[flang-commits] [flang] [flang] Add nsw to DO loop parameters (PR #113854)

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https://github.com/jeanPerier approved this pull request.

Looks good to me (please address Tom's questions).

I verified that at least gfortran/ifort are optimizing the following program assuming that "n+1" cannot wrap:

```
subroutine foo(x, n, m)
  integer :: n, m
  integer :: x(m)
  do i=n,n+1
    x(i) = i
  end do
end subroutine
```

They both optimize this into two executions of the body without branches, which also what LLVM does after your patch. So there is a precedent in leveraging the language semantics here and this won't come as a surprise for existing application.

https://github.com/llvm/llvm-project/pull/113854