1664 lines · cpp
1//===- MipsConstantIslandPass.cpp - Emit Pc Relative loads ----------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// This pass is used to make Pc relative loads of constants.10// For now, only Mips16 will use this.11//12// Loading constants inline is expensive on Mips16 and it's in general better13// to place the constant nearby in code space and then it can be loaded with a14// simple 16 bit load instruction.15//16// The constants can be not just numbers but addresses of functions and labels.17// This can be particularly helpful in static relocation mode for embedded18// non-linux targets.19//20//===----------------------------------------------------------------------===//21 22#include "Mips.h"23#include "Mips16InstrInfo.h"24#include "MipsMachineFunction.h"25#include "MipsSubtarget.h"26#include "llvm/ADT/STLExtras.h"27#include "llvm/ADT/SmallVector.h"28#include "llvm/ADT/Statistic.h"29#include "llvm/ADT/StringRef.h"30#include "llvm/CodeGen/MachineBasicBlock.h"31#include "llvm/CodeGen/MachineConstantPool.h"32#include "llvm/CodeGen/MachineFunction.h"33#include "llvm/CodeGen/MachineFunctionPass.h"34#include "llvm/CodeGen/MachineInstr.h"35#include "llvm/CodeGen/MachineInstrBuilder.h"36#include "llvm/CodeGen/MachineOperand.h"37#include "llvm/CodeGen/MachineRegisterInfo.h"38#include "llvm/Config/llvm-config.h"39#include "llvm/IR/Constants.h"40#include "llvm/IR/DataLayout.h"41#include "llvm/IR/DebugLoc.h"42#include "llvm/IR/Function.h"43#include "llvm/IR/Type.h"44#include "llvm/Support/CommandLine.h"45#include "llvm/Support/Compiler.h"46#include "llvm/Support/Debug.h"47#include "llvm/Support/ErrorHandling.h"48#include "llvm/Support/Format.h"49#include "llvm/Support/raw_ostream.h"50#include <cassert>51#include <cstdint>52#include <iterator>53#include <vector>54 55using namespace llvm;56 57#define DEBUG_TYPE "mips-constant-islands"58 59STATISTIC(NumCPEs, "Number of constpool entries");60STATISTIC(NumSplit, "Number of uncond branches inserted");61STATISTIC(NumCBrFixed, "Number of cond branches fixed");62STATISTIC(NumUBrFixed, "Number of uncond branches fixed");63 64// FIXME: This option should be removed once it has received sufficient testing.65static cl::opt<bool>66AlignConstantIslands("mips-align-constant-islands", cl::Hidden, cl::init(true),67 cl::desc("Align constant islands in code"));68 69// Rather than do make check tests with huge amounts of code, we force70// the test to use this amount.71static cl::opt<int> ConstantIslandsSmallOffset(72 "mips-constant-islands-small-offset",73 cl::init(0),74 cl::desc("Make small offsets be this amount for testing purposes"),75 cl::Hidden);76 77// For testing purposes we tell it to not use relaxed load forms so that it78// will split blocks.79static cl::opt<bool> NoLoadRelaxation(80 "mips-constant-islands-no-load-relaxation",81 cl::init(false),82 cl::desc("Don't relax loads to long loads - for testing purposes"),83 cl::Hidden);84 85static unsigned int branchTargetOperand(MachineInstr *MI) {86 switch (MI->getOpcode()) {87 case Mips::Bimm16:88 case Mips::BimmX16:89 case Mips::Bteqz16:90 case Mips::BteqzX16:91 case Mips::Btnez16:92 case Mips::BtnezX16:93 case Mips::JalB16:94 return 0;95 case Mips::BeqzRxImm16:96 case Mips::BeqzRxImmX16:97 case Mips::BnezRxImm16:98 case Mips::BnezRxImmX16:99 return 1;100 }101 llvm_unreachable("Unknown branch type");102}103 104static unsigned int longformBranchOpcode(unsigned int Opcode) {105 switch (Opcode) {106 case Mips::Bimm16:107 case Mips::BimmX16:108 return Mips::BimmX16;109 case Mips::Bteqz16:110 case Mips::BteqzX16:111 return Mips::BteqzX16;112 case Mips::Btnez16:113 case Mips::BtnezX16:114 return Mips::BtnezX16;115 case Mips::JalB16:116 return Mips::JalB16;117 case Mips::BeqzRxImm16:118 case Mips::BeqzRxImmX16:119 return Mips::BeqzRxImmX16;120 case Mips::BnezRxImm16:121 case Mips::BnezRxImmX16:122 return Mips::BnezRxImmX16;123 }124 llvm_unreachable("Unknown branch type");125}126 127// FIXME: need to go through this whole constant islands port and check128// the math for branch ranges and clean this up and make some functions129// to calculate things that are done many times identically.130// Need to refactor some of the code to call this routine.131static unsigned int branchMaxOffsets(unsigned int Opcode) {132 unsigned Bits, Scale;133 switch (Opcode) {134 case Mips::Bimm16:135 Bits = 11;136 Scale = 2;137 break;138 case Mips::BimmX16:139 Bits = 16;140 Scale = 2;141 break;142 case Mips::BeqzRxImm16:143 Bits = 8;144 Scale = 2;145 break;146 case Mips::BeqzRxImmX16:147 Bits = 16;148 Scale = 2;149 break;150 case Mips::BnezRxImm16:151 Bits = 8;152 Scale = 2;153 break;154 case Mips::BnezRxImmX16:155 Bits = 16;156 Scale = 2;157 break;158 case Mips::Bteqz16:159 Bits = 8;160 Scale = 2;161 break;162 case Mips::BteqzX16:163 Bits = 16;164 Scale = 2;165 break;166 case Mips::Btnez16:167 Bits = 8;168 Scale = 2;169 break;170 case Mips::BtnezX16:171 Bits = 16;172 Scale = 2;173 break;174 default:175 llvm_unreachable("Unknown branch type");176 }177 unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale;178 return MaxOffs;179}180 181namespace {182 183 using Iter = MachineBasicBlock::iterator;184 using ReverseIter = MachineBasicBlock::reverse_iterator;185 186 /// MipsConstantIslands - Due to limited PC-relative displacements, Mips187 /// requires constant pool entries to be scattered among the instructions188 /// inside a function. To do this, it completely ignores the normal LLVM189 /// constant pool; instead, it places constants wherever it feels like with190 /// special instructions.191 ///192 /// The terminology used in this pass includes:193 /// Islands - Clumps of constants placed in the function.194 /// Water - Potential places where an island could be formed.195 /// CPE - A constant pool entry that has been placed somewhere, which196 /// tracks a list of users.197 198 class MipsConstantIslands : public MachineFunctionPass {199 /// BasicBlockInfo - Information about the offset and size of a single200 /// basic block.201 struct BasicBlockInfo {202 /// Offset - Distance from the beginning of the function to the beginning203 /// of this basic block.204 ///205 /// Offsets are computed assuming worst case padding before an aligned206 /// block. This means that subtracting basic block offsets always gives a207 /// conservative estimate of the real distance which may be smaller.208 ///209 /// Because worst case padding is used, the computed offset of an aligned210 /// block may not actually be aligned.211 unsigned Offset = 0;212 213 /// Size - Size of the basic block in bytes. If the block contains214 /// inline assembly, this is a worst case estimate.215 ///216 /// The size does not include any alignment padding whether from the217 /// beginning of the block, or from an aligned jump table at the end.218 unsigned Size = 0;219 220 BasicBlockInfo() = default;221 222 unsigned postOffset() const { return Offset + Size; }223 };224 225 std::vector<BasicBlockInfo> BBInfo;226 227 /// WaterList - A sorted list of basic blocks where islands could be placed228 /// (i.e. blocks that don't fall through to the following block, due229 /// to a return, unreachable, or unconditional branch).230 std::vector<MachineBasicBlock*> WaterList;231 232 /// NewWaterList - The subset of WaterList that was created since the233 /// previous iteration by inserting unconditional branches.234 SmallPtrSet<MachineBasicBlock *, 4> NewWaterList;235 236 using water_iterator = std::vector<MachineBasicBlock *>::iterator;237 238 /// CPUser - One user of a constant pool, keeping the machine instruction239 /// pointer, the constant pool being referenced, and the max displacement240 /// allowed from the instruction to the CP. The HighWaterMark records the241 /// highest basic block where a new CPEntry can be placed. To ensure this242 /// pass terminates, the CP entries are initially placed at the end of the243 /// function and then move monotonically to lower addresses. The244 /// exception to this rule is when the current CP entry for a particular245 /// CPUser is out of range, but there is another CP entry for the same246 /// constant value in range. We want to use the existing in-range CP247 /// entry, but if it later moves out of range, the search for new water248 /// should resume where it left off. The HighWaterMark is used to record249 /// that point.250 struct CPUser {251 MachineInstr *MI;252 MachineInstr *CPEMI;253 MachineBasicBlock *HighWaterMark;254 255 private:256 unsigned MaxDisp;257 unsigned LongFormMaxDisp; // mips16 has 16/32 bit instructions258 // with different displacements259 unsigned LongFormOpcode;260 261 public:262 bool NegOk;263 264 CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp,265 bool neg,266 unsigned longformmaxdisp, unsigned longformopcode)267 : MI(mi), CPEMI(cpemi), MaxDisp(maxdisp),268 LongFormMaxDisp(longformmaxdisp), LongFormOpcode(longformopcode),269 NegOk(neg){270 HighWaterMark = CPEMI->getParent();271 }272 273 /// getMaxDisp - Returns the maximum displacement supported by MI.274 unsigned getMaxDisp() const {275 unsigned xMaxDisp = ConstantIslandsSmallOffset?276 ConstantIslandsSmallOffset: MaxDisp;277 return xMaxDisp;278 }279 280 void setMaxDisp(unsigned val) {281 MaxDisp = val;282 }283 284 unsigned getLongFormMaxDisp() const {285 return LongFormMaxDisp;286 }287 288 unsigned getLongFormOpcode() const {289 return LongFormOpcode;290 }291 };292 293 /// CPUsers - Keep track of all of the machine instructions that use various294 /// constant pools and their max displacement.295 std::vector<CPUser> CPUsers;296 297 /// CPEntry - One per constant pool entry, keeping the machine instruction298 /// pointer, the constpool index, and the number of CPUser's which299 /// reference this entry.300 struct CPEntry {301 MachineInstr *CPEMI;302 unsigned CPI;303 unsigned RefCount;304 305 CPEntry(MachineInstr *cpemi, unsigned cpi, unsigned rc = 0)306 : CPEMI(cpemi), CPI(cpi), RefCount(rc) {}307 };308 309 /// CPEntries - Keep track of all of the constant pool entry machine310 /// instructions. For each original constpool index (i.e. those that311 /// existed upon entry to this pass), it keeps a vector of entries.312 /// Original elements are cloned as we go along; the clones are313 /// put in the vector of the original element, but have distinct CPIs.314 std::vector<std::vector<CPEntry>> CPEntries;315 316 /// ImmBranch - One per immediate branch, keeping the machine instruction317 /// pointer, conditional or unconditional, the max displacement,318 /// and (if isCond is true) the corresponding unconditional branch319 /// opcode.320 struct ImmBranch {321 MachineInstr *MI;322 unsigned MaxDisp : 31;323 LLVM_PREFERRED_TYPE(bool)324 unsigned isCond : 1;325 int UncondBr;326 327 ImmBranch(MachineInstr *mi, unsigned maxdisp, bool cond, int ubr)328 : MI(mi), MaxDisp(maxdisp), isCond(cond), UncondBr(ubr) {}329 };330 331 /// ImmBranches - Keep track of all the immediate branch instructions.332 ///333 std::vector<ImmBranch> ImmBranches;334 335 /// HasFarJump - True if any far jump instruction has been emitted during336 /// the branch fix up pass.337 bool HasFarJump;338 339 const MipsSubtarget *STI = nullptr;340 const Mips16InstrInfo *TII;341 MipsFunctionInfo *MFI;342 MachineFunction *MF = nullptr;343 MachineConstantPool *MCP = nullptr;344 345 unsigned PICLabelUId;346 bool PrescannedForConstants = false;347 348 void initPICLabelUId(unsigned UId) {349 PICLabelUId = UId;350 }351 352 unsigned createPICLabelUId() {353 return PICLabelUId++;354 }355 356 public:357 static char ID;358 359 MipsConstantIslands() : MachineFunctionPass(ID) {}360 361 StringRef getPassName() const override { return "Mips Constant Islands"; }362 363 bool runOnMachineFunction(MachineFunction &F) override;364 365 MachineFunctionProperties getRequiredProperties() const override {366 return MachineFunctionProperties().setNoVRegs();367 }368 369 void doInitialPlacement(std::vector<MachineInstr*> &CPEMIs);370 CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI);371 Align getCPEAlign(const MachineInstr &CPEMI);372 void initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs);373 unsigned getOffsetOf(MachineInstr *MI) const;374 unsigned getUserOffset(CPUser&) const;375 void dumpBBs();376 377 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset,378 unsigned Disp, bool NegativeOK);379 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset,380 const CPUser &U);381 382 void computeBlockSize(MachineBasicBlock *MBB);383 MachineBasicBlock *splitBlockBeforeInstr(MachineInstr &MI);384 void updateForInsertedWaterBlock(MachineBasicBlock *NewBB);385 void adjustBBOffsetsAfter(MachineBasicBlock *BB);386 bool decrementCPEReferenceCount(unsigned CPI, MachineInstr* CPEMI);387 int findInRangeCPEntry(CPUser& U, unsigned UserOffset);388 int findLongFormInRangeCPEntry(CPUser& U, unsigned UserOffset);389 bool findAvailableWater(CPUser&U, unsigned UserOffset,390 water_iterator &WaterIter);391 void createNewWater(unsigned CPUserIndex, unsigned UserOffset,392 MachineBasicBlock *&NewMBB);393 bool handleConstantPoolUser(unsigned CPUserIndex);394 void removeDeadCPEMI(MachineInstr *CPEMI);395 bool removeUnusedCPEntries();396 bool isCPEntryInRange(MachineInstr *MI, unsigned UserOffset,397 MachineInstr *CPEMI, unsigned Disp, bool NegOk,398 bool DoDump = false);399 bool isWaterInRange(unsigned UserOffset, MachineBasicBlock *Water,400 CPUser &U, unsigned &Growth);401 bool isBBInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp);402 bool fixupImmediateBr(ImmBranch &Br);403 bool fixupConditionalBr(ImmBranch &Br);404 bool fixupUnconditionalBr(ImmBranch &Br);405 406 void prescanForConstants();407 };408 409} // end anonymous namespace410 411char MipsConstantIslands::ID = 0;412 413bool MipsConstantIslands::isOffsetInRange414 (unsigned UserOffset, unsigned TrialOffset,415 const CPUser &U) {416 return isOffsetInRange(UserOffset, TrialOffset,417 U.getMaxDisp(), U.NegOk);418}419 420#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)421/// print block size and offset information - debugging422LLVM_DUMP_METHOD void MipsConstantIslands::dumpBBs() {423 for (unsigned J = 0, E = BBInfo.size(); J !=E; ++J) {424 const BasicBlockInfo &BBI = BBInfo[J];425 dbgs() << format("%08x %bb.