MipsConstantIslandPass.cpp revision 50d3b27f431a213a53a0240849a8ce65dc46c8a5
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// 70// For testing purposes we tell it to not use relaxed load forms so that it 71// will split blocks. 72// 73static cl::opt<bool> NoLoadRelaxation( 74 "mips-constant-islands-no-load-relaxation", 75 cl::init(false), 76 cl::desc("Don't relax loads to long loads - for testing purposes"), 77 cl::Hidden); 78 79 80namespace { 81 82 83 typedef MachineBasicBlock::iterator Iter; 84 typedef MachineBasicBlock::reverse_iterator ReverseIter; 85 86 /// MipsConstantIslands - Due to limited PC-relative displacements, Mips 87 /// requires constant pool entries to be scattered among the instructions 88 /// inside a function. To do this, it completely ignores the normal LLVM 89 /// constant pool; instead, it places constants wherever it feels like with 90 /// special instructions. 91 /// 92 /// The terminology used in this pass includes: 93 /// Islands - Clumps of constants placed in the function. 94 /// Water - Potential places where an island could be formed. 95 /// CPE - A constant pool entry that has been placed somewhere, which 96 /// tracks a list of users. 97 98 class MipsConstantIslands : public MachineFunctionPass { 99 100 /// BasicBlockInfo - Information about the offset and size of a single 101 /// basic block. 102 struct BasicBlockInfo { 103 /// Offset - Distance from the beginning of the function to the beginning 104 /// of this basic block. 105 /// 106 /// Offsets are computed assuming worst case padding before an aligned 107 /// block. This means that subtracting basic block offsets always gives a 108 /// conservative estimate of the real distance which may be smaller. 109 /// 110 /// Because worst case padding is used, the computed offset of an aligned 111 /// block may not actually be aligned. 112 unsigned Offset; 113 114 /// Size - Size of the basic block in bytes. If the block contains 115 /// inline assembly, this is a worst case estimate. 116 /// 117 /// The size does not include any alignment padding whether from the 118 /// beginning of the block, or from an aligned jump table at the end. 119 unsigned Size; 120 121 // FIXME: ignore LogAlign for this patch 122 // 123 unsigned postOffset(unsigned LogAlign = 0) const { 124 unsigned PO = Offset + Size; 125 return PO; 126 } 127 128 BasicBlockInfo() : Offset(0), Size(0) {} 129 130 }; 131 132 std::vector<BasicBlockInfo> BBInfo; 133 134 /// WaterList - A sorted list of basic blocks where islands could be placed 135 /// (i.e. blocks that don't fall through to the following block, due 136 /// to a return, unreachable, or unconditional branch). 137 std::vector<MachineBasicBlock*> WaterList; 138 139 /// NewWaterList - The subset of WaterList that was created since the 140 /// previous iteration by inserting unconditional branches. 141 SmallSet<MachineBasicBlock*, 4> NewWaterList; 142 143 typedef std::vector<MachineBasicBlock*>::iterator water_iterator; 144 145 /// CPUser - One user of a constant pool, keeping the machine instruction 146 /// pointer, the constant pool being referenced, and the max displacement 147 /// allowed from the instruction to the CP. The HighWaterMark records the 148 /// highest basic block where a new CPEntry can be placed. To ensure this 149 /// pass terminates, the CP entries are initially placed at the end of the 150 /// function and then move monotonically to lower addresses. The 151 /// exception to this rule is when the current CP entry for a particular 152 /// CPUser is out of range, but there is another CP entry for the same 153 /// constant value in range. We want to use the existing in-range CP 154 /// entry, but if it later moves out of range, the search for new water 155 /// should resume where it left off. The HighWaterMark is used to record 156 /// that point. 157 struct CPUser { 158 MachineInstr *MI; 159 MachineInstr *CPEMI; 160 MachineBasicBlock *HighWaterMark; 161 private: 162 unsigned MaxDisp; 163 unsigned LongFormMaxDisp; // mips16 has 16/32 bit instructions 164 // with different displacements 165 unsigned LongFormOpcode; 166 public: 167 bool NegOk; 168 CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp, 169 bool neg, 170 unsigned longformmaxdisp, unsigned longformopcode) 171 : MI(mi), CPEMI(cpemi), MaxDisp(maxdisp), 172 LongFormMaxDisp(longformmaxdisp), LongFormOpcode(longformopcode), 173 NegOk(neg){ 174 HighWaterMark = CPEMI->getParent(); 175 } 176 /// getMaxDisp - Returns the maximum displacement supported by MI. 177 unsigned getMaxDisp() const { 178 unsigned xMaxDisp = ConstantIslandsSmallOffset? 179 ConstantIslandsSmallOffset: MaxDisp; 180 return xMaxDisp; 181 } 182 void setMaxDisp(unsigned val) { 183 MaxDisp = val; 184 } 185 unsigned getLongFormMaxDisp() const { 186 return LongFormMaxDisp; 187 } 188 unsigned getLongFormOpcode() const { 189 return LongFormOpcode; 190 } 191 }; 192 193 /// CPUsers - Keep track of all of the machine instructions that use various 194 /// constant pools and their max displacement. 195 std::vector<CPUser> CPUsers; 196 197 /// CPEntry - One per constant pool entry, keeping the machine instruction 198 /// pointer, the constpool index, and the number of CPUser's which 199 /// reference this entry. 200 struct CPEntry { 201 MachineInstr *CPEMI; 202 unsigned CPI; 203 unsigned RefCount; 204 CPEntry(MachineInstr *cpemi, unsigned cpi, unsigned rc = 0) 205 : CPEMI(cpemi), CPI(cpi), RefCount(rc) {} 206 }; 207 208 /// CPEntries - Keep track of all of the constant pool entry machine 209 /// instructions. For each original constpool index (i.e. those that 210 /// existed upon entry to this pass), it keeps a vector of entries. 211 /// Original elements are cloned as we go along; the clones are 212 /// put in the vector of the original element, but have distinct CPIs. 213 std::vector<std::vector<CPEntry> > CPEntries; 214 215 /// ImmBranch - One per immediate branch, keeping the machine instruction 216 /// pointer, conditional or unconditional, the max displacement, 217 /// and (if isCond is true) the corresponding unconditional branch 218 /// opcode. 219 struct ImmBranch { 220 MachineInstr *MI; 221 unsigned MaxDisp : 31; 222 bool isCond : 1; 223 int UncondBr; 224 ImmBranch(MachineInstr *mi, unsigned maxdisp, bool cond, int ubr) 225 : MI(mi), MaxDisp(maxdisp), isCond(cond), UncondBr(ubr) {} 226 }; 227 228 /// ImmBranches - Keep track of all the immediate branch instructions. 