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llvm-project/llvm/lib/CodeGen/RegAllocLocal.cpp

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//===-- RegAllocLocal.cpp - A BasicBlock generic register allocator -------===//
//
// This register allocator allocates registers to a basic block at a time,
// attempting to keep values in registers and reusing registers as appropriate.
//
//===----------------------------------------------------------------------===//
#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/CodeGen/LiveVariables.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "Support/Statistic.h"
#include "Support/CommandLine.h"
#include <iostream>
namespace {
Statistic<> NumSpilled ("ra-local", "Number of registers spilled");
Statistic<> NumReloaded("ra-local", "Number of registers reloaded");
cl::opt<bool> DisableKill("no-kill", cl::Hidden,
cl::desc("Disable register kill in local-ra"));
class RA : public MachineFunctionPass {
const TargetMachine *TM;
MachineFunction *MF;
const MRegisterInfo *RegInfo;
LiveVariables *LV;
// StackSlotForVirtReg - Maps SSA Regs => frame index where these values are
// spilled
std::map<unsigned, int> StackSlotForVirtReg;
// Virt2PhysRegMap - This map contains entries for each virtual register
// that is currently available in a physical register.
//
std::map<unsigned, unsigned> Virt2PhysRegMap;
// PhysRegsUsed - This map contains entries for each physical register that
// currently has a value (ie, it is in Virt2PhysRegMap). The value mapped
// to is the virtual register corresponding to the physical register (the
// inverse of the Virt2PhysRegMap), or 0. The value is set to 0 if this
// register is pinned because it is used by a future instruction.
//
std::map<unsigned, unsigned> PhysRegsUsed;
// PhysRegsUseOrder - This contains a list of the physical registers that
// currently have a virtual register value in them. This list provides an
// ordering of registers, imposing a reallocation order. This list is only
// used if all registers are allocated and we have to spill one, in which
// case we spill the least recently used register. Entries at the front of
// the list are the least recently used registers, entries at the back are
// the most recently used.
//
std::vector<unsigned> PhysRegsUseOrder;
// VirtRegModified - This bitset contains information about which virtual
// registers need to be spilled back to memory when their registers are
// scavenged. If a virtual register has simply been rematerialized, there
// is no reason to spill it to memory when we need the register back.
//
std::vector<bool> VirtRegModified;
void markVirtRegModified(unsigned Reg, bool Val = true) {
assert(Reg >= MRegisterInfo::FirstVirtualRegister && "Illegal VirtReg!");
Reg -= MRegisterInfo::FirstVirtualRegister;
if (VirtRegModified.size() <= Reg) VirtRegModified.resize(Reg+1);
VirtRegModified[Reg] = Val;
}
bool isVirtRegModified(unsigned Reg) const {
assert(Reg >= MRegisterInfo::FirstVirtualRegister && "Illegal VirtReg!");
assert(Reg - MRegisterInfo::FirstVirtualRegister < VirtRegModified.size()
&& "Illegal virtual register!");
return VirtRegModified[Reg - MRegisterInfo::FirstVirtualRegister];
}
void MarkPhysRegRecentlyUsed(unsigned Reg) {
assert(!PhysRegsUseOrder.empty() && "No registers used!");
if (PhysRegsUseOrder.back() == Reg) return; // Already most recently used
for (unsigned i = PhysRegsUseOrder.size(); i != 0; --i)
if (areRegsEqual(Reg, PhysRegsUseOrder[i-1])) {
unsigned RegMatch = PhysRegsUseOrder[i-1]; // remove from middle
PhysRegsUseOrder.erase(PhysRegsUseOrder.begin()+i-1);
// Add it to the end of the list
PhysRegsUseOrder.push_back(RegMatch);
if (RegMatch == Reg)
return; // Found an exact match, exit early
}
}
public:
virtual const char *getPassName() const {
return "Local Register Allocator";
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
if (!DisableKill)
AU.addRequired<LiveVariables>();
AU.addRequiredID(PHIEliminationID);
MachineFunctionPass::getAnalysisUsage(AU);
}
private:
/// runOnMachineFunction - Register allocate the whole function
bool runOnMachineFunction(MachineFunction &Fn);
/// AllocateBasicBlock - Register allocate the specified basic block.
void AllocateBasicBlock(MachineBasicBlock &MBB);
/// areRegsEqual - This method returns true if the specified registers are
/// related to each other. To do this, it checks to see if they are equal
/// or if the first register is in the alias set of the second register.
