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//===- InlineSpiller.cpp - Insert spills and restores inline --------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// The inline spiller modifies the machine function directly instead of
// inserting spills and restores in VirtRegMap.
#include "SplitKit.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervalCalc.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/LiveRangeEdit.h"
#include "llvm/CodeGen/LiveStacks.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineInstrBundle.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/CodeGen/Spiller.h"
#include "llvm/CodeGen/StackMaps.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetOpcodes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/Support/BlockFrequency.h"
#include "llvm/Support/BranchProbability.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <iterator>
#include <tuple>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "regalloc"
STATISTIC(NumSpilledRanges, "Number of spilled live ranges");
STATISTIC(NumSnippets, "Number of spilled snippets");
STATISTIC(NumSpills, "Number of spills inserted");
STATISTIC(NumSpillsRemoved, "Number of spills removed");
STATISTIC(NumReloads, "Number of reloads inserted");
STATISTIC(NumReloadsRemoved, "Number of reloads removed");
STATISTIC(NumFolded, "Number of folded stack accesses");
STATISTIC(NumFoldedLoads, "Number of folded loads");
STATISTIC(NumRemats, "Number of rematerialized defs for spilling");
static cl::opt<bool> DisableHoisting("disable-spill-hoist", cl::Hidden,
cl::desc("Disable inline spill hoisting"));
static cl::opt<bool>
cl::init(false), cl::Hidden,
cl::desc("Restrict remat for statepoint operands"));
namespace {
class HoistSpillHelper : private LiveRangeEdit::Delegate {
MachineFunction &MF;
LiveIntervals &LIS;
LiveStacks &LSS;
AliasAnalysis *AA;
MachineDominatorTree &MDT;
MachineLoopInfo &Loops;
VirtRegMap &VRM;
MachineRegisterInfo &MRI;
const TargetInstrInfo &TII;
const TargetRegisterInfo &TRI;
const MachineBlockFrequencyInfo &MBFI;
InsertPointAnalysis IPA;
// Map from StackSlot to the LiveInterval of the original register.
// Note the LiveInterval of the original register may have been deleted
// after it is spilled. We keep a copy here to track the range where
// spills can be moved.
DenseMap<int, std::unique_ptr<LiveInterval>> StackSlotToOrigLI;
// Map from pair of (StackSlot and Original VNI) to a set of spills which
// have the same stackslot and have equal values defined by Original VNI.
// These spills are mergeable and are hoist candiates.
using MergeableSpillsMap =
MapVector<std::pair<int, VNInfo *>, SmallPtrSet<MachineInstr *, 16>>;
MergeableSpillsMap MergeableSpills;
/// This is the map from original register to a set containing all its
/// siblings. To hoist a spill to another BB, we need to find out a live
/// sibling there and use it as the source of the new spill.
DenseMap<Register, SmallSetVector<Register, 16>> Virt2SiblingsMap;
bool isSpillCandBB(LiveInterval &OrigLI, VNInfo &OrigVNI,
MachineBasicBlock &BB, Register &LiveReg);
void rmRedundantSpills(
SmallPtrSet<MachineInstr *, 16> &Spills,
SmallVectorImpl<MachineInstr *> &SpillsToRm,
DenseMap<MachineDomTreeNode *, MachineInstr *> &SpillBBToSpill);
void getVisitOrders(
MachineBasicBlock *Root, SmallPtrSet<MachineInstr *, 16> &Spills,
SmallVectorImpl<MachineDomTreeNode *> &Orders,
SmallVectorImpl<MachineInstr *> &SpillsToRm,
DenseMap<MachineDomTreeNode *, unsigned> &SpillsToKeep,
DenseMap<MachineDomTreeNode *, MachineInstr *> &SpillBBToSpill);
void runHoistSpills(LiveInterval &OrigLI, VNInfo &OrigVNI,
SmallPtrSet<MachineInstr *, 16> &Spills,
SmallVectorImpl<MachineInstr *> &SpillsToRm,
DenseMap<MachineBasicBlock *, unsigned> &SpillsToIns);
HoistSpillHelper(MachineFunctionPass &pass, MachineFunction &mf,
VirtRegMap &vrm)
: MF(mf), LIS(pass.getAnalysis<LiveIntervals>()),
Loops(pass.getAnalysis<MachineLoopInfo>()), VRM(vrm),
MRI(mf.getRegInfo()), TII(*mf.getSubtarget().getInstrInfo()),
IPA(LIS, mf.getNumBlockIDs()) {}
void addToMergeableSpills(MachineInstr &Spill, int StackSlot,
unsigned Original);
bool rmFromMergeableSpills(MachineInstr &Spill, int StackSlot);
void hoistAllSpills();
void LRE_DidCloneVirtReg(Register, Register) override;
class InlineSpiller : public Spiller {
MachineFunction &MF;
LiveIntervals &LIS;
LiveStacks &LSS;
AliasAnalysis *AA;
MachineDominatorTree &MDT;
MachineLoopInfo &Loops;
VirtRegMap &VRM;
MachineRegisterInfo &MRI;
const TargetInstrInfo &TII;
const TargetRegisterInfo &TRI;
const MachineBlockFrequencyInfo &MBFI;
// Variables that are valid during spill(), but used by multiple methods.
LiveRangeEdit *Edit;
LiveInterval *StackInt;
int StackSlot;
Register Original;
// All registers to spill to StackSlot, including the main register.
SmallVector<Register, 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;
// Dead defs generated during spilling.
SmallVector<MachineInstr*, 8> DeadDefs;
// Object records spills information and does the hoisting.
HoistSpillHelper HSpiller;
~InlineSpiller() override = default;
InlineSpiller(MachineFunctionPass &pass, MachineFunction &mf, VirtRegMap &vrm)
: MF(mf), LIS(pass.getAnalysis<LiveIntervals>()),
Loops(pass.getAnalysis<MachineLoopInfo>()), VRM(vrm),
MRI(mf.getRegInfo()), TII(*mf.getSubtarget().getInstrInfo()),
HSpiller(pass, mf, vrm) {}
void spill(LiveRangeEdit &) override;
void postOptimization() override;
bool isSnippet(const LiveInterval &SnipLI);
void collectRegsToSpill();
bool isRegToSpill(Register Reg) { return is_contained(RegsToSpill, Reg); }
bool isSibling(Register Reg);
bool hoistSpillInsideBB(LiveInterval &SpillLI, MachineInstr &CopyMI);
void eliminateRedundantSpills(LiveInterval &LI, VNInfo *VNI);
void markValueUsed(LiveInterval*, VNInfo*);
bool canGuaranteeAssignmentAfterRemat(Register VReg, MachineInstr &MI);
bool reMaterializeFor(LiveInterval &, MachineInstr &MI);
void reMaterializeAll();
bool coalesceStackAccess(MachineInstr *MI, Register Reg);
bool foldMemoryOperand(ArrayRef<std::pair<MachineInstr *, unsigned>>,
MachineInstr *LoadMI = nullptr);
void insertReload(Register VReg, SlotIndex, MachineBasicBlock::iterator MI);
void insertSpill(Register VReg, bool isKill, MachineBasicBlock::iterator MI);
void spillAroundUses(Register Reg);
void spillAll();
} // end anonymous namespace
Spiller::~Spiller() = default;
void Spiller::anchor() {}
Spiller *llvm::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 Register isFullCopyOf(const MachineInstr &MI, Register Reg) {
if (!MI.isFullCopy())
return Register();
if (MI.getOperand(0).getReg() == Reg)
return MI.getOperand(1).getReg();
if (MI.getOperand(1).getReg() == Reg)
return MI.getOperand(0).getReg();
return Register();
static void getVDefInterval(const MachineInstr &MI, LiveIntervals &LIS) {
for (unsigned I = 0, E = MI.getNumOperands(); I != E; ++I) {
const MachineOperand &MO = MI.getOperand(I);
if (MO.isReg() && MO.isDef() && Register::isVirtualRegister(MO.getReg()))
/// 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) {
Register 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 = nullptr;
// Check that all uses satisfy our criteria.
