On 7/17/24 11:04 PM, Nathaniel Shead wrote:
On Wed, Jul 17, 2024 at 01:12:34PM -0400, Jason Merrill wrote:
On 5/1/24 11:27 AM, Jason Merrill wrote:
On 5/1/24 07:11, Patrick Palka wrote:
On Wed, 1 May 2024, Nathaniel Shead wrote:
Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?
-- >8 --
When calling instantiate_pending_templates at end of parsing, any new
functions that are instantiated from this point have their module
purview set based on the current value of module_kind.
This is unideal, however, as the modules code will then treat these
instantiations as reachable and cause large swathes of the GMF to be
emitted into the module CMI, despite no code in the actual module
purview referencing it.
This patch fixes this by also remembering the value of module_kind when
the instantiation was deferred, and restoring it when doing this
deferred instantiation. That way newly instantiated declarations
appropriately get a DECL_MODULE_PURVIEW_P appropriate for where the
instantiation was required, meaning that GMF entities won't be counted
as reachable unless referenced by an actually reachable entity.
Note that purviewness and attachment etc. is generally only determined
by the base template: this is purely for determining whether a
specialisation was declared in the module purview and hence whether it
should be streamed out. See the comment on 'set_instantiating_module'.
PR c++/114630
PR c++/114795
gcc/cp/ChangeLog:
* cp-tree.h (struct tinst_level): Add field for tracking
module_kind.
* pt.cc (push_tinst_level_loc): Cache module_kind in new_level.
(reopen_tinst_level): Restore module_kind from level.
(instantiate_pending_templates): Save and restore module_kind so
it isn't affected by reopen_tinst_level.
LGTM. Another approach is to instantiate all so-far deferred
instantiations and vtables once we reach the start of the module
purview, but your approach is much cleaner.
Hmm, I actually think I like the approach of instantiating at that point
better, so that instantiations in the GMF can't depend on things in
module purview.
And probably do the same again when switching to the private module
fragment, when that's implemented.
Patrick mentioned these patches again today; I still think this is the right
approach, particularly for the private module fragment.
That said, could we just clear module_kind at EOF? As you say, only the
purviewness of the template matters for implicit instantiations. It is
seeming to me like "set_instantiating_module" should only apply for explicit
instantiations, at the point of the explicit instantiation declaration.
Jason
Yup, I agree that this is the right approach, since as you say we'll
need to do this for private module fragment anyway; I've just left this
on the backburner because it didn't look particularly easy to do neatly
and have been focussing on crashes instead for now.
That sounds like a good idea, I've given that a shot and it succeeds
bootstrap + regtest (so far just modules.exp) on x86_64-pc-linux-gnu.
Here's the patch, OK for trunk if full regtest succeeds?
Is there a test that an explicit instantiation in module purview is not
discarded? OK if so.
-- >8 --
Subject: [PATCH v2] c++/modules: Clear module_purview_p at EOF [PR114630]
When calling instantiate_pending_templates at end of parsing, any new
functions that are instantiated from this point have their module
purview set based on the current value of module_kind.
This is unideal, however, as the modules code will then treat these
instantiations as reachable and cause large swathes of the GMF to be
emitted into the module CMI, despite no code in the actual module
purview referencing it.
Note that purviewness and attachment etc. is generally only determined
by the base template: this is purely for determining whether a
specialisation was declared in the module purview and hence whether it
should be streamed out. See the comment on 'set_instantiating_module'.
As such, this patch fixes the issue by clearing MK_PURVIEW and MK_ATTACH
from module_kind at EOF. This ensures that deferred instantiations
don't get marked as purview and retained in the module CMI
unnecessarily. We also add a new test to ensure that all code in the
standard library headers are properly discarded to prevent regressions.
For future work we probably want to eagerly perform any deferred
instantiations at the end of the global module fragment, which will
avoid this issue as well. We will need to do this before any private
module fragments (once we support them) regardless.
PR c++/114630
PR c++/114795
gcc/cp/ChangeLog:
* decl2.cc (c_parse_final_cleanups): Clear MK_PURVIEW and
MK_ATTACH flags.
gcc/testsuite/ChangeLog:
* g++.dg/modules/xtreme-header.h: Include new header files.
* g++.dg/modules/gmf-3.C: New test.
* g++.dg/modules/gmf-4.C: New test.
* g++.dg/modules/xtreme-header-8.C: New test.
Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
---
gcc/cp/decl2.cc | 4 +++
gcc/testsuite/g++.dg/modules/gmf-3.C | 13 +++++++++
gcc/testsuite/g++.dg/modules/gmf-4.C | 27 +++++++++++++++++++
.../g++.dg/modules/xtreme-header-8.C | 9 +++++++
gcc/testsuite/g++.dg/modules/xtreme-header.h | 25 +++++++++++------
5 files changed, 70 insertions(+), 8 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/modules/gmf-3.C
create mode 100644 gcc/testsuite/g++.dg/modules/gmf-4.C
create mode 100644 gcc/testsuite/g++.dg/modules/xtreme-header-8.C
diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index 6d674684931..acabf65e136 100644
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -5168,6 +5168,10 @@ c_parse_final_cleanups (void)
/* FIXME - huh? was input_line -= 1;*/
+ /* Clear module kind so that deferred instantiations don't get unnecessarily
+ marked as purview, preventing GMF discarding. */
+ module_kind &= ~(MK_PURVIEW | MK_ATTACH);
+
/* We now have to write out all the stuff we put off writing out.
These include:
diff --git a/gcc/testsuite/g++.dg/modules/gmf-3.C b/gcc/testsuite/g++.dg/modules/gmf-3.C
new file mode 100644
index 00000000000..e52ae904ea9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/gmf-3.C
@@ -0,0 +1,13 @@
+// PR c++/114630
+// { dg-additional-options "-fmodules-ts -Wno-global-module
-fdump-lang-module" }
+// { dg-module-cmi M }
+
+module;
+template <typename> struct allocator {
+ allocator() {}
+};
+template class allocator<wchar_t>;
+export module M;
+
+// The whole GMF should be discarded here
+// { dg-final { scan-lang-dump "Wrote 0 clusters" module } }
diff --git a/gcc/testsuite/g++.dg/modules/gmf-4.C
b/gcc/testsuite/g++.dg/modules/gmf-4.C
new file mode 100644
index 00000000000..c95bc782cea
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/gmf-4.C
@@ -0,0 +1,27 @@
+// PR c++/114630
+// { dg-additional-options "-fmodules-ts -Wno-global-module
-fdump-lang-module" }
+// { dg-module-cmi M }
+
+// Deferred instantiation of GM virtual functions should not place
+// newly discovered declarations in the module purview
+
+module;
+
+template <typename T>
+void go() {
+ extern T fn_decl();
+}
+
+template <typename T>
+struct S {
+ virtual void f() {
+ go<char>();
+ }
+};
+
+S<int> s;
+
+export module M;
+
+// The whole GMF should be discarded here
+// { dg-final { scan-lang-dump "Wrote 0 clusters" module } }
diff --git a/gcc/testsuite/g++.dg/modules/xtreme-header-8.C
b/gcc/testsuite/g++.dg/modules/xtreme-header-8.C
new file mode 100644
index 00000000000..b0d0ae87534
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/xtreme-header-8.C
@@ -0,0 +1,9 @@
+// { dg-additional-options "-fmodules-ts -fdump-lang-module" }
+// { dg-module-cmi empty }
+
+module;
+#include "xtreme-header.h"
+export module empty;
+
+// The whole GMF should be discarded here
+// { dg-final { scan-lang-dump "Wrote 0 clusters" module } }
diff --git a/gcc/testsuite/g++.dg/modules/xtreme-header.h
b/gcc/testsuite/g++.dg/modules/xtreme-header.h
index 3147aaf00f4..6f98a3acecd 100644
--- a/gcc/testsuite/g++.dg/modules/xtreme-header.h
+++ b/gcc/testsuite/g++.dg/modules/xtreme-header.h
@@ -89,7 +89,6 @@
// C++20
#if __cplusplus > 201703
-#if 1
#include <version>
#include <barrier>
#include <bit>
@@ -98,6 +97,7 @@
#if __cpp_coroutines
#include <coroutine>
#endif
+#include <format>
#include <latch>
#include <numbers>
#include <ranges>
@@ -106,24 +106,33 @@
#include <span>
#include <stop_token>
#include <syncstream>
-#if 0
-// Unimplemented
-#include <format>
-#endif
-#endif
#endif
// C++23
#if __cplusplus > 202002L
#include <expected>
+#include <generator>
+#include <print>
#include <spanstream>
#include <stacktrace>
+#include <stdfloat>
#if 0
// Unimplemented
#include <flat_map>
#include <flat_set>
-#include <generator>
#include <mdspan>
-#include <print>
+#endif
+#endif
+
+// C++26
+#if __cplusplus > 202302L
+#if 0
+// Unimplemented
+#include <debugging>
+#include <execution>
+#include <hazard_pointer>
+#include <linalg>
+#include <rcu>
+#include <text_encoding>
#endif
#endif
