Move machine code rewriter and spiller outside the register

allocator.

The implementation is completely rewritten and now employs several
optimizations not exercised before. For example for 164.gzip we have
997 loads and 699 stores vs the 1221 loads and 880 stores we have
before.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11798 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/RegAllocLinearScan.cpp

@@ -10,6 +10,7 @@
 // This file implements a linear scan register allocator.
 //
 //===----------------------------------------------------------------------===//
+
 #define DEBUG_TYPE "regalloc"
 #include "llvm/Function.h"
 #include "llvm/CodeGen/LiveVariables.h"
@@ -18,28 +19,21 @@
 #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/Support/CFG.h"
 #include "Support/Debug.h"
-#include "Support/DepthFirstIterator.h"
-#include "Support/Statistic.h"
-#include "Support/STLExtras.h"
 #include "LiveIntervals.h"
 #include "PhysRegTracker.h"
 #include "VirtRegMap.h"
 #include <algorithm>
+#include <iostream>
+
 using namespace llvm;
 
 namespace {
-    Statistic<> numStores("ra-linearscan", "Number of stores added");
-    Statistic<> numLoads ("ra-linearscan", "Number of loads added");
-
     class RA : public MachineFunctionPass {
     private:
         MachineFunction* mf_;
         const TargetMachine* tm_;
-        const TargetInstrInfo* tii_;
         const MRegisterInfo* mri_;
         LiveIntervals* li_;
         typedef std::list<LiveIntervals::Interval*> IntervalPtrs;
@@ -48,8 +42,6 @@ namespace {
         std::auto_ptr<PhysRegTracker> prt_;
         std::auto_ptr<VirtRegMap> vrm_;
 
-        int instrAdded_;
-
         typedef std::vector<float> SpillWeights;
         SpillWeights spillWeights_;
 
@@ -70,6 +62,9 @@ namespace {
         void releaseMemory();
 
     private:
+        /// linearScan - the linear scan algorithm
+        void linearScan();
+
         /// initIntervalSets - initializa the four interval sets:
         /// unhandled, fixed, active and inactive
         void initIntervalSets(LiveIntervals::Intervals& li);
@@ -90,10 +85,6 @@ namespace {
         /// is available, or spill.
         void assignRegOrStackSlotAtInterval(IntervalPtrs::value_type cur);
 
-        /// addSpillCode - adds spill code for interval. The interval
-        /// must be modified by LiveIntervals::updateIntervalForSpill.
-        void addSpillCode(IntervalPtrs::value_type li, int slot);
-
         ///
         /// register handling helpers
         ///
@@ -152,7 +143,6 @@ void RA::releaseMemory()
 bool RA::runOnMachineFunction(MachineFunction &fn) {
     mf_ = &fn;
     tm_ = &fn.getTarget();
-    tii_ = &tm_->getInstrInfo();
     mri_ = tm_->getRegisterInfo();
     li_ = &getAnalysis<LiveIntervals>();
     if (!prt_.get()) prt_.reset(new PhysRegTracker(*mri_));
@@ -160,6 +150,15 @@ bool RA::runOnMachineFunction(MachineFunction &fn) {
 
     initIntervalSets(li_->getIntervals());
 
+    linearScan();
+
+    eliminateVirtRegs(*mf_, *vrm_);
+
+    return true;
+}
+
+void RA::linearScan()
+{
     // linear scan algorithm
     DEBUG(std::cerr << "********** LINEAR SCAN **********\n");
     DEBUG(std::cerr << "********** Function: "
@@ -223,63 +222,6 @@ bool RA::runOnMachineFunction(MachineFunction &fn) {
     }
 
