[gcc r14-8350] c++: Fix handling of extern templates in modules [PR112820]

[gcc r14-8350] c++: Fix handling of extern templates in modules [PR112820]

[Nathaniel Shead]

https://gcc.gnu.org/g:affef534b0335592336c82918f15242576e2ab8f

commit r14-8350-gaffef534b0335592336c82918f15242576e2ab8f
Author: Nathaniel Shead <nathanieloshead@gmail.com>
Date:   Wed Jan 17 16:50:39 2024 +1100

    c++: Fix handling of extern templates in modules [PR112820]
    
    Currently, extern templates are detected by looking for the
    DECL_EXTERNAL flag on a TYPE_DECL. However, this is incorrect:
    TYPE_DECLs don't actually set this flag, and it happens to work by
    coincidence due to TYPE_DECL_SUPPRESS_DEBUG happening to use the same
    underlying bit. This however causes issues with other TYPE_DECLs that
    also happen to have suppressed debug information.
    
    Instead, this patch reworks the logic so CLASSTYPE_INTERFACE_ONLY is
    always emitted into the module BMI and can then be used to check for an
    extern template correctly.
    
    Otherwise, for other declarations we always want to redetermine this:
    even for declarations from the GMF, we may change our mind on whether to
    import or export depending on decisions made later in the TU after
    importing so we shouldn't decide this now, or necessarily reuse what the
    module we'd imported had decided.
    
    Some of this may need to change in the future to account for
    https://github.com/itanium-cxx-abi/cxx-abi/issues/170.
    
            PR c++/112820
            PR c++/102607
    
    gcc/cp/ChangeLog:
    
            * module.cc (trees_out::lang_type_bools): Write interface_only
            and interface_unknown.
            (trees_in::lang_type_bools): Read the above flags.
            (trees_in::decl_value): Reset CLASSTYPE_INTERFACE_* except for
            extern templates.
            (trees_in::read_class_def): Remove buggy extern template
            handling.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/modules/debug-2_a.C: New test.
            * g++.dg/modules/debug-2_b.C: New test.
            * g++.dg/modules/debug-2_c.C: New test.
            * g++.dg/modules/debug-3_a.C: New test.
            * g++.dg/modules/debug-3_b.C: New test.
    
    Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>

Diff:
---
 gcc/cp/module.cc                         | 37 ++++++++++++++++++--------------
 gcc/testsuite/g++.dg/modules/debug-2_a.C |  9 ++++++++
 gcc/testsuite/g++.dg/modules/debug-2_b.C |  8 +++++++
 gcc/testsuite/g++.dg/modules/debug-2_c.C |  9 ++++++++
 gcc/testsuite/g++.dg/modules/debug-3_a.C |  8 +++++++
 gcc/testsuite/g++.dg/modules/debug-3_b.C |  9 ++++++++
 6 files changed, 64 insertions(+), 16 deletions(-)

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 8db662c0267..70785493561 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -5806,10 +5806,8 @@ trees_out::lang_type_bools (tree t)
 
   WB ((lang->gets_delete >> 0) & 1);
   WB ((lang->gets_delete >> 1) & 1);
-  // Interfaceness is recalculated upon reading.  May have to revisit?
-  // How do dllexport and dllimport interact across a module?
-  // lang->interface_only
-  // lang->interface_unknown
+  WB (lang->interface_only);
+  WB (lang->interface_unknown);
   WB (lang->contains_empty_class_p);
   WB (lang->anon_aggr);
   WB (lang->non_zero_init);
@@ -5877,9 +5875,8 @@ trees_in::lang_type_bools (tree t)
   v = b () << 0;
   v |= b () << 1;
   lang->gets_delete = v;
-  // lang->interface_only
-  // lang->interface_unknown
-  lang->interface_unknown = true; // Redetermine interface
+  RB (lang->interface_only);
+  RB (lang->interface_unknown);
   RB (lang->contains_empty_class_p);
   RB (lang->anon_aggr);
   RB (lang->non_zero_init);
@@ -8246,6 +8243,23 @@ trees_in::decl_value ()
 	/* Set the TEMPLATE_DECL's type.  */
 	TREE_TYPE (decl) = TREE_TYPE (inner);
 
