[llvm] [VP][RISCV] Add vp.cttz.elts intrinsic and its RISC-V codegen (PR #90502)

[Craig Topper via llvm-commits]

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@@ -4056,6 +4060,29 @@ SDValue DAGTypeLegalizer::SplitVecOp_FP_TO_XINT_SAT(SDNode *N) {
   return DAG.getNode(ISD::CONCAT_VECTORS, dl, ResVT, Lo, Hi);
 }
 
+SDValue DAGTypeLegalizer::SplitVecOp_VP_CttzElements(SDNode *N) {
+  SDLoc DL(N);
+  EVT ResVT = N->getValueType(0);
+
+  SDValue Lo, Hi;
+  SDValue VecOp = N->getOperand(0);
+  GetSplitVector(VecOp, Lo, Hi);
+
+  auto [MaskLo, MaskHi] = SplitMask(N->getOperand(1));
+  auto [EVLLo, EVLHi] =
+      DAG.SplitEVL(N->getOperand(2), VecOp.getValueType(), DL);
+  SDValue VLo = DAG.getZExtOrTrunc(EVLLo, DL, ResVT);
+
+  // if VP_CTTZ_ELTS(Lo) != EVLLo => VP_CTTZ_ELTS(Lo).
+  // else => EVLLo + VP_CTTZ_ELTS / VP_CTTZ_ELTS_ZERO_UNDEF(Hi).
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topperc wrote:

The use of '/' in an arithmetic expression makes this look like division when first reading it.

https://github.com/llvm/llvm-project/pull/90502