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

[via llvm-commits]

================
@@ -1994,3 +1997,124 @@ void VPlanTransforms::handleUncountableEarlyExit(
   Builder.createNaryOp(VPInstruction::BranchOnCond, AnyExitTaken);
   LatchExitingBranch->eraseFromParent();
 }
+
+static bool supportedLoad(VPWidenRecipe *R0, VPValue *V, unsigned Idx) {
+  if (auto *W = dyn_cast_or_null<VPWidenLoadRecipe>(V->getDefiningRecipe()))
+    return !W->getMask() && (R0->getOperand(0) == V || R0->getOperand(1) == V);
+
+  if (auto *IR = dyn_cast_or_null<VPInterleaveRecipe>(V->getDefiningRecipe()))
----------------
ayalz wrote:

```suggestion
  if (auto *InterleaveLoadV = dyn_cast<VPInterleaveRecipe>(RecipeV))
```
we know its an interleaved load rather than store, having reached it from a user.

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