MipsConstantIslandPass.cpp revision 1101cde7707b4dda9385ac399b2ff83e0ef494cd
1//===-- MipsConstantIslandPass.cpp - Emit Pc Relative loads----------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// 11// This pass is used to make Pc relative loads of constants. 12// For now, only Mips16 will use this. 13// 14// Loading constants inline is expensive on Mips16 and it's in general better 15// to place the constant nearby in code space and then it can be loaded with a 16// simple 16 bit load instruction. 17// 18// The constants can be not just numbers but addresses of functions and labels. 19// This can be particularly helpful in static relocation mode for embedded 20// non linux targets. 21// 22// 23 24#define DEBUG_TYPE "mips-constant-islands" 25 26#include "Mips.h" 27#include "MCTargetDesc/MipsBaseInfo.h" 28#include "MipsMachineFunction.h" 29#include "MipsTargetMachine.h" 30#include "llvm/ADT/Statistic.h" 31#include "llvm/CodeGen/MachineBasicBlock.h" 32#include "llvm/CodeGen/MachineFunctionPass.h" 33#include "llvm/CodeGen/MachineInstrBuilder.h" 34#include "llvm/CodeGen/MachineRegisterInfo.h" 35#include "llvm/IR/Function.h" 36#include "llvm/Support/CommandLine.h" 37#include "llvm/Support/Debug.h" 38#include "llvm/Support/InstIterator.h" 39#include "llvm/Support/MathExtras.h" 40#include "llvm/Support/raw_ostream.h" 41#include "llvm/Target/TargetInstrInfo.h" 42#include "llvm/Target/TargetMachine.h" 43#include "llvm/Target/TargetRegisterInfo.h" 44#include "llvm/Support/Format.h" 45#include <algorithm> 46 47using namespace llvm; 48 49STATISTIC(NumCPEs, "Number of constpool entries"); 50STATISTIC(NumSplit, "Number of uncond branches inserted"); 51STATISTIC(NumCBrFixed, "Number of cond branches fixed"); 52STATISTIC(NumUBrFixed, "Number of uncond branches fixed"); 53 54// FIXME: This option should be removed once it has received sufficient testing. 55static cl::opt<bool> 56AlignConstantIslands("mips-align-constant-islands", cl::Hidden, cl::init(true), 57 cl::desc("Align constant islands in code")); 58 59 60// Rather than do make check tests with huge amounts of code, we force 61// the test to use this amount. 62// 63static cl::opt<int> ConstantIslandsSmallOffset( 64 "mips-constant-islands-small-offset", 65 cl::init(0), 66 cl::desc("Make small offsets be this amount for testing purposes"), 67 cl::Hidden); 68 69 70namespace { 71 72 73 typedef MachineBasicBlock::iterator Iter; 74 typedef MachineBasicBlock::reverse_iterator ReverseIter; 75 76 /// MipsConstantIslands - Due to limited PC-relative displacements, Mips 77 /// requires constant pool entries to be scattered among the instructions 78 /// inside a function. To do this, it completely ignores the normal LLVM 79 /// constant pool; instead, it places constants wherever it feels like with 80 /// special instructions. 81 /// 82 /// The terminology used in this pass includes: 83 /// Islands - Clumps of constants placed in the function. 84 /// Water - Potential places where an island could be formed. 85 /// CPE - A constant pool entry that has been placed somewhere, which 86 /// tracks a list of users. 87 88 class MipsConstantIslands : public MachineFunctionPass { 89 90 /// BasicBlockInfo - Information about the offset and size of a single 91 /// basic block. 92 struct BasicBlockInfo { 93 /// Offset - Distance from the beginning of the function to the beginning 94 /// of this basic block. 95 /// 96 /// Offsets are computed assuming worst case padding before an aligned 97 /// block. This means that subtracting basic block offsets always gives a 98 /// conservative estimate of the real distance which may be smaller. 99 /// 100 /// Because worst case padding is used, the computed offset of an aligned 101 /// block may not actually be aligned. 102 unsigned Offset; 103 104 /// Size - Size of the basic block in bytes. If the block contains 105 /// inline assembly, this is a worst case estimate. 106 /// 107 /// The size does not include any alignment padding whether from the 108 /// beginning of the block, or from an aligned jump table at the end. 109 unsigned Size; 110 111 // FIXME: ignore LogAlign for this patch 112 // 113 unsigned postOffset(unsigned LogAlign = 0) const { 114 unsigned PO = Offset + Size; 115 return PO; 116 } 117 118 BasicBlockInfo() : Offset(0), Size(0) {} 119 120 }; 121 122 std::vector<BasicBlockInfo> BBInfo; 123 124 /// WaterList - A sorted list of basic blocks where islands could be placed 125 /// (i.e. blocks that don't fall through to the following block, due 126 /// to a return, unreachable, or unconditional branch). 127 std::vector<MachineBasicBlock*> WaterList; 128 129 /// NewWaterList - The subset of WaterList that was created since the 130 /// previous iteration by inserting unconditional branches. 131 SmallSet<MachineBasicBlock*, 4> NewWaterList; 132 133 typedef std::vector<MachineBasicBlock*>::iterator water_iterator; 134 135 /// CPUser - One user of a constant pool, keeping the machine instruction 136 /// pointer, the constant pool being referenced, and the max displacement 137 /// allowed from the instruction to the CP. The HighWaterMark records the 138 /// highest basic block where a new CPEntry can be placed. To ensure this 139 /// pass terminates, the CP entries are initially placed at the end of the 140 /// function and then move monotonically to lower addresses. The 141 /// exception to this rule is when the current CP entry for a particular 142 /// CPUser is out of range, but there is another CP entry for the same 143 /// constant value in range. We want to use the existing in-range CP 144 /// entry, but if it later moves out of range, the search for new water 145 /// should resume where it left off. The HighWaterMark is used to record 146 /// that point. 147 struct CPUser { 148 MachineInstr *MI; 149 MachineInstr *CPEMI; 150 MachineBasicBlock *HighWaterMark; 151 private: 152 unsigned MaxDisp; 153 unsigned LongFormMaxDisp; // mips16 has 16/32 bit instructions 154 // with different displacements 155 unsigned LongFormOpcode; 156 public: 157 bool NegOk; 158 CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp, 159 bool neg, 160 unsigned longformmaxdisp, unsigned longformopcode) 161 : MI(mi), CPEMI(cpemi), MaxDisp(maxdisp), 162 LongFormMaxDisp(longformmaxdisp), LongFormOpcode(longformopcode), 163 NegOk(neg){ 164 HighWaterMark = CPEMI->getParent(); 165 } 166 /// getMaxDisp - Returns the maximum displacement supported by MI. 167 unsigned getMaxDisp() const { 168 unsigned xMaxDisp = ConstantIslandsSmallOffset? 169 ConstantIslandsSmallOffset: MaxDisp; 170 return xMaxDisp; 171 } 172 unsigned getLongFormMaxDisp() const { 173 return LongFormMaxDisp; 174 } 175 unsigned getLongFormOpcode() const { 176 return LongFormOpcode; 177 } 178 }; 179 180 /// CPUsers - Keep track of all of the machine instructions that use various 181 /// constant pools and their max displacement. 182 std::vector<CPUser> CPUsers; 183 184 /// CPEntry - One per constant pool entry, keeping the machine instruction 185 /// pointer, the constpool index, and the number of CPUser's which 186 /// reference this entry. 187 struct CPEntry { 188 MachineInstr *CPEMI; 189 unsigned CPI; 190 unsigned RefCount; 191 CPEntry(MachineInstr *cpemi, unsigned cpi, unsigned rc = 0) 192 : CPEMI(cpemi), CPI(cpi), RefCount(rc) {} 193 }; 194 195 /// CPEntries - Keep track of all of the constant pool entry machine 196 /// instructions. For each original constpool index (i.e. those that 197 /// existed upon entry to this pass), it keeps a vector of entries. 