+      /* Redetermine whether we need to import or export this declaration
+	 for this TU.  But for extern templates we know we must import:
+	 they'll be defined in a different TU.
+	 FIXME: How do dllexport and dllimport interact across a module?
+	 See also https://github.com/itanium-cxx-abi/cxx-abi/issues/170.
+	 May have to revisit?  */
+      if (type
+	  && CLASS_TYPE_P (type)
+	  && TYPE_LANG_SPECIFIC (type)
+	  && !(CLASSTYPE_EXPLICIT_INSTANTIATION (type)
+	       && CLASSTYPE_INTERFACE_KNOWN (type)
+	       && CLASSTYPE_INTERFACE_ONLY (type)))
+	{
+	  CLASSTYPE_INTERFACE_ONLY (type) = false;
+	  CLASSTYPE_INTERFACE_UNKNOWN (type) = true;
+	}
+
       /* Add to specialization tables now that constraints etc are
 	 added.  */
       if (mk == MK_partial)
@@ -12068,15 +12082,6 @@ trees_in::read_class_def (tree defn, tree maybe_template)
   bool installing = maybe_dup && !TYPE_SIZE (type);
   if (installing)
     {
-      if (DECL_EXTERNAL (defn) && TYPE_LANG_SPECIFIC (type))
-	{
-	  /* We don't deal with not-really-extern, because, for a
-	     module you want the import to be the interface, and for a
-	     header-unit, you're doing it wrong.  */
-	  CLASSTYPE_INTERFACE_UNKNOWN (type) = false;
-	  CLASSTYPE_INTERFACE_ONLY (type) = true;
-	}
-
       if (maybe_dup != defn)
 	{
 	  // FIXME: This is needed on other defns too, almost
diff --git a/gcc/testsuite/g++.dg/modules/debug-2_a.C b/gcc/testsuite/g++.dg/modules/debug-2_a.C
new file mode 100644
index 00000000000..eed0905542b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/debug-2_a.C
@@ -0,0 +1,9 @@
+// PR c++/112820
+// { dg-additional-options "-fmodules-ts -g" }
+// { dg-module-cmi io }
+
+export module io;
+
+export struct error {
+  virtual const char* what() const noexcept;
+};
diff --git a/gcc/testsuite/g++.dg/modules/debug-2_b.C b/gcc/testsuite/g++.dg/modules/debug-2_b.C
new file mode 100644
index 00000000000..fc9afbc02e0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/debug-2_b.C
@@ -0,0 +1,8 @@
+// PR c++/112820
+// { dg-additional-options "-fmodules-ts -g" }
+
+module io;
+
+const char* error::what() const noexcept {
+  return "bla";
+}
diff --git a/gcc/testsuite/g++.dg/modules/debug-2_c.C b/gcc/testsuite/g++.dg/modules/debug-2_c.C
new file mode 100644
index 00000000000..37117f69dcd
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/debug-2_c.C
@@ -0,0 +1,9 @@
+// PR c++/112820
+// { dg-module-do link }
+// { dg-additional-options "-fmodules-ts -g" }
+
+import io;
+
+int main() {
+  error{};
+}
diff --git a/gcc/testsuite/g++.dg/modules/debug-3_a.C b/gcc/testsuite/g++.dg/modules/debug-3_a.C
new file mode 100644
index 00000000000..9e33d8260fd
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/debug-3_a.C
@@ -0,0 +1,8 @@
+// PR c++/102607
+// { dg-additional-options "-fmodules-ts -g" }
+// { dg-module-cmi mod }
+
+export module mod;
+export struct B {
+  virtual ~B() = default;
+};
diff --git a/gcc/testsuite/g++.dg/modules/debug-3_b.C b/gcc/testsuite/g++.dg/modules/debug-3_b.C
new file mode 100644
index 00000000000..03c78b71b5d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/debug-3_b.C
@@ -0,0 +1,9 @@
+// PR c++/102607
+// { dg-module-do link }
+// { dg-additional-options "-fmodules-ts -g" }
+
+import mod;
+int main() {
+  struct D : B {};
+  (void)D{};
+}