1 //===-- RegAllocLocal.cpp - A BasicBlock generic register allocator -------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This register allocator allocates registers to a basic block at a time,
11 // attempting to keep values in registers and reusing registers as appropriate.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "regalloc"
16 #include "llvm/CodeGen/Passes.h"
17 #include "llvm/CodeGen/MachineFunctionPass.h"
18 #include "llvm/CodeGen/MachineInstr.h"
19 #include "llvm/CodeGen/SSARegMap.h"
20 #include "llvm/CodeGen/MachineFrameInfo.h"
21 #include "llvm/CodeGen/LiveVariables.h"
22 #include "llvm/CodeGen/TwoAddressInstructionPass.h"
23 #include "llvm/Target/TargetInstrInfo.h"
24 #include "llvm/Target/TargetMachine.h"
25 #include "Support/CommandLine.h"
26 #include "Support/Debug.h"
27 #include "Support/Statistic.h"
33 Statistic<> NumSpilled ("ra-local", "Number of registers spilled");
34 Statistic<> NumReloaded("ra-local", "Number of registers reloaded");
35 cl::opt<bool> DisableKill("disable-kill", cl::Hidden,
36 cl::desc("Disable register kill in local-ra"));
38 class RA : public MachineFunctionPass {
39 const TargetMachine *TM;
41 const MRegisterInfo *RegInfo;
44 // StackSlotForVirtReg - Maps virtual regs to the frame index where these
45 // values are spilled.
46 std::map<unsigned, int> StackSlotForVirtReg;
48 // Virt2PhysRegMap - This map contains entries for each virtual register
49 // that is currently available in a physical register.
51 std::map<unsigned, unsigned> Virt2PhysRegMap;
53 // PhysRegsUsed - This map contains entries for each physical register that
54 // currently has a value (ie, it is in Virt2PhysRegMap). The value mapped
55 // to is the virtual register corresponding to the physical register (the
56 // inverse of the Virt2PhysRegMap), or 0. The value is set to 0 if this
57 // register is pinned because it is used by a future instruction.
59 std::map<unsigned, unsigned> PhysRegsUsed;
61 // PhysRegsUseOrder - This contains a list of the physical registers that
62 // currently have a virtual register value in them. This list provides an
63 // ordering of registers, imposing a reallocation order. This list is only
64 // used if all registers are allocated and we have to spill one, in which
65 // case we spill the least recently used register. Entries at the front of
66 // the list are the least recently used registers, entries at the back are
67 // the most recently used.
69 std::vector<unsigned> PhysRegsUseOrder;
71 // VirtRegModified - This bitset contains information about which virtual
72 // registers need to be spilled back to memory when their registers are
73 // scavenged. If a virtual register has simply been rematerialized, there
74 // is no reason to spill it to memory when we need the register back.
76 std::vector<bool> VirtRegModified;
78 void markVirtRegModified(unsigned Reg, bool Val = true) {
79 assert(Reg >= MRegisterInfo::FirstVirtualRegister && "Illegal VirtReg!");
80 Reg -= MRegisterInfo::FirstVirtualRegister;
81 if (VirtRegModified.size() <= Reg) VirtRegModified.resize(Reg+1);
82 VirtRegModified[Reg] = Val;
85 bool isVirtRegModified(unsigned Reg) const {
86 assert(Reg >= MRegisterInfo::FirstVirtualRegister && "Illegal VirtReg!");
87 assert(Reg - MRegisterInfo::FirstVirtualRegister < VirtRegModified.size()
88 && "Illegal virtual register!");
89 return VirtRegModified[Reg - MRegisterInfo::FirstVirtualRegister];
92 void MarkPhysRegRecentlyUsed(unsigned Reg) {
93 assert(!PhysRegsUseOrder.empty() && "No registers used!");
94 if (PhysRegsUseOrder.back() == Reg) return; // Already most recently used
96 for (unsigned i = PhysRegsUseOrder.size(); i != 0; --i)
97 if (areRegsEqual(Reg, PhysRegsUseOrder[i-1])) {
98 unsigned RegMatch = PhysRegsUseOrder[i-1]; // remove from middle
99 PhysRegsUseOrder.erase(PhysRegsUseOrder.begin()+i-1);
100 // Add it to the end of the list
101 PhysRegsUseOrder.push_back(RegMatch);
103 return; // Found an exact match, exit early
108 virtual const char *getPassName() const {
109 return "Local Register Allocator";
112 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
114 AU.addRequired<LiveVariables>();
115 AU.addRequiredID(PHIEliminationID);
116 AU.addRequired<TwoAddressInstructionPass>();
117 MachineFunctionPass::getAnalysisUsage(AU);
121 /// runOnMachineFunction - Register allocate the whole function
122 bool runOnMachineFunction(MachineFunction &Fn);
124 /// AllocateBasicBlock - Register allocate the specified basic block.