229 /// 230 std::vector<ImmBranch> ImmBranches; 231 232 /// HasFarJump - True if any far jump instruction has been emitted during 233 /// the branch fix up pass. 234 bool HasFarJump; 235 236 const TargetMachine &TM; 237 bool IsPIC; 238 unsigned ABI; 239 const MipsSubtarget *STI; 240 const MipsInstrInfo *TII; 241 MipsFunctionInfo *MFI; 242 MachineFunction *MF; 243 MachineConstantPool *MCP; 244 245 unsigned PICLabelUId; 246 bool PrescannedForConstants; 247 248 void initPICLabelUId(unsigned UId) { 249 PICLabelUId = UId; 250 } 251 252 253 unsigned createPICLabelUId() { 254 return PICLabelUId++; 255 } 256 257 public: 258 static char ID; 259 MipsConstantIslands(TargetMachine &tm) 260 : MachineFunctionPass(ID), TM(tm), 261 IsPIC(TM.getRelocationModel() == Reloc::PIC_), 262 ABI(TM.getSubtarget<MipsSubtarget>().getTargetABI()), 263 STI(&TM.getSubtarget<MipsSubtarget>()), MF(0), MCP(0), 264 PrescannedForConstants(false){} 265 266 virtual const char *getPassName() const { 267 return "Mips Constant Islands"; 268 } 269 270 bool runOnMachineFunction(MachineFunction &F); 271 272 void doInitialPlacement(std::vector<MachineInstr*> &CPEMIs); 273 CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI); 274 unsigned getCPELogAlign(const MachineInstr *CPEMI); 275 void initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs); 276 unsigned getOffsetOf(MachineInstr *MI) const; 277 unsigned getUserOffset(CPUser&) const; 278 void dumpBBs(); 279 void verify(); 280 281 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 282 unsigned Disp, bool NegativeOK); 283 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 284 const CPUser &U); 285 286 bool isLongFormOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 287 const CPUser &U); 288 289 void computeBlockSize(MachineBasicBlock *MBB); 290 MachineBasicBlock *splitBlockBeforeInstr(MachineInstr *MI); 291 void updateForInsertedWaterBlock(MachineBasicBlock *NewBB); 292 void adjustBBOffsetsAfter(MachineBasicBlock *BB); 293 bool decrementCPEReferenceCount(unsigned CPI, MachineInstr* CPEMI); 294 int findInRangeCPEntry(CPUser& U, unsigned UserOffset); 295 int findLongFormInRangeCPEntry(CPUser& U, unsigned UserOffset); 296 bool findAvailableWater(CPUser&U, unsigned UserOffset, 297 water_iterator &WaterIter); 298 void createNewWater(unsigned CPUserIndex, unsigned UserOffset, 299 MachineBasicBlock *&NewMBB); 300 bool handleConstantPoolUser(unsigned CPUserIndex); 301 void removeDeadCPEMI(MachineInstr *CPEMI); 302 bool removeUnusedCPEntries(); 303 bool isCPEntryInRange(MachineInstr *MI, unsigned UserOffset, 304 MachineInstr *CPEMI, unsigned Disp, bool NegOk, 305 bool DoDump = false); 306 bool isWaterInRange(unsigned UserOffset, MachineBasicBlock *Water, 307 CPUser &U, unsigned &Growth); 308 bool isBBInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp); 309 bool fixupImmediateBr(ImmBranch &Br); 310 bool fixupConditionalBr(ImmBranch &Br); 311 bool fixupUnconditionalBr(ImmBranch &Br); 312 313 void prescanForConstants(); 314 315 private: 316 317 }; 318 319 char MipsConstantIslands::ID = 0; 320} // end of anonymous namespace 321 322 323bool MipsConstantIslands::isLongFormOffsetInRange 324 (unsigned UserOffset, unsigned TrialOffset, 325 const CPUser &U) { 326 return isOffsetInRange(UserOffset, TrialOffset, 327 U.getLongFormMaxDisp(), U.NegOk); 328} 329 330bool MipsConstantIslands::isOffsetInRange 331 (unsigned UserOffset, unsigned TrialOffset, 332 const CPUser &U) { 333 return isOffsetInRange(UserOffset, TrialOffset, 334 U.getMaxDisp(), U.NegOk); 335} 336/// print block size and offset information - debugging 337void MipsConstantIslands::dumpBBs() { 338 DEBUG({ 339 for (unsigned J = 0, E = BBInfo.size(); J !=E; ++J) { 340 const BasicBlockInfo &BBI = BBInfo[J]; 341 dbgs() << format("%08x BB#%u\t", BBI.Offset, J) 342 << format(" size=%#x\n", BBInfo[J].Size); 343 } 344 }); 345} 346/// createMipsLongBranchPass - Returns a pass that converts branches to long 347/// branches. 348FunctionPass *llvm::createMipsConstantIslandPass(MipsTargetMachine &tm) { 349 return new MipsConstantIslands(tm); 350} 351 352bool MipsConstantIslands::runOnMachineFunction(MachineFunction &mf) { 353 // The intention is for this to be a mips16 only pass for now 354 // FIXME: 355 MF = &mf; 356 MCP = mf.getConstantPool(); 357 DEBUG(dbgs() << "constant island machine function " << "\n"); 358 if (!TM.getSubtarget<MipsSubtarget>().inMips16Mode() || 359 !MipsSubtarget::useConstantIslands()) { 360 return false; 361 } 362 TII = (const MipsInstrInfo*)MF->getTarget().getInstrInfo(); 363 MFI = MF->getInfo<MipsFunctionInfo>(); 364 DEBUG(dbgs() << "constant island processing " << "\n"); 365 // 366 // will need to make predermination if there is any constants we need to 367 // put in constant islands. TBD. 368 // 369 if (!PrescannedForConstants) prescanForConstants(); 370 371 HasFarJump = false; 372 // This pass invalidates liveness information when it splits basic blocks. 373 MF->getRegInfo().invalidateLiveness(); 374 375 // Renumber all of the machine basic blocks in the function, guaranteeing that 376 // the numbers agree with the position of the block in the function. 377 MF->RenumberBlocks(); 378 379 bool MadeChange = false; 380 381 // Perform the initial placement of the constant pool entries. To start with, 382 // we put them all at the end of the function. 383 std::vector<MachineInstr*> CPEMIs; 384 if (!MCP->isEmpty()) 385 doInitialPlacement(CPEMIs); 386 387 /// The next UID to take is the first unused one. 388 initPICLabelUId(CPEMIs.size()); 389 390 // Do the initial scan of the function, building up information about the 391 // sizes of each block, the location of all the water, and finding all of the 392 // constant pool users. 393 initializeFunctionInfo(CPEMIs); 394 CPEMIs.clear(); 395 DEBUG(dumpBBs()); 396 397 /// Remove dead constant pool entries. 398 MadeChange |= removeUnusedCPEntries(); 399 400 // Iteratively place constant pool entries and fix up branches until there 401 // is no change. 402 unsigned NoCPIters = 0, NoBRIters = 0; 403 (void)NoBRIters; 404 while (true) { 405 DEBUG(dbgs() << "Beginning CP iteration #" << NoCPIters << '\n'); 406 bool CPChange = false; 407 for (unsigned i = 0, e = CPUsers.size(); i != e; ++i) 408 CPChange |= handleConstantPoolUser(i); 409 if (CPChange && ++NoCPIters > 30) 410 report_fatal_error("Constant Island pass failed to converge!"); 411 DEBUG(dumpBBs()); 412 413 // Clear NewWaterList now. If we split a block for branches, it should 414 // appear as "new water" for the next iteration of constant pool placement. 415 NewWaterList.clear(); 416 417 DEBUG(dbgs() << "Beginning BR iteration #" << NoBRIters << '\n'); 418 bool BRChange = false; 419#ifdef IN_PROGRESS 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#endif 426 if (!CPChange && !BRChange) 427 break; 428 MadeChange = true; 429 } 430 431 DEBUG(dbgs() << '\n'; dumpBBs()); 432 433 BBInfo.clear(); 434 WaterList.clear(); 435 CPUsers.clear(); 436 CPEntries.clear(); 437 ImmBranches.clear(); 438 return MadeChange; 439} 440 441/// doInitialPlacement - Perform the initial placement of the constant pool 442/// entries. To start with, we put them all at the end of the function. 443void 444MipsConstantIslands::doInitialPlacement(std::vector<MachineInstr*> &CPEMIs) { 445 // Create the basic block to hold the CPE's. 446 MachineBasicBlock *BB = MF->CreateMachineBasicBlock(); 447 MF->push_back(BB); 448 449 450 // MachineConstantPool measures alignment in bytes. We measure in log2(bytes). 451 unsigned MaxAlign = Log2_32(MCP->getConstantPoolAlignment()); 452 453 // Mark the basic block as required by the const-pool. 454 // If AlignConstantIslands isn't set, use 4-byte alignment for everything. 