RFR: 8317376: Minor improvements to the 'this' escape analyzer [v2]

[Archie Cobbs]

> Please review several fixes and improvements to the `this-escape` lint warning analyzer.
> 
> The goal here is to apply some relatively simple logical fixes that improve the precision and accuracy of the analyzer, and capture the remaining low-hanging fruit so we can consider the analyzer relatively complete with respect to what's feasible with its current design.
> 
> Although the changes are small from a logical point of view, they generate a fairly large patch due to impact of refactoring (sorry!). Most of the patch derives from the first two changes listed below.
> 
> The changes are summarized here:
> 
> #### 1. Generalize how we categorize references
> 
> The `Ref` class hierarchy models the various ways in which, at any point during the execution of a constructor or some other method/constructor that it invokes, there can be live references to the original object under construction lying around. We then look for places where one of these `Ref`'s might be passed to a subclass method. In other words, the analyzer keeps track of these references and watches what happens to them as the code executes so it can catch them trying to "escape".
> 
> Previously the `Ref` categories were:
> * `ThisRef` - The current instance of the (non-static) method or constructor being analyzed
> * `OuterRef` - The current outer instance of the (non-static) method or constructor being analyzed
> * `VarRef` - A local variable or method parameter currently in scope
> * `ExprRef` - An object reference sitting on top of the Java execution stack
> * `YieldRef` - The current switch expression's yield value(s)
> * `ReturnRef` - The current method's return value(s)
> 
> For each of those types, we further classified the "indirection" of the reference, i.e., whether the reference was direct (from the thing itself) or indirect (from something the thing referenced).
> 
> The problem with that hierarchy is that we could only track outer instance references that happened to be associated with the current instance. So we might know that `this` had an outer instance reference, but if we said `var x = this` we wouldn't know that `x` had an outer instance reference.
> 
> In other words, we should be treating "via an outer instance" as just another flavor of indirection along with "direct" and "indirect".
> 
> As a result, with this patch the `OuterRef` class goes away and a new `Indirection` enum has been created, with values `DIRECT`, `INDIRECT`, and `OUTER`.
> 
> #### 2. Track the types of all references
> 
> By keeping track of the actual type of...

Archie Cobbs has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains six commits:

 - Merge branch 'master' into JDK-8317376
 - Merge branch 'master' into JDK-8317376
 - Merge branch 'master' into JDK-8317376
 - Javadoc++
 - Merge branch 'master' into JDK-8317376
 - Several improvements to the 'this' escape analyzer.
   
   - Track direct, indirect, and outer references for all Ref types.
   - Keep type information about all references to improve tracking precision.
   - Track enhanced for() invocations of iterator(), hasNext(), and next().
   - Don't report an escape of a non-public outer instances as a leak.
   - Fix omitted tracking of references from newly instantiated instances.
   - Fix omitted tracking of leaks via lambda return values.
   - Remove unneccesary suppressions of this-escape lint warning.

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Changes: https://git.openjdk.org/jdk/pull/16208/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16208&range=01
  Stats: 871 lines in 20 files changed: 513 ins; 148 del; 210 mod
  Patch: https://git.openjdk.org/jdk/pull/16208.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16208/head:pull/16208

PR: https://git.openjdk.org/jdk/pull/16208