MipsConstantIslandPass.cpp revision 5aeb5e530e11a1473ecddb126b72cd4e37fada81
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 "Mips16InstrInfo.h" 29#include "MipsMachineFunction.h" 30#include "MipsTargetMachine.h" 31#include "llvm/ADT/Statistic.h" 32#include "llvm/CodeGen/MachineBasicBlock.h" 33#include "llvm/CodeGen/MachineFunctionPass.h" 34#include "llvm/CodeGen/MachineInstrBuilder.h" 35#include "llvm/CodeGen/MachineRegisterInfo.h" 36#include "llvm/IR/Function.h" 37#include "llvm/Support/CommandLine.h" 38#include "llvm/Support/Debug.h" 39#include "llvm/Support/InstIterator.h" 40#include "llvm/Support/MathExtras.h" 41#include "llvm/Support/raw_ostream.h" 42#include "llvm/Target/TargetInstrInfo.h" 43#include "llvm/Target/TargetMachine.h" 44#include "llvm/Target/TargetRegisterInfo.h" 45#include "llvm/Support/Format.h" 46#include <algorithm> 47 48using namespace llvm; 49 50STATISTIC(NumCPEs, "Number of constpool entries"); 51STATISTIC(NumSplit, "Number of uncond branches inserted"); 52STATISTIC(NumCBrFixed, "Number of cond branches fixed"); 53STATISTIC(NumUBrFixed, "Number of uncond branches fixed"); 54 55// FIXME: This option should be removed once it has received sufficient testing. 56static cl::opt<bool> 57AlignConstantIslands("mips-align-constant-islands", cl::Hidden, cl::init(true), 58 cl::desc("Align constant islands in code")); 59 60 61// Rather than do make check tests with huge amounts of code, we force 62// the test to use this amount. 63// 64static cl::opt<int> ConstantIslandsSmallOffset( 65 "mips-constant-islands-small-offset", 66 cl::init(0), 67 cl::desc("Make small offsets be this amount for testing purposes"), 68 cl::Hidden); 69 70// 71// For testing purposes we tell it to not use relaxed load forms so that it 72// will split blocks. 73// 74static cl::opt<bool> NoLoadRelaxation( 75 "mips-constant-islands-no-load-relaxation", 76 cl::init(false), 77 cl::desc("Don't relax loads to long loads - for testing purposes"), 78 cl::Hidden); 79 80 81namespace { 82 83 84 typedef MachineBasicBlock::iterator Iter; 85 typedef MachineBasicBlock::reverse_iterator ReverseIter; 86 87 /// MipsConstantIslands - Due to limited PC-relative displacements, Mips 88 /// requires constant pool entries to be scattered among the instructions 89 /// inside a function. To do this, it completely ignores the normal LLVM 90 /// constant pool; instead, it places constants wherever it feels like with 91 /// special instructions. 92 /// 93 /// The terminology used in this pass includes: 94 /// Islands - Clumps of constants placed in the function. 95 /// Water - Potential places where an island could be formed. 96 /// CPE - A constant pool entry that has been placed somewhere, which 97 /// tracks a list of users. 98 99 class MipsConstantIslands : public MachineFunctionPass { 100 101 /// BasicBlockInfo - Information about the offset and size of a single 102 /// basic block. 103 struct BasicBlockInfo { 104 /// Offset - Distance from the beginning of the function to the beginning 105 /// of this basic block. 106 /// 107 /// Offsets are computed assuming worst case padding before an aligned 108 /// block. This means that subtracting basic block offsets always gives a 109 /// conservative estimate of the real distance which may be smaller. 110 /// 111 /// Because worst case padding is used, the computed offset of an aligned 112 /// block may not actually be aligned. 113 unsigned Offset; 114 115 /// Size - Size of the basic block in bytes. If the block contains 116 /// inline assembly, this is a worst case estimate. 117 /// 118 /// The size does not include any alignment padding whether from the 119 /// beginning of the block, or from an aligned jump table at the end. 120 unsigned Size; 121 122 // FIXME: ignore LogAlign for this patch 123 // 124 unsigned postOffset(unsigned LogAlign = 0) const { 125 unsigned PO = Offset + Size; 126 return PO; 127 } 128 129 BasicBlockInfo() : Offset(0), Size(0) {} 130 131 }; 132 133 std::vector<BasicBlockInfo> BBInfo; 134 135 /// WaterList - A sorted list of basic blocks where islands could be placed 136 /// (i.e. blocks that don't fall through to the following block, due 137 /// to a return, unreachable, or unconditional branch). 138 std::vector<MachineBasicBlock*> WaterList; 139 140 /// NewWaterList - The subset of WaterList that was created since the 141 /// previous iteration by inserting unconditional branches. 142 SmallSet<MachineBasicBlock*, 4> NewWaterList; 143 144 typedef std::vector<MachineBasicBlock*>::iterator water_iterator; 145 146 /// CPUser - One user of a constant pool, keeping the machine instruction 147 /// pointer, the constant pool being referenced, and the max displacement 148 /// allowed from the instruction to the CP. The HighWaterMark records the 149 /// highest basic block where a new CPEntry can be placed. To ensure this 150 /// pass terminates, the CP entries are initially placed at the end of the 151 /// function and then move monotonically to lower addresses. The 152 /// exception to this rule is when the current CP entry for a particular 153 /// CPUser is out of range, but there is another CP entry for the same 154 /// constant value in range. We want to use the existing in-range CP 155 /// entry, but if it later moves out of range, the search for new water 156 /// should resume where it left off. The HighWaterMark is used to record 157 /// that point. 158 struct CPUser { 159 MachineInstr *MI; 160 MachineInstr *CPEMI; 161 MachineBasicBlock *HighWaterMark; 162 private: 163 unsigned MaxDisp; 164 unsigned LongFormMaxDisp; // mips16 has 16/32 bit instructions 165 // with different displacements 166 unsigned LongFormOpcode; 167 public: 168 bool NegOk; 169 CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp, 170 bool neg, 171 unsigned longformmaxdisp, unsigned longformopcode) 172 : MI(mi), CPEMI(cpemi), MaxDisp(maxdisp), 173 LongFormMaxDisp(longformmaxdisp), LongFormOpcode(longformopcode), 174 NegOk(neg){ 175 HighWaterMark = CPEMI->getParent(); 176 } 177 /// getMaxDisp - Returns the maximum displacement supported by MI. 178 unsigned getMaxDisp() const { 179 unsigned xMaxDisp = ConstantIslandsSmallOffset? 180 ConstantIslandsSmallOffset: MaxDisp; 181 return xMaxDisp; 182 } 183 void setMaxDisp(unsigned val) { 184 MaxDisp = val; 185 } 186 unsigned getLongFormMaxDisp() const { 187 return LongFormMaxDisp; 188 } 189 unsigned getLongFormOpcode() const { 190 return LongFormOpcode; 191 } 192 }; 193 194 /// CPUsers - Keep track of all of the machine instructions that use various 195 /// constant pools and their max displacement. 196 std::vector<CPUser> CPUsers; 197 198 /// CPEntry - One per constant pool entry, keeping the machine instruction 199 /// pointer, the constpool index, and the number of CPUser's which 200 /// reference this entry. 201 struct CPEntry { 202 MachineInstr *CPEMI; 203 unsigned CPI; 204 unsigned RefCount; 205 CPEntry(MachineInstr *cpemi, unsigned cpi, unsigned rc = 0) 206 : CPEMI(cpemi), CPI(cpi), RefCount(rc) {} 207 }; 208 209 /// CPEntries - Keep track of all of the constant pool entry machine 210 /// instructions. For each original constpool index (i.e. those that 211 /// existed upon entry to this pass), it keeps a vector of entries. 