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llvm-mirror/lib/CodeGen/InlineSpiller.cpp
Jakob Stoklund Olesen 0e9c54a422 Avoid hoisting spills when looking at a copy from another register that is also 
about to be spilled.

This can only happen when two extra snippet registers are included in the spill,
and there is a copy between them. Hoisting the spill creates problems because
the hoist will mark the copy for later dead code elimination, and spilling the
second register will turn the copy into a spill.

<rdar://problem/9420853>

llvm-svn: 131192
2011-05-11 18:25:10 +00:00

1037 lines
37 KiB
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//===-------- InlineSpiller.cpp - Insert spills and restores inline -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// The inline spiller modifies the machine function directly instead of
// inserting spills and restores in VirtRegMap.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "regalloc"
#include "Spiller.h"
#include "LiveRangeEdit.h"
#include "VirtRegMap.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
STATISTIC(NumSpilledRanges, "Number of spilled live ranges");
STATISTIC(NumSnippets, "Number of snippets included in spills");
STATISTIC(NumSpills, "Number of spills inserted");
STATISTIC(NumReloads, "Number of reloads inserted");
STATISTIC(NumFolded, "Number of folded stack accesses");
STATISTIC(NumFoldedLoads, "Number of folded loads");
STATISTIC(NumRemats, "Number of rematerialized defs for spilling");
STATISTIC(NumOmitReloadSpill, "Number of omitted spills after reloads");
STATISTIC(NumHoistLocal, "Number of locally hoisted spills");
STATISTIC(NumHoistGlobal, "Number of globally hoisted spills");
STATISTIC(NumRedundantSpills, "Number of redundant spills identified");
namespace {
class InlineSpiller : public Spiller {
MachineFunctionPass &Pass;
MachineFunction &MF;
LiveIntervals &LIS;
LiveStacks &LSS;
AliasAnalysis *AA;
MachineDominatorTree &MDT;
MachineLoopInfo &Loops;
VirtRegMap &VRM;
MachineFrameInfo &MFI;
MachineRegisterInfo &MRI;
const TargetInstrInfo &TII;
const TargetRegisterInfo &TRI;
// Variables that are valid during spill(), but used by multiple methods.
LiveRangeEdit *Edit;
LiveInterval *StackInt;
int StackSlot;
unsigned Original;
// All registers to spill to StackSlot, including the main register.
SmallVector<unsigned, 8> RegsToSpill;
// All COPY instructions to/from snippets.
// They are ignored since both operands refer to the same stack slot.
SmallPtrSet<MachineInstr*, 8> SnippetCopies;
// Values that failed to remat at some point.
SmallPtrSet<VNInfo*, 8> UsedValues;
// Information about a value that was defined by a copy from a sibling
// register.
struct SibValueInfo {
// True when all reaching defs were reloads: No spill is necessary.
bool AllDefsAreReloads;
// The preferred register to spill.
unsigned SpillReg;
// The value of SpillReg that should be spilled.
VNInfo *SpillVNI;
// A defining instruction that is not a sibling copy or a reload, or NULL.
// This can be used as a template for rematerialization.
MachineInstr *DefMI;
SibValueInfo(unsigned Reg, VNInfo *VNI)
: AllDefsAreReloads(false), SpillReg(Reg), SpillVNI(VNI), DefMI(0) {}
};
// Values in RegsToSpill defined by sibling copies.
typedef DenseMap<VNInfo*, SibValueInfo> SibValueMap;
SibValueMap SibValues;
// Dead defs generated during spilling.
SmallVector<MachineInstr*, 8> DeadDefs;
~InlineSpiller() {}
public:
InlineSpiller(MachineFunctionPass &pass,
MachineFunction &mf,
VirtRegMap &vrm)
: Pass(pass),
MF(mf),
LIS(pass.getAnalysis<LiveIntervals>()),
LSS(pass.getAnalysis<LiveStacks>()),
AA(&pass.getAnalysis<AliasAnalysis>()),
MDT(pass.getAnalysis<MachineDominatorTree>()),
Loops(pass.getAnalysis<MachineLoopInfo>()),
VRM(vrm),
MFI(*mf.getFrameInfo()),
MRI(mf.getRegInfo()),
TII(*mf.getTarget().getInstrInfo()),
TRI(*mf.getTarget().getRegisterInfo()) {}
void spill(LiveRangeEdit &);
private:
bool isSnippet(const LiveInterval &SnipLI);
void collectRegsToSpill();
bool isRegToSpill(unsigned Reg) {
return std::find(RegsToSpill.begin(),
RegsToSpill.end(), Reg) != RegsToSpill.end();
}
bool isSibling(unsigned Reg);
MachineInstr *traceSiblingValue(unsigned, VNInfo*, VNInfo*);
void analyzeSiblingValues();
bool hoistSpill(LiveInterval &SpillLI, MachineInstr *CopyMI);
void eliminateRedundantSpills(LiveInterval &LI, VNInfo *VNI);
void markValueUsed(LiveInterval*, VNInfo*);
bool reMaterializeFor(LiveInterval&, MachineBasicBlock::iterator MI);
void reMaterializeAll();
bool coalesceStackAccess(MachineInstr *MI, unsigned Reg);
bool foldMemoryOperand(MachineBasicBlock::iterator MI,
const SmallVectorImpl<unsigned> &Ops,
MachineInstr *LoadMI = 0);
void insertReload(LiveInterval &NewLI, SlotIndex,
MachineBasicBlock::iterator MI);
void insertSpill(LiveInterval &NewLI, const LiveInterval &OldLI,
SlotIndex, MachineBasicBlock::iterator MI);
void spillAroundUses(unsigned Reg);
void spillAll();
};
}
namespace llvm {
Spiller *createInlineSpiller(MachineFunctionPass &pass,
MachineFunction &mf,
VirtRegMap &vrm) {
return new InlineSpiller(pass, mf, vrm);
}
}
//===----------------------------------------------------------------------===//
// Snippets
//===----------------------------------------------------------------------===//
// When spilling a virtual register, we also spill any snippets it is connected
// to. The snippets are small live ranges that only have a single real use,
// leftovers from live range splitting. Spilling them enables memory operand
// folding or tightens the live range around the single use.