///
bool areRegsEqual(unsigned R1, unsigned R2) const {
if (R1 == R2) return true;
if (const unsigned *AliasSet = RegInfo->getAliasSet(R2))
for (unsigned i = 0; AliasSet[i]; ++i)
if (AliasSet[i] == R1) return true;
return false;
}
/// getStackSpaceFor - This returns the frame index of the specified virtual
/// register on the stack, allocating space if neccesary.
int getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC);
void removePhysReg(unsigned PhysReg);
/// spillVirtReg - This method spills the value specified by PhysReg into
/// the virtual register slot specified by VirtReg. It then updates the RA
/// data structures to indicate the fact that PhysReg is now available.
///
void spillVirtReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned VirtReg, unsigned PhysReg);
/// spillPhysReg - This method spills the specified physical register into
/// the virtual register slot associated with it.
///
void spillPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned PhysReg);
/// assignVirtToPhysReg - This method updates local state so that we know
/// that PhysReg is the proper container for VirtReg now. The physical
/// register must not be used for anything else when this is called.
///
void assignVirtToPhysReg(unsigned VirtReg, unsigned PhysReg);
/// liberatePhysReg - Make sure the specified physical register is available
/// for use. If there is currently a value in it, it is either moved out of
/// the way or spilled to memory.
///
void liberatePhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned PhysReg);
/// isPhysRegAvailable - Return true if the specified physical register is
/// free and available for use. This also includes checking to see if
/// aliased registers are all free...
///
bool isPhysRegAvailable(unsigned PhysReg) const;
/// getFreeReg - Look to see if there is a free register available in the
/// specified register class. If not, return 0.
///
unsigned getFreeReg(const TargetRegisterClass *RC);
/// getReg - Find a physical register to hold the specified virtual
/// register. If all compatible physical registers are used, this method
/// spills the last used virtual register to the stack, and uses that
/// register.
///
unsigned getReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned VirtReg);
/// reloadVirtReg - This method loads the specified virtual register into a
/// physical register, returning the physical register chosen. This updates
/// the regalloc data structures to reflect the fact that the virtual reg is
/// now alive in a physical register, and the previous one isn't.
///
unsigned reloadVirtReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I, unsigned VirtReg);
};
}
/// getStackSpaceFor - This allocates space for the specified virtual
/// register to be held on the stack.
int RA::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;
}
/// removePhysReg - This method marks the specified physical register as no
/// longer being in use.
///
void RA::removePhysReg(unsigned PhysReg) {
PhysRegsUsed.erase(PhysReg); // PhyReg no longer used
std::vector<unsigned>::iterator It =
std::find(PhysRegsUseOrder.begin(), PhysRegsUseOrder.end(), PhysReg);
assert(It != PhysRegsUseOrder.end() &&
"Spilled a physical register, but it was not in use list!");
PhysRegsUseOrder.erase(It);
}
/// spillVirtReg - This method spills the value specified by PhysReg into the
/// virtual register slot specified by VirtReg. It then updates the RA data
/// structures to indicate the fact that PhysReg is now available.
///
void RA::spillVirtReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned VirtReg, unsigned PhysReg) {
// If this is just a marker register, we don't need to spill it.
if (VirtReg != 0) {
const TargetRegisterClass *RegClass =
MF->getSSARegMap()->getRegClass(VirtReg);
int FrameIndex = getStackSpaceFor(VirtReg, RegClass);
// If we need to spill this value, do so now...
if (isVirtRegModified(VirtReg)) {
// Add move instruction(s)
RegInfo->storeRegToStackSlot(MBB, I, PhysReg, FrameIndex, RegClass);
++NumSpilled; // Update statistics
}
Virt2PhysRegMap.erase(VirtReg); // VirtReg no longer available
}
removePhysReg(PhysReg);
}
/// spillPhysReg - This method spills the specified physical register into the
/// virtual register slot associated with it.
///
void RA::spillPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned PhysReg) {
std::map<unsigned, unsigned>::iterator PI = PhysRegsUsed.find(PhysReg);
if (PI != PhysRegsUsed.end()) { // Only spill it if it's used!
spillVirtReg(MBB, I, PI->second, PhysReg);
} else if (const unsigned *AliasSet = RegInfo->getAliasSet(PhysReg)) {
// If the selected register aliases any other registers, we must make
// sure that one of the aliases isn't alive...
for (unsigned i = 0; AliasSet[i]; ++i) {
PI = PhysRegsUsed.find(AliasSet[i]);
if (PI != PhysRegsUsed.end()) // Spill aliased register...
spillVirtReg(MBB, I, PI->second, AliasSet[i]);
}
}
}
/// assignVirtToPhysReg - This method updates local state so that we know
/// that PhysReg is the proper container for VirtReg now. The physical
/// register must not be used for anything else when this is called.
