Merging the linear scan register allocator in trunk. It currently passes most tests under test/Programs/SingleSource/Benchmarks/Shootout so development will continue on trunk. The allocator is not enabled by default. You will need to pass -regallo=linearscan to lli or llc to use it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10103 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 777 insertions, 0 deletions

diff --git a/lib/CodeGen/RegAllocLinearScan.cpp b/lib/CodeGen/RegAllocLinearScan.cpp
new file mode 100644
index 0000000000..f78be0f1ca
--- /dev/null
+++ b/lib/CodeGen/RegAllocLinearScan.cpp
@@ -0,0 +1,777 @@
+//===-- RegAllocLinearScan.cpp - Linear Scan register allocator -----------===//
+//
+//                     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 a linear scan register allocator.
+//
+//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "regalloc"
+#include "llvm/Function.h"
+#include "llvm/CodeGen/LiveIntervals.h"
+#include "llvm/CodeGen/LiveVariables.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/SSARegMap.h"
+#include "llvm/Target/MRegisterInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetRegInfo.h"
+#include "llvm/Support/CFG.h"
+#include "Support/Debug.h"
+#include "Support/DepthFirstIterator.h"
+#include "Support/Statistic.h"
+#include "Support/STLExtras.h"
+#include <iostream>
+
+using namespace llvm;
+
+namespace {
+    Statistic<> numSpilled ("ra-linearscan", "Number of registers spilled");
+    Statistic<> numReloaded("ra-linearscan", "Number of registers reloaded");
+
+    class RA : public MachineFunctionPass {
+    public:
+        typedef std::vector<const LiveIntervals::Interval*> IntervalPtrs;
+
+    private:
+        MachineFunction* mf_;
+        const TargetMachine* tm_;
+        const MRegisterInfo* mri_;
+        MachineBasicBlock* currentMbb_;
+        MachineBasicBlock::iterator currentInstr_;
+        typedef LiveIntervals::Intervals Intervals;
+        const Intervals* li_;
+        IntervalPtrs active_, inactive_;
+
+        typedef std::vector<unsigned> Regs;
+        Regs tempUseOperands_;
+        Regs tempDefOperands_;
+
+        Regs reserved_;
+
+        typedef LiveIntervals::MachineBasicBlockPtrs MachineBasicBlockPtrs;
+        MachineBasicBlockPtrs mbbs_;
+
+        typedef std::vector<unsigned> Phys2VirtMap;
+        Phys2VirtMap p2vMap_;
+
+        typedef std::map<unsigned, unsigned> Virt2PhysMap;
+        Virt2PhysMap v2pMap_;
+
+        typedef std::map<unsigned, int> Virt2StackSlotMap;
+        Virt2StackSlotMap v2ssMap_;
+
+        int instrAdded_;
+
+    public:
+        virtual const char* getPassName() const {
+            return "Linear Scan Register Allocator";
+        }
+
+        virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+            AU.addRequired<LiveVariables>();
+            AU.addRequired<LiveIntervals>();
+            MachineFunctionPass::getAnalysisUsage(AU);
+        }
+
+    private:
+        /// runOnMachineFunction - register allocate the whole function
+        bool runOnMachineFunction(MachineFunction&);
+
+        /// processActiveIntervals - expire old intervals and move
+        /// non-overlapping ones to the incative list
+        void processActiveIntervals(Intervals::const_iterator cur);
+
+        /// processInactiveIntervals - expire old intervals and move
+        /// overlapping ones to the active list
+        void processInactiveIntervals(Intervals::const_iterator cur);
+
+        /// assignStackSlotAtInterval - choose and spill
+        /// interval. Currently we spill the interval with the last
+        /// end point in the active and inactive lists and the current
+        /// interval
+        void assignStackSlotAtInterval(Intervals::const_iterator cur);
+
+        ///
+        /// register handling helpers
+        ///
+
+        /// reservePhysReg - reserves a physical register and spills
+        /// any value assigned to it if any
+        void reservePhysReg(unsigned reg);
+
+        /// clearReservedPhysReg - marks pysical register as free for
+        /// use
