2 files changed, 19 insertions, 4 deletions
diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index 38bf5dd..1faa046 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -351,15 +351,23 @@ getLoadLoadClobberFullWidthSize(const Value *MemLocBase, int64_t MemLocOffs,
 /// getPointerDependencyFrom - Return the instruction on which a memory
 /// location depends.  If isLoad is true, this routine ignores may-aliases with
 /// read-only operations.  If isLoad is false, this routine ignores may-aliases
-/// with reads from read-only locations.
+/// with reads from read-only locations.  If possible, pass the query
+/// instruction as well; this function may take advantage of the metadata
+/// annotated to the query instruction to refine the result.
 MemDepResult MemoryDependenceAnalysis::
 getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad, 
-                         BasicBlock::iterator ScanIt, BasicBlock *BB) {
+                         BasicBlock::iterator ScanIt, BasicBlock *BB,
+                         Instruction *QueryInst) {
 
   const Value *MemLocBase = 0;
   int64_t MemLocOffset = 0;
-
   unsigned Limit = BlockScanLimit;
+  bool isInvariantLoad = false;
+  if (isLoad && QueryInst) {
+    LoadInst *LI = dyn_cast<LoadInst>(QueryInst);
+    if (LI && LI->getMetadata(LLVMContext::MD_invariant_load) != 0)
+      isInvariantLoad = true;
+  }
 
   // Walk backwards through the basic block, looking for dependencies.
   while (ScanIt != BB->begin()) {
@@ -474,6 +482,8 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
         continue;
       if (R == AliasAnalysis::MustAlias)
         return MemDepResult::getDef(Inst);
+      if (isInvariantLoad)
+       continue;
       return MemDepResult::getClobber(Inst);
     }
 
@@ -571,7 +581,7 @@ MemDepResult MemoryDependenceAnalysis::getDependency(Instruction *QueryInst) {
         isLoad |= II->getIntrinsicID() == Intrinsic::lifetime_start;
 
       LocalCache = getPointerDependencyFrom(MemLoc, isLoad, ScanPos,
-                                            QueryParent);
+                                            QueryParent, QueryInst);
     } else if (isa<CallInst>(QueryInst) || isa<InvokeInst>(QueryInst)) {
       CallSite QueryCS(QueryInst);
       bool isReadOnly = AA->onlyReadsMemory(QueryCS);
diff --git a/lib/IR/LLVMContext.cpp b/lib/IR/LLVMContext.cpp
index b73cd03..883bb98 100644
--- a/lib/IR/LLVMContext.cpp
+++ b/lib/IR/LLVMContext.cpp
@@ -58,6 +58,11 @@ LLVMContext::LLVMContext() : pImpl(new LLVMContextImpl(*this)) {
   unsigned TBAAStructID = getMDKindID("tbaa.struct");
   assert(TBAAStructID == MD_tbaa_struct && "tbaa.struct kind id drifted");
   (void)TBAAStructID;
+
+  // Create the 'invariant.load' metadata kind.
+  unsigned InvariantLdId = getMDKindID("invariant.load");
+  assert(InvariantLdId == MD_invariant_load && "invariant.load kind id drifted");
+  (void)InvariantLdId;
 }
 LLVMContext::~LLVMContext() { delete pImpl; }