125 void AllocateBasicBlock(MachineBasicBlock &MBB);
128 /// areRegsEqual - This method returns true if the specified registers are
129 /// related to each other. To do this, it checks to see if they are equal
130 /// or if the first register is in the alias set of the second register.
132 bool areRegsEqual(unsigned R1, unsigned R2) const {
133 if (R1 == R2) return true;
134 for (const unsigned *AliasSet = RegInfo->getAliasSet(R2);
135 *AliasSet; ++AliasSet) {
136 if (*AliasSet == R1) return true;
141 /// getStackSpaceFor - This returns the frame index of the specified virtual
142 /// register on the stack, allocating space if necessary.
143 int getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC);
145 /// removePhysReg - This method marks the specified physical register as no
146 /// longer being in use.
148 void removePhysReg(unsigned PhysReg);
150 /// spillVirtReg - This method spills the value specified by PhysReg into
151 /// the virtual register slot specified by VirtReg. It then updates the RA
152 /// data structures to indicate the fact that PhysReg is now available.
154 void spillVirtReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
155 unsigned VirtReg, unsigned PhysReg);
157 /// spillPhysReg - This method spills the specified physical register into
158 /// the virtual register slot associated with it. If OnlyVirtRegs is set to
159 /// true, then the request is ignored if the physical register does not
160 /// contain a virtual register.
162 void spillPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
163 unsigned PhysReg, bool OnlyVirtRegs = false);
165 /// assignVirtToPhysReg - This method updates local state so that we know
166 /// that PhysReg is the proper container for VirtReg now. The physical
167 /// register must not be used for anything else when this is called.
169 void assignVirtToPhysReg(unsigned VirtReg, unsigned PhysReg);
171 /// liberatePhysReg - Make sure the specified physical register is available
172 /// for use. If there is currently a value in it, it is either moved out of
173 /// the way or spilled to memory.
175 void liberatePhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
178 /// isPhysRegAvailable - Return true if the specified physical register is
179 /// free and available for use. This also includes checking to see if
180 /// aliased registers are all free...
182 bool isPhysRegAvailable(unsigned PhysReg) const;
184 /// getFreeReg - Look to see if there is a free register available in the
185 /// specified register class. If not, return 0.
187 unsigned getFreeReg(const TargetRegisterClass *RC);
189 /// getReg - Find a physical register to hold the specified virtual
190 /// register. If all compatible physical registers are used, this method
191 /// spills the last used virtual register to the stack, and uses that
194 unsigned getReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
197 /// reloadVirtReg - This method loads the specified virtual register into a
198 /// physical register, returning the physical register chosen. This updates
199 /// the regalloc data structures to reflect the fact that the virtual reg is
200 /// now alive in a physical register, and the previous one isn't.
202 unsigned reloadVirtReg(MachineBasicBlock &MBB,
203 MachineBasicBlock::iterator &I, unsigned VirtReg);
205 void reloadPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
210 /// getStackSpaceFor - This allocates space for the specified virtual register
211 /// to be held on the stack.
212 int RA::getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC) {
213 // Find the location Reg would belong...
214 std::map<unsigned, int>::iterator I =StackSlotForVirtReg.lower_bound(VirtReg);
216 if (I != StackSlotForVirtReg.end() && I->first == VirtReg)
217 return I->second; // Already has space allocated?
219 // Allocate a new stack object for this spill location...
220 int FrameIdx = MF->getFrameInfo()->CreateStackObject(RC);
222 // Assign the slot...
223 StackSlotForVirtReg.insert(I, std::make_pair(VirtReg, FrameIdx));
228 /// removePhysReg - This method marks the specified physical register as no
229 /// longer being in use.
