Re: [PATCH] Fix PR 101515 (ICE in pp_cxx_unqualified_id, at cp/cxx-pretty-print.c:128)

[Qing Zhao <qing.zhao@oracle.com>]

> On Feb 11, 2022, at 1:39 PM, Jason Merrill <jason@redhat.com> wrote:
> 
> On 2/11/22 13:11, Qing Zhao wrote:
>> Hi, Jason,
>>> On Feb 11, 2022, at 11:27 AM, Jason Merrill <jason@redhat.com> wrote:
>>>>>> 
>>>>>> Sure, we might as well make this code more robust.  But we can do better than <unnamed type> if we check TYPE_PTRMEMFUNC_P.
>>>>> Okay, so what should we print to the user if it's “TYPE_PTRMEMFUNC_P”? Print nothing or some special string?
>>>>>> 
>>>>>>> 2. The second level issue is what you suggested in the above, shall we print the “compiler generated internal type”  to the user? And I agree with you that it might not be a good idea to print such compiler internal names to the user.  Are we do this right now in general? (i.e, check whether the current TYPE is a source level TYPE or a compiler internal TYPE, and then only print out the name of TYPE for the source level TYPE?) and is there a bit in the TYPE to distinguish whether a TYPE is user -level type or a compiler generated internal type?
>>>>>> 
>>>>>>>> I think the real problem comes sooner, when c_fold_indirect_ref_for_warn turns a MEM_REF with RECORD_TYPE into a COMPONENT_REF with POINTER_TYPE.
>>>>>> 
>>>>>>> What’s the major issue for this transformation? (I will study this in more details).
>>>>>> 
>>>>>> We told c_fold_indirect_ref that we want a RECORD_TYPE (the PMF as a whole) and it gave us back a POINTER_TYPE instead (the __pmf member). Folding shouldn't change the type of an expression like that.
>>>>> 
>>>>> Yes, this is not correct transformation, will study in more detail and try to fix it.
>>>> After a deeper study of commit  r11-6729-gadb520606ce3e1e1 (which triggered the ICE and introduced the new routine “c_fold_indirect_ref_for_warn”), from my understanding,  the above transformation from a RECORD_TYPE (the PMF as a whole) to POINTER_TYPE (the __pmf member) is what the function intended to do as following:
>>>> 1823 static tree
>>>> 1824 c_fold_indirect_ref_for_warn (location_t loc, tree type, tree op,
>>>> 1825                               offset_int &off)
>>>> 1826 {
>>>> …
>>>> 1870 */* ((foo *)&struct_with_foo_field)[x] => COMPONENT_REF */*
>>>> 1871   else if (TREE_CODE (optype) == RECORD_TYPE)
>>>> 1872     {
>>>> 1873       for (tree field = TYPE_FIELDS (optype);
>>>> 1874            field; field = DECL_CHAIN (field))
>>>> 1875         if (TREE_CODE (field) == FIELD_DECL
>>>> …
>>>> 1886 if(upos <= off && off < upos + el_sz)
>>>> 1887               {
>>>> 1888                 tree cop = build3_loc (loc, COMPONENT_REF, TREE_TYPE (field),
>>>> 1889                                       op, field, NULL_TREE);
>>>> 1890                 off = off - upos;
>>>> The above code was used to transform a MEM_REF to a RECORD_TYPE to a COMPONENT_REF to the corresponding FIELD.
>>> 
>>> Yes, that's what the above code would correctly do if TYPE were the pointer-to-method type.  It's wrong for this case because TYPE is unrelated to TREE_TYPE (field).
>>> 
>>> I think the problem is just this line:
>>> 
>>>>                if (tree ret = c_fold_indirect_ref_for_warn (loc, type, cop,
>>>>                                                             off))
>>>>                  return ret;
>>>>                return cop;
>>>                  ^^^^^^^^^^
>>> 
>>> The recursive call does the proper type checking, but then the "return cop" line returns the COMPONENT_REF even though the type check failed. The parallel code in cxx_fold_indirect_ref_1 doesn't have this line,
