1 //=- llvm/CodeGen/DFAPacketizer.cpp - DFA Packetizer for VLIW -*- C++ -*-=====//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
9 // This class implements a deterministic finite automaton (DFA) based
10 // packetizing mechanism for VLIW architectures. It provides APIs to
11 // determine whether there exists a legal mapping of instructions to
12 // functional unit assignments in a packet. The DFA is auto-generated from
13 // the target's Schedule.td file.
15 // A DFA consists of 3 major elements: states, inputs, and transitions. For
16 // the packetizing mechanism, the input is the set of instruction classes for
17 // a target. The state models all possible combinations of functional unit
18 // consumption for a given set of instructions in a packet. A transition
19 // models the addition of an instruction to a packet. In the DFA constructed
20 // by this class, if an instruction can be added to a packet, then a valid
21 // transition exists from the corresponding state. Invalid transitions
22 // indicate that the instruction cannot be added to the current packet.
24 //===----------------------------------------------------------------------===//
26 #include "llvm/CodeGen/DFAPacketizer.h"
27 #include "llvm/CodeGen/MachineInstr.h"
28 #include "llvm/MC/MCInstrItineraries.h"
31 DFAPacketizer::DFAPacketizer(const InstrItineraryData *I, const int (*SIT)[2],
33 InstrItins(I), CurrentState(0), DFAStateInputTable(SIT),
34 DFAStateEntryTable(SET) {}
38 // ReadTable - Read the DFA transition table and update CachedTable.
40 // Format of the transition tables:
41 // DFAStateInputTable[][2] = pairs of <Input, Transition> for all valid
43 // DFAStateEntryTable[i] = Index of the first entry in DFAStateInputTable
46 void DFAPacketizer::ReadTable(unsigned int state) {
47 unsigned ThisState = DFAStateEntryTable[state];
48 unsigned NextStateInTable = DFAStateEntryTable[state+1];
49 // Early exit in case CachedTable has already contains this
50 // state's transitions.
51 if (CachedTable.count(UnsignPair(state,
52 DFAStateInputTable[ThisState][0])))
55 for (unsigned i = ThisState; i < NextStateInTable; i++)
56 CachedTable[UnsignPair(state, DFAStateInputTable[i][0])] =
57 DFAStateInputTable[i][1];
61 // canReserveResources - Check if the resources occupied by a MCInstrDesc
62 // are available in the current state.
63 bool DFAPacketizer::canReserveResources(const llvm::MCInstrDesc *MID) {
64 unsigned InsnClass = MID->getSchedClass();
65 const llvm::InstrStage *IS = InstrItins->beginStage(InsnClass);
66 unsigned FuncUnits = IS->getUnits();
67 UnsignPair StateTrans = UnsignPair(CurrentState, FuncUnits);
68 ReadTable(CurrentState);
69 return (CachedTable.count(StateTrans) != 0);
73 // reserveResources - Reserve the resources occupied by a MCInstrDesc and
74 // change the current state to reflect that change.
75 void DFAPacketizer::reserveResources(const llvm::MCInstrDesc *MID) {
76 unsigned InsnClass = MID->getSchedClass();
77 const llvm::InstrStage *IS = InstrItins->beginStage(InsnClass);
78 unsigned FuncUnits = IS->getUnits();
79 UnsignPair StateTrans = UnsignPair(CurrentState, FuncUnits);
80 ReadTable(CurrentState);
81 assert(CachedTable.count(StateTrans) != 0);
82 CurrentState = CachedTable[StateTrans];
86 // canReserveResources - Check if the resources occupied by a machine
87 // instruction are available in the current state.
88 bool DFAPacketizer::canReserveResources(llvm::MachineInstr *MI) {
89 const llvm::MCInstrDesc &MID = MI->getDesc();
90 return canReserveResources(&MID);
93 // reserveResources - Reserve the resources occupied by a machine
94 // instruction and change the current state to reflect that change.
95 void DFAPacketizer::reserveResources(llvm::MachineInstr *MI) {
96 const llvm::MCInstrDesc &MID = MI->getDesc();
97 reserveResources(&MID);