+        void clearReservedPhysReg(unsigned reg);
+
+        /// physRegAvailable - returns true if the specifed physical
+        /// register is available
+        bool physRegAvailable(unsigned physReg);
+
+        /// getFreePhysReg - return a free physical register for this
+        /// virtual register if we have one, otherwise return 0
+        unsigned getFreePhysReg(unsigned virtReg);
+
+
+        /// tempPhysRegAvailable - returns true if the specifed
+        /// temporary physical register is available
+        bool tempPhysRegAvailable(unsigned physReg);
+
+        /// getFreeTempPhysReg - return a free temprorary physical
+        /// register for this register class if we have one (should
+        /// never return 0)
+        unsigned getFreeTempPhysReg(const TargetRegisterClass* rc);
+
+        /// getFreeTempPhysReg - return a free temprorary physical
+        /// register for this virtual register if we have one (should
+        /// never return 0)
+        unsigned getFreeTempPhysReg(unsigned virtReg) {
+            const TargetRegisterClass* rc =
+                mf_->getSSARegMap()->getRegClass(virtReg);
+            return getFreeTempPhysReg(rc);
+        }
+
+        /// assignVirt2PhysReg - assigns the free physical register to
+        /// the virtual register passed as arguments
+        void assignVirt2PhysReg(unsigned virtReg, unsigned physReg);
+
+        /// clearVirtReg - free the physical register associated with this
+        /// virtual register and disassociate virtual->physical and
+        /// physical->virtual mappings
+        void clearVirtReg(unsigned virtReg);
+
+        /// assignVirt2StackSlot - assigns this virtual register to a
+        /// stack slot
+        void assignVirt2StackSlot(unsigned virtReg);
+
+        /// findOrCreateStackSlot - returns the offset of the
+        /// specified register on the stack allocating space if
+        /// necessary
+        int findOrCreateStackSlot(unsigned virtReg);
+
+        /// spillVirtReg - spills the virtual register
+        void spillVirtReg(unsigned virtReg);
+
+        /// loadPhysReg - loads to the physical register the value of
+        /// the virtual register specifed. Virtual register must have
+        /// an assigned stack slot
+        void loadVirt2PhysReg(unsigned virtReg, unsigned physReg);
+
+        void printVirt2PhysMap() const {
+            std::cerr << "allocated registers:\n";
+            for (Virt2PhysMap::const_iterator
+                     i = v2pMap_.begin(), e = v2pMap_.end(); i != e; ++i) {
+                std::cerr << '[' << i->first << ','
+                          << mri_->getName(i->second) << "]\n";
+            }
+            std::cerr << '\n';
+        }
+        void printIntervals(const char* const str,
+                            RA::IntervalPtrs::const_iterator i,
+                            RA::IntervalPtrs::const_iterator e) const {
+            if (str) std::cerr << str << " intervals:\n";
+            for (; i != e; ++i) {
+                std::cerr << "\t\t" << **i << " -> ";
+                if ((*i)->reg < MRegisterInfo::FirstVirtualRegister) {
+                    std::cerr << mri_->getName((*i)->reg);
+                }
+                else {
+                    std::cerr << mri_->getName(v2pMap_.find((*i)->reg)->second);
+                }
+                std::cerr << '\n';
+            }
+        }
+    };
+}
+
+bool RA::runOnMachineFunction(MachineFunction &fn) {
+    mf_ = &fn;
+    tm_ = &fn.getTarget();
+    mri_ = tm_->getRegisterInfo();
+    li_ = &getAnalysis<LiveIntervals>().getIntervals();
+    active_.clear();
+    inactive_.clear();
+    mbbs_ = getAnalysis<LiveIntervals>().getOrderedMachineBasicBlockPtrs();
+    p2vMap_.resize(MRegisterInfo::FirstVirtualRegister-1);
+    p2vMap_.clear();
+    v2pMap_.clear();
+    v2ssMap_.clear();
+
+    // FIXME: this will work only for the X86 backend. I need to
+    // device an algorthm to select the minimal (considering register
+    // aliasing) number of temp registers to reserve so that we have 2
+    // registers for each register class available.
