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* Convert to be a MachineFunctionPass instance 

* Use new FunctionFrameInfo object to manage stack slots instead of doing
  it directly
* Adjust to new MRegisterInfo API
* Don't take a TM as a ctor argument
* Don't keep track of which callee saved registers are modified
* Don't emit prolog/epilog code or spill/restore code for callee saved regs
* Use new allocation_order_begin/end iterators to simplify dramatically the
  logic for picking registers to allocate
* Machine PHI nodes can no longer contain constant arguments

* Use a bitvector to keep track of registers used instead of a set
* Fix problem where explicitly referenced registers would be added to
  regsused set and never removed

llvm-svn: 5196
This commit is contained in:
Chris Lattner 2002-12-28 20:42:14 +00:00
parent b4e4111d75
commit bf9d12ac8b
1 changed files with 66 additions and 173 deletions
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233
llvm/lib/CodeGen/RegAllocSimple.cpp
View File

@ -1,33 +1,37 @@
//===-- RegAllocSimple.cpp - A simple generic register allocator ----------===//
//
// This file implements a simple register allocator. *Very* simple.
// 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.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/SSARegMap.h"
#include "llvm/CodeGen/FunctionFrameInfo.h"
#include "llvm/Target/MachineInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "Support/Statistic.h"
#include <iostream>
#include <set>
namespace {
Statistic<> NumSpilled ("ra-simple", "Number of registers spilled");
Statistic<> NumReloaded("ra-simple", "Number of registers reloaded");
class RegAllocSimple : public FunctionPass {
TargetMachine &TM;
class RegAllocSimple : public MachineFunctionPass {
MachineFunction *MF;
const TargetMachine *TM;
const MRegisterInfo *RegInfo;
unsigned NumBytesAllocated;
// Maps SSA Regs => offsets on the stack where these values are stored
std::map<unsigned, unsigned> VirtReg2OffsetMap;
// 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.
std::set<unsigned> RegsUsed;
// 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
@ -35,27 +39,14 @@ namespace {
std::map<const TargetRegisterClass*, unsigned> RegClassIdx;
public:
RegAllocSimple(TargetMachine &tm)
: TM(tm), RegInfo(tm.getRegisterInfo()) {
RegsUsed.insert(RegInfo->getFramePointer());
RegsUsed.insert(RegInfo->getStackPointer());
cleanupAfterFunction();
}
bool runOnFunction(Function &Fn) {
return runOnMachineFunction(MachineFunction::get(&Fn));
}
virtual const char *getPassName() const {
return "Simple Register Allocator";
}
private:
/// runOnMachineFunction - Register allocate the whole function
bool runOnMachineFunction(MachineFunction &Fn);
private:
/// AllocateBasicBlock - Register allocate the specified basic block.
void AllocateBasicBlock(MachineBasicBlock &MBB);
@ -63,18 +54,9 @@ namespace {
/// in predecessor basic blocks.
void EliminatePHINodes(MachineBasicBlock &MBB);
/// EmitPrologue/EmitEpilogue - Use the register info object to add a
/// prologue/epilogue to the function and save/restore any callee saved
/// registers we are responsible for.
///
void EmitPrologue();
void EmitEpilogue(MachineBasicBlock &MBB);
/// getStackSpaceFor - This returns the offset of the specified virtual
/// register on the stack, allocating space if neccesary.
unsigned getStackSpaceFor(unsigned VirtReg,
const TargetRegisterClass *regClass);
int getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC);
/// Given a virtual register, return a compatible physical register that is
/// currently unused.
@ -83,30 +65,6 @@ namespace {
///
unsigned getFreeReg(unsigned virtualReg);
/// Returns all `borrowed' registers back to the free pool
void clearAllRegs() {
RegClassIdx.clear();
}
/// Invalidates any references, real or implicit, to physical registers
///
void invalidatePhysRegs(const MachineInstr *MI) {
unsigned Opcode = MI->getOpcode();
const MachineInstrDescriptor &Desc = TM.getInstrInfo().get(Opcode);
if (const unsigned *regs = Desc.ImplicitUses)
while (*regs)
RegsUsed.insert(*regs++);
if (const unsigned *regs = Desc.ImplicitDefs)
while (*regs)
RegsUsed.insert(*regs++);
}
void cleanupAfterFunction() {
VirtReg2OffsetMap.clear();
NumBytesAllocated = 4; // FIXME: This is X86 specific
}
/// Moves value from memory into that register
unsigned reloadVirtReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I, unsigned VirtReg);
@ -120,69 +78,62 @@ namespace {
/// getStackSpaceFor - This allocates space for the specified virtual
/// register to be held on the stack.
