MipsConstantIslandPass.cpp revision 14cfb10174fa443074c235a207d290a9816392f8
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 KnownAlignment; 207 CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp, 208 bool neg, 209 unsigned longformmaxdisp, unsigned longformopcode) 210 : MI(mi), CPEMI(cpemi), MaxDisp(maxdisp), 211 LongFormMaxDisp(longformmaxdisp), LongFormOpcode(longformopcode), 212 NegOk(neg), KnownAlignment(false) { 213 HighWaterMark = CPEMI->getParent(); 214 } 215 /// getMaxDisp - Returns the maximum displacement supported by MI. 216 /// Correct for unknown alignment. 217 /// Conservatively subtract 2 bytes to handle weird alignment effects. 218 unsigned getMaxDisp() const { 219 unsigned xMaxDisp = ConstantIslandsSmallOffset? 220 ConstantIslandsSmallOffset: MaxDisp; 221 return (KnownAlignment ? xMaxDisp : xMaxDisp - 2) - 2; 222 } 223 unsigned getLongFormMaxDisp() const { 224 return (KnownAlignment ? LongFormMaxDisp : LongFormMaxDisp - 2) - 2; 225 } 226 unsigned getLongFormOpcode() const { 227 return LongFormOpcode; 228 } 229 }; 230 231 /// CPUsers - Keep track of all of the machine instructions that use various 232 /// constant pools and their max displacement. 233 std::vector<CPUser> CPUsers; 234 235 /// CPEntry - One per constant pool entry, keeping the machine instruction 236 /// pointer, the constpool index, and the number of CPUser's which 237 /// reference this entry. 238 struct CPEntry { 239 MachineInstr *CPEMI; 240 unsigned CPI; 241 unsigned RefCount; 242 CPEntry(MachineInstr *cpemi, unsigned cpi, unsigned rc = 0) 243 : CPEMI(cpemi), CPI(cpi), RefCount(rc) {} 244 }; 245 246 /// CPEntries - Keep track of all of the constant pool entry machine 247 /// instructions. For each original constpool index (i.e. those that 248 /// existed upon entry to this pass), it keeps a vector of entries. 249 /// Original elements are cloned as we go along; the clones are 250 /// put in the vector of the original element, but have distinct CPIs. 251 std::vector<std::vector<CPEntry> > CPEntries; 252 253 /// ImmBranch - One per immediate branch, keeping the machine instruction 254 /// pointer, conditional or unconditional, the max displacement, 255 /// and (if isCond is true) the corresponding unconditional branch 256 /// opcode. 257 struct ImmBranch { 258 MachineInstr *MI; 259 unsigned MaxDisp : 31; 260 bool isCond : 1; 261 int UncondBr; 262 ImmBranch(MachineInstr *mi, unsigned maxdisp, bool cond, int ubr) 263 : MI(mi), MaxDisp(maxdisp), isCond(cond), UncondBr(ubr) {} 264 }; 265 266 /// ImmBranches - Keep track of all the immediate branch instructions. 267 /// 268 std::vector<ImmBranch> ImmBranches; 269 270 /// HasFarJump - True if any far jump instruction has been emitted during 271 /// the branch fix up pass. 272 bool HasFarJump; 273 274 const TargetMachine &TM; 275 bool IsPIC; 276 unsigned ABI; 277 const MipsSubtarget *STI; 278 const MipsInstrInfo *TII; 279 MipsFunctionInfo *MFI; 280 MachineFunction *MF; 281 MachineConstantPool *MCP; 282 283 unsigned PICLabelUId; 284 bool PrescannedForConstants; 285 286 void initPICLabelUId(unsigned UId) { 287 PICLabelUId = UId; 288 } 289 290 291 unsigned createPICLabelUId() { 292 return PICLabelUId++; 293 } 294 295 public: 296 static char ID; 297 MipsConstantIslands(TargetMachine &tm) 298 : MachineFunctionPass(ID), TM(tm), 299 IsPIC(TM.getRelocationModel() == Reloc::PIC_), 300 ABI(TM.getSubtarget<MipsSubtarget>().getTargetABI()), 301 STI(&TM.getSubtarget<MipsSubtarget>()), MF(0), MCP(0), 302 PrescannedForConstants(false){} 303 304 virtual const char *getPassName() const { 305 return "Mips Constant Islands"; 306 } 307 308 bool runOnMachineFunction(MachineFunction &F); 309 310 void doInitialPlacement(std::vector<MachineInstr*> &CPEMIs); 311 CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI); 312 unsigned getCPELogAlign(const MachineInstr *CPEMI); 313 void initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs); 314 unsigned getOffsetOf(MachineInstr *MI) const; 315 unsigned getUserOffset(CPUser&) const; 316 void dumpBBs(); 317 void verify(); 318 319 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 320 unsigned Disp, bool NegativeOK); 321 bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 322 const CPUser &U); 323 324 bool isLongFormOffsetInRange(unsigned UserOffset, unsigned TrialOffset, 325 const CPUser &U); 326 327 void computeBlockSize(MachineBasicBlock *MBB); 328 MachineBasicBlock *splitBlockBeforeInstr(MachineInstr *MI); 329 void updateForInsertedWaterBlock(MachineBasicBlock *NewBB); 330 void adjustBBOffsetsAfter(MachineBasicBlock *BB); 331 bool decrementCPEReferenceCount(unsigned CPI, MachineInstr* CPEMI); 332 int findInRangeCPEntry(CPUser& U, unsigned UserOffset); 333 int findLongFormInRangeCPEntry(CPUser& U, unsigned UserOffset); 334 bool findAvailableWater(CPUser&U, unsigned UserOffset, 335 water_iterator &WaterIter); 336 void createNewWater(unsigned CPUserIndex, unsigned UserOffset, 337 MachineBasicBlock *&NewMBB); 338 bool handleConstantPoolUser(unsigned CPUserIndex); 339 void removeDeadCPEMI(MachineInstr *CPEMI); 340 bool removeUnusedCPEntries(); 341 bool isCPEntryInRange(MachineInstr *MI, unsigned UserOffset, 342 MachineInstr *CPEMI, unsigned Disp, bool NegOk, 343 bool DoDump = false); 344 bool isWaterInRange(unsigned UserOffset, MachineBasicBlock *Water, 345 CPUser &U, unsigned &Growth); 346 bool isBBInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp); 347 bool fixupImmediateBr(ImmBranch &Br); 348 bool fixupConditionalBr(ImmBranch &Br); 349 bool fixupUnconditionalBr(ImmBranch &Br); 350 351 void prescanForConstants(); 352 353 private: 354 355 }; 356 357 char MipsConstantIslands::ID = 0; 358} // end of anonymous namespace 359 360 361bool MipsConstantIslands::isLongFormOffsetInRange 362 (unsigned UserOffset, unsigned TrialOffset, 363 const CPUser &U) { 364 return isOffsetInRange(UserOffset, TrialOffset, 365 U.getLongFormMaxDisp(), U.NegOk); 366} 367 368bool MipsConstantIslands::isOffsetInRange 369 (unsigned UserOffset, unsigned TrialOffset, 370 const CPUser &U) { 371 return isOffsetInRange(UserOffset, TrialOffset, 372 U.getMaxDisp(), U.NegOk); 373} 374/// print block size and offset information - debugging 375void MipsConstantIslands::dumpBBs() { 376 DEBUG({ 377 for (unsigned J = 0, E = BBInfo.size(); J !=E; ++J) { 378 const BasicBlockInfo &BBI = BBInfo[J]; 379 dbgs() << format("%08x BB#%u\t", BBI.Offset, J) 380 << " kb=" << unsigned(BBI.KnownBits) 381 << " ua=" << unsigned(BBI.Unalign) 382 << " pa=" << unsigned(BBI.PostAlign) 383 << format(" size=%#x\n", BBInfo[J].Size); 384 } 385 }); 386} 387/// createMipsLongBranchPass - Returns a pass that converts branches to long 388/// branches. 389FunctionPass *llvm::createMipsConstantIslandPass(MipsTargetMachine &tm) { 390 return new MipsConstantIslands(tm); 391} 392 393bool MipsConstantIslands::runOnMachineFunction(MachineFunction &mf) { 394 // The intention is for this to be a mips16 only pass for now 395 // FIXME: 396 MF = &mf; 397 MCP = mf.getConstantPool(); 398 DEBUG(dbgs() << "constant island machine function " << "\n"); 399 if (!TM.getSubtarget<MipsSubtarget>().inMips16Mode() || 400 !MipsSubtarget::useConstantIslands()) { 401 return false; 402 } 403 TII = (const MipsInstrInfo*)MF->getTarget().getInstrInfo(); 404 MFI = MF->getInfo<MipsFunctionInfo>(); 405 DEBUG(dbgs() << "constant island processing " << "\n"); 406 // 407 // will need to make predermination if there is any constants we need to 408 // put in constant islands. TBD. 409 // 410 if (!PrescannedForConstants) prescanForConstants(); 411 412 HasFarJump = false; 413 // This pass invalidates liveness information when it splits basic blocks. 