diff mbox series

c++: constexpr error with fn redecl in local scope [PR111132]

Message ID 20240402175237.482119-1-polacek@redhat.com
State New
Headers show
Series c++: constexpr error with fn redecl in local scope [PR111132] | expand

Commit Message

Marek Polacek April 2, 2024, 5:52 p.m. UTC 
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/13?

-- >8 --
We evaluate constexpr functions on the original, pre-genericization bodies.
That means that the function body we're evaluating will not have gone
through cp_genericize_r's "Map block scope extern declarations to visible
declarations with the same name and type in outer scopes if any".  Here:

  constexpr bool bar() { return true; } // #1
  constexpr bool foo() {
    constexpr bool bar(void); // #2
    return bar();
  }

it means that we:
1) register_constexpr_fundef (#1)
2) cp_genericize (#1)
   nothing interesting happens
3) register_constexpr_fundef (foo)
   does copy_fn, so we have two copies of the BIND_EXPR
4) cp_genericize (foo)
   this remaps #2 to #1, but only on one copy of the BIND_EXPR
5) retrieve_constexpr_fundef (foo)
   we find it, no problem
6) retrieve_constexpr_fundef (#2)
   and here #2 isn't found in constexpr_fundef_table, because
   we're working on the BIND_EXPR copy where #2 wasn't mapped to #1
   so we fail.  We've only registered #1.

It should work to use DECL_LOCAL_DECL_ALIAS (which used to be
extern_decl_map).  We evaluate constexpr functions on pre-cp_fold
bodies to avoid diagnostic problems, but the remapping I'm proposing
should not interfere with diagnostics.

This is not a problem for a global scope redeclaration; there we go
through duplicate_decls which keeps the DECL_UID:
  DECL_UID (olddecl) = olddecl_uid;
and DECL_UID is what constexpr_fundef_hasher::hash uses.

	PR c++/111132

gcc/cp/ChangeLog:

	* constexpr.cc (get_function_named_in_call): If there's
	a DECL_LOCAL_DECL_ALIAS, use it.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/constexpr-redeclaration3.C: New test.
	* g++.dg/cpp0x/constexpr-redeclaration4.C: New test.
---
 gcc/cp/constexpr.cc                           | 19 +++++++++++++++----
 .../g++.dg/cpp0x/constexpr-redeclaration3.C   | 13 +++++++++++++
 .../g++.dg/cpp0x/constexpr-redeclaration4.C   | 14 ++++++++++++++
 3 files changed, 42 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration3.C
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration4.C


base-commit: 0e64bbb8823f7b3757befc878ed177dfb59943d1

Comments

Jason Merrill April 3, 2024, 5:14 p.m. UTC | #1 
On 4/2/24 13:52, Marek Polacek wrote:
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/13?
> 
> -- >8 --
> We evaluate constexpr functions on the original, pre-genericization bodies.
> That means that the function body we're evaluating will not have gone
> through cp_genericize_r's "Map block scope extern declarations to visible
> declarations with the same name and type in outer scopes if any".  Here:
> 
>    constexpr bool bar() { return true; } // #1
>    constexpr bool foo() {
>      constexpr bool bar(void); // #2
>      return bar();
>    }
> 
> it means that we:
> 1) register_constexpr_fundef (#1)
> 2) cp_genericize (#1)
>     nothing interesting happens
> 3) register_constexpr_fundef (foo)
>     does copy_fn, so we have two copies of the BIND_EXPR
> 4) cp_genericize (foo)
>     this remaps #2 to #1, but only on one copy of the BIND_EXPR
> 5) retrieve_constexpr_fundef (foo)
>     we find it, no problem
> 6) retrieve_constexpr_fundef (#2)
>     and here #2 isn't found in constexpr_fundef_table, because
>     we're working on the BIND_EXPR copy where #2 wasn't mapped to #1
>     so we fail.  We've only registered #1.
> 
> It should work to use DECL_LOCAL_DECL_ALIAS (which used to be
> extern_decl_map).  We evaluate constexpr functions on pre-cp_fold
> bodies to avoid diagnostic problems, but the remapping I'm proposing
> should not interfere with diagnostics.
> 
> This is not a problem for a global scope redeclaration; there we go
> through duplicate_decls which keeps the DECL_UID:
>    DECL_UID (olddecl) = olddecl_uid;
> and DECL_UID is what constexpr_fundef_hasher::hash uses.
> 
> 	PR c++/111132
> 
> gcc/cp/ChangeLog:
> 
> 	* constexpr.cc (get_function_named_in_call): If there's
> 	a DECL_LOCAL_DECL_ALIAS, use it.

