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llvm-project/llvm/lib/CodeGen/RenameIndependentSubregs.cpp

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//===-- RenameIndependentSubregs.cpp - Live Interval Analysis -------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
/// Rename independent subregisters looks for virtual registers with
/// independently used subregisters and renames them to new virtual registers.
/// Example: In the following:
/// %0:sub0<read-undef> = ...
/// %0:sub1 = ...
/// use %0:sub0
/// %0:sub0 = ...
/// use %0:sub0
/// use %0:sub1
/// sub0 and sub1 are never used together, and we have two independent sub0
/// definitions. This pass will rename to:
/// %0:sub0<read-undef> = ...
/// %1:sub1<read-undef> = ...
/// use %1:sub1
/// %2:sub1<read-undef> = ...
/// use %2:sub1
/// use %0:sub0
//
//===----------------------------------------------------------------------===//
#include "LiveRangeUtils.h"
#include "PHIEliminationUtils.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
using namespace llvm;
#define DEBUG_TYPE "rename-independent-subregs"
namespace {
class RenameIndependentSubregs : public MachineFunctionPass {
public:
static char ID;
RenameIndependentSubregs() : MachineFunctionPass(ID) {}
StringRef getPassName() const override {
return "Rename Disconnected Subregister Components";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<LiveIntervals>();
AU.addPreserved<LiveIntervals>();
AU.addRequired<SlotIndexes>();
AU.addPreserved<SlotIndexes>();
MachineFunctionPass::getAnalysisUsage(AU);
}
bool runOnMachineFunction(MachineFunction &MF) override;
private:
struct SubRangeInfo {
ConnectedVNInfoEqClasses ConEQ;
LiveInterval::SubRange *SR;
unsigned Index;
SubRangeInfo(LiveIntervals &LIS, LiveInterval::SubRange &SR,
unsigned Index)
: ConEQ(LIS), SR(&SR), Index(Index) {}
};
/// Split unrelated subregister components and rename them to new vregs.
bool renameComponents(LiveInterval &LI) const;
/// Build a vector of SubRange infos and a union find set of
/// equivalence classes.
/// Returns true if more than 1 equivalence class was found.
bool findComponents(IntEqClasses &Classes,
SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
LiveInterval &LI) const;
/// Distribute the LiveInterval segments into the new LiveIntervals
/// belonging to their class.
void distribute(const IntEqClasses &Classes,
const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
const SmallVectorImpl<LiveInterval*> &Intervals) const;
/// Constructs main liverange and add missing undef+dead flags.
void computeMainRangesFixFlags(const IntEqClasses &Classes,
const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
const SmallVectorImpl<LiveInterval*> &Intervals) const;
/// Rewrite Machine Operands to use the new vreg belonging to their class.
void rewriteOperands(const IntEqClasses &Classes,
const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
const SmallVectorImpl<LiveInterval*> &Intervals) const;
LiveIntervals *LIS;
MachineRegisterInfo *MRI;
const TargetInstrInfo *TII;
};
} // end anonymous namespace
char RenameIndependentSubregs::ID;
char &llvm::RenameIndependentSubregsID = RenameIndependentSubregs::ID;
INITIALIZE_PASS_BEGIN(RenameIndependentSubregs, DEBUG_TYPE,
"Rename Independent Subregisters", false, false)
INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_END(RenameIndependentSubregs, DEBUG_TYPE,
"Rename Independent Subregisters", false, false)
bool RenameIndependentSubregs::renameComponents(LiveInterval &LI) const {
// Shortcut: We cannot have split components with a single definition.
if (LI.valnos.size() < 2)
return false;
SmallVector<SubRangeInfo, 4> SubRangeInfos;
IntEqClasses Classes;
if (!findComponents(Classes, SubRangeInfos, LI))
return false;
// Create a new VReg for each class.
