[PATCH] D81678: Introduce partialinit attribute at call sites for stricter poison analysis

[Evgenii Stepanov via Phabricator via cfe-commits]

eugenis added a comment.

Positive attribute sounds good to me (frozen is not a bad name), but the tests update change is going to be huge. Any concerns about IR size bloat? The attribute will apply to the majority of function arguments, 8 bytes per instance as far as I can see.

Good point about uninitialized variables being undef, not poison. The meaning of the attribute should be "poison or undef (even partial) in this argument is UB". An extension that specifies which bytes, or even bits, of the argument are required to be undef-free would be nice, but seems too much at this point.

Another way to design this thing that would work for MSan, but not so much for general poison/undef analysis, is to emit an intrinsic call on the pre-coerced type to force an MSan check, and then an attribute ("partialinit") on the argument to skip checking the coerced value. This way the frontend has greater control over which parts of the arguments correspond to C++-things, and what does it mean for them to be initialized. I'm not sure I like this design though.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D81678/new/

https://reviews.llvm.org/D81678