[PATCH] c++, v2: Handle argument merging push_local_extern_decl_alias [PR123825]
Jakub Jelinek
jakub@redhat.com
Wed Jan 28 13:04:46 GMT 2026
On Wed, Jan 28, 2026 at 11:35:58AM +0800, Jason Merrill wrote:
> Can we share code with duplicate_decls? The problem you're seeing seems to
> be due to the different code paths.
So like this?
2026-01-28 Jakub Jelinek <jakub@redhat.com>
PR c++/123825
* cp-tree.h (merge_decl_arguments): Declare.
* decl.cc (duplicate_decls): Outline DECL_ARGUMENTS handling
into ...
(merge_decl_arguments): ... new function.
* name-lookup.cc (push_local_extern_decl_alias): Call
merge_decl_arguments. Don't copy just the first PARM_DECL when
creating a new alias FUNCTION_DECL.
* g++.dg/reflect/has_identifier3.C: New test.
* g++.dg/reflect/identifier_of3.C: New test.
* g++.dg/cpp26/attr-indeterminate5.C: New test.
--- gcc/cp/cp-tree.h.jj 2026-01-28 12:27:52.252582912 +0100
+++ gcc/cp/cp-tree.h 2026-01-28 13:45:08.246443065 +0100
@@ -7456,6 +7456,7 @@ extern int decls_match (tree, tree, b
extern bool maybe_version_functions (tree, tree);
extern bool validate_constexpr_redeclaration (tree, tree);
extern bool merge_default_template_args (tree, tree, bool);
+extern void merge_decl_arguments (tree, tree, bool, bool, bool);
extern tree duplicate_decls (tree, tree,
bool hiding = false,
bool was_hidden = false);
--- gcc/cp/decl.cc.jj 2026-01-28 09:34:32.750243398 +0100
+++ gcc/cp/decl.cc 2026-01-28 13:44:57.963618703 +0100
@@ -1781,6 +1781,94 @@ merge_default_template_args (tree new_pa
return true;
}
+/* Helper function for duplicate_decls and push_local_extern_decl_alias.
+ Merge parameter attributes and names between NEWDECL and OLDDECL.
+ NEW_DEFINES_FUNCTION and TYPES_MATCH argument like variables in
+ duplicate_decls, EXTERN_ALIAS false for duplicate_decls and true for
+ push_local_extern_decl_alias. */
+
+void
+merge_decl_arguments (tree newdecl, tree olddecl, bool new_defines_function,
+ bool types_match, bool extern_alias)
+{
+ tree oldarg, newarg;
+ for (oldarg = DECL_ARGUMENTS (olddecl), newarg = DECL_ARGUMENTS (newdecl);
+ oldarg && newarg;
+ oldarg = DECL_CHAIN (oldarg), newarg = DECL_CHAIN (newarg))
+ {
+ DECL_ATTRIBUTES (newarg)
+ = (*targetm.merge_decl_attributes) (oldarg, newarg);
+ if (lookup_attribute (NULL, "indeterminate", DECL_ATTRIBUTES (newarg))
+ && !lookup_attribute (NULL, "indeterminate",
+ DECL_ATTRIBUTES (oldarg)))
+ {
+ auto_diagnostic_group d;
+ error_at (DECL_SOURCE_LOCATION (newarg),
+ "%<indeterminate%> attribute not specified for parameter "
+ "%qD on the first declaration of its function", newarg);
+ inform (DECL_SOURCE_LOCATION (oldarg), "earlier declaration");
+ }
+ DECL_ATTRIBUTES (oldarg) = DECL_ATTRIBUTES (newarg);
+ /* Merge names for std::meta::has_identifier and
+ std::meta::{,u8}identifier_of purposes. If they are different and
+ both oldarg and newarg are named, add flag to force that
+ std::meta::has_identifier returns false. If one is named and one is
+ unnamed, if neither is a olddecl nor newdecl is definition, propagate
+ DECL_NAME to both. Otherwise stash the old name into "old parm name"
+ artificial attribute. */
