[PATCH] D9403: llvm.noalias - Clang CodeGen for local restrict-qualified pointers

[Troy Johnson via Phabricator via cfe-commits]

troyj added a comment.

Hi, I got here via llvm-dev => https://reviews.llvm.org/D9375 => https://reviews.llvm.org/D9403 (this) and have read through everything.  I see that this patch has been stalled for about a year and I would like to know its status.  Is it waiting on a resolution in LLVM for this problem that Jeroen mentioned on llvm-dev?

  "One of the bigger problems is, that some optimization passes optimize away some (but not all) of the llvm.noalias intrinsics in a function. Because of that, the alias analysis can get confused and can identify two pointers as not-aliasing where they should be aliasing."

That's an improper optimization though, right?  If the semantics of the intrinsic are that all of them or none of them must be present for correctness, then any optimization that removes some but not all is defective.  Is the issue that these optimizations cannot tell that they are doing anything wrong?

I am interested in seeing this patch merged, so I would like to know what the obstacles are.  Thanks.


https://reviews.llvm.org/D9403