ThinLTO: don't perform incremental LTO on module without a hash

Clang always emit a hash for ThinLTO, but as other frontend are
starting to use ThinLTO, this could be a serious bug.

Differential Revision: https://reviews.llvm.org/D25379

llvm-svn: 283655

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 94a4abfb896..8d23f53eae6 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -542,8 +542,12 @@ public:
     };
 
     auto ModuleID = MBRef.getBufferIdentifier();
-    if (!Cache || !CombinedIndex.modulePaths().count(ModuleID))
-      // Cache disabled or no entry for this module in the combined index
+
+    if (!Cache || !CombinedIndex.modulePaths().count(ModuleID) ||
+        all_of(CombinedIndex.getModuleHash(ModuleID),
+               [](uint32_t V) { return V == 0; }))
+      // Cache disabled or no entry for this module in the combined index or
+      // no module hash.
       return RunThinBackend(AddStream);
 
     SmallString<40> Key;