212 /// Original elements are cloned as we go along; the clones are 213 /// put in the vector of the original element, but have distinct CPIs. 214 std::vector<std::vector<CPEntry> > CPEntries; 215 216 /// ImmBranch - One per immediate branch, keeping the machine instruction 217 /// pointer, conditional or unconditional, the max displacement, 218 /// and (if isCond is true) the corresponding unconditional branch 219 /// opcode. 220 struct ImmBranch { 221 MachineInstr *MI; 222 unsigned MaxDisp : 31; 223 bool isCond : 1; 224 int UncondBr; 225 ImmBranch(MachineInstr *mi, unsigned maxdisp, bool cond, int ubr) 226 : MI(mi), MaxDisp(maxdisp), isCond(cond), UncondBr(ubr) {} 227 }; 228 229 /// ImmBranches - Keep track of all the immediate branch instructions. 230 /// 231 std::vector<ImmBranch> ImmBranches; 232 233 /// HasFarJump - True if any far jump instruction has been emitted during 234 /// the branch fix up pass. 235 bool HasFarJump; 236 237 const TargetMachine &TM; 238 bool IsPIC; 239 unsigned ABI; 240 const MipsSubtarget *STI; 241 const Mips16InstrInfo *TII; 242 MipsFunctionInfo *MFI; 243 MachineFunction *MF; 244 MachineConstantPool *MCP; 245 246 unsigned PICLabelUId; 247 bool PrescannedForConstants; 248 249 void initPICLabelUId(unsigned UId) { 250 PICLabelUId = UId; 251 } 252 253 254 unsigned createPICLabelUId() { 255 return PICLabelUId++; 256 } 257 258 public: 259 static char ID; 260 MipsConstantIslands(TargetMachine &tm) 261 : MachineFunctionPass(ID), TM(tm), 262 IsPIC(TM.getRelocationModel() == Reloc::PIC_), 263 ABI(TM.getSubtarget<MipsSubtarget>().getTargetABI()), 264 STI(&TM.getSubtarget<MipsSubtarget>()), MF(0), MCP(0), 265 PrescannedForConstants(false){} 266 267 virtual const char *getPassName() const { 268 return "Mips Constant Islands"; 269 } 270 271 bool runOnMachineFunction(MachineFunction &F); 272 273 void doInitialPlacement(std::vector<MachineInstr*> &CPEMIs); 274 CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI); 275 unsigned getCPELogAlign(const MachineInstr *CPEMI); 276 void initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs); 277 unsigned getOffsetOf(MachineInstr *MI) const; 278 unsigned getUserOffset(CPUser&) const; 279 void dumpBBs(); 280 void verify(); 281 282 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 283 unsigned Disp, bool NegativeOK); 284 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 285 const CPUser &U); 286 287 bool isLongFormOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 288 const CPUser &U); 289 290 void computeBlockSize(MachineBasicBlock *MBB); 291 MachineBasicBlock *splitBlockBeforeInstr(MachineInstr *MI); 292 void updateForInsertedWaterBlock(MachineBasicBlock *NewBB); 293 void adjustBBOffsetsAfter(MachineBasicBlock *BB); 294 bool decrementCPEReferenceCount(unsigned CPI, MachineInstr* CPEMI); 295 int findInRangeCPEntry(CPUser& U, unsigned UserOffset); 296 int findLongFormInRangeCPEntry(CPUser& U, unsigned UserOffset); 297 bool findAvailableWater(CPUser&U, unsigned UserOffset, 298 water_iterator &WaterIter); 299 void createNewWater(unsigned CPUserIndex, unsigned UserOffset, 300 MachineBasicBlock *&NewMBB); 301 bool handleConstantPoolUser(unsigned CPUserIndex); 302 void removeDeadCPEMI(MachineInstr *CPEMI); 303 bool removeUnusedCPEntries(); 304 bool isCPEntryInRange(MachineInstr *MI, unsigned UserOffset, 305 MachineInstr *CPEMI, unsigned Disp, bool NegOk, 306 bool DoDump = false); 307 bool isWaterInRange(unsigned UserOffset, MachineBasicBlock *Water, 308 CPUser &U, unsigned &Growth); 309 bool isBBInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp); 310 bool fixupImmediateBr(ImmBranch &Br); 311 bool fixupConditionalBr(ImmBranch &Br); 312 bool fixupUnconditionalBr(ImmBranch &Br); 313 314 void prescanForConstants(); 315 316 private: 317 318 }; 319 320 char MipsConstantIslands::ID = 0; 321} // end of anonymous namespace 322 323 324bool MipsConstantIslands::isLongFormOffsetInRange 325 (unsigned UserOffset, unsigned TrialOffset, 326 const CPUser &U) { 327 return isOffsetInRange(UserOffset, TrialOffset, 328 U.getLongFormMaxDisp(), U.NegOk); 329} 330 331bool MipsConstantIslands::isOffsetInRange 332 (unsigned UserOffset, unsigned TrialOffset, 333 const CPUser &U) { 334 return isOffsetInRange(UserOffset, TrialOffset, 335 U.getMaxDisp(), U.NegOk); 336} 337/// print block size and offset information - debugging 338void MipsConstantIslands::dumpBBs() { 339 DEBUG({ 340 for (unsigned J = 0, E = BBInfo.size(); J !=E; ++J) { 341 const BasicBlockInfo &BBI = BBInfo[J]; 342 dbgs() << format("%08x BB#%u\t", BBI.Offset, J) 343 << format(" size=%#x\n", BBInfo[J].Size); 344 } 345 }); 346} 347/// createMipsLongBranchPass - Returns a pass that converts branches to long 348/// branches. 349FunctionPass *llvm::createMipsConstantIslandPass(MipsTargetMachine &tm) { 350 return new MipsConstantIslands(tm); 351} 352 353bool MipsConstantIslands::runOnMachineFunction(MachineFunction &mf) { 354 // The intention is for this to be a mips16 only pass for now 355 // FIXME: 356 MF = &mf; 357 MCP = mf.getConstantPool(); 358 DEBUG(dbgs() << "constant island machine function " << "\n"); 359 if (!TM.getSubtarget<MipsSubtarget>().inMips16Mode() || 360 !MipsSubtarget::useConstantIslands()) { 361 return false; 362 } 363 TII = (const Mips16InstrInfo*)MF->getTarget().getInstrInfo(); 364 MFI = MF->getInfo<MipsFunctionInfo>(); 365 DEBUG(dbgs() << "constant island processing " << "\n"); 366 // 367 // will need to make predermination if there is any constants we need to 368 // put in constant islands. TBD. 369 // 370 if (!PrescannedForConstants) prescanForConstants(); 371 372 HasFarJump = false; 373 // This pass invalidates liveness information when it splits basic blocks. 374 MF->getRegInfo().invalidateLiveness(); 375 376 // Renumber all of the machine basic blocks in the function, guaranteeing that 377 // the numbers agree with the position of the block in the function. 378 MF->RenumberBlocks(); 379 380 bool MadeChange = false; 381 382 // Perform the initial placement of the constant pool entries. To start with, 383 // we put them all at the end of the function. 384 std::vector<MachineInstr*> CPEMIs; 385 if (!MCP->isEmpty()) 386 doInitialPlacement(CPEMIs); 387 388 /// The next UID to take is the first unused one. 389 initPICLabelUId(CPEMIs.size()); 390 391 // Do the initial scan of the function, building up information about the 392 // sizes of each block, the location of all the water, and finding all of the 393 // constant pool users. 394 initializeFunctionInfo(CPEMIs); 395 CPEMIs.clear(); 396 DEBUG(dumpBBs()); 397 398 /// Remove dead constant pool entries. 399 MadeChange |= removeUnusedCPEntries(); 400 401 // Iteratively place constant pool entries and fix up branches until there 402 // is no change. 403 unsigned NoCPIters = 0, NoBRIters = 0; 404 (void)NoBRIters; 405 while (true) { 406 DEBUG(dbgs() << "Beginning CP iteration #" << NoCPIters << '\n'); 407 bool CPChange = false; 408 for (unsigned i = 0, e = CPUsers.size(); i != e; ++i) 409 CPChange |= handleConstantPoolUser(i); 410 if (CPChange && ++NoCPIters > 30) 411 report_fatal_error("Constant Island pass failed to converge!"); 412 DEBUG(dumpBBs()); 413 414 // Clear NewWaterList now. If we split a block for branches, it should 415 // appear as "new water" for the next iteration of constant pool placement. 