2 files changed, 17 insertions, 3 deletions
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 4fe054de370..ca4d66a540b 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -555,9 +555,17 @@ Metadata *BitcodeReaderMDValueList::getValueFwdRef(unsigned Idx) {
   if (Metadata *MD = MDValuePtrs[Idx])
     return MD;
 
-  // Create and return a placeholder, which will later be RAUW'd.
-  AnyFwdRefs = true;
+  // Track forward refs to be resolved later.
+  if (AnyFwdRefs) {
+    MinFwdRef = std::min(MinFwdRef, Idx);
+    MaxFwdRef = std::max(MaxFwdRef, Idx);
+  } else {
+    AnyFwdRefs = true;
+    MinFwdRef = MaxFwdRef = Idx;
+  }
   ++NumFwdRefs;
+
+  // Create and return a placeholder, which will later be RAUW'd.
   Metadata *MD = MDNode::getTemporary(Context, None).release();
   MDValuePtrs[Idx].reset(MD);
   return MD;
@@ -573,7 +581,8 @@ void BitcodeReaderMDValueList::tryToResolveCycles() {
     return;
 
   // Resolve any cycles.
-  for (auto &MD : MDValuePtrs) {
+  for (unsigned I = MinFwdRef, E = MaxFwdRef + 1; I != E; ++I) {
+    auto &MD = MDValuePtrs[I];
     auto *N = dyn_cast_or_null<MDNode>(MD);
     if (!N)
       continue;
@@ -581,6 +590,9 @@ void BitcodeReaderMDValueList::tryToResolveCycles() {
     assert(!N->isTemporary() && "Unexpected forward reference");
     N->resolveCycles();
   }
+
+  // Make sure we return early again until there's another forward ref.
+  AnyFwdRefs = false;
 }
 
 Type *BitcodeReader::getTypeByID(unsigned ID) {
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.h b/llvm/lib/Bitcode/Reader/BitcodeReader.h
index 7f7eb70bce9..5090be48450 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.h
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.h
@@ -99,6 +99,8 @@ public:
 class BitcodeReaderMDValueList {
   unsigned NumFwdRefs;
   bool AnyFwdRefs;
+  unsigned MinFwdRef;
+  unsigned MaxFwdRef;
   std::vector<TrackingMDRef> MDValuePtrs;
 
   LLVMContext &Context;