@capn -- Could you please look into this issue as the recent changes done to the file Shader.cpp are by you, 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=6278869345894400

Fuzzer: libFuzzer_swiftshader_vertex_routine_fuzzer
Job Type: libfuzzer_chrome_ubsan
Platform Id: linux

Crash Type: Undefined-shift
Crash Address: 
Crash State:
  sw::Shader::declareSampler
  glsl::OutputASM::declareUniform
  glsl::OutputASM::declareUniform
  
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=6278869345894400

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 6278869345894400 is verified as fixed, so closing issue as verified.

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