Perhaps this function should use cp_get_fndecl_from_callee, and this 
change should be made there instead?

Jason
Marek Polacek April 4, 2024, 6:43 p.m. UTC | #2 
On Wed, Apr 03, 2024 at 01:14:46PM -0400, Jason Merrill wrote:
> On 4/2/24 13:52, Marek Polacek wrote:
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/13?
> > 
> > -- >8 --
> > We evaluate constexpr functions on the original, pre-genericization bodies.
> > That means that the function body we're evaluating will not have gone
> > through cp_genericize_r's "Map block scope extern declarations to visible
> > declarations with the same name and type in outer scopes if any".  Here:
> > 
> >    constexpr bool bar() { return true; } // #1
> >    constexpr bool foo() {
> >      constexpr bool bar(void); // #2
> >      return bar();
> >    }
> > 
> > it means that we:
> > 1) register_constexpr_fundef (#1)
> > 2) cp_genericize (#1)
> >     nothing interesting happens
> > 3) register_constexpr_fundef (foo)
> >     does copy_fn, so we have two copies of the BIND_EXPR
> > 4) cp_genericize (foo)
> >     this remaps #2 to #1, but only on one copy of the BIND_EXPR
> > 5) retrieve_constexpr_fundef (foo)
> >     we find it, no problem
> > 6) retrieve_constexpr_fundef (#2)
> >     and here #2 isn't found in constexpr_fundef_table, because
> >     we're working on the BIND_EXPR copy where #2 wasn't mapped to #1
> >     so we fail.  We've only registered #1.
> > 
> > It should work to use DECL_LOCAL_DECL_ALIAS (which used to be
> > extern_decl_map).  We evaluate constexpr functions on pre-cp_fold
> > bodies to avoid diagnostic problems, but the remapping I'm proposing
> > should not interfere with diagnostics.
> > 
> > This is not a problem for a global scope redeclaration; there we go
> > through duplicate_decls which keeps the DECL_UID:
> >    DECL_UID (olddecl) = olddecl_uid;
> > and DECL_UID is what constexpr_fundef_hasher::hash uses.
> > 
> > 	PR c++/111132
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* constexpr.cc (get_function_named_in_call): If there's
> > 	a DECL_LOCAL_DECL_ALIAS, use it.
> 
> Perhaps this function should use cp_get_fndecl_from_callee, and this change
> should be made there instead?

It doesn't seem that get_function_named_in_call can use cp_get_fndecl_from_callee,
(or be replaced with cp_get_callee_fndecl_nofold).  We can get e.g. a CALL_EXPR
whose CALL_EXPR_FN is a TEMPLATE_ID_EXPR, and get_function_named_in_call
returns the TEMPLATE_ID_EXPR whereas cp_get_fndecl_from_callee would return
null:

  if (TREE_CODE (fn) == FUNCTION_DECL)
    return fn;
  tree type = TREE_TYPE (fn);
  if (type == NULL_TREE || !INDIRECT_TYPE_P (type))
    return NULL_TREE;
    
