[Modules] Make the AST serialization always use lexicographic order when

traversing the identifier table.

No easy test case as this table is somewhere between hard and impossible
to observe as non-deterministically ordered. The table is a hash table
but we hash the string contents and never remove entries from the table
so the growth pattern, etc, is all completely fixed. However, relying on
the hash function being deterministic is specifically against the
long-term direction of LLVM's hashing datastructures, which are intended
to provide *no* ordering guarantees. As such, this defends against these
things by sorting the identifiers. Sorting identifiers right before we
emit them to a serialized form seems a low cost for predictability here.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@233332 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/clang/Basic/IdentifierTable.h b/include/clang/Basic/IdentifierTable.h
index f540c58e5a56d69a1e4e0158dc3afb429b2bcae2..67371f51f3f9efc82b156eb955645876b0c5ef6c 100644 (file)
--- a/include/clang/Basic/IdentifierTable.h
+++ b/include/clang/Basic/IdentifierTable.h
@@ -308,7 +308,12 @@ public:
     else
       RecomputeNeedsHandleIdentifier();
   }
-  
+
+  /// \brief Provide less than operator for lexicographical sorting.
+  bool operator<(const IdentifierInfo &RHS) const {
+    return getName() < RHS.getName();
+  }
+
 private:
   /// The Preprocessor::HandleIdentifier does several special (but rare)
   /// things to identifiers of various sorts.  For example, it changes the

diff --git a/lib/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index 3f2c46d80efe81a62050f729c9347cae8da425e6..655c9fd28b5f905134f95b14b88e538e11bfce61 100644 (file)
--- a/lib/Serialization/ASTWriter.cpp
+++ b/lib/Serialization/ASTWriter.cpp
@@ -3504,10 +3504,16 @@ void ASTWriter::WriteIdentifierTable(Preprocessor &PP,
     // table to enable checking of the predefines buffer in the case
     // where the user adds new macro definitions when building the AST
     // file.
+    SmallVector<const IdentifierInfo *, 128> IIs;
     for (IdentifierTable::iterator ID = PP.getIdentifierTable().begin(),
                                 IDEnd = PP.getIdentifierTable().end();
          ID != IDEnd; ++ID)
-      getIdentifierRef(ID->second);
+      IIs.push_back(ID->second);
+    // Sort the identifiers lexicographically before getting them references so
+    // that their order is stable.
+    std::sort(IIs.begin(), IIs.end(), llvm::less_ptr<IdentifierInfo>());
+    for (const IdentifierInfo *II : IIs)
+      getIdentifierRef(II);
 
     // Create the on-disk hash table representation. We only store offsets
     // for identifiers that appear here for the first time.
@@ -4504,15 +4510,17 @@ void ASTWriter::WriteASTCore(Sema &SemaRef,
 
   // Make sure all decls associated with an identifier are registered for
   // serialization.
-  llvm::SmallVector<const IdentifierInfo*, 256> IIsToVisit;
+  llvm::SmallVector<const IdentifierInfo*, 256> IIs;
   for (IdentifierTable::iterator ID = PP.getIdentifierTable().begin(),
                               IDEnd = PP.getIdentifierTable().end();
        ID != IDEnd; ++ID) {
     const IdentifierInfo *II = ID->second;
     if (!Chain || !II->isFromAST() || II->hasChangedSinceDeserialization())
-      IIsToVisit.push_back(II);
+      IIs.push_back(II);
   }
-  for (const IdentifierInfo *II : IIsToVisit) {
+  // Sort the identifiers to visit based on their name.
+  std::sort(IIs.begin(), IIs.end(), llvm::less_ptr<IdentifierInfo>());
+  for (const IdentifierInfo *II : IIs) {
     for (IdentifierResolver::iterator D = SemaRef.IdResolver.begin(II),
                                    DEnd = SemaRef.IdResolver.end();
          D != DEnd; ++D) {