     DEBUG(std::cerr << *vrm_);
-
-    DEBUG(std::cerr << "********** REWRITE MACHINE CODE **********\n");
-    DEBUG(std::cerr << "********** Function: "
-          << mf_->getFunction()->getName() << '\n');
-
-    for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
-         mbbi != mbbe; ++mbbi) {
-        instrAdded_ = 0;
-
-        for (MachineBasicBlock::iterator mii = mbbi->begin(), mie = mbbi->end();
-             mii != mie; ++mii) {
-            DEBUG(
-                std::cerr << '[';
-                unsigned index = li_->getInstructionIndex(mii);
-                if (index == std::numeric_limits<unsigned>::max())
-                    std::cerr << '*';
-                else
-                    std::cerr << index;
-                std::cerr << "]\t";
-                mii->print(std::cerr, *tm_));
-
-            // use our current mapping and actually replace every
-            // virtual register with its allocated physical registers
-            DEBUG(std::cerr << "\t");
-            for (unsigned i = 0, e = mii->getNumOperands();
-                 i != e; ++i) {
-                MachineOperand& op = mii->getOperand(i);
-                if (op.isRegister() &&
-                    MRegisterInfo::isVirtualRegister(op.getReg())) {
-                    unsigned virtReg = op.getReg();
-                    unsigned physReg = vrm_->getPhys(virtReg);
-                    DEBUG(std::cerr << "\t[reg" << virtReg
-                          << " -> " << mri_->getName(physReg) << ']');
-                    mii->SetMachineOperandReg(i, physReg);
-                }
-            }
-            DEBUG(std::cerr << '\n');
-        }
-    }
-
-    DEBUG(std::cerr << "********** MACHINEINSTRS **********\n");
-    DEBUG(
-        for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
-             mbbi != mbbe; ++mbbi) {
-            std::cerr << mbbi->getBasicBlock()->getName() << ":\n";
-            for (MachineBasicBlock::iterator mii = mbbi->begin(),
-                     mie = mbbi->end(); mii != mie; ++mii) {
-                unsigned index = li_->getInstructionIndex(mii);
-                if (index == std::numeric_limits<unsigned>::max())
-                    std::cerr << "*\t";
-                else
-                    std::cerr << index << '\t';
-                mii->print(std::cerr, *tm_);
-            }
-        });
-
-    return true;
 }
 
 void RA::initIntervalSets(LiveIntervals::Intervals& li)
@@ -450,7 +392,6 @@ void RA::assignRegOrStackSlotAtInterval(IntervalPtrs::value_type cur)
         // sorted on earliest start point and we may have changed our
         // start point.
         if (!cur->empty()) {
-            addSpillCode(cur, slot);
             IntervalPtrs::iterator it = unhandled_.begin();
             while (it != unhandled_.end() && (*it)->start() < cur->start())
                 ++it;
@@ -484,7 +425,6 @@ void RA::assignRegOrStackSlotAtInterval(IntervalPtrs::value_type cur)
             earliestStart = std::min(earliestStart, (*i)->start());
             int slot = vrm_->assignVirt2StackSlot((*i)->reg);
             li_->updateSpilledInterval(**i, slot);
-            addSpillCode(*i, slot);
         }
     }
     for (IntervalPtrs::iterator i = inactive_.begin();
@@ -497,7 +437,6 @@ void RA::assignRegOrStackSlotAtInterval(IntervalPtrs::value_type cur)
             earliestStart = std::min(earliestStart, (*i)->start());
             int slot = vrm_->assignVirt2StackSlot((*i)->reg);
             li_->updateSpilledInterval(**i, slot);
-            addSpillCode(*i, slot);
         }
     }
 
@@ -580,71 +519,6 @@ void RA::assignRegOrStackSlotAtInterval(IntervalPtrs::value_type cur)
     }
 }
 
-void RA::addSpillCode(IntervalPtrs::value_type li, int slot)
-{
-    // We scan the instructions corresponding to each range. We load
-    // when we have a use and spill at end of basic blocks or end of
-    // ranges only if the register was modified.
-    const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(li->reg);
-
-    for (LiveIntervals::Interval::Ranges::iterator i = li->ranges.begin(),
-             e = li->ranges.end(); i != e; ++i) {
-        unsigned index = i->first;
-        unsigned end = i->second;
-
-        bool loaded = false;
-
-        // skip deleted instructions. getInstructionFromIndex returns
-        // null if the instruction was deleted (because of coalescing
-        // for example)
-        while (!li_->getInstructionFromIndex(index))
-            index += LiveIntervals::InstrSlots::NUM;
-        MachineBasicBlock::iterator mi = li_->getInstructionFromIndex(index);
-        MachineBasicBlock* mbb = mi->getParent();
-        assert(mbb && "machine instruction not bound to basic block");
-
-        for (; index < end; index += LiveIntervals::InstrSlots::NUM) {
-            // ignore deleted instructions
-            while (!li_->getInstructionFromIndex(index)) index += 2;
-            mi = li_->getInstructionFromIndex(index);
-            DEBUG(std::cerr << "\t\t\t\texamining: \t\t\t\t\t"
-                  << LiveIntervals::getBaseIndex(index) << '\t';
-                  mi->print(std::cerr, *tm_));
-
-            // if it is used in this instruction load it
-            for (unsigned i = 0; i < mi->getNumOperands(); ++i) {
-                MachineOperand& mop = mi->getOperand(i);
-                if (mop.isRegister() && mop.getReg() == li->reg &&
-                    mop.isUse() && !loaded) {
-                    loaded = true;
-                    mri_->loadRegFromStackSlot(*mbb, mi, li->reg, slot, rc);
-                    ++numLoads;
-                    DEBUG(std::cerr << "\t\t\t\tadded load for reg" << li->reg
-                          << " from ss#" << slot << " before: \t"
-                          << LiveIntervals::getBaseIndex(index) << '\t';
-                          mi->print(std::cerr, *tm_));
-                }
-            }
-
-            // if it is defined in this instruction mark as dirty
-            for (unsigned i = 0; i < mi->getNumOperands(); ++i) {
-                MachineOperand& mop = mi->getOperand(i);
-                if (mop.isRegister() && mop.getReg() == li->reg &&
-                    mop.isDef()) {
-                    loaded = true;
-
-                    mri_->storeRegToStackSlot(*mbb, next(mi), li->reg, slot,rc);
-                    ++numStores;
-                    DEBUG(std::cerr << "\t\t\t\tadded store for reg" << li->reg
-                          << " to ss#" << slot << " after: \t\t"
-                          << LiveIntervals::getBaseIndex(index) << " \t";
-                          mi->print(std::cerr, *tm_));
-                }
-            }
-        }
-    }
-}
-
 unsigned RA::getFreePhysReg(IntervalPtrs::value_type cur)
 {
     const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);