///
void RA::assignVirtToPhysReg(unsigned VirtReg, unsigned PhysReg) {
assert(PhysRegsUsed.find(PhysReg) == PhysRegsUsed.end() &&
"Phys reg already assigned!");
// Update information to note the fact that this register was just used, and
// it holds VirtReg.
PhysRegsUsed[PhysReg] = VirtReg;
Virt2PhysRegMap[VirtReg] = PhysReg;
PhysRegsUseOrder.push_back(PhysReg); // New use of PhysReg
}
/// isPhysRegAvailable - Return true if the specified physical register is free
/// and available for use. This also includes checking to see if aliased
/// registers are all free...
///
bool RA::isPhysRegAvailable(unsigned PhysReg) const {
if (PhysRegsUsed.count(PhysReg)) return false;
// If the selected register aliases any other allocated registers, it is
// not free!
if (const unsigned *AliasSet = RegInfo->getAliasSet(PhysReg))
for (unsigned i = 0; AliasSet[i]; ++i)
if (PhysRegsUsed.count(AliasSet[i])) // Aliased register in use?
return false; // Can't use this reg then.
return true;
}
/// getFreeReg - Look to see if there is a free register available in the
/// specified register class. If not, return 0.
///
unsigned RA::getFreeReg(const TargetRegisterClass *RC) {
// Get iterators defining the range of registers that are valid to allocate in
// this class, which also specifies the preferred allocation order.
TargetRegisterClass::iterator RI = RC->allocation_order_begin(*MF);
TargetRegisterClass::iterator RE = RC->allocation_order_end(*MF);
for (; RI != RE; ++RI)
if (isPhysRegAvailable(*RI)) { // Is reg unused?
assert(*RI != 0 && "Cannot use register!");
return *RI; // Found an unused register!
}
return 0;
}
/// liberatePhysReg - Make sure the specified physical register is available for
/// use. If there is currently a value in it, it is either moved out of the way
/// or spilled to memory.
///
void RA::liberatePhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned PhysReg) {
// FIXME: This code checks to see if a register is available, but it really
// wants to know if a reg is available BEFORE the instruction executes. If
// called after killed operands are freed, it runs the risk of reallocating a
// used operand...
#if 0
if (isPhysRegAvailable(PhysReg)) return; // Already available...
// Check to see if the register is directly used, not indirectly used through
// aliases. If aliased registers are the ones actually used, we cannot be
// sure that we will be able to save the whole thing if we do a reg-reg copy.
std::map<unsigned, unsigned>::iterator PRUI = PhysRegsUsed.find(PhysReg);
if (PRUI != PhysRegsUsed.end()) {
unsigned VirtReg = PRUI->second; // The virtual register held...
// Check to see if there is a compatible register available. If so, we can
// move the value into the new register...
//
const TargetRegisterClass *RC = RegInfo->getRegClass(PhysReg);
if (unsigned NewReg = getFreeReg(RC)) {
// Emit the code to copy the value...
RegInfo->copyRegToReg(MBB, I, NewReg, PhysReg, RC);
// Update our internal state to indicate that PhysReg is available and Reg
// isn't.
Virt2PhysRegMap.erase(VirtReg);
removePhysReg(PhysReg); // Free the physreg
// Move reference over to new register...
assignVirtToPhysReg(VirtReg, NewReg);
return;
}
}
#endif
spillPhysReg(MBB, I, PhysReg);
}
/// getReg - Find a physical register to hold the specified virtual
/// register. If all compatible physical registers are used, this method spills
/// the last used virtual register to the stack, and uses that register.
