[llvm] [VPlan] Narrow interleave groups with distinct live-in operands. (PR #203778)

[Ramkumar Ramachandra via llvm-commits]

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@@ -5661,15 +5667,33 @@ static bool isAlreadyNarrow(VPValue *VPV) {
 
 // Convert the wide recipes defining the VPValues in \p Members feeding an
 // interleave group to a single narrow variant. The first member is reused as
-// the narrowed recipe.
-static VPValue *
-narrowInterleaveGroupOp(ArrayRef<VPValue *> Members,
-                        SmallPtrSetImpl<VPValue *> &NarrowedOps) {
+// the narrowed recipe. Newly created loop-invariant recipes (e.g. a BuildVector
+// for distinct live-ins) are inserted into \p Preheader.
+static VPValue *narrowInterleaveGroupOp(ArrayRef<VPValue *> Members,
+                                        SmallPtrSetImpl<VPValue *> &NarrowedOps,
+                                        VPBasicBlock *Preheader) {
   VPValue *V = Members.front();
   auto *R = V->getDefiningRecipe();
-  if (!R || NarrowedOps.contains(V))
+  if (NarrowedOps.contains(V))
     return V;
 
+  if (!R) {
+    // V is a live-in. If all members are the same live-in, reuse it directly.
+    if (all_of(Members, equal_to(V)))
+      return V;
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artagnon wrote:

Hm, do we need this? Will BuildVector with all-eq operands not fold to BCast due to simplifyRecipe, which will then be eliminated because only-first-lane-used, again due to simplifyRecipe I think?

https://github.com/llvm/llvm-project/pull/203778