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llvm-6502/lib/Target/Mips/MipsConstantIslandPass.cpp
Eric Christopher ec3b0fef11 Fundamentally change the MipsSubtarget replacement machinery: 
a) Move the replacement level decision to the target machine.
b) Create additional subtargets at the TargetMachine level to
   cache and make replacement easy.
c) Make the mips16 features obvious.
d) Remove the override logic as it no longer does anything.
e) Have MipsModuleDAGToDAGISel take only the target machine.
f) Have the constant islands pass grab the current subtarget
   from the MachineFunction (via the TargetMachine) instead
   of caching it.
g) Unconditionally initialize TLOF.
h) Remove the old complicated subtarget based resetting and
   replace it with simple conditionals.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213430 91177308-0d34-0410-b5e6-96231b3b80d8
2014-07-18 23:41:32 +00:00

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//===-- MipsConstantIslandPass.cpp - Emit Pc Relative loads----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//
// This pass is used to make Pc relative loads of constants.
// For now, only Mips16 will use this.
//
// Loading constants inline is expensive on Mips16 and it's in general better
// to place the constant nearby in code space and then it can be loaded with a
// simple 16 bit load instruction.
//
// The constants can be not just numbers but addresses of functions and labels.
// This can be particularly helpful in static relocation mode for embedded
// non-linux targets.
//
//
#include "Mips.h"
#include "MCTargetDesc/MipsBaseInfo.h"
#include "Mips16InstrInfo.h"
#include "MipsMachineFunction.h"
#include "MipsTargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include <algorithm>
using namespace llvm;
#define DEBUG_TYPE "mips-constant-islands"
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");
// FIXME: This option should be removed once it has received sufficient testing.
static cl::opt<bool>
AlignConstantIslands("mips-align-constant-islands", cl::Hidden, cl::init(true),
cl::desc("Align constant islands in code"));
// Rather than do make check tests with huge amounts of code, we force
// the test to use this amount.
//
static cl::opt<int> ConstantIslandsSmallOffset(
"mips-constant-islands-small-offset",
cl::init(0),
cl::desc("Make small offsets be this amount for testing purposes"),
cl::Hidden);
//
// For testing purposes we tell it to not use relaxed load forms so that it
// will split blocks.
//
static cl::opt<bool> NoLoadRelaxation(
"mips-constant-islands-no-load-relaxation",
cl::init(false),
cl::desc("Don't relax loads to long loads - for testing purposes"),
cl::Hidden);
static unsigned int branchTargetOperand(MachineInstr *MI) {
switch (MI->getOpcode()) {
case Mips::Bimm16:
case Mips::BimmX16:
case Mips::Bteqz16:
case Mips::BteqzX16:
case Mips::Btnez16:
case Mips::BtnezX16:
case Mips::JalB16:
return 0;
case Mips::BeqzRxImm16:
case Mips::BeqzRxImmX16:
case Mips::BnezRxImm16:
case Mips::BnezRxImmX16:
return 1;
}
llvm_unreachable("Unknown branch type");
}
static bool isUnconditionalBranch(unsigned int Opcode) {
switch (Opcode) {
default: return false;
case Mips::Bimm16:
case Mips::BimmX16:
case Mips::JalB16:
return true;
}
}
static unsigned int longformBranchOpcode(unsigned int Opcode) {
switch (Opcode) {
case Mips::Bimm16:
case Mips::BimmX16:
return Mips::BimmX16;
case Mips::Bteqz16:
case Mips::BteqzX16:
return Mips::BteqzX16;
case Mips::Btnez16:
case Mips::BtnezX16:
return Mips::BtnezX16;
case Mips::JalB16:
return Mips::JalB16;
case Mips::BeqzRxImm16:
case Mips::BeqzRxImmX16:
return Mips::BeqzRxImmX16;
case Mips::BnezRxImm16:
case Mips::BnezRxImmX16:
return Mips::BnezRxImmX16;
}
llvm_unreachable("Unknown branch type");
}
//
// FIXME: need to go through this whole constant islands port and check the math
// for branch ranges and clean this up and make some functions to calculate things
// that are done many times identically.
// Need to refactor some of the code to call this routine.
//
static unsigned int branchMaxOffsets(unsigned int Opcode) {
unsigned Bits, Scale;
switch (Opcode) {
case Mips::Bimm16:
Bits = 11;
Scale = 2;
break;
case Mips::BimmX16:
Bits = 16;
Scale = 2;
break;
case Mips::BeqzRxImm16:
Bits = 8;
Scale = 2;
break;
case Mips::BeqzRxImmX16:
Bits = 16;
Scale = 2;
break;
case Mips::BnezRxImm16:
Bits = 8;
Scale = 2;
break;
case Mips::BnezRxImmX16:
Bits = 16;
Scale = 2;
break;
case Mips::Bteqz16:
Bits = 8;
Scale = 2;
break;
case Mips::BteqzX16:
Bits = 16;
Scale = 2;
break;
case Mips::Btnez16:
Bits = 8;
Scale = 2;
break;
case Mips::BtnezX16:
Bits = 16;
Scale = 2;
break;
default:
llvm_unreachable("Unknown branch type");
}
unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale;
return MaxOffs;
}
namespace {
typedef MachineBasicBlock::iterator Iter;
typedef MachineBasicBlock::reverse_iterator ReverseIter;
/// MipsConstantIslands - Due to limited PC-relative displacements, Mips
/// 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 MipsConstantIslands : public MachineFunctionPass {
/// BasicBlockInfo - Information about the offset and size of a single
/// basic block.
struct BasicBlockInfo {
/// Offset - Distance from the beginning of the function to the beginning
/// of this basic block.
///
/// Offsets are computed assuming worst case padding before an aligned
/// block. This means that subtracting basic block offsets always gives a
/// conservative estimate of the real distance which may be smaller.