//
// This minimizes register pressure and maximizes the store-to-load distance for
// spill slots which can be important in tight loops.
/// isFullCopyOf - If MI is a COPY to or from Reg, return the other register,
/// otherwise return 0.
static unsigned isFullCopyOf(const MachineInstr *MI, unsigned Reg) {
if (!MI->isCopy())
return 0;
if (MI->getOperand(0).getSubReg() != 0)
return 0;
if (MI->getOperand(1).getSubReg() != 0)
return 0;
if (MI->getOperand(0).getReg() == Reg)
return MI->getOperand(1).getReg();
if (MI->getOperand(1).getReg() == Reg)
return MI->getOperand(0).getReg();
return 0;
}
/// isSnippet - Identify if a live interval is a snippet that should be spilled.
/// It is assumed that SnipLI is a virtual register with the same original as
/// Edit->getReg().
bool InlineSpiller::isSnippet(const LiveInterval &SnipLI) {
unsigned Reg = Edit->getReg();
// A snippet is a tiny live range with only a single instruction using it
// besides copies to/from Reg or spills/fills. We accept:
//
// %snip = COPY %Reg / FILL fi#
// %snip = USE %snip
// %Reg = COPY %snip / SPILL %snip, fi#
//
if (SnipLI.getNumValNums() > 2 || !LIS.intervalIsInOneMBB(SnipLI))
return false;
MachineInstr *UseMI = 0;
// Check that all uses satisfy our criteria.
for (MachineRegisterInfo::reg_nodbg_iterator
RI = MRI.reg_nodbg_begin(SnipLI.reg);
MachineInstr *MI = RI.skipInstruction();) {
// Allow copies to/from Reg.
if (isFullCopyOf(MI, Reg))
continue;
// Allow stack slot loads.
int FI;
if (SnipLI.reg == TII.isLoadFromStackSlot(MI, FI) && FI == StackSlot)
continue;
// Allow stack slot stores.
if (SnipLI.reg == TII.isStoreToStackSlot(MI, FI) && FI == StackSlot)
continue;
// Allow a single additional instruction.
if (UseMI && MI != UseMI)
return false;
UseMI = MI;
}
return true;
}
/// collectRegsToSpill - Collect live range snippets that only have a single
/// real use.
void InlineSpiller::collectRegsToSpill() {
unsigned Reg = Edit->getReg();
// Main register always spills.
RegsToSpill.assign(1, Reg);
SnippetCopies.clear();
// Snippets all have the same original, so there can't be any for an original
// register.
if (Original == Reg)
return;
for (MachineRegisterInfo::reg_iterator RI = MRI.reg_begin(Reg);
MachineInstr *MI = RI.skipInstruction();) {
unsigned SnipReg = isFullCopyOf(MI, Reg);
if (!isSibling(SnipReg))
continue;
LiveInterval &SnipLI = LIS.getInterval(SnipReg);
if (!isSnippet(SnipLI))
continue;
SnippetCopies.insert(MI);
if (isRegToSpill(SnipReg))
continue;
RegsToSpill.push_back(SnipReg);
DEBUG(dbgs() << "\talso spill snippet " << SnipLI << '\n');
++NumSnippets;
}
}
//===----------------------------------------------------------------------===//
// Sibling Values
//===----------------------------------------------------------------------===//
// After live range splitting, some values to be spilled may be defined by
// copies from sibling registers. We trace the sibling copies back to the
// original value if it still exists. We need it for rematerialization.
//
// Even when the value can't be rematerialized, we still want to determine if
// the value has already been spilled, or we may want to hoist the spill from a
// loop.
bool InlineSpiller::isSibling(unsigned Reg) {
return TargetRegisterInfo::isVirtualRegister(Reg) &&
VRM.getOriginal(Reg) == Original;
}
/// traceSiblingValue - Trace a value that is about to be spilled back to the
/// real defining instructions by looking through sibling copies. Always stay
/// within the range of OrigVNI so the registers are known to carry the same
/// value.
///
/// Determine if the value is defined by all reloads, so spilling isn't
/// necessary - the value is already in the stack slot.
///
/// Return a defining instruction that may be a candidate for rematerialization.