198 /// Original elements are cloned as we go along; the clones are 199 /// put in the vector of the original element, but have distinct CPIs. 200 std::vector<std::vector<CPEntry> > CPEntries; 201 202 /// ImmBranch - One per immediate branch, keeping the machine instruction 203 /// pointer, conditional or unconditional, the max displacement, 204 /// and (if isCond is true) the corresponding unconditional branch 205 /// opcode. 206 struct ImmBranch { 207 MachineInstr *MI; 208 unsigned MaxDisp : 31; 209 bool isCond : 1; 210 int UncondBr; 211 ImmBranch(MachineInstr *mi, unsigned maxdisp, bool cond, int ubr) 212 : MI(mi), MaxDisp(maxdisp), isCond(cond), UncondBr(ubr) {} 213 }; 214 215 /// ImmBranches - Keep track of all the immediate branch instructions. 216 /// 217 std::vector<ImmBranch> ImmBranches; 218 219 /// HasFarJump - True if any far jump instruction has been emitted during 220 /// the branch fix up pass. 221 bool HasFarJump; 222 223 const TargetMachine &TM; 224 bool IsPIC; 225 unsigned ABI; 226 const MipsSubtarget *STI; 227 const MipsInstrInfo *TII; 228 MipsFunctionInfo *MFI; 229 MachineFunction *MF; 230 MachineConstantPool *MCP; 231 232 unsigned PICLabelUId; 233 bool PrescannedForConstants; 234 235 void initPICLabelUId(unsigned UId) { 236 PICLabelUId = UId; 237 } 238 239 240 unsigned createPICLabelUId() { 241 return PICLabelUId++; 242 } 243 244 public: 245 static char ID; 246 MipsConstantIslands(TargetMachine &tm) 247 : MachineFunctionPass(ID), TM(tm), 248 IsPIC(TM.getRelocationModel() == Reloc::PIC_), 249 ABI(TM.getSubtarget<MipsSubtarget>().getTargetABI()), 250 STI(&TM.getSubtarget<MipsSubtarget>()), MF(0), MCP(0), 251 PrescannedForConstants(false){} 252 253 virtual const char *getPassName() const { 254 return "Mips Constant Islands"; 255 } 256 257 bool runOnMachineFunction(MachineFunction &F); 258 259 void doInitialPlacement(std::vector<MachineInstr*> &CPEMIs); 260 CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI); 261 unsigned getCPELogAlign(const MachineInstr *CPEMI); 262 void initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs); 263 unsigned getOffsetOf(MachineInstr *MI) const; 264 unsigned getUserOffset(CPUser&) const; 265 void dumpBBs(); 266 void verify(); 267 268 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 269 unsigned Disp, bool NegativeOK); 270 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 271 const CPUser &U); 272 273 bool isLongFormOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 274 const CPUser &U); 275 276 void computeBlockSize(MachineBasicBlock *MBB); 277 MachineBasicBlock *splitBlockBeforeInstr(MachineInstr *MI); 278 void updateForInsertedWaterBlock(MachineBasicBlock *NewBB); 279 void adjustBBOffsetsAfter(MachineBasicBlock *BB); 280 bool decrementCPEReferenceCount(unsigned CPI, MachineInstr* CPEMI); 281 int findInRangeCPEntry(CPUser& U, unsigned UserOffset); 282 int findLongFormInRangeCPEntry(CPUser& U, unsigned UserOffset); 283 bool findAvailableWater(CPUser&U, unsigned UserOffset, 284 water_iterator &WaterIter); 285 void createNewWater(unsigned CPUserIndex, unsigned UserOffset, 286 MachineBasicBlock *&NewMBB); 287 bool handleConstantPoolUser(unsigned CPUserIndex); 288 void removeDeadCPEMI(MachineInstr *CPEMI); 289 bool removeUnusedCPEntries(); 290 bool isCPEntryInRange(MachineInstr *MI, unsigned UserOffset, 291 MachineInstr *CPEMI, unsigned Disp, bool NegOk, 292 bool DoDump = false); 293 bool isWaterInRange(unsigned UserOffset, MachineBasicBlock *Water, 294 CPUser &U, unsigned &Growth); 295 bool isBBInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp); 296 bool fixupImmediateBr(ImmBranch &Br); 297 bool fixupConditionalBr(ImmBranch &Br); 298 bool fixupUnconditionalBr(ImmBranch &Br); 299 300 void prescanForConstants(); 301 302 private: 303 304 }; 305 306 char MipsConstantIslands::ID = 0; 307} // end of anonymous namespace 308 309 310bool MipsConstantIslands::isLongFormOffsetInRange 311 (unsigned UserOffset, unsigned TrialOffset, 312 const CPUser &U) { 313 return isOffsetInRange(UserOffset, TrialOffset, 314 U.getLongFormMaxDisp(), U.NegOk); 315} 316 317bool MipsConstantIslands::isOffsetInRange 318 (unsigned UserOffset, unsigned TrialOffset, 319 const CPUser &U) { 320 return isOffsetInRange(UserOffset, TrialOffset, 321 U.getMaxDisp(), U.NegOk); 322} 323/// print block size and offset information - debugging 324void MipsConstantIslands::dumpBBs() { 325 DEBUG({ 326 for (unsigned J = 0, E = BBInfo.size(); J !=E; ++J) { 327 const BasicBlockInfo &BBI = BBInfo[J]; 328 dbgs() << format("%08x BB#%u\t", BBI.Offset, J) 329 << format(" size=%#x\n", BBInfo[J].Size); 330 } 331 }); 332} 333/// createMipsLongBranchPass - Returns a pass that converts branches to long 334/// branches. 335FunctionPass *llvm::createMipsConstantIslandPass(MipsTargetMachine &tm) { 336 return new MipsConstantIslands(tm); 337} 338 339bool MipsConstantIslands::runOnMachineFunction(MachineFunction &mf) { 340 // The intention is for this to be a mips16 only pass for now 341 // FIXME: 342 MF = &mf; 343 MCP = mf.getConstantPool(); 344 DEBUG(dbgs() << "constant island machine function " << "\n"); 345 if (!TM.getSubtarget<MipsSubtarget>().inMips16Mode() || 346 !MipsSubtarget::useConstantIslands()) { 347 return false; 348 } 349 TII = (const MipsInstrInfo*)MF->getTarget().getInstrInfo(); 350 MFI = MF->getInfo<MipsFunctionInfo>(); 351 DEBUG(dbgs() << "constant island processing " << "\n"); 352 // 353 // will need to make predermination if there is any constants we need to 354 // put in constant islands. TBD. 355 // 356 if (!PrescannedForConstants) prescanForConstants(); 357 358 HasFarJump = false; 359 // This pass invalidates liveness information when it splits basic blocks. 360 MF->getRegInfo().invalidateLiveness(); 361 362 // Renumber all of the machine basic blocks in the function, guaranteeing that 363 // the numbers agree with the position of the block in the function. 364 MF->RenumberBlocks(); 365 366 bool MadeChange = false; 367 368 // Perform the initial placement of the constant pool entries. To start with, 369 // we put them all at the end of the function. 370 std::vector<MachineInstr*> CPEMIs; 371 if (!MCP->isEmpty()) 372 doInitialPlacement(CPEMIs); 373 374 /// The next UID to take is the first unused one. 375 initPICLabelUId(CPEMIs.size()); 376 377 // Do the initial scan of the function, building up information about the 378 // sizes of each block, the location of all the water, and finding all of the 379 // constant pool users. 380 initializeFunctionInfo(CPEMIs); 381 CPEMIs.clear(); 382 DEBUG(dumpBBs()); 383 384 /// Remove dead constant pool entries. 385 MadeChange |= removeUnusedCPEntries(); 386 387 // Iteratively place constant pool entries and fix up branches until there 388 // is no change. 389 unsigned NoCPIters = 0, NoBRIters = 0; 390 (void)NoBRIters; 391 while (true) { 392 DEBUG(dbgs() << "Beginning CP iteration #" << NoCPIters << '\n'); 393 bool CPChange = false; 394 for (unsigned i = 0, e = CPUsers.size(); i != e; ++i) 395 CPChange |= handleConstantPoolUser(i); 396 if (CPChange && ++NoCPIters > 30) 397 report_fatal_error("Constant Island pass failed to converge!"); 398 DEBUG(dumpBBs()); 399 400 // Clear NewWaterList now. If we split a block for branches, it should 401 // appear as "new water" for the next iteration of constant pool placement. 