RFR: 8320353: Reenable stringop-overflow warnings

[Kim Barrett]

On Wed, 2 Jul 2025 13:51:24 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Hi, please consider the following changes:
>> 
>> this PR addresses the issue of stringop-overflow warnings produced by GCC. The compiler does think that the thread pointer returned by `JavaThread::current()` can be null, though it cant. The thread pointer ends up being an argument in `__atomic_load`, and the compiler reports the warning related to argument of that method. 
>> 
>> The patch adds a hint to the compiler by means of `__builtin_unreachable()` intrinsic, which tells the compiler that certain piece of code will never be reached (case of thread pointer being null). This solves the issue. 
>> 
>> Tested in tiers 1-3 and GHA.
>
> src/hotspot/share/jvmci/jvmciCodeInstaller.cpp line 936:
> 
>> 934:     __builtin_unreachable();
>> 935:   }
>> 936: #endif
> 
> I think this could be replaced with asserting non-null.  A failed assert calls a noreturn reporting
> function.

Although I wonder why the assert in Thread::current() isn't sufficient? Maybe non-null info isn't
propagating through the cast to JavaThread?

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

PR Review Comment: https://git.openjdk.org/jdk/pull/26067#discussion_r2181311538