///
MachineInstr *InlineSpiller::traceSiblingValue(unsigned UseReg, VNInfo *UseVNI,
VNInfo *OrigVNI) {
DEBUG(dbgs() << "Tracing value " << PrintReg(UseReg) << ':'
<< UseVNI->id << '@' << UseVNI->def << '\n');
SmallPtrSet<VNInfo*, 8> Visited;
SmallVector<std::pair<unsigned, VNInfo*>, 8> WorkList;
WorkList.push_back(std::make_pair(UseReg, UseVNI));
// Best spill candidate seen so far. This must dominate UseVNI.
SibValueInfo SVI(UseReg, UseVNI);
MachineBasicBlock *UseMBB = LIS.getMBBFromIndex(UseVNI->def);
unsigned SpillDepth = Loops.getLoopDepth(UseMBB);
bool SeenOrigPHI = false; // Original PHI met.
do {
unsigned Reg;
VNInfo *VNI;
tie(Reg, VNI) = WorkList.pop_back_val();
if (!Visited.insert(VNI))
continue;
// Is this value a better spill candidate?
if (!isRegToSpill(Reg)) {
MachineBasicBlock *MBB = LIS.getMBBFromIndex(VNI->def);
if (MBB != UseMBB && MDT.dominates(MBB, UseMBB)) {
// This is a valid spill location dominating UseVNI.
// Prefer to spill at a smaller loop depth.
unsigned Depth = Loops.getLoopDepth(MBB);
if (Depth < SpillDepth) {
DEBUG(dbgs() << " spill depth " << Depth << ": " << PrintReg(Reg)
<< ':' << VNI->id << '@' << VNI->def << '\n');
SVI.SpillReg = Reg;
SVI.SpillVNI = VNI;
SpillDepth = Depth;
}
}
}
// Trace through PHI-defs created by live range splitting.
if (VNI->isPHIDef()) {
if (VNI->def == OrigVNI->def) {
DEBUG(dbgs() << " orig phi value " << PrintReg(Reg) << ':'
<< VNI->id << '@' << VNI->def << '\n');
SeenOrigPHI = true;
continue;
}
// Get values live-out of predecessors.
LiveInterval &LI = LIS.getInterval(Reg);
MachineBasicBlock *MBB = LIS.getMBBFromIndex(VNI->def);
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
PE = MBB->pred_end(); PI != PE; ++PI) {
VNInfo *PVNI = LI.getVNInfoAt(LIS.getMBBEndIdx(*PI).getPrevSlot());
if (PVNI)
WorkList.push_back(std::make_pair(Reg, PVNI));
}
continue;
}
MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def);
assert(MI && "Missing def");
// Trace through sibling copies.
if (unsigned SrcReg = isFullCopyOf(MI, Reg)) {
if (isSibling(SrcReg)) {
LiveInterval &SrcLI = LIS.getInterval(SrcReg);
VNInfo *SrcVNI = SrcLI.getVNInfoAt(VNI->def.getUseIndex());
assert(SrcVNI && "Copy from non-existing value");
DEBUG(dbgs() << " copy of " << PrintReg(SrcReg) << ':'
<< SrcVNI->id << '@' << SrcVNI->def << '\n');
WorkList.push_back(std::make_pair(SrcReg, SrcVNI));
continue;
}
}
// Track reachable reloads.
int FI;
if (Reg == TII.isLoadFromStackSlot(MI, FI) && FI == StackSlot) {
DEBUG(dbgs() << " reload " << PrintReg(Reg) << ':'
<< VNI->id << "@" << VNI->def << '\n');
SVI.AllDefsAreReloads = true;
continue;
}
// We have an 'original' def. Don't record trivial cases.
if (VNI == UseVNI) {
DEBUG(dbgs() << "Not a sibling copy.\n");
return MI;
}
// Potential remat candidate.
DEBUG(dbgs() << " def " << PrintReg(Reg) << ':'
<< VNI->id << '@' << VNI->def << '\t' << *MI);
SVI.DefMI = MI;
} while (!WorkList.empty());
if (SeenOrigPHI || SVI.DefMI)
SVI.AllDefsAreReloads = false;
DEBUG({
if (SVI.AllDefsAreReloads)
dbgs() << "All defs are reloads.\n";
else
dbgs() << "Prefer to spill " << PrintReg(SVI.SpillReg) << ':'
<< SVI.SpillVNI->id << '@' << SVI.SpillVNI->def << '\n';
});
SibValues.insert(std::make_pair(UseVNI, SVI));
return SVI.DefMI;
}
/// analyzeSiblingValues - Trace values defined by sibling copies back to
/// something that isn't a sibling copy.
