Introducing the WebKit FTL JIT
<p><pre><code>    > Profile-driven compilation implies that we might invoke an optimizing
    > compiler while the function is running and we may want to transfer the
    > function’s execution into optimized code in the middle of a loop; to our
    > knowledge the FTL is the first compiler to do on-stack-replacement for
    > hot-loop transfer into LLVM-compiled code.
</code></pre>
Reading this practically made my hair stand on end, it is one hell of a technical feat, considering especially they had no ability to pre-plan so that both LLVM and their previous engine would maintain identical stack layouts in their designs. It's really insane they got this to work at all.<p>I was reminded of the old story about a search engine that tried to supplant JS with a Java bytecode-clone because at the time it was widely believed Javascript had reached its evolutionary limit. How times change!