Updating c++ default standard to c++20 for 14.1.X

[smuzaffar]

Hi,
We are ready to update the default c++ standard to c++20 for 14.1.X. cms-sw/cmsdist#9288 changes the default to c++20. There are few known issues with it

• CLANG: Needs Fixes for CLANG_X+CPP20 #45428 otherwise we get build errors
• GCC 13 IB will failed as we are missing gcc-mirror/gcc@96482ff fix from GCC. I would suggest that we update GCC to 13.3.0 which contains this fix but then we will have couple of errors from nvcc
  • https://forums.developer.nvidia.com/t/builtin-ia32-ldtilecfg-and-builtin-ia32-sttilecfg-are-undefined/298516
  • https://gitlab.com/-/snippets/3684272

Note that we do not build 14.1.0 releases for gcc13 yet, so we can let that IB fail and wait for cuda update. We can also apply the gcc patch on top of existing 13.2.1 which should allow to build gcc 13 (except the existing array-bound error #45340) and then update to gcc 13.3.0 when cuda supports it. This requires two full rebuild of our externals.

I prefer that we move to GCC 13.3.0 and wait for cuda update

[cmsbuild]

cms-bot internal usage

[cmsbuild]

A new Issue was created by @smuzaffar.

@Dr15Jones, @antoniovilela, @makortel, @rappoccio, @sextonkennedy, @smuzaffar can you please review it and eventually sign/assign? Thanks.

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[smuzaffar]

I prefer that we move to GCC 13.3.0 and wait for cuda update

@fwyzard , do you have any preference ?

[fwyzard]

Depends if we want to have a gcc13 14.1.0 release.

14.1.0 is going to be used for the heavy ions data taking, so I would prefer to switch to a newer CUDA version only after an extensive validation.

Given that such new CUDA version does not exist yet, I'm not very comfortable with having to switch any time soon.

On the other hand, if we do not care about having a gcc13 14.1.0 release, and we can leave the IBs failing into the next release cycle, then I don't have any reason to object.

[smuzaffar]

There is no urgency to move to gcc 13 for 14.1.0 , atleast there are no plans yet to use it for cmssw production architecture.

OK, to be on the safe side, we can stay with gcc 13.2.1 + gcc-mirror/gcc@96482ff to atleast have working IBs.

[smuzaffar]

Today's 11h00 will be built with c++20

[makortel]

assign core

[cmsbuild]

New categories assigned: core

@Dr15Jones,@makortel,@smuzaffar you have been requested to review this Pull request/Issue and eventually sign? Thanks

[makortel]

@smuzaffar Do we have any reason to keep this issue open, or could it be closed?

[smuzaffar]

+core

@makortel , this is complete