///
/// Keep track of values that may be rematerializable.
void InlineSpiller::analyzeSiblingValues() {
SibValues.clear();
// No siblings at all?
if (Edit->getReg() == Original)
return;
LiveInterval &OrigLI = LIS.getInterval(Original);
for (unsigned i = 0, e = RegsToSpill.size(); i != e; ++i) {
unsigned Reg = RegsToSpill[i];
LiveInterval &LI = LIS.getInterval(Reg);
for (LiveInterval::const_vni_iterator VI = LI.vni_begin(),
VE = LI.vni_end(); VI != VE; ++VI) {
VNInfo *VNI = *VI;
if (VNI->isUnused())
continue;
MachineInstr *DefMI = 0;
// Check possible sibling copies.
if (VNI->isPHIDef() || VNI->getCopy()) {
VNInfo *OrigVNI = OrigLI.getVNInfoAt(VNI->def);
if (OrigVNI->def != VNI->def)
DefMI = traceSiblingValue(Reg, VNI, OrigVNI);
}
if (!DefMI && !VNI->isPHIDef())
DefMI = LIS.getInstructionFromIndex(VNI->def);
if (DefMI && Edit->checkRematerializable(VNI, DefMI, TII, AA)) {
DEBUG(dbgs() << "Value " << PrintReg(Reg) << ':' << VNI->id << '@'
<< VNI->def << " may remat from " << *DefMI);
}
}
}
}
/// hoistSpill - Given a sibling copy that defines a value to be spilled, insert
/// a spill at a better location.
bool InlineSpiller::hoistSpill(LiveInterval &SpillLI, MachineInstr *CopyMI) {
SlotIndex Idx = LIS.getInstructionIndex(CopyMI);
VNInfo *VNI = SpillLI.getVNInfoAt(Idx.getDefIndex());
assert(VNI && VNI->def == Idx.getDefIndex() && "Not defined by copy");
SibValueMap::iterator I = SibValues.find(VNI);
if (I == SibValues.end())
return false;
const SibValueInfo &SVI = I->second;
// Let the normal folding code deal with the boring case.
if (!SVI.AllDefsAreReloads && SVI.SpillVNI == VNI)
return false;
// SpillReg may have been deleted by remat and DCE.
if (!LIS.hasInterval(SVI.SpillReg)) {
DEBUG(dbgs() << "Stale interval: " << PrintReg(SVI.SpillReg) << '\n');
SibValues.erase(I);
return false;
}
LiveInterval &SibLI = LIS.getInterval(SVI.SpillReg);
if (!SibLI.containsValue(SVI.SpillVNI)) {
DEBUG(dbgs() << "Stale value: " << PrintReg(SVI.SpillReg) << '\n');
SibValues.erase(I);
return false;
}
// Conservatively extend the stack slot range to the range of the original
// value. We may be able to do better with stack slot coloring by being more
// careful here.
assert(StackInt && "No stack slot assigned yet.");
LiveInterval &OrigLI = LIS.getInterval(Original);
VNInfo *OrigVNI = OrigLI.getVNInfoAt(Idx);
StackInt->MergeValueInAsValue(OrigLI, OrigVNI, StackInt->getValNumInfo(0));
DEBUG(dbgs() << "\tmerged orig valno " << OrigVNI->id << ": "
<< *StackInt << '\n');
// Already spilled everywhere.
if (SVI.AllDefsAreReloads) {
++NumOmitReloadSpill;
return true;
}
// We are going to spill SVI.SpillVNI immediately after its def, so clear out
// any later spills of the same value.
eliminateRedundantSpills(SibLI, SVI.SpillVNI);
MachineBasicBlock *MBB = LIS.getMBBFromIndex(SVI.SpillVNI->def);
MachineBasicBlock::iterator MII;
if (SVI.SpillVNI->isPHIDef())
MII = MBB->SkipPHIsAndLabels(MBB->begin());
else {
MachineInstr *DefMI = LIS.getInstructionFromIndex(SVI.SpillVNI->def);
assert(DefMI && "Defining instruction disappeared");
MII = DefMI;
++MII;
}
// Insert spill without kill flag immediately after def.
TII.storeRegToStackSlot(*MBB, MII, SVI.SpillReg, false, StackSlot,
MRI.getRegClass(SVI.SpillReg), &TRI);
--MII; // Point to store instruction.
LIS.InsertMachineInstrInMaps(MII);
VRM.addSpillSlotUse(StackSlot, MII);
DEBUG(dbgs() << "\thoisted: " << SVI.SpillVNI->def << '\t' << *MII);
if (MBB == CopyMI->getParent())
++NumHoistLocal;
else
++NumHoistGlobal;
return true;
}
/// eliminateRedundantSpills - SLI:VNI is known to be on the stack. Remove any
/// redundant spills of this value in SLI.reg and sibling copies.
void InlineSpiller::eliminateRedundantSpills(LiveInterval &SLI, VNInfo *VNI) {
assert(VNI && "Missing value");
SmallVector<std::pair<LiveInterval*, VNInfo*>, 8> WorkList;
WorkList.push_back(std::make_pair(&SLI, VNI));
assert(StackInt && "No stack slot assigned yet.");
do {
LiveInterval *LI;
tie(LI, VNI) = WorkList.pop_back_val();
unsigned Reg = LI->reg;
DEBUG(dbgs() << "Checking redundant spills for "
<< VNI->id << '@' << VNI->def << " in " << *LI << '\n');
// Regs to spill are taken care of.
if (isRegToSpill(Reg))
continue;
// Add all of VNI's live range to StackInt.
