Predator and CL could not provide any possible suspects.
Using the code search, Assigning it to the concern capn@ for his recent work on file "Optimizer.cpp"

capn@  -- Could you please look into this issue, kindly reassign if it has nothing to do with your changes.
Thank You.

ClusterFuzz has detected this issue as fixed in range 521492:521536.

Detailed report: https://clusterfuzz.com/testcase?key=5499163910602752

Fuzzer: libFuzzer_swiftshader_vertex_routine_fuzzer
Job Type: libfuzzer_chrome_ubsan
Platform Id: linux

Crash Type: Null-dereference READ
Crash Address: 0x0000000000c1
Crash State:
  Ice::Variable::classof
  Optimizer::deleteInstruction
  Optimizer::deleteInstruction
  
Sanitizer: undefined (UBSAN)

Regressed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=512956:512987
Fixed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=521492:521536

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=5499163910602752

See https://chromium.googlesource.com/chromium/src/+/master/testing/libfuzzer/reference.md for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.

ClusterFuzz testcase 5499163910602752 is verified as fixed, so closing issue as verified.

If this is incorrect, please add ClusterFuzz-Wrong label and re-open the issue.