+
+    // reserve R32: EDI, EBX,
+    //         R16:  DI,  BX,
+    //         R8:   DH,  BH,
+    //         RFP: FP5, FP6
+    reserved_.push_back(19); /* EDI */
+    reserved_.push_back(17); /* EBX */
+    reserved_.push_back(12); /*  DI */
+    reserved_.push_back( 7); /*  BX */
+    reserved_.push_back(11); /*  DH */
+    reserved_.push_back( 4); /*  BH */
+    reserved_.push_back(28); /* FP5 */
+    reserved_.push_back(29); /* FP6 */
+
+    // liner scan algorithm
+    for (Intervals::const_iterator
+             i = li_->begin(), e = li_->end(); i != e; ++i) {
+        DEBUG(std::cerr << "processing current interval: " << *i << '\n');
+
+        DEBUG(printIntervals("\tactive", active_.begin(), active_.end()));
+        DEBUG(printIntervals("\tinactive", inactive_.begin(), inactive_.end()));
+
+        processActiveIntervals(i);
+        // processInactiveIntervals(i);
+
+        // if this register is preallocated, look for an interval that
+        // overlaps with it and assign it to a memory location
+        if (i->reg < MRegisterInfo::FirstVirtualRegister) {
+            for (IntervalPtrs::iterator
+                     ai = active_.begin(), ae = active_.end(); ai != ae; ++ai) {
+                unsigned virtReg = (*ai)->reg;
+                Virt2PhysMap::const_iterator it = v2pMap_.find(virtReg);
+                if (it != v2pMap_.end() && it->second == i->reg) {
+                    active_.erase(ai);
+                    clearVirtReg(virtReg);
+                    break;
+                }
+            }
+            reservePhysReg(i->reg);
+            active_.push_back(&*i);
+        }
+        // otherwise we are allocating a virtual register. try to find
+        // a free physical register or spill an interval in order to
+        // assign it one (we could spill the current though).
+        else {
+            unsigned physReg = getFreePhysReg(i->reg);
+            if (!physReg) {
+                assignStackSlotAtInterval(i);
+            }
+            else {
+                assignVirt2PhysReg(i->reg, physReg);
+                active_.push_back(&*i);
+            }
+        }
+    }
+    DEBUG(std::cerr << "finished register allocation\n");
+    DEBUG(printVirt2PhysMap());
+
+    DEBUG(std::cerr << "Rewrite machine code:\n");
+    for (MachineBasicBlockPtrs::iterator
+             mbbi = mbbs_.begin(), mbbe = mbbs_.end(); mbbi != mbbe; ++mbbi) {
+        instrAdded_ = 0;
+        currentMbb_ = *mbbi;
+
+        for (currentInstr_ = currentMbb_->begin();
+             currentInstr_ != currentMbb_->end(); ++currentInstr_) {
+
+            DEBUG(std::cerr << "\tinstruction: ";
+                  (*currentInstr_)->print(std::cerr, *tm_););
+            DEBUG(std::cerr << "\t\tspilling temporarily defined operands "
+                  "of previous instruction:\n");
+            for (unsigned i = 0, e = tempDefOperands_.size(); i != e; ++i) {
+                spillVirtReg(tempDefOperands_[i]);
+            }
+            tempDefOperands_.clear();
+
+            // use our current mapping and actually replace and
+            // virtual register with its allocated physical registers
+            DEBUG(std::cerr << "\t\treplacing virtual registers with mapped "
+                  "physical registers:\n");
+            for (unsigned i = 0, e = (*currentInstr_)->getNumOperands();
+                 i != e; ++i) {
+                MachineOperand& op = (*currentInstr_)->getOperand(i);
+                if (op.isVirtualRegister()) {
+                    unsigned virtReg = op.getAllocatedRegNum();
+                    unsigned physReg = v2pMap_[virtReg];
