> On Aug 18, 2021, at 2:19 AM, Richard Biener <rguent...@suse.de> wrote:
>
> On Tue, 17 Aug 2021, Qing Zhao wrote:
>
>>
>>
>>> On Aug 17, 2021, at 10:04 AM, Qing Zhao via Gcc-patches
>>> <gcc-patches@gcc.gnu.org> wrote:
>>>
>>>
>>>
>>>> On Aug 16, 2021, at 11:48 AM, Qing Zhao via Gcc-patches
>>>> <gcc-patches@gcc.gnu.org> wrote:
>>>>
>>>>>> From the above IR file after “FRE”, we can see that the major issue with
>>>>>> this IR is:
>>>>>>
>>>>>> The address taken auto variable “alt_reloc” has been completely replaced
>>>>>> by the temporary variable “_1” in all
>>>>>> the uses of the original “alt_reloc”.
>>>>>
>>>>> Well, this can happen with regular code as well, there's no need for
>>>>> .DEFERRED_INIT. This is the usual problem with reporting uninitialized
>>>>> uses late.
>>>>>
>>>>> IMHO this shouldn't be a blocker. The goal of zero "regressions" wrt
>>>>> -Wuninitialized isn't really achievable.
>>>>
>>>> Okay. Sounds reasonable to me too.
>>>>
>>>>>
>>>>>> The major problem with such IR is, during uninitialized analysis phase,
>>>>>> the original use of “alt_reloc” disappeared completely.
>>>>>> So, the warning cannot be reported.
>>>>>>
>>>>>>
>>>>>> My questions:
>>>>>>
>>>>>> 1. Is it possible to get the original “alt_reloc” through the temporary
>>>>>> variable “_1” with some available information recorded in the IR?
>>>>>> 2. If not, then we have to record the relationship between “alt_reloc”
>>>>>> and “_1” when the original “alt_reloc” is replaced by “_1” and get such
>>>>>> relationship during
>>>>>> Uninitialized analysis phase. Is this doable?
>>>>>
>>>>> Well, you could add a fake argument to .DEFERRED_INIT for the purpose of
>>>>> diagnostics. The difficulty is to avoid tracking it as actual use so
>>>>> you could for example pass a string with the declarations name though
>>>>> this wouldn't give the association with the actual decl.
>>>> Good suggestion, I can try this a little bit.
>>>
>>> I tried this yesterday, added the 4th argument to .DEFERRED_INIT as:
>>>
>>> 1st argument: SIZE of the DECL;
>>> 2nd argument: INIT_TYPE;
>>> 3rd argument: IS_VLA, 0 NO, 1 YES;
>>> + 4th argument: The NAME for the DECL;
>>>
>>> - as LHS = DEFERRED_INIT (SIZE of the DECL, INIT_TYPE, IS_VLA)
>>> + as LHS = DEFERRED_INIT (SIZE of the DECL, INIT_TYPE, IS_VLA, NAME)
>>>
>>> + tree name_node
>>> + = build_string_literal (IDENTIFIER_LENGTH (DECL_NAME (decl)),
>>> + IDENTIFIER_POINTER (DECL_NAME (decl)));
>>>
>>> tree call = build_call_expr_internal_loc (UNKNOWN_LOCATION,
>>> IFN_DEFERRED_INIT,
>>> - TREE_TYPE (decl), 3,
>>> + TREE_TYPE (decl), 4,
>>> decl_size, init_type_node,
>>> - is_vla_node);
>>> + is_vla_node, name_node);
>>>
>>>
>>> And got the following IR in .uninit1 dump:
>>>
>>>
>>> ….
>>>
>>> _1 = .DEFERRED_INIT (4, 2, 0, &"alt_reloc"[0]);
>>> if (_1 != 0)
>>> ….
>>>
>>>
>>> My questions:
>>>
>>> 1. Is “build_string_literal” the correct utility routine to use for this
>>> new argument?
>>> 2. Will Such string literal nodes have potential other impact?
>>
>> I tried to get the 4th argument from the call to .DEFERED_INIT during
>> uninitialized variable analysis in tree-ssa-uninit.c:
>>
>> @@ -197,18 +197,25 @@ warn_uninit (enum opt_code wc, tree t, tree expr, tree
>> var,
>> the COMPLEX_EXPRs real part in that case. See PR71581. */
>> if (expr == NULL_TREE
>> && var == NULL_TREE
>> - && SSA_NAME_VAR (t) == NULL_TREE
>> - && is_gimple_assign (SSA_NAME_DEF_STMT (t))
>> - && gimple_assign_rhs_code (SSA_NAME_DEF_STMT (t)) == COMPLEX_EXPR)
>> - {
>> - tree v = gimple_assign_rhs1 (SSA_NAME_DEF_STMT (t));
>> - if (TREE_CODE (v) == SSA_NAME
>> - && has_undefined_value_p (v)
>> - && zerop (gimple_assign_rhs2 (SSA_NAME_DEF_STMT (t))))
>> + && SSA_NAME_VAR (t) == NULL_TREE)
>> + {
>> + if (is_gimple_assign (SSA_NAME_DEF_STMT (t))
>> + && (gimple_assign_rhs_code (SSA_NAME_DEF_STMT (t)) ==
>> COMPLEX_EXPR))
>> {
>> - expr = SSA_NAME_VAR (v);
>> - var = expr;
>> + tree v = gimple_assign_rhs1 (SSA_NAME_DEF_STMT (t));
>> + if (TREE_CODE (v) == SSA_NAME
>> + && has_undefined_value_p (v)
>> + && zerop (gimple_assign_rhs2 (SSA_NAME_DEF_STMT (t))))
>> + {
>> + expr = SSA_NAME_VAR (v);
>> + var = expr;
>> + }
>> }
>> + else if (gimple_call_internal_p (SSA_NAME_DEF_STMT (t),
>> IFN_DEFERRED_INIT))
>> + {
>> + expr = gimple_call_arg (SSA_NAME_DEF_STMT (t), 3);
>> + var = expr;
>> + }
>> }
>>
>> However, this 4th argument is not a regular variable, it’s just an ADDR_EXPR
>> that includes the constant string for the name of
>> the deleted variable.
>> If we’d like to report the warning based on this ADDR_EXPR, a complete new
>> code to report the warnings other than the current one that based on
>> “Variables” need to be added, this might make the code very ugly.
>>
>> My questions:
>>
>> 1. Is there better way to do this?
>
> Adding a variable as extra argument won't work, so no, I don't see a nice
> way of carrying the extra information. Btw, if you make sure to set
> the location of the .DEFERRED_INIT call to the DECL_SOURCE_LOCATION
> of the decl we initialize,
This should be easy to do.
> we should be able to diagnose sth like
>
> warning: variable is used uninitialized
> note: variable declared here
I.e, report the warnings without the name of the variable?
>
> and point to the correct declartion point which should reveal the
> variable name (to the user, not to the compiler).
>
>> 1. As you mentioned before, it’s very unrealistic to meet the goal of “zero
>> regression” for -Wuninitialized, can we leave this part of work in a later
>> patch to improve
>> The warning for “address taken” auto variables?
>
> Yes, as said, I'd simply ignore this particular issue for now since I
> don't see a good way to fix it.
Okay, I will just ignore this issue for now and resolve it in a later patch.
How about the testing cases that are currently failed due to this issue? Should
I keep them but mark them as expected failure?
Qing
>
> Richard.
