//===-- SimpleRegisterCoalescing.cpp - Register Coalescing ----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a simple register coalescing pass that attempts to
// aggressively coalesce every register copy that it can.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "regcoalescing"
#include "llvm/CodeGen/SimpleRegisterCoalescing.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "VirtRegMap.h"
#include "llvm/Value.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/SSARegMap.h"
#include "llvm/Target/MRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
#include <cmath>
using namespace llvm;
STATISTIC(numJoins , "Number of interval joins performed");
STATISTIC(numPeep , "Number of identity moves eliminated after coalescing");
STATISTIC(numAborts , "Number of times interval joining aborted");
char SimpleRegisterCoalescing::ID = 0;
namespace {
static cl::opt<bool>
EnableJoining("join-liveintervals",
cl::desc("Coalesce copies (default=true)"),
cl::init(true));
RegisterPass<SimpleRegisterCoalescing>
X("simple-register-coalescing", "Simple Register Coalescing");
}
const PassInfo *llvm::SimpleRegisterCoalescingID = X.getPassInfo();
void SimpleRegisterCoalescing::getAnalysisUsage(AnalysisUsage &AU) const {
//AU.addPreserved<LiveVariables>();
AU.addPreserved<LiveIntervals>();
AU.addPreservedID(PHIEliminationID);
AU.addPreservedID(TwoAddressInstructionPassID);
AU.addRequired<LiveVariables>();
AU.addRequired<LiveIntervals>();
AU.addRequired<LoopInfo>();
MachineFunctionPass::getAnalysisUsage(AU);
}
/// AdjustCopiesBackFrom - We found a non-trivially-coalescable copy with IntA
/// being the source and IntB being the dest, thus this defines a value number
/// in IntB. If the source value number (in IntA) is defined by a copy from B,
/// see if we can merge these two pieces of B into a single value number,
/// eliminating a copy. For example:
///
/// A3 = B0
/// ...
/// B1 = A3 <- this copy
///
/// In this case, B0 can be extended to where the B1 copy lives, allowing the B1
/// value number to be replaced with B0 (which simplifies the B liveinterval).
///
/// This returns true if an interval was modified.
///
bool SimpleRegisterCoalescing::AdjustCopiesBackFrom(LiveInterval &IntA, LiveInterval &IntB,
MachineInstr *CopyMI) {
unsigned CopyIdx = li_->getDefIndex(li_->getInstructionIndex(CopyMI));
// BValNo is a value number in B that is defined by a copy from A. 'B3' in
// the example above.
LiveInterval::iterator BLR = IntB.FindLiveRangeContaining(CopyIdx);
VNInfo *BValNo = BLR->valno;
// Get the location that B is defined at. Two options: either this value has
// an unknown definition point or it is defined at CopyIdx. If unknown, we
// can't process it.
if (!BValNo->reg) return false;
assert(BValNo->def == CopyIdx &&
"Copy doesn't define the value?");
// AValNo is the value number in A that defines the copy, A0 in the example.
LiveInterval::iterator AValLR = IntA.FindLiveRangeContaining(CopyIdx-1);
VNInfo *AValNo = AValLR->valno;
// If AValNo is defined as a copy from IntB, we can potentially process this.
// Get the instruction that defines this value number.
unsigned SrcReg = AValNo->reg;
if (!SrcReg) return false; // Not defined by a copy.
// If the value number is not defined by a copy instruction, ignore it.
// If the source register comes from an interval other than IntB, we can't
// handle this.
if (rep(SrcReg) != IntB.reg) return false;
// Get the LiveRange in IntB that this value number starts with.
LiveInterval::iterator ValLR = IntB.FindLiveRangeContaining(AValNo->def-1);
// Make sure that the end of the live range is inside the same block as
// CopyMI.
MachineInstr *ValLREndInst = li_->getInstructionFromIndex(ValLR->end-1);
if (!ValLREndInst ||
ValLREndInst->getParent() != CopyMI->getParent()) return false;
// Okay, we now know that ValLR ends in the same block that the CopyMI
// live-range starts. If there are no intervening live ranges between them in
// IntB, we can merge them.
if (ValLR+1 != BLR) return false;
// If a live interval is a physical register, conservatively check if any
// of its sub-registers is overlapping the live interval of the virtual
// register. If so, do not coalesce.
if (MRegisterInfo::isPhysicalRegister(IntB.reg) &&
*mri_->getSubRegisters(IntB.reg)) {
for (const unsigned* SR = mri_->getSubRegisters(IntB.reg); *SR; ++SR)
if (li_->hasInterval(*SR) && IntA.overlaps(li_->getInterval(*SR))) {
DOUT << "Interfere with sub-register ";
DEBUG(li_->getInterval(*SR).print(DOUT, mri_));
return false;
}
}
DOUT << "\nExtending: "; IntB.print(DOUT, mri_);
unsigned FillerStart = ValLR->end, FillerEnd = BLR->start;
// We are about to delete CopyMI, so need to remove it as the 'instruction
// that defines this value #'. Update the the valnum with the new defining
// instruction #.
BValNo->def = FillerStart;
BValNo->reg = 0;
// Okay, we can merge them. We need to insert a new liverange:
// [ValLR.end, BLR.begin) of either value number, then we merge the
// two value numbers.
