Hi,
I have met the following issue when I tried to implement the following into
tree-object-size.cc:
(And this took me quite some time, still don’t know what’s the best solution)
> On Apr 16, 2025, at 10:46, Qing Zhao <qing.z...@oracle.com> wrote:
>
> 3. When generating the reference to the field member in tree-object-size, we
> should guard this reference with a checking
> on the pointer to the structure is valid. i.e:
>
> struct annotated {
> size_t count;
> char array[] __attribute__((counted_by (count)));
> };
>
> static size_t __attribute__((__noinline__)) size_of (struct annotated * obj)
> {
> return __builtin_dynamic_object_size (obj, 1);
> }
>
> When we try to generate the reference to obj->count when evaluating
> __builtin_dynamic_object_size (obj, 1),
> We should generate the following:
>
> If (obj != NULL)
> * (&obj->count)
>
> To make sure that the pointer to the structure object is valid first.
>
Then as I generate the following size_expr in tree-object-size.cc:
Breakpoint 1, gimplify_size_expressions (osi=0xffffffffdf30)
at ../../latest-gcc-write/gcc/tree-object-size.cc:1178
1178 force_gimple_operand (size_expr, &seq, true, NULL);
(gdb) call debug_generic_expr(size_expr)
_4 = obj_2(D) != 0B ? (sizetype) (int) MAX_EXPR <(sizetype) MAX_EXPR <MEM <int>
[(void *)&*obj_2(D)], 0> + 4, 4> : 18446744073709551615
When calling “force_gimple_operand” for the above size_expr, I got the
following ICE in gimplify_modify_expr, at gimplify.cc:7505:
(gdb) c
Continuing.
during GIMPLE pass: objsz
dump file: a-t.c.110t.objsz1
In function ‘size_of’:
cc1: internal compiler error: in gimplify_modify_expr, at gimplify.cc:7505
0x36feb67 internal_error(char const*, ...)
../../latest-gcc-write/gcc/diagnostic-global-context.cc:517
0x36ccd67 fancy_abort(char const*, int, char const*)
../../latest-gcc-write/gcc/diagnostic.cc:1749
0x14fa8ab gimplify_modify_expr
../../latest-gcc-write/gcc/gimplify.cc:7505
0x15354c3 gimplify_expr(tree_node**, gimple**, gimple**, bool (*)(tree_node*),
int)
../../latest-gcc-write/gcc/gimplify.cc:19530
0x14fe1b3 gimplify_stmt(tree_node**, gimple**)
../../latest-gcc-write/gcc/gimplify.cc:8458
….
0x1b07757 gimplify_size_expressions
../../latest-gcc-write/gcc/tree-object-size.cc:1178
I debugged into this a little bit, and found that the following are the reason
for the assertion failure in the routine “gimplify_modify_expr” of gimplify.cc:
1. The assertion failure is:
7502 if (gimplify_ctxp->into_ssa && is_gimple_reg (*to_p))
7503 {
7504 /* We should have got an SSA name from the start. */
7505 gcc_assert (TREE_CODE (*to_p) == SSA_NAME
7506 || ! gimple_in_ssa_p (cfun));
7507 }
2. The above assertion failure is issued for the following temporary tree:
(gdb) call debug_generic_expr(*to_p)
iftmp.2
(gdb) call debug_generic_expr(*expr_p)
iftmp.2 = (sizetype) _10
In the above, the temporary variable “iftmp.2” triggered the assertion since
it’s NOT a SSA_NAME but the gimple_in_ssa_p (cfun) is TRUE.
3. As I checked, this temporary variable “iftmp.2” was generated at line 5498
in the routine “gimplify_cond_expr” of gimplify.cc:
5477 /* If this COND_EXPR has a value, copy the values into a temporary
within
5478 the arms. */
5479 if (!VOID_TYPE_P (type))
5480 {
…..
5498 tmp = create_tmp_var (type, "iftmp”);
...
5537 }
4. And then later, this temporary created here “iftmp.2” triggered the
assertion failure.
Right now, I have the following questions:
1. Can I generate a size_expr as complicate as the following in
tree-object-size.cc:
_4 = obj_2(D) != 0B ? (sizetype) (int) MAX_EXPR <(sizetype) MAX_EXPR <MEM <int>
[(void *)&*obj_2(D)], 0> + 4, 4> : 18446744073709551615
2. If Yes to 1, is this a bug in “gimplify_cond_expr”? Shall we call
“make_ssa_name” after the call to “create_tmp_var” if “gimple_in_ssa_p(cfun)”
is TRUE?
3. If No to 1, how can we check whether the pointer is zero before dereference
from it to access its field?
Thanks a lot for any hints.
Qing
