diff options
Diffstat (limited to 'contrib/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp')
| -rw-r--r-- | contrib/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp | 2258 |
1 files changed, 2258 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp b/contrib/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp new file mode 100644 index 000000000000..be1a37e3e362 --- /dev/null +++ b/contrib/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp @@ -0,0 +1,2258 @@ +//===-- ARMConstantIslandPass.cpp - ARM constant islands ------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file contains a pass that splits the constant pool up into 'islands' +// which are scattered through-out the function. This is required due to the +// limited pc-relative displacements that ARM has. +// +//===----------------------------------------------------------------------===// + +#include "ARM.h" +#include "ARMBasicBlockInfo.h" +#include "ARMMachineFunctionInfo.h" +#include "MCTargetDesc/ARMAddressingModes.h" +#include "Thumb2InstrInfo.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/CodeGen/MachineConstantPool.h" +#include "llvm/CodeGen/MachineFunctionPass.h" +#include "llvm/CodeGen/MachineJumpTableInfo.h" +#include "llvm/CodeGen/MachineRegisterInfo.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/Format.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Target/TargetMachine.h" +#include <algorithm> +using namespace llvm; + +#define DEBUG_TYPE "arm-cp-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"); +STATISTIC(NumTBs, "Number of table branches generated"); +STATISTIC(NumT2CPShrunk, "Number of Thumb2 constantpool instructions shrunk"); +STATISTIC(NumT2BrShrunk, "Number of Thumb2 immediate branches shrunk"); +STATISTIC(NumCBZ, "Number of CBZ / CBNZ formed"); +STATISTIC(NumJTMoved, "Number of jump table destination blocks moved"); +STATISTIC(NumJTInserted, "Number of jump table intermediate blocks inserted"); + + +static cl::opt<bool> +AdjustJumpTableBlocks("arm-adjust-jump-tables", cl::Hidden, cl::init(true), + cl::desc("Adjust basic block layout to better use TB[BH]")); + +static cl::opt<unsigned> +CPMaxIteration("arm-constant-island-max-iteration", cl::Hidden, cl::init(30), + cl::desc("The max number of iteration for converge")); + +static cl::opt<bool> SynthesizeThumb1TBB( + "arm-synthesize-thumb-1-tbb", cl::Hidden, cl::init(true), + cl::desc("Use compressed jump tables in Thumb-1 by synthesizing an " + "equivalent to the TBB/TBH instructions")); + +namespace { + /// ARMConstantIslands - Due to limited PC-relative displacements, ARM + /// requires constant pool entries to be scattered among the instructions + /// inside a function. To do this, it completely ignores the normal LLVM + /// constant pool; instead, it places constants wherever it feels like with + /// special instructions. + /// + /// The terminology used in this pass includes: + /// Islands - Clumps of constants placed in the function. + /// Water - Potential places where an island could be formed. + /// CPE - A constant pool entry that has been placed somewhere, which + /// tracks a list of users. + class ARMConstantIslands : public MachineFunctionPass { + + 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; + unsigned MaxDisp; + bool NegOk; + bool IsSoImm; + bool KnownAlignment; + CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp, + bool neg, bool soimm) + : MI(mi), CPEMI(cpemi), MaxDisp(maxdisp), NegOk(neg), IsSoImm(soimm), + KnownAlignment(false) { + HighWaterMark = CPEMI->getParent(); + } + /// getMaxDisp - Returns the maximum displacement supported by MI. + /// Correct for unknown alignment. + /// Conservatively subtract 2 bytes to handle weird alignment effects. + unsigned getMaxDisp() const { + return (KnownAlignment ? MaxDisp : MaxDisp - 2) - 2; + } + }; + + /// 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. + /// + /// The first half of CPEntries contains generic constants, the second half + /// contains jump tables. Use getCombinedIndex on a generic CPEMI to look up + /// which vector it will be in here. + std::vector<std::vector<CPEntry> > CPEntries; + + /// Maps a JT index to the offset in CPEntries containing copies of that + /// table. The equivalent map for a CONSTPOOL_ENTRY is the identity. + DenseMap<int, int> JumpTableEntryIndices; + + /// Maps a JT index to the LEA that actually uses the index to calculate its + /// base address. + DenseMap<int, int> JumpTableUserIndices; + + /// 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; + unsigned UncondBr; + ImmBranch(MachineInstr *mi, unsigned maxdisp, bool cond, unsigned ubr) + : MI(mi), MaxDisp(maxdisp), isCond(cond), UncondBr(ubr) {} + }; + + /// ImmBranches - Keep track of all the immediate branch instructions. + /// + std::vector<ImmBranch> ImmBranches; + + /// PushPopMIs - Keep track of all the Thumb push / pop instructions. + /// + SmallVector<MachineInstr*, 4> PushPopMIs; + + /// T2JumpTables - Keep track of all the Thumb2 jumptable instructions. + SmallVector<MachineInstr*, 4> T2JumpTables; + + /// HasFarJump - True if any far jump instruction has been emitted during + /// the branch fix up pass. + bool HasFarJump; + + MachineFunction *MF; + MachineConstantPool *MCP; + const ARMBaseInstrInfo *TII; + const ARMSubtarget *STI; + ARMFunctionInfo *AFI; + bool isThumb; + bool isThumb1; + bool isThumb2; + bool isPositionIndependentOrROPI; + public: + static char ID; + ARMConstantIslands() : MachineFunctionPass(ID) {} + + bool runOnMachineFunction(MachineFunction &MF) override; + + MachineFunctionProperties getRequiredProperties() const override { + return MachineFunctionProperties().set( + MachineFunctionProperties::Property::NoVRegs); + } + + StringRef getPassName() const override { + return "ARM constant island placement and branch shortening pass"; + } + + private: + void doInitialConstPlacement(std::vector<MachineInstr *> &CPEMIs); + void doInitialJumpTablePlacement(std::vector<MachineInstr *> &CPEMIs); + bool BBHasFallthrough(MachineBasicBlock *MBB); + CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI); + unsigned getCPELogAlign(const MachineInstr *CPEMI); + void scanFunctionJumpTables(); + void initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs); + MachineBasicBlock *splitBlockBeforeInstr(MachineInstr *MI); + void updateForInsertedWaterBlock(MachineBasicBlock *NewBB); + void adjustBBOffsetsAfter(MachineBasicBlock *BB); + bool decrementCPEReferenceCount(unsigned CPI, MachineInstr* CPEMI); + unsigned getCombinedIndex(const MachineInstr *CPEMI); + int findInRangeCPEntry(CPUser& U, unsigned UserOffset); + bool findAvailableWater(CPUser&U, unsigned UserOffset, + water_iterator &WaterIter, bool CloserWater); + void createNewWater(unsigned CPUserIndex, unsigned UserOffset, + MachineBasicBlock *&NewMBB); + bool handleConstantPoolUser(unsigned CPUserIndex, bool CloserWater); + 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); + bool