Reland "[LV]: Teach LV to recursively (de)interleave." (llvm#125094)

This patch relands the changes from "[LV]: Teach LV to recursively
(de)interleave.llvm#122989"
    Reason for revert:
- The patch exposed an assert in the vectorizer related to VF difference
between
legacy cost model and VPlan-based cost model because of uncalculated
cost for
VPInstruction which is created by VPlanTransforms as a replacement to
'or disjoint'
       instruction.
VPlanTransforms do that instructions change when there are memory
interleaving and
predicated blocks, but that change didn't cause problems because at most
cases the cost
      difference between legacy/new models is not noticeable.
    - Issue is fixed by llvm#125434

Original patch: llvm#89018
Reviewed-by: paulwalker-arm, Mel-Chen

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -3439,10 +3439,10 @@ 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)
+  // For scalable vectors, the only interleave factor currently supported
+  // must be power of 2 since we require the (de)interleave2 intrinsics
+  // instead of shufflevectors.
+  if (VF.isScalable() && !isPowerOf2_32(InterleaveFactor))
     return false;
 
   // If the group involves a non-integral pointer, we may not be able to
@@ -9311,9 +9311,9 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
                      CM.getWideningDecision(IG->getInsertPos(), VF) ==
                          LoopVectorizationCostModel::CM_Interleave);
       // For scalable vectors, the only interleave factor currently supported
-      // is 2 since we require the (de)interleave2 intrinsics instead of
-      // shufflevectors.
-      assert((!Result || !VF.isScalable() || IG->getFactor() == 2) &&
+      // must be power of 2 since we require the (de)interleave2 intrinsics
+      // instead of shufflevectors.
+      assert((!Result || !VF.isScalable() || isPowerOf2_32(IG->getFactor())) &&
              "Unsupported interleave factor for scalable vectors");
       return Result;
     };

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -2915,10 +2915,21 @@ static Value *interleaveVectors(IRBuilderBase &Builder, ArrayRef<Value *> Vals,
   // Scalable vectors cannot use arbitrary shufflevectors (only splats), so
   // must use intrinsics to interleave.
   if (VecTy->isScalableTy()) {
-    VectorType *WideVecTy = VectorType::getDoubleElementsVectorType(VecTy);
-    return Builder.CreateIntrinsic(WideVecTy, Intrinsic::vector_interleave2,
-                                   Vals,
-                                   /*FMFSource=*/nullptr, Name);
+    assert(isPowerOf2_32(Factor) && "Unsupported interleave factor for "
+                                    "scalable vectors, must be power of 2");
+    SmallVector<Value *> InterleavingValues(Vals);
+    // When interleaving, the number of values will be shrunk until we have the
+    // single final interleaved value.
+    auto *InterleaveTy = cast<VectorType>(InterleavingValues[0]->getType());
+    for (unsigned Midpoint = Factor / 2; Midpoint > 0; Midpoint /= 2) {
+      InterleaveTy = VectorType::getDoubleElementsVectorType(InterleaveTy);
+      for (unsigned I = 0; I < Midpoint; ++I)
+        InterleavingValues[I] = Builder.CreateIntrinsic(
+            InterleaveTy, Intrinsic::vector_interleave2,
+            {InterleavingValues[I], InterleavingValues[Midpoint + I]},
+            /*FMFSource=*/nullptr, Name);
+    }
+    return InterleavingValues[0];
   }
 
