Looks like an issue in the ANGLE parser... I can help you go through the repro steps if you need.

 Issue 629517  has been merged into this issue.

 Issue 629519  has been merged into this issue.

Good fuzzer! Will investigate.

The following revision refers to this bug:
  https://chromium.googlesource.com/angle/angle/+/461e3af89f0f11bb10dd74db4b3513d1c45f9920

commit 461e3af89f0f11bb10dd74db4b3513d1c45f9920
Author: Jamie Madill <jmadill@chromium.org>
Date: Thu Jul 21 22:15:34 2016

preprocessor: Fix negative shift with bad ids.

Fix this by producing an error on undefined or negative shifts.

BUG= 629518 

Change-Id: Idfca5ed3fc8e557f6178408f3426a5ef2ce7cf14
Reviewed-on: https://chromium-review.googlesource.com/362020
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>

[modify] https://crrev.com/461e3af89f0f11bb10dd74db4b3513d1c45f9920/src/compiler/preprocessor/ExpressionParser.y
[modify] https://crrev.com/461e3af89f0f11bb10dd74db4b3513d1c45f9920/src/tests/compiler_tests/MalformedShader_test.cpp
[modify] https://crrev.com/461e3af89f0f11bb10dd74db4b3513d1c45f9920/src/compiler/preprocessor/ExpressionParser.cpp
[modify] https://crrev.com/461e3af89f0f11bb10dd74db4b3513d1c45f9920/src/tests/preprocessor_tests/define_test.cpp
[modify] https://crrev.com/461e3af89f0f11bb10dd74db4b3513d1c45f9920/src/compiler/preprocessor/DiagnosticsBase.cpp
[modify] https://crrev.com/461e3af89f0f11bb10dd74db4b3513d1c45f9920/src/compiler/preprocessor/DiagnosticsBase.h

ClusterFuzz has detected this issue as fixed in range 407329:407362.

Detailed report: https://cluster-fuzz.appspot.com/testcase?key=5992143097430016

Fuzzer: libfuzzer_gpu_fuzzer
Job Type: libfuzzer_chrome_ubsan
Platform Id: linux

Crash Type: Undefined-shift
Crash Address: 
Crash State:
  ppparse
  pp::ExpressionParser::parse
  pp::DirectiveParser::parseLine
  
Regressed: https://cluster-fuzz.appspot.com/revisions?job=libfuzzer_chrome_ubsan&range=405489:405645
Fixed: https://cluster-fuzz.appspot.com/revisions?job=libfuzzer_chrome_ubsan&range=407329:407362

Minimized Testcase (2.07 Kb): https://cluster-fuzz.appspot.com/download/AMIfv948njD63WZQk80M1iQtld7Qpbpsn4Kr6eQJ9yzlYU-ERtjb0erIwTINcJsQ7Fsz08ASYnz1pxLFHm7Q5_BEVv5rsyNPm2EbNr4_Zka8C0G_rOXWhUX31Cngdmf_S5ca4pLN6V1kO01c9uPiGEW1F9YM11nrzQ?testcase_id=5992143097430016

See https://chromium.googlesource.com/chromium/src/+/master/testing/libfuzzer/reproducing.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 is verified as fixed, closing issue.

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