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Initial checkin of Prolog/Epilog code inserter, which is an important part 

of the abstract frame representation

llvm-svn: 5198
This commit is contained in:
Chris Lattner 2002-12-28 20:43:30 +00:00
parent 2ca5e23403
commit c8b36e6362
1 changed files with 247 additions and 0 deletions
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llvm/lib/CodeGen/PrologEpilogInserter.cpp Normal file
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//===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===//
//
// This pass is responsible for finalizing the functions frame layout, saving
// callee saved registers, and for emitting prolog & epilog code for the
// function.
//
// This pass must be run after register allocation. After this pass is
// executed, it is illegal to construct MO_FrameIndex operands.
//
//===----------------------------------------------------------------------===//
#include "llvm/Pass.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/FunctionFrameInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/MRegisterInfo.h"
#include "llvm/Target/MachineFrameInfo.h"
#include "llvm/Target/MachineInstrInfo.h"
namespace {
struct PEI : public FunctionPass {
bool runOnFunction(Function &Fn) {
return runOnMachineFunction(MachineFunction::get(&Fn));
}
/// runOnMachineFunction - Insert prolog/epilog code and replace abstract
/// frame indexes with appropriate references.
///
bool runOnMachineFunction(MachineFunction &Fn) {
// Scan the function for modified caller saved registers and insert spill
// code for any caller saved registers that are modified. Also calculate
// the MaxCallFrameSize and HasCalls variables for the function's frame
// information and eliminates call frame pseudo instructions.
saveCallerSavedRegisters(Fn);
// Allow the target machine to make final modifications to the function
// before the frame layout is finalized.
Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn);
// Calculate actual frame offsets for all of the abstract stack objects...
calculateFrameObjectOffsets(Fn);
// Replace all MO_FrameIndex operands with physical register references
// and actual offsets.
//
replaceFrameIndices(Fn);
// Add prolog and epilog code to the function.
insertPrologEpilogCode(Fn);
return true;
}
private:
void saveCallerSavedRegisters(MachineFunction &Fn);
void calculateFrameObjectOffsets(MachineFunction &Fn);
void replaceFrameIndices(MachineFunction &Fn);
void insertPrologEpilogCode(MachineFunction &Fn);
};
}
/// createPrologEpilogCodeInserter - This function returns a pass that inserts
/// prolog and epilog code, and eliminates abstract frame references.
///
Pass *createPrologEpilogCodeInserter() { return new PEI(); }
/// saveCallerSavedRegisters - Scan the function for modified caller saved
/// registers and insert spill code for any caller saved registers that are
/// modified. Also calculate the MaxCallFrameSize and HasCalls variables for
/// the function's frame information and eliminates call frame pseudo
/// instructions.
///
void PEI::saveCallerSavedRegisters(MachineFunction &Fn) {
const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
const TargetFrameInfo &FrameInfo = Fn.getTarget().getFrameInfo();
// Get the callee saved register list...
const unsigned *CSRegs = RegInfo->getCalleeSaveRegs();
// Get the function call frame set-up and tear-down instruction opcode
int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode();
int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode();
// Early exit for targets which have no callee saved registers and no call
// frame setup/destroy pseudo instructions.
if ((CSRegs == 0 || CSRegs[0] == 0) &&
FrameSetupOpcode == -1 && FrameDestroyOpcode == -1)
return;
// This bitset contains an entry for each physical register for the target...
std::vector<bool> ModifiedRegs(MRegisterInfo::FirstVirtualRegister);
unsigned MaxCallFrameSize = 0;
bool HasCalls = false;
for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); )
if ((*I)->getOpcode() == FrameSetupOpcode ||
(*I)->getOpcode() == FrameDestroyOpcode) {
assert((*I)->getNumOperands() == 1 && "Call Frame Setup/Destroy Pseudo"
" instructions should have a single immediate argument!");
unsigned Size = (*I)->getOperand(0).getImmedValue();
if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
HasCalls = true;
RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I);
} else {
for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i) {
MachineOperand &MO = (*I)->getOperand(i);
assert(!MO.isVirtualRegister() &&
"Register allocation must be performed!");
if (MO.isPhysicalRegister() && MO.opIsDef())
ModifiedRegs[MO.getReg()] = true; // Register is modified
}
++I;
}
FunctionFrameInfo *FFI = Fn.getFrameInfo();
FFI->setHasCalls(HasCalls);
FFI->setMaxCallFrameSize(MaxCallFrameSize);
// Now figure out which *callee saved* registers are modified by the current
// function, thus needing to be saved and restored in the prolog/epilog.