///
/// Because worst case padding is used, the computed offset of an aligned
/// block may not actually be aligned.
unsigned Offset;
/// Size - Size of the basic block in bytes. If the block contains
/// inline assembly, this is a worst case estimate.
///
/// The size does not include any alignment padding whether from the
/// beginning of the block, or from an aligned jump table at the end.
unsigned Size;
// FIXME: ignore LogAlign for this patch
//
unsigned postOffset(unsigned LogAlign = 0) const {
unsigned PO = Offset + Size;
return PO;
}
BasicBlockInfo() : Offset(0), Size(0) {}
};
std::vector<BasicBlockInfo> BBInfo;
/// 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;
/// NewWaterList - The subset of WaterList that was created since the
/// previous iteration by inserting unconditional branches.
SmallSet<MachineBasicBlock*, 4> NewWaterList;
typedef std::vector<MachineBasicBlock*>::iterator water_iterator;
/// 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. The HighWaterMark records the
/// highest basic block where a new CPEntry can be placed. To ensure this
/// pass terminates, the CP entries are initially placed at the end of the
/// function and then move monotonically to lower addresses. The
/// exception to this rule is when the current CP entry for a particular
/// CPUser is out of range, but there is another CP entry for the same
/// constant value in range. We want to use the existing in-range CP
/// entry, but if it later moves out of range, the search for new water
/// should resume where it left off. The HighWaterMark is used to record
/// that point.
struct CPUser {
MachineInstr *MI;
MachineInstr *CPEMI;
MachineBasicBlock *HighWaterMark;
private:
unsigned MaxDisp;
unsigned LongFormMaxDisp; // mips16 has 16/32 bit instructions
// with different displacements
unsigned LongFormOpcode;
public:
bool NegOk;
CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp,
bool neg,
unsigned longformmaxdisp, unsigned longformopcode)
: MI(mi), CPEMI(cpemi), MaxDisp(maxdisp),
LongFormMaxDisp(longformmaxdisp), LongFormOpcode(longformopcode),
NegOk(neg){
HighWaterMark = CPEMI->getParent();
}
/// getMaxDisp - Returns the maximum displacement supported by MI.
unsigned getMaxDisp() const {
unsigned xMaxDisp = ConstantIslandsSmallOffset?
ConstantIslandsSmallOffset: MaxDisp;
return xMaxDisp;
}
void setMaxDisp(unsigned val) {
MaxDisp = val;
}
unsigned getLongFormMaxDisp() const {
return LongFormMaxDisp;
}
unsigned getLongFormOpcode() const {
return LongFormOpcode;
}
};
/// 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;
/// HasFarJump - True if any far jump instruction has been emitted during
/// the branch fix up pass.
bool HasFarJump;
const TargetMachine &TM;
bool IsPIC;
unsigned ABI;
const MipsSubtarget *STI;
const Mips16InstrInfo *TII;
MipsFunctionInfo *MFI;
MachineFunction *MF;
MachineConstantPool *MCP;
unsigned PICLabelUId;
bool PrescannedForConstants;
void initPICLabelUId(unsigned UId) {
PICLabelUId = UId;
}
unsigned createPICLabelUId() {
return PICLabelUId++;
}
public:
static char ID;
MipsConstantIslands(TargetMachine &tm)
: MachineFunctionPass(ID), TM(tm),
IsPIC(TM.getRelocationModel() == Reloc::PIC_),
ABI(TM.getSubtarget<MipsSubtarget>().getTargetABI()), STI(nullptr),
MF(nullptr), MCP(nullptr), PrescannedForConstants(false) {}
const char *getPassName() const override {
return "Mips Constant Islands";
}
bool runOnMachineFunction(MachineFunction &F) override;
void doInitialPlacement(std::vector<MachineInstr*> &CPEMIs);
CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI);
unsigned getCPELogAlign(const MachineInstr *CPEMI);
void initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs);
unsigned getOffsetOf(MachineInstr *MI) const;
unsigned getUserOffset(CPUser&) const;
void dumpBBs();
bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset,
unsigned Disp, bool NegativeOK);
bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset,
const CPUser &U);
void computeBlockSize(MachineBasicBlock *MBB);
MachineBasicBlock *splitBlockBeforeInstr(MachineInstr *MI);
void updateForInsertedWaterBlock(MachineBasicBlock *NewBB);
void adjustBBOffsetsAfter(MachineBasicBlock *BB);
bool decrementCPEReferenceCount(unsigned CPI, MachineInstr* CPEMI);
int findInRangeCPEntry(CPUser& U, unsigned UserOffset);
int findLongFormInRangeCPEntry(CPUser& U, unsigned UserOffset);
bool findAvailableWater(CPUser&U, unsigned UserOffset,
water_iterator &WaterIter);
void createNewWater(unsigned CPUserIndex, unsigned UserOffset,
MachineBasicBlock *&NewMBB);
bool handleConstantPoolUser(unsigned CPUserIndex);
void removeDeadCPEMI(MachineInstr *CPEMI);
bool removeUnusedCPEntries();
bool isCPEntryInRange(MachineInstr *MI, unsigned UserOffset,
MachineInstr *CPEMI, unsigned Disp, bool NegOk,
bool DoDump = false);
bool isWaterInRange(unsigned UserOffset, MachineBasicBlock *Water,
CPUser &U, unsigned &Growth);
bool isBBInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp);
bool fixupImmediateBr(ImmBranch &Br);
bool fixupConditionalBr(ImmBranch &Br);
bool fixupUnconditionalBr(ImmBranch &Br);
void prescanForConstants();
private:
};
char MipsConstantIslands::ID = 0;
} // end of anonymous namespace
bool MipsConstantIslands::isOffsetInRange
(unsigned UserOffset, unsigned TrialOffset,
const CPUser &U) {
return isOffsetInRange(UserOffset, TrialOffset,
U.getMaxDisp(), U.NegOk);
}
/// print block size and offset information - debugging
void MipsConstantIslands::dumpBBs() {
DEBUG({
for (unsigned J = 0, E = BBInfo.size(); J !=E; ++J) {
const BasicBlockInfo &BBI = BBInfo[J];
dbgs() << format("%08x BB#%u\t", BBI.Offset, J)
<< format(" size=%#x\n", BBInfo[J].Size);
}
});
}
/// createMipsLongBranchPass - Returns a pass that converts branches to long
/// branches.