402 NewWaterList.clear(); 403 404 DEBUG(dbgs() << "Beginning BR iteration #" << NoBRIters << '\n'); 405 bool BRChange = false; 406#ifdef IN_PROGRESS 407 for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i) 408 BRChange |= fixupImmediateBr(ImmBranches[i]); 409 if (BRChange && ++NoBRIters > 30) 410 report_fatal_error("Branch Fix Up pass failed to converge!"); 411 DEBUG(dumpBBs()); 412#endif 413 if (!CPChange && !BRChange) 414 break; 415 MadeChange = true; 416 } 417 418 DEBUG(dbgs() << '\n'; dumpBBs()); 419 420 BBInfo.clear(); 421 WaterList.clear(); 422 CPUsers.clear(); 423 CPEntries.clear(); 424 ImmBranches.clear(); 425 return MadeChange; 426} 427 428/// doInitialPlacement - Perform the initial placement of the constant pool 429/// entries. To start with, we put them all at the end of the function. 430void 431MipsConstantIslands::doInitialPlacement(std::vector<MachineInstr*> &CPEMIs) { 432 // Create the basic block to hold the CPE's. 433 MachineBasicBlock *BB = MF->CreateMachineBasicBlock(); 434 MF->push_back(BB); 435 436 437 // MachineConstantPool measures alignment in bytes. We measure in log2(bytes). 438 unsigned MaxAlign = Log2_32(MCP->getConstantPoolAlignment()); 439 440 // Mark the basic block as required by the const-pool. 441 // If AlignConstantIslands isn't set, use 4-byte alignment for everything. 442 BB->setAlignment(AlignConstantIslands ? MaxAlign : 2); 443 444 // The function needs to be as aligned as the basic blocks. The linker may 445 // move functions around based on their alignment. 446 MF->ensureAlignment(BB->getAlignment()); 447 448 // Order the entries in BB by descending alignment. That ensures correct 449 // alignment of all entries as long as BB is sufficiently aligned. Keep 450 // track of the insertion point for each alignment. We are going to bucket 451 // sort the entries as they are created. 452 SmallVector<MachineBasicBlock::iterator, 8> InsPoint(MaxAlign + 1, BB->end()); 453 454 // Add all of the constants from the constant pool to the end block, use an 455 // identity mapping of CPI's to CPE's. 456 const std::vector<MachineConstantPoolEntry> &CPs = MCP->getConstants(); 457 458 const DataLayout &TD = *MF->getTarget().getDataLayout(); 459 for (unsigned i = 0, e = CPs.size(); i != e; ++i) { 460 unsigned Size = TD.getTypeAllocSize(CPs[i].getType()); 461 assert(Size >= 4 && "Too small constant pool entry"); 462 unsigned Align = CPs[i].getAlignment(); 463 assert(isPowerOf2_32(Align) && "Invalid alignment"); 464 // Verify that all constant pool entries are a multiple of their alignment. 465 // If not, we would have to pad them out so that instructions stay aligned. 466 assert((Size % Align) == 0 && "CP Entry not multiple of 4 bytes!"); 467 468 // Insert CONSTPOOL_ENTRY before entries with a smaller alignment. 469 unsigned LogAlign = Log2_32(Align); 470 MachineBasicBlock::iterator InsAt = InsPoint[LogAlign]; 471 472 MachineInstr *CPEMI = 473 BuildMI(*BB, InsAt, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY)) 474 .addImm(i).addConstantPoolIndex(i).addImm(Size); 475 476 CPEMIs.push_back(CPEMI); 477 478 // Ensure that future entries with higher alignment get inserted before 479 // CPEMI. This is bucket sort with iterators. 480 for (unsigned a = LogAlign + 1; a <= MaxAlign; ++a) 481 if (InsPoint[a] == InsAt) 482 InsPoint[a] = CPEMI; 483 // Add a new CPEntry, but no corresponding CPUser yet. 484 std::vector<CPEntry> CPEs; 485 CPEs.push_back(CPEntry(CPEMI, i)); 486 CPEntries.push_back(CPEs); 487 ++NumCPEs; 488 DEBUG(dbgs() << "Moved CPI#" << i << " to end of function, size = " 489 << Size << ", align = " << Align <<'\n'); 490 } 491 DEBUG(BB->dump()); 492} 493 494/// BBHasFallthrough - Return true if the specified basic block can fallthrough 495/// into the block immediately after it. 496static bool BBHasFallthrough(MachineBasicBlock *MBB) { 497 // Get the next machine basic block in the function. 498 MachineFunction::iterator MBBI = MBB; 499 // Can't fall off end of function. 500 if (llvm::next(MBBI) == MBB->getParent()->end()) 501 return false; 502 503 MachineBasicBlock *NextBB = llvm::next(MBBI); 504 for (MachineBasicBlock::succ_iterator I = MBB->succ_begin(), 505 E = MBB->succ_end(); I != E; ++I) 506 if (*I == NextBB) 507 return true; 508 509 return false; 510} 511 512/// findConstPoolEntry - Given the constpool index and CONSTPOOL_ENTRY MI, 513/// look up the corresponding CPEntry. 514MipsConstantIslands::CPEntry 515*MipsConstantIslands::findConstPoolEntry(unsigned CPI, 516 const MachineInstr *CPEMI) { 517 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 518 // Number of entries per constpool index should be small, just do a 519 // linear search. 520 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 521 if (CPEs[i].CPEMI == CPEMI) 522 return &CPEs[i]; 523 } 524 return NULL; 525} 526 527/// getCPELogAlign - Returns the required alignment of the constant pool entry 528/// represented by CPEMI. Alignment is measured in log2(bytes) units. 529unsigned MipsConstantIslands::getCPELogAlign(const MachineInstr *CPEMI) { 530 assert(CPEMI && CPEMI->getOpcode() == Mips::CONSTPOOL_ENTRY); 531 532 // Everything is 4-byte aligned unless AlignConstantIslands is set. 533 if (!AlignConstantIslands) 534 return 2; 535 536 unsigned CPI = CPEMI->getOperand(1).getIndex(); 537 assert(CPI < MCP->getConstants().size() && "Invalid constant pool index."); 538 unsigned Align = MCP->getConstants()[CPI].getAlignment(); 539 assert(isPowerOf2_32(Align) && "Invalid CPE alignment"); 540 return Log2_32(Align); 541} 542 543/// initializeFunctionInfo - Do the initial scan of the function, building up 544/// information about the sizes of each block, the location of all the water, 545/// and finding all of the constant pool users. 546void MipsConstantIslands:: 547initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs) { 548 BBInfo.clear(); 549 BBInfo.resize(MF->getNumBlockIDs()); 550 551 // First thing, compute the size of all basic blocks, and see if the function 552 // has any inline assembly in it. If so, we have to be conservative about 553 // alignment assumptions, as we don't know for sure the size of any 554 // instructions in the inline assembly. 555 for (MachineFunction::iterator I = MF->begin(), E = MF->end(); I != E; ++I) 556 computeBlockSize(I); 557 558 559 // Compute block offsets. 560 adjustBBOffsetsAfter(MF->begin()); 561 562 // Now go back through the instructions and build up our data structures. 563 for (MachineFunction::iterator MBBI = MF->begin(), E = MF->end(); 564 MBBI != E; ++MBBI) { 565 MachineBasicBlock &MBB = *MBBI; 566 567 // If this block doesn't fall through into the next MBB, then this is 568 // 'water' that a constant pool island could be placed. 569 if (!BBHasFallthrough(&MBB)) 570 WaterList.push_back(&MBB); 571 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); 572 I != E; ++I) { 573 if (I->isDebugValue()) 574 continue; 575 576 int Opc = I->getOpcode(); 577#ifdef IN_PROGRESS 578 if (I->isBranch()) { 579 bool isCond = false; 580 unsigned Bits = 0; 581 unsigned Scale = 1; 582 int UOpc = Opc; 583 switch (Opc) { 584 default: 585 continue; // Ignore other JT branches 586 } 587 // Record this immediate branch. 