unsigned Reg = LI.reg;
const TargetRegisterClass *RegClass = MRI->getRegClass(Reg);
SmallVector<LiveInterval*, 4> Intervals;
Intervals.push_back(&LI);
LLVM_DEBUG(dbgs() << printReg(Reg) << ": Found " << Classes.getNumClasses()
<< " equivalence classes.\n");
LLVM_DEBUG(dbgs() << printReg(Reg) << ": Splitting into newly created:");
for (unsigned I = 1, NumClasses = Classes.getNumClasses(); I < NumClasses;
++I) {
unsigned NewVReg = MRI->createVirtualRegister(RegClass);
LiveInterval &NewLI = LIS->createEmptyInterval(NewVReg);
Intervals.push_back(&NewLI);
LLVM_DEBUG(dbgs() << ' ' << printReg(NewVReg));
}
LLVM_DEBUG(dbgs() << '\n');
rewriteOperands(Classes, SubRangeInfos, Intervals);
distribute(Classes, SubRangeInfos, Intervals);
computeMainRangesFixFlags(Classes, SubRangeInfos, Intervals);
return true;
}
bool RenameIndependentSubregs::findComponents(IntEqClasses &Classes,
SmallVectorImpl<RenameIndependentSubregs::SubRangeInfo> &SubRangeInfos,
LiveInterval &LI) const {
// First step: Create connected components for the VNInfos inside the
// subranges and count the global number of such components.
unsigned NumComponents = 0;
for (LiveInterval::SubRange &SR : LI.subranges()) {
SubRangeInfos.push_back(SubRangeInfo(*LIS, SR, NumComponents));
ConnectedVNInfoEqClasses &ConEQ = SubRangeInfos.back().ConEQ;
unsigned NumSubComponents = ConEQ.Classify(SR);
NumComponents += NumSubComponents;
}
// Shortcut: With only 1 subrange, the normal separate component tests are
// enough and we do not need to perform the union-find on the subregister
// segments.
if (SubRangeInfos.size() < 2)
return false;
// Next step: Build union-find structure over all subranges and merge classes
// across subranges when they are affected by the same MachineOperand.
const TargetRegisterInfo &TRI = *MRI->getTargetRegisterInfo();
Classes.grow(NumComponents);
unsigned Reg = LI.reg;
for (const MachineOperand &MO : MRI->reg_nodbg_operands(Reg)) {
if (!MO.isDef() && !MO.readsReg())
continue;
unsigned SubRegIdx = MO.getSubReg();
LaneBitmask LaneMask = TRI.getSubRegIndexLaneMask(SubRegIdx);
unsigned MergedID = ~0u;
for (RenameIndependentSubregs::SubRangeInfo &SRInfo : SubRangeInfos) {
const LiveInterval::SubRange &SR = *SRInfo.SR;
if ((SR.LaneMask & LaneMask).none())
continue;
SlotIndex Pos = LIS->getInstructionIndex(*MO.getParent());
Pos = MO.isDef() ? Pos.getRegSlot(MO.isEarlyClobber())
: Pos.getBaseIndex();
const VNInfo *VNI = SR.getVNInfoAt(Pos);
if (VNI == nullptr)
continue;
// Map to local representant ID.
unsigned LocalID = SRInfo.ConEQ.getEqClass(VNI);
// Global ID
unsigned ID = LocalID + SRInfo.Index;
// Merge other sets
MergedID = MergedID == ~0u ? ID : Classes.join(MergedID, ID);
}
}
// Early exit if we ended up with a single equivalence class.