IntB.addRange(LiveRange(FillerStart, FillerEnd, BValNo));
// If the IntB live range is assigned to a physical register, and if that
// physreg has aliases,
if (MRegisterInfo::isPhysicalRegister(IntB.reg)) {
// Update the liveintervals of sub-registers.
for (const unsigned *AS = mri_->getSubRegisters(IntB.reg); *AS; ++AS) {
LiveInterval &AliasLI = li_->getInterval(*AS);
AliasLI.addRange(LiveRange(FillerStart, FillerEnd,
AliasLI.getNextValue(FillerStart, 0)));
}
}
// Okay, merge "B1" into the same value number as "B0".
if (BValNo != ValLR->valno)
IntB.MergeValueNumberInto(BValNo, ValLR->valno);
DOUT << " result = "; IntB.print(DOUT, mri_);
DOUT << "\n";
// If the source instruction was killing the source register before the
// merge, unset the isKill marker given the live range has been extended.
int UIdx = ValLREndInst->findRegisterUseOperandIdx(IntB.reg, true);
if (UIdx != -1)
ValLREndInst->getOperand(UIdx).unsetIsKill();
// Finally, delete the copy instruction.
li_->RemoveMachineInstrFromMaps(CopyMI);
CopyMI->eraseFromParent();
++numPeep;
return true;
}
/// JoinCopy - Attempt to join intervals corresponding to SrcReg/DstReg,
/// which are the src/dst of the copy instruction CopyMI. This returns true
/// if the copy was successfully coalesced away, or if it is never possible
/// to coalesce this copy, due to register constraints. It returns
/// false if it is not currently possible to coalesce this interval, but
/// it may be possible if other things get coalesced.
bool SimpleRegisterCoalescing::JoinCopy(MachineInstr *CopyMI,
unsigned SrcReg, unsigned DstReg, bool PhysOnly) {
DOUT << li_->getInstructionIndex(CopyMI) << '\t' << *CopyMI;
// Get representative registers.
unsigned repSrcReg = rep(SrcReg);
unsigned repDstReg = rep(DstReg);
// If they are already joined we continue.
if (repSrcReg == repDstReg) {
DOUT << "\tCopy already coalesced.\n";
return true; // Not coalescable.
}
bool SrcIsPhys = MRegisterInfo::isPhysicalRegister(repSrcReg);
bool DstIsPhys = MRegisterInfo::isPhysicalRegister(repDstReg);
if (PhysOnly && !SrcIsPhys && !DstIsPhys)
// Only joining physical registers with virtual registers in this round.
return true;
// If they are both physical registers, we cannot join them.
if (SrcIsPhys && DstIsPhys) {
DOUT << "\tCan not coalesce physregs.\n";
return true; // Not coalescable.
}
// We only join virtual registers with allocatable physical registers.
if (SrcIsPhys && !allocatableRegs_[repSrcReg]) {
DOUT << "\tSrc reg is unallocatable physreg.\n";
return true; // Not coalescable.
}
if (DstIsPhys && !allocatableRegs_[repDstReg]) {
DOUT << "\tDst reg is unallocatable physreg.\n";
return true; // Not coalescable.
}
// If they are not of the same register class, we cannot join them.
if (differingRegisterClasses(repSrcReg, repDstReg)) {
DOUT << "\tSrc/Dest are different register classes.\n";
return true; // Not coalescable.
}
LiveInterval &SrcInt = li_->getInterval(repSrcReg);
LiveInterval &DstInt = li_->getInterval(repDstReg);
assert(SrcInt.reg == repSrcReg && DstInt.reg == repDstReg &&
"Register mapping is horribly broken!");
DOUT << "\t\tInspecting "; SrcInt.print(DOUT, mri_);
DOUT << " and "; DstInt.print(DOUT, mri_);
DOUT << ": ";
// Check if it is necessary to propagate "isDead" property before intervals
// are joined.
MachineOperand *mopd = CopyMI->findRegisterDefOperand(DstReg);
bool isDead = mopd->isDead();
bool isShorten = false;
unsigned SrcStart = 0, RemoveStart = 0;
unsigned SrcEnd = 0, RemoveEnd = 0;
if (isDead) {
unsigned CopyIdx = li_->getInstructionIndex(CopyMI);
LiveInterval::iterator SrcLR =
SrcInt.FindLiveRangeContaining(li_->getUseIndex(CopyIdx));
RemoveStart = SrcStart = SrcLR->start;
RemoveEnd = SrcEnd = SrcLR->end;
// The instruction which defines the src is only truly dead if there are
// no intermediate uses and there isn't a use beyond the copy.
// FIXME: find the last use, mark is kill and shorten the live range.
if (SrcEnd > li_->getDefIndex(CopyIdx)) {
isDead = false;
} else {
MachineOperand *MOU;
MachineInstr *LastUse= lastRegisterUse(SrcStart, CopyIdx, repSrcReg, MOU);
if (LastUse) {
// Shorten the liveinterval to the end of last use.
MOU->setIsKill();
isDead = false;
isShorten = true;
RemoveStart = li_->getDefIndex(li_->getInstructionIndex(LastUse));
RemoveEnd = SrcEnd;
} else {
MachineInstr *SrcMI = li_->getInstructionFromIndex(SrcStart);
if (SrcMI) {
MachineOperand *mops = findDefOperand(SrcMI, repSrcReg);
if (mops)
// A dead def should have a single cycle interval.
++RemoveStart;
}
}
}
}
// We need to be careful about coalescing a source physical register with a
// virtual register. Once the coalescing is done, it cannot be broken and
// these are not spillable! If the destination interval uses are far away,
// think twice about coalescing them!
if (!mopd->isDead() && (SrcIsPhys || DstIsPhys)) {
LiveInterval &JoinVInt = SrcIsPhys ? DstInt : SrcInt;
unsigned JoinVReg = SrcIsPhys ? repDstReg : repSrcReg;
unsigned JoinPReg = SrcIsPhys ? repSrcReg : repDstReg;
const TargetRegisterClass *RC = mf_->getSSARegMap()->getRegClass(JoinVReg);
unsigned Threshold = allocatableRCRegs_[RC].count();
// If the virtual register live interval is long has it has low use desity,
// do not join them, instead mark the physical register as its allocation
// preference.
unsigned Length = JoinVInt.getSize() / InstrSlots::NUM;
LiveVariables::VarInfo &vi = lv_->getVarInfo(JoinVReg);
if (Length > Threshold &&
(((float)vi.NumUses / Length) < (1.0 / Threshold))) {
JoinVInt.preference = JoinPReg;
++numAborts;
DOUT << "\tMay tie down a physical register, abort!\n";
return false;
}
}
// Okay, attempt to join these two intervals. On failure, this returns false.
