maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity
llvm-project/llvm/lib/CodeGen/LiveVariables.cpp

448 lines
16 KiB
C++
Raw Blame History

//===-- LiveVariables.cpp - Live Variable Analysis for Machine Code -------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and 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/Target/MRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Config/alloca.h"
#include <algorithm>
using namespace llvm;
static RegisterPass<LiveVariables> X("livevars", "Live Variable Analysis");
void LiveVariables::VarInfo::dump() const {
cerr << "Register Defined by: ";
if (DefInst)
cerr << *DefInst;
else
cerr << "<null>\n";
cerr << " Alive in blocks: ";
for (unsigned i = 0, e = AliveBlocks.size(); i != e; ++i)
if (AliveBlocks[i]) cerr << i << ", ";
cerr << "\n Killed by:";
if (Kills.empty())
cerr << " No instructions.\n";
else {
for (unsigned i = 0, e = Kills.size(); i != e; ++i)
cerr << "\n #" << i << ": " << *Kills[i];
cerr << "\n";
}
}
LiveVariables::VarInfo &LiveVariables::getVarInfo(unsigned RegIdx) {
assert(MRegisterInfo::isVirtualRegister(RegIdx) &&
"getVarInfo: not a virtual register!");
RegIdx -= MRegisterInfo::FirstVirtualRegister;
if (RegIdx >= VirtRegInfo.size()) {
if (RegIdx >= 2*VirtRegInfo.size())
VirtRegInfo.resize(RegIdx*2);
else
VirtRegInfo.resize(2*VirtRegInfo.size());
}
return VirtRegInfo[RegIdx];
}
bool LiveVariables::KillsRegister(MachineInstr *MI, unsigned Reg) const {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isKill()) {
if (RegInfo->regsOverlap(Reg, MO.getReg()))
return true;
}
}
return false;
}
bool LiveVariables::RegisterDefIsDead(MachineInstr *MI, unsigned Reg) const {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isDead())
if (RegInfo->regsOverlap(Reg, MO.getReg()))
return true;
}
return false;
}
bool LiveVariables::ModifiesRegister(MachineInstr *MI, unsigned Reg) const {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isDef()) {
if (RegInfo->regsOverlap(Reg, MO.getReg()))
return true;
}
}
return false;
}
void LiveVariables::MarkVirtRegAliveInBlock(VarInfo &VRInfo,
MachineBasicBlock *MBB) {
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 == VRInfo.DefInst->getParent()) return; // Terminate recursion
if (VRInfo.AliveBlocks.size() <= BBNum)
VRInfo.AliveBlocks.resize(BBNum+1); // Make space...
if (VRInfo.AliveBlocks[BBNum])
return; // We already know the block is live
// Mark the variable known alive in this bb
VRInfo.AliveBlocks[BBNum] = true;
for (MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(),
E = MBB->pred_end(); PI != E; ++PI)
MarkVirtRegAliveInBlock(VRInfo, *PI);
}
void LiveVariables::HandleVirtRegUse(VarInfo &VRInfo, MachineBasicBlock *MBB,
MachineInstr *MI) {
assert(VRInfo.DefInst && "Register use before def!");
// 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
assert(MBB != VRInfo.DefInst->getParent() &&
"Should have kill for defblock!");
// Add a new kill entry for this basic block.
VRInfo.Kills.push_back(MI);
// Update all dominating blocks to mark them known live.
for (MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(),
E = MBB->pred_end(); PI != E; ++PI)
MarkVirtRegAliveInBlock(VRInfo, *PI);
}
void LiveVariables::addRegisterKilled(unsigned IncomingReg, MachineInstr *MI) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isUse() && MO.getReg() == IncomingReg) {
MO.setIsKill();
break;
}
}
}
void LiveVariables::addRegisterDead(unsigned IncomingReg, MachineInstr *MI) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isDef() && MO.getReg() == IncomingReg) {
MO.setIsDead();
break;
}
}
}
void LiveVariables::HandlePhysRegUse(unsigned Reg, MachineInstr *MI) {
PhysRegInfo[Reg] = MI;
PhysRegUsed[Reg] = true;
for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
unsigned Alias = *AliasSet; ++AliasSet) {
PhysRegInfo[Alias] = MI;
PhysRegUsed[Alias] = true;
}
}
void LiveVariables::HandlePhysRegDef(unsigned Reg, MachineInstr *MI) {
// Does this kill a previous version of this register?
