1 files changed, 16 insertions, 2 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 14b7b58cfc1..209abf9234d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2353,9 +2353,23 @@ void SelectionDAG::computeKnownBits(SDValue Op, KnownBits &Known,
     break;
   }
   case ISD::CTTZ:
-  case ISD::CTTZ_ZERO_UNDEF:
+  case ISD::CTTZ_ZERO_UNDEF: {
+    computeKnownBits(Op.getOperand(0), Known2, DemandedElts, Depth + 1);
+    // If we have a known 1, its position is our upper bound.
+    unsigned PossibleTZ = Known2.One.countTrailingZeros();
+    unsigned LowBits = Log2_32(PossibleTZ) + 1;
+    Known.Zero.setBitsFrom(LowBits);
+    break;
+  }
   case ISD::CTLZ:
-  case ISD::CTLZ_ZERO_UNDEF:
+  case ISD::CTLZ_ZERO_UNDEF: {
+    computeKnownBits(Op.getOperand(0), Known2, DemandedElts, Depth + 1);
+    // If we have a known 1, its position is our upper bound.
+    unsigned PossibleLZ = Known2.One.countLeadingZeros();
+    unsigned LowBits = Log2_32(PossibleLZ) + 1;
+    Known.Zero.setBitsFrom(LowBits);
+    break;
+  }
   case ISD::CTPOP: {
     Known.Zero.setBitsFrom(Log2_32(BitWidth)+1);
     break;