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

[Patrick Palka <ppalka@redhat.com>]

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On Sat, 4 Feb 2023, Jason Merrill wrote:

> On 2/4/23 20:41, Jason Merrill wrote:
> > On 2/4/23 20:08, Patrick Palka wrote:
> > > On Sat, 4 Feb 2023, Jason Merrill wrote:
> > > 
> > > > 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.
> > > 
> > > Indeed changing dependent_name seems best, but I'm worried about such a
> > > refactoring to write_expression causing unintended mangling changes at
> > > this stage.  Because it seems the CALL_EXPR case of write_expression
> > > isn't the user of the dependent_name branch of write_expression, at
> > > least according to the following patch which causes us to ICE on
> > > mangle{37,57,58,76}.C:
> > 
> > Yeah, I tried the same thing.  Maybe for GCC 13 better to add a new function
> > rather than change the current one.

Sounds good, like so?  Only regtested so far.  Full bootstrap and
regtest running on x86_64-pc-linux-gnu.

-- >8 --

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

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 a FUNCTION_DECL 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 overall CALL_EXPRs are dependent, via a new
convenience function call_expr_dependent_name that is like dependent_name
but also checks dependence of the overall CALL_EXPR.

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:

	* cp-tree.h (call_expr_dependent_name): Declare.
	* pt.cc (iterative_hash_template_arg) <case CALL_EXPR>: Use
	call_expr_dependent_name instead of dependent_name.
	* tree.cc (call_expr_dependent_name): Define.
	(called_fns_equal): Adjust to take two CALL_EXPRs instead of
	CALL_EXPR_FNs thereof.  Use call_expr_dependent_name instead
	of dependent_name.
	(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/cp-tree.h                        |  1 +
 gcc/cp/pt.cc                            |  2 +-
 gcc/cp/tree.cc                          | 24 +++++++++++++++++++-----
 gcc/testsuite/g++.dg/cpp0x/overload5.C  | 12 ++++++++++++
 gcc/testsuite/g++.dg/cpp0x/overload5a.C | 10 ++++++++++
 gcc/testsuite/g++.dg/cpp0x/overload6.C  | 16 ++++++++++++++++
 6 files changed, 59 insertions(+), 6 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/cp-tree.h b/gcc/cp/cp-tree.h
index 00b2bffc85c..ef601182d4b 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7902,6 +7902,7 @@ extern tree lookup_maybe_add			(tree fns, tree lookup,
 extern int is_overloaded_fn			(tree) ATTRIBUTE_PURE;
 extern bool really_overloaded_fn		(tree) ATTRIBUTE_PURE;
 extern tree dependent_name			(tree);
+extern tree call_expr_dependent_name		(tree);
 extern tree maybe_get_fns			(tree) ATTRIBUTE_PURE;
 extern tree get_fns				(tree) ATTRIBUTE_PURE;
 extern tree get_first_fn			(tree) ATTRIBUTE_PURE;
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 255332dc0c1..9f3fc1fa089 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -1841,7 +1841,7 @@ iterative_hash_template_arg (tree arg, hashval_t val)
     case CALL_EXPR:
       {
 	tree fn = CALL_EXPR_FN (arg);
-	if (tree name = dependent_name (fn))
+	if (tree name = call_expr_dependent_name (arg))
 	  {
 	    if (TREE_CODE (fn) == TEMPLATE_ID_EXPR)
 	      val = iterative_hash_template_arg (TREE_OPERAND (fn, 1), val);
diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index c1da868732b..880bd4f9bcf 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -2608,6 +2608,18 @@ dependent_name (tree x)
   return NULL_TREE;
 }
 
+/* Like dependent_name, but takes the overall CALL_EXPR and checks its
+   dependence.  */
+
+tree
+call_expr_dependent_name (tree x)
+{
+  if (TREE_TYPE (x) != NULL_TREE)
+    /* X isn't dependent, so its callee isn't a dependent name.  */
+    return NULL_TREE;
+  return dependent_name (CALL_EXPR_FN (x));
+}
+
 /* Returns true iff X is an expression for an overloaded function
    whose type cannot be known without performing overload
    resolution.  */
@@ -3870,16 +3882,18 @@ 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)
 {
   /* 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 = call_expr_dependent_name (t1);
+  tree name2 = call_expr_dependent_name (t2);
+  t1 = CALL_EXPR_FN (t1);
+  t2 = CALL_EXPR_FN (t2);
   if (name1 || name2)
     {
       tree targs1 = NULL_TREE, targs2 = NULL_TREE;
@@ -4037,7 +4051,7 @@ 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" }
+}
-- 
2.39.1.409.ga6a323b31e



> 
> mangle76 seems like a bug where we're producing (and testing for) the wrong
> mangling -- mangling (*this). that doesn't exist in the source. clang gets it
> right.
> 
> mangle5{7,8} has the right mangling, we're just using dependent_name to mangle
> function names that aren't dependent names (because they're template arguments
> in both cases, and qualified in the latter).
> 
> > > diff --git a/gcc/cp/mangle.cc b/gcc/cp/mangle.cc
> > > index f2cda3be2cf..700857f8f3c 100644
> > > --- a/gcc/cp/mangle.cc
> > > +++ b/gcc/cp/mangle.cc
> > > @@ -3450,6 +3450,7 @@ write_expression (tree expr)
> > >       }
> > >     else if (dependent_name (expr))
> > >       {
> > > +      gcc_unreachable ();
> > >         tree name = dependent_name (expr);
> > >         if (IDENTIFIER_ANY_OP_P (name))
> > >       {
> > > @@ -3554,7 +3555,19 @@ write_expression (tree expr)
> > >           && type_dependent_expression_p_push (expr))
> > >             fn = OVL_NAME (fn);
> > > -        write_expression (fn);
> > > +        if (tree name = dependent_name (fn))
> > > +          {
> > > +        if (IDENTIFIER_ANY_OP_P (name))
> > > +          {
> > > +            if (abi_version_at_least (16))
> > > +              write_string ("on");
> > > +            if (abi_warn_or_compat_version_crosses (16))
> > > +              G.need_abi_warning = 1;
> > > +          }
> > > +        write_unqualified_id (name);
> > > +          }
> > > +        else
> > > +          write_expression (fn);
> > >         }
> > >         for (i = 0; i < call_expr_nargs (expr); ++i)
> > > 
> > > And since the CALL_EXPR case of write_expression looks through an
> > > ADDR_EXPR callee before recursing, IIUC the refactoring would need to
> > > make dependent_name look through an ADDR_EXPR callee as well, which
> > > seems like a desirable/correct change but I'm worried that might have
> > > unintended consequences as well.
> > > 
> > > > 
> > > > >          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" }
> > > > > +}
> > > > 
> > > > 
> > > 
> > 
> 
>