Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2506,6 +2506,7 @@
     LLVM_FALLTHROUGH;
   }
   case ISD::ADD:
+  case ISD::ADDC:
   case ISD::ADDE: {
     // Output known-0 bits are known if clear or set in both the low clear bits
     // common to both LHS & RHS.  For example, 8+(X<<3) is known to have the
@@ -2526,7 +2527,7 @@
     KnownZeroLow = std::min(KnownZeroLow,
                             KnownZero2.countTrailingOnes());
 
-    if (Opcode == ISD::ADD) {
+    if (Opcode == ISD::ADD || Opcode == ISD::ADDC) {
       KnownZero |= APInt::getLowBitsSet(BitWidth, KnownZeroLow);
       if (KnownZeroHigh > 1)
         KnownZero |= APInt::getHighBitsSet(BitWidth, KnownZeroHigh - 1);
@@ -2924,6 +2925,7 @@
     }
     break;
   case ISD::ADD:
+  case ISD::ADDC:
     // Add can have at most one carry bit.  Thus we know that the output
     // is, at worst, one more bit than the inputs.
     Tmp = ComputeNumSignBits(Op.getOperand(0), Depth+1);
Index: test/CodeGen/X86/known-bits.ll
===================================================================
--- test/CodeGen/X86/known-bits.ll
+++ test/CodeGen/X86/known-bits.ll
@@ -103,3 +103,67 @@
   %E156 = extractelement <4 x i1> %Cmp117, i32 2
   br label %CF
 }
+
+define i32 @knownbits_mask_add_lshr(i32 %a0, i32 %a1) nounwind {
+; X32-LABEL: knownbits_mask_add_lshr:
+; X32:       # BB#0:
+; X32-NEXT:    xorl %eax, %eax
+; X32-NEXT:    retl
+;
+; X64-LABEL: knownbits_mask_add_lshr:
+; X64:       # BB#0:
+; X64-NEXT:    xorl %eax, %eax
+; X64-NEXT:    retq
+  %1 = and i32 %a0, 32767
+  %2 = and i32 %a1, 32766
+  %3 = add i32 %1, %2
+  %4 = lshr i32 %3, 17
+  ret i32 %4
+}
+
+define i128 @knownbits_mask_addc_shl(i64 %a0, i64 %a1, i64 %a2) nounwind {
+; X32-LABEL: knownbits_mask_addc_shl:
+; X32:       # BB#0:
+; X32-NEXT:    pushl %edi
+; X32-NEXT:    pushl %esi
+; X32-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X32-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; X32-NEXT:    movl {{[0-9]+}}(%esp), %edx
+; X32-NEXT:    movl $-1024, %esi # imm = 0xFC00
+; X32-NEXT:    movl {{[0-9]+}}(%esp), %edi
+; X32-NEXT:    andl %esi, %edi
+; X32-NEXT:    andl {{[0-9]+}}(%esp), %esi
+; X32-NEXT:    addl %edi, %esi
+; X32-NEXT:    adcl {{[0-9]+}}(%esp), %edx
+; X32-NEXT:    adcl $0, %ecx
+; X32-NEXT:    shldl $22, %edx, %ecx
+; X32-NEXT:    shldl $22, %esi, %edx
+; X32-NEXT:    movl %edx, 8(%eax)
+; X32-NEXT:    movl %ecx, 12(%eax)
+; X32-NEXT:    movl $0, 4(%eax)
+; X32-NEXT:    movl $0, (%eax)
+; X32-NEXT:    popl %esi
+; X32-NEXT:    popl %edi
+; X32-NEXT:    retl $4
+;
+; X64-LABEL: knownbits_mask_addc_shl:
+; X64:       # BB#0:
+; X64-NEXT:    andq $-1024, %rdi # imm = 0xFC00
+; X64-NEXT:    andq $-1024, %rsi # imm = 0xFC00
+; X64-NEXT:    addq %rdi, %rsi
+; X64-NEXT:    sbbq %rax, %rax
+; X64-NEXT:    subl %eax, %edx
+; X64-NEXT:    shldq $54, %rsi, %rdx
+; X64-NEXT:    xorl %eax, %eax
+; X64-NEXT:    retq
+  %1 = and i64 %a0, -1024
+  %2 = zext i64 %1 to i128
+  %3 = and i64 %a1, -1024
+  %4 = zext i64 %3 to i128
+  %5 = add i128 %2, %4
+  %6 = zext i64 %a2 to i128
+  %7 = shl i128 %6, 64
+  %8 = add i128 %5, %7
+  %9 = shl i128 %8, 54
+  ret i128 %9
+}