lib/Target/TargetSchedInfo.cpp

//===-- SchedInfo.cpp - Generic code to support target schedulers ----------==//
//
// This file implements the generic part of a Scheduler description for a
// target.  This functionality is defined in the llvm/Target/SchedInfo.h file.
//
//===----------------------------------------------------------------------===//

#include "llvm/Target/MachineSchedInfo.h"

// External object describing the machine instructions
// Initialized only when the TargetMachine class is created
// and reset when that class is destroyed.
// 
const MachineInstrDescriptor* TargetInstrDescriptors = 0;

resourceId_t MachineResource::nextId = 0;

// Check if fromRVec and toRVec have *any* common entries.
// Assume the vectors are sorted in increasing order.
// Algorithm copied from function set_intersection() for sorted ranges
// (stl_algo.h).
//
inline static bool
RUConflict(const vector<resourceId_t>& fromRVec,
	   const vector<resourceId_t>& toRVec)
{
  
  unsigned fN = fromRVec.size(), tN = toRVec.size(); 
  unsigned fi = 0, ti = 0;

  while (fi < fN && ti < tN)
    {
      if (fromRVec[fi] < toRVec[ti])
	++fi;
      else if (toRVec[ti] < fromRVec[fi])
	++ti;
      else
	return true;
    }
  return false;
}


static cycles_t
ComputeMinGap(const InstrRUsage &fromRU, 
	      const InstrRUsage &toRU)
{
  cycles_t minGap = 0;
  
  if (fromRU.numBubbles > 0)
    minGap = fromRU.numBubbles;
  
  if (minGap < fromRU.numCycles)
    {
      // only need to check from cycle `minGap' onwards
      for (cycles_t gap=minGap; gap <= fromRU.numCycles-1; gap++)
	{
	  // check if instr. #2 can start executing `gap' cycles after #1
	  // by checking for resource conflicts in each overlapping cycle
	  cycles_t numOverlap = min(fromRU.numCycles - gap, toRU.numCycles);
	  for (cycles_t c = 0; c <= numOverlap-1; c++)
	    if (RUConflict(fromRU.resourcesByCycle[gap + c],
			   toRU.resourcesByCycle[c]))
	      {
		// conflict found so minGap must be more than `gap'
		minGap = gap+1;
		break;
	      }
	}
    }
  
  return minGap;
}


//---------------------------------------------------------------------------
// class MachineSchedInfo
//	Interface to machine description for instruction scheduling
//---------------------------------------------------------------------------

MachineSchedInfo::MachineSchedInfo(const TargetMachine&    tgt,
                                   int                     NumSchedClasses,
                                   const InstrClassRUsage* ClassRUsages,
                                   const InstrRUsageDelta* UsageDeltas,
                                   const InstrIssueDelta*  IssueDeltas,
                                   unsigned int		   NumUsageDeltas,
                                   unsigned int		   NumIssueDeltas)
  : target(tgt),
    numSchedClasses(NumSchedClasses), mii(& tgt.getInstrInfo()),
    classRUsages(ClassRUsages), usageDeltas(UsageDeltas),
    issueDeltas(IssueDeltas), numUsageDeltas(NumUsageDeltas),
    numIssueDeltas(NumIssueDeltas)
{}

void
MachineSchedInfo::initializeResources()
{
  assert(MAX_NUM_SLOTS >= (int)getMaxNumIssueTotal()
	 && "Insufficient slots for static data! Increase MAX_NUM_SLOTS");
  
  // First, compute common resource usage info for each class because
  // most instructions will probably behave the same as their class.
  // Cannot allocate a vector of InstrRUsage so new each one.
  // 
  vector<InstrRUsage> instrRUForClasses;
  instrRUForClasses.resize(numSchedClasses);
  for (InstrSchedClass sc = 0; sc < numSchedClasses; sc++) {
    // instrRUForClasses.push_back(new InstrRUsage);
    instrRUForClasses[sc].setMaxSlots(getMaxNumIssueTotal());
    instrRUForClasses[sc] = classRUsages[sc];
  }
  
  computeInstrResources(instrRUForClasses);
  computeIssueGaps(instrRUForClasses);
}


void
MachineSchedInfo::computeInstrResources(const vector<InstrRUsage>&
					instrRUForClasses)
{
  int numOpCodes =  mii->getNumRealOpCodes();
  instrRUsages.resize(numOpCodes);
  
  // First get the resource usage information from the class resource usages.
  for (MachineOpCode op = 0; op < numOpCodes; ++op) {
    InstrSchedClass sc = getSchedClass(op);
    assert(sc >= 0 && sc < numSchedClasses);
    instrRUsages[op] = instrRUForClasses[sc];
  }
  
  // Now, modify the resource usages as specified in the deltas.
  for (unsigned i = 0; i < numUsageDeltas; ++i) {
    MachineOpCode op = usageDeltas[i].opCode;
    assert(op < numOpCodes);
    instrRUsages[op].addUsageDelta(usageDeltas[i]);
  }
  
  // Then modify the issue restrictions as specified in the deltas.
  for (unsigned i = 0; i < numIssueDeltas; ++i) {
    MachineOpCode op = issueDeltas[i].opCode;
    assert(op < numOpCodes);
    instrRUsages[issueDeltas[i].opCode].addIssueDelta(issueDeltas[i]);
  }
}


void
MachineSchedInfo::computeIssueGaps(const vector<InstrRUsage>&
				   instrRUForClasses)
{
  int numOpCodes =  mii->getNumRealOpCodes();
  instrRUsages.resize(numOpCodes);
  
  assert(numOpCodes < (1 << MAX_OPCODE_SIZE) - 1
         && "numOpCodes invalid for implementation of class OpCodePair!");
  
  // First, compute issue gaps between pairs of classes based on common
  // resources usages for each class, because most instruction pairs will
  // usually behave the same as their class.
  // 
  int classPairGaps[numSchedClasses][numSchedClasses];
  for (InstrSchedClass fromSC=0; fromSC < numSchedClasses; fromSC++)
    for (InstrSchedClass toSC=0; toSC < numSchedClasses; toSC++)
      {
	int classPairGap = ComputeMinGap(instrRUForClasses[fromSC],
					 instrRUForClasses[toSC]);
	classPairGaps[fromSC][toSC] = classPairGap; 
      }
  
  // Now, for each pair of instructions, use the class pair gap if both
  // instructions have identical resource usage as their respective classes.
  // If not, recompute the gap for the pair from scratch.
  
  longestIssueConflict = 0;
  
  for (MachineOpCode fromOp=0; fromOp < numOpCodes; fromOp++)
    for (MachineOpCode toOp=0; toOp < numOpCodes; toOp++)
      {
	int instrPairGap = 
	  (instrRUsages[fromOp].sameAsClass && instrRUsages[toOp].sameAsClass)
	  ? classPairGaps[getSchedClass(fromOp)][getSchedClass(toOp)]
	  : ComputeMinGap(instrRUsages[fromOp], instrRUsages[toOp]);
      
	if (instrPairGap > 0)
	  {
	    issueGaps[OpCodePair(fromOp,toOp)] = instrPairGap;
	    conflictLists[fromOp].push_back(toOp);
	    longestIssueConflict = max(longestIssueConflict, instrPairGap);
	  }
      }
}