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llvm-6502/lib/Target/ARM/ARMConstantIslandPass.cpp
Torok Edwin c23197a26f llvm_unreachable->llvm_unreachable(0), LLVM_UNREACHABLE->llvm_unreachable. 
This adds location info for all llvm_unreachable calls (which is a macro now) in
!NDEBUG builds.
In NDEBUG builds location info and the message is off (it only prints
"UREACHABLE executed").


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75640 91177308-0d34-0410-b5e6-96231b3b80d8
2009-07-14 16:55:14 +00:00

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//===-- ARMConstantIslandPass.cpp - ARM constant islands --------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file 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/Support/ErrorHandling.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 {
/// 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;
bool isThumb1Only;
bool isThumb2;
public:
static char ID;
ARMConstantIslands() : MachineFunctionPass(&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();
isThumb1Only = AFI->isThumb1OnlyFunction();
isThumb2 = AFI->isThumb2Function();
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.
AFI->initConstPoolEntryUId(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 = Fn.CreateMachineBasicBlock();
Fn.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.getTypeAllocSize(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, DebugLoc::getUnknownLoc(), 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 += TII->GetInstSizeInBytes(I);
int Opc = I->getOpcode();
if (I->getDesc().isBranch()) {
bool isCond = false;
unsigned Bits = 0;
unsigned Scale = 1;
int UOpc = Opc;
switch (Opc) {
case ARM::tBR_JTr:
case ARM::t2BR_JTr:
case ARM::t2BR_JTm:
case ARM::t2BR_JTadd:
// 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;
case ARM::t2Bcc:
isCond = true;
UOpc = ARM::t2B;
Bits = 20;
Scale = 2;
break;
case ARM::t2B:
Bits = 24;
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).isCPI()) {
// 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->getDesc().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;
}
llvm_unreachable("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;
// addrmode6 has no immediate offset.
case ARMII::AddrModeT1_1:
Bits = 5; // +offset_5
break;
case ARMII::AddrModeT1_2:
Bits = 5;
Scale = 2; // +(offset_5*2)
break;
case ARMII::AddrModeT1_4:
Bits = 5;
Scale = 4; // +(offset_5*4)
break;
case ARMII::AddrModeT1_s:
Bits = 8;
Scale = 4; // +(offset_8*4)
break;
case ARMII::AddrModeT2_pc:
Bits = 12; // +-offset_12
break;
}
// Remember that this is a user of a CP entry.
unsigned CPI = I->getOperand(op).getIndex();
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 += TII->GetInstSizeInBytes(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();
MachineFunction &MF = *OrigBB->getParent();
// Create a new MBB for the code after the OrigBB.
MachineBasicBlock *NewBB =
MF.CreateMachineBasicBlock(OrigBB->getBasicBlock());
MachineFunction::iterator MBBI = OrigBB; ++MBBI;
MF.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.
// There doesn't seem to be meaningful DebugInfo available; this doesn't
// correspond to anything in the source.
unsigned Opc = isThumb ? (isThumb2 ? ARM::t2B : ARM::tB) : ARM::B;
BuildMI(OrigBB, DebugLoc::getUnknownLoc(), TII->get(Opc)).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.
MF.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 += TII->GetInstSizeInBytes(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);
}
#ifndef NDEBUG
/// 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
|| PredMI->getOpcode() == ARM::t2B)
return PredMI->getOperand(0).getMBB() == Succ;
return false;
}
#endif // NDEBUG
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)
|| (prior(MBB->end())->getOpcode() == ARM::t2BR_JTr)
|| (prior(MBB->end())->getOpcode() == ARM::t2BR_JTm)
|| (prior(MBB->end())->getOpcode() == ARM::t2BR_JTadd))
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).getIndex();
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).isCPI()) {
UserMI->getOperand(j).setIndex(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) {
switch (Opc) {
case ARM::tB:
return ((1<<10)-1)*2;
case ARM::t2B:
return ((1<<23)-1)*2;
default:
break;
}
return ((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 ? ((isThumb2) ? ARM::t2B : ARM::tB) : ARM::B;
BuildMI(UserMBB, DebugLoc::getUnknownLoc(),
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+TII->GetInstSizeInBytes(UserMI);
Offset < BaseInsertOffset;
Offset += TII->GetInstSizeInBytes(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 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).getIndex();
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 = AFI->createConstPoolEntryUId();
// 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 = Fn.CreateMachineBasicBlock();
Fn.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, DebugLoc::getUnknownLoc(),
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).isCPI()) {
UserMI->getOperand(i).setIndex(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).getMBB();
// 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 a branch.
bool
ARMConstantIslands::FixUpUnconditionalBr(MachineFunction &Fn, ImmBranch &Br) {
MachineInstr *MI = Br.MI;
MachineBasicBlock *MBB = MI->getParent();
assert(isThumb && !isThumb2 && "Expected a Thumb-1 function!");
// Use BL to implement far jump.
Br.MaxDisp = (1 << 21) * 2;
MI->setDesc(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).getMBB();
// Add an 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).getImm();
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)) == prior(MBB->end()) &&
BMI->getOpcode() == Br.UncondBr) {
// Last MI in the BB is an unconditional branch. Can we simply invert the
// condition and swap destinations:
// beq L1
// b L2
// =>
// bne L2
// b L1
MachineBasicBlock *NewDest = BMI->getOperand(0).getMBB();
if (BBIsInRange(MI, NewDest, Br.MaxDisp)) {
DOUT << " Invert Bcc condition and swap its destination with " << *BMI;
BMI->getOperand(0).setMBB(DestBB);
MI->getOperand(0).setMBB(NewDest);
MI->getOperand(1).setImm(CC);
return true;
}
}
}
if (NeedSplit) {
SplitBlockBeforeInstr(MI);
// No need for the branch to the next block. We're adding an unconditional
// branch to the destination.
int delta = TII->GetInstSizeInBytes(&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, DebugLoc::getUnknownLoc(),
TII->get(MI->getOpcode()))
.addMBB(NextBB).addImm(CC).addReg(CCReg);
Br.MI = &MBB->back();
BBSizes[MBB->getNumber()] += TII->GetInstSizeInBytes(&MBB->back());
BuildMI(MBB, DebugLoc::getUnknownLoc(), TII->get(Br.UncondBr)).addMBB(DestBB);
BBSizes[MBB->getNumber()] += TII->GetInstSizeInBytes(&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()] -= TII->GetInstSizeInBytes(MI);
MI->eraseFromParent();
// The net size change is an addition of one unconditional branch.
int delta = TII->GetInstSizeInBytes(&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(), MI->getDebugLoc(), TII->get(ARM::tBX_RET));
MI->eraseFromParent();
MadeChange = true;
}
}
return MadeChange;
}
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