[llvm] [VPlan] Add transformation to narrow interleave groups. (PR #106441)

[via llvm-commits]

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@@ -1555,3 +1591,129 @@ void VPlanTransforms::createInterleaveGroups(
       }
   }
 }
+
+static bool supportedLoad(VPWidenRecipe *R0, VPValue *V, unsigned Idx) {
+  if (auto *W = dyn_cast_or_null<VPWidenLoadRecipe>(V->getDefiningRecipe())) {
+    if (W->getMask())
+      return false;
+    return !W->getMask() && (R0->getOperand(0) == V || R0->getOperand(1) == V);
+  }
+
+  if (auto *IR = dyn_cast_or_null<VPInterleaveRecipe>(V->getDefiningRecipe())) {
+    return IR->getInterleaveGroup()->getFactor() ==
+               IR->getInterleaveGroup()->getNumMembers() &&
+           IR->getVPValue(Idx) == V;
+  }
+  return false;
+}
+
+/// Returns true of \p IR is a consecutive interleave group with \p VF members.
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ayalz wrote:

```suggestion
/// Returns true of \p IR is a full interleave group with factor and number of members both equal to \p VF.
```

https://github.com/llvm/llvm-project/pull/106441