for (MachineRegisterInfo::reg_instr_nodbg_iterator
RI = MRI.reg_instr_nodbg_begin(SnipLI.reg()),
E = MRI.reg_instr_nodbg_end();
RI != E;) {
MachineInstr &MI = *RI++;
// Allow copies to/from Reg.
if (isFullCopyOf(MI, Reg))
// Allow stack slot loads.
int FI;
if (SnipLI.reg() == TII.isLoadFromStackSlot(MI, FI) && FI == StackSlot)
// Allow stack slot stores.
if (SnipLI.reg() == TII.isStoreToStackSlot(MI, FI) && FI == StackSlot)
// 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() {
Register Reg = Edit->getReg();
// Main register always spills.
RegsToSpill.assign(1, Reg);
// Snippets all have the same original, so there can't be any for an original
// register.
if (Original == Reg)
for (MachineRegisterInfo::reg_instr_iterator
RI = MRI.reg_instr_begin(Reg), E = MRI.reg_instr_end(); RI != E; ) {
MachineInstr &MI = *RI++;
Register SnipReg = isFullCopyOf(MI, Reg);
if (!isSibling(SnipReg))
LiveInterval &SnipLI = LIS.getInterval(SnipReg);
if (!isSnippet(SnipLI))
if (isRegToSpill(SnipReg))
LLVM_DEBUG(dbgs() << "\talso spill snippet " << SnipLI << '\n');
bool InlineSpiller::isSibling(Register Reg) {
return Reg.isVirtual() && VRM.getOriginal(Reg) == Original;
/// It is beneficial to spill to earlier place in the same BB in case
/// as follows:
/// There is an alternative def earlier in the same MBB.
/// Hoist the spill as far as possible in SpillMBB. This can ease
/// register pressure:
/// x = def
/// y = use x
/// s = copy x
/// Hoisting the spill of s to immediately after the def removes the
/// interference between x and y:
/// x = def
/// spill x
/// y = use killed x
/// This hoist only helps when the copy kills its source.
bool InlineSpiller::hoistSpillInsideBB(LiveInterval &SpillLI,
MachineInstr &CopyMI) {
SlotIndex Idx = LIS.getInstructionIndex(CopyMI);
#ifndef NDEBUG
VNInfo *VNI = SpillLI.getVNInfoAt(Idx.getRegSlot());
assert(VNI && VNI->def == Idx.getRegSlot() && "Not defined by copy");
Register SrcReg = CopyMI.getOperand(1).getReg();
LiveInterval &SrcLI = LIS.getInterval(SrcReg);
VNInfo *SrcVNI = SrcLI.getVNInfoAt(Idx);
LiveQueryResult SrcQ = SrcLI.Query(Idx);
MachineBasicBlock *DefMBB = LIS.getMBBFromIndex(SrcVNI->def);
if (DefMBB != CopyMI.getParent() || !SrcQ.isKill())
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));
LLVM_DEBUG(dbgs() << "\tmerged orig valno " << OrigVNI->id << ": "
<< *StackInt << '\n');
// We are going to spill SrcVNI immediately after its def, so clear out
// any later spills of the same value.
eliminateRedundantSpills(SrcLI, SrcVNI);
MachineBasicBlock *MBB = LIS.getMBBFromIndex(SrcVNI->def);
MachineBasicBlock::iterator MII;
if (SrcVNI->isPHIDef())
MII = MBB->SkipPHIsLabelsAndDebug(MBB->begin());
else {
MachineInstr *DefMI = LIS.getInstructionFromIndex(SrcVNI->def);
assert(DefMI && "Defining instruction disappeared");
MII = DefMI;
MachineInstrSpan MIS(MII, MBB);
// Insert spill without kill flag immediately after def.
TII.storeRegToStackSlot(*MBB, MII, SrcReg, false, StackSlot,
MRI.getRegClass(SrcReg), &TRI);
LIS.InsertMachineInstrRangeInMaps(MIS.begin(), MII);
for (const MachineInstr &MI : make_range(MIS.begin(), MII))
getVDefInterval(MI, LIS);
--MII; // Point to store instruction.
LLVM_DEBUG(dbgs() << "\thoisted: " << SrcVNI->def << '\t' << *MII);
// If there is only 1 store instruction is required for spill, add it
// to mergeable list. In X86 AMX, 2 intructions are required to store.
// We disable the merge for this case.
if (MIS.begin() == MII)
HSpiller.addToMergeableSpills(*MII, StackSlot, Original);
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;
std::tie(LI, VNI) = WorkList.pop_back_val();
Register Reg = LI->reg();
LLVM_DEBUG(dbgs() << "Checking redundant spills for " << VNI->id << '@'
<< VNI->def << " in " << *LI << '\n');
// Regs to spill are taken care of.
if (isRegToSpill(Reg))
// Add all of VNI's live range to StackInt.
