MipsConstantIslandPass.cpp revision a2e6e6bcf8cc37ad91b130b9d02d9fe951fbb4d1
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/// UnknownPadding - Return the worst case padding that could result from 70/// unknown offset bits. This does not include alignment padding caused by 71/// known offset bits. 72/// 73/// @param LogAlign log2(alignment) 74/// @param KnownBits Number of known low offset bits. 75static inline unsigned UnknownPadding(unsigned LogAlign, unsigned KnownBits) { 76 if (KnownBits < LogAlign) 77 return (1u << LogAlign) - (1u << KnownBits); 78 return 0; 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 /// KnownBits - The number of low bits in Offset that are known to be 123 /// exact. The remaining bits of Offset are an upper bound. 124 uint8_t KnownBits; 125 126 /// Unalign - When non-zero, the block contains instructions (inline asm) 127 /// of unknown size. The real size may be smaller than Size bytes by a 128 /// multiple of 1 << Unalign. 129 uint8_t Unalign; 130 131 /// PostAlign - When non-zero, the block terminator contains a .align 132 /// directive, so the end of the block is aligned to 1 << PostAlign 133 /// bytes. 134 uint8_t PostAlign; 135 136 BasicBlockInfo() : Offset(0), Size(0), KnownBits(0), Unalign(0), 137 PostAlign(0) {} 138 139 /// Compute the number of known offset bits internally to this block. 140 /// This number should be used to predict worst case padding when 141 /// splitting the block. 142 unsigned internalKnownBits() const { 143 unsigned Bits = Unalign ? Unalign : KnownBits; 144 // If the block size isn't a multiple of the known bits, assume the 145 // worst case padding. 146 if (Size & ((1u << Bits) - 1)) 147 Bits = countTrailingZeros(Size); 148 return Bits; 149 } 150 151 /// Compute the offset immediately following this block. If LogAlign is 152 /// specified, return the offset the successor block will get if it has 153 /// this alignment. 154 unsigned postOffset(unsigned LogAlign = 0) const { 155 unsigned PO = Offset + Size; 156 return PO; 157 } 158 159 /// Compute the number of known low bits of postOffset. If this block 160 /// contains inline asm, the number of known bits drops to the 161 /// instruction alignment. An aligned terminator may increase the number 162 /// of know bits. 163 /// If LogAlign is given, also consider the alignment of the next block. 164 unsigned postKnownBits(unsigned LogAlign = 0) const { 165 return std::max(std::max(unsigned(PostAlign), LogAlign), 166 internalKnownBits()); 167 } 168 }; 169 170 std::vector<BasicBlockInfo> BBInfo; 171 172 /// WaterList - A sorted list of basic blocks where islands could be placed 173 /// (i.e. blocks that don't fall through to the following block, due 174 /// to a return, unreachable, or unconditional branch). 175 std::vector<MachineBasicBlock*> WaterList; 176 177 /// NewWaterList - The subset of WaterList that was created since the 178 /// previous iteration by inserting unconditional branches. 179 SmallSet<MachineBasicBlock*, 4> NewWaterList; 180 181 typedef std::vector<MachineBasicBlock*>::iterator water_iterator; 182 183 /// CPUser - One user of a constant pool, keeping the machine instruction 184 /// pointer, the constant pool being referenced, and the max displacement 185 /// allowed from the instruction to the CP. The HighWaterMark records the 186 /// highest basic block where a new CPEntry can be placed. To ensure this 187 /// pass terminates, the CP entries are initially placed at the end of the 188 /// function and then move monotonically to lower addresses. The 189 /// exception to this rule is when the current CP entry for a particular 190 /// CPUser is out of range, but there is another CP entry for the same 191 /// constant value in range. We want to use the existing in-range CP 192 /// entry, but if it later moves out of range, the search for new water 193 /// should resume where it left off. The HighWaterMark is used to record 194 /// that point. 195 struct CPUser { 196 MachineInstr *MI; 197 MachineInstr *CPEMI; 198 MachineBasicBlock *HighWaterMark; 199 private: 200 unsigned MaxDisp; 201 unsigned LongFormMaxDisp; // mips16 has 16/32 bit instructions 202 // with different displacements 203 unsigned LongFormOpcode; 204 public: 205 bool NegOk; 206 bool IsSoImm; 207 bool KnownAlignment; 208 CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp, 209 bool neg, bool soimm, 210 unsigned longformmaxdisp, unsigned longformopcode) 211 : MI(mi), CPEMI(cpemi), MaxDisp(maxdisp), 212 LongFormMaxDisp(longformmaxdisp), LongFormOpcode(longformopcode), 213 NegOk(neg), IsSoImm(soimm), KnownAlignment(false) { 214 HighWaterMark = CPEMI->getParent(); 215 } 216 /// getMaxDisp - Returns the maximum displacement supported by MI. 217 /// Correct for unknown alignment. 218 /// Conservatively subtract 2 bytes to handle weird alignment effects. 219 unsigned getMaxDisp() const { 220 unsigned xMaxDisp = ConstantIslandsSmallOffset? 221 ConstantIslandsSmallOffset: MaxDisp; 222 return (KnownAlignment ? xMaxDisp : xMaxDisp - 2) - 2; 223 } 224 unsigned getLongFormMaxDisp() const { 225 return (KnownAlignment ? LongFormMaxDisp : LongFormMaxDisp - 2) - 2; 226 } 227 unsigned getLongFormOpcode() const { 228 return LongFormOpcode; 229 } 230 }; 231 232 /// CPUsers - Keep track of all of the machine instructions that use various 233 /// constant pools and their max displacement. 234 std::vector<CPUser> CPUsers; 235 236 /// CPEntry - One per constant pool entry, keeping the machine instruction 237 /// pointer, the constpool index, and the number of CPUser's which 238 /// reference this entry. 239 struct CPEntry { 240 MachineInstr *CPEMI; 241 unsigned CPI; 242 unsigned RefCount; 243 CPEntry(MachineInstr *cpemi, unsigned cpi, unsigned rc = 0) 244 : CPEMI(cpemi), CPI(cpi), RefCount(rc) {} 245 }; 246 247 /// CPEntries - Keep track of all of the constant pool entry machine 248 /// instructions. For each original constpool index (i.e. those that 249 /// existed upon entry to this pass), it keeps a vector of entries. 250 /// Original elements are cloned as we go along; the clones are 251 /// put in the vector of the original element, but have distinct CPIs. 252 std::vector<std::vector<CPEntry> > CPEntries; 253 254 /// ImmBranch - One per immediate branch, keeping the machine instruction 255 /// pointer, conditional or unconditional, the max displacement, 256 /// and (if isCond is true) the corresponding unconditional branch 257 /// opcode. 258 struct ImmBranch { 259 MachineInstr *MI; 260 unsigned MaxDisp : 31; 261 bool isCond : 1; 262 int UncondBr; 263 ImmBranch(MachineInstr *mi, unsigned maxdisp, bool cond, int ubr) 264 : MI(mi), MaxDisp(maxdisp), isCond(cond), UncondBr(ubr) {} 265 }; 266 267 /// ImmBranches - Keep track of all the immediate branch instructions. 