c++/modules: Stream unmergeable temporaries by value again [PR114856]

In r14-9266-g2823b4d96d9ec4 I gave all temporary vars a DECL_CONTEXT,
including those at namespace or global scope, so that they could be
properly merged across importers.  However, not all of these temporary
vars are actually supposed to be mergeable.

For instance, in the attached testcase we have an unnamed temporary var
used in the NSDMI of a class member, which cannot properly merged -- but
it also doesn't need to be, as it'll be thrown away when the class type
itself is merged anyway.

This patch reverts the change made above and instead makes a weaker
adjustment that only causes temporary vars with linkage have a
DECL_CONTEXT to merge from.  This way these unnamed, "unmergeable"
temporaries are properly streamed by value again.

	PR c++/114856

gcc/cp/ChangeLog:

	* call.cc (make_temporary_var_for_ref_to_temp): Set context for
	temporaries with linkage.
	* init.cc (create_temporary_var): Revert to only set context
	when in a function decl.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/pr114856.h: New test.
	* g++.dg/modules/pr114856_a.H: New test.
	* g++.dg/modules/pr114856_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>
Reviewed-by: Patrick Palka <ppalka@redhat.com>

5 files changed, 26 insertions, 1 deletions

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 7c4ecf0..e058da7 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -13802,6 +13802,9 @@ make_temporary_var_for_ref_to_temp (tree decl, tree type)
       tree name = mangle_ref_init_variable (decl);
       DECL_NAME (var) = name;
       SET_DECL_ASSEMBLER_NAME (var, name);
+
+      /* Set the context to make the variable mergeable in modules.  */
+      DECL_CONTEXT (var) = current_scope ();
     }
   else
     /* Create a new cleanup level if necessary.  */
diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index c1b5b74..7bb98f4 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -4287,7 +4287,7 @@ create_temporary_var (tree type)
   TREE_USED (decl) = 1;
   DECL_ARTIFICIAL (decl) = 1;
   DECL_IGNORED_P (decl) = 1;
-  DECL_CONTEXT (decl) = current_scope ();
+  DECL_CONTEXT (decl) = current_function_decl;
 
   return decl;
 }
diff --git a/gcc/testsuite/g++.dg/modules/pr114856.h b/gcc/testsuite/g++.dg/modules/pr114856.h
new file mode 100644
index 0000000..b1a3c2c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr114856.h
@@ -0,0 +1,12 @@
+// PR c++/114856
+
+#include <initializer_list>
+struct A {
+  ~A();
+};
+struct V {
+  V(std::initializer_list<A>);
+};
+struct data {
+  V v{{}};
+};
diff --git a/gcc/testsuite/g++.dg/modules/pr114856_a.H b/gcc/testsuite/g++.dg/modules/pr114856_a.H
new file mode 100644
index 0000000..6195277
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr114856_a.H
@@ -0,0 +1,5 @@
+// PR c++/114856
+// { dg-additional-options "-fmodule-header" }
+// { dg-module-cmi {} }
+
+#include "pr114856.h"
diff --git a/gcc/testsuite/g++.dg/modules/pr114856_b.C b/gcc/testsuite/g++.dg/modules/pr114856_b.C
new file mode 100644
index 0000000..f81dc8b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr114856_b.C
@@ -0,0 +1,5 @@
+// PR c++/114856
+// { dg-additional-options "-fmodules-ts" }
+
+#include "pr114856.h"
+import "pr114856_a.H";