re PR middle-end/81719 (Range-based for loop on short fixed size array generates…

re PR middle-end/81719 (Range-based for loop on short fixed size array generates long unrolled loop)

2017-08-08  Richard Biener  <rguenther@suse.de>

	PR middle-end/81719
	* tree-ssa-loop-niter.c: Include tree-dfa.h.
	(expand_simple_operations): Also look through ADDR_EXPRs with
	MEM_REF bases treating them as POINTER_PLUS_EXPR.

	* g++.dg/tree-ssa/pr81719.C: New testcase.

From-SVN: r250954

gcc/ChangeLog

 2017-08-08  Richard Biener  <rguenther@suse.de>
 
+	PR middle-end/81719
+	* tree-ssa-loop-niter.c: Include tree-dfa.h.
+	(expand_simple_operations): Also look through ADDR_EXPRs with
+	MEM_REF bases treating them as POINTER_PLUS_EXPR.
+
+2017-08-08  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/81723
 	* tree-vect-slp.c (struct bst_traits): New hash traits.
 	(bst_fail): New global.

gcc/testsuite/ChangeLog

 2017-08-08  Richard Biener  <rguenther@suse.de>
 
+	PR middle-end/81719
+	* g++.dg/tree-ssa/pr81719.C: New testcase.
+
+2017-08-08  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/81723
 	* gfortran.dg/pr81723.f: New testcase.
 

gcc/testsuite/g++.dg/tree-ssa/pr81719.C

+/* { dg-do compile { target c++11 } } */
+/* { dg-options "-O3 -fdump-tree-optimized" } */
+
+typedef int Items[2];
+
+struct ItemArray
+{
+  Items items;
+  int sum_x2() const;
+};
+
+int ItemArray::sum_x2() const
+{
+  int total = 0;
+  for (int item : items)
+    {
+      total += item;
+    }
+  return total;
+}
+
+/* We should be able to compute the number of iterations to two, unroll
+   the loop and end up with a single basic-block in sum_x2.  */
+/* { dg-final { scan-tree-dump-times "bb" 1 "optimized" } } */

gcc/tree-ssa-loop-niter.c

@@ -42,6 +42,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-chrec.h"
 #include "tree-scalar-evolution.h"
 #include "params.h"
+#include "tree-dfa.h"
 
 
 /* The maximum number of dominator BBs we search for conditions
@@ -1980,6 +1981,21 @@ expand_simple_operations (tree expr, tree stop)
 
       if (code == SSA_NAME)
 	return expand_simple_operations (e, stop);
+      else if (code == ADDR_EXPR)
+	{
+	  HOST_WIDE_INT offset;
+	  tree base = get_addr_base_and_unit_offset (TREE_OPERAND (e, 0),
+						     &offset);
+	  if (base
+	      && TREE_CODE (base) == MEM_REF)
+	    {
+	      ee = expand_simple_operations (TREE_OPERAND (base, 0), stop);
+	      return fold_build2 (POINTER_PLUS_EXPR, TREE_TYPE (expr), ee,
+				  wide_int_to_tree (sizetype,
+						    mem_ref_offset (base)
+						    + offset));
+	    }
+	}
 
       return expr;
     }