268 /// 269 std::vector<ImmBranch> ImmBranches; 270 271 /// HasFarJump - True if any far jump instruction has been emitted during 272 /// the branch fix up pass. 273 bool HasFarJump; 274 275 const TargetMachine &TM; 276 bool IsPIC; 277 unsigned ABI; 278 const MipsSubtarget *STI; 279 const MipsInstrInfo *TII; 280 MipsFunctionInfo *MFI; 281 MachineFunction *MF; 282 MachineConstantPool *MCP; 283 284 unsigned PICLabelUId; 285 bool PrescannedForConstants; 286 287 void initPICLabelUId(unsigned UId) { 288 PICLabelUId = UId; 289 } 290 291 292 unsigned createPICLabelUId() { 293 return PICLabelUId++; 294 } 295 296 public: 297 static char ID; 298 MipsConstantIslands(TargetMachine &tm) 299 : MachineFunctionPass(ID), TM(tm), 300 IsPIC(TM.getRelocationModel() == Reloc::PIC_), 301 ABI(TM.getSubtarget<MipsSubtarget>().getTargetABI()), 302 STI(&TM.getSubtarget<MipsSubtarget>()), MF(0), MCP(0), 303 PrescannedForConstants(false){} 304 305 virtual const char *getPassName() const { 306 return "Mips Constant Islands"; 307 } 308 309 bool runOnMachineFunction(MachineFunction &F); 310 311 void doInitialPlacement(std::vector<MachineInstr*> &CPEMIs); 312 CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI); 313 unsigned getCPELogAlign(const MachineInstr *CPEMI); 314 void initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs); 315 unsigned getOffsetOf(MachineInstr *MI) const; 316 unsigned getUserOffset(CPUser&) const; 317 void dumpBBs(); 318 void verify(); 319 320 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 321 unsigned Disp, bool NegativeOK, bool IsSoImm = false); 322 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 323 const CPUser &U); 324 325 bool isLongFormOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 326 const CPUser &U); 327 328 void computeBlockSize(MachineBasicBlock *MBB); 329 MachineBasicBlock *splitBlockBeforeInstr(MachineInstr *MI); 330 void updateForInsertedWaterBlock(MachineBasicBlock *NewBB); 331 void adjustBBOffsetsAfter(MachineBasicBlock *BB); 332 bool decrementCPEReferenceCount(unsigned CPI, MachineInstr* CPEMI); 333 int findInRangeCPEntry(CPUser& U, unsigned UserOffset); 334 int findLongFormInRangeCPEntry(CPUser& U, unsigned UserOffset); 335 bool findAvailableWater(CPUser&U, unsigned UserOffset, 336 water_iterator &WaterIter); 337 void createNewWater(unsigned CPUserIndex, unsigned UserOffset, 338 MachineBasicBlock *&NewMBB); 339 bool handleConstantPoolUser(unsigned CPUserIndex); 340 void removeDeadCPEMI(MachineInstr *CPEMI); 341 bool removeUnusedCPEntries(); 342 bool isCPEntryInRange(MachineInstr *MI, unsigned UserOffset, 343 MachineInstr *CPEMI, unsigned Disp, bool NegOk, 344 bool DoDump = false); 345 bool isWaterInRange(unsigned UserOffset, MachineBasicBlock *Water, 346 CPUser &U, unsigned &Growth); 347 bool isBBInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp); 348 bool fixupImmediateBr(ImmBranch &Br); 349 bool fixupConditionalBr(ImmBranch &Br); 350 bool fixupUnconditionalBr(ImmBranch &Br); 351 352 void prescanForConstants(); 353 354 private: 355 356 }; 357 358 char MipsConstantIslands::ID = 0; 359} // end of anonymous namespace 360 361 362bool MipsConstantIslands::isLongFormOffsetInRange 363 (unsigned UserOffset, unsigned TrialOffset, 364 const CPUser &U) { 365 return isOffsetInRange(UserOffset, TrialOffset, 366 U.getLongFormMaxDisp(), U.NegOk, U.IsSoImm); 367} 368 369bool MipsConstantIslands::isOffsetInRange 370 (unsigned UserOffset, unsigned TrialOffset, 371 const CPUser &U) { 372 return isOffsetInRange(UserOffset, TrialOffset, 373 U.getMaxDisp(), U.NegOk, U.IsSoImm); 374} 375/// print block size and offset information - debugging 376void MipsConstantIslands::dumpBBs() { 377 DEBUG({ 378 for (unsigned J = 0, E = BBInfo.size(); J !=E; ++J) { 379 const BasicBlockInfo &BBI = BBInfo[J]; 380 dbgs() << format("%08x BB#%u\t", BBI.Offset, J) 381 << " kb=" << unsigned(BBI.KnownBits) 382 << " ua=" << unsigned(BBI.Unalign) 383 << " pa=" << unsigned(BBI.PostAlign) 384 << format(" size=%#x\n", BBInfo[J].Size); 385 } 386 }); 387} 388/// createMipsLongBranchPass - Returns a pass that converts branches to long 389/// branches. 390FunctionPass *llvm::createMipsConstantIslandPass(MipsTargetMachine &tm) { 391 return new MipsConstantIslands(tm); 392} 393 394bool MipsConstantIslands::runOnMachineFunction(MachineFunction &mf) { 395 // The intention is for this to be a mips16 only pass for now 396 // FIXME: 397 MF = &mf; 398 MCP = mf.getConstantPool(); 399 DEBUG(dbgs() << "constant island machine function " << "\n"); 400 if (!TM.getSubtarget<MipsSubtarget>().inMips16Mode() || 401 !MipsSubtarget::useConstantIslands()) { 402 return false; 403 } 404 TII = (const MipsInstrInfo*)MF->getTarget().getInstrInfo(); 405 MFI = MF->getInfo<MipsFunctionInfo>(); 406 DEBUG(dbgs() << "constant island processing " << "\n"); 407 // 408 // will need to make predermination if there is any constants we need to 409 // put in constant islands. TBD. 410 // 411 if (!PrescannedForConstants) prescanForConstants(); 412 413 HasFarJump = false; 414 // This pass invalidates liveness information when it splits basic blocks. 415 MF->getRegInfo().invalidateLiveness(); 416 417 // Renumber all of the machine basic blocks in the function, guaranteeing that 418 // the numbers agree with the position of the block in the function. 419 MF->RenumberBlocks(); 420 421 bool MadeChange = false; 422 423 // Perform the initial placement of the constant pool entries. To start with, 424 // we put them all at the end of the function. 425 std::vector<MachineInstr*> CPEMIs; 426 if (!MCP->isEmpty()) 427 doInitialPlacement(CPEMIs); 428 429 /// The next UID to take is the first unused one. 430 initPICLabelUId(CPEMIs.size()); 431 432 // Do the initial scan of the function, building up information about the 433 // sizes of each block, the location of all the water, and finding all of the 434 // constant pool users. 435 initializeFunctionInfo(CPEMIs); 436 CPEMIs.clear(); 437 DEBUG(dumpBBs()); 438 439 /// Remove dead constant pool entries. 440 MadeChange |= removeUnusedCPEntries(); 441 442 // Iteratively place constant pool entries and fix up branches until there 443 // is no change. 444 unsigned NoCPIters = 0, NoBRIters = 0; 445 (void)NoBRIters; 446 while (true) { 447 DEBUG(dbgs() << "Beginning CP iteration #" << NoCPIters << '\n'); 448 bool CPChange = false; 449 for (unsigned i = 0, e = CPUsers.size(); i != e; ++i) 450 CPChange |= handleConstantPoolUser(i); 451 if (CPChange && ++NoCPIters > 30) 452 report_fatal_error("Constant Island pass failed to converge!"); 453 DEBUG(dumpBBs()); 454 455 // Clear NewWaterList now. If we split a block for branches, it should 456 // appear as "new water" for the next iteration of constant pool placement. 457 NewWaterList.clear(); 458 459 DEBUG(dbgs() << "Beginning BR iteration #" << NoBRIters << '\n'); 460 bool BRChange = false; 461#ifdef IN_PROGRESS 462 for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i) 463 BRChange |= fixupImmediateBr(ImmBranches[i]); 464 if (BRChange && ++NoBRIters > 30) 465 report_fatal_error("Branch Fix Up pass failed to converge!"); 466 DEBUG(dumpBBs()); 467#endif 468 if (!CPChange && !BRChange) 469 break; 470 MadeChange = true; 471 } 472 473 DEBUG(dbgs() << '\n'; dumpBBs()); 474 475 BBInfo.clear(); 476 WaterList.clear(); 477 CPUsers.clear(); 478 CPEntries.clear(); 479 ImmBranches.clear(); 480 return MadeChange; 481} 482 483/// doInitialPlacement - Perform the initial placement of the constant pool 484/// entries. To start with, we put them all at the end of the function. 485void 486MipsConstantIslands::doInitialPlacement(std::vector<MachineInstr*> &CPEMIs) { 487 // Create the basic block to hold the CPE's. 488 MachineBasicBlock *BB = MF->CreateMachineBasicBlock(); 489 MF->push_back(BB); 490 491 492 // MachineConstantPool measures alignment in bytes. We measure in log2(bytes). 