(function() { const[arguments] = 0 })() asserts js debug shell on m-c changeset 2114ef80f6ae with --no-ion --no-threads at Assertion failure: !IsUninitializedLexical((activation.regs()).fp()->unaliasedLocal(i)), at vm/Interpreter.cpp. Debug configure options: CC="clang -Qunused-arguments" CXX="clang++ -Qunused-arguments" AR=ar AUTOCONF=/usr/local/Cellar/autoconf213/2.13/bin/autoconf213 sh /Users/skywalker/trees/mozilla-central/js/src/configure --target=x86_64-apple-darwin12.5.0 --enable-debug --enable-optimize --enable-nspr-build --enable-more-deterministic --with-ccache --enable-gczeal --enable-debug-symbols --disable-tests autoBisect shows this is probably related to the following changeset: The first bad revision is: changeset: https://hg.mozilla.org/mozilla-central/rev/a9a7f16c817b user: Eric Faust date: Thu Oct 30 17:27:03 2014 -0700 summary: Bug 611388 - |const| should be block scoped and require an initializer. (r=shu) Eric, is bug 611388 a possible regressor?

(lldb) bt 5 * thread #1: tid = 0xa3800, 0x0000000100651ead js-dbg-opt-64-dm-nsprBuild-darwin-2114ef80f6ae`Interpret(cx=<unavailable>, state=<unavailable>) + 76797 at Interpreter.cpp:2654, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0) * frame #0: 0x0000000100651ead js-dbg-opt-64-dm-nsprBuild-darwin-2114ef80f6ae`Interpret(cx=<unavailable>, state=<unavailable>) + 76797 at Interpreter.cpp:2654 frame #1: 0x000000010063f289 js-dbg-opt-64-dm-nsprBuild-darwin-2114ef80f6ae`js::RunScript(cx=0x0000000101c01f60, state=0x00007fff5fbff218) + 345 at Interpreter.cpp:432 frame #2: 0x0000000100629c42 js-dbg-opt-64-dm-nsprBuild-darwin-2114ef80f6ae`js::ExecuteKernel(cx=0x0000000101c01f60, scopeChainArg=0x0000000101d5b060, thisv=0x00007fff5fbff308, type=EXECUTE_GLOBAL, result=0x0000000000000000, script=<unavailable>, evalInFrame=<unavailable>) + 642 at Interpreter.cpp:638 frame #3: 0x00000001006528e1 js-dbg-opt-64-dm-nsprBuild-darwin-2114ef80f6ae`js::Execute(cx=0x0000000101c01f60, scopeChainArg=<unavailable>, rval=0x0000000000000000, script=<unavailable>) + 433 at Interpreter.cpp:674 frame #4: 0x0000000100499c7d js-dbg-opt-64-dm-nsprBuild-darwin-2114ef80f6ae`ExecuteScript(cx=0x0000000101c01f60, obj=JS::HandleObject at 0x00007fff5fbff3b8, scriptArg=JS::HandleScript at 0x00007fff5fbff3b0, rval=0x0000000000000000) + 253 at jsapi.cpp:4729 (lldb)

Nice find, Gary!