RFR: 8304295: VM build fails with GCC 7 after JDK-8301998

[Erik Joelsson]

On Thu, 30 Mar 2023 21:05:40 GMT, Joshua Cao <duke at openjdk.org> wrote:

> Builds successfully with GCC 7
> 
> 
> gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-15)
> Copyright (C) 2017 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

> > The build system doesn't have a convenient way of selectively disable warnings for different compiler versions. I recommend against trying to implement that here.
> > If this library is all third-party code, does it really matter that much if we disable another warning? We aren't responsible for keeping this source warning free as we can't make changes to it to anyway.
> 
> Isnt it is possible to check the TOOLCHAIN_TYPE+TOOLCHAIN_VERSION as we did here?: [3476724](https://github.com/openjdk/jdk/commit/347672464127a5d4dd847ba2a4ca30c5ff51b32c) Or we do not set such props for gcc?

As I said, it's possible, but inconvenient, and IMO not worth it for just disabling a warning. The linked example changes an optimization flag to avoid a compiler bug. That seems like a severe enough consequence to warrant such construct in the build. We want to avoid having a large amount of compiler version checks in the makefiles. In make we can only easily compare versions for equality and not ranges. 

That said, it may be worth adding a comment that this warning has only been observed with GCC 7. That will help in the future when someone tries to remove disabled warnings.

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PR Comment: https://git.openjdk.org/jdk/pull/13253#issuecomment-1491890387