493 unsigned MaxAlign = Log2_32(MCP->getConstantPoolAlignment()); 494 495 // Mark the basic block as required by the const-pool. 496 // If AlignConstantIslands isn't set, use 4-byte alignment for everything. 497 BB->setAlignment(AlignConstantIslands ? MaxAlign : 2); 498 499 // The function needs to be as aligned as the basic blocks. The linker may 500 // move functions around based on their alignment. 501 MF->ensureAlignment(BB->getAlignment()); 502 503 // Order the entries in BB by descending alignment. That ensures correct 504 // alignment of all entries as long as BB is sufficiently aligned. Keep 505 // track of the insertion point for each alignment. We are going to bucket 506 // sort the entries as they are created. 507 SmallVector<MachineBasicBlock::iterator, 8> InsPoint(MaxAlign + 1, BB->end()); 508 509 // Add all of the constants from the constant pool to the end block, use an 510 // identity mapping of CPI's to CPE's. 511 const std::vector<MachineConstantPoolEntry> &CPs = MCP->getConstants(); 512 513 const DataLayout &TD = *MF->getTarget().getDataLayout(); 514 for (unsigned i = 0, e = CPs.size(); i != e; ++i) { 515 unsigned Size = TD.getTypeAllocSize(CPs[i].getType()); 516 assert(Size >= 4 && "Too small constant pool entry"); 517 unsigned Align = CPs[i].getAlignment(); 518 assert(isPowerOf2_32(Align) && "Invalid alignment"); 519 // Verify that all constant pool entries are a multiple of their alignment. 520 // If not, we would have to pad them out so that instructions stay aligned. 521 assert((Size % Align) == 0 && "CP Entry not multiple of 4 bytes!"); 522 523 // Insert CONSTPOOL_ENTRY before entries with a smaller alignment. 524 unsigned LogAlign = Log2_32(Align); 525 MachineBasicBlock::iterator InsAt = InsPoint[LogAlign]; 526 527 MachineInstr *CPEMI = 528 BuildMI(*BB, InsAt, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY)) 529 .addImm(i).addConstantPoolIndex(i).addImm(Size); 530 531 CPEMIs.push_back(CPEMI); 532 533 // Ensure that future entries with higher alignment get inserted before 534 // CPEMI. This is bucket sort with iterators. 535 for (unsigned a = LogAlign + 1; a <= MaxAlign; ++a) 536 if (InsPoint[a] == InsAt) 537 InsPoint[a] = CPEMI; 538 // Add a new CPEntry, but no corresponding CPUser yet. 539 std::vector<CPEntry> CPEs; 540 CPEs.push_back(CPEntry(CPEMI, i)); 541 CPEntries.push_back(CPEs); 542 ++NumCPEs; 543 DEBUG(dbgs() << "Moved CPI#" << i << " to end of function, size = " 544 << Size << ", align = " << Align <<'\n'); 545 } 546 DEBUG(BB->dump()); 547} 548 549/// BBHasFallthrough - Return true if the specified basic block can fallthrough 550/// into the block immediately after it. 551static bool BBHasFallthrough(MachineBasicBlock *MBB) { 552 // Get the next machine basic block in the function. 553 MachineFunction::iterator MBBI = MBB; 554 // Can't fall off end of function. 555 if (llvm::next(MBBI) == MBB->getParent()->end()) 556 return false; 557 558 MachineBasicBlock *NextBB = llvm::next(MBBI); 559 for (MachineBasicBlock::succ_iterator I = MBB->succ_begin(), 560 E = MBB->succ_end(); I != E; ++I) 561 if (*I == NextBB) 562 return true; 563 564 return false; 565} 566 567/// findConstPoolEntry - Given the constpool index and CONSTPOOL_ENTRY MI, 568/// look up the corresponding CPEntry. 569MipsConstantIslands::CPEntry 570*MipsConstantIslands::findConstPoolEntry(unsigned CPI, 571 const MachineInstr *CPEMI) { 572 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 573 // Number of entries per constpool index should be small, just do a 574 // linear search. 575 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 576 if (CPEs[i].CPEMI == CPEMI) 577 return &CPEs[i]; 578 } 579 return NULL; 580} 581 582/// getCPELogAlign - Returns the required alignment of the constant pool entry 583/// represented by CPEMI. Alignment is measured in log2(bytes) units. 584unsigned MipsConstantIslands::getCPELogAlign(const MachineInstr *CPEMI) { 585 assert(CPEMI && CPEMI->getOpcode() == Mips::CONSTPOOL_ENTRY); 586 587 // Everything is 4-byte aligned unless AlignConstantIslands is set. 588 if (!AlignConstantIslands) 589 return 2; 590 591 unsigned CPI = CPEMI->getOperand(1).getIndex(); 592 assert(CPI < MCP->getConstants().size() && "Invalid constant pool index."); 593 unsigned Align = MCP->getConstants()[CPI].getAlignment(); 594 assert(isPowerOf2_32(Align) && "Invalid CPE alignment"); 595 return Log2_32(Align); 596} 597 598/// initializeFunctionInfo - Do the initial scan of the function, building up 599/// information about the sizes of each block, the location of all the water, 600/// and finding all of the constant pool users. 601void MipsConstantIslands:: 602initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs) { 603 BBInfo.clear(); 604 BBInfo.resize(MF->getNumBlockIDs()); 605 606 // First thing, compute the size of all basic blocks, and see if the function 607 // has any inline assembly in it. If so, we have to be conservative about 608 // alignment assumptions, as we don't know for sure the size of any 609 // instructions in the inline assembly. 610 for (MachineFunction::iterator I = MF->begin(), E = MF->end(); I != E; ++I) 611 computeBlockSize(I); 612 613 // The known bits of the entry block offset are determined by the function 614 // alignment. 615 BBInfo.front().KnownBits = MF->getAlignment(); 616 617 // Compute block offsets. 618 adjustBBOffsetsAfter(MF->begin()); 619 620 // Now go back through the instructions and build up our data structures. 621 for (MachineFunction::iterator MBBI = MF->begin(), E = MF->end(); 622 MBBI != E; ++MBBI) { 623 MachineBasicBlock &MBB = *MBBI; 624 625 // If this block doesn't fall through into the next MBB, then this is 626 // 'water' that a constant pool island could be placed. 627 if (!BBHasFallthrough(&MBB)) 628 WaterList.push_back(&MBB); 629 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); 630 I != E; ++I) { 631 if (I->isDebugValue()) 632 continue; 633 634 int Opc = I->getOpcode(); 635 if (I->isBranch()) { 636 bool isCond = false; 637 unsigned Bits = 0; 638 unsigned Scale = 1; 639 int UOpc = Opc; 640 641 switch (Opc) { 642 default: 643 continue; // Ignore other JT branches 644 } 645 // Record this immediate branch. 646 unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale; 647 ImmBranches.push_back(ImmBranch(I, MaxOffs, isCond, UOpc)); 648 649 } 650 651 652 if (Opc == Mips::CONSTPOOL_ENTRY) 653 continue; 654 655 656 // Scan the instructions for constant pool operands. 657 for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) 658 if (I->getOperand(op).isCPI()) { 659 660 // We found one. The addressing mode tells us the max displacement 661 // from the PC that this instruction permits. 662 663 // Basic size info comes from the TSFlags field. 664 unsigned Bits = 0; 665 unsigned Scale = 1; 666 bool NegOk = false; 667 bool IsSoImm = false; 668 unsigned LongFormBits = 0; 669 unsigned LongFormScale = 0; 670 unsigned LongFormOpcode = 0; 671 switch (Opc) { 672 default: 673 llvm_unreachable("Unknown addressing mode for CP reference!"); 674 case Mips::LwRxPcTcp16: 675 Bits = 8; 676 Scale = 2; 677 LongFormOpcode = Mips::LwRxPcTcpX16; 678 break; 679 case Mips::LwRxPcTcpX16: 680 Bits = 16; 681 Scale = 2; 682 break; 683 } 684 // Remember that this is a user of a CP entry. 