llvm-6502/lib/CodeGen/PrologEpilogInserter.cpp
Chris Lattner c330b68fb7 Split saveCallerSavedRegisters into two methods for clarity, and add comments.
Add support for targets that must spill certain physregs at certain locations.

Patch contributed by Nate Begeman, slightly hacked by me.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@15701 91177308-0d34-0410-b5e6-96231b3b80d8
2004-08-12 19:01:14 +00:00

344 lines
13 KiB
C++

//===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/MRegisterInfo.h"
#include "llvm/Target/TargetFrameInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
using namespace llvm;
namespace {
struct PEI : public MachineFunctionPass {
const char *getPassName() const {
return "Prolog/Epilog Insertion & Frame Finalization";
}
/// 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.
calculateCallerSavedRegisters(Fn);
// Add the code to save and restore the caller saved registers
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);
// Add prolog and epilog code to the function. This function is required
// to align the stack frame as necessary for any stack variables or
// called functions. Because of this, calculateCallerSavedRegisters
// must be called before this function in order to set the HasCalls
// and MaxCallFrameSize variables.
insertPrologEpilogCode(Fn);
// Replace all MO_FrameIndex operands with physical register references
// and actual offsets.
//
replaceFrameIndices(Fn);
RegsToSave.clear();
StackSlots.clear();
return true;
}
private:
std::vector<unsigned> RegsToSave;
std::vector<int> StackSlots;
void calculateCallerSavedRegisters(MachineFunction &Fn);
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.
///
FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); }
/// calculateCallerSavedRegisters - Scan the function for modified caller saved
/// registers. Also calculate the MaxCallFrameSize and HasCalls variables for
/// the function's frame information and eliminates call frame pseudo
/// instructions.
///
void PEI::calculateCallerSavedRegisters(MachineFunction &Fn) {
const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
const TargetFrameInfo *TFI = 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(RegInfo->getNumRegs());
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);
if (MO.isRegister() && MO.isDef()) {
assert(MRegisterInfo::isPhysicalRegister(MO.getReg()) &&
"Register allocation must be performed!");
ModifiedRegs[MO.getReg()] = true; // Register is modified
}
}
++I;
}
MachineFrameInfo *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.
//
for (unsigned i = 0; CSRegs[i]; ++i) {
unsigned Reg = CSRegs[i];
if (ModifiedRegs[Reg]) {
RegsToSave.push_back(Reg); // If modified register...
} else {
for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
*AliasSet; ++AliasSet) { // Check alias registers too...
if (ModifiedRegs[*AliasSet]) {
RegsToSave.push_back(Reg);
break;
}
}
}
}
if (RegsToSave.empty())
return; // Early exit if no caller saved registers are modified!
unsigned NumFixedSpillSlots;
std::pair<unsigned,int> *FixedSpillSlots =
TFI->getCalleeSaveSpillSlots(NumFixedSpillSlots);
// Now that we know which registers need to be saved and restored, allocate
// stack slots for them.
for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
unsigned Reg = RegsToSave[i];
int FrameIdx;
const TargetRegisterClass *RC = RegInfo->getRegClass(Reg);
// Check to see if this physreg must be spilled to a particular stack slot
// on this target.
std::pair<unsigned,int> *FixedSlot = FixedSpillSlots;
while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots &&
FixedSlot->first != Reg)
++FixedSlot;
if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) {
// Nope, just spill it anywhere convenient.
FrameIdx = FFI->CreateStackObject(RC);
} else {
// Spill it to the stack where we must.
FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->second);
}
StackSlots.push_back(FrameIdx);
}
}
/// saveCallerSavedRegisters - Insert spill code for any caller saved registers
/// that are modified in the function.
///
void PEI::saveCallerSavedRegisters(MachineFunction &Fn) {
// Early exit if no caller saved registers are modified!
if (RegsToSave.empty())
return;
const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
// 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 TargetInstrInfo &TII = *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 (!FI->empty() && TII.isReturn(FI->back().getOpcode())) {
MBB = FI;
I = MBB->end(); --I;
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;
// Loop over all of the stack objects, assigning sequential addresses...
MachineFrameInfo *FFI = Fn.getFrameInfo();
unsigned StackAlignment = TFI.getStackAlignment();
// Start at the beginning of the local area.
// The Offset is the distance from the stack top in the direction
// of stack growth -- so it's always positive.
int Offset = TFI.getOffsetOfLocalArea();
if (StackGrowsDown)
Offset = -Offset;
assert(Offset >= 0
&& "Local area offset should be in direction of stack growth");
// If there are fixed sized objects that are preallocated in the local area,
// non-fixed objects can't be allocated right at the start of local area.
// We currently don't support filling in holes in between fixed sized objects,
// so we adjust 'Offset' to point to the end of last fixed sized
// preallocated object.
for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) {
int FixedOff;
if (StackGrowsDown) {
// The maximum distance from the stack pointer is at lower address of
// the object -- which is given by offset. For down growing stack
// the offset is negative, so we negate the offset to get the distance.
FixedOff = -FFI->getObjectOffset(i);
} else {
// The maximum distance from the start pointer is at the upper
// address of the object.
FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i);
}
if (FixedOff > Offset) Offset = FixedOff;
}
for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
// If stack grows down, we need to add size of find the lowest
// address of the object.
if (StackGrowsDown)
Offset += FFI->getObjectSize(i);
unsigned Align = FFI->getObjectAlignment(i);
assert(Align <= StackAlignment && "Cannot align stack object to higher "
"alignment boundary than the stack itself!");
Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary...
if (StackGrowsDown) {
FFI->setObjectOffset(i, -Offset); // Set the computed offset
} else {
FFI->setObjectOffset(i, Offset);
Offset += FFI->getObjectSize(i);
}
}
// Align the final stack pointer offset, but only if there are calls in the
// function. This ensures that any calls to subroutines have their stack
// frames suitable aligned.
if (FFI->hasCalls())
Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment;
// Set the final value of the stack pointer...
FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea());
}
/// 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 TargetInstrInfo &TII = *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 (!I->empty() && TII.isReturn(I->back().getOpcode()))
Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I);
}
}
/// 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;
}
}