[flang-dev] [Classic flang] RFC: Switch from flang-compiler/llvm to flang-compiler/classic-flang-llvm-project

[Paszta, Michał via flang-dev]

Hello,

I have just experimentally verified that it is possible to build the
classic flang project using only the
flang-compiler/classic-flang-llvm-project release_100 with:
* gcc 9
* gcc 10 (with a few patches included)
* llvm 9/10/11

and pass all tests for all these setups.

The flang-compiler/llvm + flang-compiler/flang-driver, which are currently
suggested in the official Build Instructions, only built with gcc-9 for me
and are forks of outdated and archived stand-alone llvm mirrors.

It seems that the switch would do no harm, but would instead simplify the
build process and bring in some llvm updates from the monorepo and make it
easier to bring them in in the future.

To accomplish the switch I think we should:
1) Update the build instructions by removing steps 2,3,4,5.
2) Update the recently added Github Actions scripts to follow the new,
simpler flow.
3) (optionally) Deprecate the flang-compiler/llvm and
flang-compiler/flang-driver repos.

Detailed evidence for successful builds:
* classic-flang-llvm-project (just build and upload artifacts):
https://github.com/michalpasztamobica/classic-flang-llvm-project/actions/runs/354267060
* flang (install pre-compiled artifacts, build, install and run check-all):
https://github.com/michalpasztamobica/flang/actions/runs/354470104

There's a high chance I am missing something important here, so I will
gladly welcome your comments.

Best regards,

Michał Paszta
Senior Consultant / Senior Group Manager

Mobica Ltd.
Address: Skierniewicka 10a, 01-230 Warszawa

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