" and "deallocation" points explicit. Then > there's a data dependence on the "allocation" statement which > provides upward safety and the "deallocation" statement would > need to act as a barrier in some to be determined way. That is, > how to make optimizers preserve the lifetime end is still unsolved.
I think a verifier that ensures that all references are dominated by "lifetime start" and post-dominated by clobbers/lifetime-end would be a substantial step towards that. Agreed that data dependence on allocation would automatically ensure part of that verification, but then the problem with deallocation remains, as you say. > IMHO whatever we do should combine with the CLOBBERs we have now, > not be yet another mechanism. This seems contradictory with the ideas in your previous paragraph. I agree though, CLOBBER-as-lifetime-end makes sense and does not call for a replacement. Thanks. Alexander
