[LV] Check early for supported interleave factors with scalable types [nfc]

Previously, the cost model was returning an invalid cost.  This simply
moves the check from one place to another.  This is mostly to make the
cost modeling code a bit easier to follow.

Author: preames

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp

@@ -675,8 +675,6 @@ InstructionCost RISCVTTIImpl::getInterleavedMemoryOpCost(
     unsigned Opcode, Type *VecTy, unsigned Factor, ArrayRef<unsigned> Indices,
     Align Alignment, unsigned AddressSpace, TTI::TargetCostKind CostKind,
     bool UseMaskForCond, bool UseMaskForGaps) {
-  if (isa<ScalableVectorType>(VecTy) && Factor != 2)
-    return InstructionCost::getInvalid();
 
   // The interleaved memory access pass will lower interleaved memory ops (i.e
   // a load and store followed by a specific shuffle) to vlseg/vsseg

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -3406,6 +3406,7 @@ bool LoopVectorizationCostModel::interleavedAccessCanBeWidened(
          "Decision should not be set yet.");
   auto *Group = getInterleavedAccessGroup(I);
   assert(Group && "Must have a group.");
+  unsigned InterleaveFactor = Group->getFactor();
 
   // If the instruction's allocated size doesn't equal it's type size, it
   // requires padding and will be scalarized.
@@ -3414,9 +3415,14 @@ bool LoopVectorizationCostModel::interleavedAccessCanBeWidened(
   if (hasIrregularType(ScalarTy, DL))
     return false;
 
+  // We currently only know how to emit interleave/deinterleave with
+  // Factor=2 for scalable vectors.  This is purely an implementation
+  // limit.
+  if (VF.isScalable() && InterleaveFactor != 2)
+    return false;
+
   // If the group involves a non-integral pointer, we may not be able to
   // losslessly cast all values to a common type.
-  unsigned InterleaveFactor = Group->getFactor();
   bool ScalarNI = DL.isNonIntegralPointerType(ScalarTy);
   for (unsigned Idx = 0; Idx < InterleaveFactor; Idx++) {
     Instruction *Member = Group->getMember(Idx);