[llvm] Remove unnecessary add instructions in ctlz.i8 (PR #77615)
Leon Clark via llvm-commits
llvm-commits at lists.llvm.org
Thu Jan 11 07:27:15 PST 2024
================
@@ -3062,6 +3068,25 @@ static bool isCttzOpc(unsigned Opc) {
return Opc == ISD::CTTZ || Opc == ISD::CTTZ_ZERO_UNDEF;
}
+void AMDGPUTargetLowering::replaceCTLZResults(
+ SDValue Op, SelectionDAG &DAG, SmallVectorImpl<SDValue> &Results) const {
+ auto SL = SDLoc(Op);
+ auto Arg = Op.getOperand(0u);
+ auto ResultVT = Op.getValueType();
+
+ if (ResultVT != MVT::i8)
+ return;
+
+ assert(isCtlzOpc(Op.getOpcode()));
+ assert(ResultVT == Arg.getValueType());
+
+ auto SubVal = DAG.getConstant(24u, SL, MVT::i32);
+ auto NewOp = DAG.getNode(ISD::ZERO_EXTEND, SL, MVT::i32, Arg);
+ NewOp = DAG.getNode(Op.getOpcode(), SL, MVT::i32, NewOp);
+ NewOp = DAG.getNode(ISD::SUB, SL, MVT::i32, NewOp, SubVal);
+ Results.push_back(DAG.getNode(ISD::TRUNCATE, SL, ResultVT, NewOp));
----------------
PeddleSpam wrote:
I was following the convention of other backends to disambiguate the function from `LowerCTLZ_CTTZ`. Happy to do the push in `ReplaceNodeResults` though.
https://github.com/llvm/llvm-project/pull/77615
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