455 BB->setAlignment(AlignConstantIslands ? MaxAlign : 2); 456 457 // The function needs to be as aligned as the basic blocks. The linker may 458 // move functions around based on their alignment. 459 MF->ensureAlignment(BB->getAlignment()); 460 461 // Order the entries in BB by descending alignment. That ensures correct 462 // alignment of all entries as long as BB is sufficiently aligned. Keep 463 // track of the insertion point for each alignment. We are going to bucket 464 // sort the entries as they are created. 465 SmallVector<MachineBasicBlock::iterator, 8> InsPoint(MaxAlign + 1, BB->end()); 466 467 // Add all of the constants from the constant pool to the end block, use an 468 // identity mapping of CPI's to CPE's. 469 const std::vector<MachineConstantPoolEntry> &CPs = MCP->getConstants(); 470 471 const DataLayout &TD = *MF->getTarget().getDataLayout(); 472 for (unsigned i = 0, e = CPs.size(); i != e; ++i) { 473 unsigned Size = TD.getTypeAllocSize(CPs[i].getType()); 474 assert(Size >= 4 && "Too small constant pool entry"); 475 unsigned Align = CPs[i].getAlignment(); 476 assert(isPowerOf2_32(Align) && "Invalid alignment"); 477 // Verify that all constant pool entries are a multiple of their alignment. 478 // If not, we would have to pad them out so that instructions stay aligned. 479 assert((Size % Align) == 0 && "CP Entry not multiple of 4 bytes!"); 480 481 // Insert CONSTPOOL_ENTRY before entries with a smaller alignment. 482 unsigned LogAlign = Log2_32(Align); 483 MachineBasicBlock::iterator InsAt = InsPoint[LogAlign]; 484 485 MachineInstr *CPEMI = 486 BuildMI(*BB, InsAt, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY)) 487 .addImm(i).addConstantPoolIndex(i).addImm(Size); 488 489 CPEMIs.push_back(CPEMI); 490 491 // Ensure that future entries with higher alignment get inserted before 492 // CPEMI. This is bucket sort with iterators. 493 for (unsigned a = LogAlign + 1; a <= MaxAlign; ++a) 494 if (InsPoint[a] == InsAt) 495 InsPoint[a] = CPEMI; 496 // Add a new CPEntry, but no corresponding CPUser yet. 497 std::vector<CPEntry> CPEs; 498 CPEs.push_back(CPEntry(CPEMI, i)); 499 CPEntries.push_back(CPEs); 500 ++NumCPEs; 501 DEBUG(dbgs() << "Moved CPI#" << i << " to end of function, size = " 502 << Size << ", align = " << Align <<'\n'); 503 } 504 DEBUG(BB->dump()); 505} 506 507/// BBHasFallthrough - Return true if the specified basic block can fallthrough 508/// into the block immediately after it. 509static bool BBHasFallthrough(MachineBasicBlock *MBB) { 510 // Get the next machine basic block in the function. 511 MachineFunction::iterator MBBI = MBB; 512 // Can't fall off end of function. 513 if (llvm::next(MBBI) == MBB->getParent()->end()) 514 return false; 515 516 MachineBasicBlock *NextBB = llvm::next(MBBI); 517 for (MachineBasicBlock::succ_iterator I = MBB->succ_begin(), 518 E = MBB->succ_end(); I != E; ++I) 519 if (*I == NextBB) 520 return true; 521 522 return false; 523} 524 525/// findConstPoolEntry - Given the constpool index and CONSTPOOL_ENTRY MI, 526/// look up the corresponding CPEntry. 527MipsConstantIslands::CPEntry 528*MipsConstantIslands::findConstPoolEntry(unsigned CPI, 529 const MachineInstr *CPEMI) { 530 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 531 // Number of entries per constpool index should be small, just do a 532 // linear search. 533 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 534 if (CPEs[i].CPEMI == CPEMI) 535 return &CPEs[i]; 536 } 537 return NULL; 538} 539 540/// getCPELogAlign - Returns the required alignment of the constant pool entry 541/// represented by CPEMI. Alignment is measured in log2(bytes) units. 542unsigned MipsConstantIslands::getCPELogAlign(const MachineInstr *CPEMI) { 543 assert(CPEMI && CPEMI->getOpcode() == Mips::CONSTPOOL_ENTRY); 544 545 // Everything is 4-byte aligned unless AlignConstantIslands is set. 546 if (!AlignConstantIslands) 547 return 2; 548 549 unsigned CPI = CPEMI->getOperand(1).getIndex(); 550 assert(CPI < MCP->getConstants().size() && "Invalid constant pool index."); 551 unsigned Align = MCP->getConstants()[CPI].getAlignment(); 552 assert(isPowerOf2_32(Align) && "Invalid CPE alignment"); 553 return Log2_32(Align); 554} 555 556/// initializeFunctionInfo - Do the initial scan of the function, building up 557/// information about the sizes of each block, the location of all the water, 558/// and finding all of the constant pool users. 559void MipsConstantIslands:: 560initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs) { 561 BBInfo.clear(); 562 BBInfo.resize(MF->getNumBlockIDs()); 563 564 // First thing, compute the size of all basic blocks, and see if the function 565 // has any inline assembly in it. If so, we have to be conservative about 566 // alignment assumptions, as we don't know for sure the size of any 567 // instructions in the inline assembly. 568 for (MachineFunction::iterator I = MF->begin(), E = MF->end(); I != E; ++I) 569 computeBlockSize(I); 570 571 572 // Compute block offsets. 573 adjustBBOffsetsAfter(MF->begin()); 574 575 // Now go back through the instructions and build up our data structures. 576 for (MachineFunction::iterator MBBI = MF->begin(), E = MF->end(); 577 MBBI != E; ++MBBI) { 578 MachineBasicBlock &MBB = *MBBI; 579 580 // If this block doesn't fall through into the next MBB, then this is 581 // 'water' that a constant pool island could be placed. 582 if (!BBHasFallthrough(&MBB)) 583 WaterList.push_back(&MBB); 584 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); 585 I != E; ++I) { 586 if (I->isDebugValue()) 587 continue; 588 589 int Opc = I->getOpcode(); 590#ifdef IN_PROGRESS 591 if (I->isBranch()) { 592 bool isCond = false; 593 unsigned Bits = 0; 594 unsigned Scale = 1; 595 int UOpc = Opc; 596 switch (Opc) { 597 default: 598 continue; // Ignore other JT branches 599 } 600 // Record this immediate branch. 601 unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale; 602 ImmBranches.push_back(ImmBranch(I, MaxOffs, isCond, UOpc)); 603 } 604#endif 605 606 if (Opc == Mips::CONSTPOOL_ENTRY) 607 continue; 608 609 610 // Scan the instructions for constant pool operands. 611 for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) 612 if (I->getOperand(op).isCPI()) { 613 614 // We found one. The addressing mode tells us the max displacement 615 // from the PC that this instruction permits. 616 617 // Basic size info comes from the TSFlags field. 618 unsigned Bits = 0; 619 unsigned Scale = 1; 620 bool NegOk = false; 621 unsigned LongFormBits = 0; 622 unsigned LongFormScale = 0; 623 unsigned LongFormOpcode = 0; 624 switch (Opc) { 625 default: 626 llvm_unreachable("Unknown addressing mode for CP reference!"); 627 case Mips::LwRxPcTcp16: 628 Bits = 8; 629 Scale = 4; 630 LongFormOpcode = Mips::LwRxPcTcpX16; 631 LongFormBits = 16; 632 LongFormScale = 1; 633 break; 634 case Mips::LwRxPcTcpX16: 635 Bits = 16; 636 Scale = 1; 637 NegOk = true; 638 break; 639 } 640 // Remember that this is a user of a CP entry. 