[llvm-branch-commits] [flang] [flang] Introduce custom loop nest generation for loops in workshare construct (PR #101445)

[Ivan R. Ivanov via llvm-branch-commits]

ivanradanov wrote:

No you are right, sorry for the back and forth, as you said, since a wsloop can only be nested in a omp.parallel it is immediately obvious that it binds to the omp.parallel threads so that makes sense.

My only concern was that at some point some transformation (perhaps in the future, because I don't think anything transforms `wsloop`s currently) could make the assumption that all (or none) of the threads of the team an `omp.parallel` launches will execute the parent block of a `wsloop` that binds to that team.

I thought this was a fair assumption for an optimization/transformation to make because if for example only one of the threads executes a wsloop it would not produce the intended result. (for example it adds an operation immediately before the wsloop which is supposed to be executed by all threads in the omp.parallel. that operation would then be erroneously wrapped in an omp.single in LowerWorkshare.) So the intention was to guard against a potential error like that. Let me know if I am wrong here since I am sure people here have more experience than me on this. 

I can see that if no transformation can make that assumption, then it is perfectly safe to use `omp.wsloop` instead of `workdistribute.loop_wrapper`. I am fine with both ways and can make that change if you think it is better. (In fact that is what the initial version of this PR did. I decided to introduce the workshare.loop_wrapper later because I was concerned about a potential issue like above)

https://github.com/llvm/llvm-project/pull/101445