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llvm-mirror/lib/Target/ARM/ARMConstantIslandPass.cpp
Dale Johannesen eb2c2823e3 ARM: make branch folder remove unconditional branches 
following jump tables that it earlier inserted.  This
would be OK on other targets but is needed for correctness
only on ARM (constant islands needs to find jump tables).

llvm-svn: 39782
2007-07-12 16:45:35 +00:00

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//===-- 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. The two-byte pads required for Thumb alignment are
/// counted as part of the following block (i.e., the offset and size for
/// a padded block will both be ==2 mod 4).
std::vector<unsigned> BBSizes;
/// BBOffsets - the offset of each MBB in bytes, starting from 0.
/// The two-byte pads required for Thumb alignment are counted as part of
/// the following block.
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) {}
};
/// ImmBranches - 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;
ARMFunctionInfo *AFI;
bool isThumb;
public:
static char ID;
ARMConstantIslands() : MachineFunctionPass((intptr_t)&ID) {}
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);
int LookForExistingCPEntry(CPUser& U, unsigned UserOffset);
bool LookForWater(CPUser&U, unsigned UserOffset,
MachineBasicBlock** NewMBB);
MachineBasicBlock* AcceptWater(MachineBasicBlock *WaterBB,
std::vector<MachineBasicBlock*>::iterator IP);
void CreateNewWater(unsigned CPUserIndex, unsigned UserOffset,
MachineBasicBlock** NewMBB);
bool HandleConstantPoolUser(MachineFunction &Fn, unsigned CPUserIndex);
void RemoveDeadCPEMI(MachineInstr *CPEMI);
bool RemoveUnusedCPEntries();
bool CPEIsInRange(MachineInstr *MI, unsigned UserOffset,
MachineInstr *CPEMI, unsigned Disp,
bool DoDump);
bool WaterIsInRange(unsigned UserOffset, MachineBasicBlock *Water,
CPUser &U);
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;
void dumpBBs();
void verify(MachineFunction &Fn);
};
char ARMConstantIslands::ID = 0;
}
/// verify - check BBOffsets, BBSizes, alignment of islands
void ARMConstantIslands::verify(MachineFunction &Fn) {
assert(BBOffsets.size() == BBSizes.size());
for (unsigned i = 1, e = BBOffsets.size(); i != e; ++i)
assert(BBOffsets[i-1]+BBSizes[i-1] == BBOffsets[i]);
if (isThumb) {
for (MachineFunction::iterator MBBI = Fn.begin(), E = Fn.end();
MBBI != E; ++MBBI) {
MachineBasicBlock *MBB = MBBI;
if (!MBB->empty() &&
MBB->begin()->getOpcode() == ARM::CONSTPOOL_ENTRY)
assert((BBOffsets[MBB->getNumber()]%4 == 0 &&
BBSizes[MBB->getNumber()]%4 == 0) ||
(BBOffsets[MBB->getNumber()]%4 != 0 &&
BBSizes[MBB->getNumber()]%4 != 0));
}
}
}
/// print block size and offset information - debugging
void ARMConstantIslands::dumpBBs() {
for (unsigned J = 0, E = BBOffsets.size(); J !=E; ++J) {
DOUT << "block " << J << " offset " << BBOffsets[J] <<
" size " << BBSizes[J] << "\n";
}
}
/// 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>();
isThumb = AFI->isThumbFunction();
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();
/// Thumb functions containing constant pools get 2-byte alignment. This is so
/// we can keep exact track of where the alignment padding goes. Set default.
AFI->setAlign(isThumb ? 1U : 2U);
// 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);
if (isThumb)
AFI->setAlign(2U);
}
/// 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();
/// Remove dead constant pool entries.
RemoveUnusedCPEntries();
// 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, i);
DEBUG(dumpBBs());
for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
Change |= FixUpImmediateBr(Fn, ImmBranches[i]);
DEBUG(dumpBBs());
if (!Change)
break;
MadeChange = true;
}
// After a while, this might be made debug-only, but it is not expensive.
verify(Fn);
// 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->isLRSpilledForFarJump() && isThumb)
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) {
case ARM::tBR_JTr:
// A Thumb table jump may involve padding; for the offsets to
// be right, functions containing these must be 4-byte aligned.