414 MF->getRegInfo().invalidateLiveness(); 415 416 // Renumber all of the machine basic blocks in the function, guaranteeing that 417 // the numbers agree with the position of the block in the function. 418 MF->RenumberBlocks(); 419 420 bool MadeChange = false; 421 422 // Perform the initial placement of the constant pool entries. To start with, 423 // we put them all at the end of the function. 424 std::vector<MachineInstr*> CPEMIs; 425 if (!MCP->isEmpty()) 426 doInitialPlacement(CPEMIs); 427 428 /// The next UID to take is the first unused one. 429 initPICLabelUId(CPEMIs.size()); 430 431 // Do the initial scan of the function, building up information about the 432 // sizes of each block, the location of all the water, and finding all of the 433 // constant pool users. 434 initializeFunctionInfo(CPEMIs); 435 CPEMIs.clear(); 436 DEBUG(dumpBBs()); 437 438 /// Remove dead constant pool entries. 439 MadeChange |= removeUnusedCPEntries(); 440 441 // Iteratively place constant pool entries and fix up branches until there 442 // is no change. 443 unsigned NoCPIters = 0, NoBRIters = 0; 444 (void)NoBRIters; 445 while (true) { 446 DEBUG(dbgs() << "Beginning CP iteration #" << NoCPIters << '\n'); 447 bool CPChange = false; 448 for (unsigned i = 0, e = CPUsers.size(); i != e; ++i) 449 CPChange |= handleConstantPoolUser(i); 450 if (CPChange && ++NoCPIters > 30) 451 report_fatal_error("Constant Island pass failed to converge!"); 452 DEBUG(dumpBBs()); 453 454 // Clear NewWaterList now. If we split a block for branches, it should 455 // appear as "new water" for the next iteration of constant pool placement. 456 NewWaterList.clear(); 457 458 DEBUG(dbgs() << "Beginning BR iteration #" << NoBRIters << '\n'); 459 bool BRChange = false; 460#ifdef IN_PROGRESS 461 for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i) 462 BRChange |= fixupImmediateBr(ImmBranches[i]); 463 if (BRChange && ++NoBRIters > 30) 464 report_fatal_error("Branch Fix Up pass failed to converge!"); 465 DEBUG(dumpBBs()); 466#endif 467 if (!CPChange && !BRChange) 468 break; 469 MadeChange = true; 470 } 471 472 DEBUG(dbgs() << '\n'; dumpBBs()); 473 474 BBInfo.clear(); 475 WaterList.clear(); 476 CPUsers.clear(); 477 CPEntries.clear(); 478 ImmBranches.clear(); 479 return MadeChange; 480} 481 482/// doInitialPlacement - Perform the initial placement of the constant pool 483/// entries. To start with, we put them all at the end of the function. 484void 485MipsConstantIslands::doInitialPlacement(std::vector<MachineInstr*> &CPEMIs) { 486 // Create the basic block to hold the CPE's. 487 MachineBasicBlock *BB = MF->CreateMachineBasicBlock(); 488 MF->push_back(BB); 489 490 491 // MachineConstantPool measures alignment in bytes. We measure in log2(bytes). 492 unsigned MaxAlign = Log2_32(MCP->getConstantPoolAlignment()); 493 494 // Mark the basic block as required by the const-pool. 495 // If AlignConstantIslands isn't set, use 4-byte alignment for everything. 496 BB->setAlignment(AlignConstantIslands ? MaxAlign : 2); 497 498 // The function needs to be as aligned as the basic blocks. The linker may 499 // move functions around based on their alignment. 