Re: [PATCH] c++: equivalence of non-dependent calls [PR107461]

[Jason Merrill <jason@redhat.com>]

On 2/4/23 15:31, Patrick Palka wrote:
> After r13-5684-g59e0376f607805 the (pruned) callee of a non-dependent
> CALL_EXPR is a bare FUNCTION_DECL rather than ADDR_EXPR of FUNCTION_DECL.
> This innocent change revealed that cp_tree_equal doesn't first check
> dependentness of a CALL_EXPR before treating the callee as a dependent
> name, which manifests as us incorrectly accepting the first two
> testcases below and rejecting the third:
> 
>   * In the first testcase, cp_tree_equal incorrectly returns true for
>     the two non-dependent CALL_EXPRs f(0) and f(0) (whose CALL_EXPR_FN
>     are different FUNCTION_DECLs) and so we treat #2 as a redeclaration
>     of #1.
> 
>   * Same issue in the second testcase, for f<int*>() and f<char>().
> 
>   * In the third testcase, cp_tree_equal incorrectly returns true for
>     f<int>() and f<void(*)(int)>() which causes us to conflate the two
>     dependent specializations A<decltype(f<int>()(U()))> and
>     A<decltype(f<void(*)(int)>()(U()))>, leading to a bogus error.
> 
> This patch fixes this by making called_fns_equal treat two callees as
> dependent names only if the CALL_EXPRs in question are dependent.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk/12?  Patch generated with -w to ignore noisy whitespace changes.
> 
> 	PR c++/107461
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (iterative_hash_template_arg) <case CALL_EXPR>: Treat
> 	the callee as a dependent name only if the CALL_EXPR is
> 	dependent.
> 	* tree.cc (called_fns_equal): Take two CALL_EXPRs instead of
> 	CALL_EXPR_FNs thereof.  As above.
> 	(cp_tree_equal) <case CALL_EXPR>: Adjust call to called_fns_equal.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/overload5.C: New test.
> 	* g++.dg/cpp0x/overload5a.C: New test.
> 	* g++.dg/cpp0x/overload6.C: New test.
> ---
>   gcc/cp/pt.cc                            |  1 +
>   gcc/cp/tree.cc                          | 33 ++++++++++++++-----------
>   gcc/testsuite/g++.dg/cpp0x/overload5.C  | 12 +++++++++
>   gcc/testsuite/g++.dg/cpp0x/overload5a.C | 10 ++++++++
>   gcc/testsuite/g++.dg/cpp0x/overload6.C  | 16 ++++++++++++
>   5 files changed, 58 insertions(+), 14 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/overload5.C
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/overload5a.C
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/overload6.C
> 
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 255332dc0c1..c9360240cd2 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -1841,6 +1841,7 @@ iterative_hash_template_arg (tree arg, hashval_t val)
>       case CALL_EXPR:
>         {
>   	tree fn = CALL_EXPR_FN (arg);
> +	if (TREE_TYPE (arg) == NULL_TREE)

How about changing dependent_name to take the CALL_EXPR rather than the 
CALL_EXPR_FN?  That would mean some changes to write_expression to move 
the dependent_name handling into the CALL_EXPR handling, but that 
doesn't seem like a bad thing.  Other callers seem like a trivial change.

