Disallow EXTRACT_LAST_REDUCTION for reduction chains

gcc.dg/vect/vect-cond-reduc-5.c was ICEing for SVE because we
tried to use an extract-last reduction for a chain of COND_EXPRs.
Adding support for the chained case would be too invasive for stage 3
so this patch explicitly forbids it instead.  I've filed PR92884 for
the possible future work.

2019-12-10  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-loop.c (vectorizable_reduction): Don't use
	EXTRACT_LAST_REDUCTION for chained reductions.

From-SVN: r279161

gcc/ChangeLog

 2019-12-10  Richard Sandiford  <richard.sandiford@arm.com>
 
+	* tree-vect-loop.c (vectorizable_reduction): Don't use
+	EXTRACT_LAST_REDUCTION for chained reductions.
+
+2019-12-10  Richard Sandiford  <richard.sandiford@arm.com>
+
 	* ipa-utils.h (get_odr_name_for_type): Check for a TYPE_DECL.
 	* ipa-devirt.c (warn_types_mismatch): Don't call xstrdup for the
 	second demangled name.

gcc/tree-vect-loop.c

@@ -6196,8 +6196,9 @@ vectorizable_reduction (stmt_vec_info stmt_info, slp_tree slp_node,
 	  return false;
 	}
 
-      if (direct_internal_fn_supported_p (IFN_FOLD_EXTRACT_LAST,
-					  vectype_in, OPTIMIZE_FOR_SPEED))
+      if (reduc_chain_length == 1
+	  && direct_internal_fn_supported_p (IFN_FOLD_EXTRACT_LAST,
+					     vectype_in, OPTIMIZE_FOR_SPEED))
 	{
 	  if (dump_enabled_p ())
 	    dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,