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<std::pair<unsigned, const TargetRegisterClass*> > 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 unsigned MaxCallFrameSize = 0;
115 bool HasCalls = false;
117 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
118 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); )
119 if (I->getOpcode() == FrameSetupOpcode ||
120 I->getOpcode() == FrameDestroyOpcode) {
121 assert(I->getNumOperands() >= 1 && "Call Frame Setup/Destroy Pseudo"
122 " instructions should have a single immediate argument!");
123 unsigned Size = I->getOperand(0).getImmedValue();
124 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
126 RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I++);
131 MachineFrameInfo *FFI = Fn.getFrameInfo();
132 FFI->setHasCalls(HasCalls);
133 FFI->setMaxCallFrameSize(MaxCallFrameSize);
135 // Now figure out which *callee saved* registers are modified by the current
136 // function, thus needing to be saved and restored in the prolog/epilog.
138 const bool *PhysRegsUsed = Fn.getUsedPhysregs();
139 const TargetRegisterClass* const *CSRegClasses =
140 RegInfo->getCalleeSaveRegClasses();
141 for (unsigned i = 0; CSRegs[i]; ++i) {
142 unsigned Reg = CSRegs[i];
143 if (PhysRegsUsed[Reg]) {
144 // If the reg is modified, save it!
145 RegsToSave.push_back(std::make_pair(Reg, CSRegClasses[i]));
147 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
148 *AliasSet; ++AliasSet) { // Check alias registers too.
149 if (PhysRegsUsed[*AliasSet]) {
150 RegsToSave.push_back(std::make_pair(Reg, CSRegClasses[i]));
157 if (RegsToSave.empty())
158 return; // Early exit if no caller saved registers are modified!
160 unsigned NumFixedSpillSlots;
161 const std::pair<unsigned,int> *FixedSpillSlots =
162 TFI->getCalleeSaveSpillSlots(NumFixedSpillSlots);
164 // Now that we know which registers need to be saved and restored, allocate
165 // stack slots for them.
166 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
167 unsigned Reg = RegsToSave[i].first;
168 const TargetRegisterClass *RC = RegsToSave[i].second;
170 // Check to see if this physreg must be spilled to a particular stack slot
172 const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots;
173 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots &&
174 FixedSlot->first != Reg)
178 if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) {
179 // Nope, just spill it anywhere convenient.
180 FrameIdx = FFI->CreateStackObject(RC->getSize(), RC->getAlignment());
182 // Spill it to the stack where we must.
183 FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->second);
185 StackSlots.push_back(FrameIdx);
189 /// saveCallerSavedRegisters - Insert spill code for any caller saved registers
190 /// that are modified in the function.
192 void PEI::saveCallerSavedRegisters(MachineFunction &Fn) {
193 // Early exit if no caller saved registers are modified!
194 if (RegsToSave.empty())
197 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
199 // Now that we have a stack slot for each register to be saved, insert spill
200 // code into the entry block.
201 MachineBasicBlock *MBB = Fn.begin();
202 MachineBasicBlock::iterator I = MBB->begin();
203 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
204 // Insert the spill to the stack frame.
205 RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i].first, StackSlots[i],
206 RegsToSave[i].second);
209 // Add code to restore the callee-save registers in each exiting block.
210 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
211 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI)
212 // If last instruction is a return instruction, add an epilogue.
213 if (!FI->empty() && TII.isReturn(FI->back().getOpcode())) {
217 // Skip over all terminator instructions, which are part of the return
219 MachineBasicBlock::iterator I2 = I;
220 while (I2 != MBB->begin() && TII.isTerminatorInstr((--I2)->getOpcode()))
223 bool AtStart = I == MBB->begin();
224 MachineBasicBlock::iterator BeforeI = I;
228 // Restore all registers immediately before the return and any terminators
230 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
231 RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i].first,
232 StackSlots[i], RegsToSave[i].second);
233 assert(I != MBB->begin() &&
234 "loadRegFromStackSlot didn't insert any code!");
235 // Insert in reverse order. loadRegFromStackSlot can insert multiple
248 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
249 /// abstract stack objects.
251 void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
252 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo();
254 bool StackGrowsDown =
255 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
257 // Loop over all of the stack objects, assigning sequential addresses...
258 MachineFrameInfo *FFI = Fn.getFrameInfo();
260 unsigned StackAlignment = TFI.getStackAlignment();
261 unsigned MaxAlign = 0;
263 // Start at the beginning of the local area.
264 // The Offset is the distance from the stack top in the direction
265 // of stack growth -- so it's always positive.
266 int Offset = TFI.getOffsetOfLocalArea();
270 && "Local area offset should be in direction of stack growth");
272 // If there are fixed sized objects that are preallocated in the local area,
273 // non-fixed objects can't be allocated right at the start of local area.
274 // We currently don't support filling in holes in between fixed sized objects,
275 // so we adjust 'Offset' to point to the end of last fixed sized
276 // preallocated object.
277 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) {
279 if (StackGrowsDown) {
280 // The maximum distance from the stack pointer is at lower address of
281 // the object -- which is given by offset. For down growing stack
282 // the offset is negative, so we negate the offset to get the distance.
283 FixedOff = -FFI->getObjectOffset(i);
285 // The maximum distance from the start pointer is at the upper
286 // address of the object.
287 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i);
289 if (FixedOff > Offset) Offset = FixedOff;
292 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
293 // If stack grows down, we need to add size of find the lowest
294 // address of the object.
296 Offset += FFI->getObjectSize(i);
298 unsigned Align = FFI->getObjectAlignment(i);
299 // If the alignment of this object is greater than that of the stack, then
300 // increase the stack alignment to match.
301 MaxAlign = std::max(MaxAlign, Align);
302 // Adjust to alignment boundary
303 Offset = (Offset+Align-1)/Align*Align;
305 if (StackGrowsDown) {
306 FFI->setObjectOffset(i, -Offset); // Set the computed offset
308 FFI->setObjectOffset(i, Offset);
309 Offset += FFI->getObjectSize(i);
313 // Align the final stack pointer offset, but only if there are calls in the
314 // function. This ensures that any calls to subroutines have their stack
315 // frames suitable aligned.
317 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment;
319 // Set the final value of the stack pointer...
320 FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea());
322 // Remember the required stack alignment in case targets need it to perform
323 // dynamic stack alignment.
324 FFI->setMaxAlignment(MaxAlign);
328 /// insertPrologEpilogCode - Scan the function for modified caller saved
329 /// registers, insert spill code for these caller saved registers, then add
330 /// prolog and epilog code to the function.
332 void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
333 // Add prologue to the function...
334 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn);
336 // Add epilogue to restore the callee-save registers in each exiting block
337 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
338 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
339 // If last instruction is a return instruction, add an epilogue
340 if (!I->empty() && TII.isReturn(I->back().getOpcode()))
341 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I);
346 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
347 /// register references and actual offsets.
349 void PEI::replaceFrameIndices(MachineFunction &Fn) {
350 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
352 const TargetMachine &TM = Fn.getTarget();
353 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!");
354 const MRegisterInfo &MRI = *TM.getRegisterInfo();
356 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
357 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
358 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
359 if (I->getOperand(i).isFrameIndex()) {
360 // If this instruction has a FrameIndex operand, we need to use that
361 // target machine register info object to eliminate it.
362 MRI.eliminateFrameIndex(I);