[llvm] [VPlan] Don't bail creating interleave group if it has dead members (PR #208415)

[Luke Lau via llvm-commits]

================
@@ -3815,27 +3815,29 @@ void VPlanTransforms::createInterleaveGroups(
   // single VPInterleaveRecipe at its insertion point.
   VPDominatorTree VPDT(Plan);
   for (const auto *IG : InterleaveGroups) {
-    // Skip interleave groups where members don't have recipes. This can happen
-    // when removeDeadRecipes removes recipes that are part of interleave groups
-    // but have no users.
-    if (llvm::any_of(IG->members(), [&IRMemberToRecipe](Instruction *Member) {
-          return !IRMemberToRecipe.contains(Member);
-        }))
+    VPWidenMemoryRecipe *Start = nullptr;
+    Instruction *StartMember = nullptr;
+    for (auto *Member : IG->members())
+      if (VPWidenMemoryRecipe *R = IRMemberToRecipe.lookup(Member)) {
+        StartMember = Member;
+        Start = R;
+        break;
+      }
+    if (!StartMember) // All member recipes are dead, so the group is dead.
       continue;
-
-    auto *Start = IRMemberToRecipe.lookup(IG->getMember(0));
     VPIRMetadata InterleaveMD(*Start);
     SmallVector<VPValue *, 4> StoredValues;
-    if (auto *StoreR = dyn_cast<VPWidenStoreRecipe>(Start->getAsRecipe()))
-      StoredValues.push_back(StoreR->getStoredValue());
-    for (unsigned I = 1; I < IG->getFactor(); ++I) {
+    for (unsigned I = 0; I < IG->getFactor(); ++I) {
       Instruction *MemberI = IG->getMember(I);
       if (!MemberI)
         continue;
-      VPWidenMemoryRecipe *MemoryR = IRMemberToRecipe.lookup(MemberI);
-      if (auto *StoreR = dyn_cast<VPWidenStoreRecipe>(MemoryR->getAsRecipe()))
-        StoredValues.push_back(StoreR->getStoredValue());
-      InterleaveMD.intersect(*MemoryR);
+      if (VPWidenMemoryRecipe *MemoryR = IRMemberToRecipe.lookup(MemberI)) {
+        if (auto *StoreR = dyn_cast<VPWidenStoreRecipe>(MemoryR->getAsRecipe()))
+          StoredValues.push_back(StoreR->getStoredValue());
+        InterleaveMD.intersect(*MemoryR);
+      } else {
+        InterleaveMD.intersect(VPIRMetadata(*MemberI));
----------------
lukel97 wrote:

Precommitted a test in 52ac228b834d6c9d4698bfd05935f2b9b029a35d, changes in a48c1736f9867fcf62f948ede66523aabc490681. 

> If possible, I think it would be good to avoid using the metadata from the IR instruction

We could just also completely drop the metadata if there's a dead member. But its worth noting that `VPInterleaveRecipe::execute` already re-applies the IR instruction metadata:

```
    applyMetadata(*NewLoad);
    // TODO: Also manage existing metadata using VPIRMetadata.
    Group->addMetadata(NewLoad);
```

So maybe it would be good to handle those in tandem in a separate change.

https://github.com/llvm/llvm-project/pull/208415