RFR: JDK-8300531: Update MSVC optimization flags to match GCC/Clang [v10]

[Magnus Ihse Bursie]

On Sat, 18 Feb 2023 18:21:44 GMT, Justin King <jcking at openjdk.org> wrote:

>> Update MSVC CFlags to be more consistent with other compilers. Also disables RTTI in a simliar manner to GCC/Clang for the JVM.
>
> Justin King has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add comments clarifying -Oy-
>   
>   Signed-off-by: Justin King <jcking at google.com>

The new title is showing much clearer what you want to achieve, thanks for that. But I'd like to re-iterate what Erik said early on:

> Changing the global optimization flags is a pretty big and potentially intrusive change. [...] I don't think making the number after the O in the flags match what we use for other compilers is motivation enough to warrant a change like this. 

That is, just making the flags "match" is not motivation enough to accept such a change. This needs to be thoroughly tested, and then communicated and discussed with the wider JDK community, including but not limited to, engineers specifically involved in performance testing, evaluation and improvements.

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PR: https://git.openjdk.org/jdk/pull/12073