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llvm-mirror/lib/CodeGen/RegAllocSimple.cpp
2003-11-11 22:41:34 +00:00

241 lines
8.5 KiB
C++

//===-- RegAllocSimple.cpp - A simple generic 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 simple register allocator. *Very* simple: It immediate
// spills every value right after it is computed, and it reloads all used
// operands from the spill area to temporary registers before each instruction.
// It does not keep values in registers across instructions.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "regalloc"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/SSARegMap.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "Support/Debug.h"
#include "Support/Statistic.h"
#include <iostream>
namespace llvm {
namespace {
Statistic<> NumSpilled ("ra-simple", "Number of registers spilled");
Statistic<> NumReloaded("ra-simple", "Number of registers reloaded");
class RegAllocSimple : public MachineFunctionPass {
MachineFunction *MF;
const TargetMachine *TM;
const MRegisterInfo *RegInfo;
// StackSlotForVirtReg - Maps SSA Regs => frame index on the stack where
// these values are spilled
std::map<unsigned, int> StackSlotForVirtReg;
// RegsUsed - Keep track of what registers are currently in use. This is a
// bitset.
std::vector<bool> RegsUsed;
// RegClassIdx - Maps RegClass => which index we can take a register
// from. Since this is a simple register allocator, when we need a register
// of a certain class, we just take the next available one.
std::map<const TargetRegisterClass*, unsigned> RegClassIdx;
public:
virtual const char *getPassName() const {
return "Simple Register Allocator";
}
/// runOnMachineFunction - Register allocate the whole function
bool runOnMachineFunction(MachineFunction &Fn);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredID(PHIEliminationID); // Eliminate PHI nodes
MachineFunctionPass::getAnalysisUsage(AU);
}
private:
/// AllocateBasicBlock - Register allocate the specified basic block.
void AllocateBasicBlock(MachineBasicBlock &MBB);
/// getStackSpaceFor - This returns the offset of the specified virtual
/// register on the stack, allocating space if necessary.
int getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC);
/// Given a virtual register, return a compatible physical register that is
/// currently unused.
///
/// Side effect: marks that register as being used until manually cleared
///
unsigned getFreeReg(unsigned virtualReg);
/// Moves value from memory into that register
unsigned reloadVirtReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I, unsigned VirtReg);
/// Saves reg value on the stack (maps virtual register to stack value)
void spillVirtReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned VirtReg, unsigned PhysReg);
};
}
/// getStackSpaceFor - This allocates space for the specified virtual
/// register to be held on the stack.
int RegAllocSimple::getStackSpaceFor(unsigned VirtReg,
const TargetRegisterClass *RC) {
// Find the location VirtReg would belong...
std::map<unsigned, int>::iterator I =
StackSlotForVirtReg.lower_bound(VirtReg);
if (I != StackSlotForVirtReg.end() && I->first == VirtReg)
return I->second; // Already has space allocated?
// Allocate a new stack object for this spill location...
int FrameIdx = MF->getFrameInfo()->CreateStackObject(RC);
// Assign the slot...
