Work around a memory leak caught by the LSAN bot.

Fundamentally the problem here is that SILPassManager is creating an IRGenModule
without calling finalize() on it under some circumstances. It would be better to
fix that instead.

rdar://123923517
(cherry picked from commit 0742c01)

Author: adrian-prantl

lib/IRGen/IRGenDebugInfo.cpp

@@ -204,6 +204,12 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
                      IRGenModule &IGM, llvm::Module &M,
                      StringRef MainOutputFilenameForDebugInfo,
                      StringRef PrivateDiscriminator);
+  ~IRGenDebugInfoImpl() {
+    // FIXME: SILPassManager sometimes creates an IGM and doesn't finalize it.
+    if (!FwdDeclTypes.empty())
+      finalize();
+    assert(FwdDeclTypes.empty() && "finalize() was not called");
+  }
   void finalize();
 
   void setCurrentLoc(IRBuilder &Builder, const SILDebugScope *DS,
@@ -2549,6 +2555,7 @@ void IRGenDebugInfoImpl::finalize() {
     finalize(cast<llvm::MDNode>(Ty.second),
              llvm::cast_or_null<llvm::DIType>(DIRefMap.lookup(UID)), UID);
   }
+  FwdDeclTypes.clear();
 
   // Finalize the DIBuilder.
   DBuilder.finalize();

lib/IRGen/IRGenModule.cpp

@@ -1947,6 +1947,9 @@ bool IRGenModule::finalize() {
   // Finalize clang IR-generation.
   finalizeClangCodeGen();
 
+  if (DebugInfo)
+    DebugInfo->finalize();
+
   // If that failed, report failure up and skip the final clean-up.
   if (!ClangCodeGen->GetModule())
     return false;
@@ -1955,8 +1958,6 @@ bool IRGenModule::finalize() {
   emitAutolinkInfo();
   emitGlobalLists();
   emitUsedConditionals();
-  if (DebugInfo)
-    DebugInfo->finalize();
   cleanupClangCodeGenMetadata();
 
   // Clean up DSOLocal & DLLImport attributes, they cannot be applied together.