RFR: 8261585: Restore HandleArea used in Deoptimization::uncommon_trap

[Coleen Phillimore]

On Thu, 11 Feb 2021 14:42:59 GMT, Hui Shi <hshi at openjdk.org> wrote:

> Add HandleMark in Deoptimization::uncommon_trap before Deoptimization::fetch_unroll_info_helper, avoid reference hold in HandleArea increase object lifetime. Then object lifetime will be consistent with/without uncommon trap.
> 
> For test case in commit, WeakReference is expected cleared after GC, but it fails with option "-XX:-Inline -XX:-TieredCompilation -XX:CompileCommand=compileonly,UncommonTrapLeak.foo -XX:CompileThreshold=100 -XX:-BackgroundCompilation". Reference's referent object is still alive after "foo" finish, because with uncommon trap, oops are recorded in HandleArea and HandleArea is not poped when uncommon trap process finish.
> 
> When Deoptimization::fetch_unroll_info_helper return, all oops in deoptimized frames are saved in Deoptimization::UnrollBlock or Thread data structure, HandleArea can be poped safely.
> 1. local and expression oops raw address is stored in vframeArrayElement _locals/_expressions as intptr
> 2. return value restore, raw oop recoreded in frame // (oop *)map->location(rax->as_VMReg());
> 3. exception object, raw oop recorded on Thread._exception_oop
> 
> In deoptimize blob entry, JRT_BLOCK_ENTRY(Deoptimization::fetch_unroll_info) has HandleMarkCleaner, HandleArea is restored after Deoptimization::fetch_unroll_info_helper finish. So it's also safe to add HandleMark in Deoptimization::uncommon_trap before fetch_unroll_info_helper.

Marked as reviewed by coleenp (Reviewer).

src/hotspot/share/runtime/deoptimization.cpp line 2468:

> 2466:     uncommon_trap_inner(thread, trap_request);
> 2467:   }
> 2468:   HandleMark hm(thread);

This is fine. I generally prefer the HandleMark closer to the lifetimes of the Handles that it protects.  If you put this HandleMark in fetch_unroll_info_helper() would it be needed before the line:
  Handle exceptionObject;
Or are there Handles created before there?
Given how complicated this code is, where you have the HandleMark is fine.  Well done finding this bug and writing a test for it!

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PR: https://git.openjdk.java.net/jdk/pull/2526