Enable vectorization for unknown tripcount in very cheap cost model but disable epilog vectorization.

gcc/ChangeLog:

	* tree-vect-loop.cc (vect_analyze_loop_costing): Enable
	vectorization for LOOP_VINFO_PEELING_FOR_NITER in very cheap
	cost model.
	(vect_analyze_loop): Disable epilogue vectorization in very
	cheap cost model.
	* doc/invoke.texi: Adjust documents for very-cheap cost model.

2 files changed, 7 insertions, 10 deletions

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index c0c8bf1..12477e6 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -14315,13 +14315,10 @@ counts that will likely execute faster than when executing the original
 scalar loop.  The @samp{cheap} model disables vectorization of
 loops where doing so would be cost prohibitive for example due to
 required runtime checks for data dependence or alignment but otherwise
-is equal to the @samp{dynamic} model.  The @samp{very-cheap} model only
-allows vectorization if the vector code would entirely replace the
-scalar code that is being vectorized.  For example, if each iteration
-of a vectorized loop would only be able to handle exactly four iterations
-of the scalar loop, the @samp{very-cheap} model would only allow
-vectorization if the scalar iteration count is known to be a multiple
-of four.
+is equal to the @samp{dynamic} model.  The @samp{very-cheap} model disables
+vectorization of loops when any runtime check for data dependence or alignment
+is required, it also disables vectorization of epilogue loops but otherwise is
+equal to the @samp{cheap} model.
 
 The default cost model depends on other optimization flags and is
 either @samp{dynamic} or @samp{cheap}.
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 9be50aa..ade72a5 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -2375,8 +2375,7 @@ vect_analyze_loop_costing (loop_vec_info loop_vinfo,
      a copy of the scalar code (even if we might be able to vectorize it).  */
   if (loop_cost_model (loop) == VECT_COST_MODEL_VERY_CHEAP
       && (LOOP_VINFO_PEELING_FOR_ALIGNMENT (loop_vinfo)
-	  || LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo)
-	  || LOOP_VINFO_PEELING_FOR_NITER (loop_vinfo)))
+	  || LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo)))
     {
       if (dump_enabled_p ())
 	dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
@@ -3683,7 +3682,8 @@ vect_analyze_loop (class loop *loop, gimple *loop_vectorized_call,
 			   /* No code motion support for multiple epilogues so for now
 			      not supported when multiple exits.  */
 			 && !LOOP_VINFO_EARLY_BREAKS (first_loop_vinfo)
-			 && !loop->simduid);
+			 && !loop->simduid
+			 && loop_cost_model (loop) > VECT_COST_MODEL_VERY_CHEAP);
   if (!vect_epilogues)
     return first_loop_vinfo;