Can someone explain where things like IMPLICIT_DEF_FR64 come from?
I believe something is noticing a use before def and inserting some kind of
bogus code to compensate. The machine instructions look like this (x86):

  %reg1069<def> = IMPLICIT_DEF_FR64
  FsMOVLPDmr %reg0, 1, %reg0, 0, %reg1069

This is no good -- it stores to zero.



IMPLICIT_DEF is a value defined by an 'undef' instruction:

It can come from source program or produced as result of optimization.