%u\t", BBI.Offset, J)426 << format(" size=%#x\n", BBInfo[J].Size);427 }428}429#endif430 431bool MipsConstantIslands::runOnMachineFunction(MachineFunction &mf) {432 // The intention is for this to be a mips16 only pass for now433 // FIXME:434 MF = &mf;435 MCP = mf.getConstantPool();436 STI = &mf.getSubtarget<MipsSubtarget>();437 LLVM_DEBUG(dbgs() << "constant island machine function "438 << "\n");439 if (!STI->inMips16Mode() || !MipsSubtarget::useConstantIslands()) {440 return false;441 }442 TII = (const Mips16InstrInfo *)STI->getInstrInfo();443 MFI = MF->getInfo<MipsFunctionInfo>();444 LLVM_DEBUG(dbgs() << "constant island processing "445 << "\n");446 //447 // will need to make predermination if there is any constants we need to448 // put in constant islands. TBD.449 //450 if (!PrescannedForConstants) prescanForConstants();451 452 HasFarJump = false;453 // This pass invalidates liveness information when it splits basic blocks.454 MF->getRegInfo().invalidateLiveness();455 456 // Renumber all of the machine basic blocks in the function, guaranteeing that457 // the numbers agree with the position of the block in the function.458 MF->RenumberBlocks();459 460 bool MadeChange = false;461 462 // Perform the initial placement of the constant pool entries. To start with,463 // we put them all at the end of the function.464 std::vector<MachineInstr*> CPEMIs;465 if (!MCP->isEmpty())466 doInitialPlacement(CPEMIs);467 468 /// The next UID to take is the first unused one.469 initPICLabelUId(CPEMIs.size());470 471 // Do the initial scan of the function, building up information about the472 // sizes of each block, the location of all the water, and finding all of the473 // constant pool users.474 initializeFunctionInfo(CPEMIs);475 CPEMIs.clear();476 LLVM_DEBUG(dumpBBs());477 478 /// Remove dead constant pool entries.479 MadeChange |= removeUnusedCPEntries();480 481 // Iteratively place constant pool entries and fix up branches until there482 // is no change.483 unsigned NoCPIters = 0, NoBRIters = 0;484 (void)NoBRIters;485 while (true) {486 LLVM_DEBUG(dbgs() << "Beginning CP iteration #" << NoCPIters << '\n');487 bool CPChange = false;488 for (unsigned i = 0, e = CPUsers.size(); i != e; ++i)489 CPChange |= handleConstantPoolUser(i);490 if (CPChange && ++NoCPIters > 30)491 report_fatal_error("Constant Island pass failed to converge!");492 LLVM_DEBUG(dumpBBs());493 494 // Clear NewWaterList now. If we split a block for branches, it should495 // appear as "new water" for the next iteration of constant pool placement.496 NewWaterList.clear();497 498 LLVM_DEBUG(dbgs() << "Beginning BR iteration #" << NoBRIters << '\n');499 bool BRChange = false;500 for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)501 BRChange |= fixupImmediateBr(ImmBranches[i]);502 if (BRChange && ++NoBRIters > 30)503 report_fatal_error("Branch Fix Up pass failed to converge!");504 LLVM_DEBUG(dumpBBs());505 if (!CPChange && !BRChange)506 break;507 MadeChange = true;508 }509 510 LLVM_DEBUG(dbgs() << '\n'; dumpBBs());511 512 BBInfo.clear();513 WaterList.clear();514 CPUsers.clear();515 CPEntries.clear();516 ImmBranches.clear();517 return MadeChange;518}519 520/// doInitialPlacement - Perform the initial placement of the constant pool521/// entries. To start with, we put them all at the end of the function.522void523MipsConstantIslands::doInitialPlacement(std::vector<MachineInstr*> &CPEMIs) {524 // Create the basic block to hold the CPE's.525 MachineBasicBlock *BB = MF->CreateMachineBasicBlock();526 MF->push_back(BB);527 528 // MachineConstantPool measures alignment in bytes. We measure in log2(bytes).529 const Align MaxAlign = MCP->getConstantPoolAlign();530 531 // Mark the basic block as required by the const-pool.532 // If AlignConstantIslands isn't set, use 4-byte alignment for everything.533 BB->setAlignment(AlignConstantIslands ? MaxAlign : Align(4));534 535 // The function needs to be as aligned as the basic blocks. The linker may536 // move functions around based on their alignment.537 MF->ensureAlignment(BB->getAlignment());538 539 // Order the entries in BB by descending alignment. That ensures correct540 // alignment of all entries as long as BB is sufficiently aligned. Keep541 // track of the insertion point for each alignment. We are going to bucket542 // sort the entries as they are created.543 SmallVector<MachineBasicBlock::iterator, 8> InsPoint(Log2(MaxAlign) + 1,544 BB->end());545 546 // Add all of the constants from the constant pool to the end block, use an547 // identity mapping of CPI's to CPE's.548 const std::vector<MachineConstantPoolEntry> &CPs = MCP->getConstants();549 550 const DataLayout &TD = MF->getDataLayout();551 for (unsigned i = 0, e = CPs.size(); i != e; ++i) {552 unsigned Size = CPs[i].getSizeInBytes(TD);553 assert(Size >= 4 && "Too small constant pool entry");554 Align Alignment = CPs[i].getAlign();555 // Verify that all constant pool entries are a multiple of their alignment.556 // If not, we would have to pad them out so that instructions stay aligned.557 assert(isAligned(Alignment, Size) && "CP Entry not multiple of 4 bytes!");558 559 // Insert CONSTPOOL_ENTRY before entries with a smaller alignment.560 unsigned LogAlign = Log2(Alignment);561 MachineBasicBlock::iterator InsAt = InsPoint[LogAlign];562 563 MachineInstr *CPEMI =564 BuildMI(*BB, InsAt, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY))565 .addImm(i).addConstantPoolIndex(i).addImm(Size);566 567 CPEMIs.push_back(CPEMI);568 569 // Ensure that future entries with higher alignment get inserted before570 // CPEMI. This is bucket sort with iterators.571 for (unsigned a = LogAlign + 1; a <= Log2(MaxAlign); ++a)572 if (InsPoint[a] == InsAt)573 InsPoint[a] = CPEMI;574 // Add a new CPEntry, but no corresponding CPUser yet.575 CPEntries.emplace_back(1, CPEntry(CPEMI, i));576 ++NumCPEs;577 LLVM_DEBUG(dbgs() << "Moved CPI#" << i << " to end of function, size = "578 << Size << ", align = " << Alignment.value() << '\n');579 }580 LLVM_DEBUG(BB->dump());581}582 583/// BBHasFallthrough - Return true if the specified basic block can fallthrough584/// into the block immediately after it.585static bool BBHasFallthrough(MachineBasicBlock *MBB) {586 // Get the next machine basic block in the function.587 MachineFunction::iterator MBBI = MBB->getIterator();588 // Can't fall off end of function.589 if (std::next(MBBI) == MBB->getParent()->end())590 return false;591 592 MachineBasicBlock *NextBB = &*std::next(MBBI);593 return llvm::is_contained(MBB->successors(), NextBB);594}595 596/// findConstPoolEntry - Given the constpool index and CONSTPOOL_ENTRY MI,597/// look up the corresponding CPEntry.598MipsConstantIslands::CPEntry599*MipsConstantIslands::findConstPoolEntry(unsigned CPI,600 const MachineInstr *CPEMI) {601 std::vector<CPEntry> &CPEs = CPEntries[CPI];602 // Number of entries per constpool index should be small, just do a603 // linear search.604 for (CPEntry &CPE : CPEs) {605 if (CPE.CPEMI == CPEMI)606 return &CPE;607 }608 return nullptr;609}610 611/// getCPEAlign - Returns the required alignment of the constant pool entry612/// represented by CPEMI. Alignment is measured in log2(bytes) units.613Align MipsConstantIslands::getCPEAlign(const MachineInstr &CPEMI) {614 assert(CPEMI.getOpcode() == Mips::CONSTPOOL_ENTRY);615 616 // Everything is 4-byte aligned unless AlignConstantIslands is set.617 if (!AlignConstantIslands)618 return Align(4);619 620 unsigned CPI = CPEMI.getOperand(1).getIndex();621 assert(CPI < MCP->getConstants().size() && "Invalid constant pool index.");622 return MCP->getConstants()[CPI].getAlign();623}624 625/// initializeFunctionInfo - Do the initial scan of the function, building up626/// information about the sizes of each block, the location of all the water,627/// and finding all of the constant pool users.628void MipsConstantIslands::629initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs) {630 BBInfo.clear();631 BBInfo.resize(MF->getNumBlockIDs());632 633 // First thing, compute the size of all basic blocks, and see if the function634 // has any inline assembly in it. If so, we have to be conservative about635 // alignment assumptions, as we don't know for sure the size of any636 // instructions in the inline assembly.637 for (MachineBasicBlock &MBB : *MF)638 computeBlockSize(&MBB);639 640 // Compute block offsets.641 adjustBBOffsetsAfter(&MF->front());642 643 // Now go back through the instructions and build up our data structures.644 for (MachineBasicBlock &MBB : *MF) {645 // If this block doesn't fall through into the next MBB, then this is646 // 'water' that a constant pool island could be placed.647 if (!BBHasFallthrough(&MBB))648 WaterList.push_back(&MBB);649 for (MachineInstr &MI : MBB) {650 if (MI.isDebugInstr())651 