>> Just compared the routine “cxx_fold_indirect_ref_1” and “c_fold_indirect_ref_for_warn”, looks like there are more places that have such difference, for example,
>> In “cxx_fold_indirect_ref_1”:
>>   /* ((foo *)&fooarray)[x] => fooarray[x] */
>>   else if (TREE_CODE (optype) == ARRAY_TYPE
>>            && tree_fits_uhwi_p (TYPE_SIZE_UNIT (TREE_TYPE (optype)))
>>            && !integer_zerop (TYPE_SIZE_UNIT (TREE_TYPE (optype))))
>> …
>>       if (tree_fits_uhwi_p (min_val))
>>         {
>>           tree index = size_int (idx + tree_to_uhwi (min_val));
>>           op = build4_loc (loc, ARRAY_REF, TREE_TYPE (optype), op, index,
>>                            NULL_TREE, NULL_TREE);
>> 	  return cxx_fold_indirect_ref_1 (ctx, loc, type, op, rem,
>>                                           empty_base);
>> 	}
>> However, in “c_fold_indirect_ref_for_warn”, the corresponding part is:
>>   /* ((foo *)&fooarray)[x] => fooarray[x] */
>>   if (TREE_CODE (optype) == ARRAY_TYPE
>>       && TYPE_SIZE_UNIT (TREE_TYPE (optype))
>>       && TREE_CODE (TYPE_SIZE_UNIT (TREE_TYPE (optype))) == INTEGER_CST
>>       && !integer_zerop (TYPE_SIZE_UNIT (TREE_TYPE (optype))))
>> …
>>       if (TREE_CODE (min_val) == INTEGER_CST)
>>         {
>>           tree index
>>             = wide_int_to_tree (sizetype, idx + wi::to_offset (min_val));
>>           op = build4_loc (loc, ARRAY_REF, TREE_TYPE (optype), op, index,
>>                            NULL_TREE, NULL_TREE);
>>           off = rem;
>>           if (tree ret = c_fold_indirect_ref_for_warn (loc, type, op, off))
>>             return ret;
>>           return op;
>>         }
>> The exactly same difference as for “RECORD_TYPE”. So, I suspect that it’s a typo for “RECORD_TYPE” in “c_fold_indirect_ref_for_warn”.
>>> and removing it fixes the testcase, so I see
>>> 
>>> warning: ‘*(ptrmemfunc*)&x.ptrmemfunc::ptr’ is used uninitialized
>> The question is:
>> For the following IR:
>>   struct sp x;
>>   void (*<T389>) (void) _1;
>>  ...
>>   <bb 2> [local count: 1073741824]:
>>   _1 = MEM[(struct ptrmemfunc_U *)&x].ptr;
>>   _7 = _1 != 8B;
>> Which message is better:
>> 1. warning: ‘*(ptrmemfunc*)&x.ptrmemfunc::ptr’ is used uninitialized
>> Or
>> 2. warning: ‘*(ptrmemfunc*)((char*)&x + offsetof(void (S::*)(),__PTRMEMFUNC)).ptrmemfunc::ptr’ is used uninitialized
>> From the source code:
>> ====
>> struct S
>> {
>>   int j;
>> };
>> struct T : public S
>> {
>>   virtual void h () {}
>> };
>> struct ptrmemfunc
>> {
>>   void (*ptr) ();
>> };
>> typedef void (S::*sp)();
>> int main ()
>> {
>>   T t;
>>   sp x;
>>   ptrmemfunc *xp = (ptrmemfunc *) &x;
>>   if (xp->ptr != ((void (*)())(sizeof(void *))))
>>     return 1;
>> }
>> ====
>> The reference “xp->ptr” went through from “x” to “xp”, and there is a clear type casting from S::__PTRMEMFUNC to ptrmemfunc::ptr.
>> Shall we emit such type casting to the user?
> 
> But there is no such cast in the source; the cast is (ptrmemfunc*)&x, which appears in the fixed message.

still a little confused here:  the original type for “x” is “sp” (is “sp” equal to “S::__PTRMEMFUNC”?), then it was casted to “ptrmemfunc *”.
So, should this type conversion from “S::__PTRMEMFUNC” to “ptrmemfunc *” be exposed to the user in the message? 

Qing
> 
> Though *(ptrmemfunc*)&x.ptrmemfunc::ptr is wrong syntax, it should be ((ptrmemfunc*)&x)->ptr
> 
> Jakub, this is your code from r11-6729; from the comment on that commit it sounds like you were deliberately ignoring type incompatibility here, and my suggested fix changes two lines in uninit-40.c.  What do you think should happen for this testcase?
> 
> Jason