685 unsigned CPI = I->getOperand(op).getIndex(); 686 MachineInstr *CPEMI = CPEMIs[CPI]; 687 unsigned MaxOffs = ((1 << Bits)-1) * Scale; 688 unsigned LongFormMaxOffs = ((1 << LongFormBits)-1) * LongFormScale; 689 CPUsers.push_back(CPUser(I, CPEMI, MaxOffs, NegOk, 690 IsSoImm, LongFormMaxOffs, 691 LongFormOpcode)); 692 693 // Increment corresponding CPEntry reference count. 694 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI); 695 assert(CPE && "Cannot find a corresponding CPEntry!"); 696 CPE->RefCount++; 697 698 // Instructions can only use one CP entry, don't bother scanning the 699 // rest of the operands. 700 break; 701 702 } 703 704 } 705 } 706 707} 708 709/// computeBlockSize - Compute the size and some alignment information for MBB. 710/// This function updates BBInfo directly. 711void MipsConstantIslands::computeBlockSize(MachineBasicBlock *MBB) { 712 BasicBlockInfo &BBI = BBInfo[MBB->getNumber()]; 713 BBI.Size = 0; 714 BBI.Unalign = 0; 715 BBI.PostAlign = 0; 716 717 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E; 718 ++I) 719 BBI.Size += TII->GetInstSizeInBytes(I); 720 721} 722 723/// getOffsetOf - Return the current offset of the specified machine instruction 724/// from the start of the function. This offset changes as stuff is moved 725/// around inside the function. 726unsigned MipsConstantIslands::getOffsetOf(MachineInstr *MI) const { 727 MachineBasicBlock *MBB = MI->getParent(); 728 729 // The offset is composed of two things: the sum of the sizes of all MBB's 730 // before this instruction's block, and the offset from the start of the block 731 // it is in. 732 unsigned Offset = BBInfo[MBB->getNumber()].Offset; 733 734 // Sum instructions before MI in MBB. 735 for (MachineBasicBlock::iterator I = MBB->begin(); &*I != MI; ++I) { 736 assert(I != MBB->end() && "Didn't find MI in its own basic block?"); 737 Offset += TII->GetInstSizeInBytes(I); 738 } 739 return Offset; 740} 741 742/// CompareMBBNumbers - Little predicate function to sort the WaterList by MBB 743/// ID. 744static bool CompareMBBNumbers(const MachineBasicBlock *LHS, 745 const MachineBasicBlock *RHS) { 746 return LHS->getNumber() < RHS->getNumber(); 747} 748 749/// updateForInsertedWaterBlock - When a block is newly inserted into the 750/// machine function, it upsets all of the block numbers. Renumber the blocks 751/// and update the arrays that parallel this numbering. 752void MipsConstantIslands::updateForInsertedWaterBlock 753 (MachineBasicBlock *NewBB) { 754 // Renumber the MBB's to keep them consecutive. 755 NewBB->getParent()->RenumberBlocks(NewBB); 756 757 // Insert an entry into BBInfo to align it properly with the (newly 758 // renumbered) block numbers. 759 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo()); 760 761 // Next, update WaterList. Specifically, we need to add NewMBB as having 762 // available water after it. 763 water_iterator IP = 764 std::lower_bound(WaterList.begin(), WaterList.end(), NewBB, 765 CompareMBBNumbers); 766 WaterList.insert(IP, NewBB); 767} 768 769/// getUserOffset - Compute the offset of U.MI as seen by the hardware 770/// displacement computation. Update U.KnownAlignment to match its current 771/// basic block location. 772unsigned MipsConstantIslands::getUserOffset(CPUser &U) const { 773 unsigned UserOffset = getOffsetOf(U.MI); 774 const BasicBlockInfo &BBI = BBInfo[U.MI->getParent()->getNumber()]; 775 unsigned KnownBits = BBI.internalKnownBits(); 776 777 // The value read from PC is offset from the actual instruction address. 778 779 780 // Because of inline assembly, we may not know the alignment (mod 4) of U.MI. 781 // Make sure U.getMaxDisp() returns a constrained range. 782 U.KnownAlignment = (KnownBits >= 2); 783 784 785 return UserOffset; 786} 787 788/// Split the basic block containing MI into two blocks, which are joined by 789/// an unconditional branch. Update data structures and renumber blocks to 790/// account for this change and returns the newly created block. 791MachineBasicBlock *MipsConstantIslands::splitBlockBeforeInstr 792 (MachineInstr *MI) { 793 MachineBasicBlock *OrigBB = MI->getParent(); 794 795 // Create a new MBB for the code after the OrigBB. 796 MachineBasicBlock *NewBB = 797 MF->CreateMachineBasicBlock(OrigBB->getBasicBlock()); 798 MachineFunction::iterator MBBI = OrigBB; ++MBBI; 799 MF->insert(MBBI, NewBB); 800 801 // Splice the instructions starting with MI over to NewBB. 802 NewBB->splice(NewBB->end(), OrigBB, MI, OrigBB->end()); 803 804 // Add an unconditional branch from OrigBB to NewBB. 805 // Note the new unconditional branch is not being recorded. 806 // There doesn't seem to be meaningful DebugInfo available; this doesn't 807 // correspond to anything in the source. 808 BuildMI(OrigBB, DebugLoc(), TII->get(Mips::BimmX16)).addMBB(NewBB); 809 ++NumSplit; 810 811 // Update the CFG. All succs of OrigBB are now succs of NewBB. 812 NewBB->transferSuccessors(OrigBB); 813 814 // OrigBB branches to NewBB. 815 OrigBB->addSuccessor(NewBB); 816 817 // Update internal data structures to account for the newly inserted MBB. 818 // This is almost the same as updateForInsertedWaterBlock, except that 819 // the Water goes after OrigBB, not NewBB. 820 MF->RenumberBlocks(NewBB); 821 822 // Insert an entry into BBInfo to align it properly with the (newly 823 // renumbered) block numbers. 824 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo()); 825 826 // Next, update WaterList. Specifically, we need to add OrigMBB as having 827 // available water after it (but not if it's already there, which happens 828 // when splitting before a conditional branch that is followed by an 829 // unconditional branch - in that case we want to insert NewBB). 830 water_iterator IP = 831 std::lower_bound(WaterList.begin(), WaterList.end(), OrigBB, 832 CompareMBBNumbers); 833 MachineBasicBlock* WaterBB = *IP; 834 if (WaterBB == OrigBB) 835 WaterList.insert(llvm::next(IP), NewBB); 836 else 837 WaterList.insert(IP, OrigBB); 838 NewWaterList.insert(OrigBB); 839 840 // Figure out how large the OrigBB is. As the first half of the original 841 // block, it cannot contain a tablejump. The size includes 842 // the new jump we added. (It should be possible to do this without 843 // recounting everything, but it's very confusing, and this is rarely 844 // executed.) 845 computeBlockSize(OrigBB); 846 847 // Figure out how large the NewMBB is. As the second half of the original 848 // block, it may contain a tablejump. 849 computeBlockSize(NewBB); 850 851 // All BBOffsets following these blocks must be modified. 852 adjustBBOffsetsAfter(OrigBB); 853 854 return NewBB; 855} 856 857 858 859/// isOffsetInRange - Checks whether UserOffset (the location of a constant pool 860/// reference) is within MaxDisp of TrialOffset (a proposed location of a 861/// constant pool entry). 862/// UserOffset is computed by getUserOffset above to include PC adjustments. If 863/// the mod 4 alignment of UserOffset is not known, the uncertainty must be 864/// subtracted from MaxDisp instead. CPUser::getMaxDisp() does that. 865bool MipsConstantIslands::isOffsetInRange(unsigned UserOffset, 866 unsigned TrialOffset, unsigned MaxDisp, 867 bool NegativeOK, bool IsSoImm) { 868 if (UserOffset <= TrialOffset) { 869 // User before the Trial. 870 if (TrialOffset - UserOffset <= MaxDisp) 871 return true; 872 // FIXME: Make use full range of soimm values. 