+ if (flag_reflection && DECL_NAME (oldarg) != DECL_NAME (newarg))
+ {
+ if (DECL_NAME (oldarg) && DECL_NAME (newarg))
+ {
+ /* Different names. */
+ MULTIPLE_NAMES_PARM_P (oldarg) = 1;
+ MULTIPLE_NAMES_PARM_P (newarg) = 1;
+ }
+ else if (!new_defines_function
+ && types_match
+ && DECL_INITIAL (olddecl) == NULL_TREE)
+ {
+ /* For 2 non-definitions with matching types, one is named and
+ one unnamed, propagate name to both. */
+ if (DECL_NAME (oldarg))
+ DECL_NAME (newarg) = DECL_NAME (oldarg);
+ else
+ DECL_NAME (oldarg) = DECL_NAME (newarg);
+ }
+ /* Depending on which PARM_DECL we'll keep, look at the other
+ PARM_DECL's name. */
+ else if (tree name = ((new_defines_function || !types_match)
+ ? DECL_NAME (oldarg) : DECL_NAME (newarg)))
+ {
+ tree opn = lookup_attribute ("old parm name",
+ DECL_ATTRIBUTES (oldarg));
+ if (opn)
+ {
+ if (TREE_VALUE (TREE_VALUE (opn)) == name)
+ /* Name already in "old parm name" attribute. */;
+ else
+ {
+ /* Different names. */
+ MULTIPLE_NAMES_PARM_P (oldarg) = 1;
+ MULTIPLE_NAMES_PARM_P (newarg) = 1;
+ }
+ }
+ else
+ {
+ /* Save name into attribute. */
+ DECL_ATTRIBUTES (newarg)
+ = tree_cons (get_identifier ("old parm name"),
+ tree_cons (NULL_TREE, name, NULL_TREE),
+ DECL_ATTRIBUTES (newarg));
+ DECL_ATTRIBUTES (oldarg) = DECL_ATTRIBUTES (newarg);
+ }
+ }
+ else if (extern_alias)
+ DECL_NAME (newarg) = DECL_NAME (oldarg);
+ }
+ }
+}
+
/* If NEWDECL is a redeclaration of OLDDECL, merge the declarations.
If the redeclaration is invalid, a diagnostic is issued, and the
error_mark_node is returned. Otherwise, OLDDECL is returned.
@@ -3038,88 +3126,8 @@ duplicate_decls (tree newdecl, tree oldd
if (TREE_CODE (newdecl) == FUNCTION_DECL)
{
- tree parm;
-
- /* Merge parameter attributes. */
- tree oldarg, newarg;
- for (oldarg = DECL_ARGUMENTS (olddecl),
- newarg = DECL_ARGUMENTS (newdecl);
- oldarg && newarg;
- oldarg = DECL_CHAIN (oldarg), newarg = DECL_CHAIN (newarg))
- {
- DECL_ATTRIBUTES (newarg)
- = (*targetm.merge_decl_attributes) (oldarg, newarg);
- if (lookup_attribute (NULL, "indeterminate",
- DECL_ATTRIBUTES (newarg))
- && !lookup_attribute (NULL, "indeterminate",
- DECL_ATTRIBUTES (oldarg)))
- {
- auto_diagnostic_group d;
- error_at (DECL_SOURCE_LOCATION (newarg),
- "%<indeterminate%> attribute not specified "
- "for parameter %qD on the first declaration of "
- "its function", newarg);
- inform (DECL_SOURCE_LOCATION (oldarg),
- "earlier declaration");
- }
- DECL_ATTRIBUTES (oldarg) = DECL_ATTRIBUTES (newarg);
- /* Merge names for std::meta::has_identifier and
- std::meta::{,u8}identifier_of purposes. If they are different
- and both oldarg and newarg are named, add flag to force that
- std::meta::has_identifier returns false. If one is named and
- one is unnamed, if neither is a olddecl nor newdecl is definition,
- propagate DECL_NAME to both. Otherwise stash the old name into
- "old parm name" artificial attribute. */
- if (flag_reflection && DECL_NAME (oldarg) != DECL_NAME (newarg))
- {
- if (DECL_NAME (oldarg) && DECL_NAME (newarg))
- {
- /* Different names. */
- MULTIPLE_NAMES_PARM_P (oldarg) = 1;
- MULTIPLE_NAMES_PARM_P (newarg) = 1;
- }
- else if (!new_defines_function
- && types_match
