Add option to join live intervals. Two intervals are joined if there

is a move between two registers, at least one of the registers is
virtual and the two live intervals do not overlap.

This results in about 40% reduction in intervals, 30% decrease in the
register allocators running time and a 20% increase in peephole
optimizations (mainly move eliminations).

The option can be enabled by passing -join-liveintervals where
appropriate.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10965 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveIntervalAnalysis.h

@@ -26,6 +26,7 @@
 #include <iostream>
 #include <list>
 #include <map>
+#include <vector>
 
 namespace llvm {
 
@@ -39,10 +40,9 @@ namespace llvm {
             typedef std::pair<unsigned, unsigned> Range;
             typedef std::vector<Range> Ranges;
             unsigned reg;   // the register of this interval
-            unsigned hint;
             float weight;   // weight of this interval (number of uses
                             // * 10^loopDepth)
-            Ranges ranges;  // the ranges this register is valid
+            Ranges ranges;  // the ranges in which this register is live
 
             Interval(unsigned r);
 
@@ -66,10 +66,12 @@ namespace llvm {
 
             void addRange(unsigned start, unsigned end);
 
-        private:
+            void join(const Interval& other);
-            void mergeRangesForward(Ranges::iterator it);
 
-            void mergeRangesBackward(Ranges::iterator it);
+        private:
+            Ranges::iterator mergeRangesForward(Ranges::iterator it);
+
+            Ranges::iterator mergeRangesBackward(Ranges::iterator it);
         };
 
         struct StartPointComp {
@@ -85,6 +87,7 @@ namespace llvm {
         };
 
         typedef std::list<Interval> Intervals;
+        typedef std::map<unsigned, unsigned> Reg2RegMap;
         typedef std::vector<MachineBasicBlock*> MachineBasicBlockPtrs;
 
     private:
@@ -104,11 +107,15 @@ namespace llvm {
         typedef std::map<unsigned, Intervals::iterator> Reg2IntervalMap;
         Reg2IntervalMap r2iMap_;
 
+        Reg2RegMap r2rMap_;
+
         Intervals intervals_;
 
     public:
         virtual void getAnalysisUsage(AnalysisUsage &AU) const;
+
         Intervals& getIntervals() { return intervals_; }
+
         MachineBasicBlockPtrs getOrderedMachineBasicBlockPtrs() const {
             MachineBasicBlockPtrs result;
             for (MbbIndex2MbbMap::const_iterator
@@ -119,6 +126,13 @@ namespace llvm {
             return result;
         }
 
+        const Reg2RegMap& getJoinedRegMap() const {
+            return r2rMap_;
+        }
+
+        /// rep - returns the representative of this register
+        unsigned rep(unsigned reg);
+
     private:
         /// runOnMachineFunction - pass entry point
         bool runOnMachineFunction(MachineFunction&);
@@ -126,6 +140,8 @@ namespace llvm {
         /// computeIntervals - compute live intervals
         void computeIntervals();
 
+        /// joinIntervals - join compatible live intervals
+        void joinIntervals();
 
         /// handleRegisterDef - update intervals for a register def
         /// (calls handlePhysicalRegisterDef and

include/llvm/CodeGen/LiveIntervals.h

@@ -26,6 +26,7 @@
 #include <iostream>
 #include <list>
 #include <map>
+#include <vector>
 
 namespace llvm {
 
@@ -39,10 +40,9 @@ namespace llvm {
             typedef std::pair<unsigned, unsigned> Range;
             typedef std::vector<Range> Ranges;
             unsigned reg;   // the register of this interval
-            unsigned hint;
             float weight;   // weight of this interval (number of uses
                             // * 10^loopDepth)
-            Ranges ranges;  // the ranges this register is valid
+            Ranges ranges;  // the ranges in which this register is live
 
             Interval(unsigned r);
 
@@ -66,10 +66,12 @@ namespace llvm {
 
             void addRange(unsigned start, unsigned end);
 
-        private:
+            void join(const Interval& other);
-            void mergeRangesForward(Ranges::iterator it);
 
