[llvm] [VPlan] Recursively match operands of interleave group (PR #164839)

[Florian Hahn via llvm-commits]

================
@@ -4108,25 +4116,51 @@ VPlanTransforms::expandSCEVs(VPlan &Plan, ScalarEvolution &SE) {
   return ExpandedSCEVs;
 }
 
-/// Returns true if \p V is VPWidenLoadRecipe or VPInterleaveRecipe that can be
-/// converted to a narrower recipe. \p V is used by a wide recipe that feeds a
-/// store interleave group at index \p Idx, \p WideMember0 is the recipe feeding
-/// the same interleave group at index 0. A VPWidenLoadRecipe can be narrowed to
-/// an index-independent load if it feeds all wide ops at all indices (\p OpV
-/// must be the operand at index \p OpIdx for both the recipe at lane 0, \p
-/// WideMember0). A VPInterleaveRecipe can be narrowed to a wide load, if \p V
-/// is defined at \p Idx of a load interleave group.
-static bool canNarrowLoad(VPWidenRecipe *WideMember0, unsigned OpIdx,
-                          VPValue *OpV, unsigned Idx) {
-  auto *DefR = OpV->getDefiningRecipe();
-  if (!DefR)
-    return WideMember0->getOperand(OpIdx) == OpV;
-  if (auto *W = dyn_cast<VPWidenLoadRecipe>(DefR))
-    return !W->getMask() && WideMember0->getOperand(OpIdx) == OpV;
-
-  if (auto *IR = dyn_cast<VPInterleaveRecipe>(DefR))
-    return IR->getInterleaveGroup()->isFull() && IR->getVPValue(Idx) == OpV;
-  return false;
+/// Returns true if the \p StoredValues of an interleave group match. It does
+/// this by going through operands recursively until it hits the leaf cases:
+/// VPWidenLoadRecipe, VPInterleaveRecipe, and live-ins.
+static bool interleaveStoredValuesMatch(ArrayRef<VPValue *> StoredValues) {
----------------
fhahn wrote:

I think we should be able to keep the current recursive structure and still generalize it to catch the motivating cases?

It seems the current PR tries to generalize along multiple dimensions, but it would probably be good to do step by-step.

Support chains of wide recipes could be done as in https://github.com/llvm/llvm-project/pull/167309 + https://github.com/llvm/llvm-project/pull/167310

https://github.com/llvm/llvm-project/pull/164839