231 void RA::removePhysReg(unsigned PhysReg) {
232 PhysRegsUsed.erase(PhysReg); // PhyReg no longer used
234 std::vector<unsigned>::iterator It =
235 std::find(PhysRegsUseOrder.begin(), PhysRegsUseOrder.end(), PhysReg);
236 assert(It != PhysRegsUseOrder.end() &&
237 "Spilled a physical register, but it was not in use list!");
238 PhysRegsUseOrder.erase(It);
242 /// spillVirtReg - This method spills the value specified by PhysReg into the
243 /// virtual register slot specified by VirtReg. It then updates the RA data
244 /// structures to indicate the fact that PhysReg is now available.
246 void RA::spillVirtReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
247 unsigned VirtReg, unsigned PhysReg) {
248 if (!VirtReg && DisableKill) return;
249 assert(VirtReg && "Spilling a physical register is illegal!"
250 " Must not have appropriate kill for the register or use exists beyond"
251 " the intended one.");
252 DEBUG(std::cerr << " Spilling register " << RegInfo->getName(PhysReg);
253 std::cerr << " containing %reg" << VirtReg;
254 if (!isVirtRegModified(VirtReg))
255 std::cerr << " which has not been modified, so no store necessary!");
257 // Otherwise, there is a virtual register corresponding to this physical
258 // register. We only need to spill it into its stack slot if it has been
260 if (isVirtRegModified(VirtReg)) {
261 const TargetRegisterClass *RC = MF->getSSARegMap()->getRegClass(VirtReg);
262 int FrameIndex = getStackSpaceFor(VirtReg, RC);
263 DEBUG(std::cerr << " to stack slot #" << FrameIndex);
264 RegInfo->storeRegToStackSlot(MBB, I, PhysReg, FrameIndex, RC);
265 ++NumSpilled; // Update statistics
267 Virt2PhysRegMap.erase(VirtReg); // VirtReg no longer available
269 DEBUG(std::cerr << "\n");
270 removePhysReg(PhysReg);
274 /// spillPhysReg - This method spills the specified physical register into the
275 /// virtual register slot associated with it. If OnlyVirtRegs is set to true,
276 /// then the request is ignored if the physical register does not contain a
277 /// virtual register.
279 void RA::spillPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
280 unsigned PhysReg, bool OnlyVirtRegs) {
281 std::map<unsigned, unsigned>::iterator PI = PhysRegsUsed.find(PhysReg);
282 if (PI != PhysRegsUsed.end()) { // Only spill it if it's used!
283 if (PI->second || !OnlyVirtRegs)
284 spillVirtReg(MBB, I, PI->second, PhysReg);
286 // If the selected register aliases any other registers, we must make
287 // sure that one of the aliases isn't alive...
288 for (const unsigned *AliasSet = RegInfo->getAliasSet(PhysReg);
289 *AliasSet; ++AliasSet) {
290 PI = PhysRegsUsed.find(*AliasSet);
291 if (PI != PhysRegsUsed.end()) // Spill aliased register...
292 if (PI->second || !OnlyVirtRegs)
293 spillVirtReg(MBB, I, PI->second, *AliasSet);
299 /// assignVirtToPhysReg - This method updates local state so that we know
300 /// that PhysReg is the proper container for VirtReg now. The physical
301 /// register must not be used for anything else when this is called.
303 void RA::assignVirtToPhysReg(unsigned VirtReg, unsigned PhysReg) {
304 assert(PhysRegsUsed.find(PhysReg) == PhysRegsUsed.end() &&
305 "Phys reg already assigned!");
306 // Update information to note the fact that this register was just used, and
308 PhysRegsUsed[PhysReg] = VirtReg;
309 Virt2PhysRegMap[VirtReg] = PhysReg;
310 PhysRegsUseOrder.push_back(PhysReg); // New use of PhysReg
314 /// isPhysRegAvailable - Return true if the specified physical register is free
315 /// and available for use. This also includes checking to see if aliased
316 /// registers are all free...
318 bool RA::isPhysRegAvailable(unsigned PhysReg) const {
319 if (PhysRegsUsed.count(PhysReg)) return false;
321 // If the selected register aliases any other allocated registers, it is
323 for (const unsigned *AliasSet = RegInfo->getAliasSet(PhysReg);
324 *AliasSet; ++AliasSet)
325 if (PhysRegsUsed.count(*AliasSet)) // Aliased register in use?
