[llvm-branch-commits] [llvm] 8f299fd - Fixed false ThinLTO cache misses problem (PR 45819).

[Tom Stellard via llvm-branch-commits]

Author: romanova-ekaterina
Date: 2020-06-22T16:10:37-07:00
New Revision: 8f299fd2cff7d99c1aacf602ee50e96ded59d706

URL: https://github.com/llvm/llvm-project/commit/8f299fd2cff7d99c1aacf602ee50e96ded59d706
DIFF: https://github.com/llvm/llvm-project/commit/8f299fd2cff7d99c1aacf602ee50e96ded59d706.diff

LOG: Fixed false ThinLTO cache misses problem (PR 45819).

We relied on the fact that the iterators walks through the elements of a
DenseSet in a deterministic order (which is not true). This caused
ThinLTO cache misses. This patch addresses this problem.
See PR 45819 for additional information
https://bugs.llvm.org/show_bug.cgi?id=45819

Differential Revision: https://reviews.llvm.org/D79772

(cherry picked from commit 252892fea7088abbeff9476e0ecbacc091d135a0)

Added: 
    

Modified: 
    llvm/lib/LTO/LTO.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 297b11de17a9..fa2f0777897b 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -147,8 +147,17 @@ void llvm::computeLTOCacheKey(
   // Include the hash for the current module
   auto ModHash = Index.getModuleHash(ModuleID);
   Hasher.update(ArrayRef<uint8_t>((uint8_t *)&ModHash[0], sizeof(ModHash)));
+
+  std::vector<uint64_t> ExportsGUID;
+  ExportsGUID.reserve(ExportList.size());
   for (const auto &VI : ExportList) {
     auto GUID = VI.getGUID();
+    ExportsGUID.push_back(GUID);
+  }
+
+  // Sort the export list elements GUIDs.
+  llvm::sort(ExportsGUID);
+  for (uint64_t GUID : ExportsGUID) {
     // The export list can impact the internalization, be conservative here
     Hasher.update(ArrayRef<uint8_t>((uint8_t *)&GUID, sizeof(GUID)));
   }
@@ -156,12 +165,23 @@ void llvm::computeLTOCacheKey(
   // Include the hash for every module we import functions from. The set of
   // imported symbols for each module may affect code generation and is
   // sensitive to link order, so include that as well.
-  for (auto &Entry : ImportList) {
-    auto ModHash = Index.getModuleHash(Entry.first());
+  using ImportMapIteratorTy = FunctionImporter::ImportMapTy::const_iterator;
+  std::vector<ImportMapIteratorTy> ImportModulesVector;
+  ImportModulesVector.reserve(ImportList.size());
+
+  for (ImportMapIteratorTy It = ImportList.begin(); It != ImportList.end();
+       ++It) {
+    ImportModulesVector.push_back(It);
+  }
+  llvm::sort(ImportModulesVector,
+             [](const ImportMapIteratorTy &Lhs, const ImportMapIteratorTy &Rhs)
+                 -> bool { return Lhs->getKey() < Rhs->getKey(); });
+  for (const ImportMapIteratorTy &EntryIt : ImportModulesVector) {
+    auto ModHash = Index.getModuleHash(EntryIt->first());
     Hasher.update(ArrayRef<uint8_t>((uint8_t *)&ModHash[0], sizeof(ModHash)));
 
-    AddUint64(Entry.second.size());
-    for (auto &Fn : Entry.second)
+    AddUint64(EntryIt->second.size());
+    for (auto &Fn : EntryIt->second)
       AddUint64(Fn);
   }