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

Mon May 6 21:08:01 UTC 2024

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(adr_t->is_known_instance_field()) failed: instance required` failure was caused because RAM uses `PhaseMacroExpand::can_eliminate_allocation` to check if an allocation can be eliminated and that method wasn't checking that the allocation uses an exact type or not.

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.

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Commit messages:
 - Fix bad type when UseCompressedPointers is disabled.
 - Phi merging nullable inputs needs to be nullable.
 - SR allocate needs to be of exact type.

Changes: https://git.openjdk.org/jdk/pull/19111/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19111&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330565
  Stats: 20 lines in 3 files changed: 20 ins; 0 del; 0 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