// Otherwise, if one of the intervals being joined is a physreg, this method
// always canonicalizes DstInt to be it. The output "SrcInt" will not have
// been modified, so we can use this information below to update aliases.
bool Swapped = false;
if (JoinIntervals(DstInt, SrcInt, Swapped)) {
if (isDead) {
// Result of the copy is dead. Propagate this property.
if (SrcStart == 0) {
assert(MRegisterInfo::isPhysicalRegister(repSrcReg) &&
"Live-in must be a physical register!");
// Live-in to the function but dead. Remove it from entry live-in set.
// JoinIntervals may end up swapping the two intervals.
mf_->begin()->removeLiveIn(repSrcReg);
} else {
MachineInstr *SrcMI = li_->getInstructionFromIndex(SrcStart);
if (SrcMI) {
MachineOperand *mops = findDefOperand(SrcMI, repSrcReg);
if (mops)
mops->setIsDead();
}
}
}
if (isShorten || isDead) {
// Shorten the destination live interval.
if (Swapped)
SrcInt.removeRange(RemoveStart, RemoveEnd);
}
} else {
// Coalescing failed.
// If we can eliminate the copy without merging the live ranges, do so now.
if (AdjustCopiesBackFrom(SrcInt, DstInt, CopyMI))
return true;
// Otherwise, we are unable to join the intervals.
DOUT << "Interference!\n";
return false;
}
LiveInterval *ResSrcInt = &SrcInt;
LiveInterval *ResDstInt = &DstInt;
if (Swapped) {
std::swap(repSrcReg, repDstReg);
std::swap(ResSrcInt, ResDstInt);
}
assert(MRegisterInfo::isVirtualRegister(repSrcReg) &&
"LiveInterval::join didn't work right!");
// If we're about to merge live ranges into a physical register live range,
// we have to update any aliased register's live ranges to indicate that they
// have clobbered values for this range.
if (MRegisterInfo::isPhysicalRegister(repDstReg)) {
// Unset unnecessary kills.
if (!ResDstInt->containsOneValue()) {
for (LiveInterval::Ranges::const_iterator I = ResSrcInt->begin(),
E = ResSrcInt->end(); I != E; ++I)
unsetRegisterKills(I->start, I->end, repDstReg);
}
// Update the liveintervals of sub-registers.
for (const unsigned *AS = mri_->getSubRegisters(repDstReg); *AS; ++AS)
li_->getInterval(*AS).MergeInClobberRanges(*ResSrcInt);
} else {
// Merge use info if the destination is a virtual register.
LiveVariables::VarInfo& dVI = lv_->getVarInfo(repDstReg);
LiveVariables::VarInfo& sVI = lv_->getVarInfo(repSrcReg);
dVI.NumUses += sVI.NumUses;
}
DOUT << "\n\t\tJoined. Result = "; ResDstInt->print(DOUT, mri_);
DOUT << "\n";
// Remember these liveintervals have been joined.
JoinedLIs.set(repSrcReg - MRegisterInfo::FirstVirtualRegister);
if (MRegisterInfo::isVirtualRegister(repDstReg))
JoinedLIs.set(repDstReg - MRegisterInfo::FirstVirtualRegister);
// repSrcReg is guarateed to be the register whose live interval that is
// being merged.
li_->removeInterval(repSrcReg);
r2rMap_[repSrcReg] = repDstReg;
// Finally, delete the copy instruction.
li_->RemoveMachineInstrFromMaps(CopyMI);
CopyMI->eraseFromParent();
++numPeep;
++numJoins;
return true;
}
/// ComputeUltimateVN - Assuming we are going to join two live intervals,
/// compute what the resultant value numbers for each value in the input two
/// ranges will be. This is complicated by copies between the two which can
/// and will commonly cause multiple value numbers to be merged into one.
///
/// VN is the value number that we're trying to resolve. InstDefiningValue
/// keeps track of the new InstDefiningValue assignment for the result
/// LiveInterval. ThisFromOther/OtherFromThis are sets that keep track of
/// whether a value in this or other is a copy from the opposite set.
/// ThisValNoAssignments/OtherValNoAssignments keep track of value #'s that have
/// already been assigned.
///
/// ThisFromOther[x] - If x is defined as a copy from the other interval, this
/// contains the value number the copy is from.
///
static unsigned ComputeUltimateVN(VNInfo *VNI,
SmallVector<VNInfo*, 16> &NewVNInfo,
DenseMap<VNInfo*, VNInfo*> &ThisFromOther,
DenseMap<VNInfo*, VNInfo*> &OtherFromThis,
SmallVector<int, 16> &ThisValNoAssignments,
SmallVector<int, 16> &OtherValNoAssignments) {
unsigned VN = VNI->id;
// If the VN has already been computed, just return it.
if (ThisValNoAssignments[VN] >= 0)
return ThisValNoAssignments[VN];
// assert(ThisValNoAssignments[VN] != -2 && "Cyclic case?");
// If this val is not a copy from the other val, then it must be a new value
// number in the destination.
DenseMap<VNInfo*, VNInfo*>::iterator I = ThisFromOther.find(VNI);
if (I == ThisFromOther.end()) {
NewVNInfo.push_back(VNI);
return ThisValNoAssignments[VN] = NewVNInfo.size()-1;
}
VNInfo *OtherValNo = I->second;
// Otherwise, this *is* a copy from the RHS. If the other side has already
// been computed, return it.
if (OtherValNoAssignments[OtherValNo->id] >= 0)
return ThisValNoAssignments[VN] = OtherValNoAssignments[OtherValNo->id];
// Mark this value number as currently being computed, then ask what the
// ultimate value # of the other value is.
