https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104303
--- Comment #6 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
OK, tree-ssa-alias is using:
if (ref_may_access_global_memory_p (ref))
to determine if the access to S9b.6_22 may be used by the call. I expected
this to return true because memory pointed to S9b.6_22 is escaping and thus it
is accessible from global memory accesses.
However the implementation does:
/* Return ture if REF may access global memory. */
bool
ref_may_access_global_memory_p (ao_ref *ref)
{
if (!ref->ref)
return true;
tree base = ao_ref_base (ref);
if (TREE_CODE (base) == MEM_REF
|| TREE_CODE (base) == TARGET_MEM_REF)
{
if (ptr_deref_may_alias_global_p (TREE_OPERAND (base, 0)))
return true;
}
else
{
if (!auto_var_in_fn_p (base, current_function_decl)
|| pt_solution_includes (&cfun->gimple_df->escaped,
base))
return true;
}
return false;
}
so for automatic variables we check "escaped" flag, but since this is heap
alocated we go the ptr_deref_may_alias_global_p path which checks:
/* Return true, if dereferencing PTR may alias with a global variable. */
bool
ptr_deref_may_alias_global_p (tree ptr)
{
struct ptr_info_def *pi;
/* If we end up with a pointer constant here that may point
to global memory. */
if (TREE_CODE (ptr) != SSA_NAME)
return true;
pi = SSA_NAME_PTR_INFO (ptr);
/* If we do not have points-to information for this variable,
we have to punt. */
if (!pi)
return true;
/* ??? This does not use TBAA to prune globals ptr may not access. */
return pt_solution_includes_global (&pi->pt);
}
So this predicate tests something different - it tests if the deref can alias
global variable, not global memory in a sense of anything accessible from
outside world.
So I want to also return true on points to set that contains escaped?
diff --git a/gcc/tree-ssa-alias.cc b/gcc/tree-ssa-alias.cc
index 50bd47b31f3..9e34f76c3cb 100644
--- a/gcc/tree-ssa-alias.cc
+++ b/gcc/tree-ssa-alias.cc
@@ -2578,8 +2578,24 @@ ref_may_access_global_memory_p (ao_ref *ref)
if (TREE_CODE (base) == MEM_REF
|| TREE_CODE (base) == TARGET_MEM_REF)
{
- if (ptr_deref_may_alias_global_p (TREE_OPERAND (base, 0)))
+ struct ptr_info_def *pi;
+ tree ptr = TREE_OPERAND (base, 0);
+
+ /* If we end up with a pointer constant here that may point
+ to global memory. */
+ if (TREE_CODE (ptr) != SSA_NAME)
+ return true;
+
+ pi = SSA_NAME_PTR_INFO (ptr);
+
+ /* If we do not have points-to information for this variable,
+ we have to punt. */
+ if (!pi)
return true;
+
+ /* ??? This does not use TBAA to prune globals ptr may not access. */
+ return pt_solution_includes_global (&pi->pt)
+ || pi->pt.vars_contains_escaped;
}
else
{