416 NewWaterList.clear(); 417 418 DEBUG(dbgs() << "Beginning BR iteration #" << NoBRIters << '\n'); 419 bool BRChange = false; 420 for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i) 421 BRChange |= fixupImmediateBr(ImmBranches[i]); 422 if (BRChange && ++NoBRIters > 30) 423 report_fatal_error("Branch Fix Up pass failed to converge!"); 424 DEBUG(dumpBBs()); 425 if (!CPChange && !BRChange) 426 break; 427 MadeChange = true; 428 } 429 430 DEBUG(dbgs() << '\n'; dumpBBs()); 431 432 BBInfo.clear(); 433 WaterList.clear(); 434 CPUsers.clear(); 435 CPEntries.clear(); 436 ImmBranches.clear(); 437 return MadeChange; 438} 439 440/// doInitialPlacement - Perform the initial placement of the constant pool 441/// entries. To start with, we put them all at the end of the function. 442void 443MipsConstantIslands::doInitialPlacement(std::vector<MachineInstr*> &CPEMIs) { 444 // Create the basic block to hold the CPE's. 445 MachineBasicBlock *BB = MF->CreateMachineBasicBlock(); 446 MF->push_back(BB); 447 448 449 // MachineConstantPool measures alignment in bytes. We measure in log2(bytes). 450 unsigned MaxAlign = Log2_32(MCP->getConstantPoolAlignment()); 451 452 // Mark the basic block as required by the const-pool. 453 // If AlignConstantIslands isn't set, use 4-byte alignment for everything. 454 BB->setAlignment(AlignConstantIslands ? MaxAlign : 2); 455 456 // The function needs to be as aligned as the basic blocks. The linker may 457 // move functions around based on their alignment. 458 MF->ensureAlignment(BB->getAlignment()); 459 460 // Order the entries in BB by descending alignment. That ensures correct 461 // alignment of all entries as long as BB is sufficiently aligned. Keep 462 // track of the insertion point for each alignment. We are going to bucket 463 // sort the entries as they are created. 464 SmallVector<MachineBasicBlock::iterator, 8> InsPoint(MaxAlign + 1, BB->end()); 465 466 // Add all of the constants from the constant pool to the end block, use an 467 // identity mapping of CPI's to CPE's. 468 const std::vector<MachineConstantPoolEntry> &CPs = MCP->getConstants(); 469 470 const DataLayout &TD = *MF->getTarget().getDataLayout(); 471 for (unsigned i = 0, e = CPs.size(); i != e; ++i) { 472 unsigned Size = TD.getTypeAllocSize(CPs[i].getType()); 473 assert(Size >= 4 && "Too small constant pool entry"); 474 unsigned Align = CPs[i].getAlignment(); 475 assert(isPowerOf2_32(Align) && "Invalid alignment"); 476 // Verify that all constant pool entries are a multiple of their alignment. 477 // If not, we would have to pad them out so that instructions stay aligned. 478 assert((Size % Align) == 0 && "CP Entry not multiple of 4 bytes!"); 479 480 // Insert CONSTPOOL_ENTRY before entries with a smaller alignment. 481 unsigned LogAlign = Log2_32(Align); 482 MachineBasicBlock::iterator InsAt = InsPoint[LogAlign]; 483 484 MachineInstr *CPEMI = 485 BuildMI(*BB, InsAt, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY)) 486 .addImm(i).addConstantPoolIndex(i).addImm(Size); 487 488 CPEMIs.push_back(CPEMI); 489 490 // Ensure that future entries with higher alignment get inserted before 491 // CPEMI. This is bucket sort with iterators. 492 for (unsigned a = LogAlign + 1; a <= MaxAlign; ++a) 493 if (InsPoint[a] == InsAt) 494 InsPoint[a] = CPEMI; 495 // Add a new CPEntry, but no corresponding CPUser yet. 496 std::vector<CPEntry> CPEs; 497 CPEs.push_back(CPEntry(CPEMI, i)); 498 CPEntries.push_back(CPEs); 499 ++NumCPEs; 500 DEBUG(dbgs() << "Moved CPI#" << i << " to end of function, size = " 501 << Size << ", align = " << Align <<'\n'); 502 } 503 DEBUG(BB->dump()); 504} 505 506/// BBHasFallthrough - Return true if the specified basic block can fallthrough 507/// into the block immediately after it. 508static bool BBHasFallthrough(MachineBasicBlock *MBB) { 509 // Get the next machine basic block in the function. 510 MachineFunction::iterator MBBI = MBB; 511 // Can't fall off end of function. 512 if (llvm::next(MBBI) == MBB->getParent()->end()) 513 return false; 514 515 MachineBasicBlock *NextBB = llvm::next(MBBI); 516 for (MachineBasicBlock::succ_iterator I = MBB->succ_begin(), 517 E = MBB->succ_end(); I != E; ++I) 518 if (*I == NextBB) 519 return true; 520 521 return false; 522} 523 524/// findConstPoolEntry - Given the constpool index and CONSTPOOL_ENTRY MI, 525/// look up the corresponding CPEntry. 526MipsConstantIslands::CPEntry 527*MipsConstantIslands::findConstPoolEntry(unsigned CPI, 528 const MachineInstr *CPEMI) { 529 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 530 // Number of entries per constpool index should be small, just do a 531 // linear search. 532 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 533 if (CPEs[i].CPEMI == CPEMI) 534 return &CPEs[i]; 535 } 536 return NULL; 537} 538 539/// getCPELogAlign - Returns the required alignment of the constant pool entry 540/// represented by CPEMI. Alignment is measured in log2(bytes) units. 541unsigned MipsConstantIslands::getCPELogAlign(const MachineInstr *CPEMI) { 542 assert(CPEMI && CPEMI->getOpcode() == Mips::CONSTPOOL_ENTRY); 543 544 // Everything is 4-byte aligned unless AlignConstantIslands is set. 545 if (!AlignConstantIslands) 546 return 2; 547 548 unsigned CPI = CPEMI->getOperand(1).getIndex(); 549 assert(CPI < MCP->getConstants().size() && "Invalid constant pool index."); 550 unsigned Align = MCP->getConstants()[CPI].getAlignment(); 551 assert(isPowerOf2_32(Align) && "Invalid CPE alignment"); 552 return Log2_32(Align); 553} 554 555/// initializeFunctionInfo - Do the initial scan of the function, building up 556/// information about the sizes of each block, the location of all the water, 557/// and finding all of the constant pool users. 558void MipsConstantIslands:: 559initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs) { 560 BBInfo.clear(); 561 BBInfo.resize(MF->getNumBlockIDs()); 562 563 // First thing, compute the size of all basic blocks, and see if the function 564 // has any inline assembly in it. If so, we have to be conservative about 565 // alignment assumptions, as we don't know for sure the size of any 566 // instructions in the inline assembly. 567 for (MachineFunction::iterator I = MF->begin(), E = MF->end(); I != E; ++I) 568 computeBlockSize(I); 569 570 571 // Compute block offsets. 572 adjustBBOffsetsAfter(MF->begin()); 573 574 // Now go back through the instructions and build up our data structures. 575 for (MachineFunction::iterator MBBI = MF->begin(), E = MF->end(); 576 MBBI != E; ++MBBI) { 577 MachineBasicBlock &MBB = *MBBI; 578 579 // If this block doesn't fall through into the next MBB, then this is 580 // 'water' that a constant pool island could be placed. 581 if (!BBHasFallthrough(&MBB)) 582 WaterList.push_back(&MBB); 583 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); 584 I != E; ++I) { 585 if (I->isDebugValue()) 586 continue; 587 588 int Opc = I->getOpcode(); 589 if (I->isBranch()) { 590 bool isCond = false; 591 unsigned Bits = 0; 592 unsigned Scale = 1; 593 int UOpc = Opc; 594 switch (Opc) { 595 default: 596 continue; // Ignore other branches for now 597 case Mips::Bimm16: 598 Bits = 11; 599 Scale = 2; 600 isCond = false; 601 break; 602 case Mips::BimmX16: 603 Bits = 16; 604 Scale = 2; 605 isCond = false; 606 } 607 // Record this immediate branch. 