[C++20] [Modules] Don't create multiple global module fragment

Since the serialization code would recognize modules by names and the
name of all global module fragment is <global>, so that the
serialization code would complain for the same module.

This patch fixes this by using a unique global module fragment in Sema.
Before this patch, the compiler would fail on an assertion complaining
the duplicated modules.

Reviewed By: urnathan, rsmith

Differential Revision: https://reviews.llvm.org/D115610

1 files changed, 13 insertions, 8 deletions

diff --git a/clang/lib/Sema/SemaModule.cpp b/clang/lib/Sema/SemaModule.cpp
index 747734f..85e5864 100644
--- a/clang/lib/Sema/SemaModule.cpp
+++ b/clang/lib/Sema/SemaModule.cpp
@@ -720,19 +720,24 @@ Decl *Sema::ActOnFinishExportDecl(Scope *S, Decl *D, SourceLocation RBraceLoc) {
 
 Module *Sema::PushGlobalModuleFragment(SourceLocation BeginLoc,
                                        bool IsImplicit) {
-  ModuleMap &Map = PP.getHeaderSearchInfo().getModuleMap();
-  Module *GlobalModule =
-      Map.createGlobalModuleFragmentForModuleUnit(BeginLoc, getCurrentModule());
-  assert(GlobalModule && "module creation should not fail");
+  // We shouldn't create new global module fragment if there is already
+  // one.
+  if (!GlobalModuleFragment) {
+    ModuleMap &Map = PP.getHeaderSearchInfo().getModuleMap();
+    GlobalModuleFragment = Map.createGlobalModuleFragmentForModuleUnit(
+        BeginLoc, getCurrentModule());
+  }
+
+  assert(GlobalModuleFragment && "module creation should not fail");
 
   // Enter the scope of the global module.
-  ModuleScopes.push_back({BeginLoc, GlobalModule,
+  ModuleScopes.push_back({BeginLoc, GlobalModuleFragment,
                           /*ModuleInterface=*/false,
                           /*ImplicitGlobalModuleFragment=*/IsImplicit,
-                          /*VisibleModuleSet*/{}});
-  VisibleModules.setVisible(GlobalModule, BeginLoc);
+                          /*VisibleModuleSet*/ {}});
+  VisibleModules.setVisible(GlobalModuleFragment, BeginLoc);
 
-  return GlobalModule;
+  return GlobalModuleFragment;
 }
 
 void Sema::PopGlobalModuleFragment() {