As per the  Issue 743136  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.

I think this bug was assigned incorrectly - this looks like an issue from swiftshader fuzzer rather than from ANGLE translator fuzzer. capn might be the right person to look into this.

Indeed this is a bug found by the new SwiftShader fuzzer. We'll probably adopt ANGLE's GLSL preprocessor wholesale to fix this and related issues.

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

Detailed report: https://clusterfuzz.com/testcase?key=5401136944381952

Fuzzer: libFuzzer_swiftshader_vertex_routine_fuzzer
Job Type: libfuzzer_chrome_ubsan
Platform Id: linux

Crash Type: Undefined-shift
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=5401136944381952

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 5401136944381952 is verified as fixed, so closing issue as verified.

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