Modules: Enforce that ModuleManager::removeModules deletes the tail

ModuleManager::removeModules always deletes a tail of the
ModuleManager::Chain.  Change the API to enforce that so that we can
simplify the code inside.

There's no real functionality change, although there's a slight
performance hack to loop to the First deleted module instead of the
final module in the chain (skipping the about-to-be-deleted tail).

Also document something suspicious: we fail to clean deleted modules out
of ModuleFile::Imports.

llvm-svn: 293398

1 files changed, 3 insertions, 4 deletions

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 5cebe47052d..44cef7de312 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -3643,11 +3643,10 @@ ASTReader::ASTReadResult ASTReader::ReadAST(StringRef FileName,
     for (const ImportedModule &IM : Loaded)
       LoadedSet.insert(IM.Mod);
 
-    ModuleMgr.removeModules(ModuleMgr.begin() + NumModules, ModuleMgr.end(),
-                            LoadedSet,
+    ModuleMgr.removeModules(ModuleMgr.begin() + NumModules, LoadedSet,
                             Context.getLangOpts().Modules
-                              ? &PP.getHeaderSearchInfo().getModuleMap()
-                              : nullptr);
+                                ? &PP.getHeaderSearchInfo().getModuleMap()
+                                : nullptr);
 
     // If we find that any modules are unusable, the global index is going
     // to be out-of-date. Just remove it.