1 //=- llvm/CodeGen/ScheduleHazardRecognizer.h - Scheduling Support -*- C++ -*-=// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file implements the ScheduleHazardRecognizer class, which implements 11 // hazard-avoidance heuristics for scheduling. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_CODEGEN_SCHEDULEHAZARDRECOGNIZER_H 16 #define LLVM_CODEGEN_SCHEDULEHAZARDRECOGNIZER_H 17 18 namespace llvm { 19 20 class SUnit; 21 22 /// HazardRecognizer - This determines whether or not an instruction can be 23 /// issued this cycle, and whether or not a noop needs to be inserted to handle 24 /// the hazard. 25 class ScheduleHazardRecognizer { 26 protected: 27 /// MaxLookAhead - Indicate the number of cycles in the scoreboard 28 /// state. Important to restore the state after backtracking. Additionally, 29 /// MaxLookAhead=0 identifies a fake recognizer, allowing the client to 30 /// bypass virtual calls. Currently the PostRA scheduler ignores it. 31 unsigned MaxLookAhead; 32 33 public: ScheduleHazardRecognizer()34 ScheduleHazardRecognizer(): MaxLookAhead(0) {} 35 virtual ~ScheduleHazardRecognizer(); 36 37 enum HazardType { 38 NoHazard, // This instruction can be emitted at this cycle. 39 Hazard, // This instruction can't be emitted at this cycle. 40 NoopHazard // This instruction can't be emitted, and needs noops. 41 }; 42 getMaxLookAhead()43 unsigned getMaxLookAhead() const { return MaxLookAhead; } 44 isEnabled()45 bool isEnabled() const { return MaxLookAhead != 0; } 46 47 /// atIssueLimit - Return true if no more instructions may be issued in this 48 /// cycle. 49 /// 50 /// FIXME: remove this once MachineScheduler is the only client. atIssueLimit()51 virtual bool atIssueLimit() const { return false; } 52 53 /// getHazardType - Return the hazard type of emitting this node. There are 54 /// three possible results. Either: 55 /// * NoHazard: it is legal to issue this instruction on this cycle. 56 /// * Hazard: issuing this instruction would stall the machine. If some 57 /// other instruction is available, issue it first. 58 /// * NoopHazard: issuing this instruction would break the program. If 59 /// some other instruction can be issued, do so, otherwise issue a noop. 60 virtual HazardType getHazardType(SUnit *m, int Stalls = 0) { 61 return NoHazard; 62 } 63 64 /// Reset - This callback is invoked when a new block of 65 /// instructions is about to be schedule. The hazard state should be 66 /// set to an initialized state. Reset()67 virtual void Reset() {} 68 69 /// EmitInstruction - This callback is invoked when an instruction is 70 /// emitted, to advance the hazard state. EmitInstruction(SUnit *)71 virtual void EmitInstruction(SUnit *) {} 72 73 /// PreEmitNoops - This callback is invoked prior to emitting an instruction. 74 /// It should return the number of noops to emit prior to the provided 75 /// instruction. 76 /// Note: This is only used during PostRA scheduling. EmitNoop is not called 77 /// for these noops. PreEmitNoops(SUnit *)78 virtual unsigned PreEmitNoops(SUnit *) { 79 return 0; 80 } 81 82 /// ShouldPreferAnother - This callback may be invoked if getHazardType 83 /// returns NoHazard. If, even though there is no hazard, it would be better to 84 /// schedule another available instruction, this callback should return true. ShouldPreferAnother(SUnit *)85 virtual bool ShouldPreferAnother(SUnit *) { 86 return false; 87 } 88 89 /// AdvanceCycle - This callback is invoked whenever the next top-down 90 /// instruction to be scheduled cannot issue in the current cycle, either 91 /// because of latency or resource conflicts. This should increment the 92 /// internal state of the hazard recognizer so that previously "Hazard" 93 /// instructions will now not be hazards. AdvanceCycle()94 virtual void AdvanceCycle() {} 95 96 /// RecedeCycle - This callback is invoked whenever the next bottom-up 97 /// instruction to be scheduled cannot issue in the current cycle, either 98 /// because of latency or resource conflicts. RecedeCycle()99 virtual void RecedeCycle() {} 100 101 /// EmitNoop - This callback is invoked when a noop was added to the 102 /// instruction stream. EmitNoop()103 virtual void EmitNoop() { 104 // Default implementation: count it as a cycle. 105 AdvanceCycle(); 106 } 107 }; 108 109 } 110 111 #endif 112