500 MF->ensureAlignment(BB->getAlignment()); 501 502 // Order the entries in BB by descending alignment. That ensures correct 503 // alignment of all entries as long as BB is sufficiently aligned. Keep 504 // track of the insertion point for each alignment. We are going to bucket 505 // sort the entries as they are created. 506 SmallVector<MachineBasicBlock::iterator, 8> InsPoint(MaxAlign + 1, BB->end()); 507 508 // Add all of the constants from the constant pool to the end block, use an 509 // identity mapping of CPI's to CPE's. 510 const std::vector<MachineConstantPoolEntry> &CPs = MCP->getConstants(); 511 512 const DataLayout &TD = *MF->getTarget().getDataLayout(); 513 for (unsigned i = 0, e = CPs.size(); i != e; ++i) { 514 unsigned Size = TD.getTypeAllocSize(CPs[i].getType()); 515 assert(Size >= 4 && "Too small constant pool entry"); 516 unsigned Align = CPs[i].getAlignment(); 517 assert(isPowerOf2_32(Align) && "Invalid alignment"); 518 // Verify that all constant pool entries are a multiple of their alignment. 519 // If not, we would have to pad them out so that instructions stay aligned. 520 assert((Size % Align) == 0 && "CP Entry not multiple of 4 bytes!"); 521 522 // Insert CONSTPOOL_ENTRY before entries with a smaller alignment. 523 unsigned LogAlign = Log2_32(Align); 524 MachineBasicBlock::iterator InsAt = InsPoint[LogAlign]; 525 526 MachineInstr *CPEMI = 527 BuildMI(*BB, InsAt, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY)) 528 .addImm(i).addConstantPoolIndex(i).addImm(Size); 529 530 CPEMIs.push_back(CPEMI); 531 532 // Ensure that future entries with higher alignment get inserted before 533 // CPEMI. This is bucket sort with iterators. 534 for (unsigned a = LogAlign + 1; a <= MaxAlign; ++a) 535 if (InsPoint[a] == InsAt) 536 InsPoint[a] = CPEMI; 537 // Add a new CPEntry, but no corresponding CPUser yet. 538 std::vector<CPEntry> CPEs; 539 CPEs.push_back(CPEntry(CPEMI, i)); 540 CPEntries.push_back(CPEs); 541 ++NumCPEs; 542 DEBUG(dbgs() << "Moved CPI#" << i << " to end of function, size = " 543 << Size << ", align = " << Align <<'\n'); 544 } 545 DEBUG(BB->dump()); 546} 547 548/// BBHasFallthrough - Return true if the specified basic block can fallthrough 549/// into the block immediately after it. 550static bool BBHasFallthrough(MachineBasicBlock *MBB) { 551 // Get the next machine basic block in the function. 552 MachineFunction::iterator MBBI = MBB; 553 // Can't fall off end of function. 554 if (llvm::next(MBBI) == MBB->getParent()->end()) 555 return false; 556 557 MachineBasicBlock *NextBB = llvm::next(MBBI); 558 for (MachineBasicBlock::succ_iterator I = MBB->succ_begin(), 559 E = MBB->succ_end(); I != E; ++I) 560 if (*I == NextBB) 561 return true; 562 563 return false; 564} 565 566/// findConstPoolEntry - Given the constpool index and CONSTPOOL_ENTRY MI, 567/// look up the corresponding CPEntry. 568MipsConstantIslands::CPEntry 569*MipsConstantIslands::findConstPoolEntry(unsigned CPI, 570 const MachineInstr *CPEMI) { 571 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 572 // Number of entries per constpool index should be small, just do a 573 // linear search. 574 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 575 if (CPEs[i].CPEMI == CPEMI) 576 return &CPEs[i]; 577 } 578 return NULL; 579} 580 581/// getCPELogAlign - Returns the required alignment of the constant pool entry 582/// represented by CPEMI. Alignment is measured in log2(bytes) units. 