FunctionPass *llvm::createMipsConstantIslandPass(MipsTargetMachine &tm) {
return new MipsConstantIslands(tm);
}
bool MipsConstantIslands::runOnMachineFunction(MachineFunction &mf) {
// The intention is for this to be a mips16 only pass for now
// FIXME:
MF = &mf;
MCP = mf.getConstantPool();
STI = &mf.getTarget().getSubtarget<MipsSubtarget>();
DEBUG(dbgs() << "constant island machine function " << "\n");
if (!STI->inMips16Mode() || !MipsSubtarget::useConstantIslands()) {
return false;
}
TII = (const Mips16InstrInfo*)MF->getTarget().getInstrInfo();
MFI = MF->getInfo<MipsFunctionInfo>();
DEBUG(dbgs() << "constant island processing " << "\n");
//
// will need to make predermination if there is any constants we need to
// put in constant islands. TBD.
//
if (!PrescannedForConstants) prescanForConstants();
HasFarJump = false;
// This pass invalidates liveness information when it splits basic blocks.
MF->getRegInfo().invalidateLiveness();
// Renumber all of the machine basic blocks in the function, guaranteeing that
// the numbers agree with the position of the block in the function.
MF->RenumberBlocks();
bool MadeChange = false;
// 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(CPEMIs);
/// The next UID to take is the first unused one.
initPICLabelUId(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.
initializeFunctionInfo(CPEMIs);
CPEMIs.clear();
DEBUG(dumpBBs());
/// Remove dead constant pool entries.
MadeChange |= removeUnusedCPEntries();
// Iteratively place constant pool entries and fix up branches until there
// is no change.
unsigned NoCPIters = 0, NoBRIters = 0;
(void)NoBRIters;
while (true) {
DEBUG(dbgs() << "Beginning CP iteration #" << NoCPIters << '\n');
bool CPChange = false;
for (unsigned i = 0, e = CPUsers.size(); i != e; ++i)
CPChange |= handleConstantPoolUser(i);
if (CPChange && ++NoCPIters > 30)
report_fatal_error("Constant Island pass failed to converge!");
DEBUG(dumpBBs());
// Clear NewWaterList now. If we split a block for branches, it should
// appear as "new water" for the next iteration of constant pool placement.
NewWaterList.clear();
DEBUG(dbgs() << "Beginning BR iteration #" << NoBRIters << '\n');
bool BRChange = false;
for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
BRChange |= fixupImmediateBr(ImmBranches[i]);
if (BRChange && ++NoBRIters > 30)
report_fatal_error("Branch Fix Up pass failed to converge!");
DEBUG(dumpBBs());
if (!CPChange && !BRChange)
break;
MadeChange = true;
}
DEBUG(dbgs() << '\n'; dumpBBs());
BBInfo.clear();
WaterList.clear();
CPUsers.clear();
CPEntries.clear();
ImmBranches.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
MipsConstantIslands::doInitialPlacement(std::vector<MachineInstr*> &CPEMIs) {
// Create the basic block to hold the CPE's.
MachineBasicBlock *BB = MF->CreateMachineBasicBlock();
MF->push_back(BB);
// MachineConstantPool measures alignment in bytes. We measure in log2(bytes).
unsigned MaxAlign = Log2_32(MCP->getConstantPoolAlignment());
// Mark the basic block as required by the const-pool.
// If AlignConstantIslands isn't set, use 4-byte alignment for everything.
BB->setAlignment(AlignConstantIslands ? MaxAlign : 2);
// The function needs to be as aligned as the basic blocks. The linker may
// move functions around based on their alignment.
MF->ensureAlignment(BB->getAlignment());
// Order the entries in BB by descending alignment. That ensures correct
// alignment of all entries as long as BB is sufficiently aligned. Keep
// track of the insertion point for each alignment. We are going to bucket
// sort the entries as they are created.
SmallVector<MachineBasicBlock::iterator, 8> InsPoint(MaxAlign + 1, BB->end());
// 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 = MCP->getConstants();
const DataLayout &TD = *MF->getTarget().getDataLayout();
for (unsigned i = 0, e = CPs.size(); i != e; ++i) {
unsigned Size = TD.getTypeAllocSize(CPs[i].getType());
assert(Size >= 4 && "Too small constant pool entry");
unsigned Align = CPs[i].getAlignment();
assert(isPowerOf2_32(Align) && "Invalid alignment");
// Verify that all constant pool entries are a multiple of their alignment.
// If not, we would have to pad them out so that instructions stay aligned.
assert((Size % Align) == 0 && "CP Entry not multiple of 4 bytes!");
// Insert CONSTPOOL_ENTRY before entries with a smaller alignment.
unsigned LogAlign = Log2_32(Align);
MachineBasicBlock::iterator InsAt = InsPoint[LogAlign];
MachineInstr *CPEMI =
BuildMI(*BB, InsAt, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY))
.addImm(i).addConstantPoolIndex(i).addImm(Size);
CPEMIs.push_back(CPEMI);
// Ensure that future entries with higher alignment get inserted before
// CPEMI. This is bucket sort with iterators.
for (unsigned a = LogAlign + 1; a <= MaxAlign; ++a)
if (InsPoint[a] == InsAt)
InsPoint[a] = 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;
DEBUG(dbgs() << "Moved CPI#" << i << " to end of function, size = "
<< Size << ", align = " << Align <<'\n');
}
DEBUG(BB->dump());
}
/// 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;
// Can't fall off end of function.
if (std::next(MBBI) == MBB->getParent()->end())
return false;
MachineBasicBlock *NextBB = std::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.