326 return false; // Can't use this reg then.
331 /// getFreeReg - Look to see if there is a free register available in the
332 /// specified register class. If not, return 0.
334 unsigned RA::getFreeReg(const TargetRegisterClass *RC) {
335 // Get iterators defining the range of registers that are valid to allocate in
336 // this class, which also specifies the preferred allocation order.
337 TargetRegisterClass::iterator RI = RC->allocation_order_begin(*MF);
338 TargetRegisterClass::iterator RE = RC->allocation_order_end(*MF);
340 for (; RI != RE; ++RI)
341 if (isPhysRegAvailable(*RI)) { // Is reg unused?
342 assert(*RI != 0 && "Cannot use register!");
343 return *RI; // Found an unused register!
349 /// liberatePhysReg - Make sure the specified physical register is available for
350 /// use. If there is currently a value in it, it is either moved out of the way
351 /// or spilled to memory.
353 void RA::liberatePhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
355 // FIXME: This code checks to see if a register is available, but it really
356 // wants to know if a reg is available BEFORE the instruction executes. If
357 // called after killed operands are freed, it runs the risk of reallocating a
360 if (isPhysRegAvailable(PhysReg)) return; // Already available...
362 // Check to see if the register is directly used, not indirectly used through
363 // aliases. If aliased registers are the ones actually used, we cannot be
364 // sure that we will be able to save the whole thing if we do a reg-reg copy.
365 std::map<unsigned, unsigned>::iterator PRUI = PhysRegsUsed.find(PhysReg);
366 if (PRUI != PhysRegsUsed.end()) {
367 unsigned VirtReg = PRUI->second; // The virtual register held...
369 // Check to see if there is a compatible register available. If so, we can
370 // move the value into the new register...
372 const TargetRegisterClass *RC = RegInfo->getRegClass(PhysReg);
373 if (unsigned NewReg = getFreeReg(RC)) {
374 // Emit the code to copy the value...
375 RegInfo->copyRegToReg(MBB, I, NewReg, PhysReg, RC);
377 // Update our internal state to indicate that PhysReg is available and Reg
379 Virt2PhysRegMap.erase(VirtReg);
380 removePhysReg(PhysReg); // Free the physreg
382 // Move reference over to new register...
383 assignVirtToPhysReg(VirtReg, NewReg);
388 spillPhysReg(MBB, I, PhysReg);
392 /// getReg - Find a physical register to hold the specified virtual
393 /// register. If all compatible physical registers are used, this method spills
394 /// the last used virtual register to the stack, and uses that register.
396 unsigned RA::getReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
398 const TargetRegisterClass *RC = MF->getSSARegMap()->getRegClass(VirtReg);
400 // First check to see if we have a free register of the requested type...
401 unsigned PhysReg = getFreeReg(RC);
403 // If we didn't find an unused register, scavenge one now!
405 assert(!PhysRegsUseOrder.empty() && "No allocated registers??");
407 // Loop over all of the preallocated registers from the least recently used
408 // to the most recently used. When we find one that is capable of holding
409 // our register, use it.
410 for (unsigned i = 0; PhysReg == 0; ++i) {
411 assert(i != PhysRegsUseOrder.size() &&
412 "Couldn't find a register of the appropriate class!");
414 unsigned R = PhysRegsUseOrder[i];
416 // We can only use this register if it holds a virtual register (ie, it
417 // can be spilled). Do not use it if it is an explicitly allocated
418 // physical register!
419 assert(PhysRegsUsed.count(R) &&
420 "PhysReg in PhysRegsUseOrder, but is not allocated?");
421 if (PhysRegsUsed[R]) {
422 // If the current register is compatible, use it.
423 if (RegInfo->getRegClass(R) == RC) {
427 // If one of the registers aliased to the current register is
428 // compatible, use it.
429 for (const unsigned *AliasSet = RegInfo->getAliasSet(R);
430 *AliasSet; ++AliasSet) {
431 if (RegInfo->getRegClass(*AliasSet) == RC) {
432 PhysReg = *AliasSet; // Take an aliased register
440 assert(PhysReg && "Physical register not assigned!?!?");
442 // At this point PhysRegsUseOrder[i] is the least recently used register of
443 // compatible register class. Spill it to memory and reap its remains.
444 spillPhysReg(MBB, I, PhysReg);
447 // Now that we know which register we need to assign this to, do it now!