Marek
Jason Merrill April 4, 2024, 9:28 p.m. UTC | #3 
On 4/4/24 14:43, Marek Polacek wrote:
> On Wed, Apr 03, 2024 at 01:14:46PM -0400, Jason Merrill wrote:
>> On 4/2/24 13:52, Marek Polacek wrote:
>>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/13?
>>>
>>> -- >8 --
>>> We evaluate constexpr functions on the original, pre-genericization bodies.
>>> That means that the function body we're evaluating will not have gone
>>> through cp_genericize_r's "Map block scope extern declarations to visible
>>> declarations with the same name and type in outer scopes if any".  Here:
>>>
>>>     constexpr bool bar() { return true; } // #1
>>>     constexpr bool foo() {
>>>       constexpr bool bar(void); // #2
>>>       return bar();
>>>     }
>>>
>>> it means that we:
>>> 1) register_constexpr_fundef (#1)
>>> 2) cp_genericize (#1)
>>>      nothing interesting happens
>>> 3) register_constexpr_fundef (foo)
>>>      does copy_fn, so we have two copies of the BIND_EXPR
>>> 4) cp_genericize (foo)
>>>      this remaps #2 to #1, but only on one copy of the BIND_EXPR
>>> 5) retrieve_constexpr_fundef (foo)
>>>      we find it, no problem
>>> 6) retrieve_constexpr_fundef (#2)
>>>      and here #2 isn't found in constexpr_fundef_table, because
>>>      we're working on the BIND_EXPR copy where #2 wasn't mapped to #1
>>>      so we fail.  We've only registered #1.
>>>
>>> It should work to use DECL_LOCAL_DECL_ALIAS (which used to be
>>> extern_decl_map).  We evaluate constexpr functions on pre-cp_fold
>>> bodies to avoid diagnostic problems, but the remapping I'm proposing
>>> should not interfere with diagnostics.
>>>
>>> This is not a problem for a global scope redeclaration; there we go
>>> through duplicate_decls which keeps the DECL_UID:
>>>     DECL_UID (olddecl) = olddecl_uid;
>>> and DECL_UID is what constexpr_fundef_hasher::hash uses.
>>>
>>> 	PR c++/111132
>>>
>>> gcc/cp/ChangeLog:
>>>
>>> 	* constexpr.cc (get_function_named_in_call): If there's
>>> 	a DECL_LOCAL_DECL_ALIAS, use it.
>>
>> Perhaps this function should use cp_get_fndecl_from_callee, and this change
>> should be made there instead?
> 
> It doesn't seem that get_function_named_in_call can use cp_get_fndecl_from_callee,
> (or be replaced with cp_get_callee_fndecl_nofold).  We can get e.g. a CALL_EXPR
> whose CALL_EXPR_FN is a TEMPLATE_ID_EXPR, and get_function_named_in_call
> returns the TEMPLATE_ID_EXPR whereas cp_get_fndecl_from_callee would return
> null:
> 
>    if (TREE_CODE (fn) == FUNCTION_DECL)
>      return fn;
>    tree type = TREE_TYPE (fn);
>    if (type == NULL_TREE || !INDIRECT_TYPE_P (type))
>      return NULL_TREE;

Why couldn't this function use cp_get_fndecl_from_callee and return the 
original argument if that function returns null?

Jason
diff mbox series

Patch

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index fa346fe01c9..b47f0e984c0 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -702,15 +702,26 @@  build_constexpr_constructor_member_initializers (tree type, tree body)
 
 /* We have an expression tree T that represents a call, either CALL_EXPR
    or AGGR_INIT_EXPR.  If the call is lexically to a named function,
-   retrun the _DECL for that function.  */
+   return the _DECL for that function.  */
 
 static tree
 get_function_named_in_call (tree t)
 {
   tree fun = cp_get_callee (t);
-  if (fun && TREE_CODE (fun) == ADDR_EXPR
-      && TREE_CODE (TREE_OPERAND (fun, 0)) == FUNCTION_DECL)
-    fun = TREE_OPERAND (fun, 0);
+  if (fun)
+    {
+      if (TREE_CODE (fun) == ADDR_EXPR
+	  && TREE_CODE (TREE_OPERAND (fun, 0)) == FUNCTION_DECL)
+	fun = TREE_OPERAND (fun, 0);
+      /* We evaluate constexpr functions on the original, pre-genericization
+	 bodies.  So block-scope extern declarations have not been mapped to
+	 declarations in outer scopes.  Use the namespace-scope declaration,
+	 if any, so that retrieve_constexpr_fundef can find it (PR111132).  */
+      if (TREE_CODE (fun) == FUNCTION_DECL && DECL_LOCAL_DECL_P (fun))
+	if (tree alias = DECL_LOCAL_DECL_ALIAS (fun))
+	  if (alias != error_mark_node)
+	    fun = alias;
+    }
   return fun;
 }
 
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration3.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration3.C
new file mode 100644
index 00000000000..2b41b456fc3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration3.C
@@ -0,0 +1,13 @@ 
+// PR c++/111132
+// { dg-do compile { target c++11 } }
+
+constexpr bool bar(void) {
+    return true;
+}
+
+constexpr bool foo() {
+    constexpr bool bar(void);
+    return bar();
+}
+
+static_assert(foo(), "");
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration4.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration4.C
new file mode 100644
index 00000000000..c58247218c6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-redeclaration4.C
@@ -0,0 +1,14 @@ 
+// PR c++/111132
+// { dg-do compile { target c++11 } }
+
+constexpr bool bar(void) {
+    return true;
+}
+
+constexpr bool bar(void);
+
+constexpr bool foo() {
+    return bar();
+}
+
+static_assert(foo(), "");