CbC/CbC_llvm: lib/Target/Mips/MipsConstantIslandPass.cpp comparison

comparison lib/Target/Mips/MipsConstantIslandPass.cpp @ 0:95c75e76d11b LLVM3.4

LLVM 3.4

author	Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date	Thu, 12 Dec 2013 13:56:28 +0900
parents
children	e4204d083e25

comparison

equal deleted inserted replaced

--1:000000000000
+:95c75e76d11b
+//===-- 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.
+//
+//
+#define DEBUG_TYPE "mips-constant-islands"
+#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/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/InstIterator.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 "llvm/Support/Format.h"
+#include <algorithm>
+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");
+// 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);
+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(&TM.getSubtarget<MipsSubtarget>()), MF(0), MCP(0),
+PrescannedForConstants(false){}
+virtual const char *getPassName() const {
+return "Mips Constant Islands";
+}
+bool runOnMachineFunction(MachineFunction &F);
+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();
+void verify();
+bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset,
+unsigned Disp, bool NegativeOK);
+bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset,
+const CPUser &U);
+bool isLongFormOffsetInRange(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::isLongFormOffsetInRange
+(unsigned UserOffset, unsigned TrialOffset,
+const CPUser &U) {
+return isOffsetInRange(UserOffset, TrialOffset,
+U.getLongFormMaxDisp(), U.NegOk);
+}
+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();
+DEBUG(dbgs() << "constant island machine function " << "\n");
+if (!TM.getSubtarget<MipsSubtarget>().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 (llvm::next(MBBI) == MBB->getParent()->end())
+return false;
+MachineBasicBlock *NextBB = llvm::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 NULL;
+}
+/// 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;
+}
+// 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 = 16;
+LongFormScale = 1;
+break;
+case Mips::LwRxPcTcpX16:
+Bits = 16;
+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(llvm::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 = 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 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 == NULL)
+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 == NULL)
+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 = prior(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 = llvm::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 = llvm::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 = llvm::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 = prior(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);
+// 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(llvm::prior(MachineFunction::iterator(NewIsland)));
+// No existing clone of this CPE is within range.
+// We will be generating a new clone.  Get a UID for it.
+unsigned ID = createPICLabelUId();
+// 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 = NULL;
+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;
+MachineBasicBlock *DestBB = MI->getOperand(0).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();
+// Use BL to implement far jump.
+Br.MaxDisp = ((1 << 16)-1) * 2;
+MI->setDesc(TII->get(Mips::BimmX16));
+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;
+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:
+unsigned CCReg = 0;  // FIXME
+unsigned CC=0; //FIXME
+// 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 (llvm::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 (isBBInRange(MI, NewDest, Br.MaxDisp)) {
+DEBUG(dbgs() << "  Invert Bcc condition and swap its destination with "
+<< *BMI);
+BMI->getOperand(0).setMBB(DestBB);
+MI->getOperand(0).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 = llvm::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.
+BuildMI(MBB, DebugLoc(), TII->get(MI->getOpcode()))
+.addMBB(NextBB).addImm(CC).addReg(CCReg);
+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;
+PrescannedForConstants = true;
+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: {
+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;
+}
+}
+}
+}

Mercurial > hg > CbC > CbC_llvm

comparison lib/Target/Mips/MipsConstantIslandPass.cpp @ 0:95c75e76d11b LLVM3.4