StackInt->MergeValueInAsValue(*LI, VNI, StackInt->getValNumInfo(0));
DEBUG(dbgs() << "Merged to stack int: " << *StackInt << '\n');
// Find all spills and copies of VNI.
for (MachineRegisterInfo::use_nodbg_iterator UI = MRI.use_nodbg_begin(Reg);
MachineInstr *MI = UI.skipInstruction();) {
if (!MI->isCopy() && !MI->getDesc().mayStore())
continue;
SlotIndex Idx = LIS.getInstructionIndex(MI);
if (LI->getVNInfoAt(Idx) != VNI)
continue;
// Follow sibling copies down the dominator tree.
if (unsigned DstReg = isFullCopyOf(MI, Reg)) {
if (isSibling(DstReg)) {
LiveInterval &DstLI = LIS.getInterval(DstReg);
VNInfo *DstVNI = DstLI.getVNInfoAt(Idx.getDefIndex());
assert(DstVNI && "Missing defined value");
assert(DstVNI->def == Idx.getDefIndex() && "Wrong copy def slot");
WorkList.push_back(std::make_pair(&DstLI, DstVNI));
}
continue;
}
// Erase spills.
int FI;
if (Reg == TII.isStoreToStackSlot(MI, FI) && FI == StackSlot) {
DEBUG(dbgs() << "Redundant spill " << Idx << '\t' << *MI);
// eliminateDeadDefs won't normally remove stores, so switch opcode.
MI->setDesc(TII.get(TargetOpcode::KILL));
DeadDefs.push_back(MI);
++NumRedundantSpills;
}
}
} while (!WorkList.empty());
}
//===----------------------------------------------------------------------===//
// Rematerialization
//===----------------------------------------------------------------------===//
/// markValueUsed - Remember that VNI failed to rematerialize, so its defining
/// instruction cannot be eliminated. See through snippet copies
void InlineSpiller::markValueUsed(LiveInterval *LI, VNInfo *VNI) {
SmallVector<std::pair<LiveInterval*, VNInfo*>, 8> WorkList;
WorkList.push_back(std::make_pair(LI, VNI));
do {
tie(LI, VNI) = WorkList.pop_back_val();
if (!UsedValues.insert(VNI))
continue;
if (VNI->isPHIDef()) {
MachineBasicBlock *MBB = LIS.getMBBFromIndex(VNI->def);
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
PE = MBB->pred_end(); PI != PE; ++PI) {
VNInfo *PVNI = LI->getVNInfoAt(LIS.getMBBEndIdx(*PI).getPrevSlot());
if (PVNI)
WorkList.push_back(std::make_pair(LI, PVNI));
}
continue;
}
// Follow snippet copies.
MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def);
if (!SnippetCopies.count(MI))
continue;
LiveInterval &SnipLI = LIS.getInterval(MI->getOperand(1).getReg());
assert(isRegToSpill(SnipLI.reg) && "Unexpected register in copy");
VNInfo *SnipVNI = SnipLI.getVNInfoAt(VNI->def.getUseIndex());
assert(SnipVNI && "Snippet undefined before copy");
WorkList.push_back(std::make_pair(&SnipLI, SnipVNI));
} while (!WorkList.empty());
}
/// reMaterializeFor - Attempt to rematerialize before MI instead of reloading.
bool InlineSpiller::reMaterializeFor(LiveInterval &VirtReg,
MachineBasicBlock::iterator MI) {
SlotIndex UseIdx = LIS.getInstructionIndex(MI).getUseIndex();
VNInfo *ParentVNI = VirtReg.getVNInfoAt(UseIdx);
if (!ParentVNI) {
DEBUG(dbgs() << "\tadding <undef> flags: ");
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isUse() && MO.getReg() == VirtReg.reg)
MO.setIsUndef();
}
DEBUG(dbgs() << UseIdx << '\t' << *MI);
return true;
}
if (SnippetCopies.count(MI))
return false;
// Use an OrigVNI from traceSiblingValue when ParentVNI is a sibling copy.
LiveRangeEdit::Remat RM(ParentVNI);
SibValueMap::const_iterator SibI = SibValues.find(ParentVNI);
if (SibI != SibValues.end())
RM.OrigMI = SibI->second.DefMI;
if (!Edit->canRematerializeAt(RM, UseIdx, false, LIS)) {
markValueUsed(&VirtReg, ParentVNI);
DEBUG(dbgs() << "\tcannot remat for " << UseIdx << '\t' << *MI);
return false;
}
// If the instruction also writes VirtReg.reg, it had better not require the
// same register for uses and defs.
bool Reads, Writes;
SmallVector<unsigned, 8> Ops;
tie(Reads, Writes) = MI->readsWritesVirtualRegister(VirtReg.reg, &Ops);
if (Writes) {
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(Ops[i]);
if (MO.isUse() ? MI->isRegTiedToDefOperand(Ops[i]) : MO.getSubReg()) {
markValueUsed(&VirtReg, ParentVNI);
DEBUG(dbgs() << "\tcannot remat tied reg: " << UseIdx << '\t' << *MI);
return false;
}
}
}
// Before rematerializing into a register for a single instruction, try to
// fold a load into the instruction. That avoids allocating a new register.
if (RM.OrigMI->getDesc().canFoldAsLoad() &&
foldMemoryOperand(MI, Ops, RM.OrigMI)) {
Edit->markRematerialized(RM.ParentVNI);
++NumFoldedLoads;
return true;
}
// Alocate a new register for the remat.