641 unsigned CPI = I->getOperand(op).getIndex(); 642 MachineInstr *CPEMI = CPEMIs[CPI]; 643 unsigned MaxOffs = ((1 << Bits)-1) * Scale; 644 unsigned LongFormMaxOffs = ((1 << LongFormBits)-1) * LongFormScale; 645 CPUsers.push_back(CPUser(I, CPEMI, MaxOffs, NegOk, 646 LongFormMaxOffs, LongFormOpcode)); 647 648 // Increment corresponding CPEntry reference count. 649 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI); 650 assert(CPE && "Cannot find a corresponding CPEntry!"); 651 CPE->RefCount++; 652 653 // Instructions can only use one CP entry, don't bother scanning the 654 // rest of the operands. 655 break; 656 657 } 658 659 } 660 } 661 662} 663 664/// computeBlockSize - Compute the size and some alignment information for MBB. 665/// This function updates BBInfo directly. 666void MipsConstantIslands::computeBlockSize(MachineBasicBlock *MBB) { 667 BasicBlockInfo &BBI = BBInfo[MBB->getNumber()]; 668 BBI.Size = 0; 669 670 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E; 671 ++I) 672 BBI.Size += TII->GetInstSizeInBytes(I); 673 674} 675 676/// getOffsetOf - Return the current offset of the specified machine instruction 677/// from the start of the function. This offset changes as stuff is moved 678/// around inside the function. 679unsigned MipsConstantIslands::getOffsetOf(MachineInstr *MI) const { 680 MachineBasicBlock *MBB = MI->getParent(); 681 682 // The offset is composed of two things: the sum of the sizes of all MBB's 683 // before this instruction's block, and the offset from the start of the block 684 // it is in. 685 unsigned Offset = BBInfo[MBB->getNumber()].Offset; 686 687 // Sum instructions before MI in MBB. 688 for (MachineBasicBlock::iterator I = MBB->begin(); &*I != MI; ++I) { 689 assert(I != MBB->end() && "Didn't find MI in its own basic block?"); 690 Offset += TII->GetInstSizeInBytes(I); 691 } 692 return Offset; 693} 694 695/// CompareMBBNumbers - Little predicate function to sort the WaterList by MBB 696/// ID. 697static bool CompareMBBNumbers(const MachineBasicBlock *LHS, 698 const MachineBasicBlock *RHS) { 699 return LHS->getNumber() < RHS->getNumber(); 700} 701 702/// updateForInsertedWaterBlock - When a block is newly inserted into the 703/// machine function, it upsets all of the block numbers. Renumber the blocks 704/// and update the arrays that parallel this numbering. 705void MipsConstantIslands::updateForInsertedWaterBlock 706 (MachineBasicBlock *NewBB) { 707 // Renumber the MBB's to keep them consecutive. 708 NewBB->getParent()->RenumberBlocks(NewBB); 709 710 // Insert an entry into BBInfo to align it properly with the (newly 711 // renumbered) block numbers. 712 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo()); 713 714 // Next, update WaterList. Specifically, we need to add NewMBB as having 715 // available water after it. 716 water_iterator IP = 717 std::lower_bound(WaterList.begin(), WaterList.end(), NewBB, 718 CompareMBBNumbers); 719 WaterList.insert(IP, NewBB); 720} 721 722unsigned MipsConstantIslands::getUserOffset(CPUser &U) const { 723 return getOffsetOf(U.MI); 724} 725 726/// Split the basic block containing MI into two blocks, which are joined by 727/// an unconditional branch. Update data structures and renumber blocks to 728/// account for this change and returns the newly created block. 729MachineBasicBlock *MipsConstantIslands::splitBlockBeforeInstr 730 (MachineInstr *MI) { 731 MachineBasicBlock *OrigBB = MI->getParent(); 732 733 // Create a new MBB for the code after the OrigBB. 734 MachineBasicBlock *NewBB = 735 MF->CreateMachineBasicBlock(OrigBB->getBasicBlock()); 736 MachineFunction::iterator MBBI = OrigBB; ++MBBI; 737 MF->insert(MBBI, NewBB); 738 739 // Splice the instructions starting with MI over to NewBB. 740 NewBB->splice(NewBB->end(), OrigBB, MI, OrigBB->end()); 741 742 // Add an unconditional branch from OrigBB to NewBB. 743 // Note the new unconditional branch is not being recorded. 744 // There doesn't seem to be meaningful DebugInfo available; this doesn't 745 // correspond to anything in the source. 746 BuildMI(OrigBB, DebugLoc(), TII->get(Mips::BimmX16)).addMBB(NewBB); 747 ++NumSplit; 748 749 // Update the CFG. All succs of OrigBB are now succs of NewBB. 750 NewBB->transferSuccessors(OrigBB); 751 752 // OrigBB branches to NewBB. 753 OrigBB->addSuccessor(NewBB); 754 755 // Update internal data structures to account for the newly inserted MBB. 756 // This is almost the same as updateForInsertedWaterBlock, except that 757 // the Water goes after OrigBB, not NewBB. 758 MF->RenumberBlocks(NewBB); 759 760 // Insert an entry into BBInfo to align it properly with the (newly 761 // renumbered) block numbers. 762 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo()); 763 764 // Next, update WaterList. Specifically, we need to add OrigMBB as having 765 // available water after it (but not if it's already there, which happens 766 // when splitting before a conditional branch that is followed by an 767 // unconditional branch - in that case we want to insert NewBB). 768 water_iterator IP = 769 std::lower_bound(WaterList.begin(), WaterList.end(), OrigBB, 770 CompareMBBNumbers); 771 MachineBasicBlock* WaterBB = *IP; 772 if (WaterBB == OrigBB) 773 WaterList.insert(llvm::next(IP), NewBB); 774 else 775 WaterList.insert(IP, OrigBB); 776 NewWaterList.insert(OrigBB); 777 778 // Figure out how large the OrigBB is. As the first half of the original 779 // block, it cannot contain a tablejump. The size includes 780 // the new jump we added. (It should be possible to do this without 781 // recounting everything, but it's very confusing, and this is rarely 782 // executed.) 783 computeBlockSize(OrigBB); 784 785 // Figure out how large the NewMBB is. As the second half of the original 786 // block, it may contain a tablejump. 787 computeBlockSize(NewBB); 788 789 // All BBOffsets following these blocks must be modified. 790 adjustBBOffsetsAfter(OrigBB); 791 792 return NewBB; 793} 794 795 796 797/// isOffsetInRange - Checks whether UserOffset (the location of a constant pool 798/// reference) is within MaxDisp of TrialOffset (a proposed location of a 799/// constant pool entry). 800bool MipsConstantIslands::isOffsetInRange(unsigned UserOffset, 801 unsigned TrialOffset, unsigned MaxDisp, 802 bool NegativeOK) { 803 if (UserOffset <= TrialOffset) { 804 // User before the Trial. 805 if (TrialOffset - UserOffset <= MaxDisp) 806 return true; 807 } else if (NegativeOK) { 808 if (UserOffset - TrialOffset <= MaxDisp) 809 return true; 810 } 811 return false; 812} 813 814/// isWaterInRange - Returns true if a CPE placed after the specified 815/// Water (a basic block) will be in range for the specific MI. 816/// 817/// Compute how much the function will grow by inserting a CPE after Water. 