[PATCH] D93376: [LangRef] Clarify the semantics of lifetime intrinsics

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added a comment.

In D93376#2462365 <https://reviews.llvm.org/D93376#2462365>, @RalfJung wrote:

> Possibly a better fix is to avoid this "magic backward in time" effect, and instead use a flag on alloca to reflect whether memory is immediately allocated, or not. (The details of the semantics of this could still be tricky though.)

Yeah, alloca should know its 'valid' location in advance. A simple solution would be to make ptrtoint yield poison if it is executed before lifetime.start, but it sacrifies mobility of ptrtoint.


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