588 unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale; 589 ImmBranches.push_back(ImmBranch(I, MaxOffs, isCond, UOpc)); 590 } 591#endif 592 593 if (Opc == Mips::CONSTPOOL_ENTRY) 594 continue; 595 596 597 // Scan the instructions for constant pool operands. 598 for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) 599 if (I->getOperand(op).isCPI()) { 600 601 // We found one. The addressing mode tells us the max displacement 602 // from the PC that this instruction permits. 603 604 // Basic size info comes from the TSFlags field. 605 unsigned Bits = 0; 606 unsigned Scale = 1; 607 bool NegOk = false; 608 unsigned LongFormBits = 0; 609 unsigned LongFormScale = 0; 610 unsigned LongFormOpcode = 0; 611 switch (Opc) { 612 default: 613 llvm_unreachable("Unknown addressing mode for CP reference!"); 614 case Mips::LwRxPcTcp16: 615 Bits = 8; 616 Scale = 4; 617 LongFormOpcode = Mips::LwRxPcTcpX16; 618 break; 619 case Mips::LwRxPcTcpX16: 620 Bits = 16; 621 Scale = 1; 622 NegOk = true; 623 break; 624 } 625 // Remember that this is a user of a CP entry. 626 unsigned CPI = I->getOperand(op).getIndex(); 627 MachineInstr *CPEMI = CPEMIs[CPI]; 628 unsigned MaxOffs = ((1 << Bits)-1) * Scale; 629 unsigned LongFormMaxOffs = ((1 << LongFormBits)-1) * LongFormScale; 630 CPUsers.push_back(CPUser(I, CPEMI, MaxOffs, NegOk, 631 LongFormMaxOffs, LongFormOpcode)); 632 633 // Increment corresponding CPEntry reference count. 634 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI); 635 assert(CPE && "Cannot find a corresponding CPEntry!"); 636 CPE->RefCount++; 637 638 // Instructions can only use one CP entry, don't bother scanning the 639 // rest of the operands. 640 break; 641 642 } 643 644 } 645 } 646 647} 648 649/// computeBlockSize - Compute the size and some alignment information for MBB. 650/// This function updates BBInfo directly. 651void MipsConstantIslands::computeBlockSize(MachineBasicBlock *MBB) { 652 BasicBlockInfo &BBI = BBInfo[MBB->getNumber()]; 653 BBI.Size = 0; 654 655 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E; 656 ++I) 657 BBI.Size += TII->GetInstSizeInBytes(I); 658 659} 660 661/// getOffsetOf - Return the current offset of the specified machine instruction 662/// from the start of the function. This offset changes as stuff is moved 663/// around inside the function. 664unsigned MipsConstantIslands::getOffsetOf(MachineInstr *MI) const { 665 MachineBasicBlock *MBB = MI->getParent(); 666 667 // The offset is composed of two things: the sum of the sizes of all MBB's 668 // before this instruction's block, and the offset from the start of the block 669 // it is in. 670 unsigned Offset = BBInfo[MBB->getNumber()].Offset; 671 672 // Sum instructions before MI in MBB. 673 for (MachineBasicBlock::iterator I = MBB->begin(); &*I != MI; ++I) { 674 assert(I != MBB->end() && "Didn't find MI in its own basic block?"); 675 Offset += TII->GetInstSizeInBytes(I); 676 } 677 return Offset; 678} 679 680/// CompareMBBNumbers - Little predicate function to sort the WaterList by MBB 681/// ID. 682static bool CompareMBBNumbers(const MachineBasicBlock *LHS, 683 const MachineBasicBlock *RHS) { 684 return LHS->getNumber() < RHS->getNumber(); 685} 686 687/// updateForInsertedWaterBlock - When a block is newly inserted into the 688/// machine function, it upsets all of the block numbers. Renumber the blocks 689/// and update the arrays that parallel this numbering. 690void MipsConstantIslands::updateForInsertedWaterBlock 691 (MachineBasicBlock *NewBB) { 692 // Renumber the MBB's to keep them consecutive. 693 NewBB->getParent()->RenumberBlocks(NewBB); 694 695 // Insert an entry into BBInfo to align it properly with the (newly 696 // renumbered) block numbers. 697 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo()); 698 699 // Next, update WaterList. Specifically, we need to add NewMBB as having 700 // available water after it. 701 water_iterator IP = 702 std::lower_bound(WaterList.begin(), WaterList.end(), NewBB, 703 CompareMBBNumbers); 704 WaterList.insert(IP, NewBB); 705} 706 707unsigned MipsConstantIslands::getUserOffset(CPUser &U) const { 708 return getOffsetOf(U.MI); 709} 710 711/// Split the basic block containing MI into two blocks, which are joined by 712/// an unconditional branch. Update data structures and renumber blocks to 713/// account for this change and returns the newly created block. 714MachineBasicBlock *MipsConstantIslands::splitBlockBeforeInstr 715 (MachineInstr *MI) { 716 MachineBasicBlock *OrigBB = MI->getParent(); 717 718 // Create a new MBB for the code after the OrigBB. 719 MachineBasicBlock *NewBB = 720 MF->CreateMachineBasicBlock(OrigBB->getBasicBlock()); 721 MachineFunction::iterator MBBI = OrigBB; ++MBBI; 722 MF->insert(MBBI, NewBB); 723 724 // Splice the instructions starting with MI over to NewBB. 725 NewBB->splice(NewBB->end(), OrigBB, MI, OrigBB->end()); 726 727 // Add an unconditional branch from OrigBB to NewBB. 728 // Note the new unconditional branch is not being recorded. 729 // There doesn't seem to be meaningful DebugInfo available; this doesn't 730 // correspond to anything in the source. 731 BuildMI(OrigBB, DebugLoc(), TII->get(Mips::BimmX16)).addMBB(NewBB); 732 ++NumSplit; 733 734 // Update the CFG. All succs of OrigBB are now succs of NewBB. 735 NewBB->transferSuccessors(OrigBB); 736 737 // OrigBB branches to NewBB. 738 OrigBB->addSuccessor(NewBB); 739 740 // Update internal data structures to account for the newly inserted MBB. 741 // This is almost the same as updateForInsertedWaterBlock, except that 742 // the Water goes after OrigBB, not NewBB. 743 MF->RenumberBlocks(NewBB); 744 745 // Insert an entry into BBInfo to align it properly with the (newly 746 // renumbered) block numbers. 747 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo()); 748 749 // Next, update WaterList. Specifically, we need to add OrigMBB as having 750 // available water after it (but not if it's already there, which happens 751 // when splitting before a conditional branch that is followed by an 752 // unconditional branch - in that case we want to insert NewBB). 753 water_iterator IP = 754 std::lower_bound(WaterList.begin(), WaterList.end(), OrigBB, 755 CompareMBBNumbers); 756 MachineBasicBlock* WaterBB = *IP; 757 if (WaterBB == OrigBB) 758 WaterList.insert(llvm::next(IP), NewBB); 759 else 760 WaterList.insert(IP, OrigBB); 761 NewWaterList.insert(OrigBB); 762 763 // Figure out how large the OrigBB is. As the first half of the original 764 // block, it cannot contain a tablejump. The size includes 765 // the new jump we added. (It should be possible to do this without 766 // recounting everything, but it's very confusing, and this is rarely 767 // executed.) 768 computeBlockSize(OrigBB); 769 770 // Figure out how large the NewMBB is. As the second half of the original 771 // block, it may contain a tablejump. 772 computeBlockSize(NewBB); 773 774 // All BBOffsets following these blocks must be modified. 775 adjustBBOffsetsAfter(OrigBB); 776 777 return NewBB; 778} 779 780 781 782/// isOffsetInRange - Checks whether UserOffset (the location of a constant pool 783/// reference) is within MaxDisp of TrialOffset (a proposed location of a 784/// constant pool entry). 