818bool MipsConstantIslands::isWaterInRange(unsigned UserOffset, 819 MachineBasicBlock* Water, CPUser &U, 820 unsigned &Growth) { 821 unsigned CPELogAlign = getCPELogAlign(U.CPEMI); 822 unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset(CPELogAlign); 823 unsigned NextBlockOffset, NextBlockAlignment; 824 MachineFunction::const_iterator NextBlock = Water; 825 if (++NextBlock == MF->end()) { 826 NextBlockOffset = BBInfo[Water->getNumber()].postOffset(); 827 NextBlockAlignment = 0; 828 } else { 829 NextBlockOffset = BBInfo[NextBlock->getNumber()].Offset; 830 NextBlockAlignment = NextBlock->getAlignment(); 831 } 832 unsigned Size = U.CPEMI->getOperand(2).getImm(); 833 unsigned CPEEnd = CPEOffset + Size; 834 835 // The CPE may be able to hide in the alignment padding before the next 836 // block. It may also cause more padding to be required if it is more aligned 837 // that the next block. 838 if (CPEEnd > NextBlockOffset) { 839 Growth = CPEEnd - NextBlockOffset; 840 // Compute the padding that would go at the end of the CPE to align the next 841 // block. 842 Growth += OffsetToAlignment(CPEEnd, 1u << NextBlockAlignment); 843 844 // If the CPE is to be inserted before the instruction, that will raise 845 // the offset of the instruction. Also account for unknown alignment padding 846 // in blocks between CPE and the user. 847 if (CPEOffset < UserOffset) 848 UserOffset += Growth; 849 } else 850 // CPE fits in existing padding. 851 Growth = 0; 852 853 return isOffsetInRange(UserOffset, CPEOffset, U); 854} 855 856/// isCPEntryInRange - Returns true if the distance between specific MI and 857/// specific ConstPool entry instruction can fit in MI's displacement field. 858bool MipsConstantIslands::isCPEntryInRange 859 (MachineInstr *MI, unsigned UserOffset, 860 MachineInstr *CPEMI, unsigned MaxDisp, 861 bool NegOk, bool DoDump) { 862 unsigned CPEOffset = getOffsetOf(CPEMI); 863 864 if (DoDump) { 865 DEBUG({ 866 unsigned Block = MI->getParent()->getNumber(); 867 const BasicBlockInfo &BBI = BBInfo[Block]; 868 dbgs() << "User of CPE#" << CPEMI->getOperand(0).getImm() 869 << " max delta=" << MaxDisp 870 << format(" insn address=%#x", UserOffset) 871 << " in BB#" << Block << ": " 872 << format("%#x-%x\t", BBI.Offset, BBI.postOffset()) << *MI 873 << format("CPE address=%#x offset=%+d: ", CPEOffset, 874 int(CPEOffset-UserOffset)); 875 }); 876 } 877 878 return isOffsetInRange(UserOffset, CPEOffset, MaxDisp, NegOk); 879} 880 881#ifndef NDEBUG 882/// BBIsJumpedOver - Return true of the specified basic block's only predecessor 883/// unconditionally branches to its only successor. 884static bool BBIsJumpedOver(MachineBasicBlock *MBB) { 885 if (MBB->pred_size() != 1 || MBB->succ_size() != 1) 886 return false; 887 MachineBasicBlock *Succ = *MBB->succ_begin(); 888 MachineBasicBlock *Pred = *MBB->pred_begin(); 889 MachineInstr *PredMI = &Pred->back(); 890 if (PredMI->getOpcode() == Mips::BimmX16) 891 return PredMI->getOperand(0).getMBB() == Succ; 892 return false; 893} 894#endif 895 896void MipsConstantIslands::adjustBBOffsetsAfter(MachineBasicBlock *BB) { 897 unsigned BBNum = BB->getNumber(); 898 for(unsigned i = BBNum + 1, e = MF->getNumBlockIDs(); i < e; ++i) { 899 // Get the offset and known bits at the end of the layout predecessor. 900 // Include the alignment of the current block. 901 unsigned Offset = BBInfo[i - 1].Offset + BBInfo[i - 1].Size; 902 BBInfo[i].Offset = Offset; 903 } 904} 905 906/// decrementCPEReferenceCount - find the constant pool entry with index CPI 907/// and instruction CPEMI, and decrement its refcount. If the refcount 908/// becomes 0 remove the entry and instruction. Returns true if we removed 909/// the entry, false if we didn't. 910 911bool MipsConstantIslands::decrementCPEReferenceCount(unsigned CPI, 912 MachineInstr *CPEMI) { 913 // Find the old entry. Eliminate it if it is no longer used. 914 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI); 915 assert(CPE && "Unexpected!"); 916 if (--CPE->RefCount == 0) { 917 removeDeadCPEMI(CPEMI); 918 CPE->CPEMI = NULL; 919 --NumCPEs; 920 return true; 921 } 922 return false; 923} 924 925/// LookForCPEntryInRange - see if the currently referenced CPE is in range; 926/// if not, see if an in-range clone of the CPE is in range, and if so, 927/// change the data structures so the user references the clone. Returns: 928/// 0 = no existing entry found 929/// 1 = entry found, and there were no code insertions or deletions 930/// 2 = entry found, and there were code insertions or deletions 931int MipsConstantIslands::findInRangeCPEntry(CPUser& U, unsigned UserOffset) 932{ 933 MachineInstr *UserMI = U.MI; 934 MachineInstr *CPEMI = U.CPEMI; 935 936 // Check to see if the CPE is already in-range. 937 if (isCPEntryInRange(UserMI, UserOffset, CPEMI, U.getMaxDisp(), U.NegOk, 938 true)) { 939 DEBUG(dbgs() << "In range\n"); 940 return 1; 941 } 942 943 // No. Look for previously created clones of the CPE that are in range. 944 unsigned CPI = CPEMI->getOperand(1).getIndex(); 945 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 946 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 947 // We already tried this one 948 if (CPEs[i].CPEMI == CPEMI) 949 continue; 950 // Removing CPEs can leave empty entries, skip 951 if (CPEs[i].CPEMI == NULL) 952 continue; 953 if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, U.getMaxDisp(), 954 U.NegOk)) { 955 DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" 956 << CPEs[i].CPI << "\n"); 957 // Point the CPUser node to the replacement 958 U.CPEMI = CPEs[i].CPEMI; 959 // Change the CPI in the instruction operand to refer to the clone. 960 for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j) 961 if (UserMI->getOperand(j).isCPI()) { 962 UserMI->getOperand(j).setIndex(CPEs[i].CPI); 963 break; 964 } 965 // Adjust the refcount of the clone... 966 CPEs[i].RefCount++; 967 // ...and the original. If we didn't remove the old entry, none of the 968 // addresses changed, so we don't need another pass. 969 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1; 970 } 971 } 972 return 0; 973} 974 975/// LookForCPEntryInRange - see if the currently referenced CPE is in range; 976/// This version checks if the longer form of the instruction can be used to 977/// to satisfy things. 978/// if not, see if an in-range clone of the CPE is in range, and if so, 979/// change the data structures so the user references the clone. Returns: 980/// 0 = no existing entry found 981/// 1 = entry found, and there were no code insertions or deletions 982/// 2 = entry found, and there were code insertions or deletions 983int MipsConstantIslands::findLongFormInRangeCPEntry 984 (CPUser& U, unsigned UserOffset) 985{ 986 MachineInstr *UserMI = U.MI; 987 MachineInstr *CPEMI = U.CPEMI; 988 989 // Check to see if the CPE is already in-range. 990 if (isCPEntryInRange(UserMI, UserOffset, CPEMI, 991 U.getLongFormMaxDisp(), U.NegOk, 992 true)) { 993 DEBUG(dbgs() << "In range\n"); 994 UserMI->setDesc(TII->get(U.getLongFormOpcode())); 995 U.setMaxDisp(U.getLongFormMaxDisp()); 996 return 2; // instruction is longer length now 997 } 998 999 // No. Look for previously created clones of the CPE that are in range. 