MipsConstantIslands::CPEntry
*MipsConstantIslands::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 nullptr;
}
/// getCPELogAlign - Returns the required alignment of the constant pool entry
/// represented by CPEMI. Alignment is measured in log2(bytes) units.
unsigned MipsConstantIslands::getCPELogAlign(const MachineInstr *CPEMI) {
assert(CPEMI && CPEMI->getOpcode() == Mips::CONSTPOOL_ENTRY);
// Everything is 4-byte aligned unless AlignConstantIslands is set.
if (!AlignConstantIslands)
return 2;
unsigned CPI = CPEMI->getOperand(1).getIndex();
assert(CPI < MCP->getConstants().size() && "Invalid constant pool index.");
unsigned Align = MCP->getConstants()[CPI].getAlignment();
assert(isPowerOf2_32(Align) && "Invalid CPE alignment");
return Log2_32(Align);
}
/// initializeFunctionInfo - 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 MipsConstantIslands::
initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs) {
BBInfo.clear();
BBInfo.resize(MF->getNumBlockIDs());
// First thing, compute the size of all basic blocks, and see if the function
// has any inline assembly in it. If so, we have to be conservative about
// alignment assumptions, as we don't know for sure the size of any
// instructions in the inline assembly.
for (MachineFunction::iterator I = MF->begin(), E = MF->end(); I != E; ++I)
computeBlockSize(I);
// Compute block offsets.
adjustBBOffsetsAfter(MF->begin());
// Now go back through the instructions and build up our data structures.
for (MachineFunction::iterator MBBI = MF->begin(), E = MF->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);
for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
I != E; ++I) {
if (I->isDebugValue())
continue;
int Opc = I->getOpcode();
if (I->isBranch()) {
bool isCond = false;
unsigned Bits = 0;
unsigned Scale = 1;
int UOpc = Opc;
switch (Opc) {
default:
continue; // Ignore other branches for now
case Mips::Bimm16:
Bits = 11;
Scale = 2;
isCond = false;
break;
case Mips::BimmX16:
Bits = 16;
Scale = 2;
isCond = false;
break;
case Mips::BeqzRxImm16:
UOpc=Mips::Bimm16;
Bits = 8;
Scale = 2;
isCond = true;
break;
case Mips::BeqzRxImmX16:
UOpc=Mips::Bimm16;
Bits = 16;
Scale = 2;
isCond = true;
break;
case Mips::BnezRxImm16:
UOpc=Mips::Bimm16;
Bits = 8;
Scale = 2;
isCond = true;
break;
case Mips::BnezRxImmX16:
UOpc=Mips::Bimm16;
Bits = 16;
Scale = 2;
isCond = true;
break;
case Mips::Bteqz16:
UOpc=Mips::Bimm16;
Bits = 8;
Scale = 2;
isCond = true;
break;
case Mips::BteqzX16:
UOpc=Mips::Bimm16;
Bits = 16;
Scale = 2;
isCond = true;
break;
case Mips::Btnez16:
UOpc=Mips::Bimm16;
Bits = 8;
Scale = 2;
isCond = true;
break;
case Mips::BtnezX16:
UOpc=Mips::Bimm16;
Bits = 16;
Scale = 2;
isCond = true;
break;
}
// Record this immediate branch.
unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale;
ImmBranches.push_back(ImmBranch(I, MaxOffs, isCond, UOpc));
}
if (Opc == Mips::CONSTPOOL_ENTRY)
continue;
// 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;
bool NegOk = false;
unsigned LongFormBits = 0;
unsigned LongFormScale = 0;
unsigned LongFormOpcode = 0;
switch (Opc) {
default:
llvm_unreachable("Unknown addressing mode for CP reference!");
case Mips::LwRxPcTcp16:
Bits = 8;
Scale = 4;
LongFormOpcode = Mips::LwRxPcTcpX16;
LongFormBits = 14;
LongFormScale = 1;
break;
case Mips::LwRxPcTcpX16:
Bits = 14;
Scale = 1;
NegOk = true;
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;
unsigned LongFormMaxOffs = ((1 << LongFormBits)-1) * LongFormScale;
CPUsers.push_back(CPUser(I, CPEMI, MaxOffs, NegOk,
LongFormMaxOffs, LongFormOpcode));
// 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;
}
}
}
}
/// computeBlockSize - Compute the size and some alignment information for MBB.
/// This function updates BBInfo directly.
void MipsConstantIslands::computeBlockSize(MachineBasicBlock *MBB) {
BasicBlockInfo &BBI = BBInfo[MBB->getNumber()];
BBI.Size = 0;
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
++I)
BBI.Size += TII->GetInstSizeInBytes(I);
}
/// 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 MipsConstantIslands::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 = BBInfo[MBB->getNumber()].Offset;
// Sum instructions before MI in MBB.
for (MachineBasicBlock::iterator I = MBB->begin(); &*I != MI; ++I) {
assert(I != MBB->end() && "Didn't find MI in its own basic block?");
Offset += TII->GetInstSizeInBytes(I);
}
return Offset;
}
/// 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 MipsConstantIslands::updateForInsertedWaterBlock
(MachineBasicBlock *NewBB) {
// Renumber the MBB's to keep them consecutive.
NewBB->getParent()->RenumberBlocks(NewBB);
// Insert an entry into BBInfo to align it properly with the (newly
// renumbered) block numbers.
BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo());
// Next, update WaterList. Specifically, we need to add NewMBB as having
// available water after it.
water_iterator IP =
std::lower_bound(WaterList.begin(), WaterList.end(), NewBB,
CompareMBBNumbers);
WaterList.insert(IP, NewBB);
}
unsigned MipsConstantIslands::getUserOffset(CPUser &U) const {
return getOffsetOf(U.MI);
}
/// Split the basic block containing MI into two blocks, which are joined by
/// an unconditional branch. Update data structures and renumber blocks to
/// account for this change and returns the newly created block.