undoLRSpillRestore(); + bool optimizeThumb2Instructions(); + bool optimizeThumb2Branches(); + bool reorderThumb2JumpTables(); + bool preserveBaseRegister(MachineInstr *JumpMI, MachineInstr *LEAMI, + unsigned &DeadSize, bool &CanDeleteLEA, + bool &BaseRegKill); + bool optimizeThumb2JumpTables(); + MachineBasicBlock *adjustJTTargetBlockForward(MachineBasicBlock *BB, + MachineBasicBlock *JTBB); + + unsigned getOffsetOf(MachineInstr *MI) const; + unsigned getUserOffset(CPUser&) const; + void dumpBBs(); + void verify(); + + bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, + unsigned Disp, bool NegativeOK, bool IsSoImm = false); + bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, + const CPUser &U) { + return isOffsetInRange(UserOffset, TrialOffset, + U.getMaxDisp(), U.NegOk, U.IsSoImm); + } + }; + char ARMConstantIslands::ID = 0; +} + +/// verify - check BBOffsets, BBSizes, alignment of islands +void ARMConstantIslands::verify() { +#ifndef NDEBUG + assert(std::is_sorted(MF->begin(), MF->end(), + [this](const MachineBasicBlock &LHS, + const MachineBasicBlock &RHS) { + return BBInfo[LHS.getNumber()].postOffset() < + BBInfo[RHS.getNumber()].postOffset(); + })); + DEBUG(dbgs() << "Verifying " << CPUsers.size() << " CP users.\n"); + for (unsigned i = 0, e = CPUsers.size(); i != e; ++i) { + CPUser &U = CPUsers[i]; + unsigned UserOffset = getUserOffset(U); + // Verify offset using the real max displacement without the safety + // adjustment. + if (isCPEntryInRange(U.MI, UserOffset, U.CPEMI, U.getMaxDisp()+2, U.NegOk, + /* DoDump = */ true)) { + DEBUG(dbgs() << "OK\n"); + continue; + } + DEBUG(dbgs() << "Out of range.\n"); + dumpBBs(); + DEBUG(MF->dump()); + llvm_unreachable("Constant pool entry out of range!"); + } +#endif +} + +/// print block size and offset information - debugging +void ARMConstantIslands::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) + << " kb=" << unsigned(BBI.KnownBits) + << " ua=" << unsigned(BBI.Unalign) + << " pa=" << unsigned(BBI.PostAlign) + << format(" size=%#x\n", BBInfo[J].Size); + } + }); +} + +/// createARMConstantIslandPass - returns an instance of the constpool +/// island pass. +FunctionPass *llvm::createARMConstantIslandPass() { + return new ARMConstantIslands(); +} + +bool ARMConstantIslands::runOnMachineFunction(MachineFunction &mf) { + MF = &mf; + MCP = mf.getConstantPool(); + + DEBUG(dbgs() << "***** ARMConstantIslands: " + << MCP->getConstants().size() << " CP entries, aligned to " + << MCP->getConstantPoolAlignment() << " bytes *****\n"); + + STI = &static_cast<const ARMSubtarget &>(MF->getSubtarget()); + TII = STI->getInstrInfo(); + isPositionIndependentOrROPI = + STI->getTargetLowering()->isPositionIndependent() || STI->isROPI(); + AFI = MF->getInfo<ARMFunctionInfo>(); + + isThumb = AFI->isThumbFunction(); + isThumb1 = AFI->isThumb1OnlyFunction(); + isThumb2 = AFI->isThumb2Function(); + + HasFarJump = false; + bool GenerateTBB = isThumb2 || (isThumb1 && SynthesizeThumb1TBB); + + // 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(); + + // Try to reorder and otherwise adjust the block layout to make good use + // of the TB[BH] instructions. + bool MadeChange = false; + if (GenerateTBB && AdjustJumpTableBlocks) { + scanFunctionJumpTables(); + MadeChange |= reorderThumb2JumpTables(); + // Data is out of date, so clear it. It'll be re-computed later. + T2JumpTables.clear(); + // Blocks may have shifted around. Keep the numbering up to date. + MF->RenumberBlocks(); + } + + // Perform the initial placement of the constant pool entries. To start with, + // we put them all at the end of the function. + std::vector<MachineInstr*> CPEMIs; + if (!MCP->isEmpty()) + doInitialConstPlacement(CPEMIs); + + if (MF->getJumpTableInfo()) + doInitialJumpTablePlacement(CPEMIs); + + /// The next UID to take is the first unused one. + AFI->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()); + + // Functions with jump tables need an alignment of 4 because they use the ADR + // instruction, which aligns the PC to 4 bytes before adding an offset. + if (!T2JumpTables.empty()) + MF->ensureAlignment(2); + + /// 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; + while (true) { + DEBUG(dbgs() << "Beginning CP iteration #" << NoCPIters << '\n'); + bool CPChange = false; + for (unsigned i = 0, e = CPUsers.size(); i != e; ++i) + // For most inputs, it converges in no more than 5 iterations. + // If it doesn't end in 10, the input may have huge BB or many CPEs. + // In this case, we will try different heuristics. + CPChange |= handleConstantPoolUser(i, NoCPIters >= CPMaxIteration / 2); + if (CPChange && ++NoCPIters > CPMaxIteration) + 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; + } + + // Shrink 32-bit Thumb2 load and store instructions. + if (isThumb2 && !STI->prefers32BitThumb()) + MadeChange |= optimizeThumb2Instructions(); + + // Shrink 32-bit branch instructions. + if (isThumb && STI->hasV8MBaselineOps()) + MadeChange |= optimizeThumb2Branches(); + + // Optimize jump tables using TBB / TBH. + if (GenerateTBB && !STI->genExecuteOnly()) + MadeChange |= optimizeThumb2JumpTables(); + + // After a while, this might be made debug-only, but it is not expensive. + verify(); + + // If LR has been forced spilled and no far jump (i.e. BL) has been issued, + // undo the spill / restore of LR if possible. + if (isThumb && !HasFarJump && AFI->isLRSpilledForFarJump()) + MadeChange |= undoLRSpillRestore(); + + // Save the mapping between original and cloned constpool entries. + for (unsigned i = 0, e = CPEntries.size(); i != e; ++i) { + for (unsigned j = 0, je = CPEntries[i].size(); j != je; ++j) { + const CPEntry & CPE = CPEntries[i][j]; + if (CPE.CPEMI && CPE.CPEMI->getOperand(1).isCPI()) + AFI->recordCPEClone(i, CPE.CPI); + } + } + + DEBUG(dbgs() << '\n'; dumpBBs()); + + BBInfo.clear(); + WaterList.clear(); + CPUsers.clear(); + CPEntries.clear(); + JumpTableEntryIndices.clear(); + JumpTableUserIndices.clear(); + ImmBranches.clear(); + PushPopMIs.clear(); + T2JumpTables.clear(); + + return MadeChange; +} + +/// \brief Perform the initial placement of the regular constant pool entries. +/// To start with, we put them all at the end of the function. +void +ARMConstantIslands::doInitialConstPlacement(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. + BB->setAlignment(MaxAlign); + + // 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->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(ARM::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. + CPEntries.emplace_back(1, CPEntry(CPEMI, i)); + ++NumCPEs; + DEBUG(dbgs() << "Moved CPI#" << i << " to end of function, size = " + << Size << ", align = " << Align <<'\n'); + } + DEBUG(BB->dump()); +} + +/// \brief Do initial placement of the jump tables. Because Thumb2's TBB and TBH +/// instructions can be made more efficient if the jump table immediately +/// follows the instruction, it's best to place them immediately next to their +/// jumps