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

[Patrick Palka <ppalka@redhat.com>]

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?

>  
> 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
> 
>