continue;652 653 int Opc = MI.getOpcode();654 if (MI.isBranch()) {655 bool isCond = false;656 unsigned Bits = 0;657 unsigned Scale = 1;658 int UOpc = Opc;659 switch (Opc) {660 default:661 continue; // Ignore other branches for now662 case Mips::Bimm16:663 Bits = 11;664 Scale = 2;665 isCond = false;666 break;667 case Mips::BimmX16:668 Bits = 16;669 Scale = 2;670 isCond = false;671 break;672 case Mips::BeqzRxImm16:673 UOpc=Mips::Bimm16;674 Bits = 8;675 Scale = 2;676 isCond = true;677 break;678 case Mips::BeqzRxImmX16:679 UOpc=Mips::Bimm16;680 Bits = 16;681 Scale = 2;682 isCond = true;683 break;684 case Mips::BnezRxImm16:685 UOpc=Mips::Bimm16;686 Bits = 8;687 Scale = 2;688 isCond = true;689 break;690 case Mips::BnezRxImmX16:691 UOpc=Mips::Bimm16;692 Bits = 16;693 Scale = 2;694 isCond = true;695 break;696 case Mips::Bteqz16:697 UOpc=Mips::Bimm16;698 Bits = 8;699 Scale = 2;700 isCond = true;701 break;702 case Mips::BteqzX16:703 UOpc=Mips::Bimm16;704 Bits = 16;705 Scale = 2;706 isCond = true;707 break;708 case Mips::Btnez16:709 UOpc=Mips::Bimm16;710 Bits = 8;711 Scale = 2;712 isCond = true;713 break;714 case Mips::BtnezX16:715 UOpc=Mips::Bimm16;716 Bits = 16;717 Scale = 2;718 isCond = true;719 break;720 }721 // Record this immediate branch.722 unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale;723 ImmBranches.push_back(ImmBranch(&MI, MaxOffs, isCond, UOpc));724 }725 726 if (Opc == Mips::CONSTPOOL_ENTRY)727 continue;728 729 // Scan the instructions for constant pool operands.730 for (const MachineOperand &MO : MI.operands())731 if (MO.isCPI()) {732 // We found one. The addressing mode tells us the max displacement733 // from the PC that this instruction permits.734 735 // Basic size info comes from the TSFlags field.736 unsigned Bits = 0;737 unsigned Scale = 1;738 bool NegOk = false;739 unsigned LongFormBits = 0;740 unsigned LongFormScale = 0;741 unsigned LongFormOpcode = 0;742 switch (Opc) {743 default:744 llvm_unreachable("Unknown addressing mode for CP reference!");745 case Mips::LwRxPcTcp16:746 Bits = 8;747 Scale = 4;748 LongFormOpcode = Mips::LwRxPcTcpX16;749 LongFormBits = 14;750 LongFormScale = 1;751 break;752 case Mips::LwRxPcTcpX16:753 Bits = 14;754 Scale = 1;755 NegOk = true;756 break;757 }758 // Remember that this is a user of a CP entry.759 unsigned CPI = MO.getIndex();760 MachineInstr *CPEMI = CPEMIs[CPI];761 unsigned MaxOffs = ((1 << Bits)-1) * Scale;762 unsigned LongFormMaxOffs = ((1 << LongFormBits)-1) * LongFormScale;763 CPUsers.push_back(CPUser(&MI, CPEMI, MaxOffs, NegOk, LongFormMaxOffs,764 LongFormOpcode));765 766 // Increment corresponding CPEntry reference count.767 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI);768 assert(CPE && "Cannot find a corresponding CPEntry!");769 CPE->RefCount++;770 771 // Instructions can only use one CP entry, don't bother scanning the772 // rest of the operands.773 break;774 }775 }776 }777}778 779/// computeBlockSize - Compute the size and some alignment information for MBB.780/// This function updates BBInfo directly.781void MipsConstantIslands::computeBlockSize(MachineBasicBlock *MBB) {782 BasicBlockInfo &BBI = BBInfo[MBB->getNumber()];783 BBI.Size = 0;784 785 for (const MachineInstr &MI : *MBB)786 BBI.Size += TII->getInstSizeInBytes(MI);787}788 789/// getOffsetOf - Return the current offset of the specified machine instruction790/// from the start of the function. This offset changes as stuff is moved791/// around inside the function.792unsigned MipsConstantIslands::getOffsetOf(MachineInstr *MI) const {793 MachineBasicBlock *MBB = MI->getParent();794 795 // The offset is composed of two things: the sum of the sizes of all MBB's796 // before this instruction's block, and the offset from the start of the block797 // it is in.798 unsigned Offset = BBInfo[MBB->getNumber()].Offset;799 800 // Sum instructions before MI in MBB.801 for (MachineBasicBlock::iterator I = MBB->begin(); &*I != MI; ++I) {802 assert(I != MBB->end() && "Didn't find MI in its own basic block?");803 Offset += TII->getInstSizeInBytes(*I);804 }805 return Offset;806}807 808/// CompareMBBNumbers - Little predicate function to sort the WaterList by MBB809/// ID.810static bool CompareMBBNumbers(const MachineBasicBlock *LHS,811 const MachineBasicBlock *RHS) {812 return LHS->getNumber() < RHS->getNumber();813}814 815/// updateForInsertedWaterBlock - When a block is newly inserted into the816/// machine function, it upsets all of the block numbers. Renumber the blocks817/// and update the arrays that parallel this numbering.818void MipsConstantIslands::updateForInsertedWaterBlock819 (MachineBasicBlock *NewBB) {820 // Renumber the MBB's to keep them consecutive.821 NewBB->getParent()->RenumberBlocks(NewBB);822 823 // Insert an entry into BBInfo to align it properly with the (newly824 // renumbered) block numbers.825 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo());826 827 // Next, update WaterList. Specifically, we need to add NewMBB as having828 // available water after it.829 water_iterator IP = llvm::lower_bound(WaterList, NewBB, CompareMBBNumbers);830 WaterList.insert(IP, NewBB);831}832 833unsigned MipsConstantIslands::getUserOffset(CPUser &U) const {834 return getOffsetOf(U.MI);835}836 837/// Split the basic block containing MI into two blocks, which are joined by838/// an unconditional branch. Update data structures and renumber blocks to839/// account for this change and returns the newly created block.840MachineBasicBlock *841MipsConstantIslands::splitBlockBeforeInstr(MachineInstr &MI) {842 MachineBasicBlock *OrigBB = MI.getParent();843 844 // Create a new MBB for the code after the OrigBB.845 MachineBasicBlock *NewBB =846 MF->CreateMachineBasicBlock(OrigBB->getBasicBlock());847 MachineFunction::iterator MBBI = ++OrigBB->getIterator();848 MF->insert(MBBI, NewBB);849 850 // Splice the instructions starting with MI over to NewBB.851 NewBB->splice(NewBB->end(), OrigBB, MI, OrigBB->end());852 853 // Add an unconditional branch from OrigBB to NewBB.854 // Note the new unconditional branch is not being recorded.855 // There doesn't seem to be meaningful DebugInfo available; this doesn't856 // correspond to anything in the source.857 BuildMI(OrigBB, DebugLoc(), TII->get(Mips::Bimm16)).addMBB(NewBB);858 ++NumSplit;859 860 // Update the CFG. All succs of OrigBB are now succs of NewBB.861 NewBB->transferSuccessors(OrigBB);862 863 // OrigBB branches to NewBB.864 OrigBB->addSuccessor(NewBB);865 866 // Update internal data structures to account for the newly inserted MBB.867 // This is almost the same as updateForInsertedWaterBlock, except that868 // the Water goes after OrigBB, not NewBB.869 MF->RenumberBlocks(NewBB);870 871 // Insert an entry into BBInfo to align it properly with the (newly872 // renumbered) block numbers.873 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo());874 875 // Next, update WaterList. Specifically, we need to add OrigMBB as having876 // available water after it (but not if it's already there, which happens877 // when splitting before a conditional branch that is followed by an878 // unconditional branch - in that case we want to insert NewBB).879 water_iterator IP = llvm::lower_bound(WaterList, OrigBB, CompareMBBNumbers);880 MachineBasicBlock* WaterBB = *IP;881 if (WaterBB == OrigBB)882 WaterList.insert(std::next(IP), NewBB);883 else884 WaterList.insert(IP, OrigBB);885 NewWaterList.insert(OrigBB);886 887 // Figure out how large the OrigBB is. As the first half of the original888 // block, it cannot contain a tablejump. The size includes889 // the new jump we added. (It should be possible to do this without890 // recounting everything, but it's very