StackSlotForVirtReg.insert(I, std::make_pair(VirtReg, FrameIdx));
return FrameIdx;
}
unsigned RegAllocSimple::getFreeReg(unsigned virtualReg) {
const TargetRegisterClass* RC = MF->getSSARegMap()->getRegClass(virtualReg);
TargetRegisterClass::iterator RI = RC->allocation_order_begin(*MF);
TargetRegisterClass::iterator RE = RC->allocation_order_end(*MF);
while (1) {
unsigned regIdx = RegClassIdx[RC]++;
assert(RI+regIdx != RE && "Not enough registers!");
unsigned PhysReg = *(RI+regIdx);
if (!RegsUsed[PhysReg])
return PhysReg;
}
}
unsigned RegAllocSimple::reloadVirtReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I,
unsigned VirtReg) {
const TargetRegisterClass* RC = MF->getSSARegMap()->getRegClass(VirtReg);
int FrameIdx = getStackSpaceFor(VirtReg, RC);
unsigned PhysReg = getFreeReg(VirtReg);
// Add move instruction(s)
++NumReloaded;
RegInfo->loadRegFromStackSlot(MBB, I, PhysReg, FrameIdx, RC);
return PhysReg;
}
void RegAllocSimple::spillVirtReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I,
unsigned VirtReg, unsigned PhysReg) {
const TargetRegisterClass* RC = MF->getSSARegMap()->getRegClass(VirtReg);
int FrameIdx = getStackSpaceFor(VirtReg, RC);
// Add move instruction(s)
++NumSpilled;
RegInfo->storeRegToStackSlot(MBB, I, PhysReg, FrameIdx, RC);
}
void RegAllocSimple::AllocateBasicBlock(MachineBasicBlock &MBB) {
// loop over each instruction
for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end(); ++I) {
// Made to combat the incorrect allocation of r2 = add r1, r1
std::map<unsigned, unsigned> Virt2PhysRegMap;
MachineInstr *MI = *I;
RegsUsed.resize(MRegisterInfo::FirstVirtualRegister);
// a preliminary pass that will invalidate any registers that
// are used by the instruction (including implicit uses)
unsigned Opcode = MI->getOpcode();
const TargetInstrDescriptor &Desc = TM->getInstrInfo().get(Opcode);
const unsigned *Regs = Desc.ImplicitUses;
while (*Regs)
RegsUsed[*Regs++] = true;
Regs = Desc.ImplicitDefs;
while (*Regs)
RegsUsed[*Regs++] = true;
// Loop over uses, move from memory into registers
for (int i = MI->getNumOperands() - 1; i >= 0; --i) {
MachineOperand &op = MI->getOperand(i);
if (op.isVirtualRegister()) {
unsigned virtualReg = (unsigned) op.getAllocatedRegNum();
DEBUG(std::cerr << "op: " << op << "\n");
DEBUG(std::cerr << "\t inst[" << i << "]: ";
MI->print(std::cerr, *TM));
// make sure the same virtual register maps to the same physical
// register in any given instruction
unsigned physReg = Virt2PhysRegMap[virtualReg];
if (physReg == 0) {
if (op.opIsDefOnly() || op.opIsDefAndUse()) {
if (TM->getInstrInfo().isTwoAddrInstr(MI->getOpcode()) && i == 0) {
// must be same register number as the first operand
// This maps a = b + c into b += c, and saves b into a's spot
assert(MI->getOperand(1).isRegister() &&
MI->getOperand(1).getAllocatedRegNum() &&
MI->getOperand(1).opIsUse() &&
"Two address instruction invalid!");
physReg = MI->getOperand(1).getAllocatedRegNum();
} else {
physReg = getFreeReg(virtualReg);
}
++I;
spillVirtReg(MBB, I, virtualReg, physReg);
--I;
} else {
physReg = reloadVirtReg(MBB, I, virtualReg);
Virt2PhysRegMap[virtualReg] = physReg;
}
}
MI->SetMachineOperandReg(i, physReg);
DEBUG(std::cerr << "virt: " << virtualReg <<
", phys: " << op.getAllocatedRegNum() << "\n");
}
}
RegClassIdx.clear();
RegsUsed.clear();
}
}
/// runOnMachineFunction - Register allocate the whole function
///
bool RegAllocSimple::runOnMachineFunction(MachineFunction &Fn) {
DEBUG(std::cerr << "Machine Function " << "\n");
MF = &Fn;
TM = &MF->getTarget();
RegInfo = TM->getRegisterInfo();
// Loop over all of the basic blocks, eliminating virtual register references
for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
MBB != MBBe; ++MBB)
AllocateBasicBlock(*MBB);
StackSlotForVirtReg.clear();
return true;
}
FunctionPass *createSimpleRegisterAllocator() {
return new RegAllocSimple();
}
} // End llvm namespace