llvm-6502/lib/Target/ARM/ARMConstantIslandPass.cpp
2007-02-25 18:31:31 +00:00

1002 lines
38 KiB
C++

//===-- ARMConstantIslandPass.cpp - ARM constant islands --------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by Chris Lattner and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains a pass that splits the constant pool up into 'islands'
// which are scattered through-out the function. This is required due to the
// limited pc-relative displacements that ARM has.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "arm-cp-islands"
#include "ARM.h"
#include "ARMMachineFunctionInfo.h"
#include "ARMInstrInfo.h"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumCPEs, "Number of constpool entries");
STATISTIC(NumSplit, "Number of uncond branches inserted");
STATISTIC(NumCBrFixed, "Number of cond branches fixed");
STATISTIC(NumUBrFixed, "Number of uncond branches fixed");
namespace {
/// ARMConstantIslands - Due to limited PC-relative displacements, ARM
/// requires constant pool entries to be scattered among the instructions
/// inside a function. To do this, it completely ignores the normal LLVM
/// constant pool; instead, it places constants wherever it feels like with
/// special instructions.
///
/// The terminology used in this pass includes:
/// Islands - Clumps of constants placed in the function.
/// Water - Potential places where an island could be formed.
/// CPE - A constant pool entry that has been placed somewhere, which
/// tracks a list of users.
class VISIBILITY_HIDDEN ARMConstantIslands : public MachineFunctionPass {
/// NextUID - Assign unique ID's to CPE's.
unsigned NextUID;
/// BBSizes - The size of each MachineBasicBlock in bytes of code, indexed
/// by MBB Number.
std::vector<unsigned> BBSizes;
/// BBOffsets - the offset of each MBB in bytes, starting from 0.
std::vector<unsigned> BBOffsets;
/// WaterList - A sorted list of basic blocks where islands could be placed
/// (i.e. blocks that don't fall through to the following block, due
/// to a return, unreachable, or unconditional branch).
std::vector<MachineBasicBlock*> WaterList;
/// CPUser - One user of a constant pool, keeping the machine instruction
/// pointer, the constant pool being referenced, and the max displacement
/// allowed from the instruction to the CP.
struct CPUser {
MachineInstr *MI;
MachineInstr *CPEMI;
unsigned MaxDisp;
CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp)
: MI(mi), CPEMI(cpemi), MaxDisp(maxdisp) {}
};
/// CPUsers - Keep track of all of the machine instructions that use various
/// constant pools and their max displacement.
std::vector<CPUser> CPUsers;
/// CPEntry - One per constant pool entry, keeping the machine instruction
/// pointer, the constpool index, and the number of CPUser's which
/// reference this entry.
struct CPEntry {
MachineInstr *CPEMI;
unsigned CPI;
unsigned RefCount;
CPEntry(MachineInstr *cpemi, unsigned cpi, unsigned rc = 0)
: CPEMI(cpemi), CPI(cpi), RefCount(rc) {}
};
/// CPEntries - Keep track of all of the constant pool entry machine
/// instructions. For each original constpool index (i.e. those that
/// existed upon entry to this pass), it keeps a vector of entries.
/// Original elements are cloned as we go along; the clones are
/// put in the vector of the original element, but have distinct CPIs.
std::vector<std::vector<CPEntry> > CPEntries;
/// ImmBranch - One per immediate branch, keeping the machine instruction
/// pointer, conditional or unconditional, the max displacement,
/// and (if isCond is true) the corresponding unconditional branch
/// opcode.
struct ImmBranch {
MachineInstr *MI;
unsigned MaxDisp : 31;
bool isCond : 1;
int UncondBr;
ImmBranch(MachineInstr *mi, unsigned maxdisp, bool cond, int ubr)
: MI(mi), MaxDisp(maxdisp), isCond(cond), UncondBr(ubr) {}
};
/// Branches - Keep track of all the immediate branch instructions.
///
std::vector<ImmBranch> ImmBranches;
/// PushPopMIs - Keep track of all the Thumb push / pop instructions.
///
SmallVector<MachineInstr*, 4> PushPopMIs;
/// HasFarJump - True if any far jump instruction has been emitted during
/// the branch fix up pass.
