LegalizeDAG: Expand ctlz with ctlz_zero_undef if legal
llvm-svn: 257345
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index f46767f..5d572c4 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -2941,6 +2941,18 @@
// This trivially expands to CTLZ.
return DAG.getNode(ISD::CTLZ, dl, Op.getValueType(), Op);
case ISD::CTLZ: {
+ EVT VT = Op.getValueType();
+ unsigned len = VT.getSizeInBits();
+
+ if (TLI.isOperationLegalOrCustom(ISD::CTLZ_ZERO_UNDEF, VT)) {
+ EVT SetCCVT = getSetCCResultType(VT);
+ SDValue CTLZ = DAG.getNode(ISD::CTLZ_ZERO_UNDEF, dl, VT, Op);
+ SDValue Zero = DAG.getConstant(0, dl, VT);
+ SDValue SrcIsZero = DAG.getSetCC(dl, SetCCVT, Op, Zero, ISD::SETEQ);
+ return DAG.getNode(ISD::SELECT, dl, VT, SrcIsZero,
+ DAG.getConstant(len, dl, VT), CTLZ);
+ }
+
// for now, we do this:
// x = x | (x >> 1);
// x = x | (x >> 2);
@@ -2950,9 +2962,7 @@
// return popcount(~x);
//
// Ref: "Hacker's Delight" by Henry Warren
- EVT VT = Op.getValueType();
EVT ShVT = TLI.getShiftAmountTy(VT, DAG.getDataLayout());
- unsigned len = VT.getSizeInBits();
for (unsigned i = 0; (1U << i) <= (len / 2); ++i) {
SDValue Tmp3 = DAG.getConstant(1ULL << i, dl, ShVT);
Op = DAG.getNode(ISD::OR, dl, VT, Op,