ThisValNoAssignments[VN] = -2;
unsigned UltimateVN =
ComputeUltimateVN(OtherValNo, NewVNInfo, OtherFromThis, ThisFromOther,
OtherValNoAssignments, ThisValNoAssignments);
return ThisValNoAssignments[VN] = UltimateVN;
}
static bool InVector(VNInfo *Val, const SmallVector<VNInfo*, 8> &V) {
return std::find(V.begin(), V.end(), Val) != V.end();
}
/// SimpleJoin - Attempt to joint the specified interval into this one. The
/// caller of this method must guarantee that the RHS only contains a single
/// value number and that the RHS is not defined by a copy from this
/// interval. This returns false if the intervals are not joinable, or it
/// joins them and returns true.
bool SimpleRegisterCoalescing::SimpleJoin(LiveInterval &LHS, LiveInterval &RHS) {
assert(RHS.containsOneValue());
// Some number (potentially more than one) value numbers in the current
// interval may be defined as copies from the RHS. Scan the overlapping
// portions of the LHS and RHS, keeping track of this and looking for
// overlapping live ranges that are NOT defined as copies. If these exist, we
// cannot coalesce.
LiveInterval::iterator LHSIt = LHS.begin(), LHSEnd = LHS.end();
LiveInterval::iterator RHSIt = RHS.begin(), RHSEnd = RHS.end();
if (LHSIt->start < RHSIt->start) {
LHSIt = std::upper_bound(LHSIt, LHSEnd, RHSIt->start);
if (LHSIt != LHS.begin()) --LHSIt;
} else if (RHSIt->start < LHSIt->start) {
RHSIt = std::upper_bound(RHSIt, RHSEnd, LHSIt->start);
if (RHSIt != RHS.begin()) --RHSIt;
}
SmallVector<VNInfo*, 8> EliminatedLHSVals;
while (1) {
// Determine if these live intervals overlap.
bool Overlaps = false;
if (LHSIt->start <= RHSIt->start)
Overlaps = LHSIt->end > RHSIt->start;
else
Overlaps = RHSIt->end > LHSIt->start;
// If the live intervals overlap, there are two interesting cases: if the
// LHS interval is defined by a copy from the RHS, it's ok and we record
// that the LHS value # is the same as the RHS. If it's not, then we cannot
// coalesce these live ranges and we bail out.
if (Overlaps) {
// If we haven't already recorded that this value # is safe, check it.
if (!InVector(LHSIt->valno, EliminatedLHSVals)) {
// Copy from the RHS?
unsigned SrcReg = LHSIt->valno->reg;
if (rep(SrcReg) != RHS.reg)
return false; // Nope, bail out.
EliminatedLHSVals.push_back(LHSIt->valno);
}
// We know this entire LHS live range is okay, so skip it now.
if (++LHSIt == LHSEnd) break;
continue;
}
if (LHSIt->end < RHSIt->end) {
if (++LHSIt == LHSEnd) break;
} else {
// One interesting case to check here. It's possible that we have
// something like "X3 = Y" which defines a new value number in the LHS,
// and is the last use of this liverange of the RHS. In this case, we
// want to notice this copy (so that it gets coalesced away) even though
// the live ranges don't actually overlap.
if (LHSIt->start == RHSIt->end) {
if (InVector(LHSIt->valno, EliminatedLHSVals)) {
// We already know that this value number is going to be merged in
// if coalescing succeeds. Just skip the liverange.
if (++LHSIt == LHSEnd) break;
} else {
// Otherwise, if this is a copy from the RHS, mark it as being merged
// in.
if (rep(LHSIt->valno->reg) == RHS.reg) {
EliminatedLHSVals.push_back(LHSIt->valno);
// We know this entire LHS live range is okay, so skip it now.
if (++LHSIt == LHSEnd) break;
}
}
}
if (++RHSIt == RHSEnd) break;
}
}
// If we got here, we know that the coalescing will be successful and that
// the value numbers in EliminatedLHSVals will all be merged together. Since
// the most common case is that EliminatedLHSVals has a single number, we
// optimize for it: if there is more than one value, we merge them all into
// the lowest numbered one, then handle the interval as if we were merging
// with one value number.
VNInfo *LHSValNo;
if (EliminatedLHSVals.size() > 1) {
// Loop through all the equal value numbers merging them into the smallest
// one.
VNInfo *Smallest = EliminatedLHSVals[0];
for (unsigned i = 1, e = EliminatedLHSVals.size(); i != e; ++i) {
if (EliminatedLHSVals[i]->id < Smallest->id) {
// Merge the current notion of the smallest into the smaller one.
LHS.MergeValueNumberInto(Smallest, EliminatedLHSVals[i]);
Smallest = EliminatedLHSVals[i];
} else {
// Merge into the smallest.
LHS.MergeValueNumberInto(EliminatedLHSVals[i], Smallest);
}
}
LHSValNo = Smallest;
} else {
assert(!EliminatedLHSVals.empty() && "No copies from the RHS?");
LHSValNo = EliminatedLHSVals[0];
}
// Okay, now that there is a single LHS value number that we're merging the
// RHS into, update the value number info for the LHS to indicate that the
// value number is defined where the RHS value number was.
const VNInfo *VNI = RHS.getFirstValNumInfo();
LHSValNo->def = VNI->def;
LHSValNo->reg = VNI->reg;
// Okay, the final step is to loop over the RHS live intervals, adding them to
// the LHS.
LHS.addKills(*LHSValNo, VNI->kills);
LHS.MergeRangesInAsValue(RHS, LHSValNo);
LHS.weight += RHS.weight;
if (RHS.preference && !LHS.preference)
LHS.preference = RHS.preference;
return true;
}
/// JoinIntervals - Attempt to join these two intervals. On failure, this
/// returns false. Otherwise, if one of the intervals being joined is a
/// physreg, this method always canonicalizes LHS to be it. The output
/// "RHS" will not have been modified, so we can use this information
/// below to update aliases.
bool SimpleRegisterCoalescing::JoinIntervals(LiveInterval &LHS,
LiveInterval &RHS, bool &Swapped) {
// Compute the final value assignment, assuming that the live ranges can be
// coalesced.