Classes.compress();
unsigned NumClasses = Classes.getNumClasses();
return NumClasses > 1;
}
void RenameIndependentSubregs::rewriteOperands(const IntEqClasses &Classes,
const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
const SmallVectorImpl<LiveInterval*> &Intervals) const {
const TargetRegisterInfo &TRI = *MRI->getTargetRegisterInfo();
unsigned Reg = Intervals[0]->reg;
for (MachineRegisterInfo::reg_nodbg_iterator I = MRI->reg_nodbg_begin(Reg),
E = MRI->reg_nodbg_end(); I != E; ) {
MachineOperand &MO = *I++;
if (!MO.isDef() && !MO.readsReg())
continue;
auto *MI = MO.getParent();
SlotIndex Pos = LIS->getInstructionIndex(*MI);
Pos = MO.isDef() ? Pos.getRegSlot(MO.isEarlyClobber())
: Pos.getBaseIndex();
unsigned SubRegIdx = MO.getSubReg();
LaneBitmask LaneMask = TRI.getSubRegIndexLaneMask(SubRegIdx);
unsigned ID = ~0u;
for (const SubRangeInfo &SRInfo : SubRangeInfos) {
const LiveInterval::SubRange &SR = *SRInfo.SR;
if ((SR.LaneMask & LaneMask).none())
continue;
const VNInfo *VNI = SR.getVNInfoAt(Pos);
if (VNI == nullptr)
continue;
// Map to local representant ID.
unsigned LocalID = SRInfo.ConEQ.getEqClass(VNI);
// Global ID
ID = Classes[LocalID + SRInfo.Index];
break;
}
unsigned VReg = Intervals[ID]->reg;
MO.setReg(VReg);
if (MO.isTied() && Reg != VReg) {
/// Undef use operands are not tracked in the equivalence class,
/// but need to be updated if they are tied; take care to only
/// update the tied operand.
unsigned OperandNo = MI->getOperandNo(&MO);
unsigned TiedIdx = MI->findTiedOperandIdx(OperandNo);
MI->getOperand(TiedIdx).setReg(VReg);
// above substitution breaks the iterator, so restart.
I = MRI->reg_nodbg_begin(Reg);
}
}
// TODO: We could attempt to recompute new register classes while visiting
// the operands: Some of the split register may be fine with less constraint
// classes than the original vreg.
}
void RenameIndependentSubregs::distribute(const IntEqClasses &Classes,
const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
const SmallVectorImpl<LiveInterval*> &Intervals) const {
unsigned NumClasses = Classes.getNumClasses();
SmallVector<unsigned, 8> VNIMapping;
SmallVector<LiveInterval::SubRange*, 8> SubRanges;
BumpPtrAllocator &Allocator = LIS->getVNInfoAllocator();
for (const SubRangeInfo &SRInfo : SubRangeInfos) {
LiveInterval::SubRange &SR = *SRInfo.SR;
unsigned NumValNos = SR.valnos.size();
VNIMapping.clear();
VNIMapping.reserve(NumValNos);
SubRanges.clear();
SubRanges.resize(NumClasses-1, nullptr);
for (unsigned I = 0; I < NumValNos; ++I) {
const VNInfo &VNI = *SR.valnos[I];
unsigned LocalID = SRInfo.ConEQ.getEqClass(&VNI);
unsigned ID = Classes[LocalID + SRInfo.Index];
VNIMapping.push_back(ID);
if (ID > 0 && SubRanges[ID-1] == nullptr)
SubRanges[ID-1] = Intervals[ID]->createSubRange(Allocator, SR.LaneMask);
}
DistributeRange(SR, SubRanges.data(), VNIMapping);
}
}
static bool subRangeLiveAt(const LiveInterval &LI, SlotIndex Pos) {
for (const LiveInterval::SubRange &SR : LI.subranges()) {
if (SR.liveAt(Pos))
return true;
}
return false;
}
void RenameIndependentSubregs::computeMainRangesFixFlags(
const IntEqClasses &Classes,
const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
const SmallVectorImpl<LiveInterval*> &Intervals) const {
BumpPtrAllocator &Allocator = LIS->getVNInfoAllocator();
const SlotIndexes &Indexes = *LIS->getSlotIndexes();
for (size_t I = 0, E = Intervals.size(); I < E; ++I) {
LiveInterval &LI = *Intervals[I];
unsigned Reg = LI.reg;
LI.removeEmptySubRanges();
// There must be a def (or live-in) before every use. Splitting vregs may
// violate this principle as the splitted vreg may not have a definition on
// every path. Fix this by creating IMPLICIT_DEF instruction as necessary.
