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llvm-mirror/lib/CodeGen/LiveVariables.cpp
Arnaud A. de Grandmaison eb77bb4c66 [LiveVariables] Improve isLiveOut runtime performances. NFC. 
On large goto table based interpreters, where phi nodes can have (very) large
fan-ins, isLiveOut exhibited poor performances: about 40% of the full
codegen time was spent in PHIElim, sorting MachineBasicBlock addresses.

This patch improve the performances for such cases, and does not show
compile time regressions on the LNT, at bootstrap (llvm+clang+lldb) or
any other benchmarks we have in-house.

llvm-svn: 239510
2015-06-11 07:50:21 +00:00

809 lines
29 KiB
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//===-- LiveVariables.cpp - Live Variable Analysis for Machine Code -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the LiveVariable analysis pass. For each machine
// instruction in the function, this pass calculates the set of registers that
// are immediately dead after the instruction (i.e., the instruction calculates
// the value, but it is never used) and the set of registers that are used by
// the instruction, but are never used after the instruction (i.e., they are
// killed).
//
// This class computes live variables using a sparse implementation based on
// the machine code SSA form. This class computes live variable information for
// each virtual and _register allocatable_ physical register in a function. It
// uses the dominance properties of SSA form to efficiently compute live
// variables for virtual registers, and assumes that physical registers are only
// live within a single basic block (allowing it to do a single local analysis
// to resolve physical register lifetimes in each basic block). If a physical
// register is not register allocatable, it is not tracked. This is useful for
// things like the stack pointer and condition codes.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include <algorithm>
using namespace llvm;
char LiveVariables::ID = 0;
char &llvm::LiveVariablesID = LiveVariables::ID;
INITIALIZE_PASS_BEGIN(LiveVariables, "livevars",
"Live Variable Analysis", false, false)
INITIALIZE_PASS_DEPENDENCY(UnreachableMachineBlockElim)
INITIALIZE_PASS_END(LiveVariables, "livevars",
"Live Variable Analysis", false, false)
void LiveVariables::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredID(UnreachableMachineBlockElimID);
AU.setPreservesAll();
MachineFunctionPass::getAnalysisUsage(AU);
}
MachineInstr *
LiveVariables::VarInfo::findKill(const MachineBasicBlock *MBB) const {
for (unsigned i = 0, e = Kills.size(); i != e; ++i)
if (Kills[i]->getParent() == MBB)
return Kills[i];
return nullptr;
}
void LiveVariables::VarInfo::dump() const {
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
dbgs() << " Alive in blocks: ";
for (SparseBitVector<>::iterator I = AliveBlocks.begin(),
E = AliveBlocks.end(); I != E; ++I)
dbgs() << *I << ", ";
dbgs() << "\n Killed by:";
if (Kills.empty())
dbgs() << " No instructions.\n";
else {
for (unsigned i = 0, e = Kills.size(); i != e; ++i)
dbgs() << "\n #" << i << ": " << *Kills[i];
dbgs() << "\n";
}
#endif
}
/// getVarInfo - Get (possibly creating) a VarInfo object for the given vreg.
LiveVariables::VarInfo &LiveVariables::getVarInfo(unsigned RegIdx) {
assert(TargetRegisterInfo::isVirtualRegister(RegIdx) &&
"getVarInfo: not a virtual register!");
VirtRegInfo.grow(RegIdx);
return VirtRegInfo[RegIdx];
}
void LiveVariables::MarkVirtRegAliveInBlock(VarInfo& VRInfo,
MachineBasicBlock *DefBlock,
MachineBasicBlock *MBB,
std::vector<MachineBasicBlock*> &WorkList) {
unsigned BBNum = MBB->getNumber();
// Check to see if this basic block is one of the killing blocks. If so,
// remove it.
for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i)
if (VRInfo.Kills[i]->getParent() == MBB) {
VRInfo.Kills.erase(VRInfo.Kills.begin()+i); // Erase entry
break;
}
if (MBB == DefBlock) return; // Terminate recursion
if (VRInfo.AliveBlocks.test(BBNum))
return; // We already know the block is live
// Mark the variable known alive in this bb
VRInfo.AliveBlocks.set(BBNum);
assert(MBB != &MF->front() && "Can't find reaching def for virtreg");
WorkList.insert(WorkList.end(), MBB->pred_rbegin(), MBB->pred_rend());
}
void LiveVariables::MarkVirtRegAliveInBlock(VarInfo &VRInfo,
MachineBasicBlock *DefBlock,
MachineBasicBlock *MBB) {
std::vector<MachineBasicBlock*> WorkList;
MarkVirtRegAliveInBlock(VRInfo, DefBlock, MBB, WorkList);
while (!WorkList.empty()) {
MachineBasicBlock *Pred = WorkList.back();
WorkList.pop_back();
MarkVirtRegAliveInBlock(VRInfo, DefBlock, Pred, WorkList);
}
}
void LiveVariables::HandleVirtRegUse(unsigned reg, MachineBasicBlock *MBB,
MachineInstr *MI) {
assert(MRI->getVRegDef(reg) && "Register use before def!");
unsigned BBNum = MBB->getNumber();
VarInfo& VRInfo = getVarInfo(reg);
// Check to see if this basic block is already a kill block.
if (!VRInfo.Kills.empty() && VRInfo.Kills.back()->getParent() == MBB) {
// Yes, this register is killed in this basic block already. Increase the
// live range by updating the kill instruction.
VRInfo.Kills.back() = MI;
return;
}
#ifndef NDEBUG
for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i)
assert(VRInfo.Kills[i]->getParent() != MBB && "entry should be at end!");
#endif
// This situation can occur:
//
// ,------.
// | |
// | v
// | t2 = phi ... t1 ...
// | |
// | v
// | t1 = ...
// | ... = ... t1 ...
// | |
// `------'
//
// where there is a use in a PHI node that's a predecessor to the defining
// block. We don't want to mark all predecessors as having the value "alive"
// in this case.
if (MBB == MRI->getVRegDef(reg)->getParent()) return;
// Add a new kill entry for this basic block. If this virtual register is
// already marked as alive in this basic block, that means it is alive in at
// least one of the successor blocks, it's not a kill.
if (!VRInfo.AliveBlocks.test(BBNum))
VRInfo.Kills.push_back(MI);
// Update all dominating blocks to mark them as "known live".
for (MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(),
E = MBB->pred_end(); PI != E; ++PI)
MarkVirtRegAliveInBlock(VRInfo, MRI->getVRegDef(reg)->getParent(), *PI);
}
void LiveVariables::HandleVirtRegDef(unsigned Reg, MachineInstr *MI) {
VarInfo &VRInfo = getVarInfo(Reg);
if (VRInfo.AliveBlocks.empty())
// If vr is not alive in any block, then defaults to dead.
VRInfo.Kills.push_back(MI);
}
/// FindLastPartialDef - Return the last partial def of the specified register.
/// Also returns the sub-registers that're defined by the instruction.
MachineInstr *LiveVariables::FindLastPartialDef(unsigned Reg,
SmallSet<unsigned,4> &PartDefRegs) {
unsigned LastDefReg = 0;
unsigned LastDefDist = 0;
MachineInstr *LastDef = nullptr;
for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
unsigned SubReg = *SubRegs;
MachineInstr *Def = PhysRegDef[SubReg];
if (!Def)
continue;
unsigned Dist = DistanceMap[Def];
if (Dist > LastDefDist) {
LastDefReg = SubReg;
LastDef = Def;
LastDefDist = Dist;
}
}
if (!LastDef)
return nullptr;
PartDefRegs.insert(LastDefReg);
for (unsigned i = 0, e = LastDef->getNumOperands(); i != e; ++i) {
MachineOperand &MO = LastDef->getOperand(i);
if (!MO.isReg() || !MO.isDef() || MO.getReg() == 0)
continue;
unsigned DefReg = MO.getReg();
if (TRI->isSubRegister(Reg, DefReg)) {
for (MCSubRegIterator SubRegs(DefReg, TRI, /*IncludeSelf=*/true);
SubRegs.isValid(); ++SubRegs)
PartDefRegs.insert(*SubRegs);
}
}
return LastDef;
}
/// HandlePhysRegUse - Turn previous partial def's into read/mod/writes. Add
/// implicit defs to a machine instruction if there was an earlier def of its
/// super-register.
void LiveVariables::HandlePhysRegUse(unsigned Reg, MachineInstr *MI) {
MachineInstr *LastDef = PhysRegDef[Reg];
// If there was a previous use or a "full" def all is well.
if (!LastDef && !PhysRegUse[Reg]) {
// Otherwise, the last sub-register def implicitly defines this register.
// e.g.
// AH =
// AL = ... <imp-def EAX>, <imp-kill AH>
// = AH
// ...
// = EAX
// All of the sub-registers must have been defined before the use of Reg!
SmallSet<unsigned, 4> PartDefRegs;
MachineInstr *LastPartialDef = FindLastPartialDef(Reg, PartDefRegs);
// If LastPartialDef is NULL, it must be using a livein register.
if (LastPartialDef) {
LastPartialDef->addOperand(MachineOperand::CreateReg(Reg, true/*IsDef*/,
true/*IsImp*/));
PhysRegDef[Reg] = LastPartialDef;
SmallSet<unsigned, 8> Processed;
for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
unsigned SubReg = *SubRegs;
if (Processed.count(SubReg))
continue;
if (PartDefRegs.count(SubReg))
continue;
// This part of Reg was defined before the last partial def. It's killed
// here.
LastPartialDef->addOperand(MachineOperand::CreateReg(SubReg,
false/*IsDef*/,
true/*IsImp*/));
PhysRegDef[SubReg] = LastPartialDef;
for (MCSubRegIterator SS(SubReg, TRI); SS.isValid(); ++SS)
Processed.insert(*SS);
}
}
} else if (LastDef && !PhysRegUse[Reg] &&
!LastDef->findRegisterDefOperand(Reg))
// Last def defines the super register, add an implicit def of reg.
LastDef->addOperand(MachineOperand::CreateReg(Reg, true/*IsDef*/,
true/*IsImp*/));
// Remember this use.
for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
SubRegs.isValid(); ++SubRegs)
PhysRegUse[*SubRegs] = MI;
}
/// FindLastRefOrPartRef - Return the last reference or partial reference of
/// the specified register.
MachineInstr *LiveVariables::FindLastRefOrPartRef(unsigned Reg) {
MachineInstr *LastDef = PhysRegDef[Reg];
MachineInstr *LastUse = PhysRegUse[Reg];
if (!LastDef && !LastUse)
return nullptr;
MachineInstr *LastRefOrPartRef = LastUse ? LastUse : LastDef;
unsigned LastRefOrPartRefDist = DistanceMap[LastRefOrPartRef];
unsigned LastPartDefDist = 0;
for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
unsigned SubReg = *SubRegs;
MachineInstr *Def = PhysRegDef[SubReg];
if (Def && Def != LastDef) {
// There was a def of this sub-register in between. This is a partial
// def, keep track of the last one.
unsigned Dist = DistanceMap[Def];
if (Dist > LastPartDefDist)
LastPartDefDist = Dist;
} else if (MachineInstr *Use = PhysRegUse[SubReg]) {
unsigned Dist = DistanceMap[Use];
if (Dist > LastRefOrPartRefDist) {
LastRefOrPartRefDist = Dist;
LastRefOrPartRef = Use;
}
}
}
return LastRefOrPartRef;
}
bool LiveVariables::HandlePhysRegKill(unsigned Reg, MachineInstr *MI) {
MachineInstr *LastDef = PhysRegDef[Reg];
MachineInstr *LastUse = PhysRegUse[Reg];
if (!LastDef && !LastUse)
return false;
MachineInstr *LastRefOrPartRef = LastUse ? LastUse : LastDef;
unsigned LastRefOrPartRefDist = DistanceMap[LastRefOrPartRef];
// The whole register is used.
// AL =
// AH =
//
// = AX
// = AL, AX<imp-use, kill>
// AX =
//
// Or whole register is defined, but not used at all.
// AX<dead> =
// ...
// AX =
//
// Or whole register is defined, but only partly used.
// AX<dead> = AL<imp-def>
// = AL<kill>
// AX =
MachineInstr *LastPartDef = nullptr;
unsigned LastPartDefDist = 0;
SmallSet<unsigned, 8> PartUses;
for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
unsigned SubReg = *SubRegs;
MachineInstr *Def = PhysRegDef[SubReg];
if (Def && Def != LastDef) {
// There was a def of this sub-register in between. This is a partial
// def, keep track of the last one.
unsigned Dist = DistanceMap[Def];
if (Dist > LastPartDefDist) {
LastPartDefDist = Dist;
LastPartDef = Def;
}
continue;
}
if (MachineInstr *Use = PhysRegUse[SubReg]) {
for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true); SS.isValid();
++SS)
PartUses.insert(*SS);
unsigned Dist = DistanceMap[Use];
if (Dist > LastRefOrPartRefDist) {
LastRefOrPartRefDist = Dist;
LastRefOrPartRef = Use;
}
}
}
if (!PhysRegUse[Reg]) {
// Partial uses. Mark register def dead and add implicit def of
// sub-registers which are used.
// EAX<dead> = op AL<imp-def>
// That is, EAX def is dead but AL def extends pass it.
PhysRegDef[Reg]->addRegisterDead(Reg, TRI, true);
for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
unsigned SubReg = *SubRegs;
if (!PartUses.count(SubReg))
continue;
bool NeedDef = true;
if (PhysRegDef[Reg] == PhysRegDef[SubReg]) {
MachineOperand *MO = PhysRegDef[Reg]->findRegisterDefOperand(SubReg);
if (MO) {
NeedDef = false;
assert(!MO->isDead());
}
}
if (NeedDef)
PhysRegDef[Reg]->addOperand(MachineOperand::CreateReg(SubReg,
true/*IsDef*/, true/*IsImp*/));
MachineInstr *LastSubRef = FindLastRefOrPartRef(SubReg);
if (LastSubRef)
LastSubRef->addRegisterKilled(SubReg, TRI, true);
else {
LastRefOrPartRef->addRegisterKilled(SubReg, TRI, true);
for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true);
SS.isValid(); ++SS)
PhysRegUse[*SS] = LastRefOrPartRef;
}
for (MCSubRegIterator SS(SubReg, TRI); SS.isValid(); ++SS)
PartUses.erase(*SS);
}
} else if (LastRefOrPartRef == PhysRegDef[Reg] && LastRefOrPartRef != MI) {
if (LastPartDef)
// The last partial def kills the register.
LastPartDef->addOperand(MachineOperand::CreateReg(Reg, false/*IsDef*/,
true/*IsImp*/, true/*IsKill*/));
else {
MachineOperand *MO =
LastRefOrPartRef->findRegisterDefOperand(Reg, false, TRI);
bool NeedEC = MO->isEarlyClobber() && MO->getReg() != Reg;
// If the last reference is the last def, then it's not used at all.
// That is, unless we are currently processing the last reference itself.
LastRefOrPartRef->addRegisterDead(Reg, TRI, true);
if (NeedEC) {
// If we are adding a subreg def and the superreg def is marked early
// clobber, add an early clobber marker to the subreg def.
MO = LastRefOrPartRef->findRegisterDefOperand(Reg);
if (MO)
MO->setIsEarlyClobber();
}
}
} else
LastRefOrPartRef->addRegisterKilled(Reg, TRI, true);
return true;
}
void LiveVariables::HandleRegMask(const MachineOperand &MO) {
// Call HandlePhysRegKill() for all live registers clobbered by Mask.
// Clobbered registers are always dead, sp there is no need to use
// HandlePhysRegDef().
for (unsigned Reg = 1, NumRegs = TRI->getNumRegs(); Reg != NumRegs; ++Reg) {
// Skip dead regs.
if (!PhysRegDef[Reg] && !PhysRegUse[Reg])
continue;
// Skip mask-preserved regs.
if (!MO.clobbersPhysReg(Reg))
continue;
// Kill the largest clobbered super-register.
// This avoids needless implicit operands.
unsigned Super = Reg;
for (MCSuperRegIterator SR(Reg, TRI); SR.isValid(); ++SR)
if ((PhysRegDef[*SR] || PhysRegUse[*SR]) && MO.clobbersPhysReg(*SR))
Super = *SR;
HandlePhysRegKill(Super, nullptr);
}
}
void LiveVariables::HandlePhysRegDef(unsigned Reg, MachineInstr *MI,
SmallVectorImpl<unsigned> &Defs) {
// What parts of the register are previously defined?
SmallSet<unsigned, 32> Live;
if (PhysRegDef[Reg] || PhysRegUse[Reg]) {
for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
SubRegs.isValid(); ++SubRegs)
Live.insert(*SubRegs);
} else {
for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
unsigned SubReg = *SubRegs;
// If a register isn't itself defined, but all parts that make up of it
// are defined, then consider it also defined.
// e.g.
// AL =
// AH =
// = AX
if (Live.count(SubReg))
continue;
if (PhysRegDef[SubReg] || PhysRegUse[SubReg]) {
for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true);
SS.isValid(); ++SS)
Live.insert(*SS);
}
}
}
// Start from the largest piece, find the last time any part of the register
// is referenced.
HandlePhysRegKill(Reg, MI);
// Only some of the sub-registers are used.
for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
unsigned SubReg = *SubRegs;
if (!Live.count(SubReg))
// Skip if this sub-register isn't defined.
continue;
HandlePhysRegKill(SubReg, MI);
}
if (MI)
Defs.push_back(Reg); // Remember this def.
}
void LiveVariables::UpdatePhysRegDefs(MachineInstr *MI,
SmallVectorImpl<unsigned> &Defs) {
while (!Defs.empty()) {
unsigned Reg = Defs.back();
Defs.pop_back();
for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
SubRegs.isValid(); ++SubRegs) {
unsigned SubReg = *SubRegs;
PhysRegDef[SubReg] = MI;
PhysRegUse[SubReg] = nullptr;
}
}
}
void LiveVariables::runOnInstr(MachineInstr *MI,
SmallVectorImpl<unsigned> &Defs) {
assert(!MI->isDebugValue());
// Process all of the operands of the instruction...
unsigned NumOperandsToProcess = MI->getNumOperands();
// Unless it is a PHI node. In this case, ONLY process the DEF, not any
// of the uses. They will be handled in other basic blocks.
if (MI->isPHI())
NumOperandsToProcess = 1;
// Clear kill and dead markers. LV will recompute them.
SmallVector<unsigned, 4> UseRegs;
SmallVector<unsigned, 4> DefRegs;
SmallVector<unsigned, 1> RegMasks;
for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isRegMask()) {
RegMasks.push_back(i);
continue;
}
if (!MO.isReg() || MO.getReg() == 0)
continue;
unsigned MOReg = MO.getReg();
if (MO.isUse()) {
MO.setIsKill(false);
if (MO.readsReg())
UseRegs.push_back(MOReg);
} else /*MO.isDef()*/ {
MO.setIsDead(false);
DefRegs.push_back(MOReg);
}
}
MachineBasicBlock *MBB = MI->getParent();
// Process all uses.
for (unsigned i = 0, e = UseRegs.size(); i != e; ++i) {
unsigned MOReg = UseRegs[i];
if (TargetRegisterInfo::isVirtualRegister(MOReg))
HandleVirtRegUse(MOReg, MBB, MI);
else if (!MRI->isReserved(MOReg))
HandlePhysRegUse(MOReg, MI);
}
// Process all masked registers. (Call clobbers).
for (unsigned i = 0, e = RegMasks.size(); i != e; ++i)
HandleRegMask(MI->getOperand(RegMasks[i]));
// Process all defs.
for (unsigned i = 0, e = DefRegs.size(); i != e; ++i) {
unsigned MOReg = DefRegs[i];
if (TargetRegisterInfo::isVirtualRegister(MOReg))
HandleVirtRegDef(MOReg, MI);
else if (!MRI->isReserved(MOReg))
HandlePhysRegDef(MOReg, MI, Defs);
}
UpdatePhysRegDefs(MI, Defs);
}
void LiveVariables::runOnBlock(MachineBasicBlock *MBB, const unsigned NumRegs) {
// Mark live-in registers as live-in.
SmallVector<unsigned, 4> Defs;
for (MachineBasicBlock::livein_iterator II = MBB->livein_begin(),
EE = MBB->livein_end(); II != EE; ++II) {
assert(TargetRegisterInfo::isPhysicalRegister(*II) &&
"Cannot have a live-in virtual register!");
HandlePhysRegDef(*II, nullptr, Defs);
}
// Loop over all of the instructions, processing them.
DistanceMap.clear();
unsigned Dist = 0;
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
I != E; ++I) {
MachineInstr *MI = I;
if (MI->isDebugValue())
continue;
DistanceMap.insert(std::make_pair(MI, Dist++));
runOnInstr(MI, Defs);
}
// Handle any virtual assignments from PHI nodes which might be at the
// bottom of this basic block. We check all of our successor blocks to see
// if they have PHI nodes, and if so, we simulate an assignment at the end
// of the current block.
if (!PHIVarInfo[MBB->getNumber()].empty()) {
SmallVectorImpl<unsigned> &VarInfoVec = PHIVarInfo[MBB->getNumber()];
for (SmallVectorImpl<unsigned>::iterator I = VarInfoVec.begin(),
E = VarInfoVec.end(); I != E; ++I)
// Mark it alive only in the block we are representing.
MarkVirtRegAliveInBlock(getVarInfo(*I),MRI->getVRegDef(*I)->getParent(),
MBB);
}
// MachineCSE may CSE instructions which write to non-allocatable physical
// registers across MBBs. Remember if any reserved register is liveout.
SmallSet<unsigned, 4> LiveOuts;
for (MachineBasicBlock::const_succ_iterator SI = MBB->succ_begin(),
SE = MBB->succ_end(); SI != SE; ++SI) {
MachineBasicBlock *SuccMBB = *SI;
if (SuccMBB->isLandingPad())
continue;
for (MachineBasicBlock::livein_iterator LI = SuccMBB->livein_begin(),
LE = SuccMBB->livein_end(); LI != LE; ++LI) {
unsigned LReg = *LI;
if (!TRI->isInAllocatableClass(LReg))
// Ignore other live-ins, e.g. those that are live into landing pads.
LiveOuts.insert(LReg);
}
}
// Loop over PhysRegDef / PhysRegUse, killing any registers that are
// available at the end of the basic block.
for (unsigned i = 0; i != NumRegs; ++i)
if ((PhysRegDef[i] || PhysRegUse[i]) && !LiveOuts.count(i))
HandlePhysRegDef(i, nullptr, Defs);
}
bool LiveVariables::runOnMachineFunction(MachineFunction &mf) {
MF = &mf;
MRI = &mf.getRegInfo();
TRI = MF->getSubtarget().getRegisterInfo();
const unsigned NumRegs = TRI->getNumRegs();
PhysRegDef.assign(NumRegs, nullptr);
PhysRegUse.assign(NumRegs, nullptr);
PHIVarInfo.resize(MF->getNumBlockIDs());
PHIJoins.clear();
// FIXME: LiveIntervals will be updated to remove its dependence on
// LiveVariables to improve compilation time and eliminate bizarre pass
// dependencies. Until then, we can't change much in -O0.
if (!MRI->isSSA())
report_fatal_error("regalloc=... not currently supported with -O0");
analyzePHINodes(mf);
// Calculate live variable information in depth first order on the CFG of the
// function. This guarantees that we will see the definition of a virtual
// register before its uses due to dominance properties of SSA (except for PHI
// nodes, which are treated as a special case).
MachineBasicBlock *Entry = MF->begin();
SmallPtrSet<MachineBasicBlock*,16> Visited;
for (MachineBasicBlock *MBB : depth_first_ext(Entry, Visited)) {
runOnBlock(MBB, NumRegs);
PhysRegDef.assign(NumRegs, nullptr);
PhysRegUse.assign(NumRegs, nullptr);
}
// Convert and transfer the dead / killed information we have gathered into
// VirtRegInfo onto MI's.
for (unsigned i = 0, e1 = VirtRegInfo.size(); i != e1; ++i) {
const unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
for (unsigned j = 0, e2 = VirtRegInfo[Reg].Kills.size(); j != e2; ++j)
if (VirtRegInfo[Reg].Kills[j] == MRI->getVRegDef(Reg))
VirtRegInfo[Reg].Kills[j]->addRegisterDead(Reg, TRI);
else
VirtRegInfo[Reg].Kills[j]->addRegisterKilled(Reg, TRI);
}
// Check to make sure there are no unreachable blocks in the MC CFG for the
// function. If so, it is due to a bug in the instruction selector or some
// other part of the code generator if this happens.
#ifndef NDEBUG
for(MachineFunction::iterator i = MF->begin(), e = MF->end(); i != e; ++i)
assert(Visited.count(&*i) != 0 && "unreachable basic block found");
#endif
PhysRegDef.clear();
PhysRegUse.clear();
PHIVarInfo.clear();
return false;
}
/// replaceKillInstruction - Update register kill info by replacing a kill
/// instruction with a new one.
void LiveVariables::replaceKillInstruction(unsigned Reg, MachineInstr *OldMI,
MachineInstr *NewMI) {
VarInfo &VI = getVarInfo(Reg);
std::replace(VI.Kills.begin(), VI.Kills.end(), OldMI, NewMI);
}
/// removeVirtualRegistersKilled - Remove all killed info for the specified
/// instruction.
void LiveVariables::removeVirtualRegistersKilled(MachineInstr *MI) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isKill()) {
MO.setIsKill(false);
unsigned Reg = MO.getReg();
if (TargetRegisterInfo::isVirtualRegister(Reg)) {
bool removed = getVarInfo(Reg).removeKill(MI);
assert(removed && "kill not in register's VarInfo?");
(void)removed;
}
}
}
}
/// analyzePHINodes - Gather information about the PHI nodes in here. In
/// particular, we want to map the variable information of a virtual register
/// which is used in a PHI node. We map that to the BB the vreg is coming from.
///
void LiveVariables::analyzePHINodes(const MachineFunction& Fn) {
for (const auto &MBB : Fn)
for (const auto &BBI : MBB) {
if (!BBI.isPHI())
break;
for (unsigned i = 1, e = BBI.getNumOperands(); i != e; i += 2)
if (BBI.getOperand(i).readsReg())
PHIVarInfo[BBI.getOperand(i + 1).getMBB()->getNumber()]
.push_back(BBI.getOperand(i).getReg());
}
}
bool LiveVariables::VarInfo::isLiveIn(const MachineBasicBlock &MBB,
unsigned Reg,
MachineRegisterInfo &MRI) {
unsigned Num = MBB.getNumber();
// Reg is live-through.
if (AliveBlocks.test(Num))
return true;
// Registers defined in MBB cannot be live in.
const MachineInstr *Def = MRI.getVRegDef(Reg);
if (Def && Def->getParent() == &MBB)
return false;
// Reg was not defined in MBB, was it killed here?
return findKill(&MBB);
}
bool LiveVariables::isLiveOut(unsigned Reg, const MachineBasicBlock &MBB) {
LiveVariables::VarInfo &VI = getVarInfo(Reg);
SmallPtrSet<const MachineBasicBlock *, 8> Kills;
for (unsigned i = 0, e = VI.Kills.size(); i != e; ++i)
Kills.insert(VI.Kills[i]->getParent());
// Loop over all of the successors of the basic block, checking to see if
// the value is either live in the block, or if it is killed in the block.
for (const MachineBasicBlock *SuccMBB : MBB.successors()) {
// Is it alive in this successor?
unsigned SuccIdx = SuccMBB->getNumber();
if (VI.AliveBlocks.test(SuccIdx))
return true;
// Or is it live because there is a use in a successor that kills it?
if (Kills.count(SuccMBB))
return true;
}
return false;
}
/// addNewBlock - Add a new basic block BB as an empty succcessor to DomBB. All
/// variables that are live out of DomBB will be marked as passing live through
/// BB.
void LiveVariables::addNewBlock(MachineBasicBlock *BB,
MachineBasicBlock *DomBB,
MachineBasicBlock *SuccBB) {
const unsigned NumNew = BB->getNumber();
SmallSet<unsigned, 16> Defs, Kills;
MachineBasicBlock::iterator BBI = SuccBB->begin(), BBE = SuccBB->end();
for (; BBI != BBE && BBI->isPHI(); ++BBI) {
// Record the def of the PHI node.
Defs.insert(BBI->getOperand(0).getReg());
// All registers used by PHI nodes in SuccBB must be live through BB.
for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2)
if (BBI->getOperand(i+1).getMBB() == BB)
getVarInfo(BBI->getOperand(i).getReg()).AliveBlocks.set(NumNew);
}
// Record all vreg defs and kills of all instructions in SuccBB.
for (; BBI != BBE; ++BBI) {
for (MachineInstr::mop_iterator I = BBI->operands_begin(),
E = BBI->operands_end(); I != E; ++I) {
if (I->isReg() && TargetRegisterInfo::isVirtualRegister(I->getReg())) {
if (I->isDef())
Defs.insert(I->getReg());
else if (I->isKill())
Kills.insert(I->getReg());
}
}
}
// Update info for all live variables
for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
// If the Defs is defined in the successor it can't be live in BB.
if (Defs.count(Reg))
continue;
// If the register is either killed in or live through SuccBB it's also live
// through BB.
VarInfo &VI = getVarInfo(Reg);
if (Kills.count(Reg) || VI.AliveBlocks.test(SuccBB->getNumber()))
VI.AliveBlocks.set(NumNew);
}
}
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