I'm skeptical that the patch is right (or, rather, that it is not a 
compiler bug). According to 

http://gcc.gnu.org/viewcvs/trunk/gcc/config/i386/i386.h?view=markup

in macro REG_CLASS_CONTENTS, the class AD_REGS includes indeed EDX and 
EAX. The exact place where this gets used has varied recently quite a 
lot; it currently lives in predicates.md:

http://gcc.gnu.org/viewcvs/trunk/gcc/config/i386/constraints.md?
revision=149373&view=markup

where "A" becomes the letter denoting the AD_REGS constraint. So IIUC, 
this means that EDX is the output of the insn, and your change should 
have no effect. I suggest talking to gcc people what the problem might 
be.