fast isel question

If the FastiSel TargetSelectInstuction returns false, does that mean that the whole basic block needs to be done
without FastIsel?



No. FastISel is used as much as possible. Once it fails on some
instruction, this instruction and the rest in the BB go through
SelectionDAG. Skim through SelectionDAGISel::SelectAllBasicBlocks - the
comments there explain what's going on pretty reasonably.