1 files changed, 6 insertions, 2 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 02d44cd..d420edc 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -4705,14 +4705,18 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, const APInt &DemandedElts,
       return 1;  // Early out.
     Tmp2 = ComputeNumSignBits(Op.getOperand(1), DemandedElts, Depth + 1);
     return std::min(Tmp, Tmp2);
+  case ISD::SSUBO_CARRY:
+  case ISD::USUBO_CARRY:
+    // sub_carry(x,x,c) -> 0/-1 (sext carry)
+    if (Op.getResNo() == 0 && Op.getOperand(0) == Op.getOperand(1))
+      return VTBits;
+    [[fallthrough]];
   case ISD::SADDO:
   case ISD::UADDO:
   case ISD::SADDO_CARRY:
   case ISD::UADDO_CARRY:
   case ISD::SSUBO:
   case ISD::USUBO:
-  case ISD::SSUBO_CARRY:
-  case ISD::USUBO_CARRY:
   case ISD::SMULO:
   case ISD::UMULO:
     if (Op.getResNo() != 1)