+                    // if this virtual registers lives on the stack,
+                    // load it to a temporary physical register
+                    if (physReg) {
+                        DEBUG(std::cerr << "\t\t\t%reg" << virtReg
+                              << " -> " << mri_->getName(physReg) << '\n');
+                        (*currentInstr_)->SetMachineOperandReg(i, physReg);
+                    }
+                }
+            }
+
+            DEBUG(std::cerr << "\t\tloading temporarily used operands to "
+                  "registers:\n");
+            for (unsigned i = 0, e = (*currentInstr_)->getNumOperands();
+                 i != e; ++i) {
+                MachineOperand& op = (*currentInstr_)->getOperand(i);
+                if (op.isVirtualRegister() && op.opIsUse()) {
+                    unsigned virtReg = op.getAllocatedRegNum();
+                    unsigned physReg = v2pMap_[virtReg];
+                    if (!physReg) {
+                        physReg = getFreeTempPhysReg(virtReg);
+                    }
+                    loadVirt2PhysReg(virtReg, physReg);
+                    tempUseOperands_.push_back(virtReg);
+                    (*currentInstr_)->SetMachineOperandReg(i, physReg);
+                }
+            }
+
+            DEBUG(std::cerr << "\t\tclearing temporarily used operands:\n");
+            for (unsigned i = 0, e = tempUseOperands_.size(); i != e; ++i) {
+                clearVirtReg(tempUseOperands_[i]);
+            }
+            tempUseOperands_.clear();
+
+            DEBUG(std::cerr << "\t\tassigning temporarily defined operands to "
+                  "registers:\n");
+            for (unsigned i = 0, e = (*currentInstr_)->getNumOperands();
+                 i != e; ++i) {
+                MachineOperand& op = (*currentInstr_)->getOperand(i);
+                if (op.isVirtualRegister() && !op.opIsUse()) {
+                    unsigned virtReg = op.getAllocatedRegNum();
+                    unsigned physReg = v2pMap_[virtReg];
+                    if (!physReg) {
+                        physReg = getFreeTempPhysReg(virtReg);
+                    }
+                    if (op.opIsDefAndUse()) {
+                        loadVirt2PhysReg(virtReg, physReg);
+                    }
+                    else {
+                        assignVirt2PhysReg(virtReg, physReg);
+                    }
+                    tempDefOperands_.push_back(virtReg);
+                    (*currentInstr_)->SetMachineOperandReg(i, physReg);
+                }
+            }
+
+
+            // if the instruction is a two address instruction and the
+            // source operands are not identical we need to insert
+            // extra instructions.
+
+            unsigned opcode = (*currentInstr_)->getOpcode();
+            if (tm_->getInstrInfo().isTwoAddrInstr(opcode) &&
+                (*currentInstr_)->getOperand(0).getAllocatedRegNum() !=
+                (*currentInstr_)->getOperand(1).getAllocatedRegNum()) {
+                assert((*currentInstr_)->getOperand(1).isRegister() &&
+                       (*currentInstr_)->getOperand(1).getAllocatedRegNum() &&
+                       (*currentInstr_)->getOperand(1).opIsUse() &&
+                       "Two address instruction invalid");
+
+                unsigned regA =
+                    (*currentInstr_)->getOperand(0).getAllocatedRegNum();
+                unsigned regB =
+                    (*currentInstr_)->getOperand(1).getAllocatedRegNum();
+                unsigned regC =
+                    ((*currentInstr_)->getNumOperands() > 2 &&
+                     (*currentInstr_)->getOperand(2).isRegister()) ?
