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instead of requiring all "short description" strings to begin with two spaces. This makes these strings less mysterious, and it fixes some cases where short description strings mistakenly did not begin with two spaces. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57521 91177308-0d34-0410-b5e6-96231b3b80d8
256 lines
9.0 KiB
C++
256 lines
9.0 KiB
C++
//===-- RegAllocSimple.cpp - A simple generic register allocator ----------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements a simple register allocator. *Very* simple: It immediate
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// spills every value right after it is computed, and it reloads all used
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// operands from the spill area to temporary registers before each instruction.
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// It does not keep values in registers across instructions.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "regalloc"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/MachineFrameInfo.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/RegAllocRegistry.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/STLExtras.h"
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#include <map>
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using namespace llvm;
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STATISTIC(NumStores, "Number of stores added");
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STATISTIC(NumLoads , "Number of loads added");
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namespace {
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static RegisterRegAlloc
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simpleRegAlloc("simple", "simple register allocator",
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createSimpleRegisterAllocator);
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class VISIBILITY_HIDDEN RegAllocSimple : public MachineFunctionPass {
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public:
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static char ID;
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RegAllocSimple() : MachineFunctionPass(&ID) {}
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private:
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MachineFunction *MF;
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const TargetMachine *TM;
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const TargetRegisterInfo *TRI;
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const TargetInstrInfo *TII;
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// StackSlotForVirtReg - Maps SSA Regs => frame index on the stack where
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// these values are spilled
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std::map<unsigned, int> StackSlotForVirtReg;
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// RegsUsed - Keep track of what registers are currently in use. This is a
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// bitset.
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std::vector<bool> RegsUsed;
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// RegClassIdx - Maps RegClass => which index we can take a register
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// from. Since this is a simple register allocator, when we need a register
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// of a certain class, we just take the next available one.
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std::map<const TargetRegisterClass*, unsigned> RegClassIdx;
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public:
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virtual const char *getPassName() const {
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return "Simple Register Allocator";
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}
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/// runOnMachineFunction - Register allocate the whole function
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bool runOnMachineFunction(MachineFunction &Fn);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredID(PHIEliminationID); // Eliminate PHI nodes
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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private:
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/// AllocateBasicBlock - Register allocate the specified basic block.
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void AllocateBasicBlock(MachineBasicBlock &MBB);
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/// getStackSpaceFor - This returns the offset of the specified virtual
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/// register on the stack, allocating space if necessary.
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int getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC);
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/// Given a virtual register, return a compatible physical register that is
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/// currently unused.
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///
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/// Side effect: marks that register as being used until manually cleared
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///
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unsigned getFreeReg(unsigned virtualReg);
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/// Moves value from memory into that register
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unsigned reloadVirtReg(MachineBasicBlock &MBB,
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MachineBasicBlock::iterator I, unsigned VirtReg);
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/// Saves reg value on the stack (maps virtual register to stack value)
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void spillVirtReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator I,
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unsigned VirtReg, unsigned PhysReg);
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};
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char RegAllocSimple::ID = 0;
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}
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/// getStackSpaceFor - This allocates space for the specified virtual
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/// register to be held on the stack.
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int RegAllocSimple::getStackSpaceFor(unsigned VirtReg,
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const TargetRegisterClass *RC) {
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// Find the location VirtReg would belong...
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std::map<unsigned, int>::iterator I = StackSlotForVirtReg.find(VirtReg);
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if (I != StackSlotForVirtReg.end())
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return I->second; // Already has space allocated?
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// Allocate a new stack object for this spill location...
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int FrameIdx = MF->getFrameInfo()->CreateStackObject(RC->getSize(),
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RC->getAlignment());
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// Assign the slot...
