[llvm] [SLP] Make getSameOpcode support interchangeable instructions. (PR #127450)

[Alexey Bataev via llvm-commits]

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@@ -810,6 +810,267 @@ static std::optional<unsigned> getExtractIndex(Instruction *E) {
 
 namespace {
 
+/// Base class for representing instructions that can be interchanged with other
+/// equivalent forms. For example, multiplication by a power of 2 can be
+/// interchanged with a left shift.
+///
+/// Derived classes implement specific interchange patterns by overriding the
+/// virtual methods to define their interchange logic.
+///
+/// The class maintains a reference to the main instruction (MainOp) and
+/// provides methods to:
+/// - Check if another instruction is interchangeable (isSame)
+/// - Get the opcode for the interchangeable form (getOpcode)
+/// - Get the operands for the interchangeable form (getOperand)
+class InterchangeableInstruction {
+protected:
+  Instruction *const MainOp;
+
+public:
+  InterchangeableInstruction(Instruction *MainOp) : MainOp(MainOp) {}
+  virtual bool isSame(Instruction *I) {
+    return MainOp->getOpcode() == I->getOpcode();
+  }
+  virtual unsigned getOpcode() { return MainOp->getOpcode(); }
+  virtual SmallVector<Value *> getOperand(Instruction *I) {
+    assert(MainOp->getOpcode() == I->getOpcode());
+    return SmallVector<Value *>(MainOp->operands());
+  }
+  virtual ~InterchangeableInstruction() = default;
+};
+
+class InterchangeableBinOp final : public InterchangeableInstruction {
+  using MaskType = std::uint_fast8_t;
+  constexpr static std::initializer_list<unsigned> SupportedOp = {
+      Instruction::Add,  Instruction::Sub, Instruction::Mul, Instruction::Shl,
+      Instruction::AShr, Instruction::And, Instruction::Or,  Instruction::Xor};
+  // from high to low bit: Xor Or And Sub Add Mul AShr Shl
+  MaskType Mask = 0b11111111;
+  MaskType SeenBefore = 0;
+
+  /// Return a non-nullptr if either operand of I is a ConstantInt.
+  static std::pair<ConstantInt *, unsigned>
+  isBinOpWithConstantInt(Instruction *I) {
+    unsigned Opcode = I->getOpcode();
+    unsigned Pos = 1;
+    Constant *C;
+    if (!match(I, m_BinOp(m_Value(), m_Constant(C)))) {
+      if (Opcode == Instruction::Sub || Opcode == Instruction::Shl ||
+          Opcode == Instruction::AShr)
+        return std::make_pair(nullptr, Pos);
+      if (!match(I, m_BinOp(m_Constant(C), m_Value())))
+        return std::make_pair(nullptr, Pos);
+      Pos = 0;
+    }
+    if (auto *CI = dyn_cast<ConstantInt>(C))
+      return std::make_pair(CI, Pos);
+    if (auto *CDV = dyn_cast<ConstantDataVector>(C)) {
+      if (auto *CI = dyn_cast_if_present<ConstantInt>(CDV->getSplatValue()))
+        return std::make_pair(CI, Pos);
+    }
+    return std::make_pair(nullptr, Pos);
+  }
+
+  static MaskType opcodeToMask(unsigned Opcode) {
+    switch (Opcode) {
+    case Instruction::Shl:
+      return 0b1;
+    case Instruction::AShr:
+      return 0b10;
+    case Instruction::Mul:
+      return 0b100;
+    case Instruction::Add:
+      return 0b1000;
+    case Instruction::Sub:
+      return 0b10000;
+    case Instruction::And:
+      return 0b100000;
+    case Instruction::Or:
+      return 0b1000000;
+    case Instruction::Xor:
+      return 0b10000000;
+    }
+    llvm_unreachable("Unsupported opcode.");
+  }
+
+  bool tryAnd(MaskType X) {
+    if (Mask & X) {
+      Mask &= X;
+      return true;
+    }
+    return false;
+  }
+
+public:
+  using InterchangeableInstruction::InterchangeableInstruction;
+  bool isSame(Instruction *I) override {
+    unsigned Opcode = I->getOpcode();
+    if (!binary_search(SupportedOp, Opcode))
+      return false;
+    SeenBefore |= opcodeToMask(Opcode);
+    ConstantInt *CI = isBinOpWithConstantInt(I).first;
+    if (CI) {
+      const APInt &CIValue = CI->getValue();
+      switch (Opcode) {
+      case Instruction::Shl:
+        if (CIValue.isZero())
+          return true;
+        return tryAnd(0b101);
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alexey-bataev wrote:

Avoid using explicit magic numbers

https://github.com/llvm/llvm-project/pull/127450