Hi,
before noce_find_if_block processes a block it sets up an if_info
structure that holds the original costs. At that point the costs of
the then/else blocks have not been added so we only care about the
"if" cost.
The code originally used BRANCH_COST for that but was then changed
to COST_N_INSNS (2) - a compare and a jump.
This patch computes the jump costs via
insn_cost (if_info.jump, ...)
which is supposed to incorporate the branch costs and, in case of a CC
comparison,
pattern_cost (if_info.cond, ...)
which is supposed to account for the CC creation.
For compare_and_jump patterns insn_cost should have already computed
the right cost.
Does this "split" make sense, generally?
Bootstrapped and regtested on x86, aarch64 and power10. Regtested
on riscv.
Regards
Robin
gcc/ChangeLog:
* ifcvt.cc (noce_process_if_block): Subtract condition pattern
cost if applicable.
(noce_find_if_block): Use insn_cost and pattern_cost for
original cost.
---
gcc/ifcvt.cc | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/gcc/ifcvt.cc b/gcc/ifcvt.cc
index 58ed42673e5..305b9faed38 100644
--- a/gcc/ifcvt.cc
+++ b/gcc/ifcvt.cc
@@ -3940,7 +3940,9 @@ noce_process_if_block (struct noce_if_info *if_info)
??? Actually, instead of the branch instruction costs we might want
to use COSTS_N_INSNS (BRANCH_COST ()) as in other places. */
- unsigned potential_cost = if_info->original_cost - COSTS_N_INSNS (1);
+ unsigned potential_cost = if_info->original_cost;
+ if (cc_in_cond (if_info->cond))
+ potential_cost -= pattern_cost (if_info->cond, if_info->speed_p);
unsigned old_cost = if_info->original_cost;
if (!else_bb
&& HAVE_conditional_move
@@ -4703,11 +4705,13 @@ noce_find_if_block (basic_block test_bb, edge
then_edge, edge else_edge,
= targetm.max_noce_ifcvt_seq_cost (then_edge);
/* We'll add in the cost of THEN_BB and ELSE_BB later, when we check
that they are valid to transform. We can't easily get back to the insn
- for COND (and it may not exist if we had to canonicalize to get COND),
- and jump_insns are always given a cost of 1 by seq_cost, so treat
- both instructions as having cost COSTS_N_INSNS (1). */
- if_info.original_cost = COSTS_N_INSNS (2);
-
+ for COND (and it may not exist if we had to canonicalize to get COND).
+ Here we assume one CC compare insn (if the target uses CC) and one
+ jump insn that is costed via insn_cost. It is assumed that the
+ costs of a jump insn are dependent on the branch costs. */
+ if (cc_in_cond (if_info.cond))
+ if_info.original_cost = pattern_cost (if_info.cond, if_info.speed_p);
+ if_info.original_cost += insn_cost (if_info.jump, if_info.speed_p);
/* Do the real work. */
--
2.45.1