LiveInterval &NewLI = Edit->createFrom(Original, LIS, VRM);
NewLI.markNotSpillable();
// Finally we can rematerialize OrigMI before MI.
SlotIndex DefIdx = Edit->rematerializeAt(*MI->getParent(), MI, NewLI.reg, RM,
LIS, TII, TRI);
DEBUG(dbgs() << "\tremat: " << DefIdx << '\t'
<< *LIS.getInstructionFromIndex(DefIdx));
// Replace operands
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(Ops[i]);
if (MO.isReg() && MO.isUse() && MO.getReg() == VirtReg.reg) {
MO.setReg(NewLI.reg);
MO.setIsKill();
}
}
DEBUG(dbgs() << "\t " << UseIdx << '\t' << *MI);
VNInfo *DefVNI = NewLI.getNextValue(DefIdx, 0, LIS.getVNInfoAllocator());
NewLI.addRange(LiveRange(DefIdx, UseIdx.getDefIndex(), DefVNI));
DEBUG(dbgs() << "\tinterval: " << NewLI << '\n');
++NumRemats;
return true;
}
/// reMaterializeAll - Try to rematerialize as many uses as possible,
/// and trim the live ranges after.
void InlineSpiller::reMaterializeAll() {
// analyzeSiblingValues has already tested all relevant defining instructions.
if (!Edit->anyRematerializable(LIS, TII, AA))
return;
UsedValues.clear();
// Try to remat before all uses of snippets.
bool anyRemat = false;
for (unsigned i = 0, e = RegsToSpill.size(); i != e; ++i) {
unsigned Reg = RegsToSpill[i];
LiveInterval &LI = LIS.getInterval(Reg);
for (MachineRegisterInfo::use_nodbg_iterator
RI = MRI.use_nodbg_begin(Reg);
MachineInstr *MI = RI.skipInstruction();)
anyRemat |= reMaterializeFor(LI, MI);
}
if (!anyRemat)
return;
// Remove any values that were completely rematted.
for (unsigned i = 0, e = RegsToSpill.size(); i != e; ++i) {
unsigned Reg = RegsToSpill[i];
LiveInterval &LI = LIS.getInterval(Reg);
for (LiveInterval::vni_iterator I = LI.vni_begin(), E = LI.vni_end();
I != E; ++I) {
VNInfo *VNI = *I;
if (VNI->isUnused() || VNI->isPHIDef() || UsedValues.count(VNI))
continue;
MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def);
MI->addRegisterDead(Reg, &TRI);
if (!MI->allDefsAreDead())
continue;
DEBUG(dbgs() << "All defs dead: " << *MI);
DeadDefs.push_back(MI);
}
}
// Eliminate dead code after remat. Note that some snippet copies may be
// deleted here.
if (DeadDefs.empty())
return;
DEBUG(dbgs() << "Remat created " << DeadDefs.size() << " dead defs.\n");
Edit->eliminateDeadDefs(DeadDefs, LIS, VRM, TII);
// Get rid of deleted and empty intervals.
for (unsigned i = RegsToSpill.size(); i != 0; --i) {
unsigned Reg = RegsToSpill[i-1];
if (!LIS.hasInterval(Reg)) {
RegsToSpill.erase(RegsToSpill.begin() + (i - 1));
continue;
}
LiveInterval &LI = LIS.getInterval(Reg);
if (!LI.empty())
continue;
Edit->eraseVirtReg(Reg, LIS);
RegsToSpill.erase(RegsToSpill.begin() + (i - 1));
}
DEBUG(dbgs() << RegsToSpill.size() << " registers to spill after remat.\n");
}
//===----------------------------------------------------------------------===//
// Spilling
//===----------------------------------------------------------------------===//
/// If MI is a load or store of StackSlot, it can be removed.
bool InlineSpiller::coalesceStackAccess(MachineInstr *MI, unsigned Reg) {
int FI = 0;
unsigned InstrReg;
if (!(InstrReg = TII.isLoadFromStackSlot(MI, FI)) &&
!(InstrReg = TII.isStoreToStackSlot(MI, FI)))
return false;
// We have a stack access. Is it the right register and slot?
if (InstrReg != Reg || FI != StackSlot)
return false;
DEBUG(dbgs() << "Coalescing stack access: " << *MI);
LIS.RemoveMachineInstrFromMaps(MI);
MI->eraseFromParent();
return true;
}
/// foldMemoryOperand - Try folding stack slot references in Ops into MI.
/// @param MI Instruction using or defining the current register.
/// @param Ops Operand indices from readsWritesVirtualRegister().
/// @param LoadMI Load instruction to use instead of stack slot when non-null.
/// @return True on success, and MI will be erased.
bool InlineSpiller::foldMemoryOperand(MachineBasicBlock::iterator MI,
const SmallVectorImpl<unsigned> &Ops,
MachineInstr *LoadMI) {
// TargetInstrInfo::foldMemoryOperand only expects explicit, non-tied
// operands.
