RFR: JDK-8330795 : C2: assert((uint)type <= T_CONFLICT && _zero_type[type] != nullptr) failed: bad type with -XX:-UseCompressedClassPointers [v2]

[Cesar Soares Lucas]

> 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 incrementally with one additional commit since the last revision:

  Require vm.bits == 64 on new test.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19148/files
  - new: https://git.openjdk.org/jdk/pull/19148/files/ea64c880..91fc61de

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19148&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19148&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19148.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19148/head:pull/19148

PR: https://git.openjdk.org/jdk/pull/19148