[ThinLTO] Delay metadata materializtion in function importer

The function importer was still materializing metadata when modules were
loaded for function importing. We only want to materialize it when we
are going to invoke the metadata linking postpass. Materializing it
before function importing is not only unnecessary, but also causes
metadata referenced by imported functions to be mapped in early, and
then not connected to the rest of the module level metadata when it is
ultimately linked in.

Augmented the test case to specifically check for the metadata being
properly connected, which it wasn't before this fix.

llvm-svn: 257171

1 files changed, 9 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index d8b677b966f..d194c5e424d 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -41,15 +41,16 @@ static std::unique_ptr<Module> loadFile(const std::string &FileName,
                                         LLVMContext &Context) {
   SMDiagnostic Err;
   DEBUG(dbgs() << "Loading '" << FileName << "'\n");
-  std::unique_ptr<Module> Result = getLazyIRFileModule(FileName, Err, Context);
+  // Metadata isn't loaded or linked until after all functions are
+  // imported, after which it will be materialized and linked.
+  std::unique_ptr<Module> Result =
+      getLazyIRFileModule(FileName, Err, Context,
+                          /* ShouldLazyLoadMetadata = */ true);
   if (!Result) {
     Err.print("function-import", errs());
     return nullptr;
   }
 
-  Result->materializeMetadata();
-  UpgradeDebugInfo(*Result);
-
   return Result;
 }
 
@@ -324,6 +325,10 @@ bool FunctionImporter::importFunctions(Module &DestModule) {
        ModuleToTempMDValsMap) {
     // Load the specified source module.
     auto &SrcModule = ModuleLoaderCache(SME.getKey());
+    // The modules were created with lazy metadata loading. Materialize it
+    // now, before linking it.
+    SrcModule.materializeMetadata();
+    UpgradeDebugInfo(SrcModule);
 
     // Link in all necessary metadata from this module.
     if (TheLinker.linkInMetadata(SrcModule, SME.getValue().get()))