Regression range points to a14f22818851558ec51f04f5fa3396e242f10b78.

This is the extracted stand-alone repro:

for (var i = 0; i < 5; ++i) {}
(function() {
  "use asm";
  return function(x) {
    for (var x = 0; this.x = i; ++i) i = 0;
    return x;
  }
})()(this + "i");

I am pretty sure this is because we inserts deopting checks when deoptimization is disallowed (because asm.js).

Indeed, the new chunk JSNativeContextSpecialization::ReduceNamedAccessFromNexus does not guard against disabled deopt.

The following revision refers to this bug:
  https://chromium.googlesource.com/v8/v8.git/+/c21d1281d9a0c9db39441d798ff04d164d76259f

commit c21d1281d9a0c9db39441d798ff04d164d76259f
Author: bmeurer <bmeurer@chromium.org>
Date: Fri Feb 03 14:06:06 2017

[turbofan] Properly ensure that deoptimization is enabled.

We cannot optimize global proxy access unless deoptimization is enabled.

BUG= chromium:687990 
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2675793002
Cr-Commit-Position: refs/heads/master@{#42928}

[modify] https://crrev.com/c21d1281d9a0c9db39441d798ff04d164d76259f/src/compiler/js-native-context-specialization.cc
[add] https://crrev.com/c21d1281d9a0c9db39441d798ff04d164d76259f/test/mjsunit/regress/regress-crbug-687990.js

ClusterFuzz has detected this issue as fixed in range 42927:42928.

Detailed report: https://cluster-fuzz.appspot.com/testcase?key=4846947136700416

Fuzzer: decoder_langfuzz
Job Type: linux_asan_d8_dbg
Platform Id: linux

Crash Type: CHECK failure
Crash Address: 
Crash State:
  We should never get here - unexpected deopt info in deoptimizer.cc
  
Sanitizer: address (ASAN)

Regressed: V8: 42804:42805
Fixed: V8: 42927:42928

Reproducer Testcase: https://cluster-fuzz.appspot.com/download/AMIfv96_b_0vHFHmyPChFD3L-axWLmPJPTQ5tSkOf1r4bN506bQxDTX2_c_g1TUf6sFBtgWWbPuHEsUbuBS6VG-vSUIn76nck6r-NkgnK5GASYS1b5h5IfwatigteDrbsgdwzFOLDi6wqWs_-Gfjhc2vgRdwT7k3qSP8KDTE7c186bwUmVX10f0DdQxpWVke9au21vm6gMJjSyb-fjqJFsLHJ_QbDPeT81yms6LZBdr3uCt7WaVsEbzkd7Epq7h2t9Bp4dduWOHk4S6DsSefgtVcFR7YH8aw8SWq9yBk3plsPwwBzIlW5sN9cC5wWNXZ39v9rUgJtJdHh_NSkS4J27vE02URG9oFQ-t2NoOydatpIyNTvLRj36o?testcase_id=4846947136700416


See https://dev.chromium.org/Home/chromium-security/bugs/reproducing-clusterfuzz-bugs 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 4846947136700416 is verified as fixed, so closing issue.

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