StackInt->MergeValueInAsValue(*LI, VNI, StackInt->getValNumInfo(0));
LLVM_DEBUG(dbgs() << "Merged to stack int: " << *StackInt << '\n');
// Find all spills and copies of VNI.
for (MachineRegisterInfo::use_instr_nodbg_iterator
UI = MRI.use_instr_nodbg_begin(Reg), E = MRI.use_instr_nodbg_end();
UI != E; ) {
MachineInstr &MI = *UI++;
if (!MI.isCopy() && !MI.mayStore())
SlotIndex Idx = LIS.getInstructionIndex(MI);
if (LI->getVNInfoAt(Idx) != VNI)
// Follow sibling copies down the dominator tree.
if (Register DstReg = isFullCopyOf(MI, Reg)) {
if (isSibling(DstReg)) {
LiveInterval &DstLI = LIS.getInterval(DstReg);
VNInfo *DstVNI = DstLI.getVNInfoAt(Idx.getRegSlot());
assert(DstVNI && "Missing defined value");
assert(DstVNI->def == Idx.getRegSlot() && "Wrong copy def slot");
WorkList.push_back(std::make_pair(&DstLI, DstVNI));
// Erase spills.
int FI;
if (Reg == TII.isStoreToStackSlot(MI, FI) && FI == StackSlot) {
LLVM_DEBUG(dbgs() << "Redundant spill " << Idx << '\t' << MI);
// eliminateDeadDefs won't normally remove stores, so switch opcode.
if (HSpiller.rmFromMergeableSpills(MI, StackSlot))
} 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 {
std::tie(LI, VNI) = WorkList.pop_back_val();
if (!UsedValues.insert(VNI).second)
if (VNI->isPHIDef()) {
MachineBasicBlock *MBB = LIS.getMBBFromIndex(VNI->def);
for (MachineBasicBlock *P : MBB->predecessors()) {
VNInfo *PVNI = LI->getVNInfoBefore(LIS.getMBBEndIdx(P));
if (PVNI)
WorkList.push_back(std::make_pair(LI, PVNI));
// Follow snippet copies.
MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def);
if (!SnippetCopies.count(MI))
LiveInterval &SnipLI = LIS.getInterval(MI->getOperand(1).getReg());
assert(isRegToSpill(SnipLI.reg()) && "Unexpected register in copy");
VNInfo *SnipVNI = SnipLI.getVNInfoAt(VNI->def.getRegSlot(true));
assert(SnipVNI && "Snippet undefined before copy");
WorkList.push_back(std::make_pair(&SnipLI, SnipVNI));
} while (!WorkList.empty());
bool InlineSpiller::canGuaranteeAssignmentAfterRemat(Register VReg,
MachineInstr &MI) {
if (!RestrictStatepointRemat)
return true;
// Here's a quick explanation of the problem we're trying to handle here:
// * There are some pseudo instructions with more vreg uses than there are
// physical registers on the machine.
// * This is normally handled by spilling the vreg, and folding the reload
// into the user instruction. (Thus decreasing the number of used vregs
// until the remainder can be assigned to physregs.)
// * However, since we may try to spill vregs in any order, we can end up
// trying to spill each operand to the instruction, and then rematting it
// instead. When that happens, the new live intervals (for the remats) are
// expected to be trivially assignable (i.e. RS_Done). However, since we
// may have more remats than physregs, we're guaranteed to fail to assign
// one.
// At the moment, we only handle this for STATEPOINTs since they're the only
// pseudo op where we've seen this. If we start seeing other instructions
// with the same problem, we need to revisit this.
if (MI.getOpcode() != TargetOpcode::STATEPOINT)
return true;
// For STATEPOINTs we allow re-materialization for fixed arguments only hoping
// that number of physical registers is enough to cover all fixed arguments.
// If it is not true we need to revisit it.
for (unsigned Idx = StatepointOpers(&MI).getVarIdx(),
EndIdx = MI.getNumOperands();
Idx < EndIdx; ++Idx) {
MachineOperand &MO = MI.getOperand(Idx);
if (MO.isReg() && MO.getReg() == VReg)
return false;
return true;
/// reMaterializeFor - Attempt to rematerialize before MI instead of reloading.
bool InlineSpiller::reMaterializeFor(LiveInterval &VirtReg, MachineInstr &MI) {
// Analyze instruction
SmallVector<std::pair<MachineInstr *, unsigned>, 8> Ops;
VirtRegInfo RI = AnalyzeVirtRegInBundle(MI, VirtReg.reg(), &Ops);
if (!RI.Reads)
return false;
SlotIndex UseIdx = LIS.getInstructionIndex(MI).getRegSlot(true);
VNInfo *ParentVNI = VirtReg.getVNInfoAt(UseIdx.getBaseIndex());
if (!ParentVNI) {
LLVM_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())
LLVM_DEBUG(dbgs() << UseIdx << '\t' << MI);
return true;
if (SnippetCopies.count(&MI))
return false;
LiveInterval &OrigLI = LIS.getInterval(Original);
VNInfo *OrigVNI = OrigLI.getVNInfoAt(UseIdx);
LiveRangeEdit::Remat RM(ParentVNI);
RM.OrigMI = LIS.getInstructionFromIndex(OrigVNI->def);
if (!Edit->canRematerializeAt(RM, OrigVNI, UseIdx, false)) {
markValueUsed(&VirtReg, ParentVNI);
LLVM_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.
if (RI.Tied) {
markValueUsed(&VirtReg, ParentVNI);
LLVM_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->canFoldAsLoad() &&
foldMemoryOperand(Ops, RM.OrigMI)) {
return true;
// If we can't guarantee that we'll be able to actually assign the new vreg,
// we can't remat.
if (!canGuaranteeAssignmentAfterRemat(VirtReg.reg(), MI)) {
markValueUsed(&VirtReg, ParentVNI);
LLVM_DEBUG(dbgs() << "\tcannot remat for " << UseIdx << '\t' << MI);
return false;
// Allocate a new register for the remat.
Register NewVReg = Edit->createFrom(Original);
// Finally we can rematerialize OrigMI before MI.
SlotIndex DefIdx =
Edit->rematerializeAt(*MI.getParent(), MI, NewVReg, RM, TRI);
// We take the DebugLoc from MI, since OrigMI may be attributed to a
// different source location.
auto *NewMI = LIS.getInstructionFromIndex(DefIdx);
LLVM_DEBUG(dbgs() << "\tremat: " << DefIdx << '\t'
<< *LIS.getInstructionFromIndex(DefIdx));
// Replace operands
for (const auto &OpPair : Ops) {
MachineOperand &MO = OpPair.first->getOperand(OpPair.second);
if (MO.isReg() && MO.isUse() && MO.getReg() == VirtReg.reg()) {
LLVM_DEBUG(dbgs() << "\t " << UseIdx << '\t' << MI << '\n');
return true;
/// reMaterializeAll - Try to rematerialize as many uses as possible,
/// and trim the live ranges after.
void InlineSpiller::reMaterializeAll() {
if (!Edit->anyRematerializable(AA))
// Try to remat before all uses of snippets.
bool anyRemat = false;
for (Register Reg : RegsToSpill) {
LiveInterval &LI = LIS.getInterval(Reg);
for (MachineRegisterInfo::reg_bundle_iterator
RegI = MRI.reg_bundle_begin(Reg), E = MRI.reg_bundle_end();
RegI != E; ) {
MachineInstr &MI = *RegI++;
// Debug values are not allowed to affect codegen.
if (MI.isDebugValue())
assert(!MI.isDebugInstr() && "Did not expect to find a use in debug "
"instruction that isn't a DBG_VALUE");
anyRemat |= reMaterializeFor(LI, MI);
if (!anyRemat)
// Remove any values that were completely rematted.
for (Register Reg : RegsToSpill) {
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))
MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def);
MI->addRegisterDead(Reg, &TRI);
if (!MI->allDefsAreDead())
LLVM_DEBUG(dbgs() << "All defs dead: " << *MI);
// Eliminate dead code after remat. Note that some snippet copies may be
// deleted here.
if (DeadDefs.empty())
LLVM_DEBUG(dbgs() << "Remat created " << DeadDefs.size() << " dead defs.\n");
Edit->eliminateDeadDefs(DeadDefs, RegsToSpill, AA);
// LiveRangeEdit::eliminateDeadDef is used to remove dead define instructions
// after rematerialization. To remove a VNI for a vreg from its LiveInterval,
// LiveIntervals::removeVRegDefAt is used. However, after non-PHI VNIs are all
// removed, PHI VNI are still left in the LiveInterval.