608 unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale; 609 ImmBranches.push_back(ImmBranch(I, MaxOffs, isCond, UOpc)); 610 } 611 612 if (Opc == Mips::CONSTPOOL_ENTRY) 613 continue; 614 615 616 // Scan the instructions for constant pool operands. 617 for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) 618 if (I->getOperand(op).isCPI()) { 619 620 // We found one. The addressing mode tells us the max displacement 621 // from the PC that this instruction permits. 622 623 // Basic size info comes from the TSFlags field. 624 unsigned Bits = 0; 625 unsigned Scale = 1; 626 bool NegOk = false; 627 unsigned LongFormBits = 0; 628 unsigned LongFormScale = 0; 629 unsigned LongFormOpcode = 0; 630 switch (Opc) { 631 default: 632 llvm_unreachable("Unknown addressing mode for CP reference!"); 633 case Mips::LwRxPcTcp16: 634 Bits = 8; 635 Scale = 4; 636 LongFormOpcode = Mips::LwRxPcTcpX16; 637 LongFormBits = 16; 638 LongFormScale = 1; 639 break; 640 case Mips::LwRxPcTcpX16: 641 Bits = 16; 642 Scale = 1; 643 NegOk = true; 644 break; 645 } 646 // Remember that this is a user of a CP entry. 647 unsigned CPI = I->getOperand(op).getIndex(); 648 MachineInstr *CPEMI = CPEMIs[CPI]; 649 unsigned MaxOffs = ((1 << Bits)-1) * Scale; 650 unsigned LongFormMaxOffs = ((1 << LongFormBits)-1) * LongFormScale; 651 CPUsers.push_back(CPUser(I, CPEMI, MaxOffs, NegOk, 652 LongFormMaxOffs, LongFormOpcode)); 653 654 // Increment corresponding CPEntry reference count. 655 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI); 656 assert(CPE && "Cannot find a corresponding CPEntry!"); 657 CPE->RefCount++; 658 659 // Instructions can only use one CP entry, don't bother scanning the 660 // rest of the operands. 661 break; 662 663 } 664 665 } 666 } 667 668} 669 670/// computeBlockSize - Compute the size and some alignment information for MBB. 671/// This function updates BBInfo directly. 672void MipsConstantIslands::computeBlockSize(MachineBasicBlock *MBB) { 673 BasicBlockInfo &BBI = BBInfo[MBB->getNumber()]; 674 BBI.Size = 0; 675 676 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E; 677 ++I) 678 BBI.Size += TII->GetInstSizeInBytes(I); 679 680} 681 682/// getOffsetOf - Return the current offset of the specified machine instruction 683/// from the start of the function. This offset changes as stuff is moved 684/// around inside the function. 685unsigned MipsConstantIslands::getOffsetOf(MachineInstr *MI) const { 686 MachineBasicBlock *MBB = MI->getParent(); 687 688 // The offset is composed of two things: the sum of the sizes of all MBB's 689 // before this instruction's block, and the offset from the start of the block 690 // it is in. 691 unsigned Offset = BBInfo[MBB->getNumber()].Offset; 692 693 // Sum instructions before MI in MBB. 694 for (MachineBasicBlock::iterator I = MBB->begin(); &*I != MI; ++I) { 695 assert(I != MBB->end() && "Didn't find MI in its own basic block?"); 696 Offset += TII->GetInstSizeInBytes(I); 697 } 698 return Offset; 699} 700 701/// CompareMBBNumbers - Little predicate function to sort the WaterList by MBB 702/// ID. 703static bool CompareMBBNumbers(const MachineBasicBlock *LHS, 704 const MachineBasicBlock *RHS) { 705 return LHS->getNumber() < RHS->getNumber(); 706} 707 708/// updateForInsertedWaterBlock - When a block is newly inserted into the 709/// machine function, it upsets all of the block numbers. Renumber the blocks 710/// and update the arrays that parallel this numbering. 711void MipsConstantIslands::updateForInsertedWaterBlock 712 (MachineBasicBlock *NewBB) { 713 // Renumber the MBB's to keep them consecutive. 714 NewBB->getParent()->RenumberBlocks(NewBB); 715 716 // Insert an entry into BBInfo to align it properly with the (newly 717 // renumbered) block numbers. 718 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo()); 719 720 // Next, update WaterList. Specifically, we need to add NewMBB as having 721 // available water after it. 722 water_iterator IP = 723 std::lower_bound(WaterList.begin(), WaterList.end(), NewBB, 724 CompareMBBNumbers); 725 WaterList.insert(IP, NewBB); 726} 727 728unsigned MipsConstantIslands::getUserOffset(CPUser &U) const { 729 return getOffsetOf(U.MI); 730} 731 732/// Split the basic block containing MI into two blocks, which are joined by 733/// an unconditional branch. Update data structures and renumber blocks to 734/// account for this change and returns the newly created block. 735MachineBasicBlock *MipsConstantIslands::splitBlockBeforeInstr 736 (MachineInstr *MI) { 737 MachineBasicBlock *OrigBB = MI->getParent(); 738 739 // Create a new MBB for the code after the OrigBB. 740 MachineBasicBlock *NewBB = 741 MF->CreateMachineBasicBlock(OrigBB->getBasicBlock()); 742 MachineFunction::iterator MBBI = OrigBB; ++MBBI; 743 MF->insert(MBBI, NewBB); 744 745 // Splice the instructions starting with MI over to NewBB. 746 NewBB->splice(NewBB->end(), OrigBB, MI, OrigBB->end()); 747 748 // Add an unconditional branch from OrigBB to NewBB. 749 // Note the new unconditional branch is not being recorded. 750 // There doesn't seem to be meaningful DebugInfo available; this doesn't 751 // correspond to anything in the source. 752 BuildMI(OrigBB, DebugLoc(), TII->get(Mips::Bimm16)).addMBB(NewBB); 753 ++NumSplit; 754 755 // Update the CFG. All succs of OrigBB are now succs of NewBB. 756 NewBB->transferSuccessors(OrigBB); 757 758 // OrigBB branches to NewBB. 759 OrigBB->addSuccessor(NewBB); 760 761 // Update internal data structures to account for the newly inserted MBB. 762 // This is almost the same as updateForInsertedWaterBlock, except that 763 // the Water goes after OrigBB, not NewBB. 764 MF->RenumberBlocks(NewBB); 765 766 // Insert an entry into BBInfo to align it properly with the (newly 767 // renumbered) block numbers. 768 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo()); 769 770 // Next, update WaterList. Specifically, we need to add OrigMBB as having 771 // available water after it (but not if it's already there, which happens 772 // when splitting before a conditional branch that is followed by an 773 // unconditional branch - in that case we want to insert NewBB). 774 water_iterator IP = 775 std::lower_bound(WaterList.begin(), WaterList.end(), OrigBB, 776 CompareMBBNumbers); 777 MachineBasicBlock* WaterBB = *IP; 778 if (WaterBB == OrigBB) 779 WaterList.insert(llvm::next(IP), NewBB); 780 else 781 WaterList.insert(IP, OrigBB); 782 NewWaterList.insert(OrigBB); 783 784 // Figure out how large the OrigBB is. As the first half of the original 785 // block, it cannot contain a tablejump. The size includes 786 // the new jump we added. (It should be possible to do this without 787 // recounting everything, but it's very confusing, and this is rarely 788 // executed.) 789 computeBlockSize(OrigBB); 790 791 // Figure out how large the NewMBB is. As the second half of the original 792 // block, it may contain a tablejump. 793 computeBlockSize(NewBB); 794 795 // All BBOffsets following these blocks must be modified. 796 adjustBBOffsetsAfter(OrigBB); 797 798 return NewBB; 799} 800 801 802 803/// isOffsetInRange - Checks whether UserOffset (the location of a constant pool 804/// reference) is within MaxDisp of TrialOffset (a proposed location of a 805/// constant pool entry). 806bool MipsConstantIslands::isOffsetInRange(unsigned UserOffset, 807 unsigned TrialOffset, unsigned MaxDisp, 808 bool NegativeOK) { 809 if (UserOffset <= TrialOffset) { 810 // User before the Trial. 