583unsigned MipsConstantIslands::getCPELogAlign(const MachineInstr *CPEMI) { 584 assert(CPEMI && CPEMI->getOpcode() == Mips::CONSTPOOL_ENTRY); 585 586 // Everything is 4-byte aligned unless AlignConstantIslands is set. 587 if (!AlignConstantIslands) 588 return 2; 589 590 unsigned CPI = CPEMI->getOperand(1).getIndex(); 591 assert(CPI < MCP->getConstants().size() && "Invalid constant pool index."); 592 unsigned Align = MCP->getConstants()[CPI].getAlignment(); 593 assert(isPowerOf2_32(Align) && "Invalid CPE alignment"); 594 return Log2_32(Align); 595} 596 597/// initializeFunctionInfo - Do the initial scan of the function, building up 598/// information about the sizes of each block, the location of all the water, 599/// and finding all of the constant pool users. 600void MipsConstantIslands:: 601initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs) { 602 BBInfo.clear(); 603 BBInfo.resize(MF->getNumBlockIDs()); 604 605 // First thing, compute the size of all basic blocks, and see if the function 606 // has any inline assembly in it. If so, we have to be conservative about 607 // alignment assumptions, as we don't know for sure the size of any 608 // instructions in the inline assembly. 609 for (MachineFunction::iterator I = MF->begin(), E = MF->end(); I != E; ++I) 610 computeBlockSize(I); 611 612 // The known bits of the entry block offset are determined by the function 613 // alignment. 614 BBInfo.front().KnownBits = MF->getAlignment(); 615 616 // Compute block offsets. 617 adjustBBOffsetsAfter(MF->begin()); 618 619 // Now go back through the instructions and build up our data structures. 620 for (MachineFunction::iterator MBBI = MF->begin(), E = MF->end(); 621 MBBI != E; ++MBBI) { 622 MachineBasicBlock &MBB = *MBBI; 623 624 // If this block doesn't fall through into the next MBB, then this is 625 // 'water' that a constant pool island could be placed. 626 if (!BBHasFallthrough(&MBB)) 627 WaterList.push_back(&MBB); 628 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); 629 I != E; ++I) { 630 if (I->isDebugValue()) 631 continue; 632 633 int Opc = I->getOpcode(); 634 if (I->isBranch()) { 635 bool isCond = false; 636 unsigned Bits = 0; 637 unsigned Scale = 1; 638 int UOpc = Opc; 639 640 switch (Opc) { 641 default: 642 continue; // Ignore other JT branches 643 } 644 // Record this immediate branch. 645 unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale; 646 ImmBranches.push_back(ImmBranch(I, MaxOffs, isCond, UOpc)); 647 648 } 649 650 651 if (Opc == Mips::CONSTPOOL_ENTRY) 652 continue; 653 654 655 // Scan the instructions for constant pool operands. 656 for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) 657 if (I->getOperand(op).isCPI()) { 658 659 // We found one. The addressing mode tells us the max displacement 660 // from the PC that this instruction permits. 661 662 // Basic size info comes from the TSFlags field. 663 unsigned Bits = 0; 664 unsigned Scale = 1; 665 bool NegOk = false; 666 unsigned LongFormBits = 0; 667 unsigned LongFormScale = 0; 668 unsigned LongFormOpcode = 0; 669 switch (Opc) { 670 default: 671 llvm_unreachable("Unknown addressing mode for CP reference!"); 672 case Mips::LwRxPcTcp16: 673 Bits = 8; 674 Scale = 2; 675 LongFormOpcode = Mips::LwRxPcTcpX16; 676 break; 677 case Mips::LwRxPcTcpX16: 678 Bits = 16; 679 Scale = 2; 680 break; 681 } 682 // Remember that this is a user of a CP entry. 683 unsigned CPI = I->getOperand(op).getIndex(); 684 MachineInstr *CPEMI = CPEMIs[CPI]; 685 unsigned MaxOffs = ((1 << Bits)-1) * Scale; 686 unsigned LongFormMaxOffs = ((1 << LongFormBits)-1) * LongFormScale; 687 CPUsers.push_back(CPUser(I, CPEMI, MaxOffs, NegOk, 688 LongFormMaxOffs, LongFormOpcode)); 689 690 // Increment corresponding CPEntry reference count. 