RFR: 8310948: Fix ignored-qualifiers warning in Hotspot

[Daniel Jeliński]

On Tue, 27 Jun 2023 12:22:43 GMT, Daniel Jeliński <djelinski at openjdk.org> wrote:

> Please review this attempt to fix ignored-qualifiers warning.
> 
> Example warnings:
> 
> src/hotspot/share/oops/method.hpp:413:19: warning: 'volatile' type qualifier on return type has no effect [-Wignored-qualifiers]
>    CompiledMethod* volatile code() const;
>                    ^~~~~~~~~
> 
> 
> src/hotspot/share/jfr/periodic/jfrModuleEvent.cpp:65:20: warning: type qualifiers ignored on cast result type [-Wignored-qualifiers]
>     65 |   event.set_source((const ModuleEntry* const)from_module);
>        |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> 
> The proposed fix removes the ignored qualifiers.
> In a few AD files I replaced `const` with `constexpr` where I noticed that the method is returning a compile-time constant, and other platforms use `constexpr` on the same method.
> 
> Release, debug and slowdebug builds on Aarch64 / x64 and Mac / Linux complete without errors. Cross-compile GHA builds also pass.

David: I think this part of the spec is relevant here:
> A non-class non-array prvalue cannot be [cv-qualified](https://en.cppreference.com/w/cpp/language/cv), [...]. (Note: a function call or cast expression may result in a prvalue of non-class cv-qualified type, but the cv-qualifier is generally immediately stripped out.)

[source](https://en.cppreference.com/w/cpp/language/value_category)
given that the cv qualifiers are immediately stripped by the compiler, there's no point in providing them.

In the particular volatile pointer case: the function performs a volatile read to get the pointer value (address). That address can then be used in a non-volatile manner.

Kim: I realize that it's a big change, so thank you very much for reviewing it anyway! I was prepared to split it up, just wanted to know if this warning is something we want to fix.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/14674#issuecomment-1611905364