Check array indices in object_address_invariant_in_loop_p (PR 84357)

[Richard Sandiford]

object_address_invariant_in_loop_p ignored ARRAY_REF indices on
the basis that:

          /* Index of the ARRAY_REF was zeroed in analyze_indices, thus we only
             need to check the stride and the lower bound of the reference.  */

That was true back in 2007 when the code was added:

static void
dr_analyze_indices (struct data_reference *dr, struct loop *nest)
{
  [...]
  while (handled_component_p (aref))
    {
      if (TREE_CODE (aref) == ARRAY_REF)
        {
          op = TREE_OPERAND (aref, 1);
          access_fn = analyze_scalar_evolution (loop, op);
          access_fn = resolve_mixers (nest, access_fn);
          VEC_safe_push (tree, heap, access_fns, access_fn);

          TREE_OPERAND (aref, 1) = build_int_cst (TREE_TYPE (op), 0);
        }

      aref = TREE_OPERAND (aref, 0);
    }

but the assignment was removed a few years ago.  We were therefore
treating "two->arr[i]" and "three->arr[i]" as loop invariant.

Tested on aarch64-linux-gnu, x86_64-linux-gnu and powerpc64le-linux-gnu.
OK to install?

Richard


2018-02-14  Richard Sandiford  <richard.sandif...@linaro.org>

gcc/
        PR tree-optimization/84357
        * tree-data-ref.c (object_address_invariant_in_loop_p): Check
        operand 1 of an ARRAY_REF too.

gcc/testsuite/
        PR tree-optimization/84357
        * gcc.dg/vect/pr84357.c: New test.

Index: gcc/tree-data-ref.c
===================================================================
--- gcc/tree-data-ref.c 2018-02-08 15:16:21.784407397 +0000
+++ gcc/tree-data-ref.c 2018-02-14 09:42:14.801095011 +0000
@@ -2200,13 +2200,10 @@ object_address_invariant_in_loop_p (cons
     {
       if (TREE_CODE (obj) == ARRAY_REF)
        {
-         /* Index of the ARRAY_REF was zeroed in analyze_indices, thus we only
-            need to check the stride and the lower bound of the reference.  */
-         if (chrec_contains_symbols_defined_in_loop (TREE_OPERAND (obj, 2),
-                                                     loop->num)
-             || chrec_contains_symbols_defined_in_loop (TREE_OPERAND (obj, 3),
-                                                        loop->num))
-           return false;
+         for (int i = 1; i < 4; ++i)
+           if (chrec_contains_symbols_defined_in_loop (TREE_OPERAND (obj, i),
+                                                       loop->num))
+             return false;
        }
       else if (TREE_CODE (obj) == COMPONENT_REF)
        {
Index: gcc/testsuite/gcc.dg/vect/pr84357.c
===================================================================
--- /dev/null   2018-02-10 09:05:46.714416790 +0000
+++ gcc/testsuite/gcc.dg/vect/pr84357.c 2018-02-14 09:42:14.800095067 +0000
@@ -0,0 +1,31 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-Wall" } */
+
+#define COUNT 32
+
+typedef struct s1 {
+    unsigned char c;
+} s1;
+
+typedef struct s2
+{
+    char pad;
+    s1 arr[COUNT];
+} s2;
+
+typedef struct s3 {
+    s1 arr[COUNT];
+} s3;
+
+s2 * get_s2();
+s3 * gActiveS3;
+void foo()
+{
+    s3 * three = gActiveS3;
+    s2 * two = get_s2();
+
+    for (int i = 0; i < COUNT; i++)
+    {
+        two->arr[i].c = three->arr[i].c;
+    }
+}