// So to get rid of unused reg, we need to check whether it has non-dbg
// reference instead of whether it has non-empty interval.
unsigned ResultPos = 0;
for (Register Reg : RegsToSpill) {
if (MRI.reg_nodbg_empty(Reg)) {
assert(LIS.hasInterval(Reg) &&
(!LIS.getInterval(Reg).empty() || !MRI.reg_nodbg_empty(Reg)) &&
"Empty and not used live-range?!");
RegsToSpill[ResultPos++] = Reg;
RegsToSpill.erase(RegsToSpill.begin() + ResultPos, RegsToSpill.end());
LLVM_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, Register Reg) {
int FI = 0;
Register InstrReg = TII.isLoadFromStackSlot(*MI, FI);
bool IsLoad = InstrReg;
if (!IsLoad)
InstrReg = TII.isStoreToStackSlot(*MI, FI);
// We have a stack access. Is it the right register and slot?
if (InstrReg != Reg || FI != StackSlot)
return false;
if (!IsLoad)
HSpiller.rmFromMergeableSpills(*MI, StackSlot);
LLVM_DEBUG(dbgs() << "Coalescing stack access: " << *MI);
if (IsLoad) {
} else {
return true;
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
// Dump the range of instructions from B to E with their slot indexes.
static void dumpMachineInstrRangeWithSlotIndex(MachineBasicBlock::iterator B,
MachineBasicBlock::iterator E,
LiveIntervals const &LIS,
const char *const header,
Register VReg = Register()) {
char NextLine = '\n';
char SlotIndent = '\t';
if (std::next(B) == E) {
NextLine = ' ';
SlotIndent = ' ';
dbgs() << '\t' << header << ": " << NextLine;
for (MachineBasicBlock::iterator I = B; I != E; ++I) {
SlotIndex Idx = LIS.getInstructionIndex(*I).getRegSlot();
// If a register was passed in and this instruction has it as a
// destination that is marked as an early clobber, print the
// early-clobber slot index.
if (VReg) {
MachineOperand *MO = I->findRegisterDefOperand(VReg);
if (MO && MO->isEarlyClobber())
Idx = Idx.getRegSlot(true);
dbgs() << SlotIndent << Idx << '\t' << *I;
/// foldMemoryOperand - Try folding stack slot references in Ops into their
/// instructions.
/// @param Ops Operand indices from AnalyzeVirtRegInBundle().
/// @param LoadMI Load instruction to use instead of stack slot when non-null.
/// @return True on success.
bool InlineSpiller::
foldMemoryOperand(ArrayRef<std::pair<MachineInstr *, unsigned>> Ops,
MachineInstr *LoadMI) {
if (Ops.empty())
return false;
// Don't attempt folding in bundles.
MachineInstr *MI = Ops.front().first;
if (Ops.back().first != MI || MI->isBundled())
return false;
bool WasCopy = MI->isCopy();
Register ImpReg;
// TII::foldMemoryOperand will do what we need here for statepoint
// (fold load into use and remove corresponding def). We will replace
// uses of removed def with loads (spillAroundUses).
// For that to work we need to untie def and use to pass it through
// foldMemoryOperand and signal foldPatchpoint that it is allowed to
// fold them.
bool UntieRegs = MI->getOpcode() == TargetOpcode::STATEPOINT;
// Spill subregs if the target allows it.
// We always want to spill subregs for stackmap/patchpoint pseudos.
bool SpillSubRegs = TII.isSubregFoldable() ||
MI->getOpcode() == TargetOpcode::STATEPOINT ||
MI->getOpcode() == TargetOpcode::PATCHPOINT ||
MI->getOpcode() == TargetOpcode::STACKMAP;
// TargetInstrInfo::foldMemoryOperand only expects explicit, non-tied
// operands.
SmallVector<unsigned, 8> FoldOps;
for (const auto &OpPair : Ops) {
unsigned Idx = OpPair.second;
assert(MI == OpPair.first && "Instruction conflict during operand folding");
MachineOperand &MO = MI->getOperand(Idx);
if (MO.isImplicit()) {
ImpReg = MO.getReg();
if (!SpillSubRegs && 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 (UntieRegs || !MI->isRegTiedToDefOperand(Idx))
// If we only have implicit uses, we won't be able to fold that.
// Moreover, TargetInstrInfo::foldMemoryOperand will assert if we try!
if (FoldOps.empty())
return false;
MachineInstrSpan MIS(MI, MI->getParent());
SmallVector<std::pair<unsigned, unsigned> > TiedOps;
if (UntieRegs)
for (unsigned Idx : FoldOps) {
MachineOperand &MO = MI->getOperand(Idx);
if (!MO.isTied())
unsigned Tied = MI->findTiedOperandIdx(Idx);
if (MO.isUse())
TiedOps.emplace_back(Tied, Idx);
else {
assert(MO.isDef() && "Tied to not use and def?");
TiedOps.emplace_back(Idx, Tied);
MachineInstr *FoldMI =
LoadMI ? TII.foldMemoryOperand(*MI, FoldOps, *LoadMI, &LIS)
: TII.foldMemoryOperand(*MI, FoldOps, StackSlot, &LIS, &VRM);
if (!FoldMI) {
// Re-tie operands.
for (auto Tied : TiedOps)
MI->tieOperands(Tied.first, Tied.second);
return false;
// Remove LIS for any dead defs in the original MI not in FoldMI.
for (MIBundleOperands MO(*MI); MO.isValid(); ++MO) {
if (!MO->isReg())
Register Reg = MO->getReg();
if (!Reg || Register::isVirtualRegister(Reg) || MRI.isReserved(Reg)) {
// Skip non-Defs, including undef uses and internal reads.
if (MO->isUse())
PhysRegInfo RI = AnalyzePhysRegInBundle(*FoldMI, Reg, &TRI);
if (RI.FullyDefined)
// FoldMI does not define this physreg. Remove the LI segment.
assert(MO->isDead() && "Cannot fold physreg def");
SlotIndex Idx = LIS.getInstructionIndex(*MI).getRegSlot();
LIS.removePhysRegDefAt(Reg.asMCReg(), Idx);
int FI;
if (TII.isStoreToStackSlot(*MI, FI) &&
HSpiller.rmFromMergeableSpills(*MI, FI))
LIS.ReplaceMachineInstrInMaps(*MI, *FoldMI);
// Update the call site info.
