tree-optimization/106904 - bogus -Wstringopt-overflow with vectors

The following avoids CSE of &ps->wp to &ps->wp.hwnd confusing
-Wstringopt-overflow by making sure to produce addresses to the
biggest container from vectorization.  For this I introduce
strip_zero_offset_components which turns &ps->wp.hwnd into
&(*ps) and use that to base the vector data references on.
That will also work for addresses with variable components,
alternatively emitting pointer arithmetic via calling
get_inner_reference and gimplifying that would be possible
but likely more intrusive.

This is by no means a complete fix for all of those issues
(avoiding ADDR_EXPRs in favor of pointer arithmetic might be).
Other passes will have similar issues.

In theory that might now cause false negatives.

	PR tree-optimization/106904
	* tree.h (strip_zero_offset_components): Declare.
	* tree.cc (strip_zero_offset_components): Define.
	* tree-vect-data-refs.cc (vect_create_addr_base_for_vector_ref):
	Strip zero offset components before building the address.

	* gcc.dg/Wstringop-overflow-pr106904.c: New testcase.

1 files changed, 12 insertions, 0 deletions

diff --git a/gcc/tree.cc b/gcc/tree.cc
index b40c95a..0a51f9d 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -12014,6 +12014,18 @@ strip_invariant_refs (const_tree op)
   return op;
 }
 
+/* Strip handled components with zero offset from OP.  */
+
+tree
+strip_zero_offset_components (tree op)
+{
+  while (TREE_CODE (op) == COMPONENT_REF
+	 && integer_zerop (DECL_FIELD_OFFSET (TREE_OPERAND (op, 1)))
+	 && integer_zerop (DECL_FIELD_BIT_OFFSET (TREE_OPERAND (op, 1))))
+    op = TREE_OPERAND (op, 0);
+  return op;
+}
+
 static GTY(()) tree gcc_eh_personality_decl;
 
 /* Return the GCC personality function decl.  */