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thirdparty/clang/include/llvm/CodeGen/ScheduleHazardRecognizer.h

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+//=- llvm/CodeGen/ScheduleHazardRecognizer.h - Scheduling Support -*- C++ -*-=//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// 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 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;
+
+public:
+  ScheduleHazardRecognizer(): MaxLookAhead(0) {}
+  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 *) {}
+
+  /// 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();
+  }
+};
+
+}
+
+#endif