if (MachineInstr *LastUse = PhysRegInfo[Reg]) {
if (PhysRegUsed[Reg])
addRegisterKilled(Reg, LastUse);
else
addRegisterDead(Reg, LastUse);
}
PhysRegInfo[Reg] = MI;
PhysRegUsed[Reg] = false;
for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
unsigned Alias = *AliasSet; ++AliasSet) {
if (MachineInstr *LastUse = PhysRegInfo[Alias]) {
if (PhysRegUsed[Alias])
addRegisterKilled(Alias, LastUse);
else
addRegisterDead(Alias, LastUse);
}
PhysRegInfo[Alias] = MI;
PhysRegUsed[Alias] = false;
}
}
bool LiveVariables::runOnMachineFunction(MachineFunction &MF) {
const TargetInstrInfo &TII = *MF.getTarget().getInstrInfo();
RegInfo = MF.getTarget().getRegisterInfo();
assert(RegInfo && "Target doesn't have register information?");
ReservedRegisters = RegInfo->getReservedRegs(MF);
// PhysRegInfo - Keep track of which instruction was the last use of a
// physical register. This is a purely local property, because all physical
// register references as presumed dead across basic blocks.
//
PhysRegInfo = (MachineInstr**)alloca(sizeof(MachineInstr*) *
RegInfo->getNumRegs());
PhysRegUsed = (bool*)alloca(sizeof(bool)*RegInfo->getNumRegs());
std::fill(PhysRegInfo, PhysRegInfo+RegInfo->getNumRegs(), (MachineInstr*)0);
/// 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();
std::set<MachineBasicBlock*> Visited;
for (df_ext_iterator<MachineBasicBlock*> 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.
for (MachineBasicBlock::const_livein_iterator II = MBB->livein_begin(),
EE = MBB->livein_end(); II != EE; ++II) {
assert(MRegisterInfo::isPhysicalRegister(*II) &&
"Cannot have a live-in virtual register!");
HandlePhysRegDef(*II, 0);
}
// Loop over all of the instructions, processing them.
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
I != E; ++I) {
MachineInstr *MI = I;
// 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->getOpcode() == TargetInstrInfo::PHI)
NumOperandsToProcess = 1;
// Process all uses...
for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isRegister() && MO.isUse() && MO.getReg()) {
if (MRegisterInfo::isVirtualRegister(MO.getReg())){
HandleVirtRegUse(getVarInfo(MO.getReg()), MBB, MI);
} else if (MRegisterInfo::isPhysicalRegister(MO.getReg()) &&
!ReservedRegisters[MO.getReg()]) {
HandlePhysRegUse(MO.getReg(), MI);
}
}
}
// Process all defs...
for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isRegister() && MO.isDef() && MO.getReg()) {
if (MRegisterInfo::isVirtualRegister(MO.getReg())) {
VarInfo &VRInfo = getVarInfo(MO.getReg());
assert(VRInfo.DefInst == 0 && "Variable multiply defined!");
VRInfo.DefInst = MI;
// Defaults to dead
VRInfo.Kills.push_back(MI);
} else if (MRegisterInfo::isPhysicalRegister(MO.getReg()) &&
!ReservedRegisters[MO.getReg()]) {
HandlePhysRegDef(MO.getReg(), MI);
}
}
}
}
// 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].empty()) {
std::vector<unsigned>& VarInfoVec = PHIVarInfo[MBB];
for (std::vector<unsigned>::iterator I = VarInfoVec.begin(),
E = VarInfoVec.end(); I != E; ++I) {
VarInfo& VRInfo = getVarInfo(*I);
assert(VRInfo.DefInst && "Register use before def (or no def)!");
// Only mark it alive only in the block we are representing.
