1 //===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===//
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 pass is responsible for finalizing the functions frame layout, saving
11 // callee saved registers, and for emitting prolog & epilog code for the
14 // This pass must be run after register allocation. After this pass is
15 // executed, it is illegal to construct MO_FrameIndex operands.
17 //===----------------------------------------------------------------------===//
19 #include "llvm/CodeGen/Passes.h"
20 #include "llvm/CodeGen/MachineFunctionPass.h"
21 #include "llvm/CodeGen/MachineInstr.h"
22 #include "llvm/CodeGen/MachineFrameInfo.h"
23 #include "llvm/Target/TargetMachine.h"
24 #include "llvm/Target/MRegisterInfo.h"
25 #include "llvm/Target/TargetFrameInfo.h"
26 #include "llvm/Target/TargetInstrInfo.h"
30 struct PEI : public MachineFunctionPass {
31 const char *getPassName() const {
32 return "Prolog/Epilog Insertion & Frame Finalization";
35 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract
36 /// frame indexes with appropriate references.
38 bool runOnMachineFunction(MachineFunction &Fn) {
39 // Scan the function for modified caller saved registers and insert spill
40 // code for any caller saved registers that are modified. Also calculate
41 // the MaxCallFrameSize and HasCalls variables for the function's frame
42 // information and eliminates call frame pseudo instructions.
43 calculateCallerSavedRegisters(Fn);
45 // Add the code to save and restore the caller saved registers
46 saveCallerSavedRegisters(Fn);
48 // Allow the target machine to make final modifications to the function
49 // before the frame layout is finalized.
50 Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn);
52 // Calculate actual frame offsets for all of the abstract stack objects...
53 calculateFrameObjectOffsets(Fn);
55 // Add prolog and epilog code to the function. This function is required
56 // to align the stack frame as necessary for any stack variables or
57 // called functions. Because of this, calculateCallerSavedRegisters
58 // must be called before this function in order to set the HasCalls
59 // and MaxCallFrameSize variables.
60 insertPrologEpilogCode(Fn);
62 // Replace all MO_FrameIndex operands with physical register references
63 // and actual offsets.
65 replaceFrameIndices(Fn);
73 std::vector<unsigned> RegsToSave;
74 std::vector<int> StackSlots;
76 void calculateCallerSavedRegisters(MachineFunction &Fn);
77 void saveCallerSavedRegisters(MachineFunction &Fn);
78 void calculateFrameObjectOffsets(MachineFunction &Fn);
79 void replaceFrameIndices(MachineFunction &Fn);
80 void insertPrologEpilogCode(MachineFunction &Fn);
85 /// createPrologEpilogCodeInserter - This function returns a pass that inserts
86 /// prolog and epilog code, and eliminates abstract frame references.
88 FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); }
91 /// calculateCallerSavedRegisters - Scan the function for modified caller saved
92 /// registers. Also calculate the MaxCallFrameSize and HasCalls variables for
93 /// the function's frame information and eliminates call frame pseudo
96 void PEI::calculateCallerSavedRegisters(MachineFunction &Fn) {
97 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
98 const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo();
99 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
101 // Get the callee saved register list...
102 const unsigned *CSRegs = RegInfo->getCalleeSaveRegs();
104 // Get the function call frame set-up and tear-down instruction opcode
105 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode();
106 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode();
108 // Early exit for targets which have no callee saved registers and no call
109 // frame setup/destroy pseudo instructions.
110 if ((CSRegs == 0 || CSRegs[0] == 0) &&
111 FrameSetupOpcode == -1 && FrameDestroyOpcode == -1)
114 // This bitset contains an entry for each physical register for the target...
115 std::vector<char> ModifiedRegs(RegInfo->getNumRegs());
116 unsigned MaxCallFrameSize = 0;
117 bool HasCalls = false;
119 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
120 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); )
121 if (I->getOpcode() == FrameSetupOpcode ||
122 I->getOpcode() == FrameDestroyOpcode) {
123 assert(I->getNumOperands() == 1 && "Call Frame Setup/Destroy Pseudo"
124 " instructions should have a single immediate argument!");
125 unsigned Size = I->getOperand(0).getImmedValue();
126 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
128 RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I++);
130 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
131 MachineOperand &MO = I->getOperand(i);
132 if (MO.isRegister() && MO.isDef()) {
133 assert(MRegisterInfo::isPhysicalRegister(MO.getReg()) &&
134 "Register allocation must be performed!");
135 ModifiedRegs[MO.getReg()] = true; // Register is modified
138 // Mark any implicitly defined registers as being modified.
139 for (const unsigned *ImpDefs = TII.getImplicitDefs(I->getOpcode());
141 ModifiedRegs[*ImpDefs] = true;
146 MachineFrameInfo *FFI = Fn.getFrameInfo();
147 FFI->setHasCalls(HasCalls);
148 FFI->setMaxCallFrameSize(MaxCallFrameSize);
150 // Now figure out which *callee saved* registers are modified by the current
151 // function, thus needing to be saved and restored in the prolog/epilog.
153 for (unsigned i = 0; CSRegs[i]; ++i) {
154 unsigned Reg = CSRegs[i];
155 if (ModifiedRegs[Reg]) {
156 RegsToSave.push_back(Reg); // If modified register...
158 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
159 *AliasSet; ++AliasSet) { // Check alias registers too...