873 } else if (NegativeOK) { 874 if (UserOffset - TrialOffset <= MaxDisp) 875 return true; 876 // FIXME: Make use full range of soimm values. 877 } 878 return false; 879} 880 881/// isWaterInRange - Returns true if a CPE placed after the specified 882/// Water (a basic block) will be in range for the specific MI. 883/// 884/// Compute how much the function will grow by inserting a CPE after Water. 885bool MipsConstantIslands::isWaterInRange(unsigned UserOffset, 886 MachineBasicBlock* Water, CPUser &U, 887 unsigned &Growth) { 888 unsigned CPELogAlign = getCPELogAlign(U.CPEMI); 889 unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset(CPELogAlign); 890 unsigned NextBlockOffset, NextBlockAlignment; 891 MachineFunction::const_iterator NextBlock = Water; 892 if (++NextBlock == MF->end()) { 893 NextBlockOffset = BBInfo[Water->getNumber()].postOffset(); 894 NextBlockAlignment = 0; 895 } else { 896 NextBlockOffset = BBInfo[NextBlock->getNumber()].Offset; 897 NextBlockAlignment = NextBlock->getAlignment(); 898 } 899 unsigned Size = U.CPEMI->getOperand(2).getImm(); 900 unsigned CPEEnd = CPEOffset + Size; 901 902 // The CPE may be able to hide in the alignment padding before the next 903 // block. It may also cause more padding to be required if it is more aligned 904 // that the next block. 905 if (CPEEnd > NextBlockOffset) { 906 Growth = CPEEnd - NextBlockOffset; 907 // Compute the padding that would go at the end of the CPE to align the next 908 // block. 909 Growth += OffsetToAlignment(CPEEnd, 1u << NextBlockAlignment); 910 911 // If the CPE is to be inserted before the instruction, that will raise 912 // the offset of the instruction. Also account for unknown alignment padding 913 // in blocks between CPE and the user. 914 if (CPEOffset < UserOffset) 915 UserOffset += Growth + UnknownPadding(MF->getAlignment(), CPELogAlign); 916 } else 917 // CPE fits in existing padding. 918 Growth = 0; 919 920 return isOffsetInRange(UserOffset, CPEOffset, U); 921} 922 923/// isCPEntryInRange - Returns true if the distance between specific MI and 924/// specific ConstPool entry instruction can fit in MI's displacement field. 925bool MipsConstantIslands::isCPEntryInRange 926 (MachineInstr *MI, unsigned UserOffset, 927 MachineInstr *CPEMI, unsigned MaxDisp, 928 bool NegOk, bool DoDump) { 929 unsigned CPEOffset = getOffsetOf(CPEMI); 930 931 if (DoDump) { 932 DEBUG({ 933 unsigned Block = MI->getParent()->getNumber(); 934 const BasicBlockInfo &BBI = BBInfo[Block]; 935 dbgs() << "User of CPE#" << CPEMI->getOperand(0).getImm() 936 << " max delta=" << MaxDisp 937 << format(" insn address=%#x", UserOffset) 938 << " in BB#" << Block << ": " 939 << format("%#x-%x\t", BBI.Offset, BBI.postOffset()) << *MI 940 << format("CPE address=%#x offset=%+d: ", CPEOffset, 941 int(CPEOffset-UserOffset)); 942 }); 943 } 944 945 return isOffsetInRange(UserOffset, CPEOffset, MaxDisp, NegOk); 946} 947 948#ifndef NDEBUG 949/// BBIsJumpedOver - Return true of the specified basic block's only predecessor 950/// unconditionally branches to its only successor. 951static bool BBIsJumpedOver(MachineBasicBlock *MBB) { 952 if (MBB->pred_size() != 1 || MBB->succ_size() != 1) 953 return false; 954 MachineBasicBlock *Succ = *MBB->succ_begin(); 955 MachineBasicBlock *Pred = *MBB->pred_begin(); 956 MachineInstr *PredMI = &Pred->back(); 957 if (PredMI->getOpcode() == Mips::BimmX16) 958 return PredMI->getOperand(0).getMBB() == Succ; 959 return false; 960} 961#endif 962 963void MipsConstantIslands::adjustBBOffsetsAfter(MachineBasicBlock *BB) { 964 unsigned BBNum = BB->getNumber(); 965 for(unsigned i = BBNum + 1, e = MF->getNumBlockIDs(); i < e; ++i) { 966 // Get the offset and known bits at the end of the layout predecessor. 967 // Include the alignment of the current block. 968 unsigned Offset = BBInfo[i - 1].postOffset(); 969 BBInfo[i].Offset = Offset; 970 } 971} 972 973/// decrementCPEReferenceCount - find the constant pool entry with index CPI 974/// and instruction CPEMI, and decrement its refcount. If the refcount 975/// becomes 0 remove the entry and instruction. Returns true if we removed 976/// the entry, false if we didn't. 977 978bool MipsConstantIslands::decrementCPEReferenceCount(unsigned CPI, 979 MachineInstr *CPEMI) { 980 // Find the old entry. Eliminate it if it is no longer used. 981 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI); 982 assert(CPE && "Unexpected!"); 983 if (--CPE->RefCount == 0) { 984 removeDeadCPEMI(CPEMI); 985 CPE->CPEMI = NULL; 986 --NumCPEs; 987 return true; 988 } 989 return false; 990} 991 992/// LookForCPEntryInRange - see if the currently referenced CPE is in range; 993/// if not, see if an in-range clone of the CPE is in range, and if so, 994/// change the data structures so the user references the clone. Returns: 995/// 0 = no existing entry found 996/// 1 = entry found, and there were no code insertions or deletions 997/// 2 = entry found, and there were code insertions or deletions 998int MipsConstantIslands::findInRangeCPEntry(CPUser& U, unsigned UserOffset) 999{ 1000 MachineInstr *UserMI = U.MI; 1001 MachineInstr *CPEMI = U.CPEMI; 1002 1003 // Check to see if the CPE is already in-range. 1004 if (isCPEntryInRange(UserMI, UserOffset, CPEMI, U.getMaxDisp(), U.NegOk, 1005 true)) { 1006 DEBUG(dbgs() << "In range\n"); 1007 return 1; 1008 } 1009 1010 // No. Look for previously created clones of the CPE that are in range. 1011 unsigned CPI = CPEMI->getOperand(1).getIndex(); 1012 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 1013 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 1014 // We already tried this one 1015 if (CPEs[i].CPEMI == CPEMI) 1016 continue; 1017 // Removing CPEs can leave empty entries, skip 1018 if (CPEs[i].CPEMI == NULL) 1019 continue; 1020 if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, U.getMaxDisp(), 1021 U.NegOk)) { 1022 DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" 1023 << CPEs[i].CPI << "\n"); 1024 // Point the CPUser node to the replacement 1025 U.CPEMI = CPEs[i].CPEMI; 1026 // Change the CPI in the instruction operand to refer to the clone. 1027 for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j) 1028 if (UserMI->getOperand(j).isCPI()) { 1029 UserMI->getOperand(j).setIndex(CPEs[i].CPI); 1030 break; 1031 } 1032 // Adjust the refcount of the clone... 1033 CPEs[i].RefCount++; 1034 // ...and the original. If we didn't remove the old entry, none of the 1035 // addresses changed, so we don't need another pass. 1036 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1; 1037 } 1038 } 1039 return 0; 1040} 1041 1042/// LookForCPEntryInRange - see if the currently referenced CPE is in range; 1043/// This version checks if the longer form of the instruction can be used to 1044/// to satisfy things. 1045/// if not, see if an in-range clone of the CPE is in range, and if so, 1046/// change the data structures so the user references the clone. Returns: 1047/// 0 = no existing entry found 1048/// 1 = entry found, and there were no code insertions or deletions 1049/// 2 = entry found, and there were code insertions or deletions 1050int MipsConstantIslands::findLongFormInRangeCPEntry 1051 (CPUser& U, unsigned UserOffset) 1052{ 1053 MachineInstr *UserMI = U.MI; 1054 MachineInstr *CPEMI = U.CPEMI; 1055 1056 // Check to see if the CPE is already in-range. 