   // Fixed length. Start by concatenating all vectors into a wide vector.
@@ -3004,15 +3015,11 @@ void VPInterleaveRecipe::execute(VPTransformState &State) {
                           &InterleaveFactor](Value *MaskForGaps) -> Value * {
     if (State.VF.isScalable()) {
       assert(!MaskForGaps && "Interleaved groups with gaps are not supported.");
-      assert(InterleaveFactor == 2 &&
+      assert(isPowerOf2_32(InterleaveFactor) &&
              "Unsupported deinterleave factor for scalable vectors");
       auto *ResBlockInMask = State.get(BlockInMask);
-      SmallVector<Value *, 2> Ops = {ResBlockInMask, ResBlockInMask};
-      auto *MaskTy = VectorType::get(State.Builder.getInt1Ty(),
-                                     State.VF.getKnownMinValue() * 2, true);
-      return State.Builder.CreateIntrinsic(
-          MaskTy, Intrinsic::vector_interleave2, Ops,
-          /*FMFSource=*/nullptr, "interleaved.mask");
+      SmallVector<Value *> Ops(InterleaveFactor, ResBlockInMask);
+      return interleaveVectors(State.Builder, Ops, "interleaved.mask");
     }
 
     if (!BlockInMask)
@@ -3052,22 +3059,48 @@ void VPInterleaveRecipe::execute(VPTransformState &State) {
     ArrayRef<VPValue *> VPDefs = definedValues();
     const DataLayout &DL = State.CFG.PrevBB->getDataLayout();
     if (VecTy->isScalableTy()) {
-      assert(InterleaveFactor == 2 &&
+      assert(isPowerOf2_32(InterleaveFactor) &&
              "Unsupported deinterleave factor for scalable vectors");
 
-        // Scalable vectors cannot use arbitrary shufflevectors (only splats),
-        // so must use intrinsics to deinterleave.
-      Value *DI = State.Builder.CreateIntrinsic(
-          Intrinsic::vector_deinterleave2, VecTy, NewLoad,
-          /*FMFSource=*/nullptr, "strided.vec");
-      unsigned J = 0;
-      for (unsigned I = 0; I < InterleaveFactor; ++I) {
-        Instruction *Member = Group->getMember(I);
+      // Scalable vectors cannot use arbitrary shufflevectors (only splats),
+      // so must use intrinsics to deinterleave.
+      SmallVector<Value *> DeinterleavedValues(InterleaveFactor);
+      DeinterleavedValues[0] = NewLoad;
+      // For the case of InterleaveFactor > 2, we will have to do recursive
+      // deinterleaving, because the current available deinterleave intrinsic
+      // supports only Factor of 2, otherwise it will bailout after first
+      // iteration.
+      // When deinterleaving, the number of values will double until we
+      // have "InterleaveFactor".
+      for (unsigned NumVectors = 1; NumVectors < InterleaveFactor;
+           NumVectors *= 2) {
+        // Deinterleave the elements within the vector
+        SmallVector<Value *> TempDeinterleavedValues(NumVectors);
+        for (unsigned I = 0; I < NumVectors; ++I) {
+          auto *DiTy = DeinterleavedValues[I]->getType();
+          TempDeinterleavedValues[I] = State.Builder.CreateIntrinsic(
+              Intrinsic::vector_deinterleave2, DiTy, DeinterleavedValues[I],
+              /*FMFSource=*/nullptr, "strided.vec");
+        }
+        // Extract the deinterleaved values:
+        for (unsigned I = 0; I < 2; ++I)
+          for (unsigned J = 0; J < NumVectors; ++J)
+            DeinterleavedValues[NumVectors * I + J] =
+                State.Builder.CreateExtractValue(TempDeinterleavedValues[J], I);
+      }
 
-        if (!Member)
+#ifndef NDEBUG
+      for (Value *Val : DeinterleavedValues)
+        assert(Val && "NULL Deinterleaved Value");
+#endif
+      for (unsigned I = 0, J = 0; I < InterleaveFactor; ++I) {
+        Instruction *Member = Group->getMember(I);
+        Value *StridedVec = DeinterleavedValues[I];
+        if (!Member) {
+          // This value is not needed as it's not used
+          cast<Instruction>(StridedVec)->eraseFromParent();
           continue;
-
-        Value *StridedVec = State.Builder.CreateExtractValue(DI, I);
+        }
         // If this member has different type, cast the result type.
         if (Member->getType() != ScalarTy) {
           VectorType *OtherVTy = VectorType::get(Member->getType(), State.VF);