function g(x) { return x === x } function f(x) { return g(0 / Math.sign(x > 0)) } f(1) print(f(-1)) $ ./js-dbg-64-dm-nsprBuild-darwin-0a8b3b67715a --fuzzing-safe --no-threads --ion-eager testcase.js true $ ./js-dbg-64-dm-nsprBuild-darwin-0a8b3b67715a --fuzzing-safe --no-threads --baseline-eager testcase.js false Tested this on m-c rev 0a8b3b67715a. My configure flags are: CC="clang -Qunused-arguments" CXX="clang++ -Qunused-arguments" AR=ar AUTOCONF=/usr/local/Cellar/autoconf213/2.13/bin/autoconf213 sh ~/trees/mozilla-central/js/src/configure --target=x86_64-apple-darwin12.5.0 --enable-debug --enable-nspr-build --enable-more-deterministic --with-ccache --enable-gczeal --enable-debug-symbols --disable-tests python -u ~/fuzzing/js/compileShell.py -b "--enable-debug --enable-more-deterministic --enable-nspr-build -R ~/trees/mozilla-central" -r 0a8b3b67715a autoBisect shows this is probably related to the following changeset: The first bad revision is: changeset: https://hg.mozilla.org/mozilla-central/rev/e5d631abcd56 user: Tom Schuster date: Sun Oct 05 15:26:40 2014 +0200 summary: Bug 1073576 - Optimize strict compares with equal operands. r=h4writer Hannes, not sure if bug 1073576 is the real cause here. Thoughts?

It is debatable if bug 1073576 is the real cause. But by doing that we opened a floodgate of bugs. This is the same bug as bug 1130679. Actively looking into that.