for (const LiveInterval::SubRange &SR : LI.subranges()) {
// Search for "PHI" value numbers in the subranges. We must find a live
// value in each predecessor block, add an IMPLICIT_DEF where it is
// missing.
for (unsigned I = 0; I < SR.valnos.size(); ++I) {
const VNInfo &VNI = *SR.valnos[I];
if (VNI.isUnused() || !VNI.isPHIDef())
continue;
SlotIndex Def = VNI.def;
MachineBasicBlock &MBB = *Indexes.getMBBFromIndex(Def);
for (MachineBasicBlock *PredMBB : MBB.predecessors()) {
SlotIndex PredEnd = Indexes.getMBBEndIdx(PredMBB);
if (subRangeLiveAt(LI, PredEnd.getPrevSlot()))
continue;
MachineBasicBlock::iterator InsertPos =
llvm::findPHICopyInsertPoint(PredMBB, &MBB, Reg);
const MCInstrDesc &MCDesc = TII->get(TargetOpcode::IMPLICIT_DEF);
MachineInstrBuilder ImpDef = BuildMI(*PredMBB, InsertPos,
DebugLoc(), MCDesc, Reg);
SlotIndex DefIdx = LIS->InsertMachineInstrInMaps(*ImpDef);
SlotIndex RegDefIdx = DefIdx.getRegSlot();
for (LiveInterval::SubRange &SR : LI.subranges()) {
VNInfo *SRVNI = SR.getNextValue(RegDefIdx, Allocator);
SR.addSegment(LiveRange::Segment(RegDefIdx, PredEnd, SRVNI));
}
}
}
}
for (MachineOperand &MO : MRI->reg_nodbg_operands(Reg)) {
if (!MO.isDef())
continue;
unsigned SubRegIdx = MO.getSubReg();
if (SubRegIdx == 0)
continue;
// After assigning the new vreg we may not have any other sublanes living
// in and out of the instruction anymore. We need to add new dead and
// undef flags in these cases.
if (!MO.isUndef()) {
SlotIndex Pos = LIS->getInstructionIndex(*MO.getParent());
if (!subRangeLiveAt(LI, Pos))
MO.setIsUndef();
}
if (!MO.isDead()) {
SlotIndex Pos = LIS->getInstructionIndex(*MO.getParent()).getDeadSlot();
if (!subRangeLiveAt(LI, Pos))
MO.setIsDead();
}
}
if (I == 0)
LI.clear();
LIS->constructMainRangeFromSubranges(LI);
// A def of a subregister may be a use of other register lanes. Replacing
// such a def with a def of a different register will eliminate the use,
// and may cause the recorded live range to be larger than the actual
// liveness in the program IR.
LIS->shrinkToUses(&LI);
}
}
bool RenameIndependentSubregs::runOnMachineFunction(MachineFunction &MF) {
// Skip renaming if liveness of subregister is not tracked.
MRI = &MF.getRegInfo();
if (!MRI->subRegLivenessEnabled())
return false;
LLVM_DEBUG(dbgs() << "Renaming independent subregister live ranges in "
<< MF.getName() << '\n');
LIS = &getAnalysis<LiveIntervals>();
TII = MF.getSubtarget().getInstrInfo();
// Iterate over all vregs. Note that we query getNumVirtRegs() the newly
// created vregs end up with higher numbers but do not need to be visited as
// there can't be any further splitting.
bool Changed = false;
for (size_t I = 0, E = MRI->getNumVirtRegs(); I < E; ++I) {
unsigned Reg = TargetRegisterInfo::index2VirtReg(I);
if (!LIS->hasInterval(Reg))
continue;
LiveInterval &LI = LIS->getInterval(Reg);
if (!LI.hasSubRanges())
continue;
Changed |= renameComponents(LI);
}
return Changed;
}
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