if (MI->isCandidateForCallSiteEntry())
MI->getMF()->moveCallSiteInfo(MI, FoldMI);
// Insert any new instructions other than FoldMI into the LIS maps.
assert(!MIS.empty() && "Unexpected empty span of instructions!");
for (MachineInstr &MI : MIS)
if (&MI != FoldMI)
// TII.foldMemoryOperand may have left some implicit operands on the
// instruction. Strip them.
if (ImpReg)
for (unsigned i = FoldMI->getNumOperands(); i; --i) {
MachineOperand &MO = FoldMI->getOperand(i - 1);
if (!MO.isReg() || !MO.isImplicit())
if (MO.getReg() == ImpReg)
FoldMI->RemoveOperand(i - 1);
LLVM_DEBUG(dumpMachineInstrRangeWithSlotIndex(MIS.begin(), MIS.end(), LIS,
if (!WasCopy)
else if (Ops.front().second == 0) {
// If there is only 1 store instruction is required for spill, add it
// to mergeable list. In X86 AMX, 2 intructions are required to store.
// We disable the merge for this case.
if (std::distance(MIS.begin(), MIS.end()) <= 1)
HSpiller.addToMergeableSpills(*FoldMI, StackSlot, Original);
} else
return true;
void InlineSpiller::insertReload(Register NewVReg,
SlotIndex Idx,
MachineBasicBlock::iterator MI) {
MachineBasicBlock &MBB = *MI->getParent();
MachineInstrSpan MIS(MI, &MBB);
TII.loadRegFromStackSlot(MBB, MI, NewVReg, StackSlot,
MRI.getRegClass(NewVReg), &TRI);
LIS.InsertMachineInstrRangeInMaps(MIS.begin(), MI);
LLVM_DEBUG(dumpMachineInstrRangeWithSlotIndex(MIS.begin(), MI, LIS, "reload",
/// Check if \p Def fully defines a VReg with an undefined value.
/// If that's the case, that means the value of VReg is actually
/// not relevant.
static bool isRealSpill(const MachineInstr &Def) {
if (!Def.isImplicitDef())
return true;
assert(Def.getNumOperands() == 1 &&
"Implicit def with more than one definition");
// We can say that the VReg defined by Def is undef, only if it is
// fully defined by Def. Otherwise, some of the lanes may not be
// undef and the value of the VReg matters.
return Def.getOperand(0).getSubReg();
/// insertSpill - Insert a spill of NewVReg after MI.
void InlineSpiller::insertSpill(Register NewVReg, bool isKill,
MachineBasicBlock::iterator MI) {
// Spill are not terminators, so inserting spills after terminators will
// violate invariants in MachineVerifier.
assert(!MI->isTerminator() && "Inserting a spill after a terminator");
MachineBasicBlock &MBB = *MI->getParent();
MachineInstrSpan MIS(MI, &MBB);
MachineBasicBlock::iterator SpillBefore = std::next(MI);
bool IsRealSpill = isRealSpill(*MI);
if (IsRealSpill)
TII.storeRegToStackSlot(MBB, SpillBefore, NewVReg, isKill, StackSlot,
MRI.getRegClass(NewVReg), &TRI);
// Don't spill undef value.
// Anything works for undef, in particular keeping the memory
// uninitialized is a viable option and it saves code size and
// run time.
BuildMI(MBB, SpillBefore, MI->getDebugLoc(), TII.get(TargetOpcode::KILL))
.addReg(NewVReg, getKillRegState(isKill));
MachineBasicBlock::iterator Spill = std::next(MI);
LIS.InsertMachineInstrRangeInMaps(Spill, MIS.end());
for (const MachineInstr &MI : make_range(Spill, MIS.end()))
getVDefInterval(MI, LIS);
dumpMachineInstrRangeWithSlotIndex(Spill, MIS.end(), LIS, "spill"));
// If there is only 1 store instruction is required for spill, add it
// to mergeable list. In X86 AMX, 2 intructions are required to store.
// We disable the merge for this case.
if (IsRealSpill && std::distance(Spill, MIS.end()) <= 1)
HSpiller.addToMergeableSpills(*Spill, StackSlot, Original);
/// spillAroundUses - insert spill code around each use of Reg.
void InlineSpiller::spillAroundUses(Register Reg) {
LLVM_DEBUG(dbgs() << "spillAroundUses " << printReg(Reg) << '\n');
LiveInterval &OldLI = LIS.getInterval(Reg);
// Iterate over instructions using Reg.
for (MachineRegisterInfo::reg_bundle_iterator
RegI = MRI.reg_bundle_begin(Reg), E = MRI.reg_bundle_end();
RegI != E; ) {
MachineInstr *MI = &*(RegI++);
// Debug values are not allowed to affect codegen.
if (MI->isDebugValue()) {
// Modify DBG_VALUE now that the value is in a spill slot.
MachineBasicBlock *MBB = MI->getParent();
LLVM_DEBUG(dbgs() << "Modifying debug info due to spill:\t" << *MI);
buildDbgValueForSpill(*MBB, MI, *MI, StackSlot);
assert(!MI->isDebugInstr() && "Did not expect to find a use in debug "
"instruction that isn't a DBG_VALUE");
// Ignore copies to/from snippets. We'll delete them.
if (SnippetCopies.count(MI))
// Stack slot accesses may coalesce away.
if (coalesceStackAccess(MI, Reg))
// Analyze instruction.
SmallVector<std::pair<MachineInstr*, unsigned>, 8> Ops;
VirtRegInfo RI = AnalyzeVirtRegInBundle(*MI, 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).getRegSlot();
if (VNInfo *VNI = OldLI.getVNInfoAt(Idx.getRegSlot(true)))
if (SlotIndex::isSameInstr(Idx, VNI->def))
Idx = VNI->def;
// Check for a sibling copy.
Register SibReg = isFullCopyOf(*MI, Reg);
if (SibReg && isSibling(SibReg)) {
// This may actually be a copy between snippets.
if (isRegToSpill(SibReg)) {
LLVM_DEBUG(dbgs() << "Found new snippet copy: " << *MI);
if (RI.Writes) {
if (hoistSpillInsideBB(OldLI, *MI)) {
// This COPY is now dead, the value is already in the stack slot.
} 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(Ops))
// Create a new virtual register for spill/fill.
// FIXME: Infer regclass from instruction alone.
