re PR rtl-optimization/69535 (wrong code with -O -fno-tree-bit-ccp -fno-tree-reassoc due to use of uninitialised value)

PR rtl-opt/69535

  * combine.c (make_compound_operation): When looking through a
  subreg, make sure to re-extend to the width of the outer mode.

From-SVN: r233032