lib/CodeGen/VirtRegMap.cpp

@@ -7,20 +7,32 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This file implements the virtual register map.
+// This file implements the virtual register map. It also implements
+// the eliminateVirtRegs() function that given a virtual register map
+// and a machine function it eliminates all virtual references by
+// replacing them with physical register references and adds spill
+// code as necessary.
 //
 //===----------------------------------------------------------------------===//
 
+#define DEBUG_TYPE "regalloc"
 #include "VirtRegMap.h"
+#include "llvm/Function.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetInstrInfo.h"
 #include "Support/Statistic.h"
+#include "Support/Debug.h"
+#include "Support/STLExtras.h"
 #include <iostream>
 
 using namespace llvm;
 
 namespace {
-    Statistic<> numSpills("ra-linearscan", "Number of register spills");
+    Statistic<> numSpills("spiller", "Number of register spills");
+    Statistic<> numStores("spiller", "Number of stores added");
+    Statistic<> numLoads ("spiller", "Number of loads added");
+
 }
 
 int VirtRegMap::assignVirt2StackSlot(unsigned virtReg)
@@ -53,3 +65,148 @@ std::ostream& llvm::operator<<(std::ostream& os, const VirtRegMap& vrm)
     }
     return std::cerr << '\n';
 }
+
+namespace {
+
+    class Spiller {
+        typedef std::vector<unsigned> Phys2VirtMap;
+        typedef std::vector<bool> PhysFlag;
+
+        MachineFunction& mf_;
+        const TargetMachine& tm_;
+        const TargetInstrInfo& tii_;
+        const MRegisterInfo& mri_;
+        const VirtRegMap& vrm_;
+        Phys2VirtMap p2vMap_;
+        PhysFlag dirty_;
+
+    public:
+        Spiller(MachineFunction& mf, const VirtRegMap& vrm)
+            : mf_(mf),
+              tm_(mf_.getTarget()),
+              tii_(tm_.getInstrInfo()),
+              mri_(*tm_.getRegisterInfo()),
+              vrm_(vrm),
+              p2vMap_(mri_.getNumRegs()),
+              dirty_(mri_.getNumRegs()) {
+            DEBUG(std::cerr << "********** REWRITE MACHINE CODE **********\n");
+            DEBUG(std::cerr << "********** Function: "
+                  << mf_.getFunction()->getName() << '\n');
+        }
+
+        void eliminateVirtRegs() {
+            for (MachineFunction::iterator mbbi = mf_.begin(),
+                     mbbe = mf_.end(); mbbi != mbbe; ++mbbi) {
+                // clear map and dirty flag
+                p2vMap_.assign(p2vMap_.size(), 0);
+                dirty_.assign(dirty_.size(), false);
+                DEBUG(std::cerr << mbbi->getBasicBlock()->getName() << ":\n");
+                eliminateVirtRegsInMbb(*mbbi);
+            }
+        }
+
+    private:
+        void vacateJustPhysReg(MachineBasicBlock& mbb,
+                               MachineBasicBlock::iterator mii,
+                               unsigned physReg) {
+            unsigned virtReg = p2vMap_[physReg];
+            if (dirty_[physReg] && vrm_.hasStackSlot(virtReg)) {
+                mri_.storeRegToStackSlot(mbb, mii, physReg,
+                                         vrm_.getStackSlot(virtReg),
+                                         mri_.getRegClass(physReg));
+                ++numStores;
+                DEBUG(std::cerr << "*\t"; prior(mii)->print(std::cerr, tm_));
+            }
+            p2vMap_[physReg] = 0;
+            dirty_[physReg] = false;
+        }
+
+        void vacatePhysReg(MachineBasicBlock& mbb,
+                           MachineBasicBlock::iterator mii,
+                           unsigned physReg) {
+            vacateJustPhysReg(mbb, mii, physReg);
+            for (const unsigned* as = mri_.getAliasSet(physReg); *as; ++as)
+                vacateJustPhysReg(mbb, mii, *as);
+        }
+
+        void handleUse(MachineBasicBlock& mbb,
