https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121000
--- Comment #1 from qinzhao at gcc dot gnu.org ---
with gcc -O1 -fdump-tree-all t.c, in a-t.c.112t.objsz1, we see the object size
is generated as _22:
sizetype _26(D);
_12 = &p_18->n;
_23 = MEM <int> [(void *)_12];
_24 = MAX_EXPR <_23, 0>;
_25 = (sizetype) _24;
_22 = _26(D) * _25;
In the above, _25 is the # of element of the array, which is loaded from
&p_18->n, the counted_by field of the structure, _26 is the size of each
element, which is the size of A[m], is got as "element_size" in the following
code in gcc/tree-object-size.cc:
/* 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);
we can cleanly see that _26 is an uninitialized variable, whose initialization
has been eliminated by the previous optimization already due to it's not used
in IL at all.
>From a-t.c.007.gimple, the initialization to the "element_size" is still
available as:
_7 = (sizetype) m.0;
_8 = _7 * 4;
D.4602 = _8;
the above is eliminated by dse1.
So, it's not reliable to get the "element_size" from the TYPE_SIZE_UNIT of the
TYPE of the VLA type.