1000 unsigned CPI = CPEMI->getOperand(1).getIndex(); 1001 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 1002 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 1003 // We already tried this one 1004 if (CPEs[i].CPEMI == CPEMI) 1005 continue; 1006 // Removing CPEs can leave empty entries, skip 1007 if (CPEs[i].CPEMI == NULL) 1008 continue; 1009 if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, 1010 U.getLongFormMaxDisp(), U.NegOk)) { 1011 DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" 1012 << CPEs[i].CPI << "\n"); 1013 // Point the CPUser node to the replacement 1014 U.CPEMI = CPEs[i].CPEMI; 1015 // Change the CPI in the instruction operand to refer to the clone. 1016 for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j) 1017 if (UserMI->getOperand(j).isCPI()) { 1018 UserMI->getOperand(j).setIndex(CPEs[i].CPI); 1019 break; 1020 } 1021 // Adjust the refcount of the clone... 1022 CPEs[i].RefCount++; 1023 // ...and the original. If we didn't remove the old entry, none of the 1024 // addresses changed, so we don't need another pass. 1025 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1; 1026 } 1027 } 1028 return 0; 1029} 1030 1031/// getUnconditionalBrDisp - Returns the maximum displacement that can fit in 1032/// the specific unconditional branch instruction. 1033static inline unsigned getUnconditionalBrDisp(int Opc) { 1034 switch (Opc) { 1035 case Mips::BimmX16: 1036 return ((1<<16)-1)*2; 1037 default: 1038 break; 1039 } 1040 return ((1<<16)-1)*2; 1041} 1042 1043/// findAvailableWater - Look for an existing entry in the WaterList in which 1044/// we can place the CPE referenced from U so it's within range of U's MI. 1045/// Returns true if found, false if not. If it returns true, WaterIter 1046/// is set to the WaterList entry. 1047/// To ensure that this pass 1048/// terminates, the CPE location for a particular CPUser is only allowed to 1049/// move to a lower address, so search backward from the end of the list and 1050/// prefer the first water that is in range. 1051bool MipsConstantIslands::findAvailableWater(CPUser &U, unsigned UserOffset, 1052 water_iterator &WaterIter) { 1053 if (WaterList.empty()) 1054 return false; 1055 1056 unsigned BestGrowth = ~0u; 1057 for (water_iterator IP = prior(WaterList.end()), B = WaterList.begin();; 1058 --IP) { 1059 MachineBasicBlock* WaterBB = *IP; 1060 // Check if water is in range and is either at a lower address than the 1061 // current "high water mark" or a new water block that was created since 1062 // the previous iteration by inserting an unconditional branch. In the 1063 // latter case, we want to allow resetting the high water mark back to 1064 // this new water since we haven't seen it before. Inserting branches 1065 // should be relatively uncommon and when it does happen, we want to be 1066 // sure to take advantage of it for all the CPEs near that block, so that 1067 // we don't insert more branches than necessary. 1068 unsigned Growth; 1069 if (isWaterInRange(UserOffset, WaterBB, U, Growth) && 1070 (WaterBB->getNumber() < U.HighWaterMark->getNumber() || 1071 NewWaterList.count(WaterBB)) && Growth < BestGrowth) { 1072 // This is the least amount of required padding seen so far. 1073 BestGrowth = Growth; 1074 WaterIter = IP; 1075 DEBUG(dbgs() << "Found water after BB#" << WaterBB->getNumber() 1076 << " Growth=" << Growth << '\n'); 1077 1078 // Keep looking unless it is perfect. 1079 if (BestGrowth == 0) 1080 return true; 1081 } 1082 if (IP == B) 1083 break; 1084 } 1085 return BestGrowth != ~0u; 1086} 1087 1088/// createNewWater - No existing WaterList entry will work for 1089/// CPUsers[CPUserIndex], so create a place to put the CPE. The end of the 1090/// block is used if in range, and the conditional branch munged so control 1091/// flow is correct. Otherwise the block is split to create a hole with an 1092/// unconditional branch around it. In either case NewMBB is set to a 1093/// block following which the new island can be inserted (the WaterList 1094/// is not adjusted). 1095void MipsConstantIslands::createNewWater(unsigned CPUserIndex, 1096 unsigned UserOffset, 1097 MachineBasicBlock *&NewMBB) { 1098 CPUser &U = CPUsers[CPUserIndex]; 1099 MachineInstr *UserMI = U.MI; 1100 MachineInstr *CPEMI = U.CPEMI; 1101 unsigned CPELogAlign = getCPELogAlign(CPEMI); 1102 MachineBasicBlock *UserMBB = UserMI->getParent(); 1103 const BasicBlockInfo &UserBBI = BBInfo[UserMBB->getNumber()]; 1104 1105 // If the block does not end in an unconditional branch already, and if the 1106 // end of the block is within range, make new water there. 1107 if (BBHasFallthrough(UserMBB)) { 1108 // Size of branch to insert. 1109 unsigned Delta = 2; 1110 // Compute the offset where the CPE will begin. 1111 unsigned CPEOffset = UserBBI.postOffset(CPELogAlign) + Delta; 1112 1113 if (isOffsetInRange(UserOffset, CPEOffset, U)) { 1114 DEBUG(dbgs() << "Split at end of BB#" << UserMBB->getNumber() 1115 << format(", expected CPE offset %#x\n", CPEOffset)); 1116 NewMBB = llvm::next(MachineFunction::iterator(UserMBB)); 1117 // Add an unconditional branch from UserMBB to fallthrough block. Record 1118 // it for branch lengthening; this new branch will not get out of range, 1119 // but if the preceding conditional branch is out of range, the targets 1120 // will be exchanged, and the altered branch may be out of range, so the 1121 // machinery has to know about it. 1122 int UncondBr = Mips::BimmX16; 1123 BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB); 1124 unsigned MaxDisp = getUnconditionalBrDisp(UncondBr); 1125 ImmBranches.push_back(ImmBranch(&UserMBB->back(), 1126 MaxDisp, false, UncondBr)); 1127 BBInfo[UserMBB->getNumber()].Size += Delta; 1128 adjustBBOffsetsAfter(UserMBB); 1129 return; 1130 } 1131 } 1132 1133 // What a big block. Find a place within the block to split it. 1134 1135 // Try to split the block so it's fully aligned. Compute the latest split 1136 // point where we can add a 4-byte branch instruction, and then align to 1137 // LogAlign which is the largest possible alignment in the function. 1138 unsigned LogAlign = MF->getAlignment(); 1139 assert(LogAlign >= CPELogAlign && "Over-aligned constant pool entry"); 1140 unsigned BaseInsertOffset = UserOffset + U.getMaxDisp(); 1141 DEBUG(dbgs() << format("Split in middle of big block before %#x", 1142 BaseInsertOffset)); 1143 1144 // The 4 in the following is for the unconditional branch we'll be inserting 1145 // Alignment of the island is handled 1146 // inside isOffsetInRange. 1147 BaseInsertOffset -= 4; 1148 1149 DEBUG(dbgs() << format(", adjusted to %#x", BaseInsertOffset) 1150 << " la=" << LogAlign << '\n'); 1151 1152 // This could point off the end of the block if we've already got constant 1153 // pool entries following this block; only the last one is in the water list. 1154 // Back past any possible branches (allow for a conditional and a maximally 1155 // long unconditional). 1156 if (BaseInsertOffset + 8 >= UserBBI.postOffset()) { 1157 BaseInsertOffset = UserBBI.postOffset() - 8; 1158 DEBUG(dbgs() << format("Move inside block: %#x\n", BaseInsertOffset)); 1159 } 1160 unsigned EndInsertOffset = BaseInsertOffset + 4 + 1161 CPEMI->getOperand(2).getImm(); 1162 MachineBasicBlock::iterator MI = UserMI; 1163 ++MI; 1164 unsigned CPUIndex = CPUserIndex+1; 1165 unsigned NumCPUsers = CPUsers.size(); 1166 //MachineInstr *LastIT = 0; 1167 for (unsigned Offset = UserOffset+TII->GetInstSizeInBytes(UserMI); 1168 Offset < BaseInsertOffset; 1169 Offset += TII->GetInstSizeInBytes(MI), 1170 MI = llvm::next(MI)) { 1171 assert(MI != UserMBB->end() && "Fell off end of block"); 1172 if (CPUIndex < NumCPUsers && CPUsers[CPUIndex].MI == MI) { 1173 CPUser &U = CPUsers[CPUIndex]; 1174 if (!isOffsetInRange(Offset, EndInsertOffset, U)) { 1175 // Shift intertion point by one unit of alignment so it is within reach. 