Register NewVReg = Edit->createFrom(Reg);
if (RI.Reads)
insertReload(NewVReg, Idx, MI);
// Rewrite instruction operands.
bool hasLiveDef = false;
for (const auto &OpPair : Ops) {
MachineOperand &MO = OpPair.first->getOperand(OpPair.second);
if (MO.isUse()) {
if (!OpPair.first->isRegTiedToDefOperand(OpPair.second))
} else {
if (!MO.isDead())
hasLiveDef = true;
LLVM_DEBUG(dbgs() << "\trewrite: " << Idx << '\t' << *MI << '\n');
// FIXME: Use a second vreg if instruction has no tied ops.
if (RI.Writes)
if (hasLiveDef)
insertSpill(NewVReg, true, MI);
/// 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(), 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 (Register Reg : RegsToSpill)
LLVM_DEBUG(dbgs() << "Merged spilled regs: " << *StackInt << '\n');
// Spill around uses of all RegsToSpill.
for (Register Reg : RegsToSpill)
// Hoisted spills may cause dead code.
if (!DeadDefs.empty()) {
LLVM_DEBUG(dbgs() << "Eliminating " << DeadDefs.size() << " dead defs\n");
Edit->eliminateDeadDefs(DeadDefs, RegsToSpill, AA);
// Finally delete the SnippetCopies.
for (Register Reg : RegsToSpill) {
for (MachineRegisterInfo::reg_instr_iterator
RI = MRI.reg_instr_begin(Reg), E = MRI.reg_instr_end();
RI != E; ) {
MachineInstr &MI = *(RI++);
assert(SnippetCopies.count(&MI) && "Remaining use wasn't a snippet copy");
// FIXME: Do this with a LiveRangeEdit callback.
// Delete all spilled registers.
for (Register Reg : RegsToSpill)
void InlineSpiller::spill(LiveRangeEdit &edit) {
Edit = &edit;
assert(!Register::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 = nullptr;
LLVM_DEBUG(dbgs() << "Inline spilling "
<< TRI.getRegClassName(MRI.getRegClass(edit.getReg()))
<< ':' << edit.getParent() << "\nFrom original "
<< printReg(Original) << '\n');
assert(edit.getParent().isSpillable() &&
"Attempting to spill already spilled value.");
assert(DeadDefs.empty() && "Previous spill didn't remove dead defs");
// Remat may handle everything.
if (!RegsToSpill.empty())
Edit->calculateRegClassAndHint(MF, Loops, MBFI);
/// Optimizations after all the reg selections and spills are done.
void InlineSpiller::postOptimization() { HSpiller.hoistAllSpills(); }
/// When a spill is inserted, add the spill to MergeableSpills map.
void HoistSpillHelper::addToMergeableSpills(MachineInstr &Spill, int StackSlot,
unsigned Original) {
BumpPtrAllocator &Allocator = LIS.getVNInfoAllocator();
LiveInterval &OrigLI = LIS.getInterval(Original);
// save a copy of LiveInterval in StackSlotToOrigLI because the original
// LiveInterval may be cleared after all its references are spilled.
if (StackSlotToOrigLI.find(StackSlot) == StackSlotToOrigLI.end()) {
auto LI = std::make_unique<LiveInterval>(OrigLI.reg(), OrigLI.weight());
LI->assign(OrigLI, Allocator);
StackSlotToOrigLI[StackSlot] = std::move(LI);
SlotIndex Idx = LIS.getInstructionIndex(Spill);
VNInfo *OrigVNI = StackSlotToOrigLI[StackSlot]->getVNInfoAt(Idx.getRegSlot());
std::pair<int, VNInfo *> MIdx = std::make_pair(StackSlot, OrigVNI);
/// When a spill is removed, remove the spill from MergeableSpills map.
/// Return true if the spill is removed successfully.
bool HoistSpillHelper::rmFromMergeableSpills(MachineInstr &Spill,
int StackSlot) {
auto It = StackSlotToOrigLI.find(StackSlot);
if (It == StackSlotToOrigLI.end())
return false;
SlotIndex Idx = LIS.getInstructionIndex(Spill);
VNInfo *OrigVNI = It->second->getVNInfoAt(Idx.getRegSlot());
std::pair<int, VNInfo *> MIdx = std::make_pair(StackSlot, OrigVNI);
return MergeableSpills[MIdx].erase(&Spill);
/// Check BB to see if it is a possible target BB to place a hoisted spill,
/// i.e., there should be a living sibling of OrigReg at the insert point.
bool HoistSpillHelper::isSpillCandBB(LiveInterval &OrigLI, VNInfo &OrigVNI,
MachineBasicBlock &BB, Register &LiveReg) {
SlotIndex Idx;
Register OrigReg = OrigLI.reg();
MachineBasicBlock::iterator MI = IPA.getLastInsertPointIter(OrigLI, BB);
if (MI != BB.end())
Idx = LIS.getInstructionIndex(*MI);
Idx = LIS.getMBBEndIdx(&BB).getPrevSlot();
SmallSetVector<Register, 16> &Siblings = Virt2SiblingsMap[OrigReg];
assert(OrigLI.getVNInfoAt(Idx) == &OrigVNI && "Unexpected VNI");
for (const Register &SibReg : Siblings) {
LiveInterval &LI = LIS.getInterval(SibReg);
VNInfo *VNI = LI.getVNInfoAt(Idx);
if (VNI) {
LiveReg = SibReg;
return true;
return false;
/// Remove redundant spills in the same BB. Save those redundant spills in
/// SpillsToRm, and save the spill to keep and its BB in SpillBBToSpill map.
void HoistSpillHelper::rmRedundantSpills(
SmallPtrSet<MachineInstr *, 16> &Spills,
SmallVectorImpl<MachineInstr *> &SpillsToRm,
DenseMap<MachineDomTreeNode *, MachineInstr *> &SpillBBToSpill) {
// For each spill saw, check SpillBBToSpill[] and see if its BB already has
// another spill inside. If a BB contains more than one spill, only keep the
// earlier spill with smaller SlotIndex.
for (const auto CurrentSpill : Spills) {
MachineBasicBlock *Block = CurrentSpill->getParent();
MachineDomTreeNode *Node = MDT.getBase().getNode(Block);
MachineInstr *PrevSpill = SpillBBToSpill[Node];
if (PrevSpill) {
SlotIndex PIdx = LIS.getInstructionIndex(*PrevSpill);
SlotIndex CIdx = LIS.getInstructionIndex(*CurrentSpill);
MachineInstr *SpillToRm = (CIdx > PIdx) ? CurrentSpill : PrevSpill;
MachineInstr *SpillToKeep = (CIdx > PIdx) ? PrevSpill : CurrentSpill;
SpillBBToSpill[MDT.getBase().getNode(Block)] = SpillToKeep;
} else {
SpillBBToSpill[MDT.getBase().getNode(Block)] = CurrentSpill;
for (const auto SpillToRm : SpillsToRm)
/// Starting from \p Root find a top-down traversal order of the dominator
/// tree to visit all basic blocks containing the elements of \p Spills.
/// Redundant spills will be found and put into \p SpillsToRm at the same
/// time. \p SpillBBToSpill will be populated as part of the process and
/// maps a basic block to the first store occurring in the basic block.