AFI->setAlign(2U);
if ((Offset+MBBSize)%4 != 0)
MBBSize += 2; // padding
continue; // Does not get an entry in ImmBranches
default:
continue; // Ignore other 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;
if (I->getOpcode() == ARM::tLEApcrel) {
Bits = 8; // Taking the address of a CP entry.
break;
}
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, we may need padding
// so it's aligned on 4 byte boundary.
if (isThumb &&
!MBB.empty() &&
MBB.begin()->getOpcode() == ARM::CONSTPOOL_ENTRY &&
(Offset%4) != 0)
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()];
// If we're looking for a CONSTPOOL_ENTRY in Thumb, see if this block has
// alignment padding, and compensate if so.
if (isThumb &&
MI->getOpcode() == ARM::CONSTPOOL_ENTRY &&
Offset%4 != 0)
Offset += 2;
// 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();
// 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. (It cannot
// contain a constpool_entry or tablejump.)
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 (the location of a constant pool
/// reference) is within MaxDisp of TrialOffset (a proposed location of a
/// constant pool entry).
bool ARMConstantIslands::OffsetIsInRange(unsigned UserOffset,
unsigned TrialOffset, unsigned MaxDisp, bool NegativeOK) {
// On Thumb offsets==2 mod 4 are rounded down by the hardware for
// purposes of the displacement computation; compensate for that here.
// Effectively, the valid range of displacements is 2 bytes smaller for such
// references.
if (isThumb && UserOffset%4 !=0)
UserOffset -= 2;
// CPEs will be rounded up to a multiple of 4.
if (isThumb && TrialOffset%4 != 0)
TrialOffset += 2;
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, CPUser &U)
{
unsigned MaxDisp = U.MaxDisp;
MachineFunction::iterator I = next(MachineFunction::iterator(Water));
unsigned CPEOffset = BBOffsets[Water->getNumber()] +
BBSizes[Water->getNumber()];
// If the CPE is to be inserted before the instruction, that will raise
// the offset of the instruction. (Currently applies only to ARM, so
// no alignment compensation attempted here.)
if (CPEOffset < UserOffset)
UserOffset += U.CPEMI->getOperand(2).getImm();
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) {
unsigned CPEOffset = GetOffsetOf(CPEMI);
assert(CPEOffset%4 == 0 && "Misaligned CPE");
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; MBBI = next(MBBI);
for(unsigned i=BB->getNumber()+1; i<BB->getParent()->getNumBlockIDs(); i++) {
BBOffsets[i] += delta;
// If some existing blocks have padding, adjust the padding as needed, a
// bit tricky. delta can be negative so don't use % on that.
if (isThumb) {
MachineBasicBlock *MBB = MBBI;
if (!MBB->empty()) {
// Constant pool entries require padding.
if (MBB->begin()->getOpcode() == ARM::CONSTPOOL_ENTRY) {
unsigned oldOffset = BBOffsets[i] - delta;
if (oldOffset%4==0 && BBOffsets[i]%4!=0) {
// add new padding
BBSizes[i] += 2;
delta += 2;
} else if (oldOffset%4!=0 && BBOffsets[i]%4==0) {
// remove existing padding
BBSizes[i] -=2;
delta -= 2;
}
}
// Thumb jump tables require padding. They should be at the end;
// following unconditional branches are removed by AnalyzeBranch.
MachineInstr *ThumbJTMI = NULL;
if (prior(MBB->end())->getOpcode() == ARM::tBR_JTr)
ThumbJTMI = prior(MBB->end());
if (ThumbJTMI) {
unsigned newMIOffset = GetOffsetOf(ThumbJTMI);
unsigned oldMIOffset = newMIOffset - delta;
if (oldMIOffset%4 == 0 && newMIOffset%4 != 0) {
// remove existing padding
BBSizes[i] -= 2;
delta -= 2;
} else if (oldMIOffset%4 != 0 && newMIOffset%4 == 0) {
// add new padding
BBSizes[i] += 2;
delta += 2;
}
}
if (delta==0)
return;
}
MBBI = next(MBBI);
}
}
}
/// 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) {
// Find the old entry. Eliminate it if it is no longer used.
