Adjust inner loop cost scaling

This makes use of the estimated number of iterations of the inner loop
to limit --param vect-inner-loop-cost-factor scaling.  It also reduces
the maximum value of vect-inner-loop-cost-factor to 10000 making it
less likely to cause overflow of costs.

2021-08-23  Richard Biener  <rguenther@suse.de>

	* doc/invoke.texi (vect-inner-loop-cost-factor): Adjust.
	* params.opt (--param vect-inner-loop-cost-factor): Adjust
	maximum value.
	* tree-vect-loop.c (vect_analyze_loop_form): Initialize
	inner_loop_cost_factor to the minimum of the estimated number
	of iterations of the inner loop and vect-inner-loop-cost-factor.

1 files changed, 7 insertions, 0 deletions

diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index c521b43a..0c8d992 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -1519,6 +1519,13 @@ vect_analyze_loop_form (class loop *loop, vec_info_shared *shared)
       stmt_vec_info inner_loop_cond_info
 	= loop_vinfo->lookup_stmt (inner_loop_cond);
       STMT_VINFO_TYPE (inner_loop_cond_info) = loop_exit_ctrl_vec_info_type;
+      /* If we have an estimate on the number of iterations of the inner
+	 loop use that to limit the scale for costing, otherwise use
+	 --param vect-inner-loop-cost-factor literally.  */
+      widest_int nit;
+      if (estimated_stmt_executions (loop->inner, &nit))
+	LOOP_VINFO_INNER_LOOP_COST_FACTOR (loop_vinfo)
+	  = wi::smin (nit, param_vect_inner_loop_cost_factor).to_uhwi ();
     }
 
   gcc_assert (!loop->aux);