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

[Matt Arsenault via llvm-commits]

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@@ -1310,6 +1315,135 @@ std::optional<APInt> Vectorizer::getConstantOffsetSelects(
   return std::nullopt;
 }
 
+void Vectorizer::insertCastsToMergeClasses(EquivalenceClassMap &EQClasses) {
+  if (EQClasses.size() < 2)
+    return;
+
+  auto CopyMetaDataFromTo = [&](Instruction *Src, Instruction *Dst) {
+    SmallVector<std::pair<unsigned, MDNode *>, 4> MD;
+    Src->getAllMetadata(MD);
+    for (const auto [ID, Node] : MD) {
+      Dst->setMetadata(ID, Node);
+    }
+  };
+
+  // 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 (const auto &C : EQClasses) {
+    auto CommonTypeKind = [](Instruction *I) {
+      if (I->getType()->isIntOrIntVectorTy())
+        return 0;
+      if (I->getType()->isFPOrFPVectorTy())
+        return 1;
+      if (I->getType()->isPtrOrPtrVectorTy())
+        return 2;
+      return -1; // Invalid type kind
+    };
+
+    int FirstTypeKind = CommonTypeKind(EQClasses[C.first][0]);
+    if (FirstTypeKind != -1 && all_of(EQClasses[C.first], [&](Instruction *I) {
+          return CommonTypeKind(I) == FirstTypeKind;
+        })) {
+      ClassAllTy[C.first].set(FirstTypeKind);
+    }
+  }
+
+  // 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;
+
+      // An All-FP class should only be merged into another All-FP class.
----------------
arsenm wrote:

FPNess isn't a fundamentally interesting property

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