[LV]: Teach LV to recursively (de)interleave. (#89018)

Currently available intrinsics are only ld2/st2, which don't support interleaving factor > 2.
This patch teaches the LV to use ld2/st2 recursively to support high
interleaving factors.

Author: hassnaaHamdi

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -3576,10 +3576,10 @@ 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
@@ -9364,9 +9364,9 @@ 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

@@ -2849,10 +2849,21 @@ 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.
@@ -2938,15 +2949,11 @@ 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)
@@ -2986,22 +2993,48 @@ 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
+          static_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);