RFR: 8325880: Require minimum Open XL C/C++ version 17.1.1

[Kim Barrett]

On Tue, 5 Mar 2024 09:10:50 GMT, Joachim Kern <jkern at openjdk.org> wrote:

>>> > What does this mean? That you are not using xlc at all? Or is it clang but still with an xlc frontend, so all xlc flags etc need to stay?
>>> 
>>> The `xlc` toolchain is for the compiler versions up to 16 (xlclang++); the `clang` toolchain is for the compiler versions 17 (ibm-clang++_r) and higher. For the 17 Compiler the frontend is `clang`-ish and we are using the `clang` flags instead of the `xlc` flags. `toolchain.m4` decides on the basis of the found compiler which toolchain to use as default.
>>> 
>>> ```
>>> # On AIX the default toolchain depends on the installed (found) compiler
>>>   #   xlclang++     -> xlc toolchain
>>>   #   ibm-clang++_r -> clang toolchain
>>>   # The compiler is searched on the PATH and TOOLCHAIN_PATH
>>>   # xlclang++ has precedence over ibm-clang++_r if both are installed
>>> ```
>>> 
>>> So, if we set the minimum compiler level for AIX to 17, we can remove the xlc toolchain at all. We cannot remove every reference to xlc, because at least some headers we still use the xlc version (globalDefinitions_xlc.hpp)
>> 
>> This suggests there might be more that needs to be done here than simply
>> updating TOOLCHAIN_MINIMUM_VERSION_xlc.  I spent some time looking at the
>> relevant code, but keep getting lost in the distinction between xlc and clang.
>> Does updating that variable as proposed even work at all?
>> 
>> I'm going to need some help from you aix-ppc maintainer folks.
>
>> > > What does this mean? That you are not using xlc at all? Or is it clang but still with an xlc frontend, so all xlc flags etc need to stay?
>> > 
>> > 
>> > The `xlc` toolchain is for the compiler versions up to 16 (xlclang++); the `clang` toolchain is for the compiler versions 17 (ibm-clang++_r) and higher. For the 17 Compiler the frontend is `clang`-ish and we are using the `clang` flags instead of the `xlc` flags. `toolchain.m4` decides on the basis of the found compiler which toolchain to use as default.
>> > ```
>> > # On AIX the default toolchain depends on the installed (found) compiler
>> >   #   xlclang++     -> xlc toolchain
>> >   #   ibm-clang++_r -> clang toolchain
>> >   # The compiler is searched on the PATH and TOOLCHAIN_PATH
>> >   # xlclang++ has precedence over ibm-clang++_r if both are installed
>> > ```
>> > 
>> > 
>> >     
>> >       
>> >     
>> > 
>> >       
>> >     
>> > 
>> >     
>> >   
>> > So, if we set the minimum compiler level for AIX to 17, we can remove the xlc toolchain at all. We cannot remove every reference to xlc, because at least some headers we still use the xlc version (globalDefinitions_xlc.hpp)
>> 
>> This suggests there might be more that needs to be done here than simply updating TOOLCHAIN_MINIMUM_VERSION_xlc. I spent some time looking at the relevant code, but keep getting lost in the distinction between xlc and clang. Does updating that variable as proposed even work at all?
>> 
>> I'm going to need some help from you aix-ppc maintainer folks.
> 
> As I already mentioned, This PR is just the start shot to remove the support for the old xlc compilers below version 17. This means removing the xlc toolchain support in a follow up PR by our team. This is feasible, because the open xl compilers starting with version 17 are using the clang toolchain. So, if this PR is through we feel empowered to remove the xlc toolchain.

> Your current version still serves the purpose of disallowing usage of xlc 16 and below. Users of the old compiler will get to know which compiler to use at minimum. Users of any Open XL compilers are not affected because "TOOLCHAIN_MINIMUM_VERSION_xlc" is not used for that AFAICS. But that's ok IMHO because the minimum clang check will be in place and the supported compilers are documented (https://wiki.openjdk.org/display/Build/Supported+Build+Platforms). So, I think this PR could get integrated and the old build pipeline get removed in a separate PR. Do you agree @JoKern65?

The non-use of `TOOLCHAIN_MINIMUM_VERSION_xlc` when using the version 17 compilers is one of the things
that worried me.  (So I did correctly figure out it wouldn't be used.)  I think this means one could inadvertently use
17.1.0 rather than the desired requirement of 17.1.1.

I think raising the minimum clang version to 13 (as proposed in https://github.com/openjdk/jdk/pull/17862) doesn't
catch that either, since 17.1.0 is based on clang 13.

But if you folks are okay with this as an interim step, then I will go ahead.

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PR Comment: https://git.openjdk.org/jdk/pull/17857#issuecomment-1978476778