[llvm] [LV] Support scalable interleave groups for factors 3, 5, 6 and 7 (PR #141865)

[Luke Lau via llvm-commits]

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@@ -3377,34 +3441,43 @@ void VPInterleaveRecipe::execute(VPTransformState &State) {
     ArrayRef<VPValue *> VPDefs = definedValues();
     const DataLayout &DL = State.CFG.PrevBB->getDataLayout();
     if (VecTy->isScalableTy()) {
-      assert(isPowerOf2_32(InterleaveFactor) &&
-             "Unsupported deinterleave factor for scalable vectors");
-
       // 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) {
+
+      if (InterleaveFactor <= 8) {
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lukel97 wrote:

To clarify, even though there's no hardware with instructions for [de]interleaving memory ops @ factor > 8 (and thus no intrinsics for the interleaved access pass to lower to), we can still generate a wide load/store and perform a series of [de]interleave permutations. 

But I somewhat agree that if we're not exercising that code path in any target it should be stripped. Can I defer removing it to a separate PR so we can gain consensus there?

https://github.com/llvm/llvm-project/pull/141865