CPEntry *CPE = findConstPoolEntry(CPI, CPEMI);
assert(CPE && "Unexpected!");
if (--CPE->RefCount == 0) {
RemoveDeadCPEMI(CPEMI);
CPE->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.
return DecrementOldEntry(CPI, CPEMI) ? 2 : 1;
}
}
return 0;
}
/// 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)-1)*2 : ((1<<23)-1)*4;
}
/// AcceptWater - Small amount of common code factored out of the following.
MachineBasicBlock* ARMConstantIslands::AcceptWater(MachineBasicBlock *WaterBB,
std::vector<MachineBasicBlock*>::iterator IP) {
DOUT << "found water in range\n";
// 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);
// CPE goes before following block (NewMBB).
return next(MachineFunction::iterator(WaterBB));
}
/// LookForWater - look for an existing entry in the WaterList in which
/// we can place the CPE referenced from U so it's within range of U's MI.
/// Returns true if found, false if not. If it returns true, *NewMBB
/// is set to the WaterList entry.
/// For ARM, we prefer the water that's farthest away. For Thumb, prefer
/// water that will not introduce padding to water that will; within each
/// group, prefer the water that's farthest away.
bool ARMConstantIslands::LookForWater(CPUser &U, unsigned UserOffset,
MachineBasicBlock** NewMBB) {
std::vector<MachineBasicBlock*>::iterator IPThatWouldPad;
MachineBasicBlock* WaterBBThatWouldPad = NULL;
if (!WaterList.empty()) {
for (std::vector<MachineBasicBlock*>::iterator IP = prior(WaterList.end()),
B = WaterList.begin();; --IP) {
MachineBasicBlock* WaterBB = *IP;
if (WaterIsInRange(UserOffset, WaterBB, U)) {
if (isThumb &&
(BBOffsets[WaterBB->getNumber()] +
BBSizes[WaterBB->getNumber()])%4 != 0) {
// This is valid Water, but would introduce padding. Remember
// it in case we don't find any Water that doesn't do this.
if (!WaterBBThatWouldPad) {
WaterBBThatWouldPad = WaterBB;
IPThatWouldPad = IP;
}
} else {
*NewMBB = AcceptWater(WaterBB, IP);
return true;
}
}
if (IP == B)
break;
}
}
if (isThumb && WaterBBThatWouldPad) {
*NewMBB = AcceptWater(WaterBBThatWouldPad, IPThatWouldPad);
return true;
}
return false;
}
/// CreateNewWater - No existing WaterList entry will work for
/// CPUsers[CPUserIndex], so create a place to put the CPE. The end of the
/// block is used if in range, and the conditional branch munged so control
/// flow is correct. Otherwise the block is split to create a hole with an
/// unconditional branch around it. In either case *NewMBB is set to a
/// block following which the new island can be inserted (the WaterList
/// is not adjusted).
void ARMConstantIslands::CreateNewWater(unsigned CPUserIndex,
unsigned UserOffset, MachineBasicBlock** NewMBB) {
CPUser &U = CPUsers[CPUserIndex];
MachineInstr *UserMI = U.MI;
MachineInstr *CPEMI = U.CPEMI;
MachineBasicBlock *UserMBB = UserMI->getParent();
unsigned OffsetOfNextBlock = BBOffsets[UserMBB->getNumber()] +
BBSizes[UserMBB->getNumber()];
assert(OffsetOfNextBlock== BBOffsets[UserMBB->getNumber()+1]);
// If the use is at the end of the block, or the end of the block
// is within range, make new water there. (The addition below is
// for the unconditional branch we will be adding: 4 bytes on ARM,
// 2 on Thumb. Possible Thumb alignment padding is allowed for
// inside OffsetIsInRange.
