[PATCH] D115274: [IR][RFC] Memory region declaration intrinsic

Mon Mar 21 15:47:23 PDT 2022

lebedev.ri marked an inline comment as done.
lebedev.ri added a comment.

Thank you for taking a look!

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Comment at: llvm/docs/LangRef.rst:20876
+to be able to annotate array bounds in C family of languages,
+which may allow alloca splitting, and better alias analysis.
+
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arichardson wrote:
> Do you envision this being used for all sub-object pointer creations? If so it might need a flag to disable it since it might break some C patterns such as `container_of`.
> 
> According to https://godbolt.org/z/evTbejaMf the container_of macro results in an inbounds GEP, so with sufficient inlining things might break?
> 
> About three years ago I spent quite a lot of time enforcing sub-object bounds at runtime using CHERI. Almost all code works just fine but there are things such as container_of() that require opt-out annotations. I wrote about the incompatibilities that I found in Chapter 5 of https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-949.pdf. TL;DR: not many changes needed - about 50 annotations across the entire FreeBSD source tree. Almost all annotations due to container_of or emulation of C++ inheritance in C.
I'm not sure what you mean by "all sub-object pointer creations".

Roughly, front-ends should emit this intrinsic on some pointer with some bounds
iff they know that it would be UB to go *from that specific pointer* (aka, as per def-use)
outside of the specified bounds.

The one case we know of is C arrays within structs.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D115274/new/

https://reviews.llvm.org/D115274