unsigned RegAllocSimple::getStackSpaceFor(unsigned VirtReg,
const TargetRegisterClass *regClass) {
int RegAllocSimple::getStackSpaceFor(unsigned VirtReg,
const TargetRegisterClass *RC) {
// Find the location VirtReg would belong...
std::map<unsigned, unsigned>::iterator I =
VirtReg2OffsetMap.lower_bound(VirtReg);
std::map<unsigned, int>::iterator I =
StackSlotForVirtReg.lower_bound(VirtReg);
if (I != VirtReg2OffsetMap.end() && I->first == VirtReg)
if (I != StackSlotForVirtReg.end() && I->first == VirtReg)
return I->second; // Already has space allocated?
unsigned RegSize = regClass->getDataSize();
// Align NumBytesAllocated. We should be using TargetData alignment stuff
// to determine this, but we don't know the LLVM type associated with the
// virtual register. Instead, just align to a multiple of the size for now.
NumBytesAllocated += RegSize-1;
NumBytesAllocated = NumBytesAllocated/RegSize*RegSize;
// Allocate a new stack object for this spill location...
int FrameIdx =
MF->getFrameInfo()->CreateStackObject(RC->getSize(), RC->getAlignment());
// Assign the slot...
VirtReg2OffsetMap.insert(I, std::make_pair(VirtReg, NumBytesAllocated));
StackSlotForVirtReg.insert(I, std::make_pair(VirtReg, FrameIdx));
// Reserve the space!
NumBytesAllocated += RegSize;
return NumBytesAllocated-RegSize;
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(regIdx < RC->getNumRegs() && "Not enough registers!");
unsigned physReg = RC->getRegister(regIdx);
assert(RI+regIdx != RE && "Not enough registers!");
unsigned PhysReg = *(RI+regIdx);
if (RegsUsed.find(physReg) == RegsUsed.end())
return physReg;
else
return getFreeReg(virtualReg);
if (!RegsUsed[PhysReg])
return PhysReg;
}
}
unsigned RegAllocSimple::reloadVirtReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I,
unsigned VirtReg) {
const TargetRegisterClass* RC = MF->getSSARegMap()->getRegClass(VirtReg);
unsigned stackOffset = getStackSpaceFor(VirtReg, RC);
int FrameIdx = getStackSpaceFor(VirtReg, RC);
unsigned PhysReg = getFreeReg(VirtReg);
// Add move instruction(s)
++NumReloaded;
RegInfo->loadRegOffset2Reg(MBB, I, PhysReg, RegInfo->getFramePointer(),
-stackOffset, RC);
RegInfo->loadRegFromStackSlot(MBB, I, PhysReg, FrameIdx, RC);
return PhysReg;
}
void RegAllocSimple::spillVirtReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I,
unsigned VirtReg, unsigned PhysReg)
{
unsigned VirtReg, unsigned PhysReg) {
const TargetRegisterClass* RC = MF->getSSARegMap()->getRegClass(VirtReg);
unsigned stackOffset = getStackSpaceFor(VirtReg, RC);
int FrameIdx = getStackSpaceFor(VirtReg, RC);
// Add move instruction(s)
++NumSpilled;
RegInfo->storeReg2RegOffset(MBB, I, PhysReg, RegInfo->getFramePointer(),
-stackOffset, RC);
RegInfo->storeRegToStackSlot(MBB, I, PhysReg, FrameIdx, RC);
}
@ -190,7 +141,7 @@ void RegAllocSimple::spillVirtReg(MachineBasicBlock &MBB,
/// predecessor basic blocks.