///
unsigned RA::getReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned VirtReg) {
const TargetRegisterClass *RC = MF->getSSARegMap()->getRegClass(VirtReg);
// First check to see if we have a free register of the requested type...
unsigned PhysReg = getFreeReg(RC);
// If we didn't find an unused register, scavenge one now!
if (PhysReg == 0) {
assert(!PhysRegsUseOrder.empty() && "No allocated registers??");
// Loop over all of the preallocated registers from the least recently used
// to the most recently used. When we find one that is capable of holding
// our register, use it.
for (unsigned i = 0; PhysReg == 0; ++i) {
assert(i != PhysRegsUseOrder.size() &&
"Couldn't find a register of the appropriate class!");
unsigned R = PhysRegsUseOrder[i];
// If the current register is compatible, use it.
if (RegInfo->getRegClass(R) == RC) {
PhysReg = R;
break;
} else {
// If one of the registers aliased to the current register is
// compatible, use it.
if (const unsigned *AliasSet = RegInfo->getAliasSet(R))
for (unsigned a = 0; AliasSet[a]; ++a)
if (RegInfo->getRegClass(AliasSet[a]) == RC) {
PhysReg = AliasSet[a]; // Take an aliased register
break;
}
}
}
assert(PhysReg && "Physical register not assigned!?!?");
// At this point PhysRegsUseOrder[i] is the least recently used register of
// compatible register class. Spill it to memory and reap its remains.
spillPhysReg(MBB, I, PhysReg);
}
// Now that we know which register we need to assign this to, do it now!
assignVirtToPhysReg(VirtReg, PhysReg);
return PhysReg;
}
/// reloadVirtReg - This method loads the specified virtual register into a
/// physical register, returning the physical register chosen. This updates the
/// regalloc data structures to reflect the fact that the virtual reg is now
/// alive in a physical register, and the previous one isn't.
///
unsigned RA::reloadVirtReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I,
unsigned VirtReg) {
std::map<unsigned, unsigned>::iterator It = Virt2PhysRegMap.find(VirtReg);
if (It != Virt2PhysRegMap.end()) {
MarkPhysRegRecentlyUsed(It->second);
return It->second; // Already have this value available!
}
unsigned PhysReg = getReg(MBB, I, VirtReg);
const TargetRegisterClass *RC = MF->getSSARegMap()->getRegClass(VirtReg);
int FrameIndex = getStackSpaceFor(VirtReg, RC);
markVirtRegModified(VirtReg, false); // Note that this reg was just reloaded
// Add move instruction(s)
RegInfo->loadRegFromStackSlot(MBB, I, PhysReg, FrameIndex, RC);
++NumReloaded; // Update statistics
return PhysReg;
}
void RA::AllocateBasicBlock(MachineBasicBlock &MBB) {
// loop over each instruction
MachineBasicBlock::iterator I = MBB.begin();
for (; I != MBB.end(); ++I) {
MachineInstr *MI = *I;
const TargetInstrDescriptor &TID = TM->getInstrInfo().get(MI->getOpcode());
// Loop over the implicit uses, making sure that they are at the head of the
// use order list, so they don't get reallocated.
if (const unsigned *ImplicitUses = TID.ImplicitUses)
for (unsigned i = 0; ImplicitUses[i]; ++i)
MarkPhysRegRecentlyUsed(ImplicitUses[i]);
// Get the used operands into registers. This has the potiential to spill
// incoming values if we are out of registers.
//
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
if (MI->getOperand(i).opIsUse() &&
MI->getOperand(i).isVirtualRegister()) {
unsigned VirtSrcReg = MI->getOperand(i).getAllocatedRegNum();
unsigned PhysSrcReg = reloadVirtReg(MBB, I, VirtSrcReg);
MI->SetMachineOperandReg(i, PhysSrcReg); // Assign the input register
}
if (!DisableKill) {
// If this instruction is the last user of anything in registers, kill the
// value, freeing the register being used, so it doesn't need to be
// spilled to memory.
//
for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
KE = LV->killed_end(MI); KI != KE; ++KI) {
unsigned VirtReg = KI->second;
unsigned PhysReg = VirtReg;
if (VirtReg >= MRegisterInfo::FirstVirtualRegister) {
std::map<unsigned, unsigned>::iterator I =
Virt2PhysRegMap.find(VirtReg);
assert(I != Virt2PhysRegMap.end());
PhysReg = I->second;
Virt2PhysRegMap.erase(I);
}
if (PhysReg) {
DEBUG(std::cerr << "V: " << VirtReg << " P: " << PhysReg
<< " Killed by: " << *MI);
removePhysReg(PhysReg);
}
}
}
// Loop over all of the operands of the instruction, spilling registers that
// are defined, and marking explicit destinations in the PhysRegsUsed map.