1176 BaseInsertOffset -= 1u << LogAlign; 1177 EndInsertOffset -= 1u << LogAlign; 1178 } 1179 // This is overly conservative, as we don't account for CPEMIs being 1180 // reused within the block, but it doesn't matter much. Also assume CPEs 1181 // are added in order with alignment padding. We may eventually be able 1182 // to pack the aligned CPEs better. 1183 EndInsertOffset += U.CPEMI->getOperand(2).getImm(); 1184 CPUIndex++; 1185 } 1186 } 1187 1188 --MI; 1189 NewMBB = splitBlockBeforeInstr(MI); 1190} 1191 1192/// handleConstantPoolUser - Analyze the specified user, checking to see if it 1193/// is out-of-range. If so, pick up the constant pool value and move it some 1194/// place in-range. Return true if we changed any addresses (thus must run 1195/// another pass of branch lengthening), false otherwise. 1196bool MipsConstantIslands::handleConstantPoolUser(unsigned CPUserIndex) { 1197 CPUser &U = CPUsers[CPUserIndex]; 1198 MachineInstr *UserMI = U.MI; 1199 MachineInstr *CPEMI = U.CPEMI; 1200 unsigned CPI = CPEMI->getOperand(1).getIndex(); 1201 unsigned Size = CPEMI->getOperand(2).getImm(); 1202 // Compute this only once, it's expensive. 1203 unsigned UserOffset = getUserOffset(U); 1204 1205 // See if the current entry is within range, or there is a clone of it 1206 // in range. 1207 int result = findInRangeCPEntry(U, UserOffset); 1208 if (result==1) return false; 1209 else if (result==2) return true; 1210 1211 1212 // Look for water where we can place this CPE. 1213 MachineBasicBlock *NewIsland = MF->CreateMachineBasicBlock(); 1214 MachineBasicBlock *NewMBB; 1215 water_iterator IP; 1216 if (findAvailableWater(U, UserOffset, IP)) { 1217 DEBUG(dbgs() << "Found water in range\n"); 1218 MachineBasicBlock *WaterBB = *IP; 1219 1220 // If the original WaterList entry was "new water" on this iteration, 1221 // propagate that to the new island. This is just keeping NewWaterList 1222 // updated to match the WaterList, which will be updated below. 1223 if (NewWaterList.erase(WaterBB)) 1224 NewWaterList.insert(NewIsland); 1225 1226 // The new CPE goes before the following block (NewMBB). 1227 NewMBB = llvm::next(MachineFunction::iterator(WaterBB)); 1228 1229 } else { 1230 // No water found. 1231 // we first see if a longer form of the instrucion could have reached 1232 // the constant. in that case we won't bother to split 1233 if (!NoLoadRelaxation) { 1234 result = findLongFormInRangeCPEntry(U, UserOffset); 1235 if (result != 0) return true; 1236 } 1237 DEBUG(dbgs() << "No water found\n"); 1238 createNewWater(CPUserIndex, UserOffset, NewMBB); 1239 1240 // splitBlockBeforeInstr adds to WaterList, which is important when it is 1241 // called while handling branches so that the water will be seen on the 1242 // next iteration for constant pools, but in this context, we don't want 1243 // it. Check for this so it will be removed from the WaterList. 1244 // Also remove any entry from NewWaterList. 1245 MachineBasicBlock *WaterBB = prior(MachineFunction::iterator(NewMBB)); 1246 IP = std::find(WaterList.begin(), WaterList.end(), WaterBB); 1247 if (IP != WaterList.end()) 1248 NewWaterList.erase(WaterBB); 1249 1250 // We are adding new water. Update NewWaterList. 1251 NewWaterList.insert(NewIsland); 1252 } 1253 1254 // Remove the original WaterList entry; we want subsequent insertions in 1255 // this vicinity to go after the one we're about to insert. This 1256 // considerably reduces the number of times we have to move the same CPE 1257 // more than once and is also important to ensure the algorithm terminates. 1258 if (IP != WaterList.end()) 1259 WaterList.erase(IP); 1260 1261 // Okay, we know we can put an island before NewMBB now, do it! 1262 MF->insert(NewMBB, NewIsland); 1263 1264 // Update internal data structures to account for the newly inserted MBB. 1265 updateForInsertedWaterBlock(NewIsland); 1266 1267 // Decrement the old entry, and remove it if refcount becomes 0. 1268 decrementCPEReferenceCount(CPI, CPEMI); 1269 1270 // Now that we have an island to add the CPE to, clone the original CPE and 1271 // add it to the island. 1272 U.HighWaterMark = NewIsland; 1273 U.CPEMI = BuildMI(NewIsland, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY)) 1274 .addImm(ID).addConstantPoolIndex(CPI).addImm(Size); 1275 CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1)); 1276 ++NumCPEs; 1277 1278 // Mark the basic block as aligned as required by the const-pool entry. 1279 NewIsland->setAlignment(getCPELogAlign(U.CPEMI)); 1280 1281 // Increase the size of the island block to account for the new entry. 1282 BBInfo[NewIsland->getNumber()].Size += Size; 1283 adjustBBOffsetsAfter(llvm::prior(MachineFunction::iterator(NewIsland))); 1284 1285 // No existing clone of this CPE is within range. 1286 // We will be generating a new clone. Get a UID for it. 1287 unsigned ID = createPICLabelUId(); 1288 1289 // Finally, change the CPI in the instruction operand to be ID. 1290 for (unsigned i = 0, e = UserMI->getNumOperands(); i != e; ++i) 1291 if (UserMI->getOperand(i).isCPI()) { 1292 UserMI->getOperand(i).setIndex(ID); 1293 break; 1294 } 1295 1296 DEBUG(dbgs() << " Moved CPE to #" << ID << " CPI=" << CPI 1297 << format(" offset=%#x\n", BBInfo[NewIsland->getNumber()].Offset)); 1298 1299 return true; 1300} 1301 1302/// removeDeadCPEMI - Remove a dead constant pool entry instruction. Update 1303/// sizes and offsets of impacted basic blocks. 1304void MipsConstantIslands::removeDeadCPEMI(MachineInstr *CPEMI) { 1305 MachineBasicBlock *CPEBB = CPEMI->getParent(); 1306 unsigned Size = CPEMI->getOperand(2).getImm(); 1307 CPEMI->eraseFromParent(); 1308 BBInfo[CPEBB->getNumber()].Size -= Size; 1309 // All succeeding offsets have the current size value added in, fix this. 1310 if (CPEBB->empty()) { 1311 BBInfo[CPEBB->getNumber()].Size = 0; 1312 1313 // This block no longer needs to be aligned. 1314 CPEBB->setAlignment(0); 1315 } else 1316 // Entries are sorted by descending alignment, so realign from the front. 1317 CPEBB->setAlignment(getCPELogAlign(CPEBB->begin())); 1318 1319 adjustBBOffsetsAfter(CPEBB); 1320 // An island has only one predecessor BB and one successor BB. Check if 1321 // this BB's predecessor jumps directly to this BB's successor. This 1322 // shouldn't happen currently. 