MachineBasicBlock *MipsConstantIslands::splitBlockBeforeInstr
(MachineInstr *MI) {
MachineBasicBlock *OrigBB = MI->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.
BuildMI(OrigBB, DebugLoc(), TII->get(Mips::Bimm16)).addMBB(NewBB);
++NumSplit;
// Update the CFG. All succs of OrigBB are now succs of NewBB.
NewBB->transferSuccessors(OrigBB);
// 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 an entry into BBInfo to align it properly with the (newly
// renumbered) block numbers.
BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo());
// 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).
water_iterator IP =
std::lower_bound(WaterList.begin(), WaterList.end(), OrigBB,
CompareMBBNumbers);
MachineBasicBlock* WaterBB = *IP;
if (WaterBB == OrigBB)
WaterList.insert(std::next(IP), NewBB);
else
WaterList.insert(IP, OrigBB);
NewWaterList.insert(OrigBB);
// Figure out how large the OrigBB is. As the first half of the original
// block, it cannot contain a tablejump. The size includes
// the new jump we added. (It should be possible to do this without
// recounting everything, but it's very confusing, and this is rarely
// executed.)
computeBlockSize(OrigBB);
// Figure out how large the NewMBB is. As the second half of the original
// block, it may contain a tablejump.
computeBlockSize(NewBB);
// All BBOffsets following these blocks must be modified.
adjustBBOffsetsAfter(OrigBB);
return NewBB;
}
/// isOffsetInRange - Checks whether UserOffset (the location of a constant pool
/// reference) is within MaxDisp of TrialOffset (a proposed location of a
/// constant pool entry).
bool MipsConstantIslands::isOffsetInRange(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;
}
/// isWaterInRange - Returns true if a CPE placed after the specified
/// Water (a basic block) will be in range for the specific MI.
///
/// Compute how much the function will grow by inserting a CPE after Water.
bool MipsConstantIslands::isWaterInRange(unsigned UserOffset,
MachineBasicBlock* Water, CPUser &U,
unsigned &Growth) {
unsigned CPELogAlign = getCPELogAlign(U.CPEMI);
unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset(CPELogAlign);
unsigned NextBlockOffset, NextBlockAlignment;
MachineFunction::const_iterator NextBlock = Water;
if (++NextBlock == MF->end()) {
NextBlockOffset = BBInfo[Water->getNumber()].postOffset();
NextBlockAlignment = 0;
} else {
NextBlockOffset = BBInfo[NextBlock->getNumber()].Offset;
NextBlockAlignment = NextBlock->getAlignment();
}
unsigned Size = U.CPEMI->getOperand(2).getImm();
unsigned CPEEnd = CPEOffset + Size;
// The CPE may be able to hide in the alignment padding before the next
// block. It may also cause more padding to be required if it is more aligned
// that the next block.
if (CPEEnd > NextBlockOffset) {
Growth = CPEEnd - NextBlockOffset;
// Compute the padding that would go at the end of the CPE to align the next
// block.
Growth += OffsetToAlignment(CPEEnd, 1u << NextBlockAlignment);
// If the CPE is to be inserted before the instruction, that will raise
// the offset of the instruction. Also account for unknown alignment padding
// in blocks between CPE and the user.
if (CPEOffset < UserOffset)
UserOffset += Growth;
} else
// CPE fits in existing padding.
Growth = 0;
return isOffsetInRange(UserOffset, CPEOffset, U);
}
/// isCPEntryInRange - Returns true if the distance between specific MI and
/// specific ConstPool entry instruction can fit in MI's displacement field.
bool MipsConstantIslands::isCPEntryInRange
(MachineInstr *MI, unsigned UserOffset,
MachineInstr *CPEMI, unsigned MaxDisp,
bool NegOk, bool DoDump) {
unsigned CPEOffset = getOffsetOf(CPEMI);
if (DoDump) {
DEBUG({
unsigned Block = MI->getParent()->getNumber();
const BasicBlockInfo &BBI = BBInfo[Block];
dbgs() << "User of CPE#" << CPEMI->getOperand(0).getImm()
<< " max delta=" << MaxDisp
<< format(" insn address=%#x", UserOffset)
<< " in BB#" << Block << ": "
<< format("%#x-%x\t", BBI.Offset, BBI.postOffset()) << *MI
<< format("CPE address=%#x offset=%+d: ", CPEOffset,
int(CPEOffset-UserOffset));
});
}
return isOffsetInRange(UserOffset, CPEOffset, MaxDisp, NegOk);
}
#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() == Mips::Bimm16)
return PredMI->getOperand(0).getMBB() == Succ;
return false;
}
#endif
void MipsConstantIslands::adjustBBOffsetsAfter(MachineBasicBlock *BB) {
unsigned BBNum = BB->getNumber();
for(unsigned i = BBNum + 1, e = MF->getNumBlockIDs(); i < e; ++i) {
// Get the offset and known bits at the end of the layout predecessor.
// Include the alignment of the current block.
unsigned Offset = BBInfo[i - 1].Offset + BBInfo[i - 1].Size;
BBInfo[i].Offset = Offset;
}
}
/// decrementCPEReferenceCount - 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 MipsConstantIslands::decrementCPEReferenceCount(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 = nullptr;
--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 MipsConstantIslands::findInRangeCPEntry(CPUser& U, unsigned UserOffset)
{
MachineInstr *UserMI = U.MI;
MachineInstr *CPEMI = U.CPEMI;
// Check to see if the CPE is already in-range.
if (isCPEntryInRange(UserMI, UserOffset, CPEMI, U.getMaxDisp(), U.NegOk,
true)) {
DEBUG(dbgs() << "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 == nullptr)
continue;
if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, U.getMaxDisp(),
U.NegOk)) {
DEBUG(dbgs() << "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 decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1;
}
}
return 0;
}
/// LookForCPEntryInRange - see if the currently referenced CPE is in range;
/// This version checks if the longer form of the instruction can be used to
/// to satisfy things.
