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"
27 #include "llvm/Support/Compiler.h"
32 struct VISIBILITY_HIDDEN PEI : public MachineFunctionPass {
33 const char *getPassName() const {
34 return "Prolog/Epilog Insertion & Frame Finalization";
37 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract
38 /// frame indexes with appropriate references.
40 bool runOnMachineFunction(MachineFunction &Fn) {
41 // Get MachineDebugInfo so that we can track the construction of the
43 if (MachineDebugInfo *DI = getAnalysisToUpdate<MachineDebugInfo>()) {
44 Fn.getFrameInfo()->setMachineDebugInfo(DI);
47 // Allow the target machine to make some adjustments to the function
48 // e.g. UsedPhysRegs before calculateCalleeSavedRegisters.
49 Fn.getTarget().getRegisterInfo()->processFunctionBeforeCalleeSaveScan(Fn);
51 // Scan the function for modified callee saved registers and insert spill
52 // code for any callee saved registers that are modified. Also calculate
53 // the MaxCallFrameSize and HasCalls variables for the function's frame
54 // information and eliminates call frame pseudo instructions.
55 calculateCalleeSavedRegisters(Fn);
57 // Add the code to save and restore the callee saved registers
58 saveCalleeSavedRegisters(Fn);
60 // Allow the target machine to make final modifications to the function
61 // before the frame layout is finalized.
62 Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn);
64 // Calculate actual frame offsets for all of the abstract stack objects...
65 calculateFrameObjectOffsets(Fn);
67 // Add prolog and epilog code to the function. This function is required
68 // to align the stack frame as necessary for any stack variables or
69 // called functions. Because of this, calculateCalleeSavedRegisters
70 // must be called before this function in order to set the HasCalls
71 // and MaxCallFrameSize variables.
72 insertPrologEpilogCode(Fn);
74 // Replace all MO_FrameIndex operands with physical register references
75 // and actual offsets.
77 replaceFrameIndices(Fn);
83 // MinCSFrameIndex, MaxCSFrameIndex - Keeps the range of callee save
84 // stack frame indexes.
85 unsigned MinCSFrameIndex, MaxCSFrameIndex;
87 void calculateCalleeSavedRegisters(MachineFunction &Fn);
88 void saveCalleeSavedRegisters(MachineFunction &Fn);
89 void calculateFrameObjectOffsets(MachineFunction &Fn);
90 void replaceFrameIndices(MachineFunction &Fn);
91 void insertPrologEpilogCode(MachineFunction &Fn);
96 /// createPrologEpilogCodeInserter - This function returns a pass that inserts
97 /// prolog and epilog code, and eliminates abstract frame references.
99 FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); }
102 /// calculateCalleeSavedRegisters - Scan the function for modified callee saved
103 /// registers. Also calculate the MaxCallFrameSize and HasCalls variables for
104 /// the function's frame information and eliminates call frame pseudo
107 void PEI::calculateCalleeSavedRegisters(MachineFunction &Fn) {
108 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
109 const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo();
111 // Get the callee saved register list...
112 const unsigned *CSRegs = RegInfo->getCalleeSaveRegs();
114 // Get the function call frame set-up and tear-down instruction opcode
115 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode();
116 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode();
118 // Early exit for targets which have no callee saved registers and no call
119 // frame setup/destroy pseudo instructions.
120 if ((CSRegs == 0 || CSRegs[0] == 0) &&
121 FrameSetupOpcode == -1 && FrameDestroyOpcode == -1)
124 unsigned MaxCallFrameSize = 0;
125 bool HasCalls = false;
127 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
128 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); )
129 if (I->getOpcode() == FrameSetupOpcode ||
130 I->getOpcode() == FrameDestroyOpcode) {
131 assert(I->getNumOperands() >= 1 && "Call Frame Setup/Destroy Pseudo"
132 " instructions should have a single immediate argument!");
133 unsigned Size = I->getOperand(0).getImmedValue();
134 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
136 RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I++);
141 MachineFrameInfo *FFI = Fn.getFrameInfo();
142 FFI->setHasCalls(HasCalls);
143 FFI->setMaxCallFrameSize(MaxCallFrameSize);
145 // Now figure out which *callee saved* registers are modified by the current
146 // function, thus needing to be saved and restored in the prolog/epilog.
