aarch64: Ignore inductions when costing vector code

In practice it seems to be better not to cost a vector induction.
The scalar code generally needs the same induction but doesn't
cost it, making an apples-for-apples comparison harder.  Most
inductions also have a low latency and their cost usually gets
hidden by other operations.

Like with the previous patches, this one only becomes active if
a CPU selects use_new_vector_costs.  It should therefore have
a very low impact on other CPUs.

gcc/
	* config/aarch64/aarch64.c (aarch64_detect_vector_stmt_subtype):
	Assume a zero cost for induction phis.

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index e97e71b6e3d2c4205e31991d7a1258bfa66f3a2d..6d18d82079cb958b5ddaa6082f103daee74c0124 100644 (file)
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -14541,6 +14541,12 @@ aarch64_detect_vector_stmt_subtype (vec_info *vinfo, vect_cost_for_stmt kind,
   if (aarch64_sve_mode_p (TYPE_MODE (vectype)))
     sve_costs = aarch64_tune_params.vec_costs->sve;
 
+  /* It's generally better to avoid costing inductions, since the induction
+     will usually be hidden by other operations.  This is particularly true
+     for things like COND_REDUCTIONS.  */
+  if (is_a<gphi *> (stmt_info->stmt))
+    return 0;
+
   /* Detect cases in which vec_to_scalar is describing the extraction of a
      vector element in preparation for a scalar store.  The store itself is
      costed separately.  */