1057 if (isCPEntryInRange(UserMI, UserOffset, CPEMI, 1058 U.getLongFormMaxDisp(), U.NegOk, 1059 true)) { 1060 DEBUG(dbgs() << "In range\n"); 1061 UserMI->setDesc(TII->get(U.getLongFormOpcode())); 1062 return 2; // instruction is longer length now 1063 } 1064 1065 // No. Look for previously created clones of the CPE that are in range. 1066 unsigned CPI = CPEMI->getOperand(1).getIndex(); 1067 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 1068 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 1069 // We already tried this one 1070 if (CPEs[i].CPEMI == CPEMI) 1071 continue; 1072 // Removing CPEs can leave empty entries, skip 1073 if (CPEs[i].CPEMI == NULL) 1074 continue; 1075 if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, 1076 U.getLongFormMaxDisp(), U.NegOk)) { 1077 DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" 1078 << CPEs[i].CPI << "\n"); 1079 // Point the CPUser node to the replacement 1080 U.CPEMI = CPEs[i].CPEMI; 1081 // Change the CPI in the instruction operand to refer to the clone. 1082 for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j) 1083 if (UserMI->getOperand(j).isCPI()) { 1084 UserMI->getOperand(j).setIndex(CPEs[i].CPI); 1085 break; 1086 } 1087 // Adjust the refcount of the clone... 1088 CPEs[i].RefCount++; 1089 // ...and the original. If we didn't remove the old entry, none of the 1090 // addresses changed, so we don't need another pass. 1091 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1; 1092 } 1093 } 1094 return 0; 1095} 1096 1097/// getUnconditionalBrDisp - Returns the maximum displacement that can fit in 1098/// the specific unconditional branch instruction. 1099static inline unsigned getUnconditionalBrDisp(int Opc) { 1100 switch (Opc) { 1101 case Mips::BimmX16: 1102 return ((1<<16)-1)*2; 1103 default: 1104 break; 1105 } 1106 return ((1<<16)-1)*2; 1107} 1108 1109/// findAvailableWater - Look for an existing entry in the WaterList in which 1110/// we can place the CPE referenced from U so it's within range of U's MI. 1111/// Returns true if found, false if not. If it returns true, WaterIter 1112/// is set to the WaterList entry. 1113/// To ensure that this pass 1114/// terminates, the CPE location for a particular CPUser is only allowed to 1115/// move to a lower address, so search backward from the end of the list and 1116/// prefer the first water that is in range. 1117bool MipsConstantIslands::findAvailableWater(CPUser &U, unsigned UserOffset, 1118 water_iterator &WaterIter) { 1119 if (WaterList.empty()) 1120 return false; 1121 1122 unsigned BestGrowth = ~0u; 1123 for (water_iterator IP = prior(WaterList.end()), B = WaterList.begin();; 1124 --IP) { 1125 MachineBasicBlock* WaterBB = *IP; 1126 // Check if water is in range and is either at a lower address than the 1127 // current "high water mark" or a new water block that was created since 1128 // the previous iteration by inserting an unconditional branch. In the 1129 // latter case, we want to allow resetting the high water mark back to 1130 // this new water since we haven't seen it before. Inserting branches 1131 // should be relatively uncommon and when it does happen, we want to be 1132 // sure to take advantage of it for all the CPEs near that block, so that 1133 // we don't insert more branches than necessary. 1134 unsigned Growth; 1135 if (isWaterInRange(UserOffset, WaterBB, U, Growth) && 1136 (WaterBB->getNumber() < U.HighWaterMark->getNumber() || 1137 NewWaterList.count(WaterBB)) && Growth < BestGrowth) { 1138 // This is the least amount of required padding seen so far. 1139 BestGrowth = Growth; 1140 WaterIter = IP; 1141 DEBUG(dbgs() << "Found water after BB#" << WaterBB->getNumber() 1142 << " Growth=" << Growth << '\n'); 1143 1144 // Keep looking unless it is perfect. 1145 if (BestGrowth == 0) 1146 return true; 1147 } 1148 if (IP == B) 1149 break; 1150 } 1151 return BestGrowth != ~0u; 1152} 1153 1154/// createNewWater - No existing WaterList entry will work for 1155/// CPUsers[CPUserIndex], so create a place to put the CPE. The end of the 1156/// block is used if in range, and the conditional branch munged so control 1157/// flow is correct. Otherwise the block is split to create a hole with an 1158/// unconditional branch around it. In either case NewMBB is set to a 1159/// block following which the new island can be inserted (the WaterList 1160/// is not adjusted). 1161void MipsConstantIslands::createNewWater(unsigned CPUserIndex, 1162 unsigned UserOffset, 1163 MachineBasicBlock *&NewMBB) { 1164 CPUser &U = CPUsers[CPUserIndex]; 1165 MachineInstr *UserMI = U.MI; 1166 MachineInstr *CPEMI = U.CPEMI; 1167 unsigned CPELogAlign = getCPELogAlign(CPEMI); 1168 MachineBasicBlock *UserMBB = UserMI->getParent(); 1169 const BasicBlockInfo &UserBBI = BBInfo[UserMBB->getNumber()]; 1170 1171 // If the block does not end in an unconditional branch already, and if the 1172 // end of the block is within range, make new water there. 1173 if (BBHasFallthrough(UserMBB)) { 1174 // Size of branch to insert. 1175 unsigned Delta = 2; 1176 // Compute the offset where the CPE will begin. 1177 unsigned CPEOffset = UserBBI.postOffset(CPELogAlign) + Delta; 1178 1179 if (isOffsetInRange(UserOffset, CPEOffset, U)) { 1180 DEBUG(dbgs() << "Split at end of BB#" << UserMBB->getNumber() 1181 << format(", expected CPE offset %#x\n", CPEOffset)); 1182 NewMBB = llvm::next(MachineFunction::iterator(UserMBB)); 1183 // Add an unconditional branch from UserMBB to fallthrough block. Record 1184 // it for branch lengthening; this new branch will not get out of range, 1185 // but if the preceding conditional branch is out of range, the targets 1186 // will be exchanged, and the altered branch may be out of range, so the 1187 // machinery has to know about it. 1188 int UncondBr = Mips::BimmX16; 1189 BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB); 1190 unsigned MaxDisp = getUnconditionalBrDisp(UncondBr); 1191 ImmBranches.push_back(ImmBranch(&UserMBB->back(), 1192 MaxDisp, false, UncondBr)); 1193 BBInfo[UserMBB->getNumber()].Size += Delta; 1194 adjustBBOffsetsAfter(UserMBB); 1195 return; 1196 } 1197 } 1198 1199 // What a big block. Find a place within the block to split it. 1200 1201 // Try to split the block so it's fully aligned. Compute the latest split 1202 // point where we can add a 4-byte branch instruction, and then align to 1203 // LogAlign which is the largest possible alignment in the function. 1204 unsigned LogAlign = MF->getAlignment(); 1205 assert(LogAlign >= CPELogAlign && "Over-aligned constant pool entry"); 1206 unsigned KnownBits = UserBBI.internalKnownBits(); 1207 unsigned UPad = UnknownPadding(LogAlign, KnownBits); 1208 unsigned BaseInsertOffset = UserOffset + U.getMaxDisp() - UPad; 1209 DEBUG(dbgs() << format("Split in middle of big block before %#x", 1210 BaseInsertOffset)); 1211 1212 // The 4 in the following is for the unconditional branch we'll be inserting 1213 // Alignment of the island is handled 1214 // inside isOffsetInRange. 1215 BaseInsertOffset -= 4; 1216 1217 DEBUG(dbgs() << format(", adjusted to %#x", BaseInsertOffset) 1218 << " la=" << LogAlign 1219 << " kb=" << KnownBits 1220 << " up=" << UPad << '\n'); 1221 1222 // This could point off the end of the block if we've already got constant 1223 // pool entries following this block; only the last one is in the water list. 1224 // Back past any possible branches (allow for a conditional and a maximally 1225 // long unconditional). 