785bool MipsConstantIslands::isOffsetInRange(unsigned UserOffset, 786 unsigned TrialOffset, unsigned MaxDisp, 787 bool NegativeOK) { 788 if (UserOffset <= TrialOffset) { 789 // User before the Trial. 790 if (TrialOffset - UserOffset <= MaxDisp) 791 return true; 792 } else if (NegativeOK) { 793 if (UserOffset - TrialOffset <= MaxDisp) 794 return true; 795 } 796 return false; 797} 798 799/// isWaterInRange - Returns true if a CPE placed after the specified 800/// Water (a basic block) will be in range for the specific MI. 801/// 802/// Compute how much the function will grow by inserting a CPE after Water. 803bool MipsConstantIslands::isWaterInRange(unsigned UserOffset, 804 MachineBasicBlock* Water, CPUser &U, 805 unsigned &Growth) { 806 unsigned CPELogAlign = getCPELogAlign(U.CPEMI); 807 unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset(CPELogAlign); 808 unsigned NextBlockOffset, NextBlockAlignment; 809 MachineFunction::const_iterator NextBlock = Water; 810 if (++NextBlock == MF->end()) { 811 NextBlockOffset = BBInfo[Water->getNumber()].postOffset(); 812 NextBlockAlignment = 0; 813 } else { 814 NextBlockOffset = BBInfo[NextBlock->getNumber()].Offset; 815 NextBlockAlignment = NextBlock->getAlignment(); 816 } 817 unsigned Size = U.CPEMI->getOperand(2).getImm(); 818 unsigned CPEEnd = CPEOffset + Size; 819 820 // The CPE may be able to hide in the alignment padding before the next 821 // block. It may also cause more padding to be required if it is more aligned 822 // that the next block. 823 if (CPEEnd > NextBlockOffset) { 824 Growth = CPEEnd - NextBlockOffset; 825 // Compute the padding that would go at the end of the CPE to align the next 826 // block. 827 Growth += OffsetToAlignment(CPEEnd, 1u << NextBlockAlignment); 828 829 // If the CPE is to be inserted before the instruction, that will raise 830 // the offset of the instruction. Also account for unknown alignment padding 831 // in blocks between CPE and the user. 832 if (CPEOffset < UserOffset) 833 UserOffset += Growth; 834 } else 835 // CPE fits in existing padding. 836 Growth = 0; 837 838 return isOffsetInRange(UserOffset, CPEOffset, U); 839} 840 841/// isCPEntryInRange - Returns true if the distance between specific MI and 842/// specific ConstPool entry instruction can fit in MI's displacement field. 843bool MipsConstantIslands::isCPEntryInRange 844 (MachineInstr *MI, unsigned UserOffset, 845 MachineInstr *CPEMI, unsigned MaxDisp, 846 bool NegOk, bool DoDump) { 847 unsigned CPEOffset = getOffsetOf(CPEMI); 848 849 if (DoDump) { 850 DEBUG({ 851 unsigned Block = MI->getParent()->getNumber(); 852 const BasicBlockInfo &BBI = BBInfo[Block]; 853 dbgs() << "User of CPE#" << CPEMI->getOperand(0).getImm() 854 << " max delta=" << MaxDisp 855 << format(" insn address=%#x", UserOffset) 856 << " in BB#" << Block << ": " 857 << format("%#x-%x\t", BBI.Offset, BBI.postOffset()) << *MI 858 << format("CPE address=%#x offset=%+d: ", CPEOffset, 859 int(CPEOffset-UserOffset)); 860 }); 861 } 862 863 return isOffsetInRange(UserOffset, CPEOffset, MaxDisp, NegOk); 864} 865 866#ifndef NDEBUG 867/// BBIsJumpedOver - Return true of the specified basic block's only predecessor 868/// unconditionally branches to its only successor. 869static bool BBIsJumpedOver(MachineBasicBlock *MBB) { 870 if (MBB->pred_size() != 1 || MBB->succ_size() != 1) 871 return false; 872 MachineBasicBlock *Succ = *MBB->succ_begin(); 873 MachineBasicBlock *Pred = *MBB->pred_begin(); 874 MachineInstr *PredMI = &Pred->back(); 875 if (PredMI->getOpcode() == Mips::BimmX16) 876 return PredMI->getOperand(0).getMBB() == Succ; 877 return false; 878} 879#endif 880 881void MipsConstantIslands::adjustBBOffsetsAfter(MachineBasicBlock *BB) { 882 unsigned BBNum = BB->getNumber(); 883 for(unsigned i = BBNum + 1, e = MF->getNumBlockIDs(); i < e; ++i) { 884 // Get the offset and known bits at the end of the layout predecessor. 885 // Include the alignment of the current block. 886 unsigned Offset = BBInfo[i - 1].Offset + BBInfo[i - 1].Size; 887 BBInfo[i].Offset = Offset; 888 } 889} 890 891/// decrementCPEReferenceCount - find the constant pool entry with index CPI 892/// and instruction CPEMI, and decrement its refcount. If the refcount 893/// becomes 0 remove the entry and instruction. Returns true if we removed 894/// the entry, false if we didn't. 895 896bool MipsConstantIslands::decrementCPEReferenceCount(unsigned CPI, 897 MachineInstr *CPEMI) { 898 // Find the old entry. Eliminate it if it is no longer used. 899 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI); 900 assert(CPE && "Unexpected!"); 901 if (--CPE->RefCount == 0) { 902 removeDeadCPEMI(CPEMI); 903 CPE->CPEMI = NULL; 904 --NumCPEs; 905 return true; 906 } 907 return false; 908} 909 910/// LookForCPEntryInRange - see if the currently referenced CPE is in range; 911/// if not, see if an in-range clone of the CPE is in range, and if so, 912/// change the data structures so the user references the clone. Returns: 913/// 0 = no existing entry found 914/// 1 = entry found, and there were no code insertions or deletions 915/// 2 = entry found, and there were code insertions or deletions 916int MipsConstantIslands::findInRangeCPEntry(CPUser& U, unsigned UserOffset) 917{ 918 MachineInstr *UserMI = U.MI; 919 MachineInstr *CPEMI = U.CPEMI; 920 921 // Check to see if the CPE is already in-range. 922 if (isCPEntryInRange(UserMI, UserOffset, CPEMI, U.getMaxDisp(), U.NegOk, 923 true)) { 924 DEBUG(dbgs() << "In range\n"); 925 return 1; 926 } 927 928 // No. Look for previously created clones of the CPE that are in range. 929 unsigned CPI = CPEMI->getOperand(1).getIndex(); 930 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 931 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 932 // We already tried this one 933 if (CPEs[i].CPEMI == CPEMI) 934 continue; 935 // Removing CPEs can leave empty entries, skip 936 if (CPEs[i].CPEMI == NULL) 937 continue; 938 if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, U.getMaxDisp(), 939 U.NegOk)) { 940 DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" 941 << CPEs[i].CPI << "\n"); 942 // Point the CPUser node to the replacement 943 U.CPEMI = CPEs[i].CPEMI; 944 // Change the CPI in the instruction operand to refer to the clone. 945 for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j) 946 if (UserMI->getOperand(j).isCPI()) { 947 UserMI->getOperand(j).setIndex(CPEs[i].CPI); 948 break; 949 } 950 // Adjust the refcount of the clone... 951 CPEs[i].RefCount++; 952 // ...and the original. If we didn't remove the old entry, none of the 953 // addresses changed, so we don't need another pass. 954 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1; 955 } 956 } 957 return 0; 958} 959 960/// LookForCPEntryInRange - see if the currently referenced CPE is in range; 961/// This version checks if the longer form of the instruction can be used to 962/// to satisfy things. 963/// if not, see if an in-range clone of the CPE is in range, and if so, 964/// change the data structures so the user references the clone. Returns: 965/// 0 = no existing entry found 966/// 1 = entry found, and there were no code insertions or deletions 967/// 2 = entry found, and there were code insertions or deletions 968int MipsConstantIslands::findLongFormInRangeCPEntry 969 (CPUser& U, unsigned UserOffset) 970{ 971 MachineInstr *UserMI = U.MI; 972 MachineInstr *CPEMI = U.CPEMI; 973 974 // Check to see if the CPE is already in-range. 