/// \post SpillsToRm.union(Spills\@post) == Spills\@pre
void HoistSpillHelper::getVisitOrders(
MachineBasicBlock *Root, SmallPtrSet<MachineInstr *, 16> &Spills,
SmallVectorImpl<MachineDomTreeNode *> &Orders,
SmallVectorImpl<MachineInstr *> &SpillsToRm,
DenseMap<MachineDomTreeNode *, unsigned> &SpillsToKeep,
DenseMap<MachineDomTreeNode *, MachineInstr *> &SpillBBToSpill) {
// The set contains all the possible BB nodes to which we may hoist
// original spills.
SmallPtrSet<MachineDomTreeNode *, 8> WorkSet;
// Save the BB nodes on the path from the first BB node containing
// non-redundant spill to the Root node.
SmallPtrSet<MachineDomTreeNode *, 8> NodesOnPath;
// All the spills to be hoisted must originate from a single def instruction
// to the OrigReg. It means the def instruction should dominate all the spills
// to be hoisted. We choose the BB where the def instruction is located as
// the Root.
MachineDomTreeNode *RootIDomNode = MDT[Root]->getIDom();
// For every node on the dominator tree with spill, walk up on the dominator
// tree towards the Root node until it is reached. If there is other node
// containing spill in the middle of the path, the previous spill saw will
// be redundant and the node containing it will be removed. All the nodes on
// the path starting from the first node with non-redundant spill to the Root
// node will be added to the WorkSet, which will contain all the possible
// locations where spills may be hoisted to after the loop below is done.
for (const auto Spill : Spills) {
MachineBasicBlock *Block = Spill->getParent();
MachineDomTreeNode *Node = MDT[Block];
MachineInstr *SpillToRm = nullptr;
while (Node != RootIDomNode) {
// If Node dominates Block, and it already contains a spill, the spill in
// Block will be redundant.
if (Node != MDT[Block] && SpillBBToSpill[Node]) {
SpillToRm = SpillBBToSpill[MDT[Block]];
/// If we see the Node already in WorkSet, the path from the Node to
/// the Root node must already be traversed by another spill.
/// Then no need to repeat.
} else if (WorkSet.count(Node)) {
} else {
Node = Node->getIDom();
if (SpillToRm) {
} else {
// Add a BB containing the original spills to SpillsToKeep -- i.e.,
// set the initial status before hoisting start. The value of BBs
// containing original spills is set to 0, in order to descriminate
// with BBs containing hoisted spills which will be inserted to
// SpillsToKeep later during hoisting.
SpillsToKeep[MDT[Block]] = 0;
WorkSet.insert(NodesOnPath.begin(), NodesOnPath.end());
// Sort the nodes in WorkSet in top-down order and save the nodes
// in Orders. Orders will be used for hoisting in runHoistSpills.
unsigned idx = 0;
do {
MachineDomTreeNode *Node = Orders[idx++];
for (MachineDomTreeNode *Child : Node->children()) {
if (WorkSet.count(Child))
} while (idx != Orders.size());
assert(Orders.size() == WorkSet.size() &&
"Orders have different size with WorkSet");
#ifndef NDEBUG
LLVM_DEBUG(dbgs() << "Orders size is " << Orders.size() << "\n");
SmallVector<MachineDomTreeNode *, 32>::reverse_iterator RIt = Orders.rbegin();
for (; RIt != Orders.rend(); RIt++)
LLVM_DEBUG(dbgs() << "BB" << (*RIt)->getBlock()->getNumber() << ",");
LLVM_DEBUG(dbgs() << "\n");
/// Try to hoist spills according to BB hotness. The spills to removed will
/// be saved in \p SpillsToRm. The spills to be inserted will be saved in
/// \p SpillsToIns.
void HoistSpillHelper::runHoistSpills(
LiveInterval &OrigLI, VNInfo &OrigVNI,
SmallPtrSet<MachineInstr *, 16> &Spills,
SmallVectorImpl<MachineInstr *> &SpillsToRm,
DenseMap<MachineBasicBlock *, unsigned> &SpillsToIns) {
// Visit order of dominator tree nodes.
SmallVector<MachineDomTreeNode *, 32> Orders;
// SpillsToKeep contains all the nodes where spills are to be inserted
// during hoisting. If the spill to be inserted is an original spill
// (not a hoisted one), the value of the map entry is 0. If the spill
// is a hoisted spill, the value of the map entry is the VReg to be used
// as the source of the spill.
DenseMap<MachineDomTreeNode *, unsigned> SpillsToKeep;
// Map from BB to the first spill inside of it.
DenseMap<MachineDomTreeNode *, MachineInstr *> SpillBBToSpill;
rmRedundantSpills(Spills, SpillsToRm, SpillBBToSpill);
MachineBasicBlock *Root = LIS.getMBBFromIndex(OrigVNI.def);
getVisitOrders(Root, Spills, Orders, SpillsToRm, SpillsToKeep,
// SpillsInSubTreeMap keeps the map from a dom tree node to a pair of
// nodes set and the cost of all the spills inside those nodes.
// The nodes set are the locations where spills are to be inserted
// in the subtree of current node.
using NodesCostPair =
std::pair<SmallPtrSet<MachineDomTreeNode *, 16>, BlockFrequency>;
DenseMap<MachineDomTreeNode *, NodesCostPair> SpillsInSubTreeMap;
// Iterate Orders set in reverse order, which will be a bottom-up order
// in the dominator tree. Once we visit a dom tree node, we know its
// children have already been visited and the spill locations in the
// subtrees of all the children have been determined.
SmallVector<MachineDomTreeNode *, 32>::reverse_iterator RIt = Orders.rbegin();
for (; RIt != Orders.rend(); RIt++) {
MachineBasicBlock *Block = (*RIt)->getBlock();
// If Block contains an original spill, simply continue.
if (SpillsToKeep.find(*RIt) != SpillsToKeep.end() && !SpillsToKeep[*RIt]) {
// SpillsInSubTreeMap[*RIt].second contains the cost of spill.
SpillsInSubTreeMap[*RIt].second = MBFI.getBlockFreq(Block);
// Collect spills in subtree of current node (*RIt) to
// SpillsInSubTreeMap[*RIt].first.
for (MachineDomTreeNode *Child : (*RIt)->children()) {
if (SpillsInSubTreeMap.find(Child) == SpillsInSubTreeMap.end())
// The stmt "SpillsInSubTree = SpillsInSubTreeMap[*RIt].first" below
// should be placed before getting the begin and end iterators of
// SpillsInSubTreeMap[Child].first, or else the iterators may be
// invalidated when SpillsInSubTreeMap[*RIt] is seen the first time
// and the map grows and then the original buckets in the map are moved.