-            void mergeRangesBackward(Ranges::iterator it);
+        private:
+            Ranges::iterator mergeRangesForward(Ranges::iterator it);
+
+            Ranges::iterator mergeRangesBackward(Ranges::iterator it);
         };
 
         struct StartPointComp {
@@ -85,6 +87,7 @@ namespace llvm {
         };
 
         typedef std::list<Interval> Intervals;
+        typedef std::map<unsigned, unsigned> Reg2RegMap;
         typedef std::vector<MachineBasicBlock*> MachineBasicBlockPtrs;
 
     private:
@@ -104,11 +107,15 @@ namespace llvm {
         typedef std::map<unsigned, Intervals::iterator> Reg2IntervalMap;
         Reg2IntervalMap r2iMap_;
 
+        Reg2RegMap r2rMap_;
+
         Intervals intervals_;
 
     public:
         virtual void getAnalysisUsage(AnalysisUsage &AU) const;
+
         Intervals& getIntervals() { return intervals_; }
+
         MachineBasicBlockPtrs getOrderedMachineBasicBlockPtrs() const {
             MachineBasicBlockPtrs result;
             for (MbbIndex2MbbMap::const_iterator
@@ -119,6 +126,13 @@ namespace llvm {
             return result;
         }
 
+        const Reg2RegMap& getJoinedRegMap() const {
+            return r2rMap_;
+        }
+
+        /// rep - returns the representative of this register
+        unsigned rep(unsigned reg);
+
     private:
         /// runOnMachineFunction - pass entry point
         bool runOnMachineFunction(MachineFunction&);
@@ -126,6 +140,8 @@ namespace llvm {
         /// computeIntervals - compute live intervals
         void computeIntervals();
 
+        /// joinIntervals - join compatible live intervals
+        void joinIntervals();
 
         /// handleRegisterDef - update intervals for a register def
         /// (calls handlePhysicalRegisterDef and

lib/CodeGen/LiveIntervalAnalysis.cpp

@@ -30,6 +30,7 @@
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetRegInfo.h"
 #include "llvm/Support/CFG.h"
+#include "Support/CommandLine.h"
 #include "Support/Debug.h"
 #include "Support/DepthFirstIterator.h"
 #include "Support/Statistic.h"
@@ -44,6 +45,11 @@ namespace {
                                       "Live Interval Analysis");
 
     Statistic<> numIntervals("liveintervals", "Number of intervals");
+
+    cl::opt<bool>
+    join("join-liveintervals",
+         cl::desc("Join compatible live intervals"),
+         cl::init(false));
 };
 
 void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const
@@ -69,6 +75,7 @@ bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
     mi2iMap_.clear();
     r2iMap_.clear();
     r2iMap_.clear();
+    r2rMap_.clear();
     intervals_.clear();
 
     // number MachineInstrs
@@ -95,18 +102,17 @@ bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
     const LoopInfo& loopInfo = getAnalysis<LoopInfo>();
     const TargetInstrInfo& tii = tm_->getInstrInfo();
 
-    for (MbbIndex2MbbMap::iterator
+    for (MachineFunction::const_iterator mbbi = mf_->begin(),
-             it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
+             mbbe = mf_->end(); mbbi != mbbe; ++mbbi) {
-         it != itEnd; ++it) {
+        const MachineBasicBlock* mbb = mbbi;
-        MachineBasicBlock* mbb = it->second;
-
         unsigned loopDepth = loopInfo.getLoopDepth(mbb->getBasicBlock());
 
-        for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
+        for (MachineBasicBlock::const_iterator mii = mbb->begin(),
-             mi != miEnd; ++mi) {
+                 mie = mbb->end(); mii != mie; ++mii) {
-            MachineInstr* instr = *mi;
+            MachineInstr* mi = *mii;
-            for (int i = instr->getNumOperands() - 1; i >= 0; --i) {
+
-                MachineOperand& mop = instr->getOperand(i);
+            for (int i = mi->getNumOperands() - 1; i >= 0; --i) {
+                MachineOperand& mop = mi->getOperand(i);
 
                 if (!mop.isVirtualRegister())
                     continue;
@@ -119,6 +125,9 @@ bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
         }
     }
 
