tree.c (array_at_struct_end_p): Handle arrays at struct end with flexarrays more conservatively.

2017-05-04  Richard Biener  <rguenther@suse.de>

	* tree.c (array_at_struct_end_p): Handle arrays at struct
	end with flexarrays more conservatively.  Refactor and treat
	arrays of arrays or aggregates more strict.  Fix
	VIEW_CONVERT_EXPR handling.  Remove allow_compref argument.
	* tree.c (array_at_struct_end_p): Adjust prototype.
	* emit-rtl.c (set_mem_attributes_minus_bitpos): Adjust.
	* gimple-fold.c (get_range_strlen): Likewise.
	* tree-chkp.c (chkp_may_narrow_to_field): Likewise.

From-SVN: r247581

gcc/ChangeLog

 2017-05-04  Richard Biener  <rguenther@suse.de>
 
+	* tree.c (array_at_struct_end_p): Handle arrays at struct
+	end with flexarrays more conservatively.  Refactor and treat
+	arrays of arrays or aggregates more strict.  Fix
+	VIEW_CONVERT_EXPR handling.  Remove allow_compref argument.
+	* tree.c (array_at_struct_end_p): Adjust prototype.
+	* emit-rtl.c (set_mem_attributes_minus_bitpos): Adjust.
+	* gimple-fold.c (get_range_strlen): Likewise.
+	* tree-chkp.c (chkp_may_narrow_to_field): Likewise.
+
+2017-05-04  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/31130
 	* tree-vrp.c (needs_overflow_infinity): Remove as always returning
 	false.

gcc/emit-rtl.c

@@ -1957,7 +1957,7 @@ set_mem_attributes_minus_bitpos (rtx ref, tree t, int objectp,
 	      || (TREE_CODE (t2) == COMPONENT_REF
 		  /* For trailing arrays t2 doesn't have a size that
 		     covers all valid accesses.  */
-		  && ! array_at_struct_end_p (t, false)))
+		  && ! array_at_struct_end_p (t)))
 	    {
 	      attrs.expr = t2;
 	      attrs.offset_known_p = false;

gcc/gimple-fold.c

@@ -1235,7 +1235,7 @@ get_range_strlen (tree arg, tree length[2], bitmap *visited, int type,
 		 the NUL.
 		 Set *FLEXP to true if the array whose bound is being
 		 used is at the end of a struct.  */
-	      if (array_at_struct_end_p (arg, true))
+	      if (array_at_struct_end_p (arg))
 		*flexp = true;
 
 	      arg = TREE_OPERAND (arg, 1);

gcc/tree-chkp.c

@@ -3277,7 +3277,7 @@ chkp_may_narrow_to_field (tree ref, tree field)
   return DECL_SIZE (field) && TREE_CODE (DECL_SIZE (field)) == INTEGER_CST
     && tree_to_uhwi (DECL_SIZE (field)) != 0
     && !(flag_chkp_flexible_struct_trailing_arrays
-	 && array_at_struct_end_p (ref, true))
+	 && array_at_struct_end_p (ref))
     && (!DECL_FIELD_OFFSET (field)
 	|| TREE_CODE (DECL_FIELD_OFFSET (field)) == INTEGER_CST)
     && (!DECL_FIELD_BIT_OFFSET (field)

gcc/tree.c

@@ -13221,18 +13221,26 @@ array_ref_up_bound (tree exp)
   return NULL_TREE;
 }
 
-/* Returns true if REF is an array reference to an array at the end of
-   a structure.  If this is the case, the array may be allocated larger
-   than its upper bound implies.  When ALLOW_COMPREF is true considers
-   REF when it's a COMPONENT_REF in addition ARRAY_REF and
-   ARRAY_RANGE_REF.  */
+/* Returns true if REF is an array reference or a component reference
+   to an array at the end of a structure.
+   If this is the case, the array may be allocated larger
+   than its upper bound implies.  */
 