SmallPtrSet<MachineDomTreeNode *, 16> &SpillsInSubTree =
BlockFrequency &SubTreeCost = SpillsInSubTreeMap[*RIt].second;
SubTreeCost += SpillsInSubTreeMap[Child].second;
auto BI = SpillsInSubTreeMap[Child].first.begin();
auto EI = SpillsInSubTreeMap[Child].first.end();
SpillsInSubTree.insert(BI, EI);
SmallPtrSet<MachineDomTreeNode *, 16> &SpillsInSubTree =
BlockFrequency &SubTreeCost = SpillsInSubTreeMap[*RIt].second;
// No spills in subtree, simply continue.
if (SpillsInSubTree.empty())
// Check whether Block is a possible candidate to insert spill.
Register LiveReg;
if (!isSpillCandBB(OrigLI, OrigVNI, *Block, LiveReg))
// If there are multiple spills that could be merged, bias a little
// to hoist the spill.
BranchProbability MarginProb = (SpillsInSubTree.size() > 1)
? BranchProbability(9, 10)
: BranchProbability(1, 1);
if (SubTreeCost > MBFI.getBlockFreq(Block) * MarginProb) {
// Hoist: Move spills to current Block.
for (const auto SpillBB : SpillsInSubTree) {
// When SpillBB is a BB contains original spill, insert the spill
// to SpillsToRm.
if (SpillsToKeep.find(SpillBB) != SpillsToKeep.end() &&
!SpillsToKeep[SpillBB]) {
MachineInstr *SpillToRm = SpillBBToSpill[SpillBB];
// SpillBB will not contain spill anymore, remove it from SpillsToKeep.
// Current Block is the BB containing the new hoisted spill. Add it to
// SpillsToKeep. LiveReg is the source of the new spill.
SpillsToKeep[*RIt] = LiveReg;
dbgs() << "spills in BB: ";
for (const auto Rspill : SpillsInSubTree)
dbgs() << Rspill->getBlock()->getNumber() << " ";
dbgs() << "were promoted to BB" << (*RIt)->getBlock()->getNumber()
<< "\n";
SubTreeCost = MBFI.getBlockFreq(Block);
// For spills in SpillsToKeep with LiveReg set (i.e., not original spill),
// save them to SpillsToIns.
for (const auto &Ent : SpillsToKeep) {
if (Ent.second)
SpillsToIns[Ent.first->getBlock()] = Ent.second;
/// For spills with equal values, remove redundant spills and hoist those left
/// to less hot spots.
/// Spills with equal values will be collected into the same set in
/// MergeableSpills when spill is inserted. These equal spills are originated
/// from the same defining instruction and are dominated by the instruction.
/// Before hoisting all the equal spills, redundant spills inside in the same
/// BB are first marked to be deleted. Then starting from the spills left, walk
/// up on the dominator tree towards the Root node where the define instruction
/// is located, mark the dominated spills to be deleted along the way and
/// collect the BB nodes on the path from non-dominated spills to the define
/// instruction into a WorkSet. The nodes in WorkSet are the candidate places
/// where we are considering to hoist the spills. We iterate the WorkSet in
/// bottom-up order, and for each node, we will decide whether to hoist spills
/// inside its subtree to that node. In this way, we can get benefit locally
/// even if hoisting all the equal spills to one cold place is impossible.
void HoistSpillHelper::hoistAllSpills() {
SmallVector<Register, 4> NewVRegs;
LiveRangeEdit Edit(nullptr, NewVRegs, MF, LIS, &VRM, this);
for (unsigned i = 0, e = MRI.getNumVirtRegs(); i != e; ++i) {
Register Reg = Register::index2VirtReg(i);
Register Original = VRM.getPreSplitReg(Reg);
if (!MRI.def_empty(Reg))
// Each entry in MergeableSpills contains a spill set with equal values.
for (auto &Ent : MergeableSpills) {
int Slot = Ent.first.first;
LiveInterval &OrigLI = *StackSlotToOrigLI[Slot];
VNInfo *OrigVNI = Ent.first.second;
SmallPtrSet<MachineInstr *, 16> &EqValSpills = Ent.second;
if (Ent.second.empty())
dbgs() << "\nFor Slot" << Slot << " and VN" << OrigVNI->id << ":\n"
<< "Equal spills in BB: ";
for (const auto spill : EqValSpills)
dbgs() << spill->getParent()->getNumber() << " ";
dbgs() << "\n";
// SpillsToRm is the spill set to be removed from EqValSpills.
SmallVector<MachineInstr *, 16> SpillsToRm;
// SpillsToIns is the spill set to be newly inserted after hoisting.
DenseMap<MachineBasicBlock *, unsigned> SpillsToIns;
runHoistSpills(OrigLI, *OrigVNI, EqValSpills, SpillsToRm, SpillsToIns);
dbgs() << "Finally inserted spills in BB: ";
for (const auto &Ispill : SpillsToIns)
dbgs() << Ispill.first->getNumber() << " ";
dbgs() << "\nFinally removed spills in BB: ";
for (const auto Rspill : SpillsToRm)
dbgs() << Rspill->getParent()->getNumber() << " ";
dbgs() << "\n";
// Stack live range update.
LiveInterval &StackIntvl = LSS.getInterval(Slot);
if (!SpillsToIns.empty() || !SpillsToRm.empty())
StackIntvl.MergeValueInAsValue(OrigLI, OrigVNI,
// Insert hoisted spills.
for (auto const &Insert : SpillsToIns) {
MachineBasicBlock *BB = Insert.first;
Register LiveReg = Insert.second;
MachineBasicBlock::iterator MII = IPA.getLastInsertPointIter(OrigLI, *BB);
MachineInstrSpan MIS(MII, BB);
TII.storeRegToStackSlot(*BB, MII, LiveReg, false, Slot,
MRI.getRegClass(LiveReg), &TRI);
LIS.InsertMachineInstrRangeInMaps(MIS.begin(), MII);
for (const MachineInstr &MI : make_range(MIS.begin(), MII))
getVDefInterval(MI, LIS);
// Remove redundant spills or change them to dead instructions.
NumSpills -= SpillsToRm.size();
for (auto const RMEnt : SpillsToRm) {
for (unsigned i = RMEnt->getNumOperands(); i; --i) {
MachineOperand &MO = RMEnt->getOperand(i - 1);
if (MO.isReg() && MO.isImplicit() && MO.isDef() && !MO.isDead())
RMEnt->RemoveOperand(i - 1);
Edit.eliminateDeadDefs(SpillsToRm, None, AA);
/// For VirtReg clone, the \p New register should have the same physreg or
/// stackslot as the \p old register.
void HoistSpillHelper::LRE_DidCloneVirtReg(Register New, Register Old) {
if (VRM.hasPhys(Old))
VRM.assignVirt2Phys(New, VRM.getPhys(Old));
else if (VRM.getStackSlot(Old) != VirtRegMap::NO_STACK_SLOT)
VRM.assignVirt2StackSlot(New, VRM.getStackSlot(Old));
llvm_unreachable("VReg should be assigned either physreg or stackslot");
if (VRM.hasShape(Old))
VRM.assignVirt2Shape(New, VRM.getShape(Old));