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

[Alexey Bataev via llvm-commits]

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@@ -810,6 +810,207 @@ 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
+/// (getInterchangeableInstructionOpcode)
+/// - Get the operands for the interchangeable form
+/// (getInterchangeableInstructionOps)
+class InterchangeableInstruction {
+protected:
+  Instruction *const MainOp;
+
+  /// Return non nullptr if the right operand of I is ConstantInt.
+  static ConstantInt *isBinOpWithConstantInt(Instruction *I) {
+    Constant *C;
+    if (!match(I, m_BinOp(m_Value(), m_Constant(C))))
+      return nullptr;
+    if (auto *CI = dyn_cast<ConstantInt>(C)) {
+      return CI;
+    } else if (auto *CDV = dyn_cast<ConstantDataVector>(C)) {
+      if (auto *CI = dyn_cast_if_present<ConstantInt>(CDV->getSplatValue()))
+        return CI;
+    }
+    return nullptr;
+  }
+
+public:
+  InterchangeableInstruction(Instruction *MainOp) : MainOp(MainOp) {}
+  virtual bool isSame(Instruction *I) {
+    return MainOp->getOpcode() == I->getOpcode();
+  }
+  virtual unsigned getInterchangeableInstructionOpcode() {
+    return MainOp->getOpcode();
+  }
+  virtual SmallVector<Value *>
+  getInterchangeableInstructionOps(Instruction *I) {
+    assert(MainOp->getOpcode() == I->getOpcode());
+    return SmallVector<Value *>(MainOp->operands());
+  }
+  virtual ~InterchangeableInstruction() = default;
+};
+
+class BinOpIsNoOp final : public InterchangeableInstruction {
+  constexpr static std::initializer_list<unsigned> SupportedOp = {
+      Instruction::Add,  Instruction::Sub, Instruction::Mul, Instruction::Shl,
+      Instruction::AShr, Instruction::And, Instruction::Or,  Instruction::Xor};
+  SmallVector<unsigned> CandidateOp = SupportedOp;
+
+public:
+  using InterchangeableInstruction::InterchangeableInstruction;
+  bool isSame(Instruction *I) override {
+    unsigned Opcode = I->getOpcode();
+    if (!is_contained(SupportedOp, Opcode))
+      return false;
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alexey-bataev wrote:

Better to make it a switch to avoid linear complexity here?

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