+    // join intervals if requested
+    if (join) joinIntervals();
+
     numIntervals += intervals_.size();
 
     return true;
@@ -326,48 +335,111 @@ void LiveIntervals::computeIntervals()
                     std::ostream_iterator<Interval>(std::cerr, "\n")));
 }
 
+unsigned LiveIntervals::rep(unsigned reg)
+{
+    Reg2RegMap::iterator it = r2rMap_.find(reg);
+    if (it != r2rMap_.end())
+        return it->second = rep(it->second);
+    return reg;
+}
+
+void LiveIntervals::joinIntervals()
+{
+    DEBUG(std::cerr << "joining compatible intervals:\n");
+
+    const TargetInstrInfo& tii = tm_->getInstrInfo();
+
+    for (MachineFunction::const_iterator mbbi = mf_->begin(),
+             mbbe = mf_->end(); mbbi != mbbe; ++mbbi) {
+        const MachineBasicBlock* mbb = mbbi;
+        DEBUG(std::cerr << "machine basic block: "
+              << mbb->getBasicBlock()->getName() << "\n");
+
+        for (MachineBasicBlock::const_iterator mii = mbb->begin(),
+                 mie = mbb->end(); mii != mie; ++mii) {
+            MachineInstr* mi = *mii;
+            const TargetInstrDescriptor& tid =
+                tm_->getInstrInfo().get(mi->getOpcode());
+            DEBUG(std::cerr << "\t\tinstruction["
+                  << getInstructionIndex(mi) << "]: ";
+                  mi->print(std::cerr, *tm_););
+
+            unsigned srcReg, dstReg;
+            if (tii.isMoveInstr(*mi, srcReg, dstReg) &&
+                (srcReg >= MRegisterInfo::FirstVirtualRegister ||
+                 lv_->getAllocatablePhysicalRegisters()[srcReg]) &&
+                (dstReg >= MRegisterInfo::FirstVirtualRegister ||
+                 lv_->getAllocatablePhysicalRegisters()[dstReg])) {
+
+                // get representative registers
+                srcReg = rep(srcReg);
+                dstReg = rep(dstReg);
+
+                // if they are already joined we continue
+                if (srcReg == dstReg)
+                    continue;
+
+                Reg2IntervalMap::iterator r2iSrc = r2iMap_.find(srcReg);
+                assert(r2iSrc != r2iMap_.end());
+                Reg2IntervalMap::iterator r2iDst = r2iMap_.find(dstReg);
+                assert(r2iDst != r2iMap_.end());
+
+                Intervals::iterator srcInt = r2iSrc->second;
+                Intervals::iterator dstInt = r2iDst->second;
+
+                if (srcInt->reg < MRegisterInfo::FirstVirtualRegister) {
+                    if (dstInt->reg == srcInt->reg ||
+                        (dstInt->reg >= MRegisterInfo::FirstVirtualRegister &&
+                         !dstInt->overlaps(*srcInt))) {
+                        srcInt->join(*dstInt);
+                        r2iDst->second = r2iSrc->second;
+                        r2rMap_.insert(std::make_pair(dstInt->reg, srcInt->reg));
+                        intervals_.erase(dstInt);
+                    }
+                }
+                else if (dstInt->reg < MRegisterInfo::FirstVirtualRegister) {
+                    if (srcInt->reg == dstInt->reg ||
+                        (srcInt->reg >= MRegisterInfo::FirstVirtualRegister &&
+                         !srcInt->overlaps(*dstInt))) {
+                        dstInt->join(*srcInt);
+                        r2iSrc->second = r2iDst->second;
+                        r2rMap_.insert(std::make_pair(srcInt->reg, dstInt->reg));
+                        intervals_.erase(srcInt);
+                    }
+                }
+                else {
+                    const TargetRegisterClass *srcRc, *dstRc;
+                    srcRc = mf_->getSSARegMap()->getRegClass(srcInt->reg);
+                    dstRc = mf_->getSSARegMap()->getRegClass(dstInt->reg);
+
+                    if (srcRc == dstRc && !dstInt->overlaps(*srcInt)) {
+                        srcInt->join(*dstInt);
+                        r2iDst->second = r2iSrc->second;
+                        r2rMap_.insert(std::make_pair(dstInt->reg, srcInt->reg));
+                        intervals_.erase(dstInt);
+                    }
+                }
+            }
+        }
+    }
+
+    intervals_.sort(StartPointComp());
+    DEBUG(std::copy(intervals_.begin(), intervals_.end(),
+                    std::ostream_iterator<Interval>(std::cerr, "\n")));
+    DEBUG(for (Reg2RegMap::const_iterator i = r2rMap_.begin(),
+                   e = r2rMap_.end(); i != e; ++i)
+          std::cerr << i->first << " -> " << i->second << '\n';);
+               
+}
+
 LiveIntervals::Interval::Interval(unsigned r)
-    : reg(r), hint(0),
+    : reg(r),
       weight((r < MRegisterInfo::FirstVirtualRegister ?
               std::numeric_limits<float>::max() : 0.0F))
 {
 