811 if (TrialOffset - UserOffset <= MaxDisp) 812 return true; 813 } else if (NegativeOK) { 814 if (UserOffset - TrialOffset <= MaxDisp) 815 return true; 816 } 817 return false; 818} 819 820/// isWaterInRange - Returns true if a CPE placed after the specified 821/// Water (a basic block) will be in range for the specific MI. 822/// 823/// Compute how much the function will grow by inserting a CPE after Water. 824bool MipsConstantIslands::isWaterInRange(unsigned UserOffset, 825 MachineBasicBlock* Water, CPUser &U, 826 unsigned &Growth) { 827 unsigned CPELogAlign = getCPELogAlign(U.CPEMI); 828 unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset(CPELogAlign); 829 unsigned NextBlockOffset, NextBlockAlignment; 830 MachineFunction::const_iterator NextBlock = Water; 831 if (++NextBlock == MF->end()) { 832 NextBlockOffset = BBInfo[Water->getNumber()].postOffset(); 833 NextBlockAlignment = 0; 834 } else { 835 NextBlockOffset = BBInfo[NextBlock->getNumber()].Offset; 836 NextBlockAlignment = NextBlock->getAlignment(); 837 } 838 unsigned Size = U.CPEMI->getOperand(2).getImm(); 839 unsigned CPEEnd = CPEOffset + Size; 840 841 // The CPE may be able to hide in the alignment padding before the next 842 // block. It may also cause more padding to be required if it is more aligned 843 // that the next block. 844 if (CPEEnd > NextBlockOffset) { 845 Growth = CPEEnd - NextBlockOffset; 846 // Compute the padding that would go at the end of the CPE to align the next 847 // block. 848 Growth += OffsetToAlignment(CPEEnd, 1u << NextBlockAlignment); 849 850 // If the CPE is to be inserted before the instruction, that will raise 851 // the offset of the instruction. Also account for unknown alignment padding 852 // in blocks between CPE and the user. 853 if (CPEOffset < UserOffset) 854 UserOffset += Growth; 855 } else 856 // CPE fits in existing padding. 857 Growth = 0; 858 859 return isOffsetInRange(UserOffset, CPEOffset, U); 860} 861 862/// isCPEntryInRange - Returns true if the distance between specific MI and 863/// specific ConstPool entry instruction can fit in MI's displacement field. 864bool MipsConstantIslands::isCPEntryInRange 865 (MachineInstr *MI, unsigned UserOffset, 866 MachineInstr *CPEMI, unsigned MaxDisp, 867 bool NegOk, bool DoDump) { 868 unsigned CPEOffset = getOffsetOf(CPEMI); 869 870 if (DoDump) { 871 DEBUG({ 872 unsigned Block = MI->getParent()->getNumber(); 873 const BasicBlockInfo &BBI = BBInfo[Block]; 874 dbgs() << "User of CPE#" << CPEMI->getOperand(0).getImm() 875 << " max delta=" << MaxDisp 876 << format(" insn address=%#x", UserOffset) 877 << " in BB#" << Block << ": " 878 << format("%#x-%x\t", BBI.Offset, BBI.postOffset()) << *MI 879 << format("CPE address=%#x offset=%+d: ", CPEOffset, 880 int(CPEOffset-UserOffset)); 881 }); 882 } 883 884 return isOffsetInRange(UserOffset, CPEOffset, MaxDisp, NegOk); 885} 886 887#ifndef NDEBUG 888/// BBIsJumpedOver - Return true of the specified basic block's only predecessor 889/// unconditionally branches to its only successor. 890static bool BBIsJumpedOver(MachineBasicBlock *MBB) { 891 if (MBB->pred_size() != 1 || MBB->succ_size() != 1) 892 return false; 893 MachineBasicBlock *Succ = *MBB->succ_begin(); 894 MachineBasicBlock *Pred = *MBB->pred_begin(); 895 MachineInstr *PredMI = &Pred->back(); 896 if (PredMI->getOpcode() == Mips::Bimm16) 897 return PredMI->getOperand(0).getMBB() == Succ; 898 return false; 899} 900#endif 901 902void MipsConstantIslands::adjustBBOffsetsAfter(MachineBasicBlock *BB) { 903 unsigned BBNum = BB->getNumber(); 904 for(unsigned i = BBNum + 1, e = MF->getNumBlockIDs(); i < e; ++i) { 905 // Get the offset and known bits at the end of the layout predecessor. 906 // Include the alignment of the current block. 907 unsigned Offset = BBInfo[i - 1].Offset + BBInfo[i - 1].Size; 908 BBInfo[i].Offset = Offset; 909 } 910} 911 912/// decrementCPEReferenceCount - find the constant pool entry with index CPI 913/// and instruction CPEMI, and decrement its refcount. If the refcount 914/// becomes 0 remove the entry and instruction. Returns true if we removed 915/// the entry, false if we didn't. 916 917bool MipsConstantIslands::decrementCPEReferenceCount(unsigned CPI, 918 MachineInstr *CPEMI) { 919 // Find the old entry. Eliminate it if it is no longer used. 920 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI); 921 assert(CPE && "Unexpected!"); 922 if (--CPE->RefCount == 0) { 923 removeDeadCPEMI(CPEMI); 924 CPE->CPEMI = NULL; 925 --NumCPEs; 926 return true; 927 } 928 return false; 929} 930 931/// LookForCPEntryInRange - see if the currently referenced CPE is in range; 932/// if not, see if an in-range clone of the CPE is in range, and if so, 933/// change the data structures so the user references the clone. Returns: 934/// 0 = no existing entry found 935/// 1 = entry found, and there were no code insertions or deletions 936/// 2 = entry found, and there were code insertions or deletions 937int MipsConstantIslands::findInRangeCPEntry(CPUser& U, unsigned UserOffset) 938{ 939 MachineInstr *UserMI = U.MI; 940 MachineInstr *CPEMI = U.CPEMI; 941 942 // Check to see if the CPE is already in-range. 943 if (isCPEntryInRange(UserMI, UserOffset, CPEMI, U.getMaxDisp(), U.NegOk, 944 true)) { 945 DEBUG(dbgs() << "In range\n"); 946 return 1; 947 } 948 949 // No. Look for previously created clones of the CPE that are in range. 950 unsigned CPI = CPEMI->getOperand(1).getIndex(); 951 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 952 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 953 // We already tried this one 954 if (CPEs[i].CPEMI == CPEMI) 955 continue; 956 // Removing CPEs can leave empty entries, skip 957 if (CPEs[i].CPEMI == NULL) 958 continue; 959 if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, U.getMaxDisp(), 960 U.NegOk)) { 961 DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" 962 << CPEs[i].CPI << "\n"); 963 // Point the CPUser node to the replacement 964 U.CPEMI = CPEs[i].CPEMI; 965 // Change the CPI in the instruction operand to refer to the clone. 966 for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j) 967 if (UserMI->getOperand(j).isCPI()) { 968 UserMI->getOperand(j).setIndex(CPEs[i].CPI); 969 break; 970 } 971 // Adjust the refcount of the clone... 972 CPEs[i].RefCount++; 973 // ...and the original. If we didn't remove the old entry, none of the 974 // addresses changed, so we don't need another pass. 975 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1; 976 } 977 } 978 return 0; 979} 980 981/// LookForCPEntryInRange - see if the currently referenced CPE is in range; 982/// This version checks if the longer form of the instruction can be used to 983/// to satisfy things. 984/// if not, see if an in-range clone of the CPE is in range, and if so, 985/// change the data structures so the user references the clone. Returns: 986/// 0 = no existing entry found 987/// 1 = entry found, and there were no code insertions or deletions 988/// 2 = entry found, and there were code insertions or deletions 989int MipsConstantIslands::findLongFormInRangeCPEntry 990 (CPUser& U, unsigned UserOffset) 991{ 992 MachineInstr *UserMI = U.MI; 993 MachineInstr *CPEMI = U.CPEMI; 994 995 // Check to see if the CPE is already in-range. 