diff --git a/llvm/include/llvm/CodeGen/LiveInterval.h b/llvm/include/llvm/CodeGen/LiveInterval.h
--- a/llvm/include/llvm/CodeGen/LiveInterval.h
+++ b/llvm/include/llvm/CodeGen/LiveInterval.h
@@ -81,6 +81,8 @@
 
     /// Mark this value as unused.
     void markUnused() { def = SlotIndex(); }
+
+    void print(raw_ostream &OS) const;
   };
 
   /// Result of a LiveRange query. This class hides the implementation details
diff --git a/llvm/lib/CodeGen/LiveInterval.cpp b/llvm/lib/CodeGen/LiveInterval.cpp
--- a/llvm/lib/CodeGen/LiveInterval.cpp
+++ b/llvm/lib/CodeGen/LiveInterval.cpp
@@ -1025,18 +1025,22 @@
          ++i, ++vnum) {
       const VNInfo *vni = *i;
       if (vnum) OS << ' ';
-      OS << vnum << '@';
-      if (vni->isUnused()) {
-        OS << 'x';
-      } else {
-        OS << vni->def;
-        if (vni->isPHIDef())
-          OS << "-phi";
-      }
+      vni->print(OS);
     }
   }
 }
 
+void VNInfo::print(raw_ostream &OS) const {
+  OS << id << '@';
+  if (isUnused()) {
+    OS << 'x';
+  } else {
+    OS << def;
+    if (isPHIDef())
+      OS << "-phi";
+  }
+}
+
 void LiveInterval::SubRange::print(raw_ostream &OS) const {
   OS << " L" << PrintLaneMask(LaneMask) << ' '
      << static_cast<const LiveRange&>(*this);
diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -2326,6 +2326,26 @@
     Val() = default;
 
     bool isAnalyzed() const { return WriteLanes.any(); }
+
+    void print(raw_ostream &O) const {
+      O << " Write:" << PrintLaneMask(WriteLanes)
+        << " Valid:" << PrintLaneMask(ValidLanes) << ' ';
+      switch(Resolution) {
+      case CR_Unresolved: O << "Unresolved"; return;
+      case CR_Impossible: O << "Impossible"; return;
+      case CR_Keep: O << "Keep"; break;
+      case CR_Replace: O << "Replace"; break;
+      case CR_Merge: O << "Merge"; break;
+      case CR_Erase: O << "Erase";
+        if (Identical) O << " Identical";
+      break;
+      }
+      if (OtherVNI) O << " Other:", OtherVNI->print(O);
+      if (RedefVNI) O << " Redef:", RedefVNI->print(O);
+      if (ErasableImplicitDef) O << " ImpDef";
+      if (Pruned || PrunedComputed) O << ' ' << (Pruned ? "Pruned" : "NonPruned");
+      if (PrunedComputed) O << 'C';
+    }
   };
 
   /// One entry per value number in LI.
@@ -2442,6 +2462,30 @@
   ConflictResolution getResolution(unsigned Num) const {
     return Vals[Num].Resolution;
   }
+
+  void print(raw_ostream &O) const {
+    O << printReg(Register(Reg), TRI, SubIdx);
+    if (SubRangeJoin) O << ':' << PrintLaneMask(LaneMask);
+    O << ":\n";
+    std::string FormBuff;
+    for (unsigned ValNo = 0, E = Vals.size(); ValNo < E; ++ValNo) {
+      auto *VNI = LR.getValNumInfo(ValNo);
+      raw_string_ostream SS(FormBuff);
+      VNI->print(SS);
+      O << "\t\t" << right_justify(SS.str(), 20);
+      FormBuff.clear();
+      Vals[ValNo].print(O);
+      if (Assignments[ValNo] != -1) {
+        O << " -> ";
+        NewVNInfo[Assignments[ValNo]]->print(O);
+      }
+      O << '\n';
+    }
+  }
+
+  LLVM_DUMP_METHOD void dump() const {
+    print(dbgs());
+  }
 };
 
 } // end anonymous namespace
@@ -3291,6 +3335,12 @@
     llvm_unreachable("*** Couldn't join subrange!\n");
   }
 
+  LLVM_DEBUG(
+    dbgs() << "\t\tRHSVals "; RHSVals.dump();
+    dbgs() << "\n\t\tLHSVals "; LHSVals.dump();
+    dbgs() << '\n'
+  );
+
   // The merging algorithm in LiveInterval::join() can't handle conflicting
   // value mappings, so we need to remove any live ranges that overlap a
   // CR_Replace resolution. Collect a set of end points that can be used to
@@ -3383,6 +3433,12 @@
   if (!LHSVals.resolveConflicts(RHSVals) || !RHSVals.resolveConflicts(LHSVals))
     return false;
 
+  LLVM_DEBUG(
+    dbgs() << "\t\tRHSVals "; RHSVals.dump();
+    dbgs() << "\n\t\tLHSVals "; LHSVals.dump();
+    dbgs() << '\n'
+  );
+
   // All clear, the live ranges can be merged.
   if (RHS.hasSubRanges() || LHS.hasSubRanges()) {
     BumpPtrAllocator &Allocator = LIS->getVNInfoAllocator();