bool HasFarJump;
const TargetInstrInfo *TII;
const ARMFunctionInfo *AFI;
public:
virtual bool runOnMachineFunction(MachineFunction &Fn);
virtual const char *getPassName() const {
return "ARM constant island placement and branch shortening pass";
}
private:
void DoInitialPlacement(MachineFunction &Fn,
std::vector<MachineInstr*> &CPEMIs);
CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI);
void InitialFunctionScan(MachineFunction &Fn,
const std::vector<MachineInstr*> &CPEMIs);
MachineBasicBlock *SplitBlockBeforeInstr(MachineInstr *MI);
void UpdateForInsertedWaterBlock(MachineBasicBlock *NewBB);
void AdjustBBOffsetsAfter(MachineBasicBlock *BB, int delta);
bool DecrementOldEntry(unsigned CPI, MachineInstr* CPEMI, unsigned Size);
int LookForExistingCPEntry(CPUser& U, unsigned UserOffset);
bool HandleConstantPoolUser(MachineFunction &Fn, CPUser &U);
bool CPEIsInRange(MachineInstr *MI, unsigned UserOffset,
MachineInstr *CPEMI, unsigned Disp,
bool DoDump);
bool WaterIsInRange(unsigned UserOffset, MachineBasicBlock *Water,
unsigned Disp);
bool OffsetIsInRange(unsigned UserOffset, unsigned TrialOffset,
unsigned Disp, bool NegativeOK);
bool BBIsInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp);
bool FixUpImmediateBr(MachineFunction &Fn, ImmBranch &Br);
bool FixUpConditionalBr(MachineFunction &Fn, ImmBranch &Br);
bool FixUpUnconditionalBr(MachineFunction &Fn, ImmBranch &Br);
bool UndoLRSpillRestore();
unsigned GetOffsetOf(MachineInstr *MI) const;
};
}
/// createARMConstantIslandPass - returns an instance of the constpool
/// island pass.
FunctionPass *llvm::createARMConstantIslandPass() {
return new ARMConstantIslands();
}
bool ARMConstantIslands::runOnMachineFunction(MachineFunction &Fn) {
MachineConstantPool &MCP = *Fn.getConstantPool();
TII = Fn.getTarget().getInstrInfo();
AFI = Fn.getInfo<ARMFunctionInfo>();
HasFarJump = false;
// Renumber all of the machine basic blocks in the function, guaranteeing that
// the numbers agree with the position of the block in the function.
Fn.RenumberBlocks();
// Perform the initial placement of the constant pool entries. To start with,
// we put them all at the end of the function.
std::vector<MachineInstr*> CPEMIs;
if (!MCP.isEmpty())
DoInitialPlacement(Fn, CPEMIs);
/// The next UID to take is the first unused one.
NextUID = CPEMIs.size();
// Do the initial scan of the function, building up information about the
// sizes of each block, the location of all the water, and finding all of the
// constant pool users.
InitialFunctionScan(Fn, CPEMIs);
CPEMIs.clear();
// Iteratively place constant pool entries and fix up branches until there
// is no change.
bool MadeChange = false;
while (true) {
bool Change = false;
for (unsigned i = 0, e = CPUsers.size(); i != e; ++i)
Change |= HandleConstantPoolUser(Fn, CPUsers[i]);
for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
Change |= FixUpImmediateBr(Fn, ImmBranches[i]);
if (!Change)
break;
MadeChange = true;
}
// If LR has been forced spilled and no far jumps (i.e. BL) has been issued.
// Undo the spill / restore of LR if possible.
if (!HasFarJump && AFI->isLRForceSpilled() && AFI->isThumbFunction())
MadeChange |= UndoLRSpillRestore();
BBSizes.clear();
BBOffsets.clear();
WaterList.clear();
CPUsers.clear();
CPEntries.clear();
ImmBranches.clear();
PushPopMIs.clear();
return MadeChange;
}
/// DoInitialPlacement - Perform the initial placement of the constant pool
/// entries. To start with, we put them all at the end of the function.
void ARMConstantIslands::DoInitialPlacement(MachineFunction &Fn,
std::vector<MachineInstr*> &CPEMIs){
// Create the basic block to hold the CPE's.
MachineBasicBlock *BB = new MachineBasicBlock();
Fn.getBasicBlockList().push_back(BB);
// Add all of the constants from the constant pool to the end block, use an
// identity mapping of CPI's to CPE's.
const std::vector<MachineConstantPoolEntry> &CPs =
Fn.getConstantPool()->getConstants();
const TargetData &TD = *Fn.getTarget().getTargetData();
for (unsigned i = 0, e = CPs.size(); i != e; ++i) {
unsigned Size = TD.getTypeSize(CPs[i].getType());
// Verify that all constant pool entries are a multiple of 4 bytes. If not,
// we would have to pad them out or something so that instructions stay
// aligned.
assert((Size & 3) == 0 && "CP Entry not multiple of 4 bytes!");
MachineInstr *CPEMI =
BuildMI(BB, TII->get(ARM::CONSTPOOL_ENTRY))
.addImm(i).addConstantPoolIndex(i).addImm(Size);
CPEMIs.push_back(CPEMI);
// Add a new CPEntry, but no corresponding CPUser yet.
std::vector<CPEntry> CPEs;
CPEs.push_back(CPEntry(CPEMI, i));
CPEntries.push_back(CPEs);
NumCPEs++;
DOUT << "Moved CPI#" << i << " to end of function as #" << i << "\n";
}
}
/// BBHasFallthrough - Return true if the specified basic block can fallthrough
/// into the block immediately after it.
static bool BBHasFallthrough(MachineBasicBlock *MBB) {
// Get the next machine basic block in the function.