confusing, and this is rarely891 // executed.)892 computeBlockSize(OrigBB);893 894 // Figure out how large the NewMBB is. As the second half of the original895 // block, it may contain a tablejump.896 computeBlockSize(NewBB);897 898 // All BBOffsets following these blocks must be modified.899 adjustBBOffsetsAfter(OrigBB);900 901 return NewBB;902}903 904/// isOffsetInRange - Checks whether UserOffset (the location of a constant pool905/// reference) is within MaxDisp of TrialOffset (a proposed location of a906/// constant pool entry).907bool MipsConstantIslands::isOffsetInRange(unsigned UserOffset,908 unsigned TrialOffset, unsigned MaxDisp,909 bool NegativeOK) {910 if (UserOffset <= TrialOffset) {911 // User before the Trial.912 if (TrialOffset - UserOffset <= MaxDisp)913 return true;914 } else if (NegativeOK) {915 if (UserOffset - TrialOffset <= MaxDisp)916 return true;917 }918 return false;919}920 921/// isWaterInRange - Returns true if a CPE placed after the specified922/// Water (a basic block) will be in range for the specific MI.923///924/// Compute how much the function will grow by inserting a CPE after Water.925bool MipsConstantIslands::isWaterInRange(unsigned UserOffset,926 MachineBasicBlock* Water, CPUser &U,927 unsigned &Growth) {928 unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset();929 unsigned NextBlockOffset;930 Align NextBlockAlignment;931 MachineFunction::const_iterator NextBlock = ++Water->getIterator();932 if (NextBlock == MF->end()) {933 NextBlockOffset = BBInfo[Water->getNumber()].postOffset();934 NextBlockAlignment = Align(1);935 } else {936 NextBlockOffset = BBInfo[NextBlock->getNumber()].Offset;937 NextBlockAlignment = NextBlock->getAlignment();938 }939 unsigned Size = U.CPEMI->getOperand(2).getImm();940 unsigned CPEEnd = CPEOffset + Size;941 942 // The CPE may be able to hide in the alignment padding before the next943 // block. It may also cause more padding to be required if it is more aligned944 // that the next block.945 if (CPEEnd > NextBlockOffset) {946 Growth = CPEEnd - NextBlockOffset;947 // Compute the padding that would go at the end of the CPE to align the next948 // block.949 Growth += offsetToAlignment(CPEEnd, NextBlockAlignment);950 951 // If the CPE is to be inserted before the instruction, that will raise952 // the offset of the instruction. Also account for unknown alignment padding953 // in blocks between CPE and the user.954 if (CPEOffset < UserOffset)955 UserOffset += Growth;956 } else957 // CPE fits in existing padding.958 Growth = 0;959 960 return isOffsetInRange(UserOffset, CPEOffset, U);961}962 963/// isCPEntryInRange - Returns true if the distance between specific MI and964/// specific ConstPool entry instruction can fit in MI's displacement field.965bool MipsConstantIslands::isCPEntryInRange966 (MachineInstr *MI, unsigned UserOffset,967 MachineInstr *CPEMI, unsigned MaxDisp,968 bool NegOk, bool DoDump) {969 unsigned CPEOffset = getOffsetOf(CPEMI);970 971 if (DoDump) {972 LLVM_DEBUG({973 unsigned Block = MI->getParent()->getNumber();974 const BasicBlockInfo &BBI = BBInfo[Block];975 dbgs() << "User of CPE#" << CPEMI->getOperand(0).getImm()976 << " max delta=" << MaxDisp977 << format(" insn address=%#x", UserOffset) << " in "978 << printMBBReference(*MI->getParent()) << ": "979 << format("%#x-%x\t", BBI.Offset, BBI.postOffset()) << *MI980 << format("CPE address=%#x offset=%+d: ", CPEOffset,981 int(CPEOffset - UserOffset));982 });983 }984 985 return isOffsetInRange(UserOffset, CPEOffset, MaxDisp, NegOk);986}987 988#ifndef NDEBUG989/// BBIsJumpedOver - Return true of the specified basic block's only predecessor990/// unconditionally branches to its only successor.991static bool BBIsJumpedOver(MachineBasicBlock *MBB) {992 if (MBB->pred_size() != 1 || MBB->succ_size() != 1)993 return false;994 MachineBasicBlock *Succ = *MBB->succ_begin();995 MachineBasicBlock *Pred = *MBB->pred_begin();996 MachineInstr *PredMI = &Pred->back();997 if (PredMI->getOpcode() == Mips::Bimm16)998 return PredMI->getOperand(0).getMBB() == Succ;999 return false;1000}1001#endif1002 1003void MipsConstantIslands::adjustBBOffsetsAfter(MachineBasicBlock *BB) {1004 unsigned BBNum = BB->getNumber();1005 for(unsigned i = BBNum + 1, e = MF->getNumBlockIDs(); i < e; ++i) {1006 // Get the offset and known bits at the end of the layout predecessor.1007 // Include the alignment of the current block.1008 unsigned Offset = BBInfo[i - 1].Offset + BBInfo[i - 1].Size;1009 BBInfo[i].Offset = Offset;1010 }1011}1012 1013/// decrementCPEReferenceCount - find the constant pool entry with index CPI1014/// and instruction CPEMI, and decrement its refcount. If the refcount1015/// becomes 0 remove the entry and instruction. Returns true if we removed1016/// the entry, false if we didn't.1017bool MipsConstantIslands::decrementCPEReferenceCount(unsigned CPI,1018 MachineInstr *CPEMI) {1019 // Find the old entry. Eliminate it if it is no longer used.1020 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI);1021 assert(CPE && "Unexpected!");1022 if (--CPE->RefCount == 0) {1023 removeDeadCPEMI(CPEMI);1024 CPE->CPEMI = nullptr;1025 --NumCPEs;1026 return true;1027 }1028 return false;1029}1030 1031/// LookForCPEntryInRange - see if the currently referenced CPE is in range;1032/// if not, see if an in-range clone of the CPE is in range, and if so,1033/// change the data structures so the user references the clone. Returns:1034/// 0 = no existing entry found1035/// 1 = entry found, and there were no code insertions or deletions1036/// 2 = entry found, and there were code insertions or deletions1037int MipsConstantIslands::findInRangeCPEntry(CPUser& U, unsigned UserOffset)1038{1039 MachineInstr *UserMI = U.MI;1040 MachineInstr *CPEMI = U.CPEMI;1041 1042 // Check to see if the CPE is already in-range.1043 if (isCPEntryInRange(UserMI, UserOffset, CPEMI, U.getMaxDisp(), U.NegOk,1044 true)) {1045 LLVM_DEBUG(dbgs() << "In range\n");1046 return 1;1047 }1048 1049 // No. Look for previously created clones of the CPE that are in range.1050 unsigned CPI = CPEMI->getOperand(1).getIndex();1051 std::vector<CPEntry> &CPEs = CPEntries[CPI];1052 for (CPEntry &CPE : CPEs) {1053 // We already tried this one1054 if (CPE.CPEMI == CPEMI)1055 continue;1056 // Removing CPEs can leave empty entries, skip1057 if (CPE.CPEMI == nullptr)1058 continue;1059 if (isCPEntryInRange(UserMI, UserOffset, CPE.CPEMI, U.getMaxDisp(),1060 U.NegOk)) {1061 LLVM_DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" << CPE.CPI1062 << "\n");1063 // Point the CPUser node to the replacement1064 U.CPEMI = CPE.CPEMI;1065 // Change the CPI in the instruction operand to refer to the clone.1066 for (MachineOperand &MO : UserMI->operands())1067 if (MO.isCPI()) {1068 MO.setIndex(CPE.CPI);1069 break;1070 }1071 // Adjust the refcount of the clone...1072 CPE.RefCount++;1073 // ...and the original. If we didn't remove the old entry, none of the1074 // addresses changed, so we don't need another pass.1075 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1;1076 }1077 }1078 return 0;1079}1080 1081/// LookForCPEntryInRange - see if the currently referenced CPE is in range;1082/// This version checks if the longer form of the instruction can be used to1083/// to satisfy things.1084/// if not, see if an in-range clone of the CPE is in range, and if so,1085/// change the data structures so the user references the clone. Returns:1086/// 0 = no existing entry found1087/// 1 = entry found, and there were no code insertions or deletions1088/// 2 = entry found, and there were code insertions or deletions1089int MipsConstantIslands::findLongFormInRangeCPEntry1090 (CPUser& U, unsigned