1226 if (BaseInsertOffset + 8 >= UserBBI.postOffset()) { 1227 BaseInsertOffset = UserBBI.postOffset() - UPad - 8; 1228 DEBUG(dbgs() << format("Move inside block: %#x\n", BaseInsertOffset)); 1229 } 1230 unsigned EndInsertOffset = BaseInsertOffset + 4 + UPad + 1231 CPEMI->getOperand(2).getImm(); 1232 MachineBasicBlock::iterator MI = UserMI; 1233 ++MI; 1234 unsigned CPUIndex = CPUserIndex+1; 1235 unsigned NumCPUsers = CPUsers.size(); 1236 //MachineInstr *LastIT = 0; 1237 for (unsigned Offset = UserOffset+TII->GetInstSizeInBytes(UserMI); 1238 Offset < BaseInsertOffset; 1239 Offset += TII->GetInstSizeInBytes(MI), 1240 MI = llvm::next(MI)) { 1241 assert(MI != UserMBB->end() && "Fell off end of block"); 1242 if (CPUIndex < NumCPUsers && CPUsers[CPUIndex].MI == MI) { 1243 CPUser &U = CPUsers[CPUIndex]; 1244 if (!isOffsetInRange(Offset, EndInsertOffset, U)) { 1245 // Shift intertion point by one unit of alignment so it is within reach. 1246 BaseInsertOffset -= 1u << LogAlign; 1247 EndInsertOffset -= 1u << LogAlign; 1248 } 1249 // This is overly conservative, as we don't account for CPEMIs being 1250 // reused within the block, but it doesn't matter much. Also assume CPEs 1251 // are added in order with alignment padding. We may eventually be able 1252 // to pack the aligned CPEs better. 1253 EndInsertOffset += U.CPEMI->getOperand(2).getImm(); 1254 CPUIndex++; 1255 } 1256 } 1257 1258 --MI; 1259 NewMBB = splitBlockBeforeInstr(MI); 1260} 1261 1262/// handleConstantPoolUser - Analyze the specified user, checking to see if it 1263/// is out-of-range. If so, pick up the constant pool value and move it some 1264/// place in-range. Return true if we changed any addresses (thus must run 1265/// another pass of branch lengthening), false otherwise. 1266bool MipsConstantIslands::handleConstantPoolUser(unsigned CPUserIndex) { 1267 CPUser &U = CPUsers[CPUserIndex]; 1268 MachineInstr *UserMI = U.MI; 1269 MachineInstr *CPEMI = U.CPEMI; 1270 unsigned CPI = CPEMI->getOperand(1).getIndex(); 1271 unsigned Size = CPEMI->getOperand(2).getImm(); 1272 // Compute this only once, it's expensive. 1273 unsigned UserOffset = getUserOffset(U); 1274 1275 // See if the current entry is within range, or there is a clone of it 1276 // in range. 1277 int result = findInRangeCPEntry(U, UserOffset); 1278 if (result==1) return false; 1279 else if (result==2) return true; 1280 1281 1282 // Look for water where we can place this CPE. 1283 MachineBasicBlock *NewIsland = MF->CreateMachineBasicBlock(); 1284 MachineBasicBlock *NewMBB; 1285 water_iterator IP; 1286 if (findAvailableWater(U, UserOffset, IP)) { 1287 DEBUG(dbgs() << "Found water in range\n"); 1288 MachineBasicBlock *WaterBB = *IP; 1289 1290 // If the original WaterList entry was "new water" on this iteration, 1291 // propagate that to the new island. This is just keeping NewWaterList 1292 // updated to match the WaterList, which will be updated below. 1293 if (NewWaterList.erase(WaterBB)) 1294 NewWaterList.insert(NewIsland); 1295 1296 // The new CPE goes before the following block (NewMBB). 1297 NewMBB = llvm::next(MachineFunction::iterator(WaterBB)); 1298 1299 } else { 1300 // No water found. 1301 // we first see if a longer form of the instrucion could have reached 1302 // the constant. in that case we won't bother to split 1303#ifdef IN_PROGRESS 1304 result = findLongFormInRangeCPEntry(U, UserOffset); 1305#endif 1306 DEBUG(dbgs() << "No water found\n"); 1307 createNewWater(CPUserIndex, UserOffset, NewMBB); 1308 1309 // splitBlockBeforeInstr adds to WaterList, which is important when it is 1310 // called while handling branches so that the water will be seen on the 1311 // next iteration for constant pools, but in this context, we don't want 1312 // it. Check for this so it will be removed from the WaterList. 1313 // Also remove any entry from NewWaterList. 1314 MachineBasicBlock *WaterBB = prior(MachineFunction::iterator(NewMBB)); 1315 IP = std::find(WaterList.begin(), WaterList.end(), WaterBB); 1316 if (IP != WaterList.end()) 1317 NewWaterList.erase(WaterBB); 1318 1319 // We are adding new water. Update NewWaterList. 1320 NewWaterList.insert(NewIsland); 1321 } 1322 1323 // Remove the original WaterList entry; we want subsequent insertions in 1324 // this vicinity to go after the one we're about to insert. This 1325 // considerably reduces the number of times we have to move the same CPE 1326 // more than once and is also important to ensure the algorithm terminates. 1327 if (IP != WaterList.end()) 1328 WaterList.erase(IP); 1329 1330 // Okay, we know we can put an island before NewMBB now, do it! 1331 MF->insert(NewMBB, NewIsland); 1332 1333 // Update internal data structures to account for the newly inserted MBB. 1334 updateForInsertedWaterBlock(NewIsland); 1335 1336 // Decrement the old entry, and remove it if refcount becomes 0. 1337 decrementCPEReferenceCount(CPI, CPEMI); 1338 1339 // Now that we have an island to add the CPE to, clone the original CPE and 1340 // add it to the island. 1341 U.HighWaterMark = NewIsland; 1342 U.CPEMI = BuildMI(NewIsland, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY)) 1343 .addImm(ID).addConstantPoolIndex(CPI).addImm(Size); 1344 CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1)); 1345 ++NumCPEs; 1346 1347 // Mark the basic block as aligned as required by the const-pool entry. 1348 NewIsland->setAlignment(getCPELogAlign(U.CPEMI)); 1349 1350 // Increase the size of the island block to account for the new entry. 1351 BBInfo[NewIsland->getNumber()].Size += Size; 1352 adjustBBOffsetsAfter(llvm::prior(MachineFunction::iterator(NewIsland))); 1353 1354 // No existing clone of this CPE is within range. 1355 // We will be generating a new clone. Get a UID for it. 1356 unsigned ID = createPICLabelUId(); 1357 1358 // Finally, change the CPI in the instruction operand to be ID. 1359 for (unsigned i = 0, e = UserMI->getNumOperands(); i != e; ++i) 1360 if (UserMI->getOperand(i).isCPI()) { 1361 UserMI->getOperand(i).setIndex(ID); 1362 break; 1363 } 1364 1365 DEBUG(dbgs() << " Moved CPE to #" << ID << " CPI=" << CPI 1366 << format(" offset=%#x\n", BBInfo[NewIsland->getNumber()].Offset)); 1367 1368 return true; 1369} 1370 1371/// removeDeadCPEMI - Remove a dead constant pool entry instruction. Update 1372/// sizes and offsets of impacted basic blocks. 1373void MipsConstantIslands::removeDeadCPEMI(MachineInstr *CPEMI) { 1374 MachineBasicBlock *CPEBB = CPEMI->getParent(); 1375 unsigned Size = CPEMI->getOperand(2).getImm(); 1376 CPEMI->eraseFromParent(); 1377 BBInfo[CPEBB->getNumber()].Size -= Size; 1378 // All succeeding offsets have the current size value added in, fix this. 1379 if (CPEBB->empty()) { 1380 BBInfo[CPEBB->getNumber()].Size = 0; 1381 1382 // This block no longer needs to be aligned. 1383 CPEBB->setAlignment(0); 1384 } else 1385 // Entries are sorted by descending alignment, so realign from the front. 1386 CPEBB->setAlignment(getCPELogAlign(CPEBB->begin())); 1387 1388 adjustBBOffsetsAfter(CPEBB); 1389 // An island has only one predecessor BB and one successor BB. Check if 1390 // this BB's predecessor jumps directly to this BB's successor. This 1391 // shouldn't happen currently. 