MachineFunction::iterator MBBI = MBB;
if (next(MBBI) == MBB->getParent()->end()) // Can't fall off end of function.
return false;
MachineBasicBlock *NextBB = next(MBBI);
for (MachineBasicBlock::succ_iterator I = MBB->succ_begin(),
E = MBB->succ_end(); I != E; ++I)
if (*I == NextBB)
return true;
return false;
}
/// findConstPoolEntry - Given the constpool index and CONSTPOOL_ENTRY MI,
/// look up the corresponding CPEntry.
ARMConstantIslands::CPEntry
*ARMConstantIslands::findConstPoolEntry(unsigned CPI,
const MachineInstr *CPEMI) {
std::vector<CPEntry> &CPEs = CPEntries[CPI];
// Number of entries per constpool index should be small, just do a
// linear search.
for (unsigned i = 0, e = CPEs.size(); i != e; ++i) {
if (CPEs[i].CPEMI == CPEMI)
return &CPEs[i];
}
return NULL;
}
/// InitialFunctionScan - Do the initial scan of the function, building up
/// information about the sizes of each block, the location of all the water,
/// and finding all of the constant pool users.
void ARMConstantIslands::InitialFunctionScan(MachineFunction &Fn,
const std::vector<MachineInstr*> &CPEMIs) {
unsigned Offset = 0;
for (MachineFunction::iterator MBBI = Fn.begin(), E = Fn.end();
MBBI != E; ++MBBI) {
MachineBasicBlock &MBB = *MBBI;
// If this block doesn't fall through into the next MBB, then this is
// 'water' that a constant pool island could be placed.
if (!BBHasFallthrough(&MBB))
WaterList.push_back(&MBB);
unsigned MBBSize = 0;
for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
I != E; ++I) {
// Add instruction size to MBBSize.
MBBSize += ARM::GetInstSize(I);
int Opc = I->getOpcode();
if (TII->isBranch(Opc)) {
bool isCond = false;
unsigned Bits = 0;
unsigned Scale = 1;
int UOpc = Opc;
switch (Opc) {
default:
continue; // Ignore JT branches
case ARM::Bcc:
isCond = true;
UOpc = ARM::B;
// Fallthrough
case ARM::B:
Bits = 24;
Scale = 4;
break;
case ARM::tBcc:
isCond = true;
UOpc = ARM::tB;
Bits = 8;
Scale = 2;
break;
case ARM::tB:
Bits = 11;
Scale = 2;
break;
}
// Record this immediate branch.
unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale;
ImmBranches.push_back(ImmBranch(I, MaxOffs, isCond, UOpc));
}
if (Opc == ARM::tPUSH || Opc == ARM::tPOP_RET)
PushPopMIs.push_back(I);
// Scan the instructions for constant pool operands.
for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op)
if (I->getOperand(op).isConstantPoolIndex()) {
// We found one. The addressing mode tells us the max displacement
// from the PC that this instruction permits.
// Basic size info comes from the TSFlags field.
unsigned Bits = 0;
unsigned Scale = 1;
unsigned TSFlags = I->getInstrDescriptor()->TSFlags;
switch (TSFlags & ARMII::AddrModeMask) {
default:
// Constant pool entries can reach anything.
if (I->getOpcode() == ARM::CONSTPOOL_ENTRY)
continue;
assert(0 && "Unknown addressing mode for CP reference!");
case ARMII::AddrMode1: // AM1: 8 bits << 2
Bits = 8;
Scale = 4; // Taking the address of a CP entry.
break;
case ARMII::AddrMode2:
Bits = 12; // +-offset_12
break;
case ARMII::AddrMode3:
Bits = 8; // +-offset_8
break;
// addrmode4 has no immediate offset.
case ARMII::AddrMode5:
Bits = 8;
Scale = 4; // +-(offset_8*4)
break;
case ARMII::AddrModeT1:
Bits = 5; // +offset_5
break;
case ARMII::AddrModeT2:
Bits = 5;
Scale = 2; // +(offset_5*2)
break;
case ARMII::AddrModeT4:
Bits = 5;
Scale = 4; // +(offset_5*4)
break;
case ARMII::AddrModeTs:
Bits = 8;
Scale = 4; // +(offset_8*4)
break;
}
// Remember that this is a user of a CP entry.
unsigned CPI = I->getOperand(op).getConstantPoolIndex();
MachineInstr *CPEMI = CPEMIs[CPI];
unsigned MaxOffs = ((1 << Bits)-1) * Scale;
CPUsers.push_back(CPUser(I, CPEMI, MaxOffs));
// Increment corresponding CPEntry reference count.