to begin with. In almost all cases they'll never be moved from that +/// position. +void ARMConstantIslands::doInitialJumpTablePlacement( + std::vector<MachineInstr *> &CPEMIs) { + unsigned i = CPEntries.size(); + auto MJTI = MF->getJumpTableInfo(); + const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables(); + + MachineBasicBlock *LastCorrectlyNumberedBB = nullptr; + for (MachineBasicBlock &MBB : *MF) { + auto MI = MBB.getLastNonDebugInstr(); + if (MI == MBB.end()) + continue; + + unsigned JTOpcode; + switch (MI->getOpcode()) { + default: + continue; + case ARM::BR_JTadd: + case ARM::BR_JTr: + case ARM::tBR_JTr: + case ARM::BR_JTm: + JTOpcode = ARM::JUMPTABLE_ADDRS; + break; + case ARM::t2BR_JT: + JTOpcode = ARM::JUMPTABLE_INSTS; + break; + case ARM::tTBB_JT: + case ARM::t2TBB_JT: + JTOpcode = ARM::JUMPTABLE_TBB; + break; + case ARM::tTBH_JT: + case ARM::t2TBH_JT: + JTOpcode = ARM::JUMPTABLE_TBH; + break; + } + + unsigned NumOps = MI->getDesc().getNumOperands(); + MachineOperand JTOp = + MI->getOperand(NumOps - (MI->isPredicable() ? 2 : 1)); + unsigned JTI = JTOp.getIndex(); + unsigned Size = JT[JTI].MBBs.size() * sizeof(uint32_t); + MachineBasicBlock *JumpTableBB = MF->CreateMachineBasicBlock(); + MF->insert(std::next(MachineFunction::iterator(MBB)), JumpTableBB); + MachineInstr *CPEMI = BuildMI(*JumpTableBB, JumpTableBB->begin(), + DebugLoc(), TII->get(JTOpcode)) + .addImm(i++) + .addJumpTableIndex(JTI) + .addImm(Size); + CPEMIs.push_back(CPEMI); + CPEntries.emplace_back(1, CPEntry(CPEMI, JTI)); + JumpTableEntryIndices.insert(std::make_pair(JTI, CPEntries.size() - 1)); + if (!LastCorrectlyNumberedBB) + LastCorrectlyNumberedBB = &MBB; + } + + // If we did anything then we need to renumber the subsequent blocks. + if (LastCorrectlyNumberedBB) + MF->RenumberBlocks(LastCorrectlyNumberedBB); +} + +/// BBHasFallthrough - Return true if the specified basic block can fallthrough +/// into the block immediately after it. +bool ARMConstantIslands::BBHasFallthrough(MachineBasicBlock *MBB) { + // Get the next machine basic block in the function. + MachineFunction::iterator MBBI = MBB->getIterator(); + // Can't fall off end of function. + if (std::next(MBBI) == MBB->getParent()->end()) + return false; + + MachineBasicBlock *NextBB = &*std::next(MBBI); + if (!MBB->isSuccessor(NextBB)) + return false; + + // Try to analyze the end of the block. A potential fallthrough may already + // have an unconditional branch for whatever reason. + MachineBasicBlock *TBB, *FBB; + SmallVector<MachineOperand, 4> Cond; + bool TooDifficult = TII->analyzeBranch(*MBB, TBB, FBB, Cond); + return TooDifficult || FBB == nullptr; +} + +/// findConstPoolEntry - Given the constpool index and CONSTPOOL_ENTRY MI, +/// look up the corresponding CPEntry. +ARMConstantIslands::CPEntry +*ARMConstantIslands::findConstPoolEntry(unsigned CPI, + const MachineInstr *CPEMI) { + std::vector<CPEntry> &CPEs = CPEntries[CPI]; + // Number of entries per constpool index should be small, just do a + // linear search. + for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { + if (CPEs[i].CPEMI == CPEMI) + return &CPEs[i]; + } + return nullptr; +} + +/// getCPELogAlign - Returns the required alignment of the constant pool entry +/// represented by CPEMI. Alignment is measured in log2(bytes) units. +unsigned ARMConstantIslands::getCPELogAlign(const MachineInstr *CPEMI) { + switch (CPEMI->getOpcode()) { + case ARM::CONSTPOOL_ENTRY: + break; + case ARM::JUMPTABLE_TBB: + return isThumb1 ? 2 : 0; + case ARM::JUMPTABLE_TBH: + return isThumb1 ? 2 : 1; + case ARM::JUMPTABLE_INSTS: + return 1; + case ARM::JUMPTABLE_ADDRS: + return 2; + default: + llvm_unreachable("unknown constpool entry kind"); + } + + unsigned CPI = getCombinedIndex(CPEMI); + 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); +} + +/// scanFunctionJumpTables - Do a scan of the function, building up +/// information about the sizes of each block and the locations of all +/// the jump tables. +void ARMConstantIslands::scanFunctionJumpTables() { + for (MachineBasicBlock &MBB : *MF) { + for (MachineInstr &I : MBB) + if (I.isBranch() && + (I.getOpcode() == ARM::t2BR_JT || I.getOpcode() == ARM::tBR_JTr)) + T2JumpTables.push_back(&I); + } +} + +/// 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 ARMConstantIslands:: +initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs) { + + BBInfo = computeAllBlockSizes(MF); + + // The known bits of the entry block offset are determined by the function + // alignment. + BBInfo.front().KnownBits = MF->getAlignment(); + + // Compute block offsets and known bits. + adjustBBOffsetsAfter(&MF->front()); + + // Now go back through the instructions and build up our data structures. + for (MachineBasicBlock &MBB : *MF) { + // 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 (MachineInstr &I : MBB) { + if (I.isDebugValue()) + continue; + + unsigned Opc = I.getOpcode(); + if (I.isBranch()) { + bool isCond = false; + unsigned Bits = 0; + unsigned Scale = 1; + int UOpc = Opc; + switch (Opc) { + default: + continue; // Ignore other JT branches + case ARM::t2BR_JT: + case ARM::tBR_JTr: + T2JumpTables.push_back(&I); + continue; // Does not get an entry in ImmBranches + case ARM::Bcc: + isCond = true; + UOpc = ARM::B; + LLVM_FALLTHROUGH; + case ARM::B: + Bits = 24; + Scale = 4; + break; + case ARM::tBcc: + isCond = true; + UOpc = ARM::tB; + Bits = 8; + Scale = 2; + break; + case ARM::tB: + Bits = 11; + Scale = 2; + break; + case ARM::t2Bcc: + isCond = true; + UOpc = ARM::t2B; + Bits = 20; + Scale = 2; + break; + case ARM::t2B: + Bits = 24; + Scale = 2; + break; + } + + // Record this immediate branch. + unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale; + ImmBranches.push_back(ImmBranch(&I, MaxOffs, isCond, UOpc)); + } + + if (Opc == ARM::tPUSH || Opc == ARM::tPOP_RET) + PushPopMIs.push_back(&I); + + if (Opc == ARM::CONSTPOOL_ENTRY || Opc == ARM::JUMPTABLE_ADDRS || + Opc == ARM::JUMPTABLE_INSTS || Opc == ARM::JUMPTABLE_TBB || + Opc == ARM::JUMPTABLE_TBH) + continue; + + // Scan the instructions for constant pool operands. + for (unsigned op = 0, e = I.getNumOperands(); op != e; ++op) + if (I.getOperand(op).isCPI() || I.getOperand(op).isJTI()) { + // 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; + bool IsSoImm = false; + + switch (Opc) { + default: + llvm_unreachable("Unknown addressing mode for CP reference!"); + + // Taking the address of a CP entry. + case ARM::LEApcrel: + case ARM::LEApcrelJT: + // This takes a SoImm, which is 8 bit immediate rotated. We'll + // pretend the maximum offset is 255 * 4. Since each instruction + // 4 byte wide, this is always correct. We'll check for other + // displacements that fits in a SoImm as well. + Bits = 8; + Scale = 4; + NegOk = true; + IsSoImm = true; + break; + case ARM::t2LEApcrel: + case ARM::t2LEApcrelJT: + Bits = 12; + NegOk = true; + break; + case ARM::tLEApcrel: + case ARM::tLEApcrelJT: + Bits = 8; + Scale = 