- this patch fixes the stack slot sharing aliasing problem by making

  sure to add conflicts for unions of the same type.

Changed files:
    gcc-pr25654.patch -> 1.1.2.1

diff --git a/gcc-pr25654.patch b/gcc-pr25654.patch
new file mode 100644 (file)
index 0000000..e8c9c9b
--- /dev/null
+++ b/gcc-pr25654.patch
@@ -0,0 +1,70 @@
+--- gcc-4_1-branch/gcc/cfgexpand.c     (revision 110109)
++++ gcc-4_1-branch/gcc/cfgexpand.c     (revision 110110)
+@@ -272,11 +272,39 @@
+   gcc_assert (index < stack_vars_conflict_alloc);
+   return stack_vars_conflict[index];
+ }
+-  
++ 
++/* Returns true if TYPE is or contains a union type.  */
++
++static bool
++aggregate_contains_union_type (tree type)
++{
++  tree field;
++
++  if (TREE_CODE (type) == UNION_TYPE
++      || TREE_CODE (type) == QUAL_UNION_TYPE)
++    return true;
++  if (TREE_CODE (type) == ARRAY_TYPE)
++    return aggregate_contains_union_type (TREE_TYPE (type));
++  if (TREE_CODE (type) != RECORD_TYPE)
++    return false;
++
++  for (field = TYPE_FIELDS (type); field; field = TREE_CHAIN (field))
++    if (TREE_CODE (field) == FIELD_DECL)
++      if (aggregate_contains_union_type (TREE_TYPE (field)))
++      return true;
++
++  return false;
++}
++
+ /* A subroutine of expand_used_vars.  If two variables X and Y have alias
+    sets that do not conflict, then do add a conflict for these variables
+-   in the interference graph.  We also have to mind MEM_IN_STRUCT_P and
+-   MEM_SCALAR_P.  */
++   in the interference graph.  We also need to make sure to add conflicts
++   for union containing structures.  Else RTL alias analysis comes along
++   and due to type based aliasing rules decides that for two overlapping
++   union temporaries { short s; int i; } accesses to the same mem through
++   different types may not alias and happily reorders stores across
++   life-time boundaries of the temporaries (See PR25654).
++   We also have to mind MEM_IN_STRUCT_P and MEM_SCALAR_P.  */
+ 
+ static void
+ add_alias_set_conflicts (void)
+@@ -287,12 +315,23 @@
+     {
+       tree type_i = TREE_TYPE (stack_vars[i].decl);
+       bool aggr_i = AGGREGATE_TYPE_P (type_i);
++      bool contains_union;
+ 
++      contains_union = aggregate_contains_union_type (type_i);
+       for (j = 0; j < i; ++j)
+       {
+         tree type_j = TREE_TYPE (stack_vars[j].decl);
+         bool aggr_j = AGGREGATE_TYPE_P (type_j);
+-        if (aggr_i != aggr_j || !objects_must_conflict_p (type_i, type_j))
++        if (aggr_i != aggr_j
++            /* Either the objects conflict by means of type based
++               aliasing rules, or we need to add a conflict.  */
++            || !objects_must_conflict_p (type_i, type_j)
++            /* In case the types do not conflict ensure that access
++               to elements will conflict.  In case of unions we have
++               to be careful as type based aliasing rules may say
++               access to the same memory does not conflict.  So play
++               safe and add a conflict in this case.  */
++            || contains_union)
+           add_stack_var_conflict (i, j);
+       }
+     }