 }
 
-void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
-{
-    DEBUG(std::cerr << "\t\t\tadding range: [" << start <<','<< end << ") -> ");
-    //assert(start < end && "invalid range?");
-    Range range = std::make_pair(start, end);
-    Ranges::iterator it =
-        ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
-                      range);
-
-    mergeRangesForward(it);
-    mergeRangesBackward(it);
-    DEBUG(std::cerr << *this << '\n');
-}
-
-void LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
-{
-    for (Ranges::iterator next = it + 1;
-         next != ranges.end() && it->second >= next->first; ) {
-        it->second = std::max(it->second, next->second);
-        next = ranges.erase(next);
-    }
-}
-
-void LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
-{
-    for (Ranges::iterator prev = it - 1;
-         it != ranges.begin() && it->first <= prev->second; ) {
-        it->first = std::min(it->first, prev->first);
-        it->second = std::max(it->second, prev->second);
-        it = ranges.erase(prev);
-        prev = it - 1;
-    }
-}
-
 bool LiveIntervals::Interval::liveAt(unsigned index) const
 {
     Ranges::const_iterator r = ranges.begin();
@@ -409,6 +481,63 @@ bool LiveIntervals::Interval::overlaps(const Interval& other) const
     return false;
 }
 
+void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
+{
+    DEBUG(std::cerr << "\t\t\tadding range: [" << start <<','<< end << ") -> ");
+    //assert(start < end && "invalid range?");
+    Range range = std::make_pair(start, end);
+    Ranges::iterator it =
+        ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
+                      range);
+
+    it = mergeRangesForward(it);
+    it = mergeRangesBackward(it);
+    DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
+}
+
+void LiveIntervals::Interval::join(const LiveIntervals::Interval& other)
+{
+    DEBUG(std::cerr << "\t\t\t\tjoining intervals: "
+          << other << " and " << *this << '\n');
+    Ranges::iterator cur = ranges.begin();
+
+    for (Ranges::const_iterator i = other.ranges.begin(),
+             e = other.ranges.end(); i != e; ++i) {
+        cur = ranges.insert(std::upper_bound(cur, ranges.end(), *i), *i);
+        cur = mergeRangesForward(cur);
+        cur = mergeRangesBackward(cur);
+    }
+    if (reg >= MRegisterInfo::FirstVirtualRegister)
+        weight += other.weight;
+
+    DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
+}
+
+LiveIntervals::Interval::Ranges::iterator
+LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
+{
+    for (Ranges::iterator next = it + 1;
+         next != ranges.end() && it->second >= next->first; ) {
+        it->second = std::max(it->second, next->second);
+        next = ranges.erase(next);
+    }
+    return it;
+}
+
+LiveIntervals::Interval::Ranges::iterator
+LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
+{
+    for (Ranges::iterator prev = it - 1;
+         it != ranges.begin() && it->first <= prev->second; ) {
+        it->first = std::min(it->first, prev->first);
+        it->second = std::max(it->second, prev->second);
+        it = ranges.erase(prev);
+        prev = it - 1;
+    }
+
+    return it;
+}
+
 std::ostream& llvm::operator<<(std::ostream& os,
                                const LiveIntervals::Interval& li)
 {

lib/CodeGen/LiveIntervalAnalysis.h

@@ -26,6 +26,7 @@
 #include <iostream>
 #include <list>
 #include <map>
+#include <vector>
 
 namespace llvm {
 
@@ -39,10 +40,9 @@ namespace llvm {
             typedef std::pair<unsigned, unsigned> Range;
             typedef std::vector<Range> Ranges;
             unsigned reg;   // the register of this interval
-            unsigned hint;
             float weight;   // weight of this interval (number of uses
                             // * 10^loopDepth)
-            Ranges ranges;  // the ranges this register is valid
+            Ranges ranges;  // the ranges in which this register is live
 