4; + break; + + case ARM::LDRBi12: + case ARM::LDRi12: + case ARM::LDRcp: + case ARM::t2LDRpci: + case ARM::t2LDRHpci: + Bits = 12; // +-offset_12 + NegOk = true; + break; + + case ARM::tLDRpci: + Bits = 8; + Scale = 4; // +(offset_8*4) + break; + + case ARM::VLDRD: + case ARM::VLDRS: + Bits = 8; + Scale = 4; // +-(offset_8*4) + NegOk = true; + break; + + case ARM::tLDRHi: + Bits = 5; + Scale = 2; // +(offset_5*2) + break; + } + + // Remember that this is a user of a CP entry. + unsigned CPI = I.getOperand(op).getIndex(); + if (I.getOperand(op).isJTI()) { + JumpTableUserIndices.insert(std::make_pair(CPI, CPUsers.size())); + CPI = JumpTableEntryIndices[CPI]; + } + + MachineInstr *CPEMI = CPEMIs[CPI]; + unsigned MaxOffs = ((1 << Bits)-1) * Scale; + CPUsers.push_back(CPUser(&I, CPEMI, MaxOffs, NegOk, IsSoImm)); + + // 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; + } + } + } +} + +/// getOffsetOf - Return the current offset of the specified machine instruction +/// from the start of the function. This offset changes as stuff is moved +/// around inside the function. +unsigned ARMConstantIslands::getOffsetOf(MachineInstr *MI) const { + MachineBasicBlock *MBB = MI->getParent(); + + // The offset is composed of two things: the sum of the sizes of all MBB's + // before this instruction's block, and the offset from the start of the block + // it is in. + unsigned Offset = 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 ARMConstantIslands::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); +} + + +/// 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 *ARMConstantIslands::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->getIterator(); + MF->insert(MBBI, NewBB); + + // Splice the instructions starting with MI over to NewBB. + NewBB->splice(NewBB->end(), OrigBB, MI, OrigBB->end()); + + // Add an unconditional branch from OrigBB to NewBB. + // Note the new unconditional branch is not being recorded. + // There doesn't seem to be meaningful DebugInfo available; this doesn't + // correspond to anything in the source. + unsigned Opc = isThumb ? (isThumb2 ? ARM::t2B : ARM::tB) : ARM::B; + if (!isThumb) + BuildMI(OrigBB, DebugLoc(), TII->get(Opc)).addMBB(NewBB); + else + BuildMI(OrigBB, DebugLoc(), TII->get(Opc)).addMBB(NewBB) + .addImm(ARMCC::AL).addReg(0); + ++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(MF, OrigBB, BBInfo[OrigBB->getNumber()]); + + // Figure out how large the NewMBB is. As the second half of the original + // block, it may contain a tablejump. + computeBlockSize(MF, NewBB, BBInfo[NewBB->getNumber()]); + + // All BBOffsets following these blocks must be modified. + adjustBBOffsetsAfter(OrigBB); + + return NewBB; +} + +/// getUserOffset - Compute the offset of U.MI as seen by the hardware +/// displacement computation. Update U.KnownAlignment to match its current +/// basic block location. +unsigned ARMConstantIslands::getUserOffset(CPUser &U) const { + unsigned UserOffset = getOffsetOf(U.MI); + const BasicBlockInfo &BBI = BBInfo[U.MI->getParent()->getNumber()]; + unsigned KnownBits = BBI.internalKnownBits(); + + // The value read from PC is offset from the actual instruction address. + UserOffset += (isThumb ? 4 : 8); + + // Because of inline assembly, we may not know the alignment (mod 4) of U.MI. + // Make sure U.getMaxDisp() returns a constrained range. + U.KnownAlignment = (KnownBits >= 2); + + // On Thumb, offsets==2 mod 4 are rounded down by the hardware for + // purposes of the displacement computation; compensate for that here. + // For unknown alignments, getMaxDisp() constrains the range instead. + if (isThumb && U.KnownAlignment) + UserOffset &= ~3u; + + return UserOffset; +} + +/// isOffsetInRange - Checks whether UserOffset (the location of a constant pool +/// reference) is within MaxDisp of TrialOffset (a proposed location of a +/// constant pool entry). +/// UserOffset is computed by getUserOffset above to include PC adjustments. If +/// the mod 4 alignment of UserOffset is not known, the uncertainty must be +/// subtracted from MaxDisp instead. CPUser::getMaxDisp() does that. +bool ARMConstantIslands::isOffsetInRange(unsigned UserOffset, + unsigned TrialOffset, unsigned MaxDisp, + bool NegativeOK, bool IsSoImm) { + if (UserOffset <= TrialOffset) { + // User before the Trial. + if (TrialOffset - UserOffset <= MaxDisp) + return true; + // FIXME: Make use full range of soimm values. + } else if (NegativeOK) { + if (UserOffset - TrialOffset <= MaxDisp) + return true; + // FIXME: Make use full range of soimm values. + } + 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 ARMConstantIslands::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->getIterator(); + 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, 1ULL << 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 + UnknownPadding(MF->getAlignment(), CPELogAlign); + } 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 ARMConstantIslands::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() == ARM::B || PredMI->getOpcode() == ARM::tB + || PredMI->getOpcode() == ARM::t2B) + return PredMI->getOperand(0).getMBB() == Succ; + return false; +} +#endif // NDEBUG + +void ARMConstantIslands::adjustBBOffsetsAfter(MachineBasicBlock *BB) { + 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 LogAlign = MF->getBlockNumbered(i)->getAlignment(); + unsigned Offset = BBInfo[i - 1].postOffset(LogAlign); + unsigned KnownBits = BBInfo[i - 1].postKnownBits(LogAlign); + + // This is where block i begins. Stop if the offset is already correct, + // and we have updated 2 blocks. This is the maximum number of blocks + // changed before calling this function. + if (i > BBNum + 2 && + BBInfo[i].Offset == Offset && + BBInfo[i].KnownBits == KnownBits) + break; + + BBInfo[i].Offset = Offset; + BBInfo[i].KnownBits = KnownBits; + } +} + +/// 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 ARMConstantIslands::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; +} + +unsigned ARMConstantIslands::getCombinedIndex(const MachineInstr *CPEMI) { + if (CPEMI->getOperand(1).isCPI()) + return CPEMI->getOperand(1).getIndex(); + + return JumpTableEntryIndices[CPEMI->getOperand(1).getIndex()]; +} + +/// LookForCPEntryInRange - see if the currently referenced CPE is in range; +/// if not, see if an in-range clone of the CPE is in range, and if so, +/// change the data structures so the user references the clone. Returns: +/// 0 = no existing entry found +/// 1 = entry found, and there were no code insertions or deletions +/// 2 = entry found, and there were code insertions or deletions +int ARMConstantIslands::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 = getCombinedIndex(CPEMI); + 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; +} + +/// getUnconditionalBrDisp - Returns the maximum displacement that can fit in +/// the specific unconditional branch instruction. +static inline unsigned getUnconditionalBrDisp(int Opc) { + switch (Opc) { + case ARM::tB: + return ((1<<10)-1)*2; + case ARM::t2B: + return ((1<<23)-1)*2; + default: + break; + } + + return ((1<<23)-1)*4; +} + +/// 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. For Thumb, prefer water that will not +/// introduce padding to water that will. 