[PATCH] D93189: Introduce the `!nocapture` metadata and "nocapture_use" operand bundle

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added inline comments.


================
Comment at: llvm/test/Transforms/InstCombine/nocapture_use.ll:42
+  %tmp4 = bitcast i32* %local to i8*
+  ret i32 %tmp2
+}
----------------
jdoerfert wrote:
> aqjune wrote:
> > (Orthogonal to this patch) would it be great to explicitly state in LangRef that it is illegal for a function call to return a nocapture pointer? I can make a super short patch for this. @nlopes was also interested in this when implementing nocapture in Alive2.
> I'm not sure I understand.
> 
> FWIW, Attributor uses an internal attribute "nocapture_maybe_returned" for call arguments to improve nocapture analysis.
I meant whether this is UB or not:
```
define i8* @f(i8* nocapture %p) {
  ret i8* %p
}
```
I think it should be UB, but this doesn't seem to be explicit in LangRef.

nocapture_maybe_returned seems great..! I believe many library calls like memcpy can have this attached to their arguments. :)


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D93189/new/

https://reviews.llvm.org/D93189