[R-pkg-devel] Package submission issue - OMP reduction (flang-new)

[Ivan Krylov]

On Mon, 13 Nov 2023 16:39:45 +0100 (CET)
Romain Pierlot <romain.pierlot using u-bordeaux.fr> wrote:

> Here is the error message, and the adequate code part is joint in the
> mail : 
> 
> error:
> loc("/data/gannet/ripley/R/packages/incoming/frailtypack.Rcheck/00_pkg_src/frailtypack/src/Integrale_mult_scl.f90":1811:17):
> 'omp.reduction' op must be used within an operation supporting
> reduction clause interface error: verification of lowering to FIR
> failed 

Have you tried explaining this in the package submission comment? What
was the response? Does the reviewer need more evidence? Linking to the
LLVM issue on GitHub and/or the previous R-package-devel thread may
help.

(LLVM giveth and LLVM taketh away. While I'm sure that their
diagnostics helped improve many packages, I have encountered a few
places in the R code where clang suggested to replace boolean
expressions && and || with bitwise operations & and |. The code still
works, but now relies on boolean constants having certain exact bits
set. Replace a 1 with a 2 and things will break.)

It might be the case that CRAN cannot afford to make an exception for
this compiler bug. I can imagine a number of workarounds:

1. In your ./configure script, check for the Fortran compiler being
flang-new version 17. If the check succeeds, disable OpenMP altogether.

2. Rewrite your Fortran code so that a variable is never touched before
it is used in an OpenMP reduction. You may have to declare a new
variable for every OpenMP reduction loop inside a function.

If you don't succeed in convincing CRAN regarding the compiler bug,
which one of the two workarounds would you prefer?

-- 
Best regards,
Ivan