RFR: 8346931: Replace divisions by zero in sharedRuntimeTrans.cpp

[Kim Barrett]

On Thu, 20 Mar 2025 15:56:10 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> There are a few divisions by zero in sharedRuntimeTrans.cpp, used to "construct" NaN and -infinity. This should probably be replaced by using functionality from std::numeric_limits .

There are more potential divisions by zero in the vicinity of code
conditionalized on `CAN_USE_NAN_DEFINE` (mentioned in a comment in the JBS
issue), not all of them under the conditional.

For example, here's an unprotected one, where `z` may be zero:
https://github.com/openjdk/jdk/blame/56038fb5a156568cce2e80f5db18b10ad61c06e4/src/hotspot/share/runtime/sharedRuntimeTrans.cpp#L519
Probably zero handling should be it's own clause.

And there's the #else code for the conditional code, using `(z-z)/(z-z)` to
construct a NaN:
https://github.com/openjdk/jdk/blame/56038fb5a156568cce2e80f5db18b10ad61c06e4/src/hotspot/share/runtime/sharedRuntimeTrans.cpp#L525

Also the other use of that macro:
https://github.com/openjdk/jdk/blame/56038fb5a156568cce2e80f5db18b10ad61c06e4/src/hotspot/share/runtime/sharedRuntimeTrans.cpp#L541
(This one is also missing `{ ... }` around `then` clause.)

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Changes requested by kbarrett (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/24136#pullrequestreview-2703946566