UserOffset)1091{1092 MachineInstr *UserMI = U.MI;1093 MachineInstr *CPEMI = U.CPEMI;1094 1095 // Check to see if the CPE is already in-range.1096 if (isCPEntryInRange(UserMI, UserOffset, CPEMI,1097 U.getLongFormMaxDisp(), U.NegOk,1098 true)) {1099 LLVM_DEBUG(dbgs() << "In range\n");1100 UserMI->setDesc(TII->get(U.getLongFormOpcode()));1101 U.setMaxDisp(U.getLongFormMaxDisp());1102 return 2; // instruction is longer length now1103 }1104 1105 // No. Look for previously created clones of the CPE that are in range.1106 unsigned CPI = CPEMI->getOperand(1).getIndex();1107 std::vector<CPEntry> &CPEs = CPEntries[CPI];1108 for (CPEntry &CPE : CPEs) {1109 // We already tried this one1110 if (CPE.CPEMI == CPEMI)1111 continue;1112 // Removing CPEs can leave empty entries, skip1113 if (CPE.CPEMI == nullptr)1114 continue;1115 if (isCPEntryInRange(UserMI, UserOffset, CPE.CPEMI, U.getLongFormMaxDisp(),1116 U.NegOk)) {1117 LLVM_DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" << CPE.CPI1118 << "\n");1119 // Point the CPUser node to the replacement1120 U.CPEMI = CPE.CPEMI;1121 // Change the CPI in the instruction operand to refer to the clone.1122 for (MachineOperand &MO : UserMI->operands())1123 if (MO.isCPI()) {1124 MO.setIndex(CPE.CPI);1125 break;1126 }1127 // Adjust the refcount of the clone...1128 CPE.RefCount++;1129 // ...and the original. If we didn't remove the old entry, none of the1130 // addresses changed, so we don't need another pass.1131 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1;1132 }1133 }1134 return 0;1135}1136 1137/// getUnconditionalBrDisp - Returns the maximum displacement that can fit in1138/// the specific unconditional branch instruction.1139static inline unsigned getUnconditionalBrDisp(int Opc) {1140 switch (Opc) {1141 case Mips::Bimm16:1142 return ((1<<10)-1)*2;1143 case Mips::BimmX16:1144 return ((1<<16)-1)*2;1145 default:1146 break;1147 }1148 return ((1<<16)-1)*2;1149}1150 1151/// findAvailableWater - Look for an existing entry in the WaterList in which1152/// we can place the CPE referenced from U so it's within range of U's MI.1153/// Returns true if found, false if not. If it returns true, WaterIter1154/// is set to the WaterList entry.1155/// To ensure that this pass1156/// terminates, the CPE location for a particular CPUser is only allowed to1157/// move to a lower address, so search backward from the end of the list and1158/// prefer the first water that is in range.1159bool MipsConstantIslands::findAvailableWater(CPUser &U, unsigned UserOffset,1160 water_iterator &WaterIter) {1161 if (WaterList.empty())1162 return false;1163 1164 unsigned BestGrowth = ~0u;1165 for (water_iterator IP = std::prev(WaterList.end()), B = WaterList.begin();;1166 --IP) {1167 MachineBasicBlock* WaterBB = *IP;1168 // Check if water is in range and is either at a lower address than the1169 // current "high water mark" or a new water block that was created since1170 // the previous iteration by inserting an unconditional branch. In the1171 // latter case, we want to allow resetting the high water mark back to1172 // this new water since we haven't seen it before. Inserting branches1173 // should be relatively uncommon and when it does happen, we want to be1174 // sure to take advantage of it for all the CPEs near that block, so that1175 // we don't insert more branches than necessary.1176 unsigned Growth;1177 if (isWaterInRange(UserOffset, WaterBB, U, Growth) &&1178 (WaterBB->getNumber() < U.HighWaterMark->getNumber() ||1179 NewWaterList.count(WaterBB)) && Growth < BestGrowth) {1180 // This is the least amount of required padding seen so far.1181 BestGrowth = Growth;1182 WaterIter = IP;1183 LLVM_DEBUG(dbgs() << "Found water after " << printMBBReference(*WaterBB)1184 << " Growth=" << Growth << '\n');1185 1186 // Keep looking unless it is perfect.1187 if (BestGrowth == 0)1188 return true;1189 }1190 if (IP == B)1191 break;1192 }1193 return BestGrowth != ~0u;1194}1195 1196/// createNewWater - No existing WaterList entry will work for1197/// CPUsers[CPUserIndex], so create a place to put the CPE. The end of the1198/// block is used if in range, and the conditional branch munged so control1199/// flow is correct. Otherwise the block is split to create a hole with an1200/// unconditional branch around it. In either case NewMBB is set to a1201/// block following which the new island can be inserted (the WaterList1202/// is not adjusted).1203void MipsConstantIslands::createNewWater(unsigned CPUserIndex,1204 unsigned UserOffset,1205 MachineBasicBlock *&NewMBB) {1206 CPUser &U = CPUsers[CPUserIndex];1207 MachineInstr *UserMI = U.MI;1208 MachineInstr *CPEMI = U.CPEMI;1209 MachineBasicBlock *UserMBB = UserMI->getParent();1210 const BasicBlockInfo &UserBBI = BBInfo[UserMBB->getNumber()];1211 1212 // If the block does not end in an unconditional branch already, and if the1213 // end of the block is within range, make new water there.1214 if (BBHasFallthrough(UserMBB)) {1215 // Size of branch to insert.1216 unsigned Delta = 2;1217 // Compute the offset where the CPE will begin.1218 unsigned CPEOffset = UserBBI.postOffset() + Delta;1219 1220 if (isOffsetInRange(UserOffset, CPEOffset, U)) {1221 LLVM_DEBUG(dbgs() << "Split at end of " << printMBBReference(*UserMBB)1222 << format(", expected CPE offset %#x\n", CPEOffset));1223 NewMBB = &*++UserMBB->getIterator();1224 // Add an unconditional branch from UserMBB to fallthrough block. Record1225 // it for branch lengthening; this new branch will not get out of range,1226 // but if the preceding conditional branch is out of range, the targets1227 // will be exchanged, and the altered branch may be out of range, so the1228 // machinery has to know about it.1229 int UncondBr = Mips::Bimm16;1230 BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB);1231 unsigned MaxDisp = getUnconditionalBrDisp(UncondBr);1232 ImmBranches.push_back(ImmBranch(&UserMBB->back(),1233 MaxDisp, false, UncondBr));1234 BBInfo[UserMBB->getNumber()].Size += Delta;1235 adjustBBOffsetsAfter(UserMBB);1236 return;1237 }1238 }1239 1240 // What a big block. Find a place within the block to split it.1241 1242 // Try to split the block so it's fully aligned. Compute the latest split1243 // point where we can add a 4-byte branch instruction, and then align to1244 // Align which is the largest possible alignment in the function.1245 const Align Align = MF->getAlignment();1246 unsigned BaseInsertOffset = UserOffset + U.getMaxDisp();1247 LLVM_DEBUG(dbgs() << format("Split in middle of big block before %#x",1248 BaseInsertOffset));1249 1250 // The 4 in the following is for the unconditional branch we'll be inserting1251 // Alignment of the island is handled1252 // inside isOffsetInRange.1253 BaseInsertOffset -= 4;1254 1255 LLVM_DEBUG(dbgs() << format(", adjusted to %#x", BaseInsertOffset)1256 << " la=" << Log2(Align) << '\n');1257 1258 // This could point off the end of the block if we've already got constant1259 // pool entries following this block; only the last one is in the water list.1260 // Back past any possible branches (allow for a conditional and a maximally1261 // long unconditional).1262 if (BaseInsertOffset + 8 >= UserBBI.postOffset()) {1263 BaseInsertOffset = UserBBI.postOffset() - 8;1264 LLVM_DEBUG(dbgs() << format("Move inside block: %#x\n", BaseInsertOffset));1265 }1266 unsigned EndInsertOffset = BaseInsertOffset + 4 +1267 CPEMI->getOperand(2).getImm();1268 MachineBasicBlock::iterator MI = UserMI;1269 ++MI;1270 unsigned CPUIndex = CPUserIndex+1;1271 unsigned NumCPUsers = CPUsers.size();1272 //MachineInstr *LastIT = 0;1273 for (unsigned Offset = UserOffset + TII->getInstSizeInBytes(*UserMI);1274 Offset < BaseInsertOffset;1275 Offset += TII->getInstSizeInBytes(*MI), MI = std::next(MI)) {1276 assert(MI != UserMBB->end() && "Fell off end of block");1277 if (CPUIndex < NumCPUsers && CPUsers[CPUIndex].MI == MI) {1278 CPUser &U = CPUsers[CPUIndex];1279 if (!isOffsetInRange(Offset, EndInsertOffset, U)) {1280 // Shift intertion point by one unit of alignment so it is within reach.1281 BaseInsertOffset -= Align.value();1282 EndInsertOffset -= Align.value();1283 }1284 // This is overly conservative, as we don't account for CPEMIs being1285 // reused within the block, but it doesn't matter much. Also assume CPEs1286 // are added in order with alignment padding. We may eventually be able1287 // to pack the aligned CPEs better.1288 EndInsertOffset += U.CPEMI->getOperand(2).getImm();1289 CPUIndex++;1290 }1291 }1292 1293 NewMBB = splitBlockBeforeInstr(*--MI);1294}1295 1296/// handleConstantPoolUser - Analyze the specified user, checking to see if it1297/// is out-of-range. If so, pick up the constant pool value and move it some1298/// place in-range. Return true if we changed any addresses (thus must run1299/// another pass of branch lengthening), false otherwise.1300bool MipsConstantIslands::handleConstantPoolUser(unsigned CPUserIndex) {1301 CPUser &U = CPUsers[CPUserIndex];1302 MachineInstr *UserMI = U.MI;1303 MachineInstr *CPEMI = U.CPEMI;1304 unsigned CPI = CPEMI->getOperand(1).getIndex();1305 unsigned Size = CPEMI->getOperand(2).getImm();1306 // Compute this only once, it's expensive.1307 unsigned UserOffset = getUserOffset(U);1308 1309 // See if the current entry is within range, or there is a clone of it1310 // in range.1311 int result = findInRangeCPEntry(U, UserOffset);1312 if (result==1) return false;1313 else if (result==2) return true;1314 1315 // Look for water where we can place this CPE.1316 MachineBasicBlock *NewIsland = MF->CreateMachineBasicBlock();1317 MachineBasicBlock *NewMBB;1318 water_iterator IP;1319 if (findAvailableWater(U, UserOffset, IP)) {1320 LLVM_DEBUG(dbgs() << "Found water in range\n");1321 MachineBasicBlock *WaterBB = *IP;1322 1323 // If the original WaterList entry was "new water" on this iteration,1324 // propagate that to the new island. This is just keeping NewWaterList1325 // updated to match the WaterList, which will be updated below.1326 if (NewWaterList.erase(WaterBB))1327 NewWaterList.insert(NewIsland);1328 1329 // The new CPE goes before the following block (NewMBB).1330 NewMBB = &*++WaterBB->getIterator();1331 } else {1332 // No water found.1333 // we first see if a longer form of the instrucion could have reached1334 // the constant. in that case we won't bother to split1335 if (!NoLoadRelaxation) {1336 result = findLongFormInRangeCPEntry(U, UserOffset);1337 if (result != 0) return true;1338 }1339 LLVM_DEBUG(dbgs() << "No water found\n");1340 createNewWater(CPUserIndex, UserOffset, NewMBB);1341 1342 // splitBlockBeforeInstr adds to WaterList, which is important when it is1343 // called while handling branches so that the water will be seen on the1344 // next iteration for constant pools, but in this context, we don't want1345 // it. Check for this so it will be removed from the WaterList.1346 // Also remove any entry from NewWaterList.1347 MachineBasicBlock *WaterBB = &*--NewMBB->getIterator();1348 IP = llvm::find(WaterList, WaterBB);1349 if (IP != WaterList.end())1350 NewWaterList.erase(WaterBB);1351 1352 // We are adding new water. Update NewWaterList.1353 NewWaterList.insert(NewIsland);1354 }1355 1356 // Remove the original WaterList entry; we want subsequent insertions in1357 // this vicinity to go after the one we're about to insert. This1358 // considerably reduces the number of times we have to move the same CPE1359 // more than once and is also important to ensure the algorithm terminates.1360 if (IP != WaterList.end())1361 WaterList.erase(IP);1362 1363 // Okay, we know we can put an island before NewMBB now, do it!1364 MF->insert(NewMBB->getIterator(), NewIsland);1365 1366 // Update internal data structures to account for the newly inserted MBB.1367 updateForInsertedWaterBlock(NewIsland);1368 1369 // Decrement the old entry, and remove it if refcount becomes 0.1370 decrementCPEReferenceCount(CPI, CPEMI);1371 1372 // No existing clone of this CPE is within range.1373 // We will be generating a new clone. Get a UID for it.1374 unsigned ID = createPICLabelUId();1375 1376 // Now that we have an island to add the CPE to, clone the original CPE and1377 // add it to the island.1378 U.HighWaterMark = NewIsland;1379 U.CPEMI = BuildMI(NewIsland, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY))1380 .addImm(ID).addConstantPoolIndex(CPI).addImm(Size);1381 CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1));1382 ++NumCPEs;1383 1384 // Mark the basic block as aligned as required by the const-pool entry.1385 NewIsland->setAlignment(getCPEAlign(*U.CPEMI));1386 1387 // Increase the size of the island block to account for the new entry.1388 BBInfo[NewIsland->getNumber()].Size += Size;1389 adjustBBOffsetsAfter(&*--NewIsland->getIterator());1390 1391 // Finally, change the CPI in the instruction operand to be ID.1392 for (MachineOperand &MO : UserMI->operands())1393 if (MO.isCPI()) {1394 MO.setIndex(ID);1395 break;1396 }1397 1398 LLVM_DEBUG(1399 dbgs() << " Moved CPE to #" << ID << " CPI=" << CPI1400 << format(" offset=%#x\n", BBInfo[NewIsland->getNumber()].Offset));1401 1402 return true;1403}1404 1405/// removeDeadCPEMI - Remove a dead constant pool entry instruction. Update1406/// sizes and offsets of impacted basic blocks.1407void MipsConstantIslands::removeDeadCPEMI(MachineInstr *CPEMI) {1408 MachineBasicBlock *CPEBB = CPEMI->getParent();1409 unsigned Size = CPEMI->getOperand(2).getImm();1410 CPEMI->eraseFromParent();1411 BBInfo[CPEBB->getNumber()].Size -= Size;1412 // All succeeding offsets have the current size value added in, fix this.1413 if (CPEBB->empty()) {1414 BBInfo[CPEBB->getNumber()].Size = 0;1415 1416 // This block no longer needs to be aligned.1417 CPEBB->setAlignment(Align(1));1418 } else {1419 // Entries are sorted by descending alignment, so realign from the front.1420 CPEBB->setAlignment(getCPEAlign(*CPEBB->begin()));1421 }1422 1423 adjustBBOffsetsAfter(CPEBB);1424 // An island has only one predecessor BB and one successor BB. Check if1425 // this BB's predecessor jumps directly to this BB's successor. This1426 // shouldn't happen currently.1427 assert(!BBIsJumpedOver(CPEBB) && "How did this happen?");1428 // FIXME: remove the empty blocks after all the work is done?1429}1430 1431/// removeUnusedCPEntries - Remove constant pool entries whose refcounts1432/// are zero.1433bool MipsConstantIslands::removeUnusedCPEntries() {1434 unsigned MadeChange = false;1435 for (std::vector<CPEntry> &CPEs : CPEntries) {1436 for (CPEntry &CPE : CPEs) {1437 if (CPE.RefCount == 0 && CPE.CPEMI) {1438 removeDeadCPEMI(CPE.CPEMI);1439 CPE.CPEMI = nullptr;1440 MadeChange = true;1441 }1442 }1443 }1444 return MadeChange;1445}1446 1447/// isBBInRange - Returns true if the distance between specific MI and1448/// specific BB can fit in MI's displacement field.1449bool MipsConstantIslands::isBBInRange1450 (MachineInstr *MI,MachineBasicBlock *DestBB, unsigned MaxDisp) {1451 unsigned PCAdj = 4;1452 unsigned BrOffset = getOffsetOf(MI) + PCAdj;1453 unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset;1454 1455 LLVM_DEBUG(dbgs() << "Branch of destination " << printMBBReference(*DestBB)1456 << " from " << printMBBReference(*MI->getParent())1457 << " max delta=" << MaxDisp << " from " << getOffsetOf(MI)1458 << " to " << DestOffset << " offset "1459 << int(DestOffset - BrOffset) << "\t" << *MI);1460 