For the targets supporting low-overhead loops, IVOPTs has to take care of
   the loops which will probably be transformed in RTL doloop optimization,
   to try to make selected IV candidate set optimal.  The process of doloop
   support includes:

   1) Analyze the current loop will be transformed to doloop or not, find and
      mark its compare type IV use as doloop use (iv_group field doloop_p), and
      set flag doloop_use_p of ivopts_data to notify subsequent processings on
      doloop.  See analyze_and_mark_doloop_use and its callees for the details.
      The target hook predict_doloop_p can be used for target specific checks.

   2) Add one doloop dedicated IV cand {(may_be_zero ? 1 : (niter + 1)), +, -1},
      set flag doloop_p of iv_cand, step cost is set as zero and no extra cost
      like biv.  For cost determination between doloop IV cand and IV use, the
      target hooks doloop_cost_for_generic and doloop_cost_for_address are
      provided to add on extra costs for generic type and address type IV use.
      Zero cost is assigned to the pair between doloop IV cand and doloop IV
      use, and bound zero is set for IV elimination.

   3) With the cost setting in step 2), the current cost model based IV
      selection algorithm will process as usual, pick up doloop dedicated IV if
      profitable.

gcc/ChangeLog

2019-09-14  Kewen Lin  <linkw@gcc.gnu.org>

    PR middle-end/80791
    * config/rs6000/rs6000.c (TARGET_HAVE_COUNT_REG_DECR_P): New macro.
    (TARGET_DOLOOP_COST_FOR_GENERIC): Likewise.
    (TARGET_DOLOOP_COST_FOR_ADDRESS): Likewise.
    * target.def (have_count_reg_decr_p): New hook.
    (doloop_cost_for_generic): Likewise.
    (doloop_cost_for_address): Likewise.
    * doc/tm.texi.in (TARGET_HAVE_COUNT_REG_DECR_P): Likewise.
    (TARGET_DOLOOP_COST_FOR_GENERIC): Likewise.
    (TARGET_DOLOOP_COST_FOR_ADDRESS): Likewise.
    * doc/tm.texi: Regenerate.
    * tree-ssa-loop-ivopts.c (comp_cost::operator+=): Consider infinite cost
    addend.
    (record_group): Init doloop_p.
    (add_candidate_1): Add optional argument doloop, change the handlings
    accordingly.
    (add_candidate): Likewise.
    (generic_predict_doloop_p): Update attribute.
    (force_expr_to_var_cost): Add costing for expressions COND_EXPR/LT_EXPR/
    LE_EXPR/GT_EXPR/GE_EXPR/EQ_EXPR/NE_EXPR/UNORDERED_EXPR/ORDERED_EXPR/
    UNLT_EXPR/UNLE_EXPR/UNGT_EXPR/UNGE_EXPR/UNEQ_EXPR/LTGT_EXPR/MAX_EXPR/
    MIN_EXPR.
    (get_computation_cost): Update for doloop IV cand extra cost.    
    (determine_group_iv_cost_cond): Update for doloop IV cand.
    (determine_iv_cost): Likewise.
    (ivopts_estimate_reg_pressure): Likewise.
    (may_eliminate_iv): Update handlings for doloop IV cand.
    (add_iv_candidate_for_doloop): New function.
    (find_iv_candidates): Call function add_iv_candidate_for_doloop.
    (iv_ca_set_no_cp): Update for doloop IV cand.
    (iv_ca_set_cp): Likewise.
    (iv_ca_dump): Dump register cost.
    (find_doloop_use): New function.
    (analyze_and_mark_doloop_use): Likewise.
    (tree_ssa_iv_optimize_loop): Call function analyze_and_mark_doloop_use.

gcc/testsuite/ChangeLog

2019-09-14  Kewen Lin  <linkw@gcc.gnu.org>

    PR middle-end/80791
    * gcc.dg/tree-ssa/ivopts-3.c: Adjust for doloop change.
    * gcc.dg/tree-ssa/ivopts-lt.c: Likewise.
    * gcc.dg/tree-ssa/pr32044.c: Likewise.

From-SVN: r275713