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"
31 struct PEI : public MachineFunctionPass {
32 const char *getPassName() const {
33 return "Prolog/Epilog Insertion & Frame Finalization";
36 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract
37 /// frame indexes with appropriate references.
39 bool runOnMachineFunction(MachineFunction &Fn) {
40 // Scan the function for modified caller saved registers and insert spill
41 // code for any caller saved registers that are modified. Also calculate
42 // the MaxCallFrameSize and HasCalls variables for the function's frame
43 // information and eliminates call frame pseudo instructions.
44 saveCallerSavedRegisters(Fn);
46 // Allow the target machine to make final modifications to the function
47 // before the frame layout is finalized.
48 Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn);
50 // Calculate actual frame offsets for all of the abstract stack objects...
51 calculateFrameObjectOffsets(Fn);
53 // Add prolog and epilog code to the function.
54 insertPrologEpilogCode(Fn);
56 // Replace all MO_FrameIndex operands with physical register references
57 // and actual offsets.
59 replaceFrameIndices(Fn);
64 void saveCallerSavedRegisters(MachineFunction &Fn);
65 void calculateFrameObjectOffsets(MachineFunction &Fn);
66 void replaceFrameIndices(MachineFunction &Fn);
67 void insertPrologEpilogCode(MachineFunction &Fn);
72 /// createPrologEpilogCodeInserter - This function returns a pass that inserts
73 /// prolog and epilog code, and eliminates abstract frame references.
75 FunctionPass *createPrologEpilogCodeInserter() { return new PEI(); }
78 /// saveCallerSavedRegisters - Scan the function for modified caller saved
79 /// registers and insert spill code for any caller saved registers that are
80 /// modified. Also calculate the MaxCallFrameSize and HasCalls variables for
81 /// the function's frame information and eliminates call frame pseudo
84 void PEI::saveCallerSavedRegisters(MachineFunction &Fn) {
85 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
86 const TargetFrameInfo &FrameInfo = Fn.getTarget().getFrameInfo();
88 // Get the callee saved register list...
89 const unsigned *CSRegs = RegInfo->getCalleeSaveRegs();
91 // Get the function call frame set-up and tear-down instruction opcode
92 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode();
93 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode();
95 // Early exit for targets which have no callee saved registers and no call
96 // frame setup/destroy pseudo instructions.
97 if ((CSRegs == 0 || CSRegs[0] == 0) &&
98 FrameSetupOpcode == -1 && FrameDestroyOpcode == -1)
101 // This bitset contains an entry for each physical register for the target...
102 std::vector<bool> ModifiedRegs(MRegisterInfo::FirstVirtualRegister);
103 unsigned MaxCallFrameSize = 0;
104 bool HasCalls = false;
106 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
107 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); )
108 if ((*I)->getOpcode() == FrameSetupOpcode ||
109 (*I)->getOpcode() == FrameDestroyOpcode) {
110 assert((*I)->getNumOperands() == 1 && "Call Frame Setup/Destroy Pseudo"
111 " instructions should have a single immediate argument!");
112 unsigned Size = (*I)->getOperand(0).getImmedValue();
113 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
115 RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I);
117 for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i) {
118 MachineOperand &MO = (*I)->getOperand(i);
119 assert(!MO.isVirtualRegister() &&
120 "Register allocation must be performed!");
121 if (MO.isPhysicalRegister() && MO.isDef())
122 ModifiedRegs[MO.getReg()] = true; // Register is modified
127 MachineFrameInfo *FFI = Fn.getFrameInfo();
128 FFI->setHasCalls(HasCalls);
129 FFI->setMaxCallFrameSize(MaxCallFrameSize);
131 // Now figure out which *callee saved* registers are modified by the current
132 // function, thus needing to be saved and restored in the prolog/epilog.
134 std::vector<unsigned> RegsToSave;
135 for (unsigned i = 0; CSRegs[i]; ++i) {
136 unsigned Reg = CSRegs[i];
137 if (ModifiedRegs[Reg]) {
138 RegsToSave.push_back(Reg); // If modified register...
140 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
141 *AliasSet; ++AliasSet) { // Check alias registers too...
142 if (ModifiedRegs[*AliasSet]) {
143 RegsToSave.push_back(Reg);
150 if (RegsToSave.empty())
151 return; // Early exit if no caller saved registers are modified!
153 // Now that we know which registers need to be saved and restored, allocate
154 // stack slots for them.
155 std::vector<int> StackSlots;
156 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
157 int FrameIdx = FFI->CreateStackObject(RegInfo->getRegClass(RegsToSave[i]));
158 StackSlots.push_back(FrameIdx);
161 // Now that we have a stack slot for each register to be saved, insert spill
162 // code into the entry block...
163 MachineBasicBlock *MBB = Fn.begin();
164 MachineBasicBlock::iterator I = MBB->begin();
165 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
166 const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]);
168 // Insert the spill to the stack frame...
169 RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i], StackSlots[i], RC);
172 // Add code to restore the callee-save registers in each exiting block.
173 const TargetInstrInfo &TII = Fn.getTarget().getInstrInfo();
174 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) {
175 // If last instruction is a return instruction, add an epilogue
176 if (!FI->empty() && TII.isReturn(FI->back()->getOpcode())) {
177 MBB = FI; I = MBB->end()-1;
179 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
180 const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]);
181 RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i],StackSlots[i], RC);
182 --I; // Insert in reverse order
189 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
190 /// abstract stack objects...
192 void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
193 const TargetFrameInfo &TFI = Fn.getTarget().getFrameInfo();
195 bool StackGrowsDown =
196 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
197 assert(StackGrowsDown && "Only tested on stack down growing targets!");
199 // Loop over all of the stack objects, assigning sequential addresses...
200 MachineFrameInfo *FFI = Fn.getFrameInfo();
202 unsigned StackAlignment = TFI.getStackAlignment();
204 // Start at the beginning of the local area...
205 int Offset = TFI.getOffsetOfLocalArea();
206 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
207 Offset += FFI->getObjectSize(i); // Allocate Size bytes...
209 unsigned Align = FFI->getObjectAlignment(i);
210 assert(Align <= StackAlignment && "Cannot align stack object to higher "
211 "alignment boundary than the stack itself!");
212 Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary...
214 FFI->setObjectOffset(i, -Offset); // Set the computed offset
217 // Align the final stack pointer offset...
218 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment;
220 // Set the final value of the stack pointer...
221 FFI->setStackSize(Offset-TFI.getOffsetOfLocalArea());
225 /// insertPrologEpilogCode - Scan the function for modified caller saved
226 /// registers, insert spill code for these caller saved registers, then add
227 /// prolog and epilog code to the function.
229 void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
230 // Add prologue to the function...
231 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn);
233 // Add epilogue to restore the callee-save registers in each exiting block
234 const TargetInstrInfo &TII = Fn.getTarget().getInstrInfo();
235 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
236 // If last instruction is a return instruction, add an epilogue
237 if (!I->empty() && TII.isReturn(I->back()->getOpcode()))
238 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I);
243 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
244 /// register references and actual offsets.
246 void PEI::replaceFrameIndices(MachineFunction &Fn) {
247 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
249 const TargetMachine &TM = Fn.getTarget();
250 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!");
251 const MRegisterInfo &MRI = *TM.getRegisterInfo();
253 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
254 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
255 for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i)
256 if ((*I)->getOperand(i).isFrameIndex()) {
257 // If this instruction has a FrameIndex operand, we need to use that
258 // target machine register info object to eliminate it.
259 MRI.eliminateFrameIndex(Fn, I);
264 } // End llvm namespace