>   	  if (tree name = dependent_name (fn))
>   	    {
>   	      if (TREE_CODE (fn) == TEMPLATE_ID_EXPR)
> diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
> index c1da868732b..3a57e71b76e 100644
> --- a/gcc/cp/tree.cc
> +++ b/gcc/cp/tree.cc
> @@ -3870,16 +3870,21 @@ decl_internal_context_p (const_tree decl)
>     return !TREE_PUBLIC (decl);
>   }
>   
> -/* Subroutine of cp_tree_equal: t1 and t2 are the CALL_EXPR_FNs of two
> -   CALL_EXPRS.  Return whether they are equivalent.  */
> +/* Subroutine of cp_tree_equal: t1 and t2 are two CALL_EXPRs.
> +   Return whether their CALL_EXPR_FNs are equivalent.  */
>   
>   static bool
>   called_fns_equal (tree t1, tree t2)
> +{
> +  tree fn1 = CALL_EXPR_FN (t1);
> +  tree fn2 = CALL_EXPR_FN (t2);
> +  if (TREE_TYPE (t1) == NULL_TREE
> +      && TREE_TYPE (t2) == NULL_TREE)
>       {
>         /* Core 1321: dependent names are equivalent even if the overload sets
>   	 are different.  But do compare explicit template arguments.  */
> -  tree name1 = dependent_name (t1);
> -  tree name2 = dependent_name (t2);
> +      tree name1 = dependent_name (fn1);
> +      tree name2 = dependent_name (fn2);
>         if (name1 || name2)
>   	{
>   	  tree targs1 = NULL_TREE, targs2 = NULL_TREE;
> @@ -3891,19 +3896,19 @@ called_fns_equal (tree t1, tree t2)
>   	     of whether the function was named with a qualified- or unqualified-id.
>   	     Until that's fixed, check that we aren't looking at overload sets from
>   	     different scopes.  */
> -      if (is_overloaded_fn (t1) && is_overloaded_fn (t2)
> -	  && (DECL_CONTEXT (get_first_fn (t1))
> -	      != DECL_CONTEXT (get_first_fn (t2))))
> +	  if (is_overloaded_fn (fn1) && is_overloaded_fn (fn2)
> +	      && (DECL_CONTEXT (get_first_fn (fn1))
> +		  != DECL_CONTEXT (get_first_fn (fn2))))
>   	    return false;
>   
> -      if (TREE_CODE (t1) == TEMPLATE_ID_EXPR)
> -	targs1 = TREE_OPERAND (t1, 1);
> -      if (TREE_CODE (t2) == TEMPLATE_ID_EXPR)
> -	targs2 = TREE_OPERAND (t2, 1);
> +	  if (TREE_CODE (fn1) == TEMPLATE_ID_EXPR)
> +	    targs1 = TREE_OPERAND (fn1, 1);
> +	  if (TREE_CODE (fn2) == TEMPLATE_ID_EXPR)
> +	    targs2 = TREE_OPERAND (fn2, 1);
>   	  return cp_tree_equal (targs1, targs2);
>   	}
> -  else
> -    return cp_tree_equal (t1, t2);
> +    }
> +  return cp_tree_equal (fn1, fn2);
>   }
>   
>   bool comparing_override_contracts;
> @@ -4037,7 +4042,7 @@ cp_tree_equal (tree t1, tree t2)
>   	if (KOENIG_LOOKUP_P (t1) != KOENIG_LOOKUP_P (t2))
>   	  return false;
>   
> -	if (!called_fns_equal (CALL_EXPR_FN (t1), CALL_EXPR_FN (t2)))
> +	if (!called_fns_equal (t1, t2))
>   	  return false;
>   
>   	call_expr_arg_iterator iter1, iter2;
> diff --git a/gcc/testsuite/g++.dg/cpp0x/overload5.C b/gcc/testsuite/g++.dg/cpp0x/overload5.C
> new file mode 100644
> index 00000000000..e05b1594f51
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/overload5.C
> @@ -0,0 +1,12 @@
> +// PR c++/107461
> +// { dg-do compile { target c++11 } }
> +
> +int f(...);
> +template<class T> decltype(T() + f(0)) g(); // #1
> +
> +char f(int);
> +template<class T> decltype(T() + f(0)) g(); // #2, distinct from #1
> +
> +int main() {
> +  g<int>(); // { dg-error "ambiguous" }
> +}
> diff --git a/gcc/testsuite/g++.dg/cpp0x/overload5a.C b/gcc/testsuite/g++.dg/cpp0x/overload5a.C
> new file mode 100644
> index 00000000000..037114f199c
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/overload5a.C
> @@ -0,0 +1,10 @@
> +// PR c++/107461
> +// { dg-do compile { target c++11 } }
> +
> +template<class T> T f();
> +template<class T> decltype(T() + f<int*>()) g(); // #1
> +template<class T> decltype(T() + f<char>()) g(); // #2, distinct from #1
> +
> +int main() {
> +  g<int>(); // { dg-error "ambiguous" }
> +}
> diff --git a/gcc/testsuite/g++.dg/cpp0x/overload6.C b/gcc/testsuite/g++.dg/cpp0x/overload6.C
> new file mode 100644
> index 00000000000..1fbee0501de
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/overload6.C
> @@ -0,0 +1,16 @@
> +// PR c++/107461
> +// { dg-do compile { target c++11 } }
> +
> +template<class T> T f();
> +
> +template<class> struct A { };
> +
> +template<class T> struct B {
> +  template<class U, class = A<decltype(f<T>()(U()))>>
> +  static void g(U);
> +};
> +
> +int main() {
> +  B<int> b;
> +  B<void(*)(int)>::g(0); // { dg-bogus "no match" }
> +}