Re: [PATCH v2] c++: fix ICE with -Wduplicated-cond [PR107593]

[Jason Merrill <jason@redhat.com>]

On 1/30/23 11:00, Marek Polacek wrote:
> On Fri, Jan 27, 2023 at 06:17:00PM -0500, Patrick Palka wrote:
>> On Fri, 27 Jan 2023, Marek Polacek wrote:
>>
>>> On Fri, Jan 27, 2023 at 05:15:00PM -0500, 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?
>>>
>>> warn_duplicated_cond_add_or_warn lives in c-family/c-warn.cc so I can't
>>> use instantiation_dependent_expression_p there.  Sure, I could write a
>>> C++ wrapper but with my patch we just won't add CONDITION to the chain
>>> which I thought would work just as well.

Or maybe define instantiation_dependent_expression_p in the C front-end 
to just return false?

>> Ah that's unfortunate :( ISTM desirable to conservatively assume an
>> inst-dep cond has side effects though (possibly directly from
>> cp_parser_selection_statement), to avoid false positives as in:
>>
>>    int n;
>>
>>    template<class T> bool g() { n = 42; }
>>
>>    template<class T>
>>    void f() {
>>      if (n)
>>        ;
>>      else if (g<T>())
>>        ;
>>      else if (n)
>>        ;
>>    }
> 
> You're right, we shouldn't warn there.  So I've just added a new param
> with a default argument.  A new PR was just opened for the same problem
> so I've added another test.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> 
> -- >8 --
> 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.  Also destroy the chain when
> an inst-dependent expression is encountered to not warn in
> Wduplicated-cond4.C.
> 
> 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;
> 
> 	PR c++/107593
> 	PR c++/108597
> 
> gcc/c-family/ChangeLog:
> 
> 	* c-common.h (warn_duplicated_cond_add_or_warn): New parameter.
> 	* c-warn.cc (warn_duplicated_cond_add_or_warn): Add new parameter.
> 	Use it.
> 
> gcc/cp/ChangeLog:
> 
> 	* parser.cc (cp_parser_selection_statement): Pass the result of
> 	instantiation_dependent_expression_p down to
> 	warn_duplicated_cond_add_or_warn.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/warn/Wduplicated-cond3.C: New test.
> 	* g++.dg/warn/Wduplicated-cond4.C: New test.
> 	* g++.dg/warn/Wduplicated-cond5.C: New test.
> ---
>   gcc/c-family/c-common.h                       |  3 +-
>   gcc/c-family/c-warn.cc                        |  5 ++-
>   gcc/cp/parser.cc                              |  8 +++-
>   gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C | 38 +++++++++++++++++++
>   gcc/testsuite/g++.dg/warn/Wduplicated-cond4.C | 17 +++++++++
>   gcc/testsuite/g++.dg/warn/Wduplicated-cond5.C | 16 ++++++++
>   6 files changed, 82 insertions(+), 5 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wduplicated-cond4.C
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wduplicated-cond5.C
> 
> diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
> index bb6271d4a83..a9b47e15894 100644
> --- a/gcc/c-family/c-common.h
> +++ b/gcc/c-family/c-common.h
> @@ -1514,7 +1514,8 @@ extern void maybe_record_typedef_use (tree);
>   extern void maybe_warn_unused_local_typedefs (void);
>   extern void maybe_warn_bool_compare (location_t, enum tree_code, tree, tree);
>   extern bool maybe_warn_shift_overflow (location_t, tree, tree);
> -extern void warn_duplicated_cond_add_or_warn (location_t, tree, vec<tree> **);
> +extern void warn_duplicated_cond_add_or_warn (location_t, tree, vec<tree> **,
> +					      bool = false);
>   extern bool diagnose_mismatched_attributes (tree, tree);
>   extern tree do_warn_duplicated_branches_r (tree *, int *, void *);
>   extern void warn_for_multistatement_macros (location_t, location_t,
> diff --git a/gcc/c-family/c-warn.cc b/gcc/c-family/c-warn.cc
> index 5ed7bcab16a..b7621656f89 100644
> --- a/gcc/c-family/c-warn.cc
> +++ b/gcc/c-family/c-warn.cc
> @@ -2529,13 +2529,14 @@ maybe_warn_unused_local_typedefs (void)
>      of COND.  */
>   
>   void
> -warn_duplicated_cond_add_or_warn (location_t loc, tree cond, vec<tree> **chain)
> +warn_duplicated_cond_add_or_warn (location_t loc, tree cond, vec<tree> **chain,
> +				  bool dependent_p /*=false*/)
>   {
>     /* No chain has been created yet.  Do nothing.  */
>     if (*chain == NULL)
>       return;
>   
> -  if (TREE_SIDE_EFFECTS (cond))
> +  if (dependent_p || TREE_SIDE_EFFECTS (cond))
>       {
>         /* Uh-oh!  This condition has a side-effect, thus invalidates
>   	 the whole chain.  */
> diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> index 4cdc1cd472f..d62db229518 100644
> --- a/gcc/cp/parser.cc
> +++ b/gcc/cp/parser.cc
> @@ -13210,8 +13210,12 @@ cp_parser_selection_statement (cp_parser* parser, bool *if_p,
>   	    condition = finish_if_stmt_cond (condition, statement);
>   
>   	    if (warn_duplicated_cond)
> -	      warn_duplicated_cond_add_or_warn (token->location, condition,
> -						&chain);
> +	      {
> +		const bool dep
> +		  = instantiation_dependent_expression_p (condition);
> +		warn_duplicated_cond_add_or_warn (token->location, condition,
> +						  &chain, dep);
> +	      }
>   
>   	    /* Parse the then-clause.  */
>   	    in_statement = parser->in_statement;
> 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);
> +}
> diff --git a/gcc/testsuite/g++.dg/warn/Wduplicated-cond4.C b/gcc/testsuite/g++.dg/warn/Wduplicated-cond4.C
> new file mode 100644
> index 00000000000..41bb9f09b4f
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wduplicated-cond4.C
> @@ -0,0 +1,17 @@
> +// PR c++/107593
> +// { dg-do compile }
> +// { dg-options "-Wduplicated-cond" }
> +
> +int n;
> +
> +template<class T> bool g() { n = 42; return false; }
> +
> +template<class T>
> +void f() {
> +  if (n)
> +    ;
> +  else if (g<T>())
> +    ;
> +  else if (n)
> +    ;
> +}
> diff --git a/gcc/testsuite/g++.dg/warn/Wduplicated-cond5.C b/gcc/testsuite/g++.dg/warn/Wduplicated-cond5.C
> new file mode 100644
> index 00000000000..23a0bf212b5
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wduplicated-cond5.C
> @@ -0,0 +1,16 @@
> +// PR c++/108597
> +// { dg-do compile }
> +// { dg-options "-Wduplicated-cond" }
> +
> +template <typename T>
> +struct MyStruct {
> +
> +    void check(int &x) {
> +        if (&x == &_a) {
> +        } else if (&x == &_b) {
> +        }
> +    }
> +
> +    int _a;
> +    int _b;
> +};
> 
> base-commit: 5f8950b403f6351f125d8281d2e7430a43e7d125