SmallVector<unsigned, 8> FoldOps;
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
unsigned Idx = Ops[i];
MachineOperand &MO = MI->getOperand(Idx);
if (MO.isImplicit())
continue;
// FIXME: Teach targets to deal with subregs.
if (MO.getSubReg())
return false;
// We cannot fold a load instruction into a def.
if (LoadMI && MO.isDef())
return false;
// Tied use operands should not be passed to foldMemoryOperand.
if (!MI->isRegTiedToDefOperand(Idx))
FoldOps.push_back(Idx);
}
MachineInstr *FoldMI =
LoadMI ? TII.foldMemoryOperand(MI, FoldOps, LoadMI)
: TII.foldMemoryOperand(MI, FoldOps, StackSlot);
if (!FoldMI)
return false;
LIS.ReplaceMachineInstrInMaps(MI, FoldMI);
if (!LoadMI)
VRM.addSpillSlotUse(StackSlot, FoldMI);
MI->eraseFromParent();
DEBUG(dbgs() << "\tfolded: " << *FoldMI);
++NumFolded;
return true;
}
/// insertReload - Insert a reload of NewLI.reg before MI.
void InlineSpiller::insertReload(LiveInterval &NewLI,
SlotIndex Idx,
MachineBasicBlock::iterator MI) {
MachineBasicBlock &MBB = *MI->getParent();
TII.loadRegFromStackSlot(MBB, MI, NewLI.reg, StackSlot,
MRI.getRegClass(NewLI.reg), &TRI);
--MI; // Point to load instruction.
SlotIndex LoadIdx = LIS.InsertMachineInstrInMaps(MI).getDefIndex();
VRM.addSpillSlotUse(StackSlot, MI);
DEBUG(dbgs() << "\treload: " << LoadIdx << '\t' << *MI);
VNInfo *LoadVNI = NewLI.getNextValue(LoadIdx, 0,
LIS.getVNInfoAllocator());
NewLI.addRange(LiveRange(LoadIdx, Idx, LoadVNI));
++NumReloads;
}
/// insertSpill - Insert a spill of NewLI.reg after MI.
void InlineSpiller::insertSpill(LiveInterval &NewLI, const LiveInterval &OldLI,
SlotIndex Idx, MachineBasicBlock::iterator MI) {
MachineBasicBlock &MBB = *MI->getParent();
TII.storeRegToStackSlot(MBB, ++MI, NewLI.reg, true, StackSlot,
MRI.getRegClass(NewLI.reg), &TRI);
--MI; // Point to store instruction.
SlotIndex StoreIdx = LIS.InsertMachineInstrInMaps(MI).getDefIndex();
VRM.addSpillSlotUse(StackSlot, MI);
DEBUG(dbgs() << "\tspilled: " << StoreIdx << '\t' << *MI);
VNInfo *StoreVNI = NewLI.getNextValue(Idx, 0, LIS.getVNInfoAllocator());
NewLI.addRange(LiveRange(Idx, StoreIdx, StoreVNI));
++NumSpills;
}
/// spillAroundUses - insert spill code around each use of Reg.
void InlineSpiller::spillAroundUses(unsigned Reg) {
DEBUG(dbgs() << "spillAroundUses " << PrintReg(Reg) << '\n');
LiveInterval &OldLI = LIS.getInterval(Reg);
// Iterate over instructions using Reg.
for (MachineRegisterInfo::reg_iterator RI = MRI.reg_begin(Reg);
MachineInstr *MI = RI.skipInstruction();) {
// Debug values are not allowed to affect codegen.
if (MI->isDebugValue()) {
// Modify DBG_VALUE now that the value is in a spill slot.
uint64_t Offset = MI->getOperand(1).getImm();
const MDNode *MDPtr = MI->getOperand(2).getMetadata();
DebugLoc DL = MI->getDebugLoc();
if (MachineInstr *NewDV = TII.emitFrameIndexDebugValue(MF, StackSlot,
Offset, MDPtr, DL)) {
DEBUG(dbgs() << "Modifying debug info due to spill:" << "\t" << *MI);
MachineBasicBlock *MBB = MI->getParent();
MBB->insert(MBB->erase(MI), NewDV);
} else {
DEBUG(dbgs() << "Removing debug info due to spill:" << "\t" << *MI);
MI->eraseFromParent();
}
continue;
}
// Ignore copies to/from snippets. We'll delete them.
if (SnippetCopies.count(MI))
continue;
// Stack slot accesses may coalesce away.
if (coalesceStackAccess(MI, Reg))
continue;
// Analyze instruction.
bool Reads, Writes;
SmallVector<unsigned, 8> Ops;
tie(Reads, Writes) = MI->readsWritesVirtualRegister(Reg, &Ops);
// Find the slot index where this instruction reads and writes OldLI.
// This is usually the def slot, except for tied early clobbers.
