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

2 files changed, 13 insertions, 4 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;
diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
index 8afe13d8e16..10af9870ccb 100644
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -243,6 +243,13 @@ public:
     // export list, the hash for every single module in the import list, the
     // list of ResolvedODR for the module, and the list of preserved symbols.
 
+    // Include the hash for the current module
+    auto ModHash = Index.getModuleHash(ModuleID);
+
+    if (all_of(ModHash, [](uint32_t V) { return V == 0; }))
+      // No hash entry, no caching!
+      return;
+
     SHA1 Hasher;
 
     // Start with the compiler revision
@@ -251,8 +258,6 @@ public:
     Hasher.update(LLVM_REVISION);
 #endif
 
-    // Include the hash for the current module
-    auto ModHash = Index.getModuleHash(ModuleID);
     Hasher.update(ArrayRef<uint8_t>((uint8_t *)&ModHash[0], sizeof(ModHash)));
     for (auto F : ExportList)
       // The export list can impact the internalization, be conservative here