SmallVector<int, 16> LHSValNoAssignments;
SmallVector<int, 16> RHSValNoAssignments;
DenseMap<VNInfo*, VNInfo*> LHSValsDefinedFromRHS;
DenseMap<VNInfo*, VNInfo*> RHSValsDefinedFromLHS;
SmallVector<VNInfo*, 16> NewVNInfo;
// If a live interval is a physical register, conservatively check if any
// of its sub-registers is overlapping the live interval of the virtual
// register. If so, do not coalesce.
if (MRegisterInfo::isPhysicalRegister(LHS.reg) &&
*mri_->getSubRegisters(LHS.reg)) {
for (const unsigned* SR = mri_->getSubRegisters(LHS.reg); *SR; ++SR)
if (li_->hasInterval(*SR) && RHS.overlaps(li_->getInterval(*SR))) {
DOUT << "Interfere with sub-register ";
DEBUG(li_->getInterval(*SR).print(DOUT, mri_));
return false;
}
} else if (MRegisterInfo::isPhysicalRegister(RHS.reg) &&
*mri_->getSubRegisters(RHS.reg)) {
for (const unsigned* SR = mri_->getSubRegisters(RHS.reg); *SR; ++SR)
if (li_->hasInterval(*SR) && LHS.overlaps(li_->getInterval(*SR))) {
DOUT << "Interfere with sub-register ";
DEBUG(li_->getInterval(*SR).print(DOUT, mri_));
return false;
}
}
// Compute ultimate value numbers for the LHS and RHS values.
if (RHS.containsOneValue()) {
// Copies from a liveinterval with a single value are simple to handle and
// very common, handle the special case here. This is important, because
// often RHS is small and LHS is large (e.g. a physreg).
// Find out if the RHS is defined as a copy from some value in the LHS.
int RHSVal0DefinedFromLHS = -1;
int RHSValID = -1;
VNInfo *RHSValNoInfo = NULL;
VNInfo *RHSValNoInfo0 = RHS.getFirstValNumInfo();
unsigned RHSSrcReg = RHSValNoInfo0->reg;
if ((RHSSrcReg == 0 || rep(RHSSrcReg) != LHS.reg)) {
// If RHS is not defined as a copy from the LHS, we can use simpler and
// faster checks to see if the live ranges are coalescable. This joiner
// can't swap the LHS/RHS intervals though.
if (!MRegisterInfo::isPhysicalRegister(RHS.reg)) {
return SimpleJoin(LHS, RHS);
} else {
RHSValNoInfo = RHSValNoInfo0;
}
} else {
// It was defined as a copy from the LHS, find out what value # it is.
RHSValNoInfo = LHS.getLiveRangeContaining(RHSValNoInfo0->def-1)->valno;
RHSValID = RHSValNoInfo->id;
RHSVal0DefinedFromLHS = RHSValID;
}
LHSValNoAssignments.resize(LHS.getNumValNums(), -1);
RHSValNoAssignments.resize(RHS.getNumValNums(), -1);
NewVNInfo.resize(LHS.getNumValNums(), NULL);
// Okay, *all* of the values in LHS that are defined as a copy from RHS
// should now get updated.
for (LiveInterval::vni_iterator i = LHS.vni_begin(), e = LHS.vni_end();
i != e; ++i) {
VNInfo *VNI = *i;
unsigned VN = VNI->id;
if (unsigned LHSSrcReg = VNI->reg) {
if (rep(LHSSrcReg) != RHS.reg) {
// If this is not a copy from the RHS, its value number will be
// unmodified by the coalescing.
NewVNInfo[VN] = VNI;
LHSValNoAssignments[VN] = VN;
} else if (RHSValID == -1) {
// Otherwise, it is a copy from the RHS, and we don't already have a
// value# for it. Keep the current value number, but remember it.
LHSValNoAssignments[VN] = RHSValID = VN;
NewVNInfo[VN] = RHSValNoInfo;
LHSValsDefinedFromRHS[VNI] = RHSValNoInfo0;
} else {
// Otherwise, use the specified value #.
LHSValNoAssignments[VN] = RHSValID;
if (VN == (unsigned)RHSValID) { // Else this val# is dead.
NewVNInfo[VN] = RHSValNoInfo;
LHSValsDefinedFromRHS[VNI] = RHSValNoInfo0;
}
}
} else {
NewVNInfo[VN] = VNI;
LHSValNoAssignments[VN] = VN;
}
}
assert(RHSValID != -1 && "Didn't find value #?");
RHSValNoAssignments[0] = RHSValID;
if (RHSVal0DefinedFromLHS != -1) {
// This path doesn't go through ComputeUltimateVN so just set
// it to anything.
RHSValsDefinedFromLHS[RHSValNoInfo0] = (VNInfo*)1;
}
} else {
// Loop over the value numbers of the LHS, seeing if any are defined from
// the RHS.
for (LiveInterval::vni_iterator i = LHS.vni_begin(), e = LHS.vni_end();
i != e; ++i) {
VNInfo *VNI = *i;
unsigned ValSrcReg = VNI->reg;
if (ValSrcReg == 0) // Src not defined by a copy?
continue;
// DstReg is known to be a register in the LHS interval. If the src is
// from the RHS interval, we can use its value #.
if (rep(ValSrcReg) != RHS.reg)
continue;
// Figure out the value # from the RHS.
LHSValsDefinedFromRHS[VNI] = RHS.getLiveRangeContaining(VNI->def-1)->valno;
}
// Loop over the value numbers of the RHS, seeing if any are defined from
// the LHS.
for (LiveInterval::vni_iterator i = RHS.vni_begin(), e = RHS.vni_end();
i != e; ++i) {
VNInfo *VNI = *i;
unsigned ValSrcReg = VNI->reg;
if (ValSrcReg == 0) // Src not defined by a copy?
continue;
// DstReg is known to be a register in the RHS interval. If the src is
// from the LHS interval, we can use its value #.
if (rep(ValSrcReg) != LHS.reg)
continue;
// Figure out the value # from the LHS.