975 if (isCPEntryInRange(UserMI, UserOffset, CPEMI, 976 U.getLongFormMaxDisp(), U.NegOk, 977 true)) { 978 DEBUG(dbgs() << "In range\n"); 979 UserMI->setDesc(TII->get(U.getLongFormOpcode())); 980 return 2; // instruction is longer length now 981 } 982 983 // No. Look for previously created clones of the CPE that are in range. 984 unsigned CPI = CPEMI->getOperand(1).getIndex(); 985 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 986 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 987 // We already tried this one 988 if (CPEs[i].CPEMI == CPEMI) 989 continue; 990 // Removing CPEs can leave empty entries, skip 991 if (CPEs[i].CPEMI == NULL) 992 continue; 993 if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, 994 U.getLongFormMaxDisp(), U.NegOk)) { 995 DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" 996 << CPEs[i].CPI << "\n"); 997 // Point the CPUser node to the replacement 998 U.CPEMI = CPEs[i].CPEMI; 999 // Change the CPI in the instruction operand to refer to the clone. 1000 for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j) 1001 if (UserMI->getOperand(j).isCPI()) { 1002 UserMI->getOperand(j).setIndex(CPEs[i].CPI); 1003 break; 1004 } 1005 // Adjust the refcount of the clone... 1006 CPEs[i].RefCount++; 1007 // ...and the original. If we didn't remove the old entry, none of the 1008 // addresses changed, so we don't need another pass. 1009 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1; 1010 } 1011 } 1012 return 0; 1013} 1014 1015/// getUnconditionalBrDisp - Returns the maximum displacement that can fit in 1016/// the specific unconditional branch instruction. 1017static inline unsigned getUnconditionalBrDisp(int Opc) { 1018 switch (Opc) { 1019 case Mips::BimmX16: 1020 return ((1<<16)-1)*2; 1021 default: 1022 break; 1023 } 1024 return ((1<<16)-1)*2; 1025} 1026 1027/// findAvailableWater - Look for an existing entry in the WaterList in which 1028/// we can place the CPE referenced from U so it's within range of U's MI. 1029/// Returns true if found, false if not. If it returns true, WaterIter 1030/// is set to the WaterList entry. 1031/// To ensure that this pass 1032/// terminates, the CPE location for a particular CPUser is only allowed to 1033/// move to a lower address, so search backward from the end of the list and 1034/// prefer the first water that is in range. 1035bool MipsConstantIslands::findAvailableWater(CPUser &U, unsigned UserOffset, 1036 water_iterator &WaterIter) { 1037 if (WaterList.empty()) 1038 return false; 1039 1040 unsigned BestGrowth = ~0u; 1041 for (water_iterator IP = prior(WaterList.end()), B = WaterList.begin();; 1042 --IP) { 1043 MachineBasicBlock* WaterBB = *IP; 1044 // Check if water is in range and is either at a lower address than the 1045 // current "high water mark" or a new water block that was created since 1046 // the previous iteration by inserting an unconditional branch. In the 1047 // latter case, we want to allow resetting the high water mark back to 1048 // this new water since we haven't seen it before. Inserting branches 1049 // should be relatively uncommon and when it does happen, we want to be 1050 // sure to take advantage of it for all the CPEs near that block, so that 1051 // we don't insert more branches than necessary. 1052 unsigned Growth; 1053 if (isWaterInRange(UserOffset, WaterBB, U, Growth) && 1054 (WaterBB->getNumber() < U.HighWaterMark->getNumber() || 1055 NewWaterList.count(WaterBB)) && Growth < BestGrowth) { 1056 // This is the least amount of required padding seen so far. 1057 BestGrowth = Growth; 1058 WaterIter = IP; 1059 DEBUG(dbgs() << "Found water after BB#" << WaterBB->getNumber() 1060 << " Growth=" << Growth << '\n'); 1061 1062 // Keep looking unless it is perfect. 1063 if (BestGrowth == 0) 1064 return true; 1065 } 1066 if (IP == B) 1067 break; 1068 } 1069 return BestGrowth != ~0u; 1070} 1071 1072/// createNewWater - No existing WaterList entry will work for 1073/// CPUsers[CPUserIndex], so create a place to put the CPE. The end of the 1074/// block is used if in range, and the conditional branch munged so control 1075/// flow is correct. Otherwise the block is split to create a hole with an 1076/// unconditional branch around it. In either case NewMBB is set to a 1077/// block following which the new island can be inserted (the WaterList 1078/// is not adjusted). 1079void MipsConstantIslands::createNewWater(unsigned CPUserIndex, 1080 unsigned UserOffset, 1081 MachineBasicBlock *&NewMBB) { 1082 CPUser &U = CPUsers[CPUserIndex]; 1083 MachineInstr *UserMI = U.MI; 1084 MachineInstr *CPEMI = U.CPEMI; 1085 unsigned CPELogAlign = getCPELogAlign(CPEMI); 1086 MachineBasicBlock *UserMBB = UserMI->getParent(); 1087 const BasicBlockInfo &UserBBI = BBInfo[UserMBB->getNumber()]; 1088 1089 // If the block does not end in an unconditional branch already, and if the 1090 // end of the block is within range, make new water there. 1091 if (BBHasFallthrough(UserMBB)) { 1092 // Size of branch to insert. 1093 unsigned Delta = 2; 1094 // Compute the offset where the CPE will begin. 1095 unsigned CPEOffset = UserBBI.postOffset(CPELogAlign) + Delta; 1096 1097 if (isOffsetInRange(UserOffset, CPEOffset, U)) { 1098 DEBUG(dbgs() << "Split at end of BB#" << UserMBB->getNumber() 1099 << format(", expected CPE offset %#x\n", CPEOffset)); 1100 NewMBB = llvm::next(MachineFunction::iterator(UserMBB)); 1101 // Add an unconditional branch from UserMBB to fallthrough block. Record 1102 // it for branch lengthening; this new branch will not get out of range, 1103 // but if the preceding conditional branch is out of range, the targets 1104 // will be exchanged, and the altered branch may be out of range, so the 1105 // machinery has to know about it. 1106 int UncondBr = Mips::BimmX16; 1107 BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB); 1108 unsigned MaxDisp = getUnconditionalBrDisp(UncondBr); 1109 ImmBranches.push_back(ImmBranch(&UserMBB->back(), 1110 MaxDisp, false, UncondBr)); 1111 BBInfo[UserMBB->getNumber()].Size += Delta; 1112 adjustBBOffsetsAfter(UserMBB); 1113 return; 1114 } 1115 } 1116 1117 // What a big block. Find a place within the block to split it. 1118 1119 // Try to split the block so it's fully aligned. Compute the latest split 1120 // point where we can add a 4-byte branch instruction, and then align to 1121 // LogAlign which is the largest possible alignment in the function. 1122 unsigned LogAlign = MF->getAlignment(); 1123 assert(LogAlign >= CPELogAlign && "Over-aligned constant pool entry"); 1124 unsigned BaseInsertOffset = UserOffset + U.getMaxDisp(); 1125 DEBUG(dbgs() << format("Split in middle of big block before %#x", 1126 BaseInsertOffset)); 1127 1128 // The 4 in the following is for the unconditional branch we'll be inserting 1129 // Alignment of the island is handled 1130 // inside isOffsetInRange. 1131 BaseInsertOffset -= 4; 1132 1133 DEBUG(dbgs() << format(", adjusted to %#x", BaseInsertOffset) 1134 << " la=" << LogAlign << '\n'); 1135 1136 // This could point off the end of the block if we've already got constant 1137 // pool entries following this block; only the last one is in the water list. 1138 // Back past any possible branches (allow for a conditional and a maximally 1139 // long unconditional). 