 bool
-array_at_struct_end_p (tree ref, bool allow_compref)
+array_at_struct_end_p (tree ref)
 {
-  if (TREE_CODE (ref) != ARRAY_REF
-      && TREE_CODE (ref) != ARRAY_RANGE_REF
-      && (!allow_compref || TREE_CODE (ref) != COMPONENT_REF))
+  tree atype;
+
+  if (TREE_CODE (ref) == ARRAY_REF
+      || TREE_CODE (ref) == ARRAY_RANGE_REF)
+    {
+      atype = TREE_TYPE (TREE_OPERAND (ref, 0));
+      ref = TREE_OPERAND (ref, 0);
+    }
+  else if (TREE_CODE (ref) == COMPONENT_REF
+	   && TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 1))) == ARRAY_TYPE)
+    atype = TREE_TYPE (TREE_OPERAND (ref, 1));
+  else
     return false;
 
   while (handled_component_p (ref))
@@ -13240,19 +13248,42 @@ array_at_struct_end_p (tree ref, bool allow_compref)
       /* If the reference chain contains a component reference to a
          non-union type and there follows another field the reference
 	 is not at the end of a structure.  */
-      if (TREE_CODE (ref) == COMPONENT_REF
-	  && TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 0))) == RECORD_TYPE)
+      if (TREE_CODE (ref) == COMPONENT_REF)
 	{
-	  tree nextf = DECL_CHAIN (TREE_OPERAND (ref, 1));
-	  while (nextf && TREE_CODE (nextf) != FIELD_DECL)
-	    nextf = DECL_CHAIN (nextf);
-	  if (nextf)
-	    return false;
+	  if (TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 0))) == RECORD_TYPE)
+	    {
+	      tree nextf = DECL_CHAIN (TREE_OPERAND (ref, 1));
+	      while (nextf && TREE_CODE (nextf) != FIELD_DECL)
+		nextf = DECL_CHAIN (nextf);
+	      if (nextf)
+		return false;
+	    }
 	}
+      /* If we have a multi-dimensional array we do not consider
+         a non-innermost dimension as flex array if the whole
+	 multi-dimensional array is at struct end.
+	 Same for an array of aggregates with a trailing array
+	 member.  */
+      else if (TREE_CODE (ref) == ARRAY_REF)
+	return false;
+      else if (TREE_CODE (ref) == ARRAY_RANGE_REF)
+	;
+      /* If we view an underlying object as sth else then what we
+         gathered up to now is what we have to rely on.  */
+      else if (TREE_CODE (ref) == VIEW_CONVERT_EXPR)
+	break;
+      else
+	gcc_unreachable ();
 
       ref = TREE_OPERAND (ref, 0);
     }
 
+  /* The array now is at struct end.  Treat flexible arrays as
+     always subject to extend, even into just padding constrained by
+     an underlying decl.  */
+  if (! TYPE_SIZE (atype))
+    return true;
+
   tree size = NULL;
 
   if (TREE_CODE (ref) == MEM_REF

gcc/tree.h

@@ -4886,12 +4886,10 @@ extern tree array_ref_up_bound (tree);
    EXP, an ARRAY_REF or an ARRAY_RANGE_REF.  */
 extern tree array_ref_low_bound (tree);
 
-/* Returns true if REF is an array reference to an array at the end of
-   a structure.  If this is the case, the array may be allocated larger
-   than its upper bound implies.  When second argument is true considers
-   REF when it's a COMPONENT_REF in addition ARRAY_REF and
-   ARRAY_RANGE_REF.  */
-extern bool array_at_struct_end_p (tree, bool = false);
+/* Returns true if REF is an array reference or a component reference
+   to an array at the end of a structure.  If this is the case, the array
+   may be allocated larger than its upper bound implies.  */
+extern bool array_at_struct_end_p (tree);
 
 /* Return a tree representing the offset, in bytes, of the field referenced
    by EXP.  This does not include any offset in DECL_FIELD_BIT_OFFSET.  */