// If the block ends in an unconditional branch already, it is water,
// and is known to be out of range, so we'll always be adding a branch.)
if (&UserMBB->back() == UserMI ||
OffsetIsInRange(UserOffset, OffsetOfNextBlock + (isThumb ? 2: 4),
U.MaxDisp, !isThumb)) {
DOUT << "Split at end of block\n";
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.
// Record it for branch lengthening; this new branch will not get out of
// range, but if the preceding conditional branch is out of range, the
// targets will be exchanged, and the altered branch may be out of
// range, so the machinery has to know about it.
int UncondBr = isThumb ? ARM::tB : ARM::B;
BuildMI(UserMBB, TII->get(UncondBr)).addMBB(*NewMBB);
unsigned MaxDisp = getUnconditionalBrDisp(UncondBr);
ImmBranches.push_back(ImmBranch(&UserMBB->back(),
MaxDisp, false, UncondBr));
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. So, we make a first guess, then walk through the
// instructions between the one currently being looked at and the
// possible insertion point, and make sure any other instructions
// that reference CPEs will be able to use the same island area;
// if not, we back up the insertion point.
// The 4 in the following is for the unconditional branch we'll be
// inserting (allows for long branch on Thumb). Alignment of the
// island is handled inside OffsetIsInRange.
unsigned BaseInsertOffset = UserOffset + U.MaxDisp -4;
// This could point off the end of the block if we've already got
// constant pool entries following this block; only the last one is
// in the water list. Back past any possible branches (allow for a
// conditional and a maximally long unconditional).
if (BaseInsertOffset >= BBOffsets[UserMBB->getNumber()+1])
BaseInsertOffset = BBOffsets[UserMBB->getNumber()+1] -
(isThumb ? 6 : 8);
unsigned EndInsertOffset = BaseInsertOffset +
CPEMI->getOperand(2).getImm();
MachineBasicBlock::iterator MI = UserMI;
++MI;
unsigned CPUIndex = CPUserIndex+1;
for (unsigned Offset = UserOffset+ARM::GetInstSize(UserMI);
Offset < BaseInsertOffset;
Offset += ARM::GetInstSize(MI),
MI = next(MI)) {
if (CPUIndex < CPUsers.size() && CPUsers[CPUIndex].MI == MI) {
if (!OffsetIsInRange(Offset, EndInsertOffset,
CPUsers[CPUIndex].MaxDisp, !isThumb)) {
BaseInsertOffset -= (isThumb ? 2 : 4);
EndInsertOffset -= (isThumb ? 2 : 4);
}
// This is overly conservative, as we don't account for CPEMIs
// being reused within the block, but it doesn't matter much.
EndInsertOffset += CPUsers[CPUIndex].CPEMI->getOperand(2).getImm();
CPUIndex++;
}
}
DOUT << "Split in middle of big block\n";
*NewMBB = SplitBlockBeforeInstr(prior(MI));
}
}
/// 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,
unsigned CPUserIndex){
CPUser &U = CPUsers[CPUserIndex];
MachineInstr *UserMI = U.MI;
MachineInstr *CPEMI = U.CPEMI;
unsigned CPI = CPEMI->getOperand(1).getConstantPoolIndex();
unsigned Size = CPEMI->getOperand(2).getImm();
MachineBasicBlock *NewMBB;
// Compute this only once, it's expensive. The 4 or 8 is the value the
// hardware keeps in the PC (2 insns ahead of the reference).
unsigned UserOffset = GetOffsetOf(UserMI) + (isThumb ? 4 : 8);
// Special case: tLEApcrel are two instructions MI's. The actual user is the
// second instruction.
if (UserMI->getOpcode() == ARM::tLEApcrel)
UserOffset += 2;
// 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).
if (!LookForWater(U, UserOffset, &NewMBB)) {
// No water found.