             Interval(unsigned r);
 
@@ -66,10 +66,12 @@ namespace llvm {
 
             void addRange(unsigned start, unsigned end);
 
-        private:
+            void join(const Interval& other);
-            void mergeRangesForward(Ranges::iterator it);
 
-            void mergeRangesBackward(Ranges::iterator it);
+        private:
+            Ranges::iterator mergeRangesForward(Ranges::iterator it);
+
+            Ranges::iterator mergeRangesBackward(Ranges::iterator it);
         };
 
         struct StartPointComp {
@@ -85,6 +87,7 @@ namespace llvm {
         };
 
         typedef std::list<Interval> Intervals;
+        typedef std::map<unsigned, unsigned> Reg2RegMap;
         typedef std::vector<MachineBasicBlock*> MachineBasicBlockPtrs;
 
     private:
@@ -104,11 +107,15 @@ namespace llvm {
         typedef std::map<unsigned, Intervals::iterator> Reg2IntervalMap;
         Reg2IntervalMap r2iMap_;
 
+        Reg2RegMap r2rMap_;
+
         Intervals intervals_;
 
     public:
         virtual void getAnalysisUsage(AnalysisUsage &AU) const;
+
         Intervals& getIntervals() { return intervals_; }
+
         MachineBasicBlockPtrs getOrderedMachineBasicBlockPtrs() const {
             MachineBasicBlockPtrs result;
             for (MbbIndex2MbbMap::const_iterator
@@ -119,6 +126,13 @@ namespace llvm {
             return result;
         }
 
+        const Reg2RegMap& getJoinedRegMap() const {
+            return r2rMap_;
+        }
+
+        /// rep - returns the representative of this register
+        unsigned rep(unsigned reg);
+
     private:
         /// runOnMachineFunction - pass entry point
         bool runOnMachineFunction(MachineFunction&);
@@ -126,6 +140,8 @@ namespace llvm {
         /// computeIntervals - compute live intervals
         void computeIntervals();
 
+        /// joinIntervals - join compatible live intervals
+        void joinIntervals();
 
         /// handleRegisterDef - update intervals for a register def
         /// (calls handlePhysicalRegisterDef and

lib/CodeGen/RegAllocLinearScan.cpp

@@ -32,12 +32,15 @@ using namespace llvm;
 namespace {
     Statistic<> numSpilled ("ra-linearscan", "Number of registers spilled");
     Statistic<> numReloaded("ra-linearscan", "Number of registers reloaded");
+    Statistic<> numPeep    ("ra-linearscan",
+                            "Number of identity moves eliminated");
 
     class RA : public MachineFunctionPass {
     private:
         MachineFunction* mf_;
         const TargetMachine* tm_;
         const MRegisterInfo* mri_;
+        LiveIntervals* li_;
         MachineFunction::iterator currentMbb_;
         MachineBasicBlock::iterator currentInstr_;
         typedef std::vector<const LiveIntervals::Interval*> IntervalPtrs;
@@ -203,8 +206,8 @@ bool RA::runOnMachineFunction(MachineFunction &fn) {
     mf_ = &fn;
     tm_ = &fn.getTarget();
     mri_ = tm_->getRegisterInfo();
-
+    li_ = &getAnalysis<LiveIntervals>();
-    initIntervalSets(getAnalysis<LiveIntervals>().getIntervals());
+    initIntervalSets(li_->getIntervals());
 
     v2pMap_.clear();
     v2ssMap_.clear();
@@ -231,6 +234,7 @@ bool RA::runOnMachineFunction(MachineFunction &fn) {
     reserved_[29] = true; /* FP6 */
 
     // linear scan algorithm
+    DEBUG(std::cerr << "Machine Function\n");
 