1140 if (BaseInsertOffset + 8 >= UserBBI.postOffset()) { 1141 BaseInsertOffset = UserBBI.postOffset() - 8; 1142 DEBUG(dbgs() << format("Move inside block: %#x\n", BaseInsertOffset)); 1143 } 1144 unsigned EndInsertOffset = BaseInsertOffset + 4 + 1145 CPEMI->getOperand(2).getImm(); 1146 MachineBasicBlock::iterator MI = UserMI; 1147 ++MI; 1148 unsigned CPUIndex = CPUserIndex+1; 1149 unsigned NumCPUsers = CPUsers.size(); 1150 //MachineInstr *LastIT = 0; 1151 for (unsigned Offset = UserOffset+TII->GetInstSizeInBytes(UserMI); 1152 Offset < BaseInsertOffset; 1153 Offset += TII->GetInstSizeInBytes(MI), 1154 MI = llvm::next(MI)) { 1155 assert(MI != UserMBB->end() && "Fell off end of block"); 1156 if (CPUIndex < NumCPUsers && CPUsers[CPUIndex].MI == MI) { 1157 CPUser &U = CPUsers[CPUIndex]; 1158 if (!isOffsetInRange(Offset, EndInsertOffset, U)) { 1159 // Shift intertion point by one unit of alignment so it is within reach. 1160 BaseInsertOffset -= 1u << LogAlign; 1161 EndInsertOffset -= 1u << LogAlign; 1162 } 1163 // This is overly conservative, as we don't account for CPEMIs being 1164 // reused within the block, but it doesn't matter much. Also assume CPEs 1165 // are added in order with alignment padding. We may eventually be able 1166 // to pack the aligned CPEs better. 1167 EndInsertOffset += U.CPEMI->getOperand(2).getImm(); 1168 CPUIndex++; 1169 } 1170 } 1171 1172 --MI; 1173 NewMBB = splitBlockBeforeInstr(MI); 1174} 1175 1176/// handleConstantPoolUser - Analyze the specified user, checking to see if it 1177/// is out-of-range. If so, pick up the constant pool value and move it some 1178/// place in-range. Return true if we changed any addresses (thus must run 1179/// another pass of branch lengthening), false otherwise. 1180bool MipsConstantIslands::handleConstantPoolUser(unsigned CPUserIndex) { 1181 CPUser &U = CPUsers[CPUserIndex]; 1182 MachineInstr *UserMI = U.MI; 1183 MachineInstr *CPEMI = U.CPEMI; 1184 unsigned CPI = CPEMI->getOperand(1).getIndex(); 1185 unsigned Size = CPEMI->getOperand(2).getImm(); 1186 // Compute this only once, it's expensive. 1187 unsigned UserOffset = getUserOffset(U); 1188 1189 // See if the current entry is within range, or there is a clone of it 1190 // in range. 1191 int result = findInRangeCPEntry(U, UserOffset); 1192 if (result==1) return false; 1193 else if (result==2) return true; 1194 1195 1196 // Look for water where we can place this CPE. 1197 MachineBasicBlock *NewIsland = MF->CreateMachineBasicBlock(); 1198 MachineBasicBlock *NewMBB; 1199 water_iterator IP; 1200 if (findAvailableWater(U, UserOffset, IP)) { 1201 DEBUG(dbgs() << "Found water in range\n"); 1202 MachineBasicBlock *WaterBB = *IP; 1203 1204 // If the original WaterList entry was "new water" on this iteration, 1205 // propagate that to the new island. This is just keeping NewWaterList 1206 // updated to match the WaterList, which will be updated below. 1207 if (NewWaterList.erase(WaterBB)) 1208 NewWaterList.insert(NewIsland); 1209 1210 // The new CPE goes before the following block (NewMBB). 1211 NewMBB = llvm::next(MachineFunction::iterator(WaterBB)); 1212 1213 } else { 1214 // No water found. 1215 // we first see if a longer form of the instrucion could have reached 1216 // the constant. in that case we won't bother to split 1217#ifdef IN_PROGRESS 1218 result = findLongFormInRangeCPEntry(U, UserOffset); 1219#endif 1220 DEBUG(dbgs() << "No water found\n"); 1221 createNewWater(CPUserIndex, UserOffset, NewMBB); 1222 1223 // splitBlockBeforeInstr adds to WaterList, which is important when it is 1224 // called while handling branches so that the water will be seen on the 1225 // next iteration for constant pools, but in this context, we don't want 1226 // it. Check for this so it will be removed from the WaterList. 1227 // Also remove any entry from NewWaterList. 1228 MachineBasicBlock *WaterBB = prior(MachineFunction::iterator(NewMBB)); 1229 IP = std::find(WaterList.begin(), WaterList.end(), WaterBB); 1230 if (IP != WaterList.end()) 1231 NewWaterList.erase(WaterBB); 1232 1233 // We are adding new water. Update NewWaterList. 1234 NewWaterList.insert(NewIsland); 1235 } 1236 1237 // Remove the original WaterList entry; we want subsequent insertions in 1238 // this vicinity to go after the one we're about to insert. This 1239 // considerably reduces the number of times we have to move the same CPE 1240 // more than once and is also important to ensure the algorithm terminates. 1241 if (IP != WaterList.end()) 1242 WaterList.erase(IP); 1243 1244 // Okay, we know we can put an island before NewMBB now, do it! 1245 MF->insert(NewMBB, NewIsland); 1246 1247 // Update internal data structures to account for the newly inserted MBB. 1248 updateForInsertedWaterBlock(NewIsland); 1249 1250 // Decrement the old entry, and remove it if refcount becomes 0. 1251 decrementCPEReferenceCount(CPI, CPEMI); 1252 1253 // Now that we have an island to add the CPE to, clone the original CPE and 1254 // add it to the island. 1255 U.HighWaterMark = NewIsland; 1256 U.CPEMI = BuildMI(NewIsland, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY)) 1257 .addImm(ID).addConstantPoolIndex(CPI).addImm(Size); 1258 CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1)); 1259 ++NumCPEs; 1260 1261 // Mark the basic block as aligned as required by the const-pool entry. 1262 NewIsland->setAlignment(getCPELogAlign(U.CPEMI)); 1263 1264 // Increase the size of the island block to account for the new entry. 1265 BBInfo[NewIsland->getNumber()].Size += Size; 1266 adjustBBOffsetsAfter(llvm::prior(MachineFunction::iterator(NewIsland))); 1267 1268 // No existing clone of this CPE is within range. 1269 // We will be generating a new clone. Get a UID for it. 1270 unsigned ID = createPICLabelUId(); 1271 1272 // Finally, change the CPI in the instruction operand to be ID. 1273 for (unsigned i = 0, e = UserMI->getNumOperands(); i != e; ++i) 1274 if (UserMI->getOperand(i).isCPI()) { 1275 UserMI->getOperand(i).setIndex(ID); 1276 break; 1277 } 1278 1279 DEBUG(dbgs() << " Moved CPE to #" << ID << " CPI=" << CPI 1280 << format(" offset=%#x\n", BBInfo[NewIsland->getNumber()].Offset)); 1281 1282 return true; 1283} 1284 1285/// removeDeadCPEMI - Remove a dead constant pool entry instruction. Update 1286/// sizes and offsets of impacted basic blocks. 1287void MipsConstantIslands::removeDeadCPEMI(MachineInstr *CPEMI) { 1288 MachineBasicBlock *CPEBB = CPEMI->getParent(); 1289 unsigned Size = CPEMI->getOperand(2).getImm(); 1290 CPEMI->eraseFromParent(); 1291 BBInfo[CPEBB->getNumber()].Size -= Size; 1292 // All succeeding offsets have the current size value added in, fix this. 1293 if (CPEBB->empty()) { 1294 BBInfo[CPEBB->getNumber()].Size = 0; 1295 1296 // This block no longer needs to be aligned. 1297 CPEBB->setAlignment(0); 1298 } else 1299 // Entries are sorted by descending alignment, so realign from the front. 1300 CPEBB->setAlignment(getCPELogAlign(CPEBB->begin())); 1301 1302 adjustBBOffsetsAfter(CPEBB); 1303 // An island has only one predecessor BB and one successor BB. Check if 1304 // this BB's predecessor jumps directly to this BB's successor. This 1305 // shouldn't happen currently. 