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diff --git a/clang-r353983e/include/llvm/CodeGen/ScheduleHazardRecognizer.h b/clang-r353983e/include/llvm/CodeGen/ScheduleHazardRecognizer.h
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+//=- llvm/CodeGen/ScheduleHazardRecognizer.h - Scheduling Support -*- C++ -*-=//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the ScheduleHazardRecognizer class, which implements
+// hazard-avoidance heuristics for scheduling.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_SCHEDULEHAZARDRECOGNIZER_H
+#define LLVM_CODEGEN_SCHEDULEHAZARDRECOGNIZER_H
+
+namespace llvm {
+
+class MachineInstr;
+class SUnit;
+
+/// HazardRecognizer - This determines whether or not an instruction can be
+/// issued this cycle, and whether or not a noop needs to be inserted to handle
+/// the hazard.
+class ScheduleHazardRecognizer {
+protected:
+  /// MaxLookAhead - Indicate the number of cycles in the scoreboard
+  /// state. Important to restore the state after backtracking. Additionally,
+  /// MaxLookAhead=0 identifies a fake recognizer, allowing the client to
+  /// bypass virtual calls. Currently the PostRA scheduler ignores it.
+  unsigned MaxLookAhead = 0;
+
+public:
+  ScheduleHazardRecognizer() = default;
+  virtual ~ScheduleHazardRecognizer();
+
+  enum HazardType {
+    NoHazard,      // This instruction can be emitted at this cycle.
+    Hazard,        // This instruction can't be emitted at this cycle.
+    NoopHazard     // This instruction can't be emitted, and needs noops.
+  };
+
+  unsigned getMaxLookAhead() const { return MaxLookAhead; }
+
+  bool isEnabled() const { return MaxLookAhead != 0; }
+
+  /// atIssueLimit - Return true if no more instructions may be issued in this
+  /// cycle.
+  ///
+  /// FIXME: remove this once MachineScheduler is the only client.
+  virtual bool atIssueLimit() const { return false; }
+
+  /// getHazardType - Return the hazard type of emitting this node.  There are
+  /// three possible results.  Either:
+  ///  * NoHazard: it is legal to issue this instruction on this cycle.
+  ///  * Hazard: issuing this instruction would stall the machine.  If some
+  ///     other instruction is available, issue it first.
+  ///  * NoopHazard: issuing this instruction would break the program.  If
+  ///     some other instruction can be issued, do so, otherwise issue a noop.
+  virtual HazardType getHazardType(SUnit *m, int Stalls = 0) {
+    return NoHazard;
+  }
+
+  /// Reset - This callback is invoked when a new block of
+  /// instructions is about to be schedule. The hazard state should be
+  /// set to an initialized state.
+  virtual void Reset() {}
+
+  /// EmitInstruction - This callback is invoked when an instruction is
+  /// emitted, to advance the hazard state.
+  virtual void EmitInstruction(SUnit *) {}
+
+  /// This overload will be used when the hazard recognizer is being used
+  /// by a non-scheduling pass, which does not use SUnits.
+  virtual void EmitInstruction(MachineInstr *) {}
+
+  /// PreEmitNoops - This callback is invoked prior to emitting an instruction.
+  /// It should return the number of noops to emit prior to the provided
+  /// instruction.
+  /// Note: This is only used during PostRA scheduling. EmitNoop is not called
+  /// for these noops.
+  virtual unsigned PreEmitNoops(SUnit *) {
+    return 0;
+  }
+
+  /// This overload will be used when the hazard recognizer is being used
+  /// by a non-scheduling pass, which does not use SUnits.
+  virtual unsigned PreEmitNoops(MachineInstr *) {
+    return 0;
+  }
+
+  /// ShouldPreferAnother - This callback may be invoked if getHazardType
+  /// returns NoHazard. If, even though there is no hazard, it would be better to
+  /// schedule another available instruction, this callback should return true.
+  virtual bool ShouldPreferAnother(SUnit *) {
+    return false;
+  }
+
+  /// AdvanceCycle - This callback is invoked whenever the next top-down
+  /// instruction to be scheduled cannot issue in the current cycle, either
+  /// because of latency or resource conflicts.  This should increment the
+  /// internal state of the hazard recognizer so that previously "Hazard"
+  /// instructions will now not be hazards.
+  virtual void AdvanceCycle() {}
+
+  /// RecedeCycle - This callback is invoked whenever the next bottom-up
+  /// instruction to be scheduled cannot issue in the current cycle, either
+  /// because of latency or resource conflicts.
+  virtual void RecedeCycle() {}
+
+  /// EmitNoop - This callback is invoked when a noop was added to the
+  /// instruction stream.
+  virtual void EmitNoop() {
+    // Default implementation: count it as a cycle.
+    AdvanceCycle();
+  }
+};
+
+} // end namespace llvm
+
+#endif // LLVM_CODEGEN_SCHEDULEHAZARDRECOGNIZER_H