- && DECL_INITIAL (olddecl) == NULL_TREE)
- {
- /* For 2 non-definitions with matching types,
- one is named and one unnamed, propagate name
- to both. */
- if (DECL_NAME (oldarg))
- DECL_NAME (newarg) = DECL_NAME (oldarg);
- else
- DECL_NAME (oldarg) = DECL_NAME (newarg);
- }
- /* Depending on which PARM_DECL we'll keep, look at the other
- PARM_DECL's name. */
- else if (tree name = ((new_defines_function || !types_match)
- ? DECL_NAME (oldarg) : DECL_NAME (newarg)))
- {
- tree opn = lookup_attribute ("old parm name",
- DECL_ATTRIBUTES (oldarg));
- if (opn)
- {
- if (TREE_VALUE (TREE_VALUE (opn)) == name)
- /* Name already in "old parm name" attribute. */;
- else
- {
- /* Different names. */
- MULTIPLE_NAMES_PARM_P (oldarg) = 1;
- MULTIPLE_NAMES_PARM_P (newarg) = 1;
- }
- }
- else
- {
- /* Save name into attribute. */
- DECL_ATTRIBUTES (newarg)
- = tree_cons (get_identifier ("old parm name"),
- tree_cons (NULL_TREE, name, NULL_TREE),
- DECL_ATTRIBUTES (newarg));
- DECL_ATTRIBUTES (oldarg) = DECL_ATTRIBUTES (newarg);
- }
- }
- }
- }
+ merge_decl_arguments (newdecl, olddecl, new_defines_function,
+ types_match, false);
if (DECL_TEMPLATE_INSTANTIATION (olddecl)
&& !DECL_TEMPLATE_INSTANTIATION (newdecl))
@@ -3198,7 +3206,7 @@ duplicate_decls (tree newdecl, tree oldd
DECL_ABSTRACT_P (newdecl) = DECL_ABSTRACT_P (olddecl);
/* Update newdecl's parms to point at olddecl. */
- for (parm = DECL_ARGUMENTS (newdecl); parm;
+ for (tree parm = DECL_ARGUMENTS (newdecl); parm;
parm = DECL_CHAIN (parm))
DECL_CONTEXT (parm) = olddecl;
--- gcc/cp/name-lookup.cc.jj 2026-01-28 09:34:32.754243330 +0100
+++ gcc/cp/name-lookup.cc 2026-01-28 13:45:28.123103551 +0100
@@ -3736,6 +3736,8 @@ push_local_extern_decl_alias (tree decl)
alias = *iter;
if (!validate_constexpr_redeclaration (alias, decl))
return;
+ if (TREE_CODE (decl) == FUNCTION_DECL)
+ merge_decl_arguments (decl, alias, false, true, true);
break;
}
@@ -3749,7 +3751,9 @@ push_local_extern_decl_alias (tree decl)
for (tree *chain = &DECL_ARGUMENTS (alias);
*chain; chain = &DECL_CHAIN (*chain))
{
+ tree next = DECL_CHAIN (*chain);
*chain = copy_decl (*chain);
+ DECL_CHAIN (*chain) = next;
DECL_CONTEXT (*chain) = alias;
}
--- gcc/testsuite/g++.dg/reflect/has_identifier3.C.jj 2026-01-28 13:21:26.904852201 +0100
+++ gcc/testsuite/g++.dg/reflect/has_identifier3.C 2026-01-28 13:21:26.904852201 +0100
@@ -0,0 +1,23 @@
+// PR c++/123825
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-freflection" }
+// Test std::meta::has_identifier.
+
+#include <meta>
+
+void fun (int);
+constexpr std::meta::info r = parameters_of (^^fun)[0];
+static_assert (!has_identifier (r));
+
+void fun (int x);
+static_assert (has_identifier (r));
+
+void fun (int x);
+static_assert (has_identifier (r));
+
+void
+poison ()
+{
+ void fun (int y);
+}
+static_assert (!has_identifier (r));
--- gcc/testsuite/g++.dg/reflect/identifier_of3.C.jj 2026-01-28 13:21:26.904943481 +0100
+++ gcc/testsuite/g++.dg/reflect/identifier_of3.C 2026-01-28 13:21:26.904943481 +0100
@@ -0,0 +1,73 @@
+// PR c++/123825
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-freflection" }
+// Test std::meta::identifier_of.
