Fix pr14893.

When simplifycfg moves an instruction, it must drop metadata it doesn't know
is still valid with the preconditions changes. In particular, it must drop
the range and tbaa metadata.

The patch implements this with an utility function to drop all metadata not
in a white list.

llvm-svn: 200322

2 files changed, 53 insertions, 0 deletions

diff --git a/llvm/lib/IR/Metadata.cpp b/llvm/lib/IR/Metadata.cpp
index a32d25c92ae..ad943de88cc 100644
--- a/llvm/lib/IR/Metadata.cpp
+++ b/llvm/lib/IR/Metadata.cpp
@@ -16,6 +16,7 @@
 #include "SymbolTableListTraitsImpl.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/IR/Instruction.h"
@@ -583,6 +584,50 @@ MDNode *Instruction::getMetadataImpl(StringRef Kind) const {
   return getMetadataImpl(getContext().getMDKindID(Kind));
 }
 
+void Instruction::dropUnknownMetadata(ArrayRef<unsigned> KnownIDs) {
+  SmallSet<unsigned, 5> KnownSet;
+  KnownSet.insert(KnownIDs.begin(), KnownIDs.end());
+
+  // Drop debug if needed
+  if (KnownSet.erase(LLVMContext::MD_dbg))
+    DbgLoc = DebugLoc();
+
+  if (!hasMetadataHashEntry())
+    return; // Nothing to remove!
+
+  DenseMap<const Instruction *, LLVMContextImpl::MDMapTy> &MetadataStore =
+      getContext().pImpl->MetadataStore;
+
+  if (KnownSet.empty()) {
+    // Just drop our entry at the store.
+    MetadataStore.erase(this);
+    setHasMetadataHashEntry(false);
+    return;
+  }
+
+  LLVMContextImpl::MDMapTy &Info = MetadataStore[this];
+  unsigned I;
+  unsigned E;
+  // Walk the array and drop any metadata we don't know.
+  for (I = 0, E = Info.size(); I != E;) {
+    if (KnownSet.count(Info[I].first)) {
+      ++I;
+      continue;
+    }
+
+    Info[I] = Info.back();
+    Info.pop_back();
+    --E;
+  }
+  assert(E == Info.size());
+
+  if (E == 0) {
+    // Drop our entry at the store.
+    MetadataStore.erase(this);
+    setHasMetadataHashEntry(false);
+  }
+}
+
 /// setMetadata - Set the metadata of of the specified kind to the specified
 /// node.  This updates/replaces metadata if already present, or removes it if
 /// Node is null.
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 0401b9a7f7d..effc08edaa3 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2154,6 +2154,14 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
     Instruction *NewBonus = 0;
     if (BonusInst) {
       NewBonus = BonusInst->clone();
+
+      // If we moved a load, we cannot any longer claim any knowledge about
+      // its potential value. The previous information might have been valid
+      // only given the branch precondition.
+      // For an analogous reason, we must also drop all the metadata whose
+      // semantics we don't understand.
+      NewBonus->dropUnknownMetadata(LLVMContext::MD_dbg);
+
       PredBlock->getInstList().insert(PBI, NewBonus);
       NewBonus->takeName(BonusInst);
       BonusInst->setName(BonusInst->getName()+".old");