This implement the second phase of the classical SSA conversion: the renaming of variables but only for load & stores. The implementation doesn't use the stack based algorithm (which is quite hairy and can use a lot of memory) but a simpler solution where each BB keep track of the symbol-to-pseudo correspondance. This mapping is also done for phi-nodes (which are semantically close to loads) but the phi-nodes themselves are not renamed. This is done so that we can keep track of the unused phi-nodes and so have semi-pruned SSA. One thing worth of noticing is that in order to keep the mapping for phi-nodes it was needed to add a field to OP_PHI instructions to hold the original symbol pseudo (much like OP_LOAD). Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>