/// 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 MipsConstantIslands::findLongFormInRangeCPEntry
(CPUser& U, unsigned UserOffset)
{
MachineInstr *UserMI = U.MI;
MachineInstr *CPEMI = U.CPEMI;
// Check to see if the CPE is already in-range.
if (isCPEntryInRange(UserMI, UserOffset, CPEMI,
U.getLongFormMaxDisp(), U.NegOk,
true)) {
DEBUG(dbgs() << "In range\n");
UserMI->setDesc(TII->get(U.getLongFormOpcode()));
U.setMaxDisp(U.getLongFormMaxDisp());
return 2; // instruction is longer length now
}
// 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 == nullptr)
continue;
if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI,
U.getLongFormMaxDisp(), U.NegOk)) {
DEBUG(dbgs() << "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 decrementCPEReferenceCount(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 Mips::Bimm16:
return ((1<<10)-1)*2;
case Mips::BimmX16:
return ((1<<16)-1)*2;
default:
break;
}
return ((1<<16)-1)*2;
}
/// findAvailableWater - 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, WaterIter
/// is set to the WaterList entry.
/// To ensure that this pass
/// terminates, the CPE location for a particular CPUser is only allowed to
/// move to a lower address, so search backward from the end of the list and
/// prefer the first water that is in range.
bool MipsConstantIslands::findAvailableWater(CPUser &U, unsigned UserOffset,
water_iterator &WaterIter) {
if (WaterList.empty())
return false;
unsigned BestGrowth = ~0u;
for (water_iterator IP = std::prev(WaterList.end()), B = WaterList.begin();;
--IP) {
MachineBasicBlock* WaterBB = *IP;
// Check if water is in range and is either at a lower address than the
// current "high water mark" or a new water block that was created since
// the previous iteration by inserting an unconditional branch. In the
// latter case, we want to allow resetting the high water mark back to
// this new water since we haven't seen it before. Inserting branches
// should be relatively uncommon and when it does happen, we want to be
// sure to take advantage of it for all the CPEs near that block, so that
// we don't insert more branches than necessary.
unsigned Growth;
if (isWaterInRange(UserOffset, WaterBB, U, Growth) &&
(WaterBB->getNumber() < U.HighWaterMark->getNumber() ||
NewWaterList.count(WaterBB)) && Growth < BestGrowth) {
// This is the least amount of required padding seen so far.
BestGrowth = Growth;
WaterIter = IP;
DEBUG(dbgs() << "Found water after BB#" << WaterBB->getNumber()
<< " Growth=" << Growth << '\n');
// Keep looking unless it is perfect.
if (BestGrowth == 0)
return true;
}
if (IP == B)
break;
}
return BestGrowth != ~0u;
}
/// 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 MipsConstantIslands::createNewWater(unsigned CPUserIndex,
unsigned UserOffset,
MachineBasicBlock *&NewMBB) {
CPUser &U = CPUsers[CPUserIndex];
MachineInstr *UserMI = U.MI;
MachineInstr *CPEMI = U.CPEMI;
unsigned CPELogAlign = getCPELogAlign(CPEMI);
MachineBasicBlock *UserMBB = UserMI->getParent();
const BasicBlockInfo &UserBBI = BBInfo[UserMBB->getNumber()];
// If the block does not end in an unconditional branch already, and if the
// end of the block is within range, make new water there.
if (BBHasFallthrough(UserMBB)) {
// Size of branch to insert.
unsigned Delta = 2;
// Compute the offset where the CPE will begin.
unsigned CPEOffset = UserBBI.postOffset(CPELogAlign) + Delta;
if (isOffsetInRange(UserOffset, CPEOffset, U)) {
DEBUG(dbgs() << "Split at end of BB#" << UserMBB->getNumber()
<< format(", expected CPE offset %#x\n", CPEOffset));
NewMBB = std::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 = Mips::Bimm16;
BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB);
unsigned MaxDisp = getUnconditionalBrDisp(UncondBr);
ImmBranches.push_back(ImmBranch(&UserMBB->back(),
MaxDisp, false, UncondBr));
BBInfo[UserMBB->getNumber()].Size += Delta;
adjustBBOffsetsAfter(UserMBB);
return;
}
}
// What a big block. Find a place within the block to split it.
// Try to split the block so it's fully aligned. Compute the latest split
// point where we can add a 4-byte branch instruction, and then align to
// LogAlign which is the largest possible alignment in the function.
unsigned LogAlign = MF->getAlignment();
assert(LogAlign >= CPELogAlign && "Over-aligned constant pool entry");
unsigned BaseInsertOffset = UserOffset + U.getMaxDisp();
DEBUG(dbgs() << format("Split in middle of big block before %#x",
BaseInsertOffset));
// The 4 in the following is for the unconditional branch we'll be inserting
// Alignment of the island is handled
// inside isOffsetInRange.
BaseInsertOffset -= 4;
DEBUG(dbgs() << format(", adjusted to %#x", BaseInsertOffset)
<< " la=" << LogAlign << '\n');
// 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 + 8 >= UserBBI.postOffset()) {
BaseInsertOffset = UserBBI.postOffset() - 8;
DEBUG(dbgs() << format("Move inside block: %#x\n", BaseInsertOffset));
}
unsigned EndInsertOffset = BaseInsertOffset + 4 +
CPEMI->getOperand(2).getImm();
MachineBasicBlock::iterator MI = UserMI;
++MI;
unsigned CPUIndex = CPUserIndex+1;
unsigned NumCPUsers = CPUsers.size();
//MachineInstr *LastIT = 0;
for (unsigned Offset = UserOffset+TII->GetInstSizeInBytes(UserMI);
Offset < BaseInsertOffset;
Offset += TII->GetInstSizeInBytes(MI), MI = std::next(MI)) {
assert(MI != UserMBB->end() && "Fell off end of block");
if (CPUIndex < NumCPUsers && CPUsers[CPUIndex].MI == MI) {
CPUser &U = CPUsers[CPUIndex];
if (!isOffsetInRange(Offset, EndInsertOffset, U)) {
// Shift intertion point by one unit of alignment so it is within reach.