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StackSlotForVirtReg.insert(I, std::make_pair(VirtReg, FrameIdx));
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return FrameIdx;
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}
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unsigned RegAllocSimple::getFreeReg(unsigned virtualReg) {
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const TargetRegisterClass* RC = MF->getRegInfo().getRegClass(virtualReg);
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TargetRegisterClass::iterator RI = RC->allocation_order_begin(*MF);
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TargetRegisterClass::iterator RE = RC->allocation_order_end(*MF);
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while (1) {
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unsigned regIdx = RegClassIdx[RC]++;
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assert(RI+regIdx != RE && "Not enough registers!");
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unsigned PhysReg = *(RI+regIdx);
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if (!RegsUsed[PhysReg]) {
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MF->getRegInfo().setPhysRegUsed(PhysReg);
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return PhysReg;
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}
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}
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}
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unsigned RegAllocSimple::reloadVirtReg(MachineBasicBlock &MBB,
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MachineBasicBlock::iterator I,
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unsigned VirtReg) {
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const TargetRegisterClass* RC = MF->getRegInfo().getRegClass(VirtReg);
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int FrameIdx = getStackSpaceFor(VirtReg, RC);
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unsigned PhysReg = getFreeReg(VirtReg);
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// Add move instruction(s)
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++NumLoads;
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TII->loadRegFromStackSlot(MBB, I, PhysReg, FrameIdx, RC);
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return PhysReg;
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}
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void RegAllocSimple::spillVirtReg(MachineBasicBlock &MBB,
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MachineBasicBlock::iterator I,
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unsigned VirtReg, unsigned PhysReg) {
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const TargetRegisterClass* RC = MF->getRegInfo().getRegClass(VirtReg);
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int FrameIdx = getStackSpaceFor(VirtReg, RC);
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// Add move instruction(s)
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++NumStores;
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TII->storeRegToStackSlot(MBB, I, PhysReg, true, FrameIdx, RC);
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}
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void RegAllocSimple::AllocateBasicBlock(MachineBasicBlock &MBB) {
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// loop over each instruction
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for (MachineBasicBlock::iterator MI = MBB.begin(); MI != MBB.end(); ++MI) {
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// Made to combat the incorrect allocation of r2 = add r1, r1
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std::map<unsigned, unsigned> Virt2PhysRegMap;
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RegsUsed.resize(TRI->getNumRegs());
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// This is a preliminary pass that will invalidate any registers that are
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// used by the instruction (including implicit uses).
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const TargetInstrDesc &Desc = MI->getDesc();
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const unsigned *Regs;
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if (Desc.ImplicitUses) {
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for (Regs = Desc.ImplicitUses; *Regs; ++Regs)
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RegsUsed[*Regs] = true;
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}
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if (Desc.ImplicitDefs) {
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for (Regs = Desc.ImplicitDefs; *Regs; ++Regs) {
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RegsUsed[*Regs] = true;
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MF->getRegInfo().setPhysRegUsed(*Regs);
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}
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}
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// Loop over uses, move from memory into registers.
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for (int i = MI->getNumOperands() - 1; i >= 0; --i) {
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MachineOperand &MO = MI->getOperand(i);
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if (MO.isReg() && MO.getReg() &&
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TargetRegisterInfo::isVirtualRegister(MO.getReg())) {
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unsigned virtualReg = (unsigned) MO.getReg();
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DOUT << "op: " << MO << "\n";
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DOUT << "\t inst[" << i << "]: ";
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DEBUG(MI->print(*cerr.stream(), TM));
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// make sure the same virtual register maps to the same physical
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// register in any given instruction
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unsigned physReg = Virt2PhysRegMap[virtualReg];
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if (physReg == 0) {
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if (MO.isDef()) {
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int TiedOp = Desc.findTiedToSrcOperand(i);
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if (TiedOp == -1) {
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physReg = getFreeReg(virtualReg);
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} else {
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// must be same register number as the source operand that is
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// tied to. This maps a = b + c into b = b + c, and saves b into
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// a's spot.
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assert(MI->getOperand(TiedOp).isReg() &&
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MI->getOperand(TiedOp).getReg() &&
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MI->getOperand(TiedOp).isUse() &&
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"Two address instruction invalid!");
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physReg = MI->getOperand(TiedOp).getReg();
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}
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spillVirtReg(MBB, next(MI), virtualReg, physReg);
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} else {
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physReg = reloadVirtReg(MBB, MI, virtualReg);
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Virt2PhysRegMap[virtualReg] = physReg;
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}
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}
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MO.setReg(physReg);
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DOUT << "virt: " << virtualReg << ", phys: " << MO.getReg() << "\n";
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}
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}
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RegClassIdx.clear();
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RegsUsed.clear();
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}
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}
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/// runOnMachineFunction - Register allocate the whole function
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///
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bool RegAllocSimple::runOnMachineFunction(MachineFunction &Fn) {
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DOUT << "Machine Function\n";
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MF = &Fn;
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TM = &MF->getTarget();
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TRI = TM->getRegisterInfo();
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TII = TM->getInstrInfo();
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// Loop over all of the basic blocks, eliminating virtual register references
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for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
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MBB != MBBe; ++MBB)
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AllocateBasicBlock(*MBB);
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StackSlotForVirtReg.clear();
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return true;
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}
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FunctionPass *llvm::createSimpleRegisterAllocator() {
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return new RegAllocSimple();
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}
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