///
void RegAllocSimple::EliminatePHINodes(MachineBasicBlock &MBB) {
const MachineInstrInfo &MII = TM.getInstrInfo();
const MachineInstrInfo &MII = TM->getInstrInfo();
while (MBB.front()->getOpcode() == MachineInstrInfo::PHI) {
MachineInstr *MI = MBB.front();
@ -242,15 +193,9 @@ void RegAllocSimple::EliminatePHINodes(MachineBasicBlock &MBB) {
const TargetRegisterClass *RC =
MF->getSSARegMap()->getRegClass(virtualReg);
// Retrieve the constant value from this op, move it to target
// register of the phi
if (opVal.isImmediate()) {
RegInfo->moveImm2Reg(opBlock, opI, virtualReg,
(unsigned) opVal.getImmedValue(), RC);
} else {
RegInfo->moveReg2Reg(opBlock, opI, virtualReg,
opVal.getAllocatedRegNum(), RC);
}
assert(opVal.isVirtualRegister() &&
"Machine PHI Operands must all be virtual registers!");
RegInfo->copyRegToReg(opBlock, opI, virtualReg, opVal.getReg(), RC);
}
}
@ -268,9 +213,19 @@ void RegAllocSimple::AllocateBasicBlock(MachineBasicBlock &MBB) {
MachineInstr *MI = *I;
RegsUsed.resize(MRegisterInfo::FirstVirtualRegister);
// a preliminary pass that will invalidate any registers that
// are used by the instruction (including implicit uses)
invalidatePhysRegs(MI);
unsigned Opcode = MI->getOpcode();
const MachineInstrDescriptor &Desc = TM->getInstrInfo().get(Opcode);
if (const unsigned *Regs = Desc.ImplicitUses)
while (*Regs)
RegsUsed[*Regs++] = true;
if (const unsigned *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) {
@ -280,14 +235,14 @@ void RegAllocSimple::AllocateBasicBlock(MachineBasicBlock &MBB) {
unsigned virtualReg = (unsigned) op.getAllocatedRegNum();
DEBUG(std::cerr << "op: " << op << "\n");
DEBUG(std::cerr << "\t inst[" << i << "]: ";
MI->print(std::cerr, TM));
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.opIsDef()) {
if (TM.getInstrInfo().isTwoAddrInstr(MI->getOpcode()) && i == 0) {
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() &&
@ -312,64 +267,19 @@ void RegAllocSimple::AllocateBasicBlock(MachineBasicBlock &MBB) {
", phys: " << op.getAllocatedRegNum() << "\n");
}
}
clearAllRegs();
RegClassIdx.clear();
RegsUsed.clear();
}
}
/// EmitPrologue - Use the register info object to add a prologue to the
/// function and save any callee saved registers we are responsible for.
///
void RegAllocSimple::EmitPrologue() {
// Get a list of the callee saved registers, so that we can save them on entry
// to the function.
//
MachineBasicBlock &MBB = MF->front(); // Prolog goes in entry BB
MachineBasicBlock::iterator I = MBB.begin();
const unsigned *CSRegs = RegInfo->getCalleeSaveRegs();
for (unsigned i = 0; CSRegs[i]; ++i) {
const TargetRegisterClass *RegClass = RegInfo->getRegClass(CSRegs[i]);
unsigned Offset = getStackSpaceFor(CSRegs[i], RegClass);
// Insert the spill to the stack frame...
RegInfo->storeReg2RegOffset(MBB, I,CSRegs[i],RegInfo->getFramePointer(),
-Offset, RegClass);
++NumSpilled;
}
// Add prologue to the function...
RegInfo->emitPrologue(*MF, NumBytesAllocated);
}
/// EmitEpilogue - Use the register info object to add a epilogue to the
/// function and restore any callee saved registers we are responsible for.
///
void RegAllocSimple::EmitEpilogue(MachineBasicBlock &MBB) {
// Insert instructions before the return.
MachineBasicBlock::iterator I = MBB.end()-1;
const unsigned *CSRegs = RegInfo->getCalleeSaveRegs();
for (unsigned i = 0; CSRegs[i]; ++i) {
const TargetRegisterClass *RegClass = RegInfo->getRegClass(CSRegs[i]);
unsigned Offset = getStackSpaceFor(CSRegs[i], RegClass);
RegInfo->loadRegOffset2Reg(MBB, I, CSRegs[i],RegInfo->getFramePointer(),
-Offset, RegClass);
--I; // Insert in reverse order
++NumReloaded;
}
RegInfo->emitEpilogue(MBB, NumBytesAllocated);
}
/// 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();
// First pass: eliminate PHI instructions by inserting copies into predecessor
// blocks.
@ -382,27 +292,10 @@ bool RegAllocSimple::runOnMachineFunction(MachineFunction &Fn) {
MBB != MBBe; ++MBB)
AllocateBasicBlock(*MBB);
// Round stack allocation up to a nice alignment to keep the stack aligned
// FIXME: This is X86 specific! Move to frame manager
NumBytesAllocated = (NumBytesAllocated + 3) & ~3;
// Emit a prologue for the function...
EmitPrologue();
const MachineInstrInfo &MII = TM.getInstrInfo();
// Add epilogue to restore the callee-save registers in each exiting block
for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
MBB != MBBe; ++MBB) {
// If last instruction is a return instruction, add an epilogue
if (MII.isReturn(MBB->back()->getOpcode()))
EmitEpilogue(*MBB);
}
cleanupAfterFunction();
StackSlotForVirtReg.clear();
return true;
}
Pass *createSimpleRegisterAllocator(TargetMachine &TM) {
return new RegAllocSimple(TM);
Pass *createSimpleRegisterAllocator() {
return new RegAllocSimple();
}