CPEntry *CPE = findConstPoolEntry(CPI, CPEMI);
assert(CPE && "Cannot find a corresponding CPEntry!");
CPE->RefCount++;
// Instructions can only use one CP entry, don't bother scanning the
// rest of the operands.
break;
}
}
// In thumb mode, if this block is a constpool island, pessimistically
// assume it needs to be padded by two byte so it's aligned on 4 byte
// boundary.
if (AFI->isThumbFunction() &&
!MBB.empty() &&
MBB.begin()->getOpcode() == ARM::CONSTPOOL_ENTRY)
MBBSize += 2;
BBSizes.push_back(MBBSize);
BBOffsets.push_back(Offset);
Offset += MBBSize;
}
}
/// GetOffsetOf - Return the current offset of the specified machine instruction
/// from the start of the function. This offset changes as stuff is moved
/// around inside the function.
unsigned ARMConstantIslands::GetOffsetOf(MachineInstr *MI) const {
MachineBasicBlock *MBB = MI->getParent();
// The offset is composed of two things: the sum of the sizes of all MBB's
// before this instruction's block, and the offset from the start of the block
// it is in.
unsigned Offset = BBOffsets[MBB->getNumber()];
// Sum instructions before MI in MBB.
for (MachineBasicBlock::iterator I = MBB->begin(); ; ++I) {
assert(I != MBB->end() && "Didn't find MI in its own basic block?");
if (&*I == MI) return Offset;
Offset += ARM::GetInstSize(I);
}
}
/// CompareMBBNumbers - Little predicate function to sort the WaterList by MBB
/// ID.
static bool CompareMBBNumbers(const MachineBasicBlock *LHS,
const MachineBasicBlock *RHS) {
return LHS->getNumber() < RHS->getNumber();
}
/// UpdateForInsertedWaterBlock - When a block is newly inserted into the
/// machine function, it upsets all of the block numbers. Renumber the blocks
/// and update the arrays that parallel this numbering.
void ARMConstantIslands::UpdateForInsertedWaterBlock(MachineBasicBlock *NewBB) {
// Renumber the MBB's to keep them consequtive.
NewBB->getParent()->RenumberBlocks(NewBB);
// Insert a size into BBSizes to align it properly with the (newly
// renumbered) block numbers.
BBSizes.insert(BBSizes.begin()+NewBB->getNumber(), 0);
// Likewise for BBOffsets.
BBOffsets.insert(BBOffsets.begin()+NewBB->getNumber(), 0);
// Next, update WaterList. Specifically, we need to add NewMBB as having
// available water after it.
std::vector<MachineBasicBlock*>::iterator IP =
std::lower_bound(WaterList.begin(), WaterList.end(), NewBB,
CompareMBBNumbers);
WaterList.insert(IP, NewBB);
}
/// Split the basic block containing MI into two blocks, which are joined by
/// an unconditional branch. Update datastructures and renumber blocks to
/// account for this change and returns the newly created block.
MachineBasicBlock *ARMConstantIslands::SplitBlockBeforeInstr(MachineInstr *MI) {
MachineBasicBlock *OrigBB = MI->getParent();
bool isThumb = AFI->isThumbFunction();
// Create a new MBB for the code after the OrigBB.
MachineBasicBlock *NewBB = new MachineBasicBlock(OrigBB->getBasicBlock());
MachineFunction::iterator MBBI = OrigBB; ++MBBI;
OrigBB->getParent()->getBasicBlockList().insert(MBBI, NewBB);
// Splice the instructions starting with MI over to NewBB.
NewBB->splice(NewBB->end(), OrigBB, MI, OrigBB->end());
// Add an unconditional branch from OrigBB to NewBB.
// Note the new unconditional branch is not being recorded.
BuildMI(OrigBB, TII->get(isThumb ? ARM::tB : ARM::B)).addMBB(NewBB);
NumSplit++;
// Update the CFG. All succs of OrigBB are now succs of NewBB.
while (!OrigBB->succ_empty()) {
MachineBasicBlock *Succ = *OrigBB->succ_begin();
OrigBB->removeSuccessor(Succ);
NewBB->addSuccessor(Succ);
// This pass should be run after register allocation, so there should be no
// PHI nodes to update.
assert((Succ->empty() || Succ->begin()->getOpcode() != TargetInstrInfo::PHI)
&& "PHI nodes should be eliminated by now!");
}
// OrigBB branches to NewBB.
OrigBB->addSuccessor(NewBB);
// Update internal data structures to account for the newly inserted MBB.
// This is almost the same as UpdateForInsertedWaterBlock, except that
// the Water goes after OrigBB, not NewBB.
NewBB->getParent()->RenumberBlocks(NewBB);
// Insert a size into BBSizes to align it properly with the (newly
// renumbered) block numbers.
BBSizes.insert(BBSizes.begin()+NewBB->getNumber(), 0);
// Likewise for BBOffsets.
BBOffsets.insert(BBOffsets.begin()+NewBB->getNumber(), 0);
// Next, update WaterList. Specifically, we need to add OrigMBB as having
// available water after it (but not if it's already there, which happens
// when splitting before a conditional branch that is followed by an
// unconditional branch - in that case we want to insert NewBB).
std::vector<MachineBasicBlock*>::iterator IP =
std::lower_bound(WaterList.begin(), WaterList.end(), OrigBB,
CompareMBBNumbers);
MachineBasicBlock* WaterBB = *IP;
if (WaterBB == OrigBB)
WaterList.insert(next(IP), NewBB);
else
WaterList.insert(IP, OrigBB);
// Figure out how large the first NewMBB is.
unsigned NewBBSize = 0;
for (MachineBasicBlock::iterator I = NewBB->begin(), E = NewBB->end();
I != E; ++I)
NewBBSize += ARM::GetInstSize(I);
unsigned OrigBBI = OrigBB->getNumber();
unsigned NewBBI = NewBB->getNumber();
// Set the size of NewBB in BBSizes.
