[llvm] [LSV] Insert casts to vectorize mismatched types (PR #134436)

[Matt Arsenault via llvm-commits]

================
@@ -1310,6 +1315,116 @@ std::optional<APInt> Vectorizer::getConstantOffsetSelects(
   return std::nullopt;
 }
 
+void Vectorizer::insertCastsToMergeClasses(EquivalenceClassMap &EQClasses) {
+  if (EQClasses.size() < 2)
+    return;
+
+  // For each class, determine if all instructions are of type int, FP or ptr.
+  // This information will help us determine the type instructions should be
+  // casted into.
+  MapVector<EqClassKey, Bitset<3>> ClassAllTy;
+  for (auto C : EQClasses) {
+    if (all_of(EQClasses[C.first], [](Instruction *I) {
+          return I->getType()->isIntOrIntVectorTy();
+        }))
+      ClassAllTy[C.first].set(0);
+    else if (all_of(EQClasses[C.first], [](Instruction *I) {
+               return I->getType()->isFPOrFPVectorTy();
+             }))
+      ClassAllTy[C.first].set(1);
+    else if (all_of(EQClasses[C.first], [](Instruction *I) {
+               return I->getType()->isPtrOrPtrVectorTy();
+             }))
+      ClassAllTy[C.first].set(2);
+  }
+
+  // Loop over all equivalence classes and try to merge them. Keep track of
+  // classes that are merged into others.
+  DenseSet<EqClassKey> ClassesToErase;
+  for (auto EC1 : EQClasses) {
+    for (auto EC2 : EQClasses) {
+      // Skip if EC2 was already merged before, EC1 follows EC2 in the
+      // collection or EC1 is the same as EC2.
+      if (ClassesToErase.contains(EC2.first) || EC1 <= EC2 ||
+          EC1.first == EC2.first)
+        continue;
+
+      auto [Ptr1, AS1, TySize1, IsLoad1] = EC1.first;
+      auto [Ptr2, AS2, TySize2, IsLoad2] = EC2.first;
+
+      // Attempt to merge EC2 into EC1. Skip if the pointers, address spaces or
+      // whether the leader instruction is a load/store are different. Also skip
+      // if the scalar bitwidth of the first equivalence class is smaller than
+      // the second one to avoid reconsidering the same equivalence class pair.
+      if (Ptr1 != Ptr2 || AS1 != AS2 || IsLoad1 != IsLoad2 || TySize1 < TySize2)
+        continue;
+
+      // Ensure all instructions in EC2 can be bitcasted into NewTy.
+      /// TODO: NewTyBits is needed as stuctured binded variables cannot be
+      /// captured by a lambda until C++20.
+      auto NewTyBits = std::get<2>(EC1.first);
+      if (any_of(EC2.second, [&](Instruction *I) {
+            return DL.getTypeSizeInBits(getLoadStoreType(I)) != NewTyBits;
+          }))
+        continue;
+
+      // Create a new type for the equivalence class.
+      auto &Ctx = EC2.second[0]->getContext();
+      Type *NewTy = Type::getIntNTy(EC2.second[0]->getContext(), NewTyBits);
+      if (ClassAllTy[EC1.first].test(1) && ClassAllTy[EC2.first].test(1)) {
+        if (NewTyBits == 16)
+          NewTy = Type::getHalfTy(Ctx);
+        else if (NewTyBits == 32)
+          NewTy = Type::getFloatTy(Ctx);
+        else if (NewTyBits == 64)
+          NewTy = Type::getDoubleTy(Ctx);
----------------
arsenm wrote:

Really should avoid doing bitwidth -> fptype. This doesn't consider bfloat 

https://github.com/llvm/llvm-project/pull/134436