Hi,
After more study of all the discussion so far and the corresponding code for
suppress_warning, I think the following suggestion
Should be the best approach right now for this issue:
> SET_EXPR_LOCATION (tmp_dst, UNKNOWN_LOCATION);
> suppress_warning (tmp_dst, OPT_Wuninitialized);
> with a comment explaing why we do that?
The reason is:
After “SET_EXPR_LOCATION (tmp_dst, UNKNOWN_LOCATION)”,
152 /* Enable, or by default disable, a warning for the expression.
153 The wildcard OPT of -1 controls all warnings. */
154
155 void
156 suppress_warning (tree expr, opt_code opt /* = all_warnings */,
157 bool supp /* = true */)
158 {
159 if (opt == no_warning)
160 return;
161
162 const location_t loc = get_location (expr);
163
164 if (!RESERVED_LOCATION_P (loc))
165 supp = suppress_warning_at (loc, opt, supp) || supp;
166 set_no_warning_bit (expr, supp);
167 }
Suppress_warning will NOT call “suppress_warning_at” to involve any operation
on the hash tables. It just
simply call “set_no_warning_bit” to set the no_warning bit for the MEM_REF
expr.
And later during the routine “maybe_warn_operand” in tree-sea-uninit.cc,
“get_no_uninit_warning” will also
Simply check the no_warning bit of the MEM_REF to see whether the warning need
to be issued.
This resolved all the concerns we have so far.
I will prepare the patch based on this approach.
Let me know your opinion.
Qing
> On Feb 25, 2022, at 4:04 AM, Jakub Jelinek via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>
> On Fri, Feb 25, 2022 at 10:31:50AM +0100, Richard Biener wrote:
>> I think it's used as fallback for UNKNOWN_LOCATION, but if we "invent"
>> a creative location for the artificial stmt it will of course
>> affect other stmts/expressions using that location.
>>
>>> I think it will work.
>>
>> Yes, I think so. OTOH the uninit pass does
>>
>> /* Avoid warning if we've already done so or if the warning has been
>> suppressed. */
>> if (((warning_suppressed_p (context, OPT_Wuninitialized)
>> || (gimple_assign_single_p (context)
>> && get_no_uninit_warning (gimple_assign_rhs1 (context)))))
>> || (var && get_no_uninit_warning (var))
>> || (var_name_str
>> && warning_suppressed_p (var_def_stmt, OPT_Wuninitialized)))
>> return;
>>
>> that's a mightly complicated way to test and I'm not sure we get
>> to the bit on the stmt reliably. So maybe TREE_NO_WARNING on the
>> reference (or making sure it has UNKNOWN_LOCATION and using
>> suppress_warning on it) is a better idea after all...
>
> So
> SET_EXPR_LOCATION (tmp_dst, UNKNOWN_LOCATION);
> suppress_warning (tmp_dst, OPT_Wuninitialized);
> with a comment explaing why we do that?
> LGTM.
>
> Jakub
>
