Exists a technology that can transform an edmx into code-first? I'm aware that there have been rumors of one surfacing in a CTP in the past, but I haven't come across any new information on this.
On the forums at MSDN, a man has created his own (not yet accessible), but the EF team hasn't released anything.
Since EDMX provides many more functionality than can be implemented in code initially, there is no such tool. The only tool that can produce code-first mapping from an existing database is CTP1 EF Power Tools, however it only creates a 1:1 image of your database, with no inheritance, splitting, or other features. Power tools may also convert an existing code-first mapping into read-only EDMX.
With EF6 Tools and Visual Studio 2013 or 2012, you get the option code from the database first (see screenshot below)
Install Entity Framework 6 Tools for Visual Studio 2012 & 2013 http://www.microsoft.com/en-gb/download/details.aspx?id=40762 if you don't see this option.
This may produce code first from an existing DB but can not convert an EDMX to code first (as asked in the query) (which I assume someone wanted to do this from EDMX, would have an existing DB, unless they deleted their DB).