r600/sb: Check whether optimizations would result in reladdr conflict

r600/sb: Check whether optimizations would result in reladdr conflict

v2: * Check whether the node src and dst registers are NULL before using
      them.
    * fix a type in the commit message.

Two cases are handled with this patch:

1. If copy propagation tries to eliminated a move from a relative
   array access then it could optimize

     MOV R1, ARRAY[RELADDR_1]
     MOV R2, ARRAY[RELADDR_2]
     OP2 R3, R1 R2

   into

     OP2 R3, ARRAY[RELADDR_1], ARRAY[RELADDR_2]

   which is forbidden, because there is only one address register available.

2. When MULADD(x,a,MUL(x,c)) is handled

      MUL TMP, R1, ARRAY[RELADDR_1]
      MULLADD R3, R1, ARRAY[RELADDR_2], TMP

   by folding this into

      ADD TMP, ARRAY[RELADDR_2], ARRAY[RELADDR_1]
      MUL R3, R1, TMP

   which is also forbidden.

Test for these cases and reject the optimization if a forbidden combination
of relative access would be created.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103142
Signed-off-by: Gert Wollny <gw.fossdev@gmail.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>