BaseInsertOffset -= 1u << LogAlign;
EndInsertOffset -= 1u << LogAlign;
}
// This is overly conservative, as we don't account for CPEMIs being
// reused within the block, but it doesn't matter much. Also assume CPEs
// are added in order with alignment padding. We may eventually be able
// to pack the aligned CPEs better.
EndInsertOffset += U.CPEMI->getOperand(2).getImm();
CPUIndex++;
}
}
--MI;
NewMBB = splitBlockBeforeInstr(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 MipsConstantIslands::handleConstantPoolUser(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();
// Compute this only once, it's expensive.
unsigned UserOffset = getUserOffset(U);
// See if the current entry is within range, or there is a clone of it
// in range.
int result = findInRangeCPEntry(U, UserOffset);
if (result==1) return false;
else if (result==2) return true;
// Look for water where we can place this CPE.
MachineBasicBlock *NewIsland = MF->CreateMachineBasicBlock();
MachineBasicBlock *NewMBB;
water_iterator IP;
if (findAvailableWater(U, UserOffset, IP)) {
DEBUG(dbgs() << "Found water in range\n");
MachineBasicBlock *WaterBB = *IP;
// If the original WaterList entry was "new water" on this iteration,
// propagate that to the new island. This is just keeping NewWaterList
// updated to match the WaterList, which will be updated below.
if (NewWaterList.erase(WaterBB))
NewWaterList.insert(NewIsland);
// The new CPE goes before the following block (NewMBB).
NewMBB = std::next(MachineFunction::iterator(WaterBB));
} else {
// No water found.
// we first see if a longer form of the instrucion could have reached
// the constant. in that case we won't bother to split
if (!NoLoadRelaxation) {
result = findLongFormInRangeCPEntry(U, UserOffset);
if (result != 0) return true;
}
DEBUG(dbgs() << "No water found\n");
createNewWater(CPUserIndex, UserOffset, NewMBB);
// splitBlockBeforeInstr adds to WaterList, which is important when it is
// called while handling branches so that the water will be seen on the
// next iteration for constant pools, but in this context, we don't want
// it. Check for this so it will be removed from the WaterList.
// Also remove any entry from NewWaterList.
MachineBasicBlock *WaterBB = std::prev(MachineFunction::iterator(NewMBB));
IP = std::find(WaterList.begin(), WaterList.end(), WaterBB);
if (IP != WaterList.end())
NewWaterList.erase(WaterBB);
// We are adding new water. Update NewWaterList.
NewWaterList.insert(NewIsland);
}
// 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 and is also important to ensure the algorithm terminates.
if (IP != WaterList.end())
WaterList.erase(IP);
// Okay, we know we can put an island before NewMBB now, do it!
MF->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.
decrementCPEReferenceCount(CPI, CPEMI);
// No existing clone of this CPE is within range.
// We will be generating a new clone. Get a UID for it.
unsigned ID = createPICLabelUId();
// Now that we have an island to add the CPE to, clone the original CPE and
// add it to the island.
U.HighWaterMark = NewIsland;
U.CPEMI = BuildMI(NewIsland, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY))
.addImm(ID).addConstantPoolIndex(CPI).addImm(Size);
CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1));
++NumCPEs;
// Mark the basic block as aligned as required by the const-pool entry.
NewIsland->setAlignment(getCPELogAlign(U.CPEMI));
// Increase the size of the island block to account for the new entry.
BBInfo[NewIsland->getNumber()].Size += Size;
adjustBBOffsetsAfter(std::prev(MachineFunction::iterator(NewIsland)));
// 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;
}
DEBUG(dbgs() << " Moved CPE to #" << ID << " CPI=" << CPI
<< format(" offset=%#x\n", BBInfo[NewIsland->getNumber()].Offset));
return true;
}
/// removeDeadCPEMI - Remove a dead constant pool entry instruction. Update
/// sizes and offsets of impacted basic blocks.
void MipsConstantIslands::removeDeadCPEMI(MachineInstr *CPEMI) {
MachineBasicBlock *CPEBB = CPEMI->getParent();
unsigned Size = CPEMI->getOperand(2).getImm();
CPEMI->eraseFromParent();
BBInfo[CPEBB->getNumber()].Size -= Size;
// All succeeding offsets have the current size value added in, fix this.
if (CPEBB->empty()) {
BBInfo[CPEBB->getNumber()].Size = 0;
// This block no longer needs to be aligned.
CPEBB->setAlignment(0);
} else
// Entries are sorted by descending alignment, so realign from the front.
CPEBB->setAlignment(getCPELogAlign(CPEBB->begin()));
adjustBBOffsetsAfter(CPEBB);
// 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 MipsConstantIslands::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 = nullptr;
MadeChange = true;
}
}
}
return MadeChange;
}
/// isBBInRange - Returns true if the distance between specific MI and
/// specific BB can fit in MI's displacement field.
bool MipsConstantIslands::isBBInRange
(MachineInstr *MI,MachineBasicBlock *DestBB, unsigned MaxDisp) {
unsigned PCAdj = 4;
unsigned BrOffset = getOffsetOf(MI) + PCAdj;
unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset;
DEBUG(dbgs() << "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 MipsConstantIslands::fixupImmediateBr(ImmBranch &Br) {
MachineInstr *MI = Br.MI;
unsigned TargetOperand = branchTargetOperand(MI);
MachineBasicBlock *DestBB = MI->getOperand(TargetOperand).getMBB();
// Check to see if the DestBB is already in-range.
if (isBBInRange(MI, DestBB, Br.MaxDisp))
return false;
if (!Br.isCond)
return fixupUnconditionalBr(Br);
return fixupConditionalBr(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
MipsConstantIslands::fixupUnconditionalBr(ImmBranch &Br) {
MachineInstr *MI = Br.MI;
MachineBasicBlock *MBB = MI->getParent();
MachineBasicBlock *DestBB = MI->getOperand(0).getMBB();
// Use BL to implement far jump.
unsigned BimmX16MaxDisp = ((1 << 16)-1) * 2;
if (isBBInRange(MI, DestBB, BimmX16MaxDisp)) {
Br.MaxDisp = BimmX16MaxDisp;
MI->setDesc(TII->get(Mips::BimmX16));
}
else {
// need to give the math a more careful look here
// this is really a segment address and not
// a PC relative address. FIXME. But I think that
// just reducing the bits by 1 as I've done is correct.