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 ARMConstantIslands::findAvailableWater(CPUser &U, unsigned UserOffset, + water_iterator &WaterIter, + bool CloserWater) { + if (WaterList.empty()) + return false; + + unsigned BestGrowth = ~0u; + // The nearest water without splitting the UserBB is right after it. + // If the distance is still large (we have a big BB), then we need to split it + // if we don't converge after certain iterations. This helps the following + // situation to converge: + // BB0: + // Big BB + // BB1: + // Constant Pool + // When a CP access is out of range, BB0 may be used as water. However, + // inserting islands between BB0 and BB1 makes other accesses out of range. + MachineBasicBlock *UserBB = U.MI->getParent(); + unsigned MinNoSplitDisp = + BBInfo[UserBB->getNumber()].postOffset(getCPELogAlign(U.CPEMI)); + if (CloserWater && MinNoSplitDisp > U.getMaxDisp() / 2) + return false; + 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. + // When CloserWater is true, we try to find the lowest address after (or + // equal to) user MI's BB no matter of padding growth. + unsigned Growth; + if (isWaterInRange(UserOffset, WaterBB, U, Growth) && + (WaterBB->getNumber() < U.HighWaterMark->getNumber() || + NewWaterList.count(WaterBB) || WaterBB == U.MI->getParent()) && + 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'); + + if (CloserWater && WaterBB == U.MI->getParent()) + return true; + // Keep looking unless it is perfect and we're not looking for the lowest + // possible address. + if (!CloserWater && 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 ARMConstantIslands::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. (The addition + // below is for the unconditional branch we will be adding: 4 bytes on ARM + + // Thumb2, 2 on Thumb1. + if (BBHasFallthrough(UserMBB)) { + // Size of branch to insert. + unsigned Delta = isThumb1 ? 2 : 4; + // 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 = &*++UserMBB->getIterator(); + // Add an unconditional branch from UserMBB to fallthrough block. Record + // it for branch lengthening; this new branch will not get out of range, + // but if the preceding conditional branch is out of range, the targets + // will be exchanged, and the altered branch may be out of range, so the + // machinery has to know about it. + int UncondBr = isThumb ? ((isThumb2) ? ARM::t2B : ARM::tB) : ARM::B; + if (!isThumb) + BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB); + else + BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB) + .addImm(ARMCC::AL).addReg(0); + unsigned MaxDisp = getUnconditionalBrDisp(UncondBr); + ImmBranches.push_back(ImmBranch(&UserMBB->back(), + MaxDisp, false, UncondBr)); + computeBlockSize(MF, UserMBB, BBInfo[UserMBB->getNumber()]); + adjustBBOffsetsAfter(UserMBB); + return; + } + } + + // What a big block. Find a place within the block to split it. This is a + // little tricky on Thumb1 since instructions are 2 bytes and constant pool + // entries are 4 bytes: if instruction I references island CPE, and + // instruction I+1 references CPE', it will not work well to put CPE as far + // forward as possible, since then CPE' cannot immediately follow it (that + // location is 2 bytes farther away from I+1 than CPE was from I) and we'd + // need to create a new island. So, we make a first guess, then walk through + // the instructions between the one currently being looked at and the + // possible insertion point, and make sure any other instructions that + // reference CPEs will be able to use the same island area; if not, we back + // up the insertion point. + + // 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 KnownBits = UserBBI.internalKnownBits(); + unsigned UPad = UnknownPadding(LogAlign, KnownBits); + unsigned BaseInsertOffset = UserOffset + U.getMaxDisp() - UPad; + 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 + // (allows for long branch on Thumb1). Alignment of the island is handled + // inside isOffsetInRange. + BaseInsertOffset -= 4; + + DEBUG(dbgs() << format(", adjusted to %#x", BaseInsertOffset) + << " la=" << LogAlign + << " kb=" << KnownBits + << " up=" << UPad << '\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()) { + // Ensure BaseInsertOffset is larger than the offset of the instruction + // following UserMI so that the loop which searches for the split point + // iterates at least once. + BaseInsertOffset = + std::max(UserBBI.postOffset() - UPad - 8, + UserOffset + TII->getInstSizeInBytes(*UserMI) + 1); + DEBUG(dbgs() << format("Move inside block: %#x\n", BaseInsertOffset)); + } + unsigned EndInsertOffset = BaseInsertOffset + 4 + UPad + + CPEMI->getOperand(2).getImm(); + MachineBasicBlock::iterator MI = UserMI; + ++MI; + unsigned CPUIndex = CPUserIndex+1; + unsigned NumCPUsers = CPUsers.size(); + MachineInstr *LastIT = nullptr; + 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++; + } + + // Remember the last IT instruction. + if (MI->getOpcode() == ARM::t2IT) + LastIT = &*MI; + } + + --MI; + + // Avoid splitting an IT block. + if (LastIT) { + unsigned PredReg = 0; + ARMCC::CondCodes CC = getITInstrPredicate(*MI, PredReg); + if (CC != ARMCC::AL) + MI = LastIT; + } + + // We really must not split an IT block. + DEBUG(unsigned PredReg; + assert(!isThumb || getITInstrPredicate(*MI, PredReg) == ARMCC::AL)); + + 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 ARMConstantIslands::handleConstantPoolUser(unsigned CPUserIndex, + bool CloserWater) { + CPUser &U = CPUsers[CPUserIndex]; + MachineInstr *UserMI = U.MI; + MachineInstr *CPEMI = U.CPEMI; + unsigned CPI = getCombinedIndex(CPEMI); + 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; + + // No existing clone of this CPE is within range. + // We will be generating a new clone. Get a UID for it. + unsigned ID = AFI->createPICLabelUId(); + + // Look for water where we can place this CPE. + MachineBasicBlock *NewIsland = MF->CreateMachineBasicBlock(); + MachineBasicBlock *NewMBB; + water_iterator IP; + if (findAvailableWater(U, UserOffset, IP, CloserWater)) { + 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 = &*++WaterBB->getIterator(); + } else { + // No water found. + 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 = &*--NewMBB->getIterator(); + IP = find(WaterList, 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->getIterator(), NewIsland); + + // Update internal data structures to account for the newly inserted MBB. + updateForInsertedWaterBlock(NewIsland); + + // 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(), CPEMI->getDesc()) + .addImm(ID).addOperand(CPEMI->getOperand(1)).addImm(Size); + CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1)); + ++NumCPEs; + + // Decrement the old entry, and remove it if refcount becomes 0. + decrementCPEReferenceCount(CPI, CPEMI); + + // 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(&*--NewIsland->getIterator()); + + // 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 ARMConstantIslands::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 ARMConstantIslands::removeUnusedCPEntries() { + unsigned MadeChange = false; + for (unsigned i = 0, e = CPEntries.size(); i != e; ++i) { + std::vector<CPEntry> &CPEs = CPEntries[i]; + for (unsigned j = 0, ee = CPEs.size(); j != ee; ++j) { + if (CPEs[j].RefCount == 0 && CPEs[j].CPEMI) { + removeDeadCPEMI(CPEs[j].CPEMI); + CPEs[j].CPEMI = 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 ARMConstantIslands::isBBInRange(MachineInstr *MI,MachineBasicBlock *DestBB, + unsigned MaxDisp) { + unsigned PCAdj = isThumb ? 