RHSValsDefinedFromLHS[VNI]= LHS.getLiveRangeContaining(VNI->def-1)->valno;
}
LHSValNoAssignments.resize(LHS.getNumValNums(), -1);
RHSValNoAssignments.resize(RHS.getNumValNums(), -1);
NewVNInfo.reserve(LHS.getNumValNums() + RHS.getNumValNums());
for (LiveInterval::vni_iterator i = LHS.vni_begin(), e = LHS.vni_end();
i != e; ++i) {
VNInfo *VNI = *i;
unsigned VN = VNI->id;
if (LHSValNoAssignments[VN] >= 0 || VNI->def == ~1U)
continue;
ComputeUltimateVN(VNI, NewVNInfo,
LHSValsDefinedFromRHS, RHSValsDefinedFromLHS,
LHSValNoAssignments, RHSValNoAssignments);
}
for (LiveInterval::vni_iterator i = RHS.vni_begin(), e = RHS.vni_end();
i != e; ++i) {
VNInfo *VNI = *i;
unsigned VN = VNI->id;
if (RHSValNoAssignments[VN] >= 0 || VNI->def == ~1U)
continue;
// If this value number isn't a copy from the LHS, it's a new number.
if (RHSValsDefinedFromLHS.find(VNI) == RHSValsDefinedFromLHS.end()) {
NewVNInfo.push_back(VNI);
RHSValNoAssignments[VN] = NewVNInfo.size()-1;
continue;
}
ComputeUltimateVN(VNI, NewVNInfo,
RHSValsDefinedFromLHS, LHSValsDefinedFromRHS,
RHSValNoAssignments, LHSValNoAssignments);
}
}
// Armed with the mappings of LHS/RHS values to ultimate values, walk the
// interval lists to see if these intervals are coalescable.
LiveInterval::const_iterator I = LHS.begin();
LiveInterval::const_iterator IE = LHS.end();
LiveInterval::const_iterator J = RHS.begin();
LiveInterval::const_iterator JE = RHS.end();
// Skip ahead until the first place of potential sharing.
if (I->start < J->start) {
I = std::upper_bound(I, IE, J->start);
if (I != LHS.begin()) --I;
} else if (J->start < I->start) {
J = std::upper_bound(J, JE, I->start);
if (J != RHS.begin()) --J;
}
while (1) {
// Determine if these two live ranges overlap.
bool Overlaps;
if (I->start < J->start) {
Overlaps = I->end > J->start;
} else {
Overlaps = J->end > I->start;
}
// If so, check value # info to determine if they are really different.
if (Overlaps) {
// If the live range overlap will map to the same value number in the
// result liverange, we can still coalesce them. If not, we can't.
if (LHSValNoAssignments[I->valno->id] !=
RHSValNoAssignments[J->valno->id])
return false;
}
if (I->end < J->end) {
++I;
if (I == IE) break;
} else {
++J;
if (J == JE) break;
}
}
// If we get here, we know that we can coalesce the live ranges. Ask the
// intervals to coalesce themselves now.
if ((RHS.ranges.size() > LHS.ranges.size() &&
MRegisterInfo::isVirtualRegister(LHS.reg)) ||
MRegisterInfo::isPhysicalRegister(RHS.reg)) {
// Update kill info. Some live ranges are extended due to copy coalescing.
for (DenseMap<VNInfo*, VNInfo*>::iterator I = LHSValsDefinedFromRHS.begin(),
E = LHSValsDefinedFromRHS.end(); I != E; ++I) {
VNInfo *VNI = I->first;
unsigned LHSValID = LHSValNoAssignments[VNI->id];
LiveInterval::removeKill(*NewVNInfo[LHSValID], VNI->def);
RHS.addKills(*NewVNInfo[LHSValID], VNI->kills);
}
RHS.join(LHS, &RHSValNoAssignments[0], &LHSValNoAssignments[0], NewVNInfo);
Swapped = true;
} else {
// Update kill info. Some live ranges are extended due to copy coalescing.
for (DenseMap<VNInfo*, VNInfo*>::iterator I = RHSValsDefinedFromLHS.begin(),
E = RHSValsDefinedFromLHS.end(); I != E; ++I) {
VNInfo *VNI = I->first;
unsigned RHSValID = RHSValNoAssignments[VNI->id];
LiveInterval::removeKill(*NewVNInfo[RHSValID], VNI->def);
LHS.addKills(*NewVNInfo[RHSValID], VNI->kills);
}
LHS.join(RHS, &LHSValNoAssignments[0], &RHSValNoAssignments[0], NewVNInfo);
Swapped = false;
}
return true;
}
namespace {
// DepthMBBCompare - Comparison predicate that sort first based on the loop
// depth of the basic block (the unsigned), and then on the MBB number.
struct DepthMBBCompare {
typedef std::pair<unsigned, MachineBasicBlock*> DepthMBBPair;
bool operator()(const DepthMBBPair &LHS, const DepthMBBPair &RHS) const {
if (LHS.first > RHS.first) return true; // Deeper loops first
return LHS.first == RHS.first &&
LHS.second->getNumber() < RHS.second->getNumber();
}
};
}
void SimpleRegisterCoalescing::CopyCoalesceInMBB(MachineBasicBlock *MBB,
std::vector<CopyRec> *TryAgain, bool PhysOnly) {
DOUT << ((Value*)MBB->getBasicBlock())->getName() << ":\n";
for (MachineBasicBlock::iterator MII = MBB->begin(), E = MBB->end();
MII != E;) {
MachineInstr *Inst = MII++;
// If this isn't a copy, we can't join intervals.
unsigned SrcReg, DstReg;
if (!tii_->isMoveInstr(*Inst, SrcReg, DstReg)) continue;
if (TryAgain && !JoinCopy(Inst, SrcReg, DstReg, PhysOnly))
TryAgain->push_back(getCopyRec(Inst, SrcReg, DstReg));
}
}
void SimpleRegisterCoalescing::joinIntervals() {
DOUT << "********** JOINING INTERVALS ***********\n";
JoinedLIs.resize(li_->getNumIntervals());
JoinedLIs.reset();
std::vector<CopyRec> TryAgainList;
const LoopInfo &LI = getAnalysis<LoopInfo>();
if (LI.begin() == LI.end()) {
// If there are no loops in the function, join intervals in function order.
for (MachineFunction::iterator I = mf_->begin(), E = mf_->end();
I != E; ++I)
CopyCoalesceInMBB(I, &TryAgainList);
} else {
// Otherwise, join intervals in inner loops before other intervals.