DOUT << "No water found\n";
CreateNewWater(CPUserIndex, UserOffset, &NewMBB);
}
// 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);
// 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++;
BBOffsets[NewIsland->getNumber()] = BBOffsets[NewMBB->getNumber()];
// Compensate for .align 2 in thumb mode.
if (isThumb && BBOffsets[NewIsland->getNumber()]%4 != 0)
Size += 2;
// Increase the size of the island block to account for the new entry.
BBSizes[NewIsland->getNumber()] += Size;
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;
}
/// RemoveDeadCPEMI - Remove a dead constant pool entry instruction. Update
/// sizes and offsets of impacted basic blocks.
void ARMConstantIslands::RemoveDeadCPEMI(MachineInstr *CPEMI) {
MachineBasicBlock *CPEBB = CPEMI->getParent();
unsigned Size = CPEMI->getOperand(2).getImm();
CPEMI->eraseFromParent();
BBSizes[CPEBB->getNumber()] -= Size;
// All succeeding offsets have the current size value added in, fix this.
if (CPEBB->empty()) {
// In thumb mode, the size of island may be padded by two to compensate for
// the alignment requirement. Then 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[CPEBB->getNumber()] != 0) {
Size += BBSizes[CPEBB->getNumber()];
BBSizes[CPEBB->getNumber()] = 0;
}
}
AdjustBBOffsetsAfter(CPEBB, -Size);
// 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(CPEBB) && "How did this happen?");
// FIXME: remove the empty blocks after all the work is done?
}
/// RemoveUnusedCPEntries - Remove constant pool entries whose refcounts
/// are zero.
bool ARMConstantIslands::RemoveUnusedCPEntries() {
unsigned MadeChange = false;
for (unsigned i = 0, e = CPEntries.size(); i != e; ++i) {
std::vector<CPEntry> &CPEs = CPEntries[i];
for (unsigned j = 0, ee = CPEs.size(); j != ee; ++j) {
if (CPEs[j].RefCount == 0 && CPEs[j].CPEMI) {
RemoveDeadCPEMI(CPEs[j].CPEMI);
CPEs[j].CPEMI = NULL;
MadeChange = true;
}
}
}
return MadeChange;
}
/// 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 = isThumb ? 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
<< " from " << GetOffsetOf(MI) << " to " << DestOffset
<< " offset " << int(DestOffset-BrOffset) << "\t" << *MI;
if (BrOffset <= DestOffset) {
// Branch before the Dest.
if (DestOffset-BrOffset <= MaxDisp)
return true;
} else {
if (BrOffset-DestOffset <= MaxDisp)
return true;
}
return false;
}
/// 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(isThumb && "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;
}
/// 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);
unsigned CCReg = MI->getOperand(2).getReg();
// 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.
int delta = ARM::GetInstSize(&MBB->back());
BBSizes[MBB->getNumber()] -= delta;
MachineBasicBlock* SplitBB = next(MachineFunction::iterator(MBB));
AdjustBBOffsetsAfter(SplitBB, -delta);
MBB->back().eraseFromParent();
// BBOffsets[SplitBB] is wrong temporarily, fixed below
}
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 new conditional branch and a new unconditional 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).addReg(CCReg);
Br.MI = &MBB->back();
BBSizes[MBB->getNumber()] += ARM::GetInstSize(&MBB->back());
BuildMI(MBB, TII->get(Br.UncondBr)).addMBB(DestBB);
BBSizes[MBB->getNumber()] += ARM::GetInstSize(&MBB->back());
unsigned MaxDisp = getUnconditionalBrDisp(Br.UncondBr);
ImmBranches.push_back(ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr));
// Remove the old conditional branch. It may or may not still be in MBB.
BBSizes[MI->getParent()->getNumber()] -= ARM::GetInstSize(MI);
MI->eraseFromParent();
// The net size change is an addition of one unconditional branch.
int delta = ARM::GetInstSize(&MBB->back());
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->getOpcode() == ARM::tPOP_RET &&
MI->getOperand(0).getReg() == ARM::PC &&
MI->getNumExplicitOperands() == 1) {
BuildMI(MI->getParent(), TII->get(ARM::tBX_RET));
MI->eraseFromParent();
MadeChange = true;
}
}
return MadeChange;
}
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