> On Apr 28, 2025, at 06:49, Richard Biener <[email protected]> wrote:
>
> On Wed, Apr 23, 2025 at 6:09 PM Qing Zhao <[email protected]> wrote:
>>
>> Richard,
>>
>> Thanks a lot for the hint.
>>
>>> On Apr 23, 2025, at 04:17, Richard Biener <[email protected]>
>>> wrote:
>>>
>>>> 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 <[email protected]> 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:
>>>
>>> You shouldn't really force_gimple_operand to a MODIFY_EXPR but instead
>>> only to its RHS.
>>
>> Do you mean: instead of
>>
>> force_gimple_operand (size_expr, &seq, true, NULL);
>>
>> I should
>>
>> 1178 if (TREE_CODE (size_expr) == MODIFY_EXPR)
>> 1179 {
>> 1180 tree rhs = TREE_OPERAND (size_expr, 1);
>> 1181 force_gimple_operand (rhs, &seq, true, NULL);
>> 1182 }
>>
>> ?
>>
>> However, with this change, I got the exactly same error at the above line
>> 1181.
>> (gdb) call debug_generic_expr(rhs)
>> obj_2(D) != 0B ? (sizetype) (int) MAX_EXPR <(sizetype) MAX_EXPR <MEM <int>
>> [(void *)&*obj_2(D)], 0> + 4, 4> : 18446744073709551615
>>
>> The issue is still the same as before.
>> So, I am wondering whether the above size expression I generated has some
>> issue?
>> Or the routine “force_gimple_operand” has some bug when the tree expr is a
>> COND_EXPR expression?
>
> Well, one issue is that the true case can trap while the false case
> does not, and force_gimple_operand
> cannot create a CFG to preserve the conditional execution. If that's
> not an issue you need to
> create the COND_EXPR in gimple form from the start and not try to do
> easy by going though
> gimpification.
Okay, so, I need to create the following:
If (obj != NULL)
size = (sizetype) (int) MAX_EXPR <(sizetype) MAX_EXPR <MEM <int> [(void
*)&*obj_2(D)], 0> + 4, 4>
else
size = -1;
Directly in gimple form and insert it to the control flow of the routine.
Is there a similar example in gcc source code I can take a look at?
Thanks a lot.
Qing
> Richard.
>
>>
>> Thanks.
>>
>> Qing
>>
>> The size_expr is a COND_EXPR:
>>
>> (gdb) call debug_tree(rhs)
>> <cond_expr 0x7fffea281e10
>> type <integer_type 0x7fffea282000 sizetype public unsigned DI
>> size <integer_cst 0x7fffea262f60 constant 64>
>> unit-size <integer_cst 0x7fffea262f78 constant 8>
>> align:64 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
>> 0x7fffea282000 precision:64 min <integer_cst 0x7fffea262f90 0> max
>> <integer_cst 0x7fffea263640 18446744073709551615>>
>>
>> arg:0 <ne_expr 0x7fffea0cd0f0
>> type <boolean_type 0x7fffea282b28 _Bool public unsigned QI
>> size <integer_cst 0x7fffea284060 constant 8>
>> unit-size <integer_cst 0x7fffea284078 constant 1>
>> align:8 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
>> 0x7fffea282b28 precision:1 min <integer_cst 0x7fffea2842b8 0> max
>> <integer_cst 0x7fffea2842e8 1>>
>> arg:0 <ssa_name 0x7fffea26d9d8 type <pointer_type
>> 0x7fffea0bc7e0>
>> visited var <parm_decl 0x7fffea0bb440 obj>
>> def_stmt GIMPLE_NOP
>> version:2
>> ptr-info 0x7fffea091918>
>> arg:1 <integer_cst 0x7fffea091780 constant 0>>
>> arg:1 <nop_expr 0x7fffea0c2680 type <integer_type 0x7fffea282000 sizetype>
>> arg:0 <nop_expr 0x7fffea0c2660 type <integer_type
>> 0x7fffea2825e8 int>
>> arg:0 <max_expr 0x7fffea0cd0a0 type <integer_type
>> 0x7fffea282000 sizetype>
>> arg:0 <plus_expr 0x7fffea0cd078 type
>> <integer_type 0x7fffea282000 sizetype>
>> arg:0 <nop_expr 0x7fffea0c2640 type
>> <integer_type 0x7fffea282000 sizetype>
>> arg:0 <max_expr
>> 0x7fffea0cd050 type <integer_type 0x7fffea2825e8 int>
>> arg:0 <mem_ref 0x7fffea0cd000> arg:1 <integer_cst
>> 0x7fffea284300 0>>>
>> arg:1 <integer_cst 0x7fffea2841c8 constant 4>> arg:1
>> <integer_cst 0x7fffea2841c8 4>>>>
>> arg:2 <integer_cst 0x7fffea263640 type <integer_type 0x7fffea282000
>> sizetype> constant 18446744073709551615>>
>>
>>>
>>>> (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
