llvm dev - Feb 2020 - [RFC][LangRef][AliasAnalysis] Clarify `noalias` affects only modified objects

For AA-based memory-dependency analysis, this makes sense to me. read/read
aliasing doesn't affect anything.

My only questions is: is there any concern that this might confuse
instrumentation passes, or similar, which might do something even for read/read
cases? Does anyone know of any other use cases that might be affected by this?

 -Hal

Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

________________________________
From: Johannes Doerfert
Sent: Thursday, February 20, 2020 5:46 PM
To: LLVM-Dev
Cc: Finkel, Hal J.
Subject: [RFC][LangRef][AliasAnalysis] Clarify `noalias` affects only modified
objects

I would like to clarify that `noalias` on arguments matches `restrict`
in C99. In particular, objects need to be modified for the `noalias` to
be "effective". We basically apply this reasoning already in various
parts but I want to make it explicit now.

The wording change and the reasons are explained in
  https://reviews.llvm.org/D74935

Please let me know if there are concerns.

Thanks,
  Johannes
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