Add a deterministic finite automaton based packetizer for VLIW architectures

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145629 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 98 insertions, 0 deletions

diff --git a/lib/CodeGen/DFAPacketizer.cpp b/lib/CodeGen/DFAPacketizer.cpp
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+++ b/lib/CodeGen/DFAPacketizer.cpp
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+//=- llvm/CodeGen/DFAPacketizer.cpp - DFA Packetizer for VLIW -*- C++ -*-=====//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// This class implements a deterministic finite automaton (DFA) based
+// packetizing mechanism for VLIW architectures. It provides APIs to
+// determine whether there exists a legal mapping of instructions to
+// functional unit assignments in a packet. The DFA is auto-generated from
+// the target's Schedule.td file.
+//
+// A DFA consists of 3 major elements: states, inputs, and transitions. For
+// the packetizing mechanism, the input is the set of instruction classes for
+// a target. The state models all possible combinations of functional unit
+// consumption for a given set of instructions in a packet. A transition
+// models the addition of an instruction to a packet. In the DFA constructed
+// by this class, if an instruction can be added to a packet, then a valid
+// transition exists from the corresponding state. Invalid transitions
+// indicate that the instruction cannot be added to the current packet.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/DFAPacketizer.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/MC/MCInstrItineraries.h"
+using namespace llvm;
+
+DFAPacketizer::DFAPacketizer(const InstrItineraryData *I, const int (*SIT)[2],
+                             const unsigned* SET):
+  InstrItins(I), CurrentState(0), DFAStateInputTable(SIT),
+  DFAStateEntryTable(SET) {}
+
+
+//
+// ReadTable - Read the DFA transition table and update CachedTable
+//
+// Format of the transition tables:
+// DFAStateInputTable[][2] = pairs of <Input, Transition> for all valid
+//                           transitions
+// DFAStateEntryTable[i] = Index of the first entry in DFAStateInputTable
+//                         for the ith state
+//
+void DFAPacketizer::ReadTable(unsigned int state) {
+  unsigned ThisState = DFAStateEntryTable[state];
+  unsigned NextStateInTable = DFAStateEntryTable[state+1];
+  // Early exit in case CachedTable has already contains this
+  // state's transitions
+  if (CachedTable.count(UnsignPair(state,
+                                   DFAStateInputTable[ThisState][0])))
+    return;
+
+  for (unsigned i = ThisState; i < NextStateInTable; i++)
+    CachedTable[UnsignPair(state, DFAStateInputTable[i][0])] =
+      DFAStateInputTable[i][1];
+}
+
+
+// canReserveResources - Check if the resources occupied by a MCInstrDesc
+// are available in the current state
+bool DFAPacketizer::canReserveResources(const llvm::MCInstrDesc* MID) {
+  unsigned InsnClass = MID->getSchedClass();
+  const llvm::InstrStage* IS = InstrItins->beginStage(InsnClass);
+  unsigned FuncUnits = IS->getUnits();
+  UnsignPair StateTrans = UnsignPair(CurrentState, FuncUnits);
+  ReadTable(CurrentState);
+  return (CachedTable.count(StateTrans) != 0);
+}
+
+
+// reserveResources - Reserve the resources occupied by a MCInstrDesc and
+// change the current state to reflect that change
+void DFAPacketizer::reserveResources(const llvm::MCInstrDesc* MID) {
+  unsigned InsnClass = MID->getSchedClass();
+  const llvm::InstrStage* IS = InstrItins->beginStage(InsnClass);
+  unsigned FuncUnits = IS->getUnits();
+  UnsignPair StateTrans = UnsignPair(CurrentState, FuncUnits);
+  ReadTable(CurrentState);
+  assert(CachedTable.count(StateTrans) != 0);
+  CurrentState = CachedTable[StateTrans];
+}
+
+
+// canReserveResources - Check if the resources occupied by a machine
+// instruction are available in the current state
+bool DFAPacketizer::canReserveResources(llvm::MachineInstr* MI) {
+  const llvm::MCInstrDesc& MID = MI->getDesc();
+  return canReserveResources(&MID);
+}
+
+// reserveResources - Reserve the resources occupied by a machine
+// instruction and change the current state to reflect that change
+void DFAPacketizer::reserveResources(llvm::MachineInstr* MI) {
+  const llvm::MCInstrDesc& MID = MI->getDesc();
+  reserveResources(&MID);
+}