1306 assert(!BBIsJumpedOver(CPEBB) && "How did this happen?"); 1307 // FIXME: remove the empty blocks after all the work is done? 1308} 1309 1310/// removeUnusedCPEntries - Remove constant pool entries whose refcounts 1311/// are zero. 1312bool MipsConstantIslands::removeUnusedCPEntries() { 1313 unsigned MadeChange = false; 1314 for (unsigned i = 0, e = CPEntries.size(); i != e; ++i) { 1315 std::vector<CPEntry> &CPEs = CPEntries[i]; 1316 for (unsigned j = 0, ee = CPEs.size(); j != ee; ++j) { 1317 if (CPEs[j].RefCount == 0 && CPEs[j].CPEMI) { 1318 removeDeadCPEMI(CPEs[j].CPEMI); 1319 CPEs[j].CPEMI = NULL; 1320 MadeChange = true; 1321 } 1322 } 1323 } 1324 return MadeChange; 1325} 1326 1327/// isBBInRange - Returns true if the distance between specific MI and 1328/// specific BB can fit in MI's displacement field. 1329bool MipsConstantIslands::isBBInRange 1330 (MachineInstr *MI,MachineBasicBlock *DestBB, unsigned MaxDisp) { 1331 1332unsigned PCAdj = 4; 1333 1334 unsigned BrOffset = getOffsetOf(MI) + PCAdj; 1335 unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset; 1336 1337 DEBUG(dbgs() << "Branch of destination BB#" << DestBB->getNumber() 1338 << " from BB#" << MI->getParent()->getNumber() 1339 << " max delta=" << MaxDisp 1340 << " from " << getOffsetOf(MI) << " to " << DestOffset 1341 << " offset " << int(DestOffset-BrOffset) << "\t" << *MI); 1342 1343 if (BrOffset <= DestOffset) { 1344 // Branch before the Dest. 1345 if (DestOffset-BrOffset <= MaxDisp) 1346 return true; 1347 } else { 1348 if (BrOffset-DestOffset <= MaxDisp) 1349 return true; 1350 } 1351 return false; 1352} 1353 1354/// fixupImmediateBr - Fix up an immediate branch whose destination is too far 1355/// away to fit in its displacement field. 1356bool MipsConstantIslands::fixupImmediateBr(ImmBranch &Br) { 1357 MachineInstr *MI = Br.MI; 1358 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB(); 1359 1360 // Check to see if the DestBB is already in-range. 1361 if (isBBInRange(MI, DestBB, Br.MaxDisp)) 1362 return false; 1363 1364 if (!Br.isCond) 1365 return fixupUnconditionalBr(Br); 1366 return fixupConditionalBr(Br); 1367} 1368 1369/// fixupUnconditionalBr - Fix up an unconditional branch whose destination is 1370/// too far away to fit in its displacement field. If the LR register has been 1371/// spilled in the epilogue, then we can use BL to implement a far jump. 1372/// Otherwise, add an intermediate branch instruction to a branch. 1373bool 1374MipsConstantIslands::fixupUnconditionalBr(ImmBranch &Br) { 1375 MachineInstr *MI = Br.MI; 1376 MachineBasicBlock *MBB = MI->getParent(); 1377 // Use BL to implement far jump. 1378 Br.MaxDisp = ((1 << 16)-1) * 2; 1379 MI->setDesc(TII->get(Mips::BimmX16)); 1380 BBInfo[MBB->getNumber()].Size += 2; 1381 adjustBBOffsetsAfter(MBB); 1382 HasFarJump = true; 1383 ++NumUBrFixed; 1384 1385 DEBUG(dbgs() << " Changed B to long jump " << *MI); 1386 1387 return true; 1388} 1389 1390/// fixupConditionalBr - Fix up a conditional branch whose destination is too 1391/// far away to fit in its displacement field. It is converted to an inverse 1392/// conditional branch + an unconditional branch to the destination. 1393bool 1394MipsConstantIslands::fixupConditionalBr(ImmBranch &Br) { 1395 MachineInstr *MI = Br.MI; 1396 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB(); 1397 1398 // Add an unconditional branch to the destination and invert the branch 1399 // condition to jump over it: 1400 // blt L1 1401 // => 1402 // bge L2 1403 // b L1 1404 // L2: 1405 unsigned CCReg = 0; // FIXME 1406 unsigned CC=0; //FIXME 1407 1408 // If the branch is at the end of its MBB and that has a fall-through block, 1409 // direct the updated conditional branch to the fall-through block. Otherwise, 1410 // split the MBB before the next instruction. 1411 MachineBasicBlock *MBB = MI->getParent(); 1412 MachineInstr *BMI = &MBB->back(); 1413 bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB); 1414 1415 ++NumCBrFixed; 1416 if (BMI != MI) { 1417 if (llvm::next(MachineBasicBlock::iterator(MI)) == prior(MBB->end()) && 1418 BMI->getOpcode() == Br.UncondBr) { 1419 // Last MI in the BB is an unconditional branch. Can we simply invert the 1420 // condition and swap destinations: 1421 // beq L1 1422 // b L2 1423 // => 1424 // bne L2 1425 // b L1 1426 MachineBasicBlock *NewDest = BMI->getOperand(0).getMBB(); 1427 if (isBBInRange(MI, NewDest, Br.MaxDisp)) { 1428 DEBUG(dbgs() << " Invert Bcc condition and swap its destination with " 1429 << *BMI); 1430 BMI->getOperand(0).setMBB(DestBB); 1431 MI->getOperand(0).setMBB(NewDest); 1432 return true; 1433 } 1434 } 1435 } 1436 1437 if (NeedSplit) { 1438 splitBlockBeforeInstr(MI); 1439 // No need for the branch to the next block. We're adding an unconditional 1440 // branch to the destination. 1441 int delta = TII->GetInstSizeInBytes(&MBB->back()); 1442 BBInfo[MBB->getNumber()].Size -= delta; 1443 MBB->back().eraseFromParent(); 1444 // BBInfo[SplitBB].Offset is wrong temporarily, fixed below 1445 } 1446 MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB)); 1447 1448 DEBUG(dbgs() << " Insert B to BB#" << DestBB->getNumber() 1449 << " also invert condition and change dest. to BB#" 1450 << NextBB->getNumber() << "\n"); 1451 1452 // Insert a new conditional branch and a new unconditional branch. 1453 // Also update the ImmBranch as well as adding a new entry for the new branch. 1454 BuildMI(MBB, DebugLoc(), TII->get(MI->getOpcode())) 1455 .addMBB(NextBB).addImm(CC).addReg(CCReg); 1456 Br.MI = &MBB->back(); 1457 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back()); 1458 BuildMI(MBB, DebugLoc(), TII->get(Br.UncondBr)).addMBB(DestBB); 1459 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back()); 1460 unsigned MaxDisp = getUnconditionalBrDisp(Br.UncondBr); 1461 ImmBranches.push_back(ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr)); 1462 1463 // Remove the old conditional branch. It may or may not still be in MBB. 1464 BBInfo[MI->getParent()->getNumber()].Size -= TII->GetInstSizeInBytes(MI); 1465 MI->eraseFromParent(); 1466 adjustBBOffsetsAfter(MBB); 1467 return true; 1468} 1469 1470 1471void MipsConstantIslands::prescanForConstants() { 1472 unsigned J = 0; 1473 (void)J; 1474 PrescannedForConstants = true; 1475 for (MachineFunction::iterator B = 1476 MF->begin(), E = MF->end(); B != E; ++B) { 1477 for (MachineBasicBlock::instr_iterator I = 1478 B->instr_begin(), EB = B->instr_end(); I != EB; ++I) { 1479 switch(I->getDesc().getOpcode()) { 1480 case Mips::LwConstant32: { 1481 DEBUG(dbgs() << "constant island constant " << *I << "\n"); 1482 J = I->getNumOperands(); 1483 DEBUG(dbgs() << "num operands " << J << "\n"); 1484 MachineOperand& Literal = I->getOperand(1); 1485 if (Literal.isImm()) { 1486 int64_t V = Literal.getImm(); 1487 DEBUG(dbgs() << "literal " << V << "\n"); 1488 Type *Int32Ty = 1489 Type::getInt32Ty(MF->getFunction()->getContext()); 1490 const Constant *C = ConstantInt::get(Int32Ty, V); 1491 unsigned index = MCP->getConstantPoolIndex(C, 4); 1492 I->getOperand(2).ChangeToImmediate(index); 1493 DEBUG(dbgs() << "constant island constant " << *I << "\n"); 1494 I->setDesc(TII->get(Mips::LwRxPcTcp16)); 1495 I->RemoveOperand(1); 1496 I->RemoveOperand(1); 1497 I->addOperand(MachineOperand::CreateCPI(index, 0)); 1498 I->addOperand(MachineOperand::CreateImm(4)); 1499 } 1500 break; 1501 } 1502 default: 1503 break; 1504 } 1505 } 1506 } 1507} 1508 1509