RFR: 8365604: Null pointer dereference in src/hotspot/share/adlc/output_h.cpp ArchDesc::declareClasses() [v2]

[Artem Semenov]

> The defect has been detected and confirmed in the function ArchDesc::declareClasses() located in the file src/hotspot/share/adlc/output_h.cpp with static code analysis. This defect can potentially lead to a null pointer dereference.
> 
> The pointer instr->_matrule is dereferenced in line 1952 without checking for nullptr, although earlier in line 1858 the same pointer is checked for nullptr, which indicates that it can be null.
> 
> According to [this](https://github.com/openjdk/jdk/pull/26002#issuecomment-3023050372) comment, this PR contains fixes for similar cases in other places.

Artem Semenov has updated the pull request incrementally with two additional commits since the last revision:

 - Update src/hotspot/share/c1/c1_LinearScan.cpp
   
   Co-authored-by: David Holmes <62092539+dholmes-ora at users.noreply.github.com>
 - Update src/hotspot/share/adlc/output_h.cpp
   
   Co-authored-by: David Holmes <62092539+dholmes-ora at users.noreply.github.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26798/files
  - new: https://git.openjdk.org/jdk/pull/26798/files/80777ced..dd21148b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26798&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26798&range=00-01

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/26798.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26798/head:pull/26798

PR: https://git.openjdk.org/jdk/pull/26798