[PATCH] fold-const.c use of BRANCH_COST

[David Edelsohn]

>>>>> Jan Hubicka writes:

Jan> I would like to see this happen.  Definitly i386 CPUs are other where
Jan> BRANCH_COST choice doesn't match.  It would be nice to have separate
Jan> knobs for when optimizing for size or speed (decided using
Jan> maybe_hot_bb_p inside ifcvt.c)

	If we are going to separate all of the thresholds, should they be
target hooks or macros?

The basic breakdown is the following:

1) ifcvt.c
  a) MAX_CONDITIONAL_EXECUTE (BRANCH_COST + 1)
  b) store_flag normalize (true/false BRANCH_COST >= 2)
  c) store_flag normalize (default BRANCH_COST >= 3)
  d) store_flag addcc (BRANCH_COST >= 2)
  e) store_flag mask (BRANCH_COST >= 2)
  f) cmove arith (BRANCH_COST >= 5)

2) expmed.c
  a) div quotient jump vs shift (BRANCH_COST < 1 or < 3)
  b) emit_store_flag SCC (BRANCH_COST > 0)

3) expr.c
  a) trinary const (BRANCH_COST >= 3)
       call do_store_flag cheap (BRANCH_COST <= 1)
  b) do_store_flag SCC (BRANCH_COST >= 0)

4) fold-const.c
  a) range_test short-circuit (BRANCH_COST >= 2)
  b) fold_truthop unconditionally evaluate RHS (BRANCH_COST >= 2)


David