RFR: 8269537: memset() is called after operator new [v2]

[Leo Korinth]

> The basic problem is that we are relying on undefined behaviour, as documented in the code:
> 
> // This whole business of passing information from ResourceObj::operator new
> // to the ResourceObj constructor via fields in the "object" is technically UB.
> // But it seems to work within the limitations of HotSpot usage (such as no
> // multiple inheritance) with the compilers and compiler options we're using.
> // And it gives some possibly useful checking for misuse of ResourceObj.
> 
> 
> I am removing the undefined behaviour by passing the type of allocation through a thread local variable.
> 
> This solution has some advantages:
> 1) it is not UB
> 2) it is simpler and easier to understand
> 3) it uses less memory (I could make it use even less if I made the enum `allocation_type` a u8)
> 4) in the *very* unlikely situation that stack memory (or embedded) already equals the data calculated from the address of the object, the code will also work. 
> 
> When doing the change, I also updated  `allocated_on_stack()` to the new name `allocated_on_stack_or_embedded()` which is much harder to misinterpret.
> 
> I also disallow to "fake" the memory type by explicitly calling `ResourceObj::set_allocation_type`.
> 
> This forced me to change two places that is faking the allocation type of an embedded `GrowableArray` from  `STACK_OR_EMBEDDED` to `C_HEAP`. The faking of the type is hard to understand as a `STACK_OR_EMBEDDED` `GrowableArray` can allocate any type of object. My guess is that `GrowableArray` has changed behaviour, or maybe that it was hard to understand because the old naming of `allocated_on_stack()`. 
> 
> I have also tried to update the comments. In doing that I not only changed the comments for this change, but also for the *incorrect* advice to always delete object you allocate with new.
> 
> Testing on debug build tier1-3
> Testing on release build tier1

Leo Korinth has updated the pull request incrementally with one additional commit since the last revision:

  First update
  
  * Change backing type of ResourceObj::allocation_type to be u8. Also remove no longer needed mask and explicit zero value of STACK_OR_EMBEDDED value.
  
  * Now setting allocation type with set_type() with assert.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5387/files
  - new: https://git.openjdk.java.net/jdk/pull/5387/files/31633583..d8acedb0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5387&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5387&range=00-01

  Stats: 15 lines in 2 files changed: 7 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5387.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5387/head:pull/5387

PR: https://git.openjdk.java.net/jdk/pull/5387