diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3451,7 +3451,6 @@
     return SDValue();
   }
 
-
   auto cancelDiamond = [&](SDValue A,SDValue B) {
     SDLoc DL(N);
     SDValue NewY =
@@ -3522,46 +3521,82 @@
   SDValue Carry0 = getAsCarry(TLI, N0);
   if (!Carry0)
     return SDValue();
+
   SDValue Carry1 = getAsCarry(TLI, N1);
   if (!Carry1)
     return SDValue();
 
-  unsigned Opcode = Carry0.getOpcode();
-  if (Opcode != Carry1.getOpcode())
+  auto matchCarry = [](SDValue N, SDValue &A, SDValue &B, bool &IsAdd) {
+    unsigned Opcode = N.getOpcode();
+    IsAdd = Opcode == ISD::UADDO || Opcode == ISD::UADDO_CARRY;
+
+    if (Opcode == ISD::UADDO || Opcode == ISD::USUBO) {
+      A = N.getOperand(0);
+      B = N.getOperand(1);
+      return true;
+    }
+
+    if ((Opcode == ISD::UADDO_CARRY || Opcode == ISD::USUBO_CARRY) &&
+        isNullConstant(N.getOperand(1))) {
+      A = N.getOperand(0);
+      B = N.getOperand(2);
+      return true;
+    }
+
+    return false;
+  };
+
+  SDValue X, Y;
+  bool IsAdd;
+  if (!matchCarry(Carry0, X, Y, IsAdd))
     return SDValue();
-  if (Opcode != ISD::UADDO && Opcode != ISD::USUBO)
+
+  SDValue A, B;
+  bool IsAdd1;
+  if (!matchCarry(Carry1, A, B, IsAdd1))
+    return SDValue();
+
+  if (IsAdd != IsAdd1)
+    return SDValue();
+
+  unsigned NewOp = IsAdd ? ISD::UADDO_CARRY : ISD::USUBO_CARRY;
+  if (!TLI.isOperationLegalOrCustom(NewOp, Carry0.getValue(0).getValueType()))
     return SDValue();
 
   // Canonicalize the add/sub of A and B (the top node in the above ASCII art)
   // as Carry0 and the add/sub of the carry in as Carry1 (the middle node).
-  if (Carry1.getNode()->isOperandOf(Carry0.getNode()))
+  if (Carry0.getValue(0) == A || Carry0.getValue(0) == B) {
     std::swap(Carry0, Carry1);
+    std::swap(A, X);
+    std::swap(B, Y);
+  }
 
   // Check if nodes are connected in expected way.
-  if (Carry1.getOperand(0) != Carry0.getValue(0) &&
-      Carry1.getOperand(1) != Carry0.getValue(0))
-    return SDValue();
-
-  // The carry in value must be on the righthand side for subtraction.
-  unsigned CarryInOperandNum =
-      Carry1.getOperand(0) == Carry0.getValue(0) ? 1 : 0;
-  if (Opcode == ISD::USUBO && CarryInOperandNum != 1)
-    return SDValue();
-  SDValue CarryIn = Carry1.getOperand(CarryInOperandNum);
-
-  unsigned NewOp = Opcode == ISD::UADDO ? ISD::UADDO_CARRY : ISD::USUBO_CARRY;
-  if (!TLI.isOperationLegalOrCustom(NewOp, Carry0.getValue(0).getValueType()))
+  if (Carry1.getValue(0) != X && (!IsAdd || Carry1.getValue(0) != Y))
     return SDValue();
 
   // Verify that the carry/borrow in is plausibly a carry/borrow bit.
+  // TODO: make getAsCarry() aware of how partial carries are merged.
+  SDValue CarryIn = Carry1.getValue(0) == X ? Y : X;
   CarryIn = getAsCarry(TLI, CarryIn, true);
   if (!CarryIn)
     return SDValue();
 
   SDLoc DL(N);
   SDValue Merged =
-      DAG.getNode(NewOp, DL, Carry1->getVTList(), Carry0.getOperand(0),
-                  Carry0.getOperand(1), CarryIn);
+      DAG.getNode(NewOp, DL, Carry1->getVTList(), A, B, CarryIn);
+
+  LLVM_DEBUG(
+    dbgs() << "Combine carry diamond:\n";
+    dbgs() << "\tCarry0: "; Carry0->dump();
+    dbgs() << "\tX: "; X->dump();
+    dbgs() << "\tY: "; Y->dump();
+    dbgs() << "\tCarry1: "; Carry1->dump();
+    dbgs() << "\tA: "; A->dump();
+    dbgs() << "\tB: "; B->dump();
+    dbgs() << "\tCarryIn: "; CarryIn->dump();
+    dbgs() << "\tMerged: "; Merged->dump();
+    dbgs() << "\n");
 
   // Please note that because we have proven that the result of the UADDO/USUBO
   // of A and B feeds into the UADDO/USUBO that does the carry/borrow in, we can
@@ -3576,7 +3611,7 @@
   // carry flags; and that AND can return a constant zero.
   //
   // TODO: match other operations that can merge flags (ADD, etc)
-  DAG.ReplaceAllUsesOfValueWith(Carry1.getValue(0), Merged.getValue(0));
+  DAG.ReplaceAllUsesOfValueWith(Carry0.getValue(0), Merged.getValue(0));
   if (N->getOpcode() == ISD::AND)
     return DAG.getConstant(0, DL, MVT::i1);
   return Merged.getValue(1);