+                    (*currentInstr_)->getOperand(2).getAllocatedRegNum() :
+                    0;
+
+                const TargetRegisterClass* rc = mri_->getRegClass(regA);
+
+                // special case: "a = b op a". If b is a temporary
+                // reserved register rewrite as: "b = b op a; a = b"
+                // otherwise use a temporary reserved register t and
+                // rewrite as: "t = b; t = t op a; a = t"
+                if (regC && regA == regC) {
+                    // b is a temp reserved register
+                    if (find(reserved_.begin(), reserved_.end(),
+                             regB) != reserved_.end()) {
+                        (*currentInstr_)->SetMachineOperandReg(0, regB);
+                        ++currentInstr_;
+                        instrAdded_ += mri_->copyRegToReg(*currentMbb_,
+                                                          currentInstr_,
+                                                          regA,
+                                                          regB,
+                                                          rc);
+                        --currentInstr_;
+                    }
+                    // b is just a normal register
+                    else {
+                        unsigned tempReg = getFreeTempPhysReg(rc);
+                        assert (tempReg &&
+                                "no free temp reserved physical register?");
+                        instrAdded_ += mri_->copyRegToReg(*currentMbb_,
+                                                          currentInstr_,
+                                                          tempReg,
+                                                          regB,
+                                                          rc);
+                        (*currentInstr_)->SetMachineOperandReg(0, tempReg);
+                        (*currentInstr_)->SetMachineOperandReg(1, tempReg);
+                        ++currentInstr_;
+                        instrAdded_ += mri_->copyRegToReg(*currentMbb_,
+                                                          currentInstr_,
+                                                          regA,
+                                                          tempReg,
+                                                          rc);
+                        --currentInstr_;
+                    }
+                }
+                // "a = b op c" gets rewritten to "a = b; a = a op c"
+                else {
+                    instrAdded_ += mri_->copyRegToReg(*currentMbb_,
+                                                      currentInstr_,
+                                                      regA,
+                                                      regB,
+                                                      rc);
+                    (*currentInstr_)->SetMachineOperandReg(1, regA);
+                }
+            }
+        }
+
+        for (unsigned i = 0, e = p2vMap_.size(); i != e; ++i) {
+            assert(p2vMap_[i] != i &&
+                   "reserved physical registers at end of basic block?");
+        }
+    }
+
+    return true;
+}
+
+void RA::processActiveIntervals(Intervals::const_iterator cur)
+{
+    DEBUG(std::cerr << "\tprocessing active intervals:\n");
+    for (IntervalPtrs::iterator i = active_.begin(); i != active_.end();) {
+        unsigned reg = (*i)->reg;
+        // remove expired intervals. we expire earlier because this if
+        // an interval expires this is going to be the last use. in
+        // this case we can reuse the register for a def in the same
+        // instruction
+        if ((*i)->expired(cur->start() + 1)) {
+            DEBUG(std::cerr << "\t\tinterval " << **i << " expired\n");
+            if (reg < MRegisterInfo::FirstVirtualRegister) {
+                clearReservedPhysReg(reg);
+            }
+            else {
+                p2vMap_[v2pMap_[reg]] = 0;
+            }
+            // remove interval from active
+            i = active_.erase(i);
+        }
+        // move not active intervals to inactive list
