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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.
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 {
/// 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;
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 *) {}
/// 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;
/// 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.