4 : 8; + 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 ARMConstantIslands::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 +ARMConstantIslands::fixupUnconditionalBr(ImmBranch &Br) { + MachineInstr *MI = Br.MI; + MachineBasicBlock *MBB = MI->getParent(); + if (!isThumb1) + llvm_unreachable("fixupUnconditionalBr is Thumb1 only!"); + + // Use BL to implement far jump. + Br.MaxDisp = (1 << 21) * 2; + MI->setDesc(TII->get(ARM::tBfar)); + 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 +ARMConstantIslands::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: + ARMCC::CondCodes CC = (ARMCC::CondCodes)MI->getOperand(1).getImm(); + CC = ARMCC::getOppositeCondition(CC); + unsigned CCReg = MI->getOperand(2).getReg(); + + // If the branch is at the end of its MBB and that has a fall-through block, + // direct the updated conditional branch to the fall-through block. Otherwise, + // split the MBB before the next instruction. + MachineBasicBlock *MBB = MI->getParent(); + MachineInstr *BMI = &MBB->back(); + bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB); + + ++NumCBrFixed; + if (BMI != MI) { + if (std::next(MachineBasicBlock::iterator(MI)) == std::prev(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); + MI->getOperand(1).setImm(CC); + return true; + } + } + } + + if (NeedSplit) { + splitBlockBeforeInstr(MI); + // No need for the branch to the next block. We're adding an unconditional + // branch to the destination. + int delta = TII->getInstSizeInBytes(MBB->back()); + BBInfo[MBB->getNumber()].Size -= delta; + MBB->back().eraseFromParent(); + // BBInfo[SplitBB].Offset is wrong temporarily, fixed below + } + MachineBasicBlock *NextBB = &*++MBB->getIterator(); + + 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()); + if (isThumb) + BuildMI(MBB, DebugLoc(), TII->get(Br.UncondBr)).addMBB(DestBB) + .addImm(ARMCC::AL).addReg(0); + else + 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; +} + +/// undoLRSpillRestore - Remove Thumb push / pop instructions that only spills +/// LR / restores LR to pc. FIXME: This is done here because it's only possible +/// to do this if tBfar is not used. +bool ARMConstantIslands::undoLRSpillRestore() { + bool MadeChange = false; + for (unsigned i = 0, e = PushPopMIs.size(); i != e; ++i) { + MachineInstr *MI = PushPopMIs[i]; + // First two operands are predicates. + if (MI->getOpcode() == ARM::tPOP_RET && + MI->getOperand(2).getReg() == ARM::PC && + MI->getNumExplicitOperands() == 3) { + // Create the new insn and copy the predicate from the old. + BuildMI(MI->getParent(), MI->getDebugLoc(), TII->get(ARM::tBX_RET)) + .addOperand(MI->getOperand(0)) + .addOperand(MI->getOperand(1)); + MI->eraseFromParent(); + MadeChange = true; + } + } + return MadeChange; +} + +bool ARMConstantIslands::optimizeThumb2Instructions() { + bool MadeChange = false; + + // Shrink ADR and LDR from constantpool. + for (unsigned i = 0, e = CPUsers.size(); i != e; ++i) { + CPUser &U = CPUsers[i]; + unsigned Opcode = U.MI->getOpcode(); + unsigned NewOpc = 0; + unsigned Scale = 1; + unsigned Bits = 0; + switch (Opcode) { + default: break; + case ARM::t2LEApcrel: + if (isARMLowRegister(U.MI->getOperand(0).getReg())) { + NewOpc = ARM::tLEApcrel; + Bits = 8; + Scale = 4; + } + break; + case ARM::t2LDRpci: + if (isARMLowRegister(U.MI->getOperand(0).getReg())) { + NewOpc = ARM::tLDRpci; + Bits = 8; + Scale = 4; + } + break; + } + + if (!NewOpc) + continue; + + unsigned UserOffset = getUserOffset(U); + unsigned MaxOffs = ((1 << Bits) - 1) * Scale; + + // Be conservative with inline asm. + if (!U.KnownAlignment) + MaxOffs -= 2; + + // FIXME: Check if offset is multiple of scale if scale is not 4. + if (isCPEntryInRange(U.MI, UserOffset, U.CPEMI, MaxOffs, false, true)) { + DEBUG(dbgs() << "Shrink: " << *U.MI); + U.MI->setDesc(TII->get(NewOpc)); + MachineBasicBlock *MBB = U.MI->getParent(); + BBInfo[MBB->getNumber()].Size -= 2; + adjustBBOffsetsAfter(MBB); + ++NumT2CPShrunk; + MadeChange = true; + } + } + + return MadeChange; +} + +bool ARMConstantIslands::optimizeThumb2Branches() { + bool MadeChange = false; + + // The order in which branches appear in ImmBranches is approximately their + // order within the function body. By visiting later branches first, we reduce + // the distance between earlier forward branches and their targets, making it + // more likely that the cbn?z optimization, which can only apply to forward + // branches, will succeed. + for (unsigned i = ImmBranches.size(); i != 0; --i) { + ImmBranch &Br = ImmBranches[i-1]; + unsigned Opcode = Br.MI->getOpcode(); + unsigned NewOpc = 0; + unsigned Scale = 1; + unsigned Bits = 0; + switch (Opcode) { + default: break; + case ARM::t2B: + NewOpc = ARM::tB; + Bits = 11; + Scale = 2; + break; + case ARM::t2Bcc: { + NewOpc = ARM::tBcc; + Bits = 8; + Scale = 2; + break; + } + } + if (NewOpc) { + unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale; + MachineBasicBlock *DestBB = Br.MI->getOperand(0).getMBB(); + if (isBBInRange(Br.MI, DestBB, MaxOffs)) { + DEBUG(dbgs() << "Shrink branch: " << *Br.MI); + Br.MI->setDesc(TII->get(NewOpc)); + MachineBasicBlock *MBB = Br.MI->getParent(); + BBInfo[MBB->getNumber()].Size -= 2; + adjustBBOffsetsAfter(MBB); + ++NumT2BrShrunk; + MadeChange = true; + } + } + + Opcode = Br.MI->getOpcode(); + if (Opcode != ARM::tBcc) + continue; + + // If the conditional branch doesn't kill CPSR, then CPSR can be liveout + // so this transformation is not safe. + if (!Br.MI->killsRegister(ARM::CPSR)) + continue; + + NewOpc = 0; + unsigned PredReg = 0; + ARMCC::CondCodes Pred = getInstrPredicate(*Br.MI, PredReg); + if (Pred == ARMCC::EQ) + NewOpc = ARM::tCBZ; + else if (Pred == ARMCC::NE) + NewOpc = ARM::tCBNZ; + if (!NewOpc) + continue; + MachineBasicBlock *DestBB = Br.MI->getOperand(0).getMBB(); + // Check if the distance is within 126. Subtract starting offset by 2 + // because the cmp will be eliminated. + unsigned BrOffset = getOffsetOf(Br.MI) + 4 - 2; + unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset; + if (BrOffset < DestOffset && (DestOffset - BrOffset) <= 126) { + MachineBasicBlock::iterator CmpMI = Br.MI; + if (CmpMI != Br.MI->getParent()->begin()) { + --CmpMI; + if (CmpMI->getOpcode() == ARM::tCMPi8) { + unsigned Reg = CmpMI->getOperand(0).getReg(); + Pred = getInstrPredicate(*CmpMI, PredReg); + if (Pred == ARMCC::AL && + CmpMI->getOperand(1).getImm() == 0 && + isARMLowRegister(Reg)) { + MachineBasicBlock *MBB = Br.MI->getParent(); + DEBUG(dbgs() << "Fold: " << *CmpMI << " and: " << *Br.MI); + MachineInstr *NewBR = + BuildMI(*MBB, CmpMI, Br.MI->getDebugLoc(), TII->get(NewOpc)) + .addReg(Reg).addMBB(DestBB,Br.MI->getOperand(0).getTargetFlags()); + CmpMI->eraseFromParent(); + Br.MI->eraseFromParent(); + Br.MI = NewBR; + BBInfo[MBB->getNumber()].Size -= 2; + adjustBBOffsetsAfter(MBB); + ++NumCBZ; + MadeChange = true; + } + } + } + } + } + + return MadeChange; +} + +static bool isSimpleIndexCalc(MachineInstr &I, unsigned EntryReg, + unsigned BaseReg) { + if (I.getOpcode() != ARM::t2ADDrs) + return false; + + if (I.getOperand(0).getReg() != EntryReg) + return false; + + if (I.getOperand(1).getReg() != BaseReg) + return false; + + // FIXME: what about CC and IdxReg? + return true; +} + +/// \brief While trying to form a TBB/TBH instruction, we may (if the table +/// doesn't immediately follow the BR_JT) need access to the start of the +/// jump-table. We know one instruction that produces such a register; this +/// function works out whether that definition can be preserved to the BR_JT, +/// possibly by removing an intervening addition (which is usually needed to +/// calculate the actual entry to jump to). +bool ARMConstantIslands::preserveBaseRegister(MachineInstr *JumpMI, + MachineInstr *LEAMI, + unsigned &DeadSize, + bool &CanDeleteLEA, + bool &BaseRegKill) { + if (JumpMI->getParent() != LEAMI->getParent()) + return false; + + // Now we hope that we have at least these instructions in the basic block: + // BaseReg = t2LEA ... + // [...] + // EntryReg = t2ADDrs BaseReg, ... + // [...] + // t2BR_JT EntryReg + // + // We have to be very conservative about what we recognise here though. The + // main perturbing factors to watch out for are: + // + Spills at any point in the chain: not direct problems but we would + // expect a blocking Def of the spilled register so in practice what we + // can do is limited. + // + EntryReg == BaseReg: this is the one situation we should allow a Def + // of BaseReg, but only if the t2ADDrs can be removed. + // + Some instruction other than t2ADDrs computing the entry. Not seen in + // the wild, but we should be careful. + unsigned EntryReg = JumpMI->getOperand(0).getReg(); + unsigned BaseReg = LEAMI->getOperand(0).getReg(); + + CanDeleteLEA = true; + BaseRegKill = false; + MachineInstr *RemovableAdd = nullptr; + MachineBasicBlock::iterator I(LEAMI); + for (++I; &*I != JumpMI; ++I) { + if (isSimpleIndexCalc(*I, EntryReg, BaseReg)) { + RemovableAdd = &*I; + break; + } + + for (unsigned K = 0, E = I->getNumOperands(); K != E; ++K) { + const MachineOperand &MO = I->getOperand(K); + if (!MO.isReg() || !MO.getReg()) + continue; + if (MO.isDef() && MO.getReg() == BaseReg) + return false; + if (MO.isUse() && MO.getReg() == BaseReg) { + BaseRegKill = BaseRegKill || MO.isKill(); + CanDeleteLEA = false; + } + } + } + + if (!RemovableAdd) + return true; + + // Check the add really is removable, and that nothing else in the block + // clobbers BaseReg. + for (++I; &*I != JumpMI; ++I) { + for (unsigned K = 0, E = I->getNumOperands(); K != E; ++K) { + const MachineOperand &MO = I->getOperand(K); + if (!MO.isReg() || !MO.getReg()) + continue; + if (MO.isDef() && MO.getReg() == BaseReg) + return false; + if (MO.isUse() && MO.getReg() == EntryReg) + RemovableAdd = nullptr; + } + } + + if (RemovableAdd) { + RemovableAdd->eraseFromParent(); + DeadSize += isThumb2 ? 4 : 2; + } else if (BaseReg == EntryReg) { + // The add wasn't removable, but clobbered the base for the TBB. So we can't + // preserve it. + return false; + } + + // We reached the end of the block without seeing another definition of + // BaseReg (except, possibly the t2ADDrs, which was removed). BaseReg can be + // used in the TBB/TBH if necessary. + return true; +} + +/// \brief Returns whether CPEMI is the first instruction in the block +/// immediately following JTMI (assumed to be a TBB or TBH terminator). If so, +/// we can switch the first register to PC and usually remove the address +/// calculation that preceded it. +static bool jumpTableFollowsTB(MachineInstr *JTMI, MachineInstr *CPEMI) { + MachineFunction::iterator MBB = JTMI->getParent()->getIterator(); + MachineFunction *MF = MBB->getParent(); + ++MBB; + + return MBB != MF->end() && MBB->begin() != MBB->end() && + &*MBB->begin() == CPEMI; +} + +/// optimizeThumb2JumpTables - Use tbb / tbh instructions to generate smaller +/// jumptables when it's possible. +bool ARMConstantIslands::optimizeThumb2JumpTables() { + bool MadeChange = false; + + // FIXME: After the tables are shrunk, can we get rid some of the + // constantpool tables? + MachineJumpTableInfo *MJTI = MF->getJumpTableInfo(); + if (!MJTI) return false; + + const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables(); + for (unsigned i = 0, e = T2JumpTables.size(); i != e; ++i) { + MachineInstr *MI = T2JumpTables[i]; + const MCInstrDesc &MCID = MI->getDesc(); + unsigned NumOps = MCID.getNumOperands(); + unsigned JTOpIdx = NumOps - (MI->isPredicable() ? 2 : 1); + MachineOperand JTOP = MI->getOperand(JTOpIdx); + unsigned JTI = JTOP.getIndex(); + assert(JTI < JT.size()); + + bool ByteOk = true; + bool HalfWordOk = true; + unsigned JTOffset = getOffsetOf(MI) + 4; + const std::vector<MachineBasicBlock*> &JTBBs = JT[JTI].MBBs; + for (unsigned j = 0, ee = JTBBs.size(); j != ee; ++j) { + MachineBasicBlock *MBB = JTBBs[j]; + unsigned DstOffset = BBInfo[MBB->getNumber()].Offset; + // Negative offset is not ok. FIXME: We should change BB layout to make + // sure all the branches are forward. + if (ByteOk && (DstOffset - JTOffset) > ((1<<8)-1)*2) + ByteOk = false; + unsigned TBHLimit = ((1<<16)-1)*2; + if (HalfWordOk && (DstOffset - JTOffset) > TBHLimit) + HalfWordOk = false; + if (!ByteOk && !HalfWordOk) + break; + } + + if (!ByteOk && !HalfWordOk) + continue; + + CPUser &User = CPUsers[JumpTableUserIndices[JTI]]; + MachineBasicBlock *MBB = MI->getParent(); + if (!MI->getOperand(0).isKill()) // FIXME: needed now? + continue; + + unsigned DeadSize = 0; + bool CanDeleteLEA = false; + bool BaseRegKill = false; + + unsigned IdxReg = ~0U; + bool IdxRegKill = true; + if (isThumb2) { + IdxReg = MI->getOperand(1).getReg(); + IdxRegKill = MI->getOperand(1).isKill(); + + bool PreservedBaseReg = + preserveBaseRegister(MI, User.MI, DeadSize, CanDeleteLEA, BaseRegKill); + if (!jumpTableFollowsTB(MI, User.CPEMI) && !PreservedBaseReg) + continue; + } else { + // We're in thumb-1 mode, so we must have something like: + // %idx = tLSLri %idx, 2 + // %base = tLEApcrelJT + // %t = tLDRr %idx, %base + unsigned BaseReg = User.MI->getOperand(0).getReg(); + + if (User.MI->getIterator() == User.MI->getParent()->begin()) + continue; + MachineInstr *Shift = User.MI->getPrevNode(); + if (Shift->getOpcode() != ARM::tLSLri || + Shift->getOperand(3).getImm() != 2 || + !Shift->getOperand(2).isKill()) + continue; + IdxReg = Shift->getOperand(2).getReg(); + unsigned ShiftedIdxReg = Shift->getOperand(0).getReg(); + + MachineInstr *Load = User.MI->getNextNode(); + if (Load->getOpcode() != ARM::tLDRr) + continue; + if (Load->getOperand(1).getReg() != ShiftedIdxReg || + Load->getOperand(2).getReg() != BaseReg || + !Load->getOperand(1).isKill()) + continue; + + // If we're in PIC mode, there should be another ADD following. + if (isPositionIndependentOrROPI) { + MachineInstr *Add = Load->getNextNode(); + if (Add->getOpcode() != ARM::tADDrr || + Add->getOperand(2).getReg() != Load->getOperand(0).getReg() || + Add->getOperand(3).getReg() != BaseReg || + !Add->getOperand(2).isKill()) + continue; + if (Add->getOperand(0).getReg() != MI->getOperand(0).getReg()) + continue; + + Add->eraseFromParent(); + DeadSize += 2; + } else { + if (Load->getOperand(0).getReg() != MI->getOperand(0).getReg()) + continue; + } + + + // Now safe to delete the load and lsl. The LEA will be removed later. + CanDeleteLEA = true; + Shift->eraseFromParent(); + Load->eraseFromParent(); + DeadSize += 4; + } + + DEBUG(dbgs() << "Shrink JT: " << *MI); + MachineInstr *CPEMI = User.CPEMI; + unsigned Opc = ByteOk ? ARM::t2TBB_JT : ARM::t2TBH_JT; + if (!isThumb2) + Opc = ByteOk ? ARM::tTBB_JT : ARM::tTBH_JT; + + MachineBasicBlock::iterator MI_JT = MI; + MachineInstr *NewJTMI = + BuildMI(*MBB, MI_JT, MI->getDebugLoc(), TII->get(Opc)) + .addReg(User.MI->getOperand(0).getReg(), + getKillRegState(BaseRegKill)) + .addReg(IdxReg, getKillRegState(IdxRegKill)) + .addJumpTableIndex(JTI, JTOP.getTargetFlags()) + .addImm(CPEMI->getOperand(0).getImm()); + DEBUG(dbgs() << "BB#" << MBB->getNumber() << ": " << *NewJTMI); + + unsigned JTOpc = ByteOk ? ARM::JUMPTABLE_TBB : ARM::JUMPTABLE_TBH; + CPEMI->setDesc(TII->get(JTOpc)); + + if (jumpTableFollowsTB(MI, User.CPEMI)) { + NewJTMI->getOperand(0).setReg(ARM::PC); + NewJTMI->getOperand(0).setIsKill(false); + + if (CanDeleteLEA) { + User.MI->eraseFromParent(); + DeadSize += isThumb2 ? 4 : 2; + + // The LEA was eliminated, the TBB instruction becomes the only new user + // of the jump table. + User.MI = NewJTMI; + User.MaxDisp = 4; + User.NegOk = false; + User.IsSoImm = false; + User.KnownAlignment = false; + } else { + // The LEA couldn't be eliminated, so we must add another CPUser to + // record the TBB or TBH use. + int CPEntryIdx = JumpTableEntryIndices[JTI]; + auto &CPEs = CPEntries[CPEntryIdx]; + auto Entry = + find_if(CPEs, [&](CPEntry &E) { return E.CPEMI == User.CPEMI; }); + ++Entry->RefCount; + CPUsers.emplace_back(CPUser(NewJTMI, User.CPEMI, 4, false, false)); + } + } + + unsigned NewSize = TII->getInstSizeInBytes(*NewJTMI); + unsigned OrigSize = TII->getInstSizeInBytes(*MI); + MI->eraseFromParent(); + + int Delta = OrigSize - NewSize + DeadSize; + BBInfo[MBB->getNumber()].Size -= Delta; + adjustBBOffsetsAfter(MBB); + + ++NumTBs; + MadeChange = true; + } + + return MadeChange; +} + +/// reorderThumb2JumpTables - Adjust the function's block layout to ensure that +/// jump tables always branch forwards, since that's what tbb and tbh need. +bool ARMConstantIslands::reorderThumb2JumpTables() { + bool MadeChange = false; + + MachineJumpTableInfo *MJTI = MF->getJumpTableInfo(); + if (!MJTI) return false; + + const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables(); + for (unsigned i = 0, e = T2JumpTables.size(); i != e; ++i) { + MachineInstr *MI = T2JumpTables[i]; + const MCInstrDesc &MCID = MI->getDesc(); + unsigned NumOps = MCID.getNumOperands(); + unsigned JTOpIdx = NumOps - (MI->isPredicable() ? 2 : 1); + MachineOperand JTOP = MI->getOperand(JTOpIdx); + unsigned JTI = JTOP.getIndex(); + assert(JTI < JT.size()); + + // We prefer if target blocks for the jump table come after the jump + // instruction so we can use TB[BH]. Loop through the target blocks + // and try to adjust them such that that's true. + int JTNumber = MI->getParent()->getNumber(); + const std::vector<MachineBasicBlock*> &JTBBs = JT[JTI].MBBs; + for (unsigned j = 0, ee = JTBBs.size(); j != ee; ++j) { + MachineBasicBlock *MBB = JTBBs[j]; + int DTNumber = MBB->getNumber(); + + if (DTNumber < JTNumber) { + // The destination precedes the switch. Try to move the block forward + // so we have a positive offset. + MachineBasicBlock *NewBB = + adjustJTTargetBlockForward(MBB, MI->getParent()); + if (NewBB) + MJTI->ReplaceMBBInJumpTable(JTI, JTBBs[j], NewBB); + MadeChange = true; + } + } + } + + return MadeChange; +} + +MachineBasicBlock *ARMConstantIslands:: +adjustJTTargetBlockForward(MachineBasicBlock *BB, MachineBasicBlock *JTBB) { + // If the destination block is terminated by an unconditional branch, + // try to move it; otherwise, create a new block following the jump + // table that branches back to the actual target. This is a very simple + // heuristic. FIXME: We can definitely improve it. + MachineBasicBlock *TBB = nullptr, *FBB = nullptr; + SmallVector<MachineOperand, 4> Cond; + SmallVector<MachineOperand, 4> CondPrior; + MachineFunction::iterator BBi = BB->getIterator(); + MachineFunction::iterator OldPrior = std::prev(BBi); + + // If the block terminator isn't analyzable, don't try to move the block + bool B = TII->analyzeBranch(*BB, TBB, FBB, Cond); + + // If the block ends in an unconditional branch, move it. The prior block + // has to have an analyzable terminator for us to move this one. Be paranoid + // and make sure we're not trying to move the entry block of the function. + if (!B && Cond.empty() && BB != &MF->front() && + !TII->analyzeBranch(*OldPrior, TBB, FBB, CondPrior)) { + BB->moveAfter(JTBB); + OldPrior->updateTerminator(); + BB->updateTerminator(); + // Update numbering to account for the block being moved. + MF->RenumberBlocks(); + ++NumJTMoved; + return nullptr; + } + + // Create a new MBB for the code after the jump BB. + MachineBasicBlock *NewBB = + MF->CreateMachineBasicBlock(JTBB->getBasicBlock()); + MachineFunction::iterator MBBI = ++JTBB->getIterator(); + MF->insert(MBBI, NewBB); + + // Add an unconditional branch from NewBB to BB. + // There doesn't seem to be meaningful DebugInfo available; this doesn't + // correspond directly to anything in the source. + if (isThumb2) + BuildMI(NewBB, DebugLoc(), TII->get(ARM::t2B)) + .addMBB(BB) + .addImm(ARMCC::AL) + .addReg(0); + else + BuildMI(NewBB, DebugLoc(), TII->get(ARM::tB)) + .addMBB(BB) + .addImm(ARMCC::AL) + .addReg(0); + + // Update internal data structures to account for the newly inserted MBB. + MF->RenumberBlocks(NewBB); + + // Update the CFG. + NewBB->addSuccessor(BB); + JTBB->replaceSuccessor(BB, NewBB); + + ++NumJTInserted; + return NewBB; +} |