//
std::vector<unsigned> RegsToSave;
for (unsigned i = 0; CSRegs[i]; ++i) {
unsigned Reg = CSRegs[i];
if (ModifiedRegs[Reg]) {
RegsToSave.push_back(Reg); // If modified register...
} else if (const unsigned *AliasSet = RegInfo->getAliasSet(Reg))
for (unsigned j = 0; AliasSet[j]; ++j) // Check alias registers too...
if (ModifiedRegs[AliasSet[j]]) {
RegsToSave.push_back(Reg);
break;
}
}
if (RegsToSave.empty())
return; // Early exit if no caller saved registers are modified!
// Now that we know which registers need to be saved and restored, allocate
// stack slots for them.
std::vector<int> StackSlots;
for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]);
int FrameIdx = FFI->CreateStackObject(RC->getSize(), RC->getAlignment());
StackSlots.push_back(FrameIdx);
}
// Now that we have a stack slot for each register to be saved, insert spill
// code into the entry block...
MachineBasicBlock *MBB = Fn.begin();
MachineBasicBlock::iterator I = MBB->begin();
for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]);
// Insert the spill to the stack frame...
RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i], StackSlots[i], RC);
}
// Add code to restore the callee-save registers in each exiting block.
const MachineInstrInfo &MII = Fn.getTarget().getInstrInfo();
for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) {
// If last instruction is a return instruction, add an epilogue
if (MII.isReturn(FI->back()->getOpcode())) {
MBB = FI; I = MBB->end()-1;
for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]);
RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i],StackSlots[i], RC);
--I; // Insert in reverse order
}
}
}
}
/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
/// abstract stack objects...
///
void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
const TargetFrameInfo &TFI = Fn.getTarget().getFrameInfo();
bool StackGrowsDown =
TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
assert(StackGrowsDown && "Only tested on stack down growing targets!");
// Loop over all of the stack objects, assigning sequential addresses...
FunctionFrameInfo *FFI = Fn.getFrameInfo();
// Start at the beginning of the local area...
int Offset = -TFI.getOffsetOfLocalArea();
for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
Offset += FFI->getObjectSize(i); // Allocate Size bytes...
unsigned Align = FFI->getObjectAlignment(i);
Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary...
FFI->setObjectOffset(i, -Offset); // Set the computed offset
}
// Align the final stack pointer offset...
unsigned StackAlign = TFI.getStackAlignment();
Offset = (Offset+StackAlign-1)/StackAlign*StackAlign;
// Set the final value of the stack pointer...
FFI->setStackSize(Offset);
}
/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
/// register references and actual offsets.
///
void PEI::replaceFrameIndices(MachineFunction &Fn) {
if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
const TargetMachine &TM = Fn.getTarget();
assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!");
const MRegisterInfo &MRI = *TM.getRegisterInfo();
for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i)
if ((*I)->getOperand(i).isFrameIndex()) {
// If this instruction has a FrameIndex operand, we need to use that
// target machine register info object to eliminate it.
MRI.eliminateFrameIndex(Fn, I);
break;
}
}
/// insertPrologEpilogCode - Scan the function for modified caller saved
/// registers, insert spill code for these caller saved registers, then add
/// prolog and epilog code to the function.
///
void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
// Add prologue to the function...
Fn.getTarget().getRegisterInfo()->emitPrologue(Fn);
// Add epilogue to restore the callee-save registers in each exiting block
const MachineInstrInfo &MII = Fn.getTarget().getInstrInfo();
for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
// If last instruction is a return instruction, add an epilogue
if (MII.isReturn(I->back()->getOpcode()))
Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I);
}
}