RFR: 8358957: [ubsan]: The assert in layout_helper_boolean_diffbit() in klass.hpp needs UB to fail [v4]

[Afshin Zafari]

On Tue, 4 Nov 2025 04:26:06 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> src/hotspot/share/oops/klass.hpp line 518:
>> 
>>> 516:   static int layout_helper_boolean_diffbit() {
>>> 517:     uint zlh = checked_cast<uint>(array_layout_helper(T_BOOLEAN));
>>> 518:     uint blh = checked_cast<uint>(array_layout_helper(T_BYTE));
>> 
>> Use of check_cast is probably wrong. I think an alh is negative. Oops, my mistake. It probably doesn't fail currently because of [JDK-8314258](https://bugs.openjdk.org/browse/JDK-8314258).
>
> Note that by "my mistake" I meant it was a mistake to use `checked_cast` here.

static_cast is used.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27288#discussion_r2498695108