[llvm] [IR][RFC] Add @llvm.mask.beforefirst intrinsic (PR #203874)

[Luke Lau via llvm-commits]

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@@ -1741,6 +1747,40 @@ SDValue VectorLegalizer::ExpandLOOP_DEPENDENCE_MASK(SDNode *N) {
   return TLI.expandLoopDependenceMask(N, DAG);
 }
 
+SDValue VectorLegalizer::ExpandMASK_BEFOREFIRST(SDNode *N) {
+  // Expand to (setcc ult (step-vector), (cttz_elts x))
+  SDLoc DL(N);
+  EVT VT = N->getValueType(0);
+
+  // Try to expand via get_active_lane_mask if supported.
+  EVT BoolVT = VT.changeVectorElementType(*DAG.getContext(), MVT::i1);
+  EVT VecIdxVT = TLI.getVectorIdxTy(DAG.getDataLayout());
+  if (!TLI.shouldExpandGetActiveLaneMask(BoolVT, VecIdxVT)) {
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lukel97 wrote:

228367a39025 now always expands via get_active_lane_mask

https://github.com/llvm/llvm-project/pull/203874