BBSizes[NewBBI] = NewBBSize;
// We removed instructions from UserMBB, subtract that off from its size.
// Add 2 or 4 to the block to count the unconditional branch we added to it.
unsigned delta = isThumb ? 2 : 4;
BBSizes[OrigBBI] -= NewBBSize - delta;
// ...and adjust BBOffsets for NewBB accordingly.
BBOffsets[NewBBI] = BBOffsets[OrigBBI] + BBSizes[OrigBBI];
// All BBOffsets following these blocks must be modified.
AdjustBBOffsetsAfter(NewBB, delta);
return NewBB;
}
/// OffsetIsInRange - Checks whether UserOffset is within MaxDisp of
/// TrialOffset.
bool ARMConstantIslands::OffsetIsInRange(unsigned UserOffset,
unsigned TrialOffset, unsigned MaxDisp, bool NegativeOK) {
if (UserOffset <= TrialOffset) {
// User before the Trial.
if (TrialOffset-UserOffset <= MaxDisp)
return true;
} else if (NegativeOK) {
if (UserOffset-TrialOffset <= MaxDisp)
return true;
}
return false;
}
/// WaterIsInRange - Returns true if a CPE placed after the specified
/// Water (a basic block) will be in range for the specific MI.
bool ARMConstantIslands::WaterIsInRange(unsigned UserOffset,
MachineBasicBlock* Water, unsigned MaxDisp)
{
bool isThumb = AFI->isThumbFunction();
unsigned CPEOffset = BBOffsets[Water->getNumber()] +
BBSizes[Water->getNumber()];
// If the Water is a constpool island, it has already been aligned.
// If not, align it.
if (isThumb &&
(Water->empty() ||
Water->begin()->getOpcode() != ARM::CONSTPOOL_ENTRY))
CPEOffset += 2;
return OffsetIsInRange (UserOffset, CPEOffset, MaxDisp, !isThumb);
}
/// CPEIsInRange - Returns true if the distance between specific MI and
/// specific ConstPool entry instruction can fit in MI's displacement field.
bool ARMConstantIslands::CPEIsInRange(MachineInstr *MI, unsigned UserOffset,
MachineInstr *CPEMI,
unsigned MaxDisp, bool DoDump) {
// In thumb mode, pessimistically assumes the .align 2 before the first CPE
// in the island adds two byte padding.
bool isThumb = AFI->isThumbFunction();
unsigned AlignAdj = isThumb ? 2 : 0;
unsigned CPEOffset = GetOffsetOf(CPEMI) + AlignAdj;
if (DoDump) {
DOUT << "User of CPE#" << CPEMI->getOperand(0).getImm()
<< " max delta=" << MaxDisp
<< " insn address=" << UserOffset
<< " CPE address=" << CPEOffset
<< " offset=" << int(CPEOffset-UserOffset) << "\t" << *MI;
}
return OffsetIsInRange(UserOffset, CPEOffset, MaxDisp, !isThumb);
}
/// BBIsJumpedOver - Return true of the specified basic block's only predecessor
/// unconditionally branches to its only successor.
static bool BBIsJumpedOver(MachineBasicBlock *MBB) {
if (MBB->pred_size() != 1 || MBB->succ_size() != 1)
return false;
MachineBasicBlock *Succ = *MBB->succ_begin();
MachineBasicBlock *Pred = *MBB->pred_begin();
MachineInstr *PredMI = &Pred->back();
if (PredMI->getOpcode() == ARM::B || PredMI->getOpcode() == ARM::tB)
return PredMI->getOperand(0).getMBB() == Succ;
return false;
}
void ARMConstantIslands::AdjustBBOffsetsAfter(MachineBasicBlock *BB, int delta)
{
MachineFunction::iterator MBBI = BB->getParent()->end();
for(unsigned i=BB->getNumber()+1; i<BB->getParent()->getNumBlockIDs(); i++)
BBOffsets[i] += delta;
}
/// DecrementOldEntry - find the constant pool entry with index CPI
/// and instruction CPEMI, and decrement its refcount. If the refcount
/// becomes 0 remove the entry and instruction. Returns true if we removed
/// the entry, false if we didn't.
bool ARMConstantIslands::DecrementOldEntry(unsigned CPI, MachineInstr *CPEMI,
unsigned Size) {
// Find the old entry. Eliminate it if it is no longer used.
CPEntry *OldCPE = findConstPoolEntry(CPI, CPEMI);
assert(OldCPE && "Unexpected!");
if (--OldCPE->RefCount == 0) {
MachineBasicBlock *OldCPEBB = OldCPE->CPEMI->getParent();
if (OldCPEBB->empty()) {
// In thumb mode, the size of island is padded by two to compensate for
// the alignment requirement. Thus it will now be 2 when the block is
// empty, so fix this.
