[google gcc-4_8] Tree Loop Unrolling - Relax code size increase with -O2

[Sriraman Tallam]

Hi,

     Currently, tree unrolling pass(cunroll) does not allow any code
size growth in O2 mode.  Code size growth is permitted only if O3 or
funroll-loops/fpeel-loops is used. I have created  a patch to allow
partial code size increase in O2 mode. With funroll-loops the maximum
allowed code growth is 400 unrolled insns. I have set it to 200
unrolled insns in O2 mode.  This patch improves an image processing
benchmark by 20%. It improves most benchmarks by 1-2%. The code size
increase is <1% for all the benchmarks except the image processing
benchmark which increases by 6% (perf improves by 20%).

     I am working on getting this patch reviewed for trunk. Here is
the disussion on this:
http://gcc.gnu.org/ml/gcc-patches/2013-11/msg02643.html  I have
incorporated the comments on making the patch simpler. I will
follow-up on that patch to trunk by also getting data on limiting
complete peeling with O2.

Is this ok for the google branch?

Thanks
Sri
-------------- next part --------------
Index: opts.c
===================================================================
--- opts.c	(revision 206638)
+++ opts.c	(working copy)
@@ -855,6 +855,19 @@ finish_options (struct gcc_options *opts, struct g
             0, opts->x_param_values, opts_set->x_param_values);
     }
 
+  /* Set PARAM_MAX_COMPLETELY_PEELED_INSNS to half its original value during
+     -O2 when -funroll-loops and -fpeel-loops are not set.   */
+  if (optimize == 2 && !opts->x_flag_unroll_loops && !opts->x_flag_peel_loops
+      && !opts->x_flag_unroll_all_loops)
+
+    {
+      unsigned HOST_WIDE_INT max_completely_peeled_insns
+	= (PARAM_VALUE (PARAM_MAX_COMPLETELY_PEELED_INSNS) / 2);
+      maybe_set_param_value (PARAM_MAX_COMPLETELY_PEELED_INSNS,
+			     max_completely_peeled_insns,
+			     opts->x_param_values, opts_set->x_param_values);
+    }
+
   /* Set PARAM_MAX_STORES_TO_SINK to 0 if either vectorization or if-conversion
      is disabled.  */
   if ((!opts->x_flag_tree_loop_vectorize && !opts->x_flag_tree_slp_vectorize)
Index: tree-ssa-loop.c
===================================================================
--- tree-ssa-loop.c	(revision 206638)
+++ tree-ssa-loop.c	(working copy)
@@ -467,7 +467,7 @@ tree_complete_unroll (void)
 
   return tree_unroll_loops_completely (flag_unroll_loops
 				       || flag_peel_loops
-				       || optimize >= 3, true);
+				       || optimize >= 2, true);
 }
 
 static bool