RFR: JDK-8330565 - C2: Multiple crashes with CTW after JDK-8316991 [v2]

[Cesar Soares Lucas]

> Please consider this patch for fixing issues described in JDK-8330565 with a little overlap with issue JDK-8330795.
> 
> The `# assert(false) failed: Bad graph detected in build_loop_late` failure was caused because a string concatenation optimization using [this method](https://github.com/openjdk/jdk/blob/819f3d6fc70ff6fe54ac5f9033c17c3dd4326aa5/src/hotspot/share/opto/graphKit.cpp#L4115) adds AddP and LoadN nodes to IR graph as NotNull _and_ because RAM was not "nullyfing" phis merging nullable pointers. I was only able to reproduce this problem using a classfile/jar compiled using an "old" version of JDK.. because newer version use InvokeDynamic to do string concatenation.
> 
> The `assert((uint)type <= T_CONFLICT && _zero_type[type] != nullptr) failed: bad type` failure was caused by the fact that we didn't have a "zero value" for the type T_METADATA. The RAM patch uses that data when it creates a Phi node merging Klass loads and UseCompressedClassPointers is disabled.
>  
> 
> 
> 
> Tested with JTREG tier1-4 on Linux x86_64 & ARM64.

Cesar Soares Lucas has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - Updating branch
   
   Merge branch 'fix_bad_bad_graph' of https://github.com/JohnTortugo/jdk into fix_bad_bad_graph
 - Fix bad type when UseCompressedPointers is disabled.
 - Phi merging nullable inputs needs to be nullable.
 - SR allocate needs to be of exact type.
 - Fix bad type when UseCompressedPointers is disabled.
 - Phi merging nullable inputs needs to be nullable.
 - SR allocate needs to be of exact type.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19111/files
  - new: https://git.openjdk.org/jdk/pull/19111/files/31829d60..c8ce1502

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19111&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19111&range=00-01

  Stats: 48711 lines in 1737 files changed: 22525 ins; 21107 del; 5079 mod
  Patch: https://git.openjdk.org/jdk/pull/19111.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19111/head:pull/19111

PR: https://git.openjdk.org/jdk/pull/19111