SlotIndex Idx = LIS.getInstructionIndex(MI).getDefIndex();
if (VNInfo *VNI = OldLI.getVNInfoAt(Idx.getUseIndex()))
if (SlotIndex::isSameInstr(Idx, VNI->def))
Idx = VNI->def;
// Check for a sibling copy.
unsigned SibReg = isFullCopyOf(MI, Reg);
if (SibReg && isSibling(SibReg)) {
// This may actually be a copy between snippets.
if (isRegToSpill(SibReg)) {
DEBUG(dbgs() << "Found new snippet copy: " << *MI);
SnippetCopies.insert(MI);
continue;
}
if (Writes) {
// Hoist the spill of a sib-reg copy.
if (hoistSpill(OldLI, MI)) {
// This COPY is now dead, the value is already in the stack slot.
MI->getOperand(0).setIsDead();
DeadDefs.push_back(MI);
continue;
}
} else {
// This is a reload for a sib-reg copy. Drop spills downstream.
LiveInterval &SibLI = LIS.getInterval(SibReg);
eliminateRedundantSpills(SibLI, SibLI.getVNInfoAt(Idx));
// The COPY will fold to a reload below.
}
}
// Attempt to fold memory ops.
if (foldMemoryOperand(MI, Ops))
continue;
// Allocate interval around instruction.
// FIXME: Infer regclass from instruction alone.
LiveInterval &NewLI = Edit->createFrom(Reg, LIS, VRM);
NewLI.markNotSpillable();
if (Reads)
insertReload(NewLI, Idx, MI);
// Rewrite instruction operands.
bool hasLiveDef = false;
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(Ops[i]);
MO.setReg(NewLI.reg);
if (MO.isUse()) {
if (!MI->isRegTiedToDefOperand(Ops[i]))
MO.setIsKill();
} else {
if (!MO.isDead())
hasLiveDef = true;
}
}
DEBUG(dbgs() << "\trewrite: " << Idx << '\t' << *MI);
// FIXME: Use a second vreg if instruction has no tied ops.
if (Writes && hasLiveDef)
insertSpill(NewLI, OldLI, Idx, MI);
DEBUG(dbgs() << "\tinterval: " << NewLI << '\n');
}
}
/// spillAll - Spill all registers remaining after rematerialization.
void InlineSpiller::spillAll() {
// Update LiveStacks now that we are committed to spilling.
if (StackSlot == VirtRegMap::NO_STACK_SLOT) {
StackSlot = VRM.assignVirt2StackSlot(Original);
StackInt = &LSS.getOrCreateInterval(StackSlot, MRI.getRegClass(Original));
StackInt->getNextValue(SlotIndex(), 0, LSS.getVNInfoAllocator());
} else
StackInt = &LSS.getInterval(StackSlot);
if (Original != Edit->getReg())
VRM.assignVirt2StackSlot(Edit->getReg(), StackSlot);
assert(StackInt->getNumValNums() == 1 && "Bad stack interval values");
for (unsigned i = 0, e = RegsToSpill.size(); i != e; ++i)
StackInt->MergeRangesInAsValue(LIS.getInterval(RegsToSpill[i]),
StackInt->getValNumInfo(0));
DEBUG(dbgs() << "Merged spilled regs: " << *StackInt << '\n');
// Spill around uses of all RegsToSpill.
for (unsigned i = 0, e = RegsToSpill.size(); i != e; ++i)
spillAroundUses(RegsToSpill[i]);
// Hoisted spills may cause dead code.
if (!DeadDefs.empty()) {
DEBUG(dbgs() << "Eliminating " << DeadDefs.size() << " dead defs\n");
Edit->eliminateDeadDefs(DeadDefs, LIS, VRM, TII);
}
// Finally delete the SnippetCopies.
for (unsigned i = 0, e = RegsToSpill.size(); i != e; ++i) {
for (MachineRegisterInfo::reg_iterator RI = MRI.reg_begin(RegsToSpill[i]);
MachineInstr *MI = RI.skipInstruction();) {
assert(SnippetCopies.count(MI) && "Remaining use wasn't a snippet copy");
// FIXME: Do this with a LiveRangeEdit callback.
VRM.RemoveMachineInstrFromMaps(MI);
LIS.RemoveMachineInstrFromMaps(MI);
MI->eraseFromParent();
}
}
// Delete all spilled registers.
for (unsigned i = 0, e = RegsToSpill.size(); i != e; ++i)
Edit->eraseVirtReg(RegsToSpill[i], LIS);
}
void InlineSpiller::spill(LiveRangeEdit &edit) {
++NumSpilledRanges;
Edit = &edit;
assert(!TargetRegisterInfo::isStackSlot(edit.getReg())
&& "Trying to spill a stack slot.");
// Share a stack slot among all descendants of Original.
Original = VRM.getOriginal(edit.getReg());
StackSlot = VRM.getStackSlot(Original);
StackInt = 0;
DEBUG(dbgs() << "Inline spilling "
<< MRI.getRegClass(edit.getReg())->getName()
<< ':' << edit.getParent() << "\nFrom original "
<< LIS.getInterval(Original) << '\n');
assert(edit.getParent().isSpillable() &&
"Attempting to spill already spilled value.");
assert(DeadDefs.empty() && "Previous spill didn't remove dead defs");
collectRegsToSpill();
analyzeSiblingValues();
reMaterializeAll();
// Remat may handle everything.
if (!RegsToSpill.empty())
spillAll();
Edit->calculateRegClassAndHint(MF, LIS, Loops);
}
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