1323 assert(!BBIsJumpedOver(CPEBB) && "How did this happen?"); 1324 // FIXME: remove the empty blocks after all the work is done? 1325} 1326 1327/// removeUnusedCPEntries - Remove constant pool entries whose refcounts 1328/// are zero. 1329bool MipsConstantIslands::removeUnusedCPEntries() { 1330 unsigned MadeChange = false; 1331 for (unsigned i = 0, e = CPEntries.size(); i != e; ++i) { 1332 std::vector<CPEntry> &CPEs = CPEntries[i]; 1333 for (unsigned j = 0, ee = CPEs.size(); j != ee; ++j) { 1334 if (CPEs[j].RefCount == 0 && CPEs[j].CPEMI) { 1335 removeDeadCPEMI(CPEs[j].CPEMI); 1336 CPEs[j].CPEMI = NULL; 1337 MadeChange = true; 1338 } 1339 } 1340 } 1341 return MadeChange; 1342} 1343 1344/// isBBInRange - Returns true if the distance between specific MI and 1345/// specific BB can fit in MI's displacement field. 1346bool MipsConstantIslands::isBBInRange 1347 (MachineInstr *MI,MachineBasicBlock *DestBB, unsigned MaxDisp) { 1348 1349unsigned PCAdj = 4; 1350 1351 unsigned BrOffset = getOffsetOf(MI) + PCAdj; 1352 unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset; 1353 1354 DEBUG(dbgs() << "Branch of destination BB#" << DestBB->getNumber() 1355 << " from BB#" << MI->getParent()->getNumber() 1356 << " max delta=" << MaxDisp 1357 << " from " << getOffsetOf(MI) << " to " << DestOffset 1358 << " offset " << int(DestOffset-BrOffset) << "\t" << *MI); 1359 1360 if (BrOffset <= DestOffset) { 1361 // Branch before the Dest. 1362 if (DestOffset-BrOffset <= MaxDisp) 1363 return true; 1364 } else { 1365 if (BrOffset-DestOffset <= MaxDisp) 1366 return true; 1367 } 1368 return false; 1369} 1370 1371/// fixupImmediateBr - Fix up an immediate branch whose destination is too far 1372/// away to fit in its displacement field. 1373bool MipsConstantIslands::fixupImmediateBr(ImmBranch &Br) { 1374 MachineInstr *MI = Br.MI; 1375 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB(); 1376 1377 // Check to see if the DestBB is already in-range. 1378 if (isBBInRange(MI, DestBB, Br.MaxDisp)) 1379 return false; 1380 1381 if (!Br.isCond) 1382 return fixupUnconditionalBr(Br); 1383 return fixupConditionalBr(Br); 1384} 1385 1386/// fixupUnconditionalBr - Fix up an unconditional branch whose destination is 1387/// too far away to fit in its displacement field. If the LR register has been 1388/// spilled in the epilogue, then we can use BL to implement a far jump. 1389/// Otherwise, add an intermediate branch instruction to a branch. 1390bool 1391MipsConstantIslands::fixupUnconditionalBr(ImmBranch &Br) { 1392 MachineInstr *MI = Br.MI; 1393 MachineBasicBlock *MBB = MI->getParent(); 1394 // Use BL to implement far jump. 1395 Br.MaxDisp = ((1 << 16)-1) * 2; 1396 MI->setDesc(TII->get(Mips::BimmX16)); 1397 BBInfo[MBB->getNumber()].Size += 2; 1398 adjustBBOffsetsAfter(MBB); 1399 HasFarJump = true; 1400 ++NumUBrFixed; 1401 1402 DEBUG(dbgs() << " Changed B to long jump " << *MI); 1403 1404 return true; 1405} 1406 1407/// fixupConditionalBr - Fix up a conditional branch whose destination is too 1408/// far away to fit in its displacement field. It is converted to an inverse 1409/// conditional branch + an unconditional branch to the destination. 1410bool 1411MipsConstantIslands::fixupConditionalBr(ImmBranch &Br) { 1412 MachineInstr *MI = Br.MI; 1413 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB(); 1414 1415 // Add an unconditional branch to the destination and invert the branch 1416 // condition to jump over it: 1417 // blt L1 1418 // => 1419 // bge L2 1420 // b L1 1421 // L2: 1422 unsigned CCReg = 0; // FIXME 1423 unsigned CC=0; //FIXME 1424 1425 // If the branch is at the end of its MBB and that has a fall-through block, 1426 // direct the updated conditional branch to the fall-through block. Otherwise, 1427 // split the MBB before the next instruction. 1428 MachineBasicBlock *MBB = MI->getParent(); 1429 MachineInstr *BMI = &MBB->back(); 1430 bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB); 1431 1432 ++NumCBrFixed; 1433 if (BMI != MI) { 1434 if (llvm::next(MachineBasicBlock::iterator(MI)) == prior(MBB->end()) && 1435 BMI->getOpcode() == Br.UncondBr) { 1436 // Last MI in the BB is an unconditional branch. Can we simply invert the 1437 // condition and swap destinations: 1438 // beq L1 1439 // b L2 1440 // => 1441 // bne L2 1442 // b L1 1443 MachineBasicBlock *NewDest = BMI->getOperand(0).getMBB(); 1444 if (isBBInRange(MI, NewDest, Br.MaxDisp)) { 1445 DEBUG(dbgs() << " Invert Bcc condition and swap its destination with " 1446 << *BMI); 1447 BMI->getOperand(0).setMBB(DestBB); 1448 MI->getOperand(0).setMBB(NewDest); 1449 return true; 1450 } 1451 } 1452 } 1453 1454 if (NeedSplit) { 1455 splitBlockBeforeInstr(MI); 1456 // No need for the branch to the next block. We're adding an unconditional 1457 // branch to the destination. 1458 int delta = TII->GetInstSizeInBytes(&MBB->back()); 1459 BBInfo[MBB->getNumber()].Size -= delta; 1460 MBB->back().eraseFromParent(); 1461 // BBInfo[SplitBB].Offset is wrong temporarily, fixed below 1462 } 1463 MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB)); 1464 1465 DEBUG(dbgs() << " Insert B to BB#" << DestBB->getNumber() 1466 << " also invert condition and change dest. to BB#" 1467 << NextBB->getNumber() << "\n"); 1468 1469 // Insert a new conditional branch and a new unconditional branch. 1470 // Also update the ImmBranch as well as adding a new entry for the new branch. 1471 BuildMI(MBB, DebugLoc(), TII->get(MI->getOpcode())) 1472 .addMBB(NextBB).addImm(CC).addReg(CCReg); 1473 Br.MI = &MBB->back(); 1474 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back()); 1475 BuildMI(MBB, DebugLoc(), TII->get(Br.UncondBr)).addMBB(DestBB); 1476 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back()); 1477 unsigned MaxDisp = getUnconditionalBrDisp(Br.UncondBr); 1478 ImmBranches.push_back(ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr)); 1479 1480 // Remove the old conditional branch. It may or may not still be in MBB. 1481 BBInfo[MI->getParent()->getNumber()].Size -= TII->GetInstSizeInBytes(MI); 1482 MI->eraseFromParent(); 1483 adjustBBOffsetsAfter(MBB); 1484 return true; 1485} 1486 1487 1488void MipsConstantIslands::prescanForConstants() { 1489 unsigned J = 0; 1490 (void)J; 1491 PrescannedForConstants = true; 1492 for (MachineFunction::iterator B = 1493 MF->begin(), E = MF->end(); B != E; ++B) { 1494 for (MachineBasicBlock::instr_iterator I = 1495 B->instr_begin(), EB = B->instr_end(); I != EB; ++I) { 1496 switch(I->getDesc().getOpcode()) { 1497 case Mips::LwConstant32: { 1498 DEBUG(dbgs() << "constant island constant " << *I << "\n"); 1499 J = I->getNumOperands(); 1500 DEBUG(dbgs() << "num operands " << J << "\n"); 1501 MachineOperand& Literal = I->getOperand(1); 1502 if (Literal.isImm()) { 1503 int64_t V = Literal.getImm(); 1504 DEBUG(dbgs() << "literal " << V << "\n"); 1505 Type *Int32Ty = 1506 Type::getInt32Ty(MF->getFunction()->getContext()); 1507 const Constant *C = ConstantInt::get(Int32Ty, V); 1508 unsigned index = MCP->getConstantPoolIndex(C, 4); 1509 I->getOperand(2).ChangeToImmediate(index); 1510 DEBUG(dbgs() << "constant island constant " << *I << "\n"); 1511 I->setDesc(TII->get(Mips::LwRxPcTcp16)); 1512 I->RemoveOperand(1); 1513 I->RemoveOperand(1); 1514 I->addOperand(MachineOperand::CreateCPI(index, 0)); 1515 I->addOperand(MachineOperand::CreateImm(4)); 1516 } 1517 break; 1518 } 1519 default: 1520 break; 1521 } 1522 } 1523 } 1524} 1525 1526