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
if ((MI->getOperand(i).opIsDefOnly() || MI->getOperand(i).opIsDefAndUse()) &&
MI->getOperand(i).isPhysicalRegister()) {
unsigned Reg = MI->getOperand(i).getAllocatedRegNum();
spillPhysReg(MBB, I, Reg); // Spill any existing value in the reg
PhysRegsUsed[Reg] = 0; // It is free and reserved now
PhysRegsUseOrder.push_back(Reg);
}
// Loop over the implicit defs, spilling them as well.
if (const unsigned *ImplicitDefs = TID.ImplicitDefs)
for (unsigned i = 0; ImplicitDefs[i]; ++i) {
unsigned Reg = ImplicitDefs[i];
spillPhysReg(MBB, I, Reg);
PhysRegsUseOrder.push_back(Reg);
PhysRegsUsed[Reg] = 0; // It is free and reserved now
}
// Okay, we have allocated all of the source operands and spilled any values
// that would be destroyed by defs of this instruction. Loop over the
// implicit defs and assign them to a register, spilling incoming values if
// we need to scavenge a register.
//
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
if ((MI->getOperand(i).opIsDefOnly() || MI->getOperand(i).opIsDefAndUse())
&& MI->getOperand(i).isVirtualRegister()) {
unsigned DestVirtReg = MI->getOperand(i).getAllocatedRegNum();
unsigned DestPhysReg;
// If DestVirtReg already has a value, forget about it. Why doesn't
// getReg do this right?
std::map<unsigned, unsigned>::iterator DestI =
Virt2PhysRegMap.find(DestVirtReg);
if (DestI != Virt2PhysRegMap.end()) {
unsigned PhysReg = DestI->second;
Virt2PhysRegMap.erase(DestI);
removePhysReg(PhysReg);
}
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!");
DestPhysReg = MI->getOperand(1).getAllocatedRegNum();
liberatePhysReg(MBB, I, DestPhysReg);
assignVirtToPhysReg(DestVirtReg, DestPhysReg);
} else {
DestPhysReg = getReg(MBB, I, DestVirtReg);
}
markVirtRegModified(DestVirtReg);
MI->SetMachineOperandReg(i, DestPhysReg); // Assign the output register
}
if (!DisableKill) {
// If this instruction defines any registers that are immediately dead,
// kill them now.
//
for (LiveVariables::killed_iterator KI = LV->dead_begin(MI),
KE = LV->dead_end(MI); KI != KE; ++KI) {
unsigned VirtReg = KI->second;
unsigned PhysReg = VirtReg;
if (VirtReg >= MRegisterInfo::FirstVirtualRegister) {
std::map<unsigned, unsigned>::iterator I =
Virt2PhysRegMap.find(VirtReg);
assert(I != Virt2PhysRegMap.end());
PhysReg = I->second;
Virt2PhysRegMap.erase(I);
}
if (PhysReg) {
DEBUG(std::cerr << "V: " << VirtReg << " P: " << PhysReg
<< " dead after: " << *MI);
removePhysReg(PhysReg);
}
}
}
}
// Rewind the iterator to point to the first flow control instruction...
const TargetInstrInfo &TII = TM->getInstrInfo();
I = MBB.end();
while (I != MBB.begin() && TII.isTerminatorInstr((*(I-1))->getOpcode()))
--I;
// Spill all physical registers holding virtual registers now.
while (!PhysRegsUsed.empty())
spillVirtReg(MBB, I, PhysRegsUsed.begin()->second,
PhysRegsUsed.begin()->first);
for (std::map<unsigned, unsigned>::iterator I = Virt2PhysRegMap.begin(),
E = Virt2PhysRegMap.end(); I != E; ++I)
std::cerr << "Register still mapped: " << I->first << " -> "
<< I->second << "\n";
assert(Virt2PhysRegMap.empty() && "Virtual registers still in phys regs?");
assert(PhysRegsUseOrder.empty() && "Physical regs still allocated?");
}
/// runOnMachineFunction - Register allocate the whole function
///
bool RA::runOnMachineFunction(MachineFunction &Fn) {
DEBUG(std::cerr << "Machine Function " << "\n");
MF = &Fn;
TM = &Fn.getTarget();
RegInfo = TM->getRegisterInfo();
if (!DisableKill)
LV = &getAnalysis<LiveVariables>();
// 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();
VirtRegModified.clear();
return true;
}
Pass *createLocalRegisterAllocator() {
return new RA();
}
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