1461 if (BrOffset <= DestOffset) {1462 // Branch before the Dest.1463 if (DestOffset-BrOffset <= MaxDisp)1464 return true;1465 } else {1466 if (BrOffset-DestOffset <= MaxDisp)1467 return true;1468 }1469 return false;1470}1471 1472/// fixupImmediateBr - Fix up an immediate branch whose destination is too far1473/// away to fit in its displacement field.1474bool MipsConstantIslands::fixupImmediateBr(ImmBranch &Br) {1475 MachineInstr *MI = Br.MI;1476 unsigned TargetOperand = branchTargetOperand(MI);1477 MachineBasicBlock *DestBB = MI->getOperand(TargetOperand).getMBB();1478 1479 // Check to see if the DestBB is already in-range.1480 if (isBBInRange(MI, DestBB, Br.MaxDisp))1481 return false;1482 1483 if (!Br.isCond)1484 return fixupUnconditionalBr(Br);1485 return fixupConditionalBr(Br);1486}1487 1488/// fixupUnconditionalBr - Fix up an unconditional branch whose destination is1489/// too far away to fit in its displacement field. If the LR register has been1490/// spilled in the epilogue, then we can use BL to implement a far jump.1491/// Otherwise, add an intermediate branch instruction to a branch.1492bool1493MipsConstantIslands::fixupUnconditionalBr(ImmBranch &Br) {1494 MachineInstr *MI = Br.MI;1495 MachineBasicBlock *MBB = MI->getParent();1496 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB();1497 // Use BL to implement far jump.1498 unsigned BimmX16MaxDisp = ((1 << 16)-1) * 2;1499 if (isBBInRange(MI, DestBB, BimmX16MaxDisp)) {1500 Br.MaxDisp = BimmX16MaxDisp;1501 MI->setDesc(TII->get(Mips::BimmX16));1502 }1503 else {1504 // need to give the math a more careful look here1505 // this is really a segment address and not1506 // a PC relative address. FIXME. But I think that1507 // just reducing the bits by 1 as I've done is correct.1508 // The basic block we are branching too much be longword aligned.1509 // we know that RA is saved because we always save it right now.1510 // this requirement will be relaxed later but we also have an alternate1511 // way to implement this that I will implement that does not need jal.1512 // We should have a way to back out this alignment restriction1513 // if we "can" later. but it is not harmful.1514 //1515 DestBB->setAlignment(Align(4));1516 Br.MaxDisp = ((1<<24)-1) * 2;1517 MI->setDesc(TII->get(Mips::JalB16));1518 }1519 BBInfo[MBB->getNumber()].Size += 2;1520 adjustBBOffsetsAfter(MBB);1521 HasFarJump = true;1522 ++NumUBrFixed;1523 1524 LLVM_DEBUG(dbgs() << " Changed B to long jump " << *MI);1525 1526 return true;1527}1528 1529/// fixupConditionalBr - Fix up a conditional branch whose destination is too1530/// far away to fit in its displacement field. It is converted to an inverse1531/// conditional branch + an unconditional branch to the destination.1532bool1533MipsConstantIslands::fixupConditionalBr(ImmBranch &Br) {1534 MachineInstr *MI = Br.MI;1535 unsigned TargetOperand = branchTargetOperand(MI);1536 MachineBasicBlock *DestBB = MI->getOperand(TargetOperand).getMBB();1537 unsigned Opcode = MI->getOpcode();1538 unsigned LongFormOpcode = longformBranchOpcode(Opcode);1539 unsigned LongFormMaxOff = branchMaxOffsets(LongFormOpcode);1540 1541 // Check to see if the DestBB is already in-range.1542 if (isBBInRange(MI, DestBB, LongFormMaxOff)) {1543 Br.MaxDisp = LongFormMaxOff;1544 MI->setDesc(TII->get(LongFormOpcode));1545 return true;1546 }1547 1548 // Add an unconditional branch to the destination and invert the branch1549 // condition to jump over it:1550 // bteqz L11551 // =>1552 // bnez L21553 // b L11554 // L2:1555 1556 // If the branch is at the end of its MBB and that has a fall-through block,1557 // direct the updated conditional branch to the fall-through block. Otherwise,1558 // split the MBB before the next instruction.1559 MachineBasicBlock *MBB = MI->getParent();1560 MachineInstr *BMI = &MBB->back();1561 bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB);1562 unsigned OppositeBranchOpcode = TII->getOppositeBranchOpc(Opcode);1563 1564 ++NumCBrFixed;1565 if (BMI != MI) {1566 if (std::next(MachineBasicBlock::iterator(MI)) == std::prev(MBB->end()) &&1567 BMI->isUnconditionalBranch()) {1568 // Last MI in the BB is an unconditional branch. Can we simply invert the1569 // condition and swap destinations:1570 // beqz L11571 // b L21572 // =>1573 // bnez L21574 // b L11575 unsigned BMITargetOperand = branchTargetOperand(BMI);1576 MachineBasicBlock *NewDest =1577 BMI->getOperand(BMITargetOperand).getMBB();1578 if (isBBInRange(MI, NewDest, Br.MaxDisp)) {1579 LLVM_DEBUG(1580 dbgs() << " Invert Bcc condition and swap its destination with "1581 << *BMI);1582 MI->setDesc(TII->get(OppositeBranchOpcode));1583 BMI->getOperand(BMITargetOperand).setMBB(DestBB);1584 MI->getOperand(TargetOperand).setMBB(NewDest);1585 return true;1586 }1587 }1588 }1589 1590 if (NeedSplit) {1591 splitBlockBeforeInstr(*MI);1592 // No need for the branch to the next block. We're adding an unconditional1593 // branch to the destination.1594 int delta = TII->getInstSizeInBytes(MBB->back());1595 BBInfo[MBB->getNumber()].Size -= delta;1596 MBB->back().eraseFromParent();1597 // BBInfo[SplitBB].Offset is wrong temporarily, fixed below1598 }1599 MachineBasicBlock *NextBB = &*++MBB->getIterator();1600 1601 LLVM_DEBUG(dbgs() << " Insert B to " << printMBBReference(*DestBB)1602 << " also invert condition and change dest. to "1603 << printMBBReference(*NextBB) << "\n");1604 1605 // Insert a new conditional branch and a new unconditional branch.1606 // Also update the ImmBranch as well as adding a new entry for the new branch.1607 if (MI->getNumExplicitOperands() == 2) {1608 BuildMI(MBB, DebugLoc(), TII->get(OppositeBranchOpcode))1609 .addReg(MI->getOperand(0).getReg())1610 .addMBB(NextBB);1611 } else {1612 BuildMI(MBB, DebugLoc(), TII->get(OppositeBranchOpcode))1613 .addMBB(NextBB);1614 }1615 Br.MI = &MBB->back();1616 BBInfo[MBB->getNumber()].Size += TII->getInstSizeInBytes(MBB->back());1617 BuildMI(MBB, DebugLoc(), TII->get(Br.UncondBr)).addMBB(DestBB);1618 BBInfo[MBB->getNumber()].Size += TII->getInstSizeInBytes(MBB->back());1619 unsigned MaxDisp = getUnconditionalBrDisp(Br.UncondBr);1620 ImmBranches.push_back(ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr));1621 1622 // Remove the old conditional branch. It may or may not still be in MBB.1623 BBInfo[MI->getParent()->getNumber()].Size -= TII->getInstSizeInBytes(*MI);1624 MI->eraseFromParent();1625 adjustBBOffsetsAfter(MBB);1626 return true;1627}1628 1629void MipsConstantIslands::prescanForConstants() {1630 for (MachineBasicBlock &B : *MF) {1631 for (MachineInstr &MI : B) {1632 switch (MI.getDesc().getOpcode()) {1633 case Mips::LwConstant32: {1634 PrescannedForConstants = true;1635 LLVM_DEBUG(dbgs() << "constant island constant " << MI << "\n");1636 LLVM_DEBUG(dbgs() << "num operands " << MI.getNumOperands() << "\n");1637 MachineOperand &Literal = MI.getOperand(1);1638 if (Literal.isImm()) {1639 int64_t V = Literal.getImm();1640 LLVM_DEBUG(dbgs() << "literal " << V << "\n");1641 Type *Int32Ty = Type::getInt32Ty(MF->getFunction().getContext());1642 const Constant *C = ConstantInt::get(Int32Ty, V);1643 unsigned index = MCP->getConstantPoolIndex(C, Align(4));1644 MI.getOperand(2).ChangeToImmediate(index);1645 LLVM_DEBUG(dbgs() << "constant island constant " << MI << "\n");1646 MI.setDesc(TII->get(Mips::LwRxPcTcp16));1647 MI.removeOperand(1);1648 MI.removeOperand(1);1649 MI.addOperand(MachineOperand::CreateCPI(index, 0));1650 }1651 break;1652 }1653 default:1654 break;1655 }1656 }1657 }1658}1659 1660/// Returns a pass that converts branches to long branches.1661FunctionPass *llvm::createMipsConstantIslandPass() {1662 return new MipsConstantIslands();1663}1664