// All succeeding offsets have the current size value added in, fix this.
if (BBSizes[OldCPEBB->getNumber()] != 0) {
AdjustBBOffsetsAfter(OldCPEBB, -BBSizes[OldCPEBB->getNumber()]);
BBSizes[OldCPEBB->getNumber()] = 0;
}
// An island has only one predecessor BB and one successor BB. Check if
// this BB's predecessor jumps directly to this BB's successor. This
// shouldn't happen currently.
assert(!BBIsJumpedOver(OldCPEBB) && "How did this happen?");
// FIXME: remove the empty blocks after all the work is done?
} else {
BBSizes[OldCPEBB->getNumber()] -= Size;
// All succeeding offsets have the current size value added in, fix this.
AdjustBBOffsetsAfter(OldCPEBB, -Size);
}
OldCPE->CPEMI->eraseFromParent();
OldCPE->CPEMI = NULL;
NumCPEs--;
return true;
}
return false;
}
/// LookForCPEntryInRange - see if the currently referenced CPE is in range;
/// if not, see if an in-range clone of the CPE is in range, and if so,
/// change the data structures so the user references the clone. Returns:
/// 0 = no existing entry found
/// 1 = entry found, and there were no code insertions or deletions
/// 2 = entry found, and there were code insertions or deletions
int ARMConstantIslands::LookForExistingCPEntry(CPUser& U, unsigned UserOffset)
{
MachineInstr *UserMI = U.MI;
MachineInstr *CPEMI = U.CPEMI;
// Check to see if the CPE is already in-range.
if (CPEIsInRange(UserMI, UserOffset, CPEMI, U.MaxDisp, true)) {
DOUT << "In range\n";
return 1;
}
// No. Look for previously created clones of the CPE that are in range.
unsigned CPI = CPEMI->getOperand(1).getConstantPoolIndex();
std::vector<CPEntry> &CPEs = CPEntries[CPI];
for (unsigned i = 0, e = CPEs.size(); i != e; ++i) {
// We already tried this one
if (CPEs[i].CPEMI == CPEMI)
continue;
// Removing CPEs can leave empty entries, skip
if (CPEs[i].CPEMI == NULL)
continue;
if (CPEIsInRange(UserMI, UserOffset, CPEs[i].CPEMI, U.MaxDisp, false)) {
DOUT << "Replacing CPE#" << CPI << " with CPE#" << CPEs[i].CPI << "\n";
// Point the CPUser node to the replacement
U.CPEMI = CPEs[i].CPEMI;
// Change the CPI in the instruction operand to refer to the clone.
for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j)
if (UserMI->getOperand(j).isConstantPoolIndex()) {
UserMI->getOperand(j).setConstantPoolIndex(CPEs[i].CPI);
break;
}
// Adjust the refcount of the clone...
CPEs[i].RefCount++;
// ...and the original. If we didn't remove the old entry, none of the
// addresses changed, so we don't need another pass.
unsigned Size = CPEMI->getOperand(2).getImm();
return DecrementOldEntry(CPI, CPEMI, Size) ? 2 : 1;
}
}
return 0;
}
/// HandleConstantPoolUser - Analyze the specified user, checking to see if it
/// is out-of-range. If so, pick it up the constant pool value and move it some
/// place in-range. Return true if we changed any addresses (thus must run
/// another pass of branch lengthening), false otherwise.
bool ARMConstantIslands::HandleConstantPoolUser(MachineFunction &Fn, CPUser &U){
MachineInstr *UserMI = U.MI;
MachineInstr *CPEMI = U.CPEMI;
unsigned CPI = CPEMI->getOperand(1).getConstantPoolIndex();
unsigned Size = CPEMI->getOperand(2).getImm();
bool isThumb = AFI->isThumbFunction();
MachineBasicBlock *NewMBB;
// Compute this only once, it's expensive
unsigned UserOffset = GetOffsetOf(UserMI) + (isThumb ? 4 : 8);
// See if the current entry is within range, or there is a clone of it
// in range.
int result = LookForExistingCPEntry(U, UserOffset);
if (result==1) return false;
else if (result==2) return true;
// No existing clone of this CPE is within range.
// We will be generating a new clone. Get a UID for it.
unsigned ID = NextUID++;
// Look for water where we can place this CPE. We look for the farthest one
// away that will work. Forward references only for now (although later
// we might find some that are backwards).
bool WaterFound = false;
if (!WaterList.empty()) {
for (std::vector<MachineBasicBlock*>::iterator IP = prior(WaterList.end()),
B = WaterList.begin();; --IP) {
MachineBasicBlock* WaterBB = *IP;
if (WaterIsInRange(UserOffset, WaterBB, U.MaxDisp)) {
WaterFound = true;
DOUT << "found water in range\n";
// CPE goes before following block (NewMBB).
NewMBB = next(MachineFunction::iterator(WaterBB));
// Remove the original WaterList entry; we want subsequent
// insertions in this vicinity to go after the one we're
// about to insert. This considerably reduces the number
// of times we have to move the same CPE more than once.