996 if (isCPEntryInRange(UserMI, UserOffset, CPEMI, 997 U.getLongFormMaxDisp(), U.NegOk, 998 true)) { 999 DEBUG(dbgs() << "In range\n"); 1000 UserMI->setDesc(TII->get(U.getLongFormOpcode())); 1001 U.setMaxDisp(U.getLongFormMaxDisp()); 1002 return 2; // instruction is longer length now 1003 } 1004 1005 // No. Look for previously created clones of the CPE that are in range. 1006 unsigned CPI = CPEMI->getOperand(1).getIndex(); 1007 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 1008 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 1009 // We already tried this one 1010 if (CPEs[i].CPEMI == CPEMI) 1011 continue; 1012 // Removing CPEs can leave empty entries, skip 1013 if (CPEs[i].CPEMI == NULL) 1014 continue; 1015 if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, 1016 U.getLongFormMaxDisp(), U.NegOk)) { 1017 DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" 1018 << CPEs[i].CPI << "\n"); 1019 // Point the CPUser node to the replacement 1020 U.CPEMI = CPEs[i].CPEMI; 1021 // Change the CPI in the instruction operand to refer to the clone. 1022 for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j) 1023 if (UserMI->getOperand(j).isCPI()) { 1024 UserMI->getOperand(j).setIndex(CPEs[i].CPI); 1025 break; 1026 } 1027 // Adjust the refcount of the clone... 1028 CPEs[i].RefCount++; 1029 // ...and the original. If we didn't remove the old entry, none of the 1030 // addresses changed, so we don't need another pass. 1031 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1; 1032 } 1033 } 1034 return 0; 1035} 1036 1037/// getUnconditionalBrDisp - Returns the maximum displacement that can fit in 1038/// the specific unconditional branch instruction. 1039static inline unsigned getUnconditionalBrDisp(int Opc) { 1040 switch (Opc) { 1041 case Mips::Bimm16: 1042 return ((1<<10)-1)*2; 1043 case Mips::BimmX16: 1044 return ((1<<16)-1)*2; 1045 default: 1046 break; 1047 } 1048 return ((1<<16)-1)*2; 1049} 1050 1051/// findAvailableWater - Look for an existing entry in the WaterList in which 1052/// we can place the CPE referenced from U so it's within range of U's MI. 1053/// Returns true if found, false if not. If it returns true, WaterIter 1054/// is set to the WaterList entry. 1055/// To ensure that this pass 1056/// terminates, the CPE location for a particular CPUser is only allowed to 1057/// move to a lower address, so search backward from the end of the list and 1058/// prefer the first water that is in range. 1059bool MipsConstantIslands::findAvailableWater(CPUser &U, unsigned UserOffset, 1060 water_iterator &WaterIter) { 1061 if (WaterList.empty()) 1062 return false; 1063 1064 unsigned BestGrowth = ~0u; 1065 for (water_iterator IP = prior(WaterList.end()), B = WaterList.begin();; 1066 --IP) { 1067 MachineBasicBlock* WaterBB = *IP; 1068 // Check if water is in range and is either at a lower address than the 1069 // current "high water mark" or a new water block that was created since 1070 // the previous iteration by inserting an unconditional branch. In the 1071 // latter case, we want to allow resetting the high water mark back to 1072 // this new water since we haven't seen it before. Inserting branches 1073 // should be relatively uncommon and when it does happen, we want to be 1074 // sure to take advantage of it for all the CPEs near that block, so that 1075 // we don't insert more branches than necessary. 1076 unsigned Growth; 1077 if (isWaterInRange(UserOffset, WaterBB, U, Growth) && 1078 (WaterBB->getNumber() < U.HighWaterMark->getNumber() || 1079 NewWaterList.count(WaterBB)) && Growth < BestGrowth) { 1080 // This is the least amount of required padding seen so far. 1081 BestGrowth = Growth; 1082 WaterIter = IP; 1083 DEBUG(dbgs() << "Found water after BB#" << WaterBB->getNumber() 1084 << " Growth=" << Growth << '\n'); 1085 1086 // Keep looking unless it is perfect. 1087 if (BestGrowth == 0) 1088 return true; 1089 } 1090 if (IP == B) 1091 break; 1092 } 1093 return BestGrowth != ~0u; 1094} 1095 1096/// createNewWater - No existing WaterList entry will work for 1097/// CPUsers[CPUserIndex], so create a place to put the CPE. The end of the 1098/// block is used if in range, and the conditional branch munged so control 1099/// flow is correct. Otherwise the block is split to create a hole with an 1100/// unconditional branch around it. In either case NewMBB is set to a 1101/// block following which the new island can be inserted (the WaterList 1102/// is not adjusted). 1103void MipsConstantIslands::createNewWater(unsigned CPUserIndex, 1104 unsigned UserOffset, 1105 MachineBasicBlock *&NewMBB) { 1106 CPUser &U = CPUsers[CPUserIndex]; 1107 MachineInstr *UserMI = U.MI; 1108 MachineInstr *CPEMI = U.CPEMI; 1109 unsigned CPELogAlign = getCPELogAlign(CPEMI); 1110 MachineBasicBlock *UserMBB = UserMI->getParent(); 1111 const BasicBlockInfo &UserBBI = BBInfo[UserMBB->getNumber()]; 1112 1113 // If the block does not end in an unconditional branch already, and if the 1114 // end of the block is within range, make new water there. 1115 if (BBHasFallthrough(UserMBB)) { 1116 // Size of branch to insert. 1117 unsigned Delta = 2; 1118 // Compute the offset where the CPE will begin. 1119 unsigned CPEOffset = UserBBI.postOffset(CPELogAlign) + Delta; 1120 1121 if (isOffsetInRange(UserOffset, CPEOffset, U)) { 1122 DEBUG(dbgs() << "Split at end of BB#" << UserMBB->getNumber() 1123 << format(", expected CPE offset %#x\n", CPEOffset)); 1124 NewMBB = llvm::next(MachineFunction::iterator(UserMBB)); 1125 // Add an unconditional branch from UserMBB to fallthrough block. Record 1126 // it for branch lengthening; this new branch will not get out of range, 1127 // but if the preceding conditional branch is out of range, the targets 1128 // will be exchanged, and the altered branch may be out of range, so the 1129 // machinery has to know about it. 1130 int UncondBr = Mips::Bimm16; 1131 BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB); 1132 unsigned MaxDisp = getUnconditionalBrDisp(UncondBr); 1133 ImmBranches.push_back(ImmBranch(&UserMBB->back(), 1134 MaxDisp, false, UncondBr)); 1135 BBInfo[UserMBB->getNumber()].Size += Delta; 1136 adjustBBOffsetsAfter(UserMBB); 1137 return; 1138 } 1139 } 1140 1141 // What a big block. Find a place within the block to split it. 1142 1143 // Try to split the block so it's fully aligned. Compute the latest split 1144 // point where we can add a 4-byte branch instruction, and then align to 1145 // LogAlign which is the largest possible alignment in the function. 1146 unsigned LogAlign = MF->getAlignment(); 1147 assert(LogAlign >= CPELogAlign && "Over-aligned constant pool entry"); 1148 unsigned BaseInsertOffset = UserOffset + U.getMaxDisp(); 1149 DEBUG(dbgs() << format("Split in middle of big block before %#x", 1150 BaseInsertOffset)); 1151 1152 // The 4 in the following is for the unconditional branch we'll be inserting 1153 // Alignment of the island is handled 1154 // inside isOffsetInRange. 1155 BaseInsertOffset -= 4; 1156 1157 DEBUG(dbgs() << format(", adjusted to %#x", BaseInsertOffset) 1158 << " la=" << LogAlign << '\n'); 1159 1160 // This could point off the end of the block if we've already got constant 1161 // pool entries following this block; only the last one is in the water list. 1162 // Back past any possible branches (allow for a conditional and a maximally 1163 // long unconditional). 