1392 assert(!BBIsJumpedOver(CPEBB) && "How did this happen?"); 1393 // FIXME: remove the empty blocks after all the work is done? 1394} 1395 1396/// removeUnusedCPEntries - Remove constant pool entries whose refcounts 1397/// are zero. 1398bool MipsConstantIslands::removeUnusedCPEntries() { 1399 unsigned MadeChange = false; 1400 for (unsigned i = 0, e = CPEntries.size(); i != e; ++i) { 1401 std::vector<CPEntry> &CPEs = CPEntries[i]; 1402 for (unsigned j = 0, ee = CPEs.size(); j != ee; ++j) { 1403 if (CPEs[j].RefCount == 0 && CPEs[j].CPEMI) { 1404 removeDeadCPEMI(CPEs[j].CPEMI); 1405 CPEs[j].CPEMI = NULL; 1406 MadeChange = true; 1407 } 1408 } 1409 } 1410 return MadeChange; 1411} 1412 1413/// isBBInRange - Returns true if the distance between specific MI and 1414/// specific BB can fit in MI's displacement field. 1415bool MipsConstantIslands::isBBInRange 1416 (MachineInstr *MI,MachineBasicBlock *DestBB, unsigned MaxDisp) { 1417 1418unsigned PCAdj = 4; 1419 1420 unsigned BrOffset = getOffsetOf(MI) + PCAdj; 1421 unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset; 1422 1423 DEBUG(dbgs() << "Branch of destination BB#" << DestBB->getNumber() 1424 << " from BB#" << MI->getParent()->getNumber() 1425 << " max delta=" << MaxDisp 1426 << " from " << getOffsetOf(MI) << " to " << DestOffset 1427 << " offset " << int(DestOffset-BrOffset) << "\t" << *MI); 1428 1429 if (BrOffset <= DestOffset) { 1430 // Branch before the Dest. 1431 if (DestOffset-BrOffset <= MaxDisp) 1432 return true; 1433 } else { 1434 if (BrOffset-DestOffset <= MaxDisp) 1435 return true; 1436 } 1437 return false; 1438} 1439 1440/// fixupImmediateBr - Fix up an immediate branch whose destination is too far 1441/// away to fit in its displacement field. 1442bool MipsConstantIslands::fixupImmediateBr(ImmBranch &Br) { 1443 MachineInstr *MI = Br.MI; 1444 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB(); 1445 1446 // Check to see if the DestBB is already in-range. 1447 if (isBBInRange(MI, DestBB, Br.MaxDisp)) 1448 return false; 1449 1450 if (!Br.isCond) 1451 return fixupUnconditionalBr(Br); 1452 return fixupConditionalBr(Br); 1453} 1454 1455/// fixupUnconditionalBr - Fix up an unconditional branch whose destination is 1456/// too far away to fit in its displacement field. If the LR register has been 1457/// spilled in the epilogue, then we can use BL to implement a far jump. 1458/// Otherwise, add an intermediate branch instruction to a branch. 1459bool 1460MipsConstantIslands::fixupUnconditionalBr(ImmBranch &Br) { 1461 MachineInstr *MI = Br.MI; 1462 MachineBasicBlock *MBB = MI->getParent(); 1463 // Use BL to implement far jump. 1464 Br.MaxDisp = ((1 << 16)-1) * 2; 1465 MI->setDesc(TII->get(Mips::BimmX16)); 1466 BBInfo[MBB->getNumber()].Size += 2; 1467 adjustBBOffsetsAfter(MBB); 1468 HasFarJump = true; 1469 ++NumUBrFixed; 1470 1471 DEBUG(dbgs() << " Changed B to long jump " << *MI); 1472 1473 return true; 1474} 1475 1476/// fixupConditionalBr - Fix up a conditional branch whose destination is too 1477/// far away to fit in its displacement field. It is converted to an inverse 1478/// conditional branch + an unconditional branch to the destination. 1479bool 1480MipsConstantIslands::fixupConditionalBr(ImmBranch &Br) { 1481 MachineInstr *MI = Br.MI; 1482 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB(); 1483 1484 // Add an unconditional branch to the destination and invert the branch 1485 // condition to jump over it: 1486 // blt L1 1487 // => 1488 // bge L2 1489 // b L1 1490 // L2: 1491 unsigned CCReg = 0; // FIXME 1492 unsigned CC=0; //FIXME 1493 1494 // If the branch is at the end of its MBB and that has a fall-through block, 1495 // direct the updated conditional branch to the fall-through block. Otherwise, 1496 // split the MBB before the next instruction. 1497 MachineBasicBlock *MBB = MI->getParent(); 1498 MachineInstr *BMI = &MBB->back(); 1499 bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB); 1500 1501 ++NumCBrFixed; 1502 if (BMI != MI) { 1503 if (llvm::next(MachineBasicBlock::iterator(MI)) == prior(MBB->end()) && 1504 BMI->getOpcode() == Br.UncondBr) { 1505 // Last MI in the BB is an unconditional branch. Can we simply invert the 1506 // condition and swap destinations: 1507 // beq L1 1508 // b L2 1509 // => 1510 // bne L2 1511 // b L1 1512 MachineBasicBlock *NewDest = BMI->getOperand(0).getMBB(); 1513 if (isBBInRange(MI, NewDest, Br.MaxDisp)) { 1514 DEBUG(dbgs() << " Invert Bcc condition and swap its destination with " 1515 << *BMI); 1516 BMI->getOperand(0).setMBB(DestBB); 1517 MI->getOperand(0).setMBB(NewDest); 1518 return true; 1519 } 1520 } 1521 } 1522 1523 if (NeedSplit) { 1524 splitBlockBeforeInstr(MI); 1525 // No need for the branch to the next block. We're adding an unconditional 1526 // branch to the destination. 1527 int delta = TII->GetInstSizeInBytes(&MBB->back()); 1528 BBInfo[MBB->getNumber()].Size -= delta; 1529 MBB->back().eraseFromParent(); 1530 // BBInfo[SplitBB].Offset is wrong temporarily, fixed below 1531 } 1532 MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB)); 1533 1534 DEBUG(dbgs() << " Insert B to BB#" << DestBB->getNumber() 1535 << " also invert condition and change dest. to BB#" 1536 << NextBB->getNumber() << "\n"); 1537 1538 // Insert a new conditional branch and a new unconditional branch. 1539 // Also update the ImmBranch as well as adding a new entry for the new branch. 1540 BuildMI(MBB, DebugLoc(), TII->get(MI->getOpcode())) 1541 .addMBB(NextBB).addImm(CC).addReg(CCReg); 1542 Br.MI = &MBB->back(); 1543 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back()); 1544 BuildMI(MBB, DebugLoc(), TII->get(Br.UncondBr)).addMBB(DestBB); 1545 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back()); 1546 unsigned MaxDisp = getUnconditionalBrDisp(Br.UncondBr); 1547 ImmBranches.push_back(ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr)); 1548 1549 // Remove the old conditional branch. It may or may not still be in MBB. 1550 BBInfo[MI->getParent()->getNumber()].Size -= TII->GetInstSizeInBytes(MI); 1551 MI->eraseFromParent(); 1552 adjustBBOffsetsAfter(MBB); 1553 return true; 1554} 1555 1556 1557void MipsConstantIslands::prescanForConstants() { 1558 unsigned J = 0; 1559 (void)J; 1560 PrescannedForConstants = true; 1561 for (MachineFunction::iterator B = 1562 MF->begin(), E = MF->end(); B != E; ++B) { 1563 for (MachineBasicBlock::instr_iterator I = 1564 B->instr_begin(), EB = B->instr_end(); I != EB; ++I) { 1565 switch(I->getDesc().getOpcode()) { 1566 case Mips::LwConstant32: { 1567 DEBUG(dbgs() << "constant island constant " << *I << "\n"); 1568 J = I->getNumOperands(); 1569 DEBUG(dbgs() << "num operands " << J << "\n"); 1570 MachineOperand& Literal = I->getOperand(1); 1571 if (Literal.isImm()) { 1572 int64_t V = Literal.getImm(); 1573 DEBUG(dbgs() << "literal " << V << "\n"); 1574 Type *Int32Ty = 1575 Type::getInt32Ty(MF->getFunction()->getContext()); 1576 const Constant *C = ConstantInt::get(Int32Ty, V); 1577 unsigned index = MCP->getConstantPoolIndex(C, 4); 1578 I->getOperand(2).ChangeToImmediate(index); 1579 DEBUG(dbgs() << "constant island constant " << *I << "\n"); 1580 I->setDesc(TII->get(Mips::LwRxPcTcp16)); 1581 I->RemoveOperand(1); 1582 I->RemoveOperand(1); 1583 I->addOperand(MachineOperand::CreateCPI(index, 0)); 1584 I->addOperand(MachineOperand::CreateImm(4)); 1585 } 1586 break; 1587 } 1588 default: 1589 break; 1590 } 1591 } 1592 } 1593} 1594 1595