WaterList.erase(IP);
break;
}
if (IP == B)
break;
}
}
if (!WaterFound) {
// No water found.
DOUT << "No water found\n";
MachineBasicBlock *UserMBB = UserMI->getParent();
unsigned TrialOffset = BBOffsets[UserMBB->getNumber()] +
BBSizes[UserMBB->getNumber()] +
isThumb ? 2 : 4; /* for branch to be added */
// If the use is at the end of the block, or the end of the block
// is within range, make new water there. (If the block ends in
// an unconditional branch already, it is water, and is known to
// be out of range; so it's OK to assume above we'll be adding a Br.)
if (&UserMBB->back() == UserMI ||
OffsetIsInRange(UserOffset, TrialOffset, U.MaxDisp, !isThumb)) {
if (&UserMBB->back() == UserMI)
assert(BBHasFallthrough(UserMBB) && "Expected a fallthrough BB!");
NewMBB = next(MachineFunction::iterator(UserMBB));
// Add an unconditional branch from UserMBB to fallthrough block.
// Note the new unconditional branch is not being recorded.
BuildMI(UserMBB, TII->get(isThumb ? ARM::tB : ARM::B)).addMBB(NewMBB);
int delta = isThumb ? 2 : 4;
BBSizes[UserMBB->getNumber()] += delta;
AdjustBBOffsetsAfter(UserMBB, delta);
} else {
// What a big block. Find a place within the block to split it.
// This is a little tricky on Thumb since instructions are 2 bytes
// and constant pool entries are 4 bytes: if instruction I references
// island CPE, and instruction I+1 references CPE', it will
// not work well to put CPE as far forward as possible, since then
// CPE' cannot immediately follow it (that location is 2 bytes
// farther away from I+1 than CPE was from I) and we'd need to create
// a new island.
// Solution of last resort: split the user's MBB right after the user
// and insert a clone of the CPE into the newly created water.
MachineInstr *NextMI = next(MachineBasicBlock::iterator(UserMI));
NewMBB = SplitBlockBeforeInstr(NextMI);
}
}
// Okay, we know we can put an island before NewMBB now, do it!
MachineBasicBlock *NewIsland = new MachineBasicBlock();
Fn.getBasicBlockList().insert(NewMBB, NewIsland);
// Update internal data structures to account for the newly inserted MBB.
UpdateForInsertedWaterBlock(NewIsland);
// Decrement the old entry, and remove it if refcount becomes 0.
DecrementOldEntry(CPI, CPEMI, Size);
// Now that we have an island to add the CPE to, clone the original CPE and
// add it to the island.
U.CPEMI = BuildMI(NewIsland, TII->get(ARM::CONSTPOOL_ENTRY))
.addImm(ID).addConstantPoolIndex(CPI).addImm(Size);
CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1));
NumCPEs++;
// Compensate for .align 2 in thumb mode.
if (isThumb) Size += 2;
// Increase the size of the island block to account for the new entry.
BBSizes[NewIsland->getNumber()] += Size;
BBOffsets[NewIsland->getNumber()] = BBOffsets[NewMBB->getNumber()];
AdjustBBOffsetsAfter(NewIsland, Size);
// Finally, change the CPI in the instruction operand to be ID.
for (unsigned i = 0, e = UserMI->getNumOperands(); i != e; ++i)
if (UserMI->getOperand(i).isConstantPoolIndex()) {
UserMI->getOperand(i).setConstantPoolIndex(ID);
break;
}
DOUT << " Moved CPE to #" << ID << " CPI=" << CPI << "\t" << *UserMI;
return true;
}
/// BBIsInRange - Returns true if the distance between specific MI and
/// specific BB can fit in MI's displacement field.
bool ARMConstantIslands::BBIsInRange(MachineInstr *MI,MachineBasicBlock *DestBB,
unsigned MaxDisp) {
unsigned PCAdj = AFI->isThumbFunction() ? 4 : 8;
unsigned BrOffset = GetOffsetOf(MI) + PCAdj;
unsigned DestOffset = BBOffsets[DestBB->getNumber()];
DOUT << "Branch of destination BB#" << DestBB->getNumber()
<< " from BB#" << MI->getParent()->getNumber()
<< " max delta=" << MaxDisp
<< " at offset " << int(DestOffset-BrOffset) << "\t" << *MI;
return OffsetIsInRange(BrOffset, DestOffset, MaxDisp, true);
}
/// FixUpImmediateBr - Fix up an immediate branch whose destination is too far
/// away to fit in its displacement field.
bool ARMConstantIslands::FixUpImmediateBr(MachineFunction &Fn, ImmBranch &Br) {
MachineInstr *MI = Br.MI;
MachineBasicBlock *DestBB = MI->getOperand(0).getMachineBasicBlock();
// Check to see if the DestBB is already in-range.
if (BBIsInRange(MI, DestBB, Br.MaxDisp))
return false;
if (!Br.isCond)
return FixUpUnconditionalBr(Fn, Br);
return FixUpConditionalBr(Fn, Br);
}
/// FixUpUnconditionalBr - Fix up an unconditional branch whose destination is
/// too far away to fit in its displacement field. If the LR register has been
/// spilled in the epilogue, then we can use BL to implement a far jump.
