[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:

@skatrak 
I considered that as well, however, I did not like it because the semantics of the block that the operation is contained in is different. wsloop expects its parent block to be a parallel block which all threads will execute and all of those threads will share the work of the nested loop nest. Whereas the workshare.loop_nest op is semantically executed by a single-thread (because the workshare directive acts like it preserves the semantics of single-threaded fortran execution.).

I don't think it is currently a problem, however, if in the future someone adds some optimization or transformation that assumes that it is nested in a parallel it may break wsloops which happen to be nested in a workshare instead. (As you said it is possible to check whether it is supposed to be a workshare or parallel wsloop but an op changing its semantics or transformations dpeending on what it's nested in feels more error prone).

So that is why I opted for this approach.

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