On 6/25/25 9:02 AM, Nathaniel Shead wrote:
On Tue, Jun 24, 2025 at 12:10:09PM -0400, Patrick Palka wrote:
On Tue, 24 Jun 2025, Jason Merrill wrote:
On 6/23/25 5:41 PM, Nathaniel Shead wrote:
Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk/15?
-- >8 --
We were erroring because the TEMPLATE_DECL of the existing partial
specialisation has an undeduced return type, but the imported
declaration did not.
The root cause is similar to what was fixed in r13-2744-g4fac53d6522189,
where modules streaming code assumes that a TEMPLATE_DECL and its
DECL_TEMPLATE_RESULT will always have the same TREE_TYPE. That commit
fixed the issue by ensuring that when the type of a variable is deduced
the TEMPLATE_DECL is updated as well, but this missed handling partial
specialisations.
However, I don't think we actually care about that, since it seems that
only the type of the inner decl actually matters in practice. Instead,
this patch handles the issue on the modules side when deduping a
streamed decl, by only comparing the inner type.
PR c++/120644
gcc/cp/ChangeLog:
* decl.cc (cp_finish_decl): Remove workaround.
Hmm, if we aren't going to try to keep the type of the TEMPLATE_DECL correct,
maybe we should always set it to NULL_TREE to make sure we only look at the
inner type.
FWIW cp_finish_decl can get at the TEMPLATE_DECL of a VAR_DECL
corresponding to a partial specialization via
TI_TEMPLATE (TI_PARTIAL_INFO (DECL_TEMPLATE_INFO (decl)))
if we do want to end up keeping the two TREE_TYPEs in sync.
Thanks. On further reflection, maybe the safest approach is to just
ensure that the types are always consistent (including for partial
specs); this is what the following patch does.
Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?
-- >8 --
Subject: [PATCH] c++/modules: Ensure type of partial spec VAR_DECL is
consistent with its template [PR120644]
We were erroring because the TEMPLATE_DECL of the existing partial
specialisation has an undeduced return type, but the imported
declaration did not.
The root cause is similar to what was fixed in r13-2744-g4fac53d6522189,
where modules streaming code assumes that a TEMPLATE_DECL and its
DECL_TEMPLATE_RESULT will always have the same TREE_TYPE. That commit
fixed the issue by ensuring that when the type of a variable is deduced
the TEMPLATE_DECL is updated as well, but missed handling partial
specialisations. This patch ensures that the same adjustment is made
there as well.
PR c++/120644
gcc/cp/ChangeLog:
* decl.cc (cp_finish_decl): Also propagate type to partial
templates.
* module.cc (trees_out::decl_value): Add assertion that the
TREE_TYPE of a streamed template decl matches its inner.
(trees_in::is_matching_decl): Clarify function return type
deduction should only occur for non-TEMPLATE_DECL.
gcc/testsuite/ChangeLog:
* g++.dg/modules/auto-7.h: New test.
* g++.dg/modules/auto-7_a.H: New test.
* g++.dg/modules/auto-7_b.C: New test.
Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
Reviewed-by: Jason Merrill <ja...@redhat.com>
Reviewed-by: Patrick Palka <ppa...@redhat.com>
---
gcc/cp/decl.cc | 13 +++++++++----
gcc/cp/module.cc | 7 ++++++-
gcc/testsuite/g++.dg/modules/auto-7.h | 12 ++++++++++++
gcc/testsuite/g++.dg/modules/auto-7_a.H | 5 +++++
gcc/testsuite/g++.dg/modules/auto-7_b.C | 5 +++++
5 files changed, 37 insertions(+), 5 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/modules/auto-7.h
create mode 100644 gcc/testsuite/g++.dg/modules/auto-7_a.H
create mode 100644 gcc/testsuite/g++.dg/modules/auto-7_b.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 4fe97ffbf8f..59701197e16 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -8923,10 +8923,15 @@ cp_finish_decl (tree decl, tree init, bool
init_const_expr_p,
cp_apply_type_quals_to_decl (cp_type_quals (type), decl);
/* Update the type of the corresponding TEMPLATE_DECL to match. */
- if (DECL_LANG_SPECIFIC (decl)
- && DECL_TEMPLATE_INFO (decl)
- && DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (decl)) == decl)
- TREE_TYPE (DECL_TI_TEMPLATE (decl)) = type;
+ if (DECL_LANG_SPECIFIC (decl) && DECL_TEMPLATE_INFO (decl))
+ {
+ tree info = DECL_TEMPLATE_INFO (decl);
+ tree tmpl = TI_TEMPLATE (info);
+ if (DECL_TEMPLATE_RESULT (tmpl) == decl)
+ TREE_TYPE (tmpl) = type;
+ else if (PRIMARY_TEMPLATE_P (tmpl) && TI_PARTIAL_INFO (info))
+ TREE_TYPE (TI_TEMPLATE (TI_PARTIAL_INFO (info))) = type;
+ }
Perhaps we should update template_for_substitution to handle partial
specs and then use it here?
}
if (ensure_literal_type_for_constexpr_object (decl) == error_mark_node)
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index c99988da05b..53edb2ff203 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -8212,6 +8212,10 @@ trees_out::decl_value (tree decl, depset *dep)
inner = DECL_TEMPLATE_RESULT (decl);
inner_tag = insert (inner, WK_value);
+ /* On stream-in we assume that a template and its result will
+ have the same type. */
+ gcc_checking_assert (TREE_TYPE (decl) == TREE_TYPE (inner));
+
if (streaming_p ())
{
int code = TREE_CODE (inner);
@@ -12193,7 +12197,8 @@ trees_in::is_matching_decl (tree existing, tree decl,
bool is_typedef)
{
dump (dumper::MERGE)
&& dump ("Propagating deduced return type to %N", existing);
- FNDECL_USED_AUTO (e_inner) = true;
+ gcc_checking_assert (existing == e_inner);
+ FNDECL_USED_AUTO (existing) = true;
DECL_SAVED_AUTO_RETURN_TYPE (existing) = TREE_TYPE (e_type);
TREE_TYPE (existing) = change_return_type (TREE_TYPE (d_type),
e_type);
}
diff --git a/gcc/testsuite/g++.dg/modules/auto-7.h
b/gcc/testsuite/g++.dg/modules/auto-7.h
new file mode 100644
index 00000000000..324b60cfa0a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/auto-7.h
@@ -0,0 +1,12 @@
+// PR c++/120644
+
+enum class E { E0, E1 };
+
+template <typename T>
+constexpr auto fmt_kind = E::E0;
+
+template <typename T>
+class opt{};
+
+template <typename T>
+constexpr auto fmt_kind<opt<T>> = E::E1;
diff --git a/gcc/testsuite/g++.dg/modules/auto-7_a.H
b/gcc/testsuite/g++.dg/modules/auto-7_a.H
new file mode 100644
index 00000000000..40cb0f886c0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/auto-7_a.H
@@ -0,0 +1,5 @@
+// PR c++/120644
+// { dg-additional-options "-fmodule-header" }
+// { dg-module-cmi {} }
+
+#include "auto-7.h"
diff --git a/gcc/testsuite/g++.dg/modules/auto-7_b.C
b/gcc/testsuite/g++.dg/modules/auto-7_b.C
new file mode 100644
index 00000000000..c6ad37fd828
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/auto-7_b.C
@@ -0,0 +1,5 @@
+// PR c++/120644
+// { dg-additional-options "-fmodules -fno-module-lazy" }
+
+#include "auto-7.h"
+import "auto-7_a.H";