1164 if (BaseInsertOffset + 8 >= UserBBI.postOffset()) { 1165 BaseInsertOffset = UserBBI.postOffset() - 8; 1166 DEBUG(dbgs() << format("Move inside block: %#x\n", BaseInsertOffset)); 1167 } 1168 unsigned EndInsertOffset = BaseInsertOffset + 4 + 1169 CPEMI->getOperand(2).getImm(); 1170 MachineBasicBlock::iterator MI = UserMI; 1171 ++MI; 1172 unsigned CPUIndex = CPUserIndex+1; 1173 unsigned NumCPUsers = CPUsers.size(); 1174 //MachineInstr *LastIT = 0; 1175 for (unsigned Offset = UserOffset+TII->GetInstSizeInBytes(UserMI); 1176 Offset < BaseInsertOffset; 1177 Offset += TII->GetInstSizeInBytes(MI), 1178 MI = llvm::next(MI)) { 1179 assert(MI != UserMBB->end() && "Fell off end of block"); 1180 if (CPUIndex < NumCPUsers && CPUsers[CPUIndex].MI == MI) { 1181 CPUser &U = CPUsers[CPUIndex]; 1182 if (!isOffsetInRange(Offset, EndInsertOffset, U)) { 1183 // Shift intertion point by one unit of alignment so it is within reach. 1184 BaseInsertOffset -= 1u << LogAlign; 1185 EndInsertOffset -= 1u << LogAlign; 1186 } 1187 // This is overly conservative, as we don't account for CPEMIs being 1188 // reused within the block, but it doesn't matter much. Also assume CPEs 1189 // are added in order with alignment padding. We may eventually be able 1190 // to pack the aligned CPEs better. 1191 EndInsertOffset += U.CPEMI->getOperand(2).getImm(); 1192 CPUIndex++; 1193 } 1194 } 1195 1196 --MI; 1197 NewMBB = splitBlockBeforeInstr(MI); 1198} 1199 1200/// handleConstantPoolUser - Analyze the specified user, checking to see if it 1201/// is out-of-range. If so, pick up the constant pool value and move it some 1202/// place in-range. Return true if we changed any addresses (thus must run 1203/// another pass of branch lengthening), false otherwise. 1204bool MipsConstantIslands::handleConstantPoolUser(unsigned CPUserIndex) { 1205 CPUser &U = CPUsers[CPUserIndex]; 1206 MachineInstr *UserMI = U.MI; 1207 MachineInstr *CPEMI = U.CPEMI; 1208 unsigned CPI = CPEMI->getOperand(1).getIndex(); 1209 unsigned Size = CPEMI->getOperand(2).getImm(); 1210 // Compute this only once, it's expensive. 1211 unsigned UserOffset = getUserOffset(U); 1212 1213 // See if the current entry is within range, or there is a clone of it 1214 // in range. 1215 int result = findInRangeCPEntry(U, UserOffset); 1216 if (result==1) return false; 1217 else if (result==2) return true; 1218 1219 1220 // Look for water where we can place this CPE. 1221 MachineBasicBlock *NewIsland = MF->CreateMachineBasicBlock(); 1222 MachineBasicBlock *NewMBB; 1223 water_iterator IP; 1224 if (findAvailableWater(U, UserOffset, IP)) { 1225 DEBUG(dbgs() << "Found water in range\n"); 1226 MachineBasicBlock *WaterBB = *IP; 1227 1228 // If the original WaterList entry was "new water" on this iteration, 1229 // propagate that to the new island. This is just keeping NewWaterList 1230 // updated to match the WaterList, which will be updated below. 1231 if (NewWaterList.erase(WaterBB)) 1232 NewWaterList.insert(NewIsland); 1233 1234 // The new CPE goes before the following block (NewMBB). 1235 NewMBB = llvm::next(MachineFunction::iterator(WaterBB)); 1236 1237 } else { 1238 // No water found. 1239 // we first see if a longer form of the instrucion could have reached 1240 // the constant. in that case we won't bother to split 1241 if (!NoLoadRelaxation) { 1242 result = findLongFormInRangeCPEntry(U, UserOffset); 1243 if (result != 0) return true; 1244 } 1245 DEBUG(dbgs() << "No water found\n"); 1246 createNewWater(CPUserIndex, UserOffset, NewMBB); 1247 1248 // splitBlockBeforeInstr adds to WaterList, which is important when it is 1249 // called while handling branches so that the water will be seen on the 1250 // next iteration for constant pools, but in this context, we don't want 1251 // it. Check for this so it will be removed from the WaterList. 1252 // Also remove any entry from NewWaterList. 1253 MachineBasicBlock *WaterBB = prior(MachineFunction::iterator(NewMBB)); 1254 IP = std::find(WaterList.begin(), WaterList.end(), WaterBB); 1255 if (IP != WaterList.end()) 1256 NewWaterList.erase(WaterBB); 1257 1258 // We are adding new water. Update NewWaterList. 1259 NewWaterList.insert(NewIsland); 1260 } 1261 1262 // Remove the original WaterList entry; we want subsequent insertions in 1263 // this vicinity to go after the one we're about to insert. This 1264 // considerably reduces the number of times we have to move the same CPE 1265 // more than once and is also important to ensure the algorithm terminates. 1266 if (IP != WaterList.end()) 1267 WaterList.erase(IP); 1268 1269 // Okay, we know we can put an island before NewMBB now, do it! 1270 MF->insert(NewMBB, NewIsland); 1271 1272 // Update internal data structures to account for the newly inserted MBB. 1273 updateForInsertedWaterBlock(NewIsland); 1274 1275 // Decrement the old entry, and remove it if refcount becomes 0. 1276 decrementCPEReferenceCount(CPI, CPEMI); 1277 1278 // Now that we have an island to add the CPE to, clone the original CPE and 1279 // add it to the island. 1280 U.HighWaterMark = NewIsland; 1281 U.CPEMI = BuildMI(NewIsland, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY)) 1282 .addImm(ID).addConstantPoolIndex(CPI).addImm(Size); 1283 CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1)); 1284 ++NumCPEs; 1285 1286 // Mark the basic block as aligned as required by the const-pool entry. 1287 NewIsland->setAlignment(getCPELogAlign(U.CPEMI)); 1288 1289 // Increase the size of the island block to account for the new entry. 1290 BBInfo[NewIsland->getNumber()].Size += Size; 1291 adjustBBOffsetsAfter(llvm::prior(MachineFunction::iterator(NewIsland))); 1292 1293 // No existing clone of this CPE is within range. 1294 // We will be generating a new clone. Get a UID for it. 1295 unsigned ID = createPICLabelUId(); 1296 1297 // Finally, change the CPI in the instruction operand to be ID. 1298 for (unsigned i = 0, e = UserMI->getNumOperands(); i != e; ++i) 1299 if (UserMI->getOperand(i).isCPI()) { 1300 UserMI->getOperand(i).setIndex(ID); 1301 break; 1302 } 1303 1304 DEBUG(dbgs() << " Moved CPE to #" << ID << " CPI=" << CPI 1305 << format(" offset=%#x\n", BBInfo[NewIsland->getNumber()].Offset)); 1306 1307 return true; 1308} 1309 1310/// removeDeadCPEMI - Remove a dead constant pool entry instruction. Update 1311/// sizes and offsets of impacted basic blocks. 1312void MipsConstantIslands::removeDeadCPEMI(MachineInstr *CPEMI) { 1313 MachineBasicBlock *CPEBB = CPEMI->getParent(); 1314 unsigned Size = CPEMI->getOperand(2).getImm(); 1315 CPEMI->eraseFromParent(); 1316 BBInfo[CPEBB->getNumber()].Size -= Size; 1317 // All succeeding offsets have the current size value added in, fix this. 1318 if (CPEBB->empty()) { 1319 BBInfo[CPEBB->getNumber()].Size = 0; 1320 1321 // This block no longer needs to be aligned. 1322 CPEBB->setAlignment(0); 1323 } else 1324 // Entries are sorted by descending alignment, so realign from the front. 1325 CPEBB->setAlignment(getCPELogAlign(CPEBB->begin())); 1326 1327 adjustBBOffsetsAfter(CPEBB); 1328 // An island has only one predecessor BB and one successor BB. Check if 1329 // this BB's predecessor jumps directly to this BB's successor. This 1330 // shouldn't happen currently. 