RFR: JDK-8294902: Undefined Behavior in C2 regalloc with null references

[Vladimir Kozlov]

On Mon, 31 Oct 2022 14:40:32 GMT, Andrew Haley <aph at openjdk.org> wrote:

> This patch fixes the remaining null pointer dereference bugs that I know of.
> 
> For the main bug, C2 was using a null reference to indicate an uninitialized `Node_List`. I replaced the null reference with a static sentinel.
> 
> I also turned on `-fsanitize=null` and found and fixed a bunch of other null pointer dereferences. With this,I have run a full bootstrap and tier1 tests with `-fsanitize=null` enabled.
> 
> I have checked that the code generated by GCC is not worse in any significant way, so I don't expect to see any performance regressions.
> 
> I'd like to enable `-fsanitize=null` in debug builds to prevent regressions in this area. What do you think?

Changes are good.
Can you tell more about `-fsanitize=null` effect on libjvm size and performance of fastdebug build we use in testing? If it is only few percents I am for enabling it in debug build.

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Marked as reviewed by kvn (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10920