+//         else if (!(*i)->overlaps(curIndex)) {
+//             DEBUG(std::cerr << "\t\t\tinterval " << **i << " inactive\n");
+//             unmarkReg(virtReg);
+//             // add interval to inactive
+//             inactive_.push_back(*i);
+//             // remove interval from active
+//             i = active_.erase(i);
+//         }
+        else {
+            ++i;
+        }
+    }
+}
+
+void RA::processInactiveIntervals(Intervals::const_iterator cur)
+{
+//     DEBUG(std::cerr << "\tprocessing inactive intervals:\n");
+//     for (IntervalPtrs::iterator i = inactive_.begin(); i != inactive_.end();) {
+//         unsigned virtReg = (*i)->reg;
+//         // remove expired intervals
+//         if ((*i)->expired(curIndex)) {
+//             DEBUG(std::cerr << "\t\t\tinterval " << **i << " expired\n");
+//             freePhysReg(virtReg);
+//             // remove from inactive
+//             i = inactive_.erase(i);
+//         }
+//         // move re-activated intervals in active list
+//         else if ((*i)->overlaps(curIndex)) {
+//             DEBUG(std::cerr << "\t\t\tinterval " << **i << " active\n");
+//             markReg(virtReg);
+//             // add to active
+//             active_.push_back(*i);
+//             // remove from inactive
+//             i = inactive_.erase(i);
+//         }
+//         else {
+//             ++i;
+//         }
+//     }
+}
+
+void RA::assignStackSlotAtInterval(Intervals::const_iterator cur)
+{
+    DEBUG(std::cerr << "\t\tassigning stack slot at interval "
+          << *cur << ":\n");
+    assert(!active_.empty() &&
+           "active set cannot be empty when choosing a register to spill");
+    const TargetRegisterClass* rcCur =
+        mf_->getSSARegMap()->getRegClass(cur->reg);
+
+    // find the interval for a virtual register that ends last in
+    // active and belongs to the same register class as the current
+    // interval
+    IntervalPtrs::iterator lastEndActive = active_.begin();
+    for (IntervalPtrs::iterator e = active_.end();
+         lastEndActive != e; ++lastEndActive) {
+        if ((*lastEndActive)->reg >= MRegisterInfo::FirstVirtualRegister) {
+            const TargetRegisterClass* rc =
+                mri_->getRegClass(v2pMap_[(*lastEndActive)->reg]);
+            if (rcCur == rc) {
+                break;
+            }
+        }
+    }
+    for (IntervalPtrs::iterator i = lastEndActive, e = active_.end();
+         i != e; ++i) {
+        if ((*i)->reg >= MRegisterInfo::FirstVirtualRegister) {
+            const TargetRegisterClass* rc =
+                mri_->getRegClass(v2pMap_[(*i)->reg]);
+            if (rcCur == rc &&
+                (*lastEndActive)->end() < (*i)->end()) {
+                lastEndActive = i;
+            }
+        }
+    }
+
+    // find the interval for a virtual register that ends last in
+    // inactive and belongs to the same register class as the current
+    // interval
+    IntervalPtrs::iterator lastEndInactive = inactive_.begin();
+    for (IntervalPtrs::iterator e = inactive_.end();
+         lastEndInactive != e; ++lastEndInactive) {
+        if ((*lastEndInactive)->reg >= MRegisterInfo::FirstVirtualRegister) {
+            const TargetRegisterClass* rc =
+                mri_->getRegClass(v2pMap_[(*lastEndInactive)->reg]);
+            if (rcCur == rc) {
+                break;
+            }
+        }
+    }
+    for (IntervalPtrs::iterator i = lastEndInactive, e = inactive_.end();
+         i != e; ++i) {
+        if ((*i)->reg >= MRegisterInfo::FirstVirtualRegister) {
+            const TargetRegisterClass* rc =
+                mri_->getRegClass(v2pMap_[(*i)->reg]);
+            if (rcCur == rc &&
+                (*lastEndInactive)->end() < (*i)->end()) {
+                lastEndInactive = i;
+            }
+        }
+    }
+
+    unsigned lastEndActiveInactive = 0;
+    if (lastEndActive != active_.end() &&
+        lastEndActiveInactive < (*lastEndActive)->end()) {
+        lastEndActiveInactive = (*lastEndActive)->end();
+    }
+    if (lastEndInactive != inactive_.end() &&
