Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2161,6 +2161,44 @@
     return DAG.getNode(ISD::ADDCARRY, SDLoc(N), N->getVTList(),
                        N0.getOperand(0), N0.getOperand(1), CarryIn);
 
+  /**
+   * Sometime, after legalization, we get a 'diamond' carry chain. Because
+   * the carry cannot propagate through both path at once, it is possible to
+   * restructure the chain so that it becomes linear. After which, other
+   * combine can kick in to optimize it.
+   *
+   * The pattern:
+   *                  (uaddo A, B)
+   *                    /       \
+   *                 Carry      Sum
+   *                  /           \
+   * (addcarry 0, 0, *)  (addcarry *, 0, Z)
+   *                 \        /
+   *                 Sum   Carry
+   *                   \    /
+   *       (addcarry X, *, *)
+   *
+   * is tranformed into
+   *   (addcarry X, 0, (addcarry A, B, Z):Carry)
+   */
+  if (N1.getOpcode() == ISD::ADDCARRY &&
+      isNullConstant(N1.getOperand(0)) &&
+      isNullConstant(N1.getOperand(1)) &&
+      CarryIn.getOpcode() == ISD::ADDCARRY &&
+      isNullConstant(CarryIn.getOperand(1))) {
+    auto Y = CarryIn.getOperand(0);
+    if (Y.getOpcode() == ISD::UADDO &&
+        N1.getOperand(2).getNode() == Y.getNode()) {
+      auto NewY = DAG.getNode(ISD::ADDCARRY, SDLoc(N), Y->getVTList(),
+                              Y.getOperand(0), Y.getOperand(1),
+                              CarryIn.getOperand(2));
+      AddToWorklist(NewY.getNode());
+      return DAG.getNode(ISD::ADDCARRY, SDLoc(N), N->getVTList(), N0,
+                         DAG.getConstant(0, SDLoc(N), N0.getValueType()),
+                         NewY.getValue(1));
+    }
+  }
+
   return SDValue();
 }
 
Index: test/CodeGen/X86/addcarry.ll
===================================================================
--- test/CodeGen/X86/addcarry.ll
+++ test/CodeGen/X86/addcarry.ll
@@ -86,21 +86,14 @@
 define %scalar @pr31719(%scalar* nocapture readonly %this, %scalar %arg.b) {
 ; CHECK-LABEL: pr31719:
 ; CHECK:       # BB#0: # %entry
-; CHECK-NEXT:    addq 8(%rsi), %rcx
-; CHECK-NEXT:    sbbq %r10, %r10
-; CHECK-NEXT:    andl $1, %r10d
-; CHECK-NEXT:    addq 16(%rsi), %r8
-; CHECK-NEXT:    sbbq %rax, %rax
-; CHECK-NEXT:    andl $1, %eax
-; CHECK-NEXT:    addq 24(%rsi), %r9
 ; CHECK-NEXT:    addq (%rsi), %rdx
-; CHECK-NEXT:    adcq $0, %rcx
-; CHECK-NEXT:    adcq %r8, %r10
-; CHECK-NEXT:    adcq %r9, %rax
+; CHECK-NEXT:    adcq 8(%rsi), %rcx
+; CHECK-NEXT:    adcq 16(%rsi), %r8
+; CHECK-NEXT:    adcq 24(%rsi), %r9
 ; CHECK-NEXT:    movq %rdx, (%rdi)
 ; CHECK-NEXT:    movq %rcx, 8(%rdi)
-; CHECK-NEXT:    movq %r10, 16(%rdi)
-; CHECK-NEXT:    movq %rax, 24(%rdi)
+; CHECK-NEXT:    movq %r8, 16(%rdi)
+; CHECK-NEXT:    movq %r9, 24(%rdi)
 ; CHECK-NEXT:    movq %rdi, %rax
 ; CHECK-NEXT:    retq
 entry: