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llvm/lib/CodeGen/LiveVariables.cpp
Owen Anderson 2ab36d3502 Begin adding static dependence information to passes, which will allow us to 
perform initialization without static constructors AND without explicit initialization
by the client.  For the moment, passes are required to initialize both their
(potential) dependencies and any passes they preserve.  I hope to be able to relax
the latter requirement in the future.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@116334 91177308-0d34-0410-b5e6-96231b3b80d8
2010-10-12 19:48:12 +00:00

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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 are 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/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
using namespace llvm;
char LiveVariables::ID = 0;
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 NULL;
}
void LiveVariables::VarInfo::dump() const {
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";
}
}
/// 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!");
RegIdx -= TargetRegisterInfo::FirstVirtualRegister;
if (RegIdx >= VirtRegInfo.size()) {
if (RegIdx >= 2*VirtRegInfo.size())
VirtRegInfo.resize(RegIdx*2);
else
VirtRegInfo.resize(2*VirtRegInfo.size());
}
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);
for (MachineBasicBlock::const_pred_reverse_iterator PI = MBB->pred_rbegin(),
E = MBB->pred_rend(); PI != E; ++PI)
WorkList.push_back(*PI);
}
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);
VRInfo.NumUses++;
// 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 = NULL;
for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++SubRegs) {
MachineInstr *Def = PhysRegDef[SubReg];
if (!Def)
continue;
unsigned Dist = DistanceMap[Def];
if (Dist > LastDefDist) {
LastDefReg = SubReg;
LastDef = Def;
LastDefDist = Dist;
}
}
if (!LastDef)
return 0;
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)) {
PartDefRegs.insert(DefReg);
for (const unsigned *SubRegs = TRI->getSubRegisters(DefReg);
unsigned SubReg = *SubRegs; ++SubRegs)
PartDefRegs.insert(SubReg);
}
}
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 (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++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 (const unsigned *SS = TRI->getSubRegisters(SubReg); *SS; ++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.
PhysRegUse[Reg] = MI;
for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++SubRegs)
PhysRegUse[SubReg] = 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 0;
MachineInstr *LastRefOrPartRef = LastUse ? LastUse : LastDef;
unsigned LastRefOrPartRefDist = DistanceMap[LastRefOrPartRef];
unsigned LastPartDefDist = 0;
for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++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 = 0;
unsigned LastPartDefDist = 0;
SmallSet<unsigned, 8> PartUses;
for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++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]) {
PartUses.insert(SubReg);
for (const unsigned *SS = TRI->getSubRegisters(SubReg); *SS; ++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 (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++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);
PhysRegUse[SubReg] = LastRefOrPartRef;
for (const unsigned *SSRegs = TRI->getSubRegisters(SubReg);
unsigned SSReg = *SSRegs; ++SSRegs)
PhysRegUse[SSReg] = LastRefOrPartRef;
}
for (const unsigned *SS = TRI->getSubRegisters(SubReg); *SS; ++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::HandlePhysRegDef(unsigned Reg, MachineInstr *MI,
SmallVector<unsigned, 4> &Defs) {
// What parts of the register are previously defined?
SmallSet<unsigned, 32> Live;
if (PhysRegDef[Reg] || PhysRegUse[Reg]) {
Live.insert(Reg);
for (const unsigned *SS = TRI->getSubRegisters(Reg); *SS; ++SS)
Live.insert(*SS);
} else {
for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++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]) {
Live.insert(SubReg);
for (const unsigned *SS = TRI->getSubRegisters(SubReg); *SS; ++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 (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++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,
SmallVector<unsigned, 4> &Defs) {
while (!Defs.empty()) {
unsigned Reg = Defs.back();
Defs.pop_back();
PhysRegDef[Reg] = MI;
PhysRegUse[Reg] = NULL;
for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
unsigned SubReg = *SubRegs; ++SubRegs) {
PhysRegDef[SubReg] = MI;
PhysRegUse[SubReg] = NULL;
}
}
}
bool LiveVariables::runOnMachineFunction(MachineFunction &mf) {
MF = &mf;
MRI = &mf.getRegInfo();
TRI = MF->getTarget().getRegisterInfo();
ReservedRegisters = TRI->getReservedRegs(mf);
unsigned NumRegs = TRI->getNumRegs();
PhysRegDef = new MachineInstr*[NumRegs];
PhysRegUse = new MachineInstr*[NumRegs];
PHIVarInfo = new SmallVector<unsigned, 4>[MF->getNumBlockIDs()];
std::fill(PhysRegDef, PhysRegDef + NumRegs, (MachineInstr*)0);
std::fill(PhysRegUse, PhysRegUse + NumRegs, (MachineInstr*)0);
PHIJoins.clear();
/// Get some space for a respectable number of registers.
VirtRegInfo.resize(64);
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 (df_ext_iterator<MachineBasicBlock*, SmallPtrSet<MachineBasicBlock*,16> >
DFI = df_ext_begin(Entry, Visited), E = df_ext_end(Entry, Visited);
DFI != E; ++DFI) {
MachineBasicBlock *MBB = *DFI;
// 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, 0, 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++));
// 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;
for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || MO.getReg() == 0)
continue;
unsigned MOReg = MO.getReg();
if (MO.isUse()) {
MO.setIsKill(false);
UseRegs.push_back(MOReg);
} else /*MO.isDef()*/ {
MO.setIsDead(false);
DefRegs.push_back(MOReg);
}
}
// 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 (!ReservedRegisters[MOReg])
HandlePhysRegUse(MOReg, MI);
}
// 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 (!ReservedRegisters[MOReg])
HandlePhysRegDef(MOReg, MI, Defs);
}
UpdatePhysRegDefs(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()) {
SmallVector<unsigned, 4>& VarInfoVec = PHIVarInfo[MBB->getNumber()];
for (SmallVector<unsigned, 4>::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);
}
// Finally, if the last instruction in the block is a return, make sure to
// mark it as using all of the live-out values in the function.
// Things marked both call and return are tail calls; do not do this for
// them. The tail callee need not take the same registers as input
// that it produces as output, and there are dependencies for its input
// registers elsewhere.
if (!MBB->empty() && MBB->back().getDesc().isReturn()
&& !MBB->back().getDesc().isCall()) {
MachineInstr *Ret = &MBB->back();
for (MachineRegisterInfo::liveout_iterator
I = MF->getRegInfo().liveout_begin(),
E = MF->getRegInfo().liveout_end(); I != E; ++I) {
assert(TargetRegisterInfo::isPhysicalRegister(*I) &&
"Cannot have a live-out virtual register!");
HandlePhysRegUse(*I, Ret);
// Add live-out registers as implicit uses.
if (!Ret->readsRegister(*I))
Ret->addOperand(MachineOperand::CreateReg(*I, false, true));
}
}
// 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])
HandlePhysRegDef(i, 0, Defs);
std::fill(PhysRegDef, PhysRegDef + NumRegs, (MachineInstr*)0);
std::fill(PhysRegUse, PhysRegUse + NumRegs, (MachineInstr*)0);
}
// 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)
for (unsigned j = 0, e2 = VirtRegInfo[i].Kills.size(); j != e2; ++j)
if (VirtRegInfo[i].Kills[j] ==
MRI->getVRegDef(i + TargetRegisterInfo::FirstVirtualRegister))
VirtRegInfo[i]
.Kills[j]->addRegisterDead(i +
TargetRegisterInfo::FirstVirtualRegister,
TRI);
else
VirtRegInfo[i]
.Kills[j]->addRegisterKilled(i +
TargetRegisterInfo::FirstVirtualRegister,
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
delete[] PhysRegDef;
delete[] PhysRegUse;
delete[] PHIVarInfo;
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?");
removed = true;
}
}
}
}
/// 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 (MachineFunction::const_iterator I = Fn.begin(), E = Fn.end();
I != E; ++I)
for (MachineBasicBlock::const_iterator BBI = I->begin(), BBE = I->end();
BBI != BBE && BBI->isPHI(); ++BBI)
for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2)
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);
// 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.
std::vector<MachineBasicBlock*> OpSuccBlocks;
for (MachineBasicBlock::const_succ_iterator SI = MBB.succ_begin(),
E = MBB.succ_end(); SI != E; ++SI) {
MachineBasicBlock *SuccMBB = *SI;
// Is it alive in this successor?
unsigned SuccIdx = SuccMBB->getNumber();
if (VI.AliveBlocks.test(SuccIdx))
return true;
OpSuccBlocks.push_back(SuccMBB);
}
// Check to see if this value is live because there is a use in a successor
// that kills it.
switch (OpSuccBlocks.size()) {
case 1: {
MachineBasicBlock *SuccMBB = OpSuccBlocks[0];
for (unsigned i = 0, e = VI.Kills.size(); i != e; ++i)
if (VI.Kills[i]->getParent() == SuccMBB)
return true;
break;
}
case 2: {
MachineBasicBlock *SuccMBB1 = OpSuccBlocks[0], *SuccMBB2 = OpSuccBlocks[1];
for (unsigned i = 0, e = VI.Kills.size(); i != e; ++i)
if (VI.Kills[i]->getParent() == SuccMBB1 ||
VI.Kills[i]->getParent() == SuccMBB2)
return true;
break;
}
default:
std::sort(OpSuccBlocks.begin(), OpSuccBlocks.end());
for (unsigned i = 0, e = VI.Kills.size(); i != e; ++i)
if (std::binary_search(OpSuccBlocks.begin(), OpSuccBlocks.end(),
VI.Kills[i]->getParent()))
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();
// All registers used by PHI nodes in SuccBB must be live through BB.
for (MachineBasicBlock::const_iterator BBI = SuccBB->begin(),
BBE = SuccBB->end(); BBI != BBE && BBI->isPHI(); ++BBI)
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);
// Update info for all live variables
for (unsigned Reg = TargetRegisterInfo::FirstVirtualRegister,
E = MRI->getLastVirtReg()+1; Reg != E; ++Reg) {
VarInfo &VI = getVarInfo(Reg);
if (!VI.AliveBlocks.test(NumNew) && VI.isLiveIn(*SuccBB, Reg, *MRI))
VI.AliveBlocks.set(NumNew);
}
}
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