160 if (ModifiedRegs[*AliasSet]) {
161 RegsToSave.push_back(Reg);
168 if (RegsToSave.empty())
169 return; // Early exit if no caller saved registers are modified!
171 unsigned NumFixedSpillSlots;
172 const std::pair<unsigned,int> *FixedSpillSlots =
173 TFI->getCalleeSaveSpillSlots(NumFixedSpillSlots);
175 // Now that we know which registers need to be saved and restored, allocate
176 // stack slots for them.
177 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
178 unsigned Reg = RegsToSave[i];
180 // Check to see if this physreg must be spilled to a particular stack slot
182 const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots;
183 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots &&
184 FixedSlot->first != Reg)
188 if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) {
189 // Nope, just spill it anywhere convenient.
190 FrameIdx = FFI->CreateStackObject(RegInfo->getSpillSize(Reg)/8,
191 RegInfo->getSpillAlignment(Reg)/8);
193 // Spill it to the stack where we must.
194 FrameIdx = FFI->CreateFixedObject(RegInfo->getSpillSize(Reg)/8,
197 StackSlots.push_back(FrameIdx);
201 /// saveCallerSavedRegisters - Insert spill code for any caller saved registers
202 /// that are modified in the function.
204 void PEI::saveCallerSavedRegisters(MachineFunction &Fn) {
205 // Early exit if no caller saved registers are modified!
206 if (RegsToSave.empty())
209 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
211 // Now that we have a stack slot for each register to be saved, insert spill
212 // code into the entry block.
213 MachineBasicBlock *MBB = Fn.begin();
214 MachineBasicBlock::iterator I = MBB->begin();
215 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
216 // Insert the spill to the stack frame.
217 RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i], StackSlots[i]);
220 // Add code to restore the callee-save registers in each exiting block.
221 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
222 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI)
223 // If last instruction is a return instruction, add an epilogue.
224 if (!FI->empty() && TII.isReturn(FI->back().getOpcode())) {
228 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
229 RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i], StackSlots[i]);
230 assert(I != MBB->begin() &&
231 "loadRegFromStackSlot didn't insert any code!");
232 --I; // Insert in reverse order
238 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
239 /// abstract stack objects.
241 void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
242 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo();
244 bool StackGrowsDown =
245 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
247 // Loop over all of the stack objects, assigning sequential addresses...
248 MachineFrameInfo *FFI = Fn.getFrameInfo();
250 unsigned StackAlignment = TFI.getStackAlignment();
252 // Start at the beginning of the local area.
253 // The Offset is the distance from the stack top in the direction
254 // of stack growth -- so it's always positive.
255 int Offset = TFI.getOffsetOfLocalArea();
259 && "Local area offset should be in direction of stack growth");
261 // If there are fixed sized objects that are preallocated in the local area,
262 // non-fixed objects can't be allocated right at the start of local area.
263 // We currently don't support filling in holes in between fixed sized objects,
264 // so we adjust 'Offset' to point to the end of last fixed sized
265 // preallocated object.
266 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) {
268 if (StackGrowsDown) {
269 // The maximum distance from the stack pointer is at lower address of
270 // the object -- which is given by offset. For down growing stack
271 // the offset is negative, so we negate the offset to get the distance.
272 FixedOff = -FFI->getObjectOffset(i);
274 // The maximum distance from the start pointer is at the upper
275 // address of the object.
276 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i);
278 if (FixedOff > Offset) Offset = FixedOff;
281 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
282 // If stack grows down, we need to add size of find the lowest
283 // address of the object.
285 Offset += FFI->getObjectSize(i);
287 unsigned Align = FFI->getObjectAlignment(i);
288 assert(Align <= StackAlignment && "Cannot align stack object to higher "
289 "alignment boundary than the stack itself!");
290 Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary...
292 if (StackGrowsDown) {
293 FFI->setObjectOffset(i, -Offset); // Set the computed offset
295 FFI->setObjectOffset(i, Offset);
296 Offset += FFI->getObjectSize(i);
300 // Align the final stack pointer offset, but only if there are calls in the
301 // function. This ensures that any calls to subroutines have their stack
302 // frames suitable aligned.
304 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment;
306 // Set the final value of the stack pointer...
307 FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea());
311 /// insertPrologEpilogCode - Scan the function for modified caller saved
312 /// registers, insert spill code for these caller saved registers, then add
313 /// prolog and epilog code to the function.
315 void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
316 // Add prologue to the function...
317 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn);
319 // Add epilogue to restore the callee-save registers in each exiting block
320 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
321 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
322 // If last instruction is a return instruction, add an epilogue
323 if (!I->empty() && TII.isReturn(I->back().getOpcode()))
324 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I);
329 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
330 /// register references and actual offsets.
332 void PEI::replaceFrameIndices(MachineFunction &Fn) {
333 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
335 const TargetMachine &TM = Fn.getTarget();
336 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!");
337 const MRegisterInfo &MRI = *TM.getRegisterInfo();
339 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
340 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
341 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
342 if (I->getOperand(i).isFrameIndex()) {
343 // If this instruction has a FrameIndex operand, we need to use that
344 // target machine register info object to eliminate it.
345 MRI.eliminateFrameIndex(I);