1331 assert(!BBIsJumpedOver(CPEBB) && "How did this happen?"); 1332 // FIXME: remove the empty blocks after all the work is done? 1333} 1334 1335/// removeUnusedCPEntries - Remove constant pool entries whose refcounts 1336/// are zero. 1337bool MipsConstantIslands::removeUnusedCPEntries() { 1338 unsigned MadeChange = false; 1339 for (unsigned i = 0, e = CPEntries.size(); i != e; ++i) { 1340 std::vector<CPEntry> &CPEs = CPEntries[i]; 1341 for (unsigned j = 0, ee = CPEs.size(); j != ee; ++j) { 1342 if (CPEs[j].RefCount == 0 && CPEs[j].CPEMI) { 1343 removeDeadCPEMI(CPEs[j].CPEMI); 1344 CPEs[j].CPEMI = NULL; 1345 MadeChange = true; 1346 } 1347 } 1348 } 1349 return MadeChange; 1350} 1351 1352/// isBBInRange - Returns true if the distance between specific MI and 1353/// specific BB can fit in MI's displacement field. 1354bool MipsConstantIslands::isBBInRange 1355 (MachineInstr *MI,MachineBasicBlock *DestBB, unsigned MaxDisp) { 1356 1357unsigned PCAdj = 4; 1358 1359 unsigned BrOffset = getOffsetOf(MI) + PCAdj; 1360 unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset; 1361 1362 DEBUG(dbgs() << "Branch of destination BB#" << DestBB->getNumber() 1363 << " from BB#" << MI->getParent()->getNumber() 1364 << " max delta=" << MaxDisp 1365 << " from " << getOffsetOf(MI) << " to " << DestOffset 1366 << " offset " << int(DestOffset-BrOffset) << "\t" << *MI); 1367 1368 if (BrOffset <= DestOffset) { 1369 // Branch before the Dest. 1370 if (DestOffset-BrOffset <= MaxDisp) 1371 return true; 1372 } else { 1373 if (BrOffset-DestOffset <= MaxDisp) 1374 return true; 1375 } 1376 return false; 1377} 1378 1379/// fixupImmediateBr - Fix up an immediate branch whose destination is too far 1380/// away to fit in its displacement field. 1381bool MipsConstantIslands::fixupImmediateBr(ImmBranch &Br) { 1382 MachineInstr *MI = Br.MI; 1383 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB(); 1384 1385 // Check to see if the DestBB is already in-range. 1386 if (isBBInRange(MI, DestBB, Br.MaxDisp)) 1387 return false; 1388 1389 if (!Br.isCond) 1390 return fixupUnconditionalBr(Br); 1391 return fixupConditionalBr(Br); 1392} 1393 1394/// fixupUnconditionalBr - Fix up an unconditional branch whose destination is 1395/// too far away to fit in its displacement field. If the LR register has been 1396/// spilled in the epilogue, then we can use BL to implement a far jump. 1397/// Otherwise, add an intermediate branch instruction to a branch. 1398bool 1399MipsConstantIslands::fixupUnconditionalBr(ImmBranch &Br) { 1400 MachineInstr *MI = Br.MI; 1401 MachineBasicBlock *MBB = MI->getParent(); 1402 // Use BL to implement far jump. 1403 Br.MaxDisp = ((1 << 16)-1) * 2; 1404 MI->setDesc(TII->get(Mips::BimmX16)); 1405 BBInfo[MBB->getNumber()].Size += 2; 1406 adjustBBOffsetsAfter(MBB); 1407 HasFarJump = true; 1408 ++NumUBrFixed; 1409 1410 DEBUG(dbgs() << " Changed B to long jump " << *MI); 1411 1412 return true; 1413} 1414 1415/// fixupConditionalBr - Fix up a conditional branch whose destination is too 1416/// far away to fit in its displacement field. It is converted to an inverse 1417/// conditional branch + an unconditional branch to the destination. 1418bool 1419MipsConstantIslands::fixupConditionalBr(ImmBranch &Br) { 1420 MachineInstr *MI = Br.MI; 1421 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB(); 1422 1423 // Add an unconditional branch to the destination and invert the branch 1424 // condition to jump over it: 1425 // blt L1 1426 // => 1427 // bge L2 1428 // b L1 1429 // L2: 1430 unsigned CCReg = 0; // FIXME 1431 unsigned CC=0; //FIXME 1432 1433 // If the branch is at the end of its MBB and that has a fall-through block, 1434 // direct the updated conditional branch to the fall-through block. Otherwise, 1435 // split the MBB before the next instruction. 1436 MachineBasicBlock *MBB = MI->getParent(); 1437 MachineInstr *BMI = &MBB->back(); 1438 bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB); 1439 1440 ++NumCBrFixed; 1441 if (BMI != MI) { 1442 if (llvm::next(MachineBasicBlock::iterator(MI)) == prior(MBB->end()) && 1443 BMI->getOpcode() == Br.UncondBr) { 1444 // Last MI in the BB is an unconditional branch. Can we simply invert the 1445 // condition and swap destinations: 1446 // beq L1 1447 // b L2 1448 // => 1449 // bne L2 1450 // b L1 1451 MachineBasicBlock *NewDest = BMI->getOperand(0).getMBB(); 1452 if (isBBInRange(MI, NewDest, Br.MaxDisp)) { 1453 DEBUG(dbgs() << " Invert Bcc condition and swap its destination with " 1454 << *BMI); 1455 BMI->getOperand(0).setMBB(DestBB); 1456 MI->getOperand(0).setMBB(NewDest); 1457 return true; 1458 } 1459 } 1460 } 1461 1462 if (NeedSplit) { 1463 splitBlockBeforeInstr(MI); 1464 // No need for the branch to the next block. We're adding an unconditional 1465 // branch to the destination. 1466 int delta = TII->GetInstSizeInBytes(&MBB->back()); 1467 BBInfo[MBB->getNumber()].Size -= delta; 1468 MBB->back().eraseFromParent(); 1469 // BBInfo[SplitBB].Offset is wrong temporarily, fixed below 1470 } 1471 MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB)); 1472 1473 DEBUG(dbgs() << " Insert B to BB#" << DestBB->getNumber() 1474 << " also invert condition and change dest. to BB#" 1475 << NextBB->getNumber() << "\n"); 1476 1477 // Insert a new conditional branch and a new unconditional branch. 1478 // Also update the ImmBranch as well as adding a new entry for the new branch. 1479 BuildMI(MBB, DebugLoc(), TII->get(MI->getOpcode())) 1480 .addMBB(NextBB).addImm(CC).addReg(CCReg); 1481 Br.MI = &MBB->back(); 1482 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back()); 1483 BuildMI(MBB, DebugLoc(), TII->get(Br.UncondBr)).addMBB(DestBB); 1484 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back()); 1485 unsigned MaxDisp = getUnconditionalBrDisp(Br.UncondBr); 1486 ImmBranches.push_back(ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr)); 1487 1488 // Remove the old conditional branch. It may or may not still be in MBB. 1489 BBInfo[MI->getParent()->getNumber()].Size -= TII->GetInstSizeInBytes(MI); 1490 MI->eraseFromParent(); 1491 adjustBBOffsetsAfter(MBB); 1492 return true; 1493} 1494 1495 1496void MipsConstantIslands::prescanForConstants() { 1497 unsigned J = 0; 1498 (void)J; 1499 PrescannedForConstants = true; 1500 for (MachineFunction::iterator B = 1501 MF->begin(), E = MF->end(); B != E; ++B) { 1502 for (MachineBasicBlock::instr_iterator I = 1503 B->instr_begin(), EB = B->instr_end(); I != EB; ++I) { 1504 switch(I->getDesc().getOpcode()) { 1505 case Mips::LwConstant32: { 1506 DEBUG(dbgs() << "constant island constant " << *I << "\n"); 1507 J = I->getNumOperands(); 1508 DEBUG(dbgs() << "num operands " << J << "\n"); 1509 MachineOperand& Literal = I->getOperand(1); 1510 if (Literal.isImm()) { 1511 int64_t V = Literal.getImm(); 1512 DEBUG(dbgs() << "literal " << V << "\n"); 1513 Type *Int32Ty = 1514 Type::getInt32Ty(MF->getFunction()->getContext()); 1515 const Constant *C = ConstantInt::get(Int32Ty, V); 1516 unsigned index = MCP->getConstantPoolIndex(C, 4); 1517 I->getOperand(2).ChangeToImmediate(index); 1518 DEBUG(dbgs() << "constant island constant " << *I << "\n"); 1519 I->setDesc(TII->get(Mips::LwRxPcTcp16)); 1520 I->RemoveOperand(1); 1521 I->RemoveOperand(1); 1522 I->addOperand(MachineOperand::CreateCPI(index, 0)); 1523 I->addOperand(MachineOperand::CreateImm(4)); 1524 } 1525 break; 1526 } 1527 default: 1528 break; 1529 } 1530 } 1531 } 1532} 1533 1534