Ensure MDNode used as key in metadata linking map cannot be RAUWed

As suggested in review for r255909, add a way to ensure that temporary
MD used as keys in the MetadataToID map during ThinLTO importing are not
RAUWed.

Add support for marking an MDNode as not replaceable. Clear the new
CanReplace flag when adding a temporary MD node to the MetadataToID map
and clear it when destroying the map.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256648 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/IR/Metadata.h b/include/llvm/IR/Metadata.h
index 2ea591383f82543d22fe42233e8593f044857770..0715229a87546836f07f816d069ae0b5daddce0f 100644 (file)
--- a/include/llvm/IR/Metadata.h
+++ b/include/llvm/IR/Metadata.h
@@ -283,14 +283,20 @@ private:
   LLVMContext &Context;
   uint64_t NextIndex;
   SmallDenseMap<void *, std::pair<OwnerTy, uint64_t>, 4> UseMap;
+  /// Flag that can be set to false if this metadata should not be
+  /// RAUW'ed, e.g. if it is used as the key of a map.
+  bool CanReplace;
 
 public:
   ReplaceableMetadataImpl(LLVMContext &Context)
-      : Context(Context), NextIndex(0) {}
+      : Context(Context), NextIndex(0), CanReplace(true) {}
   ~ReplaceableMetadataImpl() {
     assert(UseMap.empty() && "Cannot destroy in-use replaceable metadata");
   }
 
+  /// Set the CanReplace flag to the given value.
+  void setCanReplace(bool Replaceable) { CanReplace = Replaceable; }
+
   LLVMContext &getContext() const { return Context; }
 
   /// \brief Replace all uses of this with MD.
@@ -901,6 +907,11 @@ public:
     Context.getReplaceableUses()->replaceAllUsesWith(MD);
   }
 
+  /// Set the CanReplace flag to the given value.
+  void setCanReplace(bool Replaceable) {
+    Context.getReplaceableUses()->setCanReplace(Replaceable);
+  }
+
   /// \brief Resolve cycles.
   ///
   /// Once all forward declarations have been resolved, force cycles to be

diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index 824a3716b831ec679792d4a7f123bbd218202f02..c7606fd488a0a7446ecb87e383aa5f7da37a5ed7 100644 (file)
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -3085,6 +3085,11 @@ void BitcodeReader::saveMetadataList(
         assert(MetadataToIDs[MD] == ID && "Inconsistent metadata value id");
         continue;
       }
+      if (N && N->isTemporary())
+        // Ensure that we assert if someone tries to RAUW this temporary
+        // metadata while it is the key of a map. The flag will be set back
+        // to true when the saved metadata list is destroyed.
+        N->setCanReplace(false);
       MetadataToIDs[MD] = ID;
     }
   }

diff --git a/lib/IR/Metadata.cpp b/lib/IR/Metadata.cpp
index ab1ba5e2035bc6ff3bed2439d4a0dc7c9083c983..f9543a658584b8f9435e5907f97c965591cd2a31 100644 (file)
--- a/lib/IR/Metadata.cpp
+++ b/lib/IR/Metadata.cpp
@@ -190,6 +190,8 @@ void ReplaceableMetadataImpl::moveRef(void *Ref, void *New,
 void ReplaceableMetadataImpl::replaceAllUsesWith(Metadata *MD) {
   assert(!(MD && isa<MDNode>(MD) && cast<MDNode>(MD)->isTemporary()) &&
          "Expected non-temp node");
+  assert(CanReplace &&
+         "Attempted to replace Metadata marked for no replacement");
 
   if (UseMap.empty())
     return;

diff --git a/lib/Linker/IRMover.cpp b/lib/Linker/IRMover.cpp
index fa6e37517fc4d766386a9259a4a40ef345712589..2e09d78a6906c1247d175e2a7b0ab95b80d6bc12 100644 (file)
--- a/lib/Linker/IRMover.cpp
+++ b/lib/Linker/IRMover.cpp
@@ -524,6 +524,23 @@ public:
       ValueMapperFlags = ValueMapperFlags | RF_HaveUnmaterializedMetadata;
   }
 
+  ~IRLinker() {
+    // In the case where we are not linking metadata, we unset the CanReplace
+    // flag on all temporary metadata in the MetadataToIDs map to ensure
+    // none was replaced while being a map key. Now that we are destructing
+    // the map, set the flag back to true, so that it is replaceable during
+    // metadata linking.
+    if (!shouldLinkMetadata()) {
+      for (auto MDI : MetadataToIDs) {
+        Metadata *MD = const_cast<Metadata *>(MDI.first);
+        MDNode *Node = dyn_cast<MDNode>(MD);
+        assert((Node && Node->isTemporary()) &&
+               "Found non-temp metadata in map when not linking metadata");
+        Node->setCanReplace(true);
+      }
+    }
+  }
+
   bool run();
   Value *materializeDeclFor(Value *V, bool ForAlias);
   void materializeInitFor(GlobalValue *New, GlobalValue *Old, bool ForAlias);