MarkVirtRegAliveInBlock(VRInfo, 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.
if (!MBB->empty() && TII.isReturn(MBB->back().getOpcode())) {
MachineInstr *Ret = &MBB->back();
for (MachineFunction::liveout_iterator I = MF.liveout_begin(),
E = MF.liveout_end(); I != E; ++I) {
assert(MRegisterInfo::isPhysicalRegister(*I) &&
"Cannot have a live-in virtual register!");
HandlePhysRegUse(*I, Ret);
// Add live-out registers as implicit uses.
Ret->addRegOperand(*I, false, true);
}
}
// Loop over PhysRegInfo, killing any registers that are available at the
// end of the basic block. This also resets the PhysRegInfo map.
for (unsigned i = 0, e = RegInfo->getNumRegs(); i != e; ++i)
if (PhysRegInfo[i])
HandlePhysRegDef(i, 0);
}
// Convert and transfer the dead / killed information we have gathered into
// VirtRegInfo onto MI's.
//
for (unsigned i = 0, e = VirtRegInfo.size(); i != e; ++i)
for (unsigned j = 0, e = VirtRegInfo[i].Kills.size(); j != e; ++j) {
if (VirtRegInfo[i].Kills[j] == VirtRegInfo[i].DefInst)
addRegisterDead(i + MRegisterInfo::FirstVirtualRegister,
VirtRegInfo[i].Kills[j]);
else
addRegisterKilled(i + MRegisterInfo::FirstVirtualRegister,
VirtRegInfo[i].Kills[j]);
}
// 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
PHIVarInfo.clear();
return false;
}
/// instructionChanged - When the address of an instruction changes, this
/// method should be called so that live variables can update its internal
/// data structures. This removes the records for OldMI, transfering them to
/// the records for NewMI.
void LiveVariables::instructionChanged(MachineInstr *OldMI,
MachineInstr *NewMI) {
// If the instruction defines any virtual registers, update the VarInfo,
// kill and dead information for the instruction.
for (unsigned i = 0, e = OldMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = OldMI->getOperand(i);
if (MO.isRegister() && MO.getReg() &&
MRegisterInfo::isVirtualRegister(MO.getReg())) {
unsigned Reg = MO.getReg();
VarInfo &VI = getVarInfo(Reg);
if (MO.isDef()) {
if (MO.isDead()) {
MO.unsetIsDead();
addVirtualRegisterDead(Reg, NewMI);
}
// Update the defining instruction.
if (VI.DefInst == OldMI)
VI.DefInst = NewMI;
}
if (MO.isUse()) {
if (MO.isKill()) {
MO.unsetIsKill();
addVirtualRegisterKilled(Reg, NewMI);
}
// If this is a kill of the value, update the VI kills list.
if (VI.removeKill(OldMI))
VI.Kills.push_back(NewMI); // Yes, there was a kill of it
}
}
}
}
/// 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.unsetIsKill();
unsigned Reg = MO.getReg();
if (MRegisterInfo::isVirtualRegister(Reg)) {
bool removed = getVarInfo(Reg).removeKill(MI);
assert(removed && "kill not in register's VarInfo?");
}
}
}
}
/// removeVirtualRegistersDead - Remove all of the dead registers for the
/// specified instruction from the live variable information.
void LiveVariables::removeVirtualRegistersDead(MachineInstr *MI) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isDead()) {
MO.unsetIsDead();
unsigned Reg = MO.getReg();
if (MRegisterInfo::isVirtualRegister(Reg)) {
bool removed = getVarInfo(Reg).removeKill(MI);
assert(removed && "kill not in register's VarInfo?");
}
}
}
}
/// 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->getOpcode() == TargetInstrInfo::PHI; ++BBI)
for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2)
PHIVarInfo[BBI->getOperand(i + 1).getMachineBasicBlock()].
push_back(BBI->getOperand(i).getReg());
}
Reference in New Issue View Git Blame Copy Permalink