+
+#include <meta>
+
+void foo (int, int x, int y, int z);
+
+int
+bar (int, int x, int y, int z, int)
+{
+ return x + y + z;
+}
+
+constexpr auto foo1 = parameters_of (^^foo)[0];
+constexpr auto foo2 = parameters_of (^^foo)[1];
+constexpr auto foo3 = parameters_of (^^foo)[2];
+constexpr auto foo4 = parameters_of (^^foo)[3];
+constexpr auto bar1 = parameters_of (^^bar)[0];
+constexpr auto bar2 = parameters_of (^^bar)[1];
+constexpr auto bar3 = parameters_of (^^bar)[2];
+constexpr auto bar4 = parameters_of (^^bar)[3];
+constexpr auto bar5 = parameters_of (^^bar)[4];
+static_assert (!has_identifier (foo1));
+static_assert (identifier_of (foo2) == std::string_view ("x"));
+static_assert (identifier_of (foo3) == std::string_view ("y"));
+static_assert (identifier_of (foo4) == std::string_view ("z"));
+static_assert (!has_identifier (bar1));
+static_assert (identifier_of (bar2) == std::string_view ("x"));
+static_assert (identifier_of (bar3) == std::string_view ("y"));
+static_assert (identifier_of (bar4) == std::string_view ("z"));
+static_assert (!has_identifier (bar5));
+
+void
+baz ()
+{
+ void foo (int w, int, int v, int z);
+ int bar (int, int, int v, int z, int u);
+ void qux (int, int x, int y, int z);
+ constexpr auto qux1 = parameters_of (^^qux)[0];
+ constexpr auto qux2 = parameters_of (^^qux)[1];
+ constexpr auto qux3 = parameters_of (^^qux)[2];
+ constexpr auto qux4 = parameters_of (^^qux)[3];
+ static_assert (!has_identifier (qux1));
+ static_assert (identifier_of (qux2) == std::string_view ("x"));
+ static_assert (identifier_of (qux3) == std::string_view ("y"));
+ static_assert (identifier_of (qux4) == std::string_view ("z"));
+}
+
+static_assert (identifier_of (foo1) == std::string_view ("w"));
+static_assert (identifier_of (foo2) == std::string_view ("x"));
+static_assert (!has_identifier (foo3));
+static_assert (identifier_of (foo4) == std::string_view ("z"));
+static_assert (!has_identifier (bar1));
+static_assert (identifier_of (bar2) == std::string_view ("x"));
+static_assert (!has_identifier (bar3));
+static_assert (identifier_of (bar4) == std::string_view ("z"));
+static_assert (identifier_of (bar5) == std::string_view ("u"));
+
+void
+fred ()
+{
+ void qux (int w, int, int v, int z);
+ constexpr auto qux1 = parameters_of (^^qux)[0];
+ constexpr auto qux2 = parameters_of (^^qux)[1];
+ constexpr auto qux3 = parameters_of (^^qux)[2];
+ constexpr auto qux4 = parameters_of (^^qux)[3];
+ static_assert (identifier_of (qux1) == std::string_view ("w"));
+ static_assert (identifier_of (qux2) == std::string_view ("x"));
+ static_assert (!has_identifier (qux3));
+ static_assert (identifier_of (qux4) == std::string_view ("z"));
+}
--- gcc/testsuite/g++.dg/cpp26/attr-indeterminate5.C.jj 2026-01-28 13:21:26.905084472 +0100
+++ gcc/testsuite/g++.dg/cpp26/attr-indeterminate5.C 2026-01-28 13:21:26.905084472 +0100
@@ -0,0 +1,23 @@
+// C++ 26 P2795R5 - Erroneous behaviour for uninitialized reads
+// { dg-do compile { target c++11 } }
+// { dg-skip-if "" { c++26 } { "-ftrivial-auto-var-init=*" } { "" } }
+
+struct S { S (); S (const S &); ~S (); int s; };
+void foo (S s); // { dg-message "earlier declaration" }
+void bar (S s [[indeterminate]]);
+void baz (S s [[indeterminate]]);
+
+void
+fred ()
+{
+ void foo (S t [[indeterminate]]); // { dg-error "'indeterminate' attribute not specified for parameter 't' on the first declaration of its function" }
+ void bar (S t [[indeterminate]]);
+ void baz (S t);
+ void qux (S t); // { dg-message "earlier declaration" }
+ void corge (S t [[indeterminate]]);
+ void garply (S t [[indeterminate]]);
+}
+
+void qux (S u [[indeterminate]]); // { dg-error "'indeterminate' attribute not specified for parameter 'u' on the first declaration of its function" }
+void corge (S u [[indeterminate]]);
+void garply (S u);
Jakub
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