448 assignVirtToPhysReg(VirtReg, PhysReg);
453 /// reloadVirtReg - This method loads the specified virtual register into a
454 /// physical register, returning the physical register chosen. This updates the
455 /// regalloc data structures to reflect the fact that the virtual reg is now
456 /// alive in a physical register, and the previous one isn't.
458 unsigned RA::reloadVirtReg(MachineBasicBlock &MBB,
459 MachineBasicBlock::iterator &I,
461 std::map<unsigned, unsigned>::iterator It = Virt2PhysRegMap.find(VirtReg);
462 if (It != Virt2PhysRegMap.end()) {
463 MarkPhysRegRecentlyUsed(It->second);
464 return It->second; // Already have this value available!
467 unsigned PhysReg = getReg(MBB, I, VirtReg);
469 const TargetRegisterClass *RC = MF->getSSARegMap()->getRegClass(VirtReg);
470 int FrameIndex = getStackSpaceFor(VirtReg, RC);
472 markVirtRegModified(VirtReg, false); // Note that this reg was just reloaded
474 DEBUG(std::cerr << " Reloading %reg" << VirtReg << " into "
475 << RegInfo->getName(PhysReg) << "\n");
477 // Add move instruction(s)
478 RegInfo->loadRegFromStackSlot(MBB, I, PhysReg, FrameIndex, RC);
479 ++NumReloaded; // Update statistics
485 void RA::AllocateBasicBlock(MachineBasicBlock &MBB) {
486 // loop over each instruction
487 MachineBasicBlock::iterator I = MBB.begin();
488 for (; I != MBB.end(); ++I) {
489 MachineInstr *MI = *I;
490 const TargetInstrDescriptor &TID = TM->getInstrInfo().get(MI->getOpcode());
491 DEBUG(std::cerr << "\nStarting RegAlloc of: " << *MI;
492 std::cerr << " Regs have values: ";
493 for (std::map<unsigned, unsigned>::const_iterator
494 I = PhysRegsUsed.begin(), E = PhysRegsUsed.end(); I != E; ++I)
495 std::cerr << "[" << RegInfo->getName(I->first)
496 << ",%reg" << I->second << "] ";
499 // Loop over the implicit uses, making sure that they are at the head of the
500 // use order list, so they don't get reallocated.
501 for (const unsigned *ImplicitUses = TID.ImplicitUses;
502 *ImplicitUses; ++ImplicitUses)
503 MarkPhysRegRecentlyUsed(*ImplicitUses);
505 // Get the used operands into registers. This has the potential to spill
506 // incoming values if we are out of registers. Note that we completely
507 // ignore physical register uses here. We assume that if an explicit
508 // physical register is referenced by the instruction, that it is guaranteed
509 // to be live-in, or the input is badly hosed.
511 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
512 if (MI->getOperand(i).isUse() &&
513 !MI->getOperand(i).isDef() &&
514 MI->getOperand(i).isVirtualRegister()){
515 unsigned VirtSrcReg = MI->getOperand(i).getAllocatedRegNum();
516 unsigned PhysSrcReg = reloadVirtReg(MBB, I, VirtSrcReg);
517 MI->SetMachineOperandReg(i, PhysSrcReg); // Assign the input register
521 // If this instruction is the last user of anything in registers, kill the
522 // value, freeing the register being used, so it doesn't need to be
523 // spilled to memory.
525 for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
526 KE = LV->killed_end(MI); KI != KE; ++KI) {
527 unsigned VirtReg = KI->second;
528 unsigned PhysReg = VirtReg;
529 if (VirtReg >= MRegisterInfo::FirstVirtualRegister) {
530 std::map<unsigned, unsigned>::iterator I =
531 Virt2PhysRegMap.find(VirtReg);
532 assert(I != Virt2PhysRegMap.end());
534 Virt2PhysRegMap.erase(I);
538 DEBUG(std::cerr << " Last use of " << RegInfo->getName(PhysReg)
539 << "[%reg" << VirtReg <<"], removing it from live set\n");
540 removePhysReg(PhysReg);
545 // Loop over all of the operands of the instruction, spilling registers that
546 // are defined, and marking explicit destinations in the PhysRegsUsed map.
