https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121000
--- Comment #4 from qinzhao at gcc dot gnu.org ---
The size of the element of the FAM actually _cannot_ reliably depends on the
original TYPE of the FAM that we passed as the 6th parameter to the
.ACCESS_WITH_SIZE:
TYPE_SIZE_UNIT (TREE_TYPE (TREE_TYPE (gimple_call_arg (call, 5))))
when the element of the FAM has a variable length type. Since the variable that
represents TYPE_SIZE_UNIT has no explicit usage in the original IL, compiler
transformations (such as DSE) that are applied before object_size phase might
eliminate the whole definition to the variable that represents the
TYPE_SIZE_UNIT of the element of the FAM.
In order to resolve this correctness issue, instead of passing the original
TYPE of the FAM as the 6th argument to .ACCESS_WITH_SIZE, we should explicitly
pass the original TYPE_SIZE_UNIT of the element TYPE of the FAM as the 6th
argument to the call to .ACCESS_WITH_SIZE.
As a result, the new ACCESS_WITH_SIZE is: (change the 6th argument to the
TYPE_SIZE_UNIT of the element TYPE of the FAM)
ACCESS_WITH_SIZE (REF_TO_OBJ, REF_TO_SIZE, CLASS_OF_SIZE,
TYPE_OF_SIZE, ACCESS_MODE, TYPE_SIZE_UNIT for element)
which returns the REF_TO_OBJ same as the 1st argument;
1st argument REF_TO_OBJ: The reference to the object;
2nd argument REF_TO_SIZE: The reference to the size of the object,
3rd argument CLASS_OF_SIZE: The size referenced by the REF_TO_SIZE represents
0: the number of bytes.
1: the number of the elements of the object type;
4th argument TYPE_OF_SIZE: A constant 0 with its TYPE being the same as the
TYPE
of the object referenced by REF_TO_SIZE
5th argument ACCESS_MODE:
-1: Unknown access semantics
0: none
1: read_only
2: write_only
3: read_write
6th argument: The TYPE_SIZE_UNIT of the element TYPE of the FAM when 3rd
argument
is 1. NULL when 3rd argument is 0.
In tree-object-size.cc, instead of the following current code to get the
"element_size":
/* The type of the 6th argument type is the pointer TYPE to the original
flexible array type. */
tree pointer_to_array_type = TREE_TYPE (gimple_call_arg (call, 5));
gcc_assert (POINTER_TYPE_P (pointer_to_array_type));
tree element_type = TREE_TYPE (TREE_TYPE (pointer_to_array_type));
tree element_size = TYPE_SIZE_UNIT (element_type);
the New code should be:
+ /* The 6th argument is the TYPE_SIZE_UNIT for the element of the original
+ flexible array. */
+ tree element_size = gimple_call_arg (call, 5);