+                       MachineBasicBlock::iterator mii,
+                       unsigned virtReg,
+                       unsigned physReg) {
+            // check if we are replacing a previous mapping
+            if (p2vMap_[physReg] != virtReg) {
+                vacatePhysReg(mbb, mii, physReg);
+                p2vMap_[physReg] = virtReg;
+                // load if necessary
+                if (vrm_.hasStackSlot(virtReg)) {
+                    mri_.loadRegFromStackSlot(mbb, mii, physReg,
+                                              vrm_.getStackSlot(virtReg),
+                                              mri_.getRegClass(physReg));
+                    ++numLoads;
+                    DEBUG(std::cerr << "*\t"; prior(mii)->print(std::cerr,tm_));
+                }
+            }
+        }
+
+        void handleDef(MachineBasicBlock& mbb,
+                       MachineBasicBlock::iterator mii,
+                       unsigned virtReg,
+                       unsigned physReg) {
+            // check if we are replacing a previous mapping
+            if (p2vMap_[physReg] != virtReg)
+                vacatePhysReg(mbb, mii, physReg);
+
+            p2vMap_[physReg] = virtReg;
+            dirty_[physReg] = true;
+        }
+
+        void eliminateVirtRegsInMbb(MachineBasicBlock& mbb) {
+            for (MachineBasicBlock::iterator mii = mbb.begin(),
+                     mie = mbb.end(); mii != mie; ++mii) {
+                // rewrite all used operands
+                for (unsigned i = 0, e = mii->getNumOperands(); i != e; ++i) {
+                    MachineOperand& op = mii->getOperand(i);
+                    if (op.isRegister() && op.isUse() &&
+                        MRegisterInfo::isVirtualRegister(op.getReg())) {
+                        unsigned physReg = vrm_.getPhys(op.getReg());
+                        handleUse(mbb, mii, op.getReg(), physReg);
+                        mii->SetMachineOperandReg(i, physReg);
+                        // mark as dirty if this is def&use
+                        if (op.isDef()) dirty_[physReg] = true;
+                    }
+                }
+
+                // spill implicit defs
+                const TargetInstrDescriptor& tid =tii_.get(mii->getOpcode());
+                for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
+                    vacatePhysReg(mbb, mii, *id);
+
+                // rewrite def operands (def&use was handled with the
+                // uses so don't check for those here)
+                for (unsigned i = 0, e = mii->getNumOperands(); i != e; ++i) {
+                    MachineOperand& op = mii->getOperand(i);
+                    if (op.isRegister() && !op.isUse())
+                        if (MRegisterInfo::isPhysicalRegister(op.getReg()))
+                            vacatePhysReg(mbb, mii, op.getReg());
+                        else {
+                            unsigned physReg = vrm_.getPhys(op.getReg());
+                            handleDef(mbb, mii, op.getReg(), physReg);
+                            mii->SetMachineOperandReg(i, physReg);
+                        }
+                }
+
+                DEBUG(std::cerr << '\t'; mii->print(std::cerr, tm_));
+            }
+
+            for (unsigned i = 1, e = p2vMap_.size(); i != e; ++i)
+                vacateJustPhysReg(mbb, mbb.getFirstTerminator(), i);
+
+        }
+    };
+}
+
+
+void llvm::eliminateVirtRegs(MachineFunction& mf, const VirtRegMap& vrm)
+{
+    Spiller(mf, vrm).eliminateVirtRegs();
+}

lib/CodeGen/VirtRegMap.h

@@ -98,6 +98,8 @@ namespace llvm {
 
     std::ostream& operator<<(std::ostream& os, const VirtRegMap& li);
 
+    void eliminateVirtRegs(MachineFunction& mf, const VirtRegMap& vrm);
+
 } // End llvm namespace
 
 #endif