[CodeGen] Replace calls to getVectorNumElements() in SelectionDAG::SplitVector

This patch replaces some invalid calls to getVectorNumElements() with calls
to getVectorMinNumElements() instead, since the code paths changed in this
patch work for both fixed and scalable vector types.

Fixes warnings in this test:

  sve-sext-zext.ll

Differential Revision: https://reviews.llvm.org/D83203

1 files changed, 11 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 0b80173cb419..806509120869 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -9639,14 +9639,22 @@ SelectionDAG::GetDependentSplitDestVTs(const EVT &VT, const EVT &EnvVT,
 std::pair<SDValue, SDValue>
 SelectionDAG::SplitVector(const SDValue &N, const SDLoc &DL, const EVT &LoVT,
                           const EVT &HiVT) {
-  assert(LoVT.getVectorNumElements() + HiVT.getVectorNumElements() <=
-         N.getValueType().getVectorNumElements() &&
+  assert(LoVT.isScalableVector() == HiVT.isScalableVector() &&
+         LoVT.isScalableVector() == N.getValueType().isScalableVector() &&
+         "Splitting vector with an invalid mixture of fixed and scalable "
+         "vector types");
+  assert(LoVT.getVectorMinNumElements() + HiVT.getVectorMinNumElements() <=
+             N.getValueType().getVectorMinNumElements() &&
          "More vector elements requested than available!");
   SDValue Lo, Hi;
   Lo =
       getNode(ISD::EXTRACT_SUBVECTOR, DL, LoVT, N, getVectorIdxConstant(0, DL));
+  // For scalable vectors it is safe to use LoVT.getVectorMinNumElements()
+  // (rather than having to use ElementCount), because EXTRACT_SUBVECTOR scales
+  // IDX with the runtime scaling factor of the result vector type. For
+  // fixed-width result vectors, that runtime scaling factor is 1.
   Hi = getNode(ISD::EXTRACT_SUBVECTOR, DL, HiVT, N,
-               getVectorIdxConstant(LoVT.getVectorNumElements(), DL));
+               getVectorIdxConstant(LoVT.getVectorMinNumElements(), DL));
   return std::make_pair(Lo, Hi);
 }