148 const bool *PhysRegsUsed = Fn.getUsedPhysregs();
149 const TargetRegisterClass* const *CSRegClasses =
150 RegInfo->getCalleeSaveRegClasses();
151 std::vector<CalleeSavedInfo> CSI;
152 for (unsigned i = 0; CSRegs[i]; ++i) {
153 unsigned Reg = CSRegs[i];
154 if (PhysRegsUsed[Reg]) {
155 // If the reg is modified, save it!
156 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i]));
158 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
159 *AliasSet; ++AliasSet) { // Check alias registers too.
160 if (PhysRegsUsed[*AliasSet]) {
161 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i]));
169 return; // Early exit if no callee 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 MinCSFrameIndex = INT_MAX;
179 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
180 unsigned Reg = CSI[i].getReg();
181 const TargetRegisterClass *RC = CSI[i].getRegClass();
183 // Check to see if this physreg must be spilled to a particular stack slot
185 const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots;
186 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots &&
187 FixedSlot->first != Reg)
191 if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) {
192 // Nope, just spill it anywhere convenient.
193 unsigned Align = RC->getAlignment();
194 unsigned StackAlign = TFI->getStackAlignment();
195 // We may not be able to sastify the desired alignment specification of
196 // the TargetRegisterClass if the stack alignment is smaller. Use the min.
197 Align = std::min(Align, StackAlign);
198 FrameIdx = FFI->CreateStackObject(RC->getSize(), Align);
199 if ((unsigned)FrameIdx < MinCSFrameIndex) MinCSFrameIndex = FrameIdx;
200 if ((unsigned)FrameIdx > MaxCSFrameIndex) MaxCSFrameIndex = FrameIdx;
202 // Spill it to the stack where we must.
203 FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->second);
205 CSI[i].setFrameIdx(FrameIdx);
208 FFI->setCalleeSavedInfo(CSI);
211 /// saveCalleeSavedRegisters - Insert spill code for any callee saved registers
212 /// that are modified in the function.
214 void PEI::saveCalleeSavedRegisters(MachineFunction &Fn) {
215 // Get callee saved register information.
216 MachineFrameInfo *FFI = Fn.getFrameInfo();
217 const std::vector<CalleeSavedInfo> &CSI = FFI->getCalleeSavedInfo();
219 // Early exit if no callee saved registers are modified!
223 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
225 // Now that we have a stack slot for each register to be saved, insert spill
226 // code into the entry block.
227 MachineBasicBlock *MBB = Fn.begin();
228 MachineBasicBlock::iterator I = MBB->begin();
229 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
230 // Insert the spill to the stack frame.
231 RegInfo->storeRegToStackSlot(*MBB, I, CSI[i].getReg(), CSI[i].getFrameIdx(),
232 CSI[i].getRegClass());
235 // Add code to restore the callee-save registers in each exiting block.
236 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
237 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI)
238 // If last instruction is a return instruction, add an epilogue.
239 if (!FI->empty() && TII.isReturn(FI->back().getOpcode())) {
243 // Skip over all terminator instructions, which are part of the return
245 MachineBasicBlock::iterator I2 = I;
246 while (I2 != MBB->begin() && TII.isTerminatorInstr((--I2)->getOpcode()))
249 bool AtStart = I == MBB->begin();
250 MachineBasicBlock::iterator BeforeI = I;
254 // Restore all registers immediately before the return and any terminators
256 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
257 RegInfo->loadRegFromStackSlot(*MBB, I, CSI[i].getReg(),
258 CSI[i].getFrameIdx(),
259 CSI[i].getRegClass());
260 assert(I != MBB->begin() &&
261 "loadRegFromStackSlot didn't insert any code!");
262 // Insert in reverse order. loadRegFromStackSlot can insert multiple
275 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
276 /// abstract stack objects.
278 void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
279 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo();
281 bool StackGrowsDown =
282 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
284 // Loop over all of the stack objects, assigning sequential addresses...
285 MachineFrameInfo *FFI = Fn.getFrameInfo();
287 unsigned StackAlignment = TFI.getStackAlignment();
288 unsigned MaxAlign = 0;
290 // Start at the beginning of the local area.
291 // The Offset is the distance from the stack top in the direction
292 // of stack growth -- so it's always positive.