+        lastEndActiveInactive < (*lastEndInactive)->end()) {
+        lastEndActiveInactive = (*lastEndInactive)->end();
+    }
+
+    if (lastEndActiveInactive > cur->end()) {
+        if (lastEndInactive == inactive_.end() ||
+            (*lastEndActive)->end() > (*lastEndInactive)->end()) {
+            assignVirt2StackSlot((*lastEndActive)->reg);
+            active_.erase(lastEndActive);
+        }
+        else {
+            assignVirt2StackSlot((*lastEndInactive)->reg);
+            inactive_.erase(lastEndInactive);
+        }
+        unsigned physReg = getFreePhysReg(cur->reg);
+        assert(physReg && "no free physical register after spill?");
+        assignVirt2PhysReg(cur->reg, physReg);
+        active_.push_back(&*cur);
+    }
+    else {
+        assignVirt2StackSlot(cur->reg);
+    }
+}
+
+void RA::reservePhysReg(unsigned physReg)
+{
+    DEBUG(std::cerr << "\t\t\treserving physical physical register: "
+          << mri_->getName(physReg) << '\n');
+    // if this register holds a value spill it
+    unsigned virtReg = p2vMap_[physReg];
+    if (virtReg != 0) {
+        assert(virtReg != physReg && "reserving an already reserved phus reg?");
+        // remove interval from active
+        for (IntervalPtrs::iterator i = active_.begin(), e = active_.end();
+             i != e; ++i) {
+            if ((*i)->reg == virtReg) {
+                active_.erase(i);
+                break;
+            }
+        }
+        spillVirtReg(virtReg);
+    }
+    p2vMap_[physReg] = physReg; // this denotes a reserved physical register
+}
+
+void RA::clearReservedPhysReg(unsigned physReg)
+{
+    DEBUG(std::cerr << "\t\t\tclearing reserved physical physical register: "
+          << mri_->getName(physReg) << '\n');
+    assert(p2vMap_[physReg] == physReg &&
+           "attempt to clear a non reserved physical register");
+    p2vMap_[physReg] = 0;
+}
+
+bool RA::physRegAvailable(unsigned physReg)
+{
+    if (p2vMap_[physReg]) {
+        return false;
+    }
+
+    // if it aliases other registers it is still not free
+    for (const unsigned* as = mri_->getAliasSet(physReg); *as; ++as) {
+        if (p2vMap_[*as]) {
+            return false;
+        }
+    }
+
+    // if it is one of the reserved registers it is still not free
+    if (find(reserved_.begin(), reserved_.end(), physReg) != reserved_.end()) {
+        return false;
+    }
+
+    return true;
+}
+
+unsigned RA::getFreePhysReg(unsigned virtReg)
+{
+    DEBUG(std::cerr << "\t\tgetting free physical register: ");
+    const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(virtReg);
+    TargetRegisterClass::iterator reg = rc->allocation_order_begin(*mf_);
+    TargetRegisterClass::iterator regEnd = rc->allocation_order_end(*mf_);
+
+    for (; reg != regEnd; ++reg) {
+        if (physRegAvailable(*reg)) {
+            assert(*reg != 0 && "Cannot use register!");
+            DEBUG(std::cerr << mri_->getName(*reg) << '\n');
+            return *reg; // Found an unused register!
+        }
+    }
+
+    DEBUG(std::cerr << "no free register\n");
+    return 0;
+}
+
+bool RA::tempPhysRegAvailable(unsigned physReg)
+{
+    assert(find(reserved_.begin(), reserved_.end(), physReg) != reserved_.end()
+           && "cannot call this method with a non reserved temp register");
+
+    if (p2vMap_[physReg]) {
+        return false;
+    }
+
+    // if it aliases other registers it is still not free
+    for (const unsigned* as = mri_->getAliasSet(physReg); *as; ++as) {
+        if (p2vMap_[*as]) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+unsigned RA::getFreeTempPhysReg(const TargetRegisterClass* rc)
+{
+    DEBUG(std::cerr << "\t\tgetting free temporary physical register: ");
+
+    for (Regs::const_iterator
+             reg = reserved_.begin(), regEnd = reserved_.end();
+         reg != regEnd; ++reg) {
+        if (rc == mri_->getRegClass(*reg) && tempPhysRegAvailable(*reg)) {
+            assert(*reg != 0 && "Cannot use register!");
+            DEBUG(std::cerr << mri_->getName(*reg) << '\n');
+            return *reg; // Found an unused register!
