[flang-dev] CMake standalone and compile flags

[Mehdi AMINI via flang-dev]

On Mon, May 4, 2020 at 10:17 AM David Truby <David.Truby at arm.com> wrote:

> Hi Mehdi,
>
> That branch enables out of tree builds; I believe there are people that
> still rely on those which is why we added that branch in when rewriting the
> CMake infrastructure.
>

I assume that folks were relying on this before the merge in the monorepo,
but are there still reason to maintain this from now on? Can we put an
end-date on it?
I'm trying to figure out if this is just a transition thing or if this is
really something useful on the long run (and why).


> There's an open review to fix a similar issue as is reported in the
> discussion you linked but it seems to have stalled on a discussion about
> whether to continue to force Werror on, perhaps you could take a look at
> that and comment there if it fixes this issue or not?
>
> The review is at https://reviews.llvm.org/D78306
>

Thanks, that was roughly what I was about to start doing!
In general I think we should avoid doing directly `set(CMAKE_CXX_FLAGS ...`
and instead use the `add_flag_if_supported` macros provided by LLVM, e.g.:
https://github.com/llvm/llvm-project/blob/master/mlir/lib/CMakeLists.txt#L2

Werror is always difficult to maintain because different compilers (and
compiler versions) have different handling (possibly even opposite!)
warnings. It is a good thing to have for developers, but it may be a bit
hostile to users to have it on by default.

-- 
Mehdi



>
>
> Thanks
> David Truby
> ------------------------------
> *From:* flang-dev <flang-dev-bounces at lists.llvm.org> on behalf of Mehdi
> AMINI via flang-dev <flang-dev at lists.llvm.org>
> *Sent:* 04 May 2020 18:12
> *To:* Flang Development List <flang-dev at lists.llvm.org>
> *Subject:* [flang-dev] CMake standalone and compile flags
>
> Hi,
>
> I was looking into fixing this error that someone has when building flang:
> https://llvm.discourse.group/t/error-when-building-with-cmake/935
>
> Then I noticed that flang/CMakeLists.txt still has this branch:
> https://github.com/llvm/llvm-project/blob/master/flang/CMakeLists.txt#L42
> ; is there anyone that relies on it or can we simplify this file and the
> way the options are setup?
>
> Thanks,
>
> --
> Mehdi
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/flang-dev/attachments/20200504/a6b05d9a/attachment-0001.html>