Re: [PATCH] c++: fix ICE with -Wduplicated-cond [PR107593]

[Jason Merrill <jason@redhat.com>]

On 1/27/23 17:15, Patrick Palka wrote:
> On Thu, 26 Jan 2023, Marek Polacek via Gcc-patches wrote:
> 
>> Here we crash because a CAST_EXPR, representing T(), doesn't have
>> its operand, and operand_equal_p's STRIP_ANY_LOCATION_WRAPPER doesn't
>> expect that.  (o_e_p is called from warn_duplicated_cond_add_or_warn.)
>>
>> In the past we've adjusted o_e_p to better cope with template codes,
>> but in this case I think we just want to avoid attempting to warn
>> about inst-dependent expressions; I don't think I've ever envisioned
>> -Wduplicated-cond to warn about them.
>>
>> The ICE started with r12-6022, two-stage name lookup for overloaded
>> operators, which gave dependent operators a TREE_TYPE (in particular,
>> DEPENDENT_OPERATOR_TYPE), so we no longer bail out here in o_e_p:
>>
>>    /* Similar, if either does not have a type (like a template id),
>>       they aren't equal.  */
>>    if (!TREE_TYPE (arg0) || !TREE_TYPE (arg1))
>>      return false;
>>
>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>>
>> 	PR c++/107593
>>
>> gcc/cp/ChangeLog:
>>
>> 	* parser.cc (cp_parser_selection_statement): Don't do
>> 	-Wduplicated-cond when the condition is dependent.
>>
>> gcc/testsuite/ChangeLog:
>>
>> 	* g++.dg/warn/Wduplicated-cond3.C: New test.
>> ---
>>   gcc/cp/parser.cc                              |  3 +-
>>   gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C | 38 +++++++++++++++++++
>>   2 files changed, 40 insertions(+), 1 deletion(-)
>>   create mode 100644 gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C
>>
>> diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
>> index 4cdc1cd472f..3df85d49e16 100644
>> --- a/gcc/cp/parser.cc
>> +++ b/gcc/cp/parser.cc
>> @@ -13209,7 +13209,8 @@ cp_parser_selection_statement (cp_parser* parser, bool *if_p,
>>   	    /* Add the condition.  */
>>   	    condition = finish_if_stmt_cond (condition, statement);
>>   
>> -	    if (warn_duplicated_cond)
>> +	    if (warn_duplicated_cond
>> +		&& !instantiation_dependent_expression_p (condition))
>>   	      warn_duplicated_cond_add_or_warn (token->location, condition,
>>   						&chain);
> 
> I noticed warn_duplicated_cond_add_or_warn already has logic to handle
> TREE_SIDE_EFFECTS conditions by invaliding the entire chain.  I wonder
> if we'd want to do the same for instantiation-dep conditions?

Makes sense.

>>   
>> diff --git a/gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C b/gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C
>> new file mode 100644
>> index 00000000000..3da054e5485
>> --- /dev/null
>> +++ b/gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C
>> @@ -0,0 +1,38 @@
>> +// PR c++/107593
>> +// { dg-do compile }
>> +// { dg-options "-Wduplicated-cond" }
>> +
>> +template <typename T>
>> +void
>> +foo ()
>> +{
>> +  if (T() && T() && int())
>> +    ;
>> +  else if (T() && T() && int())
>> +    ;
>> +}
>> +
>> +template <typename T>
>> +void bar(T a)
>> +{
>> +  if (a)
>> +    ;
>> +  else if (a)
>> +    ;
>> +}
>> +
>> +template <typename>
>> +void baz(int a)
>> +{
>> +  if (a)
>> +    ;
>> +  else if (a) // { dg-warning "duplicated" }
>> +    ;
>> +}
>> +void
>> +f ()
>> +{
>> +  foo<int>();
>> +  bar(1);
>> +  baz<int>(1);
>> +}
>>
>> base-commit: 94673a121cfc7f9d51c9d05e31795477f4dc8dc7
>> -- 
>> 2.39.1
>>
>>
>