293 int Offset = TFI.getOffsetOfLocalArea();
297 && "Local area offset should be in direction of stack growth");
299 // If there are fixed sized objects that are preallocated in the local area,
300 // non-fixed objects can't be allocated right at the start of local area.
301 // We currently don't support filling in holes in between fixed sized objects,
302 // so we adjust 'Offset' to point to the end of last fixed sized
303 // preallocated object.
304 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) {
306 if (StackGrowsDown) {
307 // The maximum distance from the stack pointer is at lower address of
308 // the object -- which is given by offset. For down growing stack
309 // the offset is negative, so we negate the offset to get the distance.
310 FixedOff = -FFI->getObjectOffset(i);
312 // The maximum distance from the start pointer is at the upper
313 // address of the object.
314 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i);
316 if (FixedOff > Offset) Offset = FixedOff;
319 // First assign frame offsets to stack objects that are used to spill
320 // callee save registers.
321 if (StackGrowsDown) {
322 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
323 if (i < MinCSFrameIndex || i > MaxCSFrameIndex)
326 // If stack grows down, we need to add size of find the lowest
327 // address of the object.
328 Offset += FFI->getObjectSize(i);
330 unsigned Align = FFI->getObjectAlignment(i);
331 // If the alignment of this object is greater than that of the stack, then
332 // increase the stack alignment to match.
333 MaxAlign = std::max(MaxAlign, Align);
334 // Adjust to alignment boundary
335 Offset = (Offset+Align-1)/Align*Align;
337 FFI->setObjectOffset(i, -Offset); // Set the computed offset
340 for (int i = FFI->getObjectIndexEnd()-1; i >= 0; --i) {
341 if ((unsigned)i < MinCSFrameIndex || (unsigned)i > MaxCSFrameIndex)
344 unsigned Align = FFI->getObjectAlignment(i);
345 // If the alignment of this object is greater than that of the stack, then
346 // increase the stack alignment to match.
347 MaxAlign = std::max(MaxAlign, Align);
348 // Adjust to alignment boundary
349 Offset = (Offset+Align-1)/Align*Align;
351 FFI->setObjectOffset(i, Offset);
352 Offset += FFI->getObjectSize(i);
356 // Then assign frame offsets to stack objects that are not used to spill
357 // callee save registers.
358 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
359 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
362 // If stack grows down, we need to add size of find the lowest
363 // address of the object.
365 Offset += FFI->getObjectSize(i);
367 unsigned Align = FFI->getObjectAlignment(i);
368 // If the alignment of this object is greater than that of the stack, then
369 // increase the stack alignment to match.
370 MaxAlign = std::max(MaxAlign, Align);
371 // Adjust to alignment boundary
372 Offset = (Offset+Align-1)/Align*Align;
374 if (StackGrowsDown) {
375 FFI->setObjectOffset(i, -Offset); // Set the computed offset
377 FFI->setObjectOffset(i, Offset);
378 Offset += FFI->getObjectSize(i);
383 // Align the final stack pointer offset, but only if there are calls in the
384 // function. This ensures that any calls to subroutines have their stack
385 // frames suitable aligned.
387 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment;
389 // Set the final value of the stack pointer...
390 FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea());
392 // Remember the required stack alignment in case targets need it to perform
393 // dynamic stack alignment.
394 assert(FFI->getMaxAlignment() == MaxAlign &&
395 "Stack alignment calculation broken!");
399 /// insertPrologEpilogCode - Scan the function for modified callee saved
400 /// registers, insert spill code for these callee saved registers, then add
401 /// prolog and epilog code to the function.
403 void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
404 // Add prologue to the function...
405 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn);
407 // Add epilogue to restore the callee-save registers in each exiting block
408 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
409 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
410 // If last instruction is a return instruction, add an epilogue
411 if (!I->empty() && TII.isReturn(I->back().getOpcode()))
412 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I);
417 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
418 /// register references and actual offsets.
420 void PEI::replaceFrameIndices(MachineFunction &Fn) {
421 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
423 const TargetMachine &TM = Fn.getTarget();
424 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!");
425 const MRegisterInfo &MRI = *TM.getRegisterInfo();
427 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
428 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
429 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
430 if (I->getOperand(i).isFrameIndex()) {
431 // If this instruction has a FrameIndex operand, we need to use that
432 // target machine register info object to eliminate it.
433 MRI.eliminateFrameIndex(I);