// Unfortunately we can't just iterate over loop hierarchy here because
// there may be more MBB's than BB's. Collect MBB's for sorting.
// Join intervals in the function prolog first. We want to join physical
// registers with virtual registers before the intervals got too long.
std::vector<std::pair<unsigned, MachineBasicBlock*> > MBBs;
for (MachineFunction::iterator I = mf_->begin(), E = mf_->end(); I != E;++I)
MBBs.push_back(std::make_pair(LI.getLoopDepth(I->getBasicBlock()), I));
// Sort by loop depth.
std::sort(MBBs.begin(), MBBs.end(), DepthMBBCompare());
// Finally, join intervals in loop nest order.
for (unsigned i = 0, e = MBBs.size(); i != e; ++i)
CopyCoalesceInMBB(MBBs[i].second, NULL, true);
for (unsigned i = 0, e = MBBs.size(); i != e; ++i)
CopyCoalesceInMBB(MBBs[i].second, &TryAgainList, false);
}
// Joining intervals can allow other intervals to be joined. Iteratively join
// until we make no progress.
bool ProgressMade = true;
while (ProgressMade) {
ProgressMade = false;
for (unsigned i = 0, e = TryAgainList.size(); i != e; ++i) {
CopyRec &TheCopy = TryAgainList[i];
if (TheCopy.MI &&
JoinCopy(TheCopy.MI, TheCopy.SrcReg, TheCopy.DstReg)) {
TheCopy.MI = 0; // Mark this one as done.
ProgressMade = true;
}
}
}
// Some live range has been lengthened due to colaescing, eliminate the
// unnecessary kills.
int RegNum = JoinedLIs.find_first();
while (RegNum != -1) {
unsigned Reg = RegNum + MRegisterInfo::FirstVirtualRegister;
unsigned repReg = rep(Reg);
LiveInterval &LI = li_->getInterval(repReg);
LiveVariables::VarInfo& svi = lv_->getVarInfo(Reg);
for (unsigned i = 0, e = svi.Kills.size(); i != e; ++i) {
MachineInstr *Kill = svi.Kills[i];
// Suppose vr1 = op vr2, x
// and vr1 and vr2 are coalesced. vr2 should still be marked kill
// unless it is a two-address operand.
if (li_->isRemoved(Kill) || hasRegisterDef(Kill, repReg))
continue;
if (LI.liveAt(li_->getInstructionIndex(Kill) + InstrSlots::NUM))
unsetRegisterKill(Kill, repReg);
}
RegNum = JoinedLIs.find_next(RegNum);
}
DOUT << "*** Register mapping ***\n";
for (int i = 0, e = r2rMap_.size(); i != e; ++i)
if (r2rMap_[i]) {
DOUT << " reg " << i << " -> ";
DEBUG(printRegName(r2rMap_[i]));
DOUT << "\n";
}
}
/// Return true if the two specified registers belong to different register
/// classes. The registers may be either phys or virt regs.
bool SimpleRegisterCoalescing::differingRegisterClasses(unsigned RegA,
unsigned RegB) const {
// Get the register classes for the first reg.
if (MRegisterInfo::isPhysicalRegister(RegA)) {
assert(MRegisterInfo::isVirtualRegister(RegB) &&
"Shouldn't consider two physregs!");
return !mf_->getSSARegMap()->getRegClass(RegB)->contains(RegA);
}
// Compare against the regclass for the second reg.
const TargetRegisterClass *RegClass = mf_->getSSARegMap()->getRegClass(RegA);
if (MRegisterInfo::isVirtualRegister(RegB))
return RegClass != mf_->getSSARegMap()->getRegClass(RegB);
else
return !RegClass->contains(RegB);
}
/// lastRegisterUse - Returns the last use of the specific register between
/// cycles Start and End. It also returns the use operand by reference. It
/// returns NULL if there are no uses.
MachineInstr *
SimpleRegisterCoalescing::lastRegisterUse(unsigned Start, unsigned End, unsigned Reg,
MachineOperand *&MOU) {
int e = (End-1) / InstrSlots::NUM * InstrSlots::NUM;
int s = Start;
while (e >= s) {
// Skip deleted instructions
MachineInstr *MI = li_->getInstructionFromIndex(e);
while ((e - InstrSlots::NUM) >= s && !MI) {
e -= InstrSlots::NUM;
MI = li_->getInstructionFromIndex(e);
}
if (e < s || MI == NULL)
return NULL;
for (unsigned i = 0, NumOps = MI->getNumOperands(); i != NumOps; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isUse() && MO.getReg() &&
mri_->regsOverlap(rep(MO.getReg()), Reg)) {
MOU = &MO;
return MI;
}
}
e -= InstrSlots::NUM;
}
return NULL;
}
/// findDefOperand - Returns the MachineOperand that is a def of the specific
/// register. It returns NULL if the def is not found.
MachineOperand *SimpleRegisterCoalescing::findDefOperand(MachineInstr *MI, unsigned Reg) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isDef() &&
mri_->regsOverlap(rep(MO.getReg()), Reg))
return &MO;
}
return NULL;
}
/// unsetRegisterKill - Unset IsKill property of all uses of specific register
/// of the specific instruction.
void SimpleRegisterCoalescing::unsetRegisterKill(MachineInstr *MI, unsigned Reg) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isKill() && MO.getReg() &&
mri_->regsOverlap(rep(MO.getReg()), Reg))
MO.unsetIsKill();
}
}
/// unsetRegisterKills - Unset IsKill property of all uses of specific register
/// between cycles Start and End.
void SimpleRegisterCoalescing::unsetRegisterKills(unsigned Start, unsigned End,
unsigned Reg) {
int e = (End-1) / InstrSlots::NUM * InstrSlots::NUM;
int s = Start;
while (e >= s) {
// Skip deleted instructions
MachineInstr *MI = li_->getInstructionFromIndex(e);
while ((e - InstrSlots::NUM) >= s && !MI) {
e -= InstrSlots::NUM;
MI = li_->getInstructionFromIndex(e);
}
if (e < s || MI == NULL)
return;
for (unsigned i = 0, NumOps = MI->getNumOperands(); i != NumOps; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isKill() && MO.getReg() &&
mri_->regsOverlap(rep(MO.getReg()), Reg)) {
MO.unsetIsKill();
}
}
e -= InstrSlots::NUM;
}
}
/// hasRegisterDef - True if the instruction defines the specific register.
