As per the  Issue 743136  and  Issue 652223  owner, assigning this issue to @oetuaho.
@oetuaho-- Could you please look into this issue, kindly reassign if it has nothing to do with your changes.
Thanks.

This issue is not in ANGLE, but in similar code in SwiftShader. Assigning capn.

Thanks, we'll take a look in due time.

pnagunoori@, any issues found by the libFuzzer_swiftshader_vertex_routine_fuzzer can be assigned to the SwiftShader team, being me and sugoi@. Thanks.

@capn -- Sure. Thanks for the update.

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

Detailed report: https://clusterfuzz.com/testcase?key=5370899007275008

Fuzzer: libFuzzer_swiftshader_vertex_routine_fuzzer
Job Type: libfuzzer_chrome_ubsan
Platform Id: linux

Crash Type: Integer-overflow
Crash Address: 
Crash State:
  ppparse
  pp::ExpressionParser::parse
  pp::DirectiveParser::parseExpressionIf
  
Sanitizer: undefined (UBSAN)

Regressed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=512576:512620
Fixed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=521492:521536

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=5370899007275008

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 5370899007275008 is verified as fixed, so closing issue as verified.

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