// The basic block we are branching too much be longword aligned.
// we know that RA is saved because we always save it right now.
// this requirement will be relaxed later but we also have an alternate
// way to implement this that I will implement that does not need jal.
// We should have a way to back out this alignment restriction if we "can" later.
// but it is not harmful.
//
DestBB->setAlignment(2);
Br.MaxDisp = ((1<<24)-1) * 2;
MI->setDesc(TII->get(Mips::JalB16));
}
BBInfo[MBB->getNumber()].Size += 2;
adjustBBOffsetsAfter(MBB);
HasFarJump = true;
++NumUBrFixed;
DEBUG(dbgs() << " 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
MipsConstantIslands::fixupConditionalBr(ImmBranch &Br) {
MachineInstr *MI = Br.MI;
unsigned TargetOperand = branchTargetOperand(MI);
MachineBasicBlock *DestBB = MI->getOperand(TargetOperand).getMBB();
unsigned Opcode = MI->getOpcode();
unsigned LongFormOpcode = longformBranchOpcode(Opcode);
unsigned LongFormMaxOff = branchMaxOffsets(LongFormOpcode);
// Check to see if the DestBB is already in-range.
if (isBBInRange(MI, DestBB, LongFormMaxOff)) {
Br.MaxDisp = LongFormMaxOff;
MI->setDesc(TII->get(LongFormOpcode));
return true;
}
// Add an unconditional branch to the destination and invert the branch
// condition to jump over it:
// bteqz L1
// =>
// bnez L2
// b L1
// L2:
// 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);
unsigned OppositeBranchOpcode = TII->getOppositeBranchOpc(Opcode);
++NumCBrFixed;
if (BMI != MI) {
if (std::next(MachineBasicBlock::iterator(MI)) == std::prev(MBB->end()) &&
isUnconditionalBranch(BMI->getOpcode())) {
// Last MI in the BB is an unconditional branch. Can we simply invert the
// condition and swap destinations:
// beqz L1
// b L2
// =>
// bnez L2
// b L1
unsigned BMITargetOperand = branchTargetOperand(BMI);
MachineBasicBlock *NewDest =
BMI->getOperand(BMITargetOperand).getMBB();
if (isBBInRange(MI, NewDest, Br.MaxDisp)) {
DEBUG(dbgs() << " Invert Bcc condition and swap its destination with "
<< *BMI);
MI->setDesc(TII->get(OppositeBranchOpcode));
BMI->getOperand(BMITargetOperand).setMBB(DestBB);
MI->getOperand(TargetOperand).setMBB(NewDest);
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());
BBInfo[MBB->getNumber()].Size -= delta;
MBB->back().eraseFromParent();
// BBInfo[SplitBB].Offset is wrong temporarily, fixed below
}
MachineBasicBlock *NextBB = std::next(MachineFunction::iterator(MBB));
DEBUG(dbgs() << " 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.
if (MI->getNumExplicitOperands() == 2) {
BuildMI(MBB, DebugLoc(), TII->get(OppositeBranchOpcode))
.addReg(MI->getOperand(0).getReg())
.addMBB(NextBB);
} else {
BuildMI(MBB, DebugLoc(), TII->get(OppositeBranchOpcode))
.addMBB(NextBB);
}
Br.MI = &MBB->back();
BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back());
BuildMI(MBB, DebugLoc(), TII->get(Br.UncondBr)).addMBB(DestBB);
BBInfo[MBB->getNumber()].Size += 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.
BBInfo[MI->getParent()->getNumber()].Size -= TII->GetInstSizeInBytes(MI);
MI->eraseFromParent();
adjustBBOffsetsAfter(MBB);
return true;
}
void MipsConstantIslands::prescanForConstants() {
unsigned J = 0;
(void)J;
for (MachineFunction::iterator B =
MF->begin(), E = MF->end(); B != E; ++B) {
for (MachineBasicBlock::instr_iterator I =
B->instr_begin(), EB = B->instr_end(); I != EB; ++I) {
switch(I->getDesc().getOpcode()) {
case Mips::LwConstant32: {
PrescannedForConstants = true;
DEBUG(dbgs() << "constant island constant " << *I << "\n");
J = I->getNumOperands();
DEBUG(dbgs() << "num operands " << J << "\n");
MachineOperand& Literal = I->getOperand(1);
if (Literal.isImm()) {
int64_t V = Literal.getImm();
DEBUG(dbgs() << "literal " << V << "\n");
Type *Int32Ty =
Type::getInt32Ty(MF->getFunction()->getContext());
const Constant *C = ConstantInt::get(Int32Ty, V);
unsigned index = MCP->getConstantPoolIndex(C, 4);
I->getOperand(2).ChangeToImmediate(index);
DEBUG(dbgs() << "constant island constant " << *I << "\n");
I->setDesc(TII->get(Mips::LwRxPcTcp16));
I->RemoveOperand(1);
I->RemoveOperand(1);
I->addOperand(MachineOperand::CreateCPI(index, 0));
I->addOperand(MachineOperand::CreateImm(4));
}
break;
}
default:
break;
}
}
}
}
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