///
bool SimpleRegisterCoalescing::hasRegisterDef(MachineInstr *MI, unsigned Reg) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isDef() &&
mri_->regsOverlap(rep(MO.getReg()), Reg))
return true;
}
return false;
}
void SimpleRegisterCoalescing::printRegName(unsigned reg) const {
if (MRegisterInfo::isPhysicalRegister(reg))
cerr << mri_->getName(reg);
else
cerr << "%reg" << reg;
}
void SimpleRegisterCoalescing::releaseMemory() {
r2rMap_.clear();
JoinedLIs.clear();
}
static bool isZeroLengthInterval(LiveInterval *li) {
for (LiveInterval::Ranges::const_iterator
i = li->ranges.begin(), e = li->ranges.end(); i != e; ++i)
if (i->end - i->start > LiveIntervals::InstrSlots::NUM)
return false;
return true;
}
bool SimpleRegisterCoalescing::runOnMachineFunction(MachineFunction &fn) {
mf_ = &fn;
tm_ = &fn.getTarget();
mri_ = tm_->getRegisterInfo();
tii_ = tm_->getInstrInfo();
li_ = &getAnalysis<LiveIntervals>();
lv_ = &getAnalysis<LiveVariables>();
DOUT << "********** SIMPLE REGISTER COALESCING **********\n"
<< "********** Function: "
<< ((Value*)mf_->getFunction())->getName() << '\n';
allocatableRegs_ = mri_->getAllocatableSet(fn);
for (MRegisterInfo::regclass_iterator I = mri_->regclass_begin(),
E = mri_->regclass_end(); I != E; ++I)
allocatableRCRegs_.insert(std::make_pair(*I,mri_->getAllocatableSet(fn, *I)));
r2rMap_.grow(mf_->getSSARegMap()->getLastVirtReg());
// Join (coalesce) intervals if requested.
if (EnableJoining) {
joinIntervals();
DOUT << "********** INTERVALS POST JOINING **********\n";
for (LiveIntervals::iterator I = li_->begin(), E = li_->end(); I != E; ++I) {
I->second.print(DOUT, mri_);
DOUT << "\n";
}
}
// perform a final pass over the instructions and compute spill
// weights, coalesce virtual registers and remove identity moves.
const LoopInfo &loopInfo = getAnalysis<LoopInfo>();
for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
mbbi != mbbe; ++mbbi) {
MachineBasicBlock* mbb = mbbi;
unsigned loopDepth = loopInfo.getLoopDepth(mbb->getBasicBlock());
for (MachineBasicBlock::iterator mii = mbb->begin(), mie = mbb->end();
mii != mie; ) {
// if the move will be an identity move delete it
unsigned srcReg, dstReg, RegRep;
if (tii_->isMoveInstr(*mii, srcReg, dstReg) &&
(RegRep = rep(srcReg)) == rep(dstReg)) {
// remove from def list
LiveInterval &RegInt = li_->getOrCreateInterval(RegRep);
MachineOperand *MO = mii->findRegisterDefOperand(dstReg);
// If def of this move instruction is dead, remove its live range from
// the dstination register's live interval.
if (MO->isDead()) {
unsigned MoveIdx = li_->getDefIndex(li_->getInstructionIndex(mii));
LiveInterval::iterator MLR = RegInt.FindLiveRangeContaining(MoveIdx);
RegInt.removeRange(MLR->start, MoveIdx+1);
if (RegInt.empty())
li_->removeInterval(RegRep);
}
li_->RemoveMachineInstrFromMaps(mii);
mii = mbbi->erase(mii);
++numPeep;
} else {
SmallSet<unsigned, 4> UniqueUses;
for (unsigned i = 0, e = mii->getNumOperands(); i != e; ++i) {
const MachineOperand &mop = mii->getOperand(i);
if (mop.isRegister() && mop.getReg() &&
MRegisterInfo::isVirtualRegister(mop.getReg())) {
// replace register with representative register
unsigned reg = rep(mop.getReg());
mii->getOperand(i).setReg(reg);
// Multiple uses of reg by the same instruction. It should not
// contribute to spill weight again.
if (UniqueUses.count(reg) != 0)
continue;
LiveInterval &RegInt = li_->getInterval(reg);
float w = (mop.isUse()+mop.isDef()) * powf(10.0F, (float)loopDepth);
RegInt.weight += w;
UniqueUses.insert(reg);
}
}
++mii;
}
}
}
for (LiveIntervals::iterator I = li_->begin(), E = li_->end(); I != E; ++I) {
LiveInterval &LI = I->second;
if (MRegisterInfo::isVirtualRegister(LI.reg)) {
// If the live interval length is essentially zero, i.e. in every live
// range the use follows def immediately, it doesn't make sense to spill
// it and hope it will be easier to allocate for this li.
if (isZeroLengthInterval(&LI))
LI.weight = HUGE_VALF;
// Slightly prefer live interval that has been assigned a preferred reg.
if (LI.preference)
LI.weight *= 1.01F;
// Divide the weight of the interval by its size. This encourages
// spilling of intervals that are large and have few uses, and
// discourages spilling of small intervals with many uses.
LI.weight /= LI.getSize();
}
}
DEBUG(dump());
return true;
}
/// print - Implement the dump method.
void SimpleRegisterCoalescing::print(std::ostream &O, const Module* m) const {
li_->print(O, m);
}