     DEBUG(printIntervals("\tunhandled", unhandled_.begin(), unhandled_.end()));
     DEBUG(printIntervals("\tfixed", fixed_.begin(), fixed_.end()));
@@ -324,15 +328,54 @@ bool RA::runOnMachineFunction(MachineFunction &fn) {
     active_.clear();
     inactive_.clear();
 
-    DEBUG(std::cerr << "finished register allocation\n");
+    typedef LiveIntervals::Reg2RegMap Reg2RegMap;
+    const Reg2RegMap& r2rMap = li_->getJoinedRegMap();
+
     DEBUG(printVirtRegAssignment());
+    DEBUG(std::cerr << "Performing coalescing on joined intervals\n");
+    // perform coalescing if we were passed joined intervals
+    for(Reg2RegMap::const_iterator i = r2rMap.begin(), e = r2rMap.end();
+        i != e; ++i) {
+        unsigned reg = i->first;
+        unsigned rep = li_->rep(reg);
+
+        assert((rep < MRegisterInfo::FirstVirtualRegister ||
+                v2pMap_.find(rep) != v2pMap_.end() ||
+                v2ssMap_.find(rep) != v2ssMap_.end()) &&
+               "representative register is not allocated!");
+
+        assert(reg >= MRegisterInfo::FirstVirtualRegister &&
+               v2pMap_.find(reg) == v2pMap_.end() &&
+               v2ssMap_.find(reg) == v2ssMap_.end() &&
+               "coalesced register is already allocated!");
+
+        if (rep < MRegisterInfo::FirstVirtualRegister) {
+            v2pMap_.insert(std::make_pair(reg, rep));
+        }
+        else {
+            Virt2PhysMap::const_iterator pr = v2pMap_.find(rep);
+            if (pr != v2pMap_.end()) {
+                v2pMap_.insert(std::make_pair(reg, pr->second));
+            }
+            else {
+                Virt2StackSlotMap::const_iterator ss = v2ssMap_.find(rep);
+                assert(ss != v2ssMap_.end());
+                v2ssMap_.insert(std::make_pair(reg, ss->second));
+            }
+        }
+    }
+
+    DEBUG(printVirtRegAssignment());
+    DEBUG(std::cerr << "finished register allocation\n");
+
+    const TargetInstrInfo& tii = tm_->getInstrInfo();
 
     DEBUG(std::cerr << "Rewrite machine code:\n");
     for (currentMbb_ = mf_->begin(); currentMbb_ != mf_->end(); ++currentMbb_) {
         instrAdded_ = 0;
 
         for (currentInstr_ = currentMbb_->begin();
-             currentInstr_ != currentMbb_->end(); ++currentInstr_) {
+             currentInstr_ != currentMbb_->end(); ) {
 
             DEBUG(std::cerr << "\tinstruction: ";
                   (*currentInstr_)->print(std::cerr, *tm_););
@@ -355,6 +398,21 @@ bool RA::runOnMachineFunction(MachineFunction &fn) {
                 }
             }
 
+            unsigned srcReg, dstReg;
+            if (tii.isMoveInstr(**currentInstr_, srcReg, dstReg) &&
+                ((srcReg < MRegisterInfo::FirstVirtualRegister &&
+                  dstReg < MRegisterInfo::FirstVirtualRegister &&
+                  srcReg == dstReg) ||
+                 (srcReg >= MRegisterInfo::FirstVirtualRegister &&
+                  dstReg >= MRegisterInfo::FirstVirtualRegister &&
+                  v2ssMap_[srcReg] == v2ssMap_[dstReg]))) {
+                delete *currentInstr_;
+                currentInstr_ = currentMbb_->erase(currentInstr_);
+                ++numPeep;
+                DEBUG(std::cerr << "\t\tdeleting instruction\n");
+                continue;
+            }
+                        
             DEBUG(std::cerr << "\t\tloading temporarily used operands to "
                   "registers:\n");
             for (unsigned i = 0, e = (*currentInstr_)->getNumOperands();
@@ -416,6 +474,7 @@ bool RA::runOnMachineFunction(MachineFunction &fn) {
             }
             --currentInstr_; // restore currentInstr_ iterator
             tempDefOperands_.clear();
+            ++currentInstr_;
         }
     }