[ThinLTO] Metadata linking for imported functions

Summary:
Second patch split out from http://reviews.llvm.org/D14752.

Maps metadata as a post-pass from each module when importing complete,
suturing up final metadata to the temporary metadata left on the
imported instructions.

This entails saving the mapping from bitcode value id to temporary
metadata in the importing pass, and from bitcode value id to final
metadata during the metadata linking postpass.

Depends on D14825.

Reviewers: dexonsmith, joker.eph

Subscribers: davidxl, llvm-commits, joker.eph

Differential Revision: http://reviews.llvm.org/D14838

llvm-svn: 255909

1 files changed, 42 insertions, 7 deletions

diff --git a/llvm/tools/llvm-link/llvm-link.cpp b/llvm/tools/llvm-link/llvm-link.cpp
index 326ecba3ae9..a32383028ae 100644
--- a/llvm/tools/llvm-link/llvm-link.cpp
+++ b/llvm/tools/llvm-link/llvm-link.cpp
@@ -106,16 +106,21 @@ static cl::opt<bool> PreserveAssemblyUseListOrder(
 // Read the specified bitcode file in and return it. This routine searches the
 // link path for the specified file to try to find it...
 //
-static std::unique_ptr<Module>
-loadFile(const char *argv0, const std::string &FN, LLVMContext &Context) {
+static std::unique_ptr<Module> loadFile(const char *argv0,
+                                        const std::string &FN,
+                                        LLVMContext &Context,
+                                        bool MaterializeMetadata = true) {
   SMDiagnostic Err;
   if (Verbose) errs() << "Loading '" << FN << "'\n";
-  std::unique_ptr<Module> Result = getLazyIRFileModule(FN, Err, Context);
+  std::unique_ptr<Module> Result =
+      getLazyIRFileModule(FN, Err, Context, !MaterializeMetadata);
   if (!Result)
     Err.print(argv0, errs());
 
-  Result->materializeMetadata();
-  UpgradeDebugInfo(*Result);
+  if (MaterializeMetadata) {
+    Result->materializeMetadata();
+    UpgradeDebugInfo(*Result);
+  }
 
   return Result;
 }
@@ -148,6 +153,8 @@ static void diagnosticHandlerWithContext(const DiagnosticInfo &DI, void *C) {
 /// Import any functions requested via the -import option.
 static bool importFunctions(const char *argv0, LLVMContext &Context,
                             Linker &L) {
+  StringMap<std::unique_ptr<DenseMap<unsigned, MDNode *>>>
+      ModuleToTempMDValsMap;
   for (const auto &Import : Imports) {
     // Identify the requested function and its bitcode source file.
     size_t Idx = Import.find(':');
@@ -159,7 +166,7 @@ static bool importFunctions(const char *argv0, LLVMContext &Context,
     std::string FileName = Import.substr(Idx + 1, std::string::npos);
 
     // Load the specified source module.
-    std::unique_ptr<Module> M = loadFile(argv0, FileName, Context);
+    std::unique_ptr<Module> M = loadFile(argv0, FileName, Context, false);
     if (!M.get()) {
       errs() << argv0 << ": error loading file '" << FileName << "'\n";
       return false;
@@ -201,11 +208,39 @@ static bool importFunctions(const char *argv0, LLVMContext &Context,
       Index = std::move(IndexOrErr.get());
     }
 
+    // Save the mapping of value ids to temporary metadata created when
+    // importing this function. If we have already imported from this module,
+    // add new temporary metadata to the existing mapping.
+    auto &TempMDVals = ModuleToTempMDValsMap[FileName];
+    if (!TempMDVals)
+      TempMDVals = llvm::make_unique<DenseMap<unsigned, MDNode *>>();
+
     // Link in the specified function.
     DenseSet<const GlobalValue *> FunctionsToImport;
     FunctionsToImport.insert(F);
     if (L.linkInModule(std::move(M), Linker::Flags::None, Index.get(),
-                       &FunctionsToImport))
+                       &FunctionsToImport, TempMDVals.get()))
+      return false;
+  }
+
+  // Now link in metadata for all modules from which we imported functions.
+  for (StringMapEntry<std::unique_ptr<DenseMap<unsigned, MDNode *>>> &SME :
+       ModuleToTempMDValsMap) {
+    // Load the specified source module.
+    std::unique_ptr<Module> M = loadFile(argv0, SME.getKey(), Context, true);
+    if (!M.get()) {
+      errs() << argv0 << ": error loading file '" << SME.getKey() << "'\n";
+      return false;
+    }
+
+    if (verifyModule(*M, &errs())) {
+      errs() << argv0 << ": " << SME.getKey()
+             << ": error: input module is broken!\n";
+      return false;
+    }
+
+    // Link in all necessary metadata from this module.
+    if (L.linkInMetadata(*M, SME.getValue().get()))
       return false;
   }
   return true;