+        }
+    }
+    assert(0 && "no free temporary physical register?");
+    return 0;
+}
+
+void RA::assignVirt2PhysReg(unsigned virtReg, unsigned physReg)
+{
+    assert((physRegAvailable(physReg) ||
+            find(reserved_.begin(),
+                 reserved_.end(),
+                 physReg) != reserved_.end()) &&
+           "attempt to allocate to a not available physical register");
+    v2pMap_[virtReg] = physReg;
+    p2vMap_[physReg] = virtReg;
+}
+
+void RA::clearVirtReg(unsigned virtReg)
+{
+    Virt2PhysMap::iterator it = v2pMap_.find(virtReg);
+    assert(it != v2pMap_.end() &&
+           "attempting to clear a not allocated virtual register");
+    unsigned physReg = it->second;
+    p2vMap_[physReg] = 0;
+    v2pMap_[virtReg] = 0; // this marks that this virtual register
+                          // lives on the stack
+    DEBUG(std::cerr << "\t\t\tcleared register " << mri_->getName(physReg)
+          << "\n");
+}
+
+void RA::assignVirt2StackSlot(unsigned virtReg)
+{
+    const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(virtReg);
+    int frameIndex = mf_->getFrameInfo()->CreateStackObject(rc);
+
+    bool inserted = v2ssMap_.insert(std::make_pair(virtReg, frameIndex)).second;
+    assert(inserted &&
+           "attempt to assign stack slot to already assigned register?");
+    // if the virtual register was previously assigned clear the mapping
+    // and free the virtual register
+    if (v2pMap_.find(virtReg) != v2pMap_.end()) {
+        clearVirtReg(virtReg);
+    }
+}
+
+int RA::findOrCreateStackSlot(unsigned virtReg)
+{
+    // use lower_bound so that we can do a possibly O(1) insert later
+    // if necessary
+    Virt2StackSlotMap::iterator it = v2ssMap_.lower_bound(virtReg);
+    if (it != v2ssMap_.end() && it->first == virtReg) {
+        return it->second;
+    }
+    const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(virtReg);
+    int frameIndex = mf_->getFrameInfo()->CreateStackObject(rc);
+
+    v2ssMap_.insert(it, std::make_pair(virtReg, frameIndex));
+
+    return frameIndex;
+}
+
+void RA::spillVirtReg(unsigned virtReg)
+{
+    DEBUG(std::cerr << "\t\t\tspilling register: " << virtReg);
+    const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(virtReg);
+    int frameIndex = findOrCreateStackSlot(virtReg);
+    DEBUG(std::cerr << " to stack slot #" << frameIndex << '\n');
+    ++numSpilled;
+    instrAdded_ += mri_->storeRegToStackSlot(*currentMbb_, currentInstr_,
+                                             v2pMap_[virtReg], frameIndex, rc);
+    clearVirtReg(virtReg);
+}
+
+void RA::loadVirt2PhysReg(unsigned virtReg, unsigned physReg)
+{
+    DEBUG(std::cerr << "\t\t\tloading register: " << virtReg);
+    const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(virtReg);
+    int frameIndex = findOrCreateStackSlot(virtReg);
+    DEBUG(std::cerr << " from stack slot #" << frameIndex << '\n');
+    ++numReloaded;
+    instrAdded_ += mri_->loadRegFromStackSlot(*currentMbb_, currentInstr_,
+                                              physReg, frameIndex, rc);
+    assignVirt2PhysReg(virtReg, physReg);
+}
+
+FunctionPass* llvm::createLinearScanRegisterAllocator() {
+    return new RA();
+}