547 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
548 if (MI->getOperand(i).isDef() &&
549 MI->getOperand(i).isPhysicalRegister()) {
550 unsigned Reg = MI->getOperand(i).getAllocatedRegNum();
551 spillPhysReg(MBB, I, Reg, true); // Spill any existing value in the reg
552 PhysRegsUsed[Reg] = 0; // It is free and reserved now
553 PhysRegsUseOrder.push_back(Reg);
556 // Loop over the implicit defs, spilling them as well.
557 for (const unsigned *ImplicitDefs = TID.ImplicitDefs;
558 *ImplicitDefs; ++ImplicitDefs) {
559 unsigned Reg = *ImplicitDefs;
560 spillPhysReg(MBB, I, Reg);
561 PhysRegsUseOrder.push_back(Reg);
562 PhysRegsUsed[Reg] = 0; // It is free and reserved now
565 // Okay, we have allocated all of the source operands and spilled any values
566 // that would be destroyed by defs of this instruction. Loop over the
567 // implicit defs and assign them to a register, spilling incoming values if
568 // we need to scavenge a register.
570 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
571 if (MI->getOperand(i).isDef() &&
572 MI->getOperand(i).isVirtualRegister()) {
573 unsigned DestVirtReg = MI->getOperand(i).getAllocatedRegNum();
574 unsigned DestPhysReg;
576 // If DestVirtReg already has a value, use it.
577 std::map<unsigned, unsigned>::iterator DestI =
578 Virt2PhysRegMap.find(DestVirtReg);
579 if (DestI != Virt2PhysRegMap.end()) {
580 DestPhysReg = DestI->second;
583 DestPhysReg = getReg(MBB, I, DestVirtReg);
585 markVirtRegModified(DestVirtReg);
586 MI->SetMachineOperandReg(i, DestPhysReg); // Assign the output register
590 // If this instruction defines any registers that are immediately dead,
593 for (LiveVariables::killed_iterator KI = LV->dead_begin(MI),
594 KE = LV->dead_end(MI); KI != KE; ++KI) {
595 unsigned VirtReg = KI->second;
596 unsigned PhysReg = VirtReg;
597 if (VirtReg >= MRegisterInfo::FirstVirtualRegister) {
598 std::map<unsigned, unsigned>::iterator I =
599 Virt2PhysRegMap.find(VirtReg);
600 assert(I != Virt2PhysRegMap.end());
602 Virt2PhysRegMap.erase(I);
606 DEBUG(std::cerr << " Register " << RegInfo->getName(PhysReg)
607 << " [%reg" << VirtReg
608 << "] is never used, removing it frame live list\n");
609 removePhysReg(PhysReg);
615 // Rewind the iterator to point to the first flow control instruction...
616 const TargetInstrInfo &TII = TM->getInstrInfo();
618 while (I != MBB.begin() && TII.isTerminatorInstr((*(I-1))->getOpcode()))
621 // Spill all physical registers holding virtual registers now.
622 while (!PhysRegsUsed.empty())
623 if (unsigned VirtReg = PhysRegsUsed.begin()->second)
624 spillVirtReg(MBB, I, VirtReg, PhysRegsUsed.begin()->first);
626 removePhysReg(PhysRegsUsed.begin()->first);
628 for (std::map<unsigned, unsigned>::iterator I = Virt2PhysRegMap.begin(),
629 E = Virt2PhysRegMap.end(); I != E; ++I)
630 std::cerr << "Register still mapped: " << I->first << " -> "
631 << I->second << "\n";
633 assert(Virt2PhysRegMap.empty() && "Virtual registers still in phys regs?");
635 // Clear any physical register which appear live at the end of the basic
636 // block, but which do not hold any virtual registers. e.g., the stack
638 PhysRegsUseOrder.clear();
642 /// runOnMachineFunction - Register allocate the whole function
644 bool RA::runOnMachineFunction(MachineFunction &Fn) {
645 DEBUG(std::cerr << "Machine Function " << "\n");
647 TM = &Fn.getTarget();
648 RegInfo = TM->getRegisterInfo();
651 LV = &getAnalysis<LiveVariables>();
653 // Loop over all of the basic blocks, eliminating virtual register references
654 for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
656 AllocateBasicBlock(*MBB);
658 StackSlotForVirtReg.clear();
659 VirtRegModified.clear();
663 FunctionPass *createLocalRegisterAllocator() {
667 } // End llvm namespace