[ThinLTO] Import local variables from the same module as caller

Summary:
We can sometimes end up with multiple copies of a local variable that
have the same GUID in the index. This happens when there are local
variables with the same name that are in different source files having the
same name/path at compile time (but compiled into different bitcode objects).

In this case make sure we import the copy in the caller's module.
This enables importing both of the variables having the same GUID
(but which will have different promoted names since the module paths,
and therefore the module hashes, will be distinct).

Importing the wrong copy is particularly problematic for read only
variables, since we must import them as a local copy whenever
referenced. Otherwise we get undefs at link time.

Note that the llvm-lto.cpp and ThinLTOCodeGenerator changes are needed
for testing the distributed index case via clang, which will be sent as
a separate clang-side patch shortly. We were previously not doing the
dead code/read only computation before computing imports when testing
distributed index generation (like it was for testing importing and
other ThinLTO mechanisms alone).

Reviewers: evgeny777

Subscribers: mehdi_amini, inglorion, eraman, steven_wu, dexonsmith, dang, llvm-commits

Differential Revision: https://reviews.llvm.org/D55047

llvm-svn: 347886

1 files changed, 26 insertions, 11 deletions

diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
index e9633b015c1..fe0f5b7d4cb 100644
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -661,37 +661,52 @@ void ThinLTOCodeGenerator::crossModuleImport(Module &TheModule,
  * Compute the list of summaries needed for importing into module.
  */
 void ThinLTOCodeGenerator::gatherImportedSummariesForModule(
-    StringRef ModulePath, ModuleSummaryIndex &Index,
+    Module &TheModule, ModuleSummaryIndex &Index,
     std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex) {
   auto ModuleCount = Index.modulePaths().size();
+  auto ModuleIdentifier = TheModule.getModuleIdentifier();
 
   // Collect for each module the list of function it defines (GUID -> Summary).
   StringMap<GVSummaryMapTy> ModuleToDefinedGVSummaries(ModuleCount);
   Index.collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
 
+  // Convert the preserved symbols set from string to GUID
+  auto GUIDPreservedSymbols = computeGUIDPreservedSymbols(
+      PreservedSymbols, Triple(TheModule.getTargetTriple()));
+
+  // Compute "dead" symbols, we don't want to import/export these!
+  computeDeadSymbolsInIndex(Index, GUIDPreservedSymbols);
+
   // Generate import/export list
   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
                            ExportLists);
 
-  llvm::gatherImportedSummariesForModule(ModulePath, ModuleToDefinedGVSummaries,
-                                         ImportLists[ModulePath],
-                                         ModuleToSummariesForIndex);
+  llvm::gatherImportedSummariesForModule(
+      ModuleIdentifier, ModuleToDefinedGVSummaries,
+      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex);
 }
 
 /**
  * Emit the list of files needed for importing into module.
  */
-void ThinLTOCodeGenerator::emitImports(StringRef ModulePath,
-                                       StringRef OutputName,
+void ThinLTOCodeGenerator::emitImports(Module &TheModule, StringRef OutputName,
                                        ModuleSummaryIndex &Index) {
   auto ModuleCount = Index.modulePaths().size();
+  auto ModuleIdentifier = TheModule.getModuleIdentifier();
 
   // Collect for each module the list of function it defines (GUID -> Summary).
   StringMap<GVSummaryMapTy> ModuleToDefinedGVSummaries(ModuleCount);
   Index.collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
 
+  // Convert the preserved symbols set from string to GUID
+  auto GUIDPreservedSymbols = computeGUIDPreservedSymbols(
+      PreservedSymbols, Triple(TheModule.getTargetTriple()));
+
+  // Compute "dead" symbols, we don't want to import/export these!
+  computeDeadSymbolsInIndex(Index, GUIDPreservedSymbols);
+
   // Generate import/export list
   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
@@ -699,13 +714,13 @@ void ThinLTOCodeGenerator::emitImports(StringRef ModulePath,
                            ExportLists);
 
   std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
-  llvm::gatherImportedSummariesForModule(ModulePath, ModuleToDefinedGVSummaries,
-                                         ImportLists[ModulePath],
-                                         ModuleToSummariesForIndex);
+  llvm::gatherImportedSummariesForModule(
+      ModuleIdentifier, ModuleToDefinedGVSummaries,
+      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex);
 
   std::error_code EC;
-  if ((EC =
-           EmitImportsFiles(ModulePath, OutputName, ModuleToSummariesForIndex)))
+  if ((EC = EmitImportsFiles(ModuleIdentifier, OutputName,
+                             ModuleToSummariesForIndex)))
     report_fatal_error(Twine("Failed to open ") + OutputName +
                        " to save imports lists\n");
 }