ThinLTO: handles modules with empty summaries

We need to add an entry in the combined-index for modules that have
a hash but otherwise empty summary, this is needed so that we can
get the hash for the module.

Also, if no entry is present in the combined index for a module, we
need to skip it when trying to compute a cache entry.

Differential Revision: https://reviews.llvm.org/D25300

llvm-svn: 283654

1 files changed, 10 insertions, 11 deletions

diff --git a/llvm/lib/IR/ModuleSummaryIndex.cpp b/llvm/lib/IR/ModuleSummaryIndex.cpp
index 6107cf40a08..9072f4bc7b1 100644
--- a/llvm/lib/IR/ModuleSummaryIndex.cpp
+++ b/llvm/lib/IR/ModuleSummaryIndex.cpp
@@ -20,8 +20,17 @@ using namespace llvm;
 // per-module instances.
 void ModuleSummaryIndex::mergeFrom(std::unique_ptr<ModuleSummaryIndex> Other,
                                    uint64_t NextModuleId) {
+  if (Other->modulePaths().empty())
+    return;
+
+  assert(Other->modulePaths().size() == 1 &&
+         "Can only merge from an single-module index at that time");
+
+  StringRef OtherModPath = Other->modulePaths().begin()->first();
+  StringRef ModPath = addModulePath(OtherModPath, NextModuleId,
+                                    Other->getModuleHash(OtherModPath))
+                          ->first();
 
-  StringRef ModPath;
   for (auto &OtherGlobalValSummaryLists : *Other) {
     GlobalValue::GUID ValueGUID = OtherGlobalValSummaryLists.first;
     GlobalValueSummaryList &List = OtherGlobalValSummaryLists.second;
@@ -31,16 +40,6 @@ void ModuleSummaryIndex::mergeFrom(std::unique_ptr<ModuleSummaryIndex> Other,
     assert(List.size() == 1);
     std::unique_ptr<GlobalValueSummary> Summary = std::move(List.front());
 
-    // Add the module path string ref for this module if we haven't already
-    // saved a reference to it.
-    if (ModPath.empty()) {
-      auto Path = Summary->modulePath();
-      ModPath = addModulePath(Path, NextModuleId, Other->getModuleHash(Path))
-                    ->first();
-    } else
-      assert(ModPath == Summary->modulePath() &&
-             "Each module in the combined map should have a unique ID");
-
     // Note the module path string ref was copied above and is still owned by
     // the original per-module index. Reset it to the new module path
     // string reference owned by the combined index.