[CodeGen] When promoting CTTZ operations to larger type, don't insert a select to detect if the input is zero to return the original size instead of the extended size. Instead just set the first bit in the zero extended part.
llvm-svn: 267280
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 688a4c4..a06932b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -4010,18 +4010,20 @@
case ISD::CTPOP:
// Zero extend the argument.
Tmp1 = DAG.getNode(ISD::ZERO_EXTEND, dl, NVT, Node->getOperand(0));
+ if (Node->getOpcode() == ISD::CTTZ) {
+ // The count is the same in the promoted type except if the original
+ // value was zero. This can be handled by setting the bit just off
+ // the top of the original type.
+ auto TopBit = APInt::getOneBitSet(NVT.getSizeInBits(),
+ OVT.getSizeInBits());
+ Tmp1 = DAG.getNode(ISD::OR, dl, NVT, Tmp1,
+ DAG.getConstant(TopBit, dl, NVT));
+ }
// Perform the larger operation. For CTPOP and CTTZ_ZERO_UNDEF, this is
// already the correct result.
Tmp1 = DAG.getNode(Node->getOpcode(), dl, NVT, Tmp1);
- if (Node->getOpcode() == ISD::CTTZ) {
- // FIXME: This should set a bit in the zero extended value instead.
- Tmp2 = DAG.getSetCC(dl, getSetCCResultType(NVT),
- Tmp1, DAG.getConstant(NVT.getSizeInBits(), dl, NVT),
- ISD::SETEQ);
- Tmp1 = DAG.getSelect(dl, NVT, Tmp2,
- DAG.getConstant(OVT.getSizeInBits(), dl, NVT), Tmp1);
- } else if (Node->getOpcode() == ISD::CTLZ ||
- Node->getOpcode() == ISD::CTLZ_ZERO_UNDEF) {
+ if (Node->getOpcode() == ISD::CTLZ ||
+ Node->getOpcode() == ISD::CTLZ_ZERO_UNDEF) {
// Tmp1 = Tmp1 - (sizeinbits(NVT) - sizeinbits(Old VT))
Tmp1 = DAG.getNode(ISD::SUB, dl, NVT, Tmp1,
DAG.getConstant(NVT.getSizeInBits() -