/// Otherwise, add an intermediate branch instruction to to a branch.
bool
ARMConstantIslands::FixUpUnconditionalBr(MachineFunction &Fn, ImmBranch &Br) {
MachineInstr *MI = Br.MI;
MachineBasicBlock *MBB = MI->getParent();
assert(AFI->isThumbFunction() && "Expected a Thumb function!");
// Use BL to implement far jump.
Br.MaxDisp = (1 << 21) * 2;
MI->setInstrDescriptor(TII->get(ARM::tBfar));
BBSizes[MBB->getNumber()] += 2;
AdjustBBOffsetsAfter(MBB, 2);
HasFarJump = true;
NumUBrFixed++;
DOUT << " Changed B to long jump " << *MI;
return true;
}
/// getUnconditionalBrDisp - Returns the maximum displacement that can fit in
/// the specific unconditional branch instruction.
static inline unsigned getUnconditionalBrDisp(int Opc) {
return (Opc == ARM::tB) ? (1<<10)*2 : (1<<23)*4;
}
/// FixUpConditionalBr - Fix up a conditional branch whose destination is too
/// far away to fit in its displacement field. It is converted to an inverse
/// conditional branch + an unconditional branch to the destination.
bool
ARMConstantIslands::FixUpConditionalBr(MachineFunction &Fn, ImmBranch &Br) {
MachineInstr *MI = Br.MI;
MachineBasicBlock *DestBB = MI->getOperand(0).getMachineBasicBlock();
// Add a unconditional branch to the destination and invert the branch
// condition to jump over it:
// blt L1
// =>
// bge L2
// b L1
// L2:
ARMCC::CondCodes CC = (ARMCC::CondCodes)MI->getOperand(1).getImmedValue();
CC = ARMCC::getOppositeCondition(CC);
// If the branch is at the end of its MBB and that has a fall-through block,
// direct the updated conditional branch to the fall-through block. Otherwise,
// split the MBB before the next instruction.
MachineBasicBlock *MBB = MI->getParent();
MachineInstr *BMI = &MBB->back();
bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB);
NumCBrFixed++;
if (BMI != MI) {
if (next(MachineBasicBlock::iterator(MI)) == MBB->back() &&
BMI->getOpcode() == Br.UncondBr) {
// Last MI in the BB is a unconditional branch. Can we simply invert the
// condition and swap destinations:
// beq L1
// b L2
// =>
// bne L2
// b L1
MachineBasicBlock *NewDest = BMI->getOperand(0).getMachineBasicBlock();
if (BBIsInRange(MI, NewDest, Br.MaxDisp)) {
DOUT << " Invert Bcc condition and swap its destination with " << *BMI;
BMI->getOperand(0).setMachineBasicBlock(DestBB);
MI->getOperand(0).setMachineBasicBlock(NewDest);
MI->getOperand(1).setImm(CC);
return true;
}
}
}
if (NeedSplit) {
SplitBlockBeforeInstr(MI);
// No need for the branch to the next block. We're adding a unconditional
// branch to the destination.
MBB->back().eraseFromParent();
}
MachineBasicBlock *NextBB = next(MachineFunction::iterator(MBB));
DOUT << " Insert B to BB#" << DestBB->getNumber()
<< " also invert condition and change dest. to BB#"
<< NextBB->getNumber() << "\n";
// Insert a unconditional branch and replace the conditional branch.
// Also update the ImmBranch as well as adding a new entry for the new branch.
BuildMI(MBB, TII->get(MI->getOpcode())).addMBB(NextBB).addImm(CC);
Br.MI = &MBB->back();
BuildMI(MBB, TII->get(Br.UncondBr)).addMBB(DestBB);
unsigned MaxDisp = getUnconditionalBrDisp(Br.UncondBr);
ImmBranches.push_back(ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr));
MI->eraseFromParent();
// Increase the size of MBB to account for the new unconditional branch.
int delta = ARM::GetInstSize(&MBB->back());
BBSizes[MBB->getNumber()] += delta;
AdjustBBOffsetsAfter(MBB, delta);
return true;
}
/// UndoLRSpillRestore - Remove Thumb push / pop instructions that only spills
/// LR / restores LR to pc.
bool ARMConstantIslands::UndoLRSpillRestore() {
bool MadeChange = false;
for (unsigned i = 0, e = PushPopMIs.size(); i != e; ++i) {
MachineInstr *MI = PushPopMIs[i];
if (MI->getNumOperands() == 1) {
if (MI->getOpcode() == ARM::tPOP_RET &&
MI->getOperand(0).getReg() == ARM::PC)
BuildMI(MI->getParent(), TII->get(ARM::tBX_RET));
MI->eraseFromParent();
MadeChange = true;
}
}
return MadeChange;
}