691 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI); 692 assert(CPE && "Cannot find a corresponding CPEntry!"); 693 CPE->RefCount++; 694 695 // Instructions can only use one CP entry, don't bother scanning the 696 // rest of the operands. 697 break; 698 699 } 700 701 } 702 } 703 704} 705 706/// computeBlockSize - Compute the size and some alignment information for MBB. 707/// This function updates BBInfo directly. 708void MipsConstantIslands::computeBlockSize(MachineBasicBlock *MBB) { 709 BasicBlockInfo &BBI = BBInfo[MBB->getNumber()]; 710 BBI.Size = 0; 711 BBI.Unalign = 0; 712 BBI.PostAlign = 0; 713 714 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E; 715 ++I) 716 BBI.Size += TII->GetInstSizeInBytes(I); 717 718} 719 720/// getOffsetOf - Return the current offset of the specified machine instruction 721/// from the start of the function. This offset changes as stuff is moved 722/// around inside the function. 723unsigned MipsConstantIslands::getOffsetOf(MachineInstr *MI) const { 724 MachineBasicBlock *MBB = MI->getParent(); 725 726 // The offset is composed of two things: the sum of the sizes of all MBB's 727 // before this instruction's block, and the offset from the start of the block 728 // it is in. 729 unsigned Offset = BBInfo[MBB->getNumber()].Offset; 730 731 // Sum instructions before MI in MBB. 732 for (MachineBasicBlock::iterator I = MBB->begin(); &*I != MI; ++I) { 733 assert(I != MBB->end() && "Didn't find MI in its own basic block?"); 734 Offset += TII->GetInstSizeInBytes(I); 735 } 736 return Offset; 737} 738 739/// CompareMBBNumbers - Little predicate function to sort the WaterList by MBB 740/// ID. 741static bool CompareMBBNumbers(const MachineBasicBlock *LHS, 742 const MachineBasicBlock *RHS) { 743 return LHS->getNumber() < RHS->getNumber(); 744} 745 746/// updateForInsertedWaterBlock - When a block is newly inserted into the 747/// machine function, it upsets all of the block numbers. Renumber the blocks 748/// and update the arrays that parallel this numbering. 749void MipsConstantIslands::updateForInsertedWaterBlock 750 (MachineBasicBlock *NewBB) { 751 // Renumber the MBB's to keep them consecutive. 752 NewBB->getParent()->RenumberBlocks(NewBB); 753 754 // Insert an entry into BBInfo to align it properly with the (newly 755 // renumbered) block numbers. 756 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo()); 757 758 // Next, update WaterList. Specifically, we need to add NewMBB as having 759 // available water after it. 760 water_iterator IP = 761 std::lower_bound(WaterList.begin(), WaterList.end(), NewBB, 762 CompareMBBNumbers); 763 WaterList.insert(IP, NewBB); 764} 765 766unsigned MipsConstantIslands::getUserOffset(CPUser &U) const { 767 return getOffsetOf(U.MI); 768} 769 770/// Split the basic block containing MI into two blocks, which are joined by 771/// an unconditional branch. Update data structures and renumber blocks to 772/// account for this change and returns the newly created block. 773MachineBasicBlock *MipsConstantIslands::splitBlockBeforeInstr 774 (MachineInstr *MI) { 775 MachineBasicBlock *OrigBB = MI->getParent(); 776 777 // Create a new MBB for the code after the OrigBB. 778 MachineBasicBlock *NewBB = 779 MF->CreateMachineBasicBlock(OrigBB->getBasicBlock()); 780 MachineFunction::iterator MBBI = OrigBB; ++MBBI; 781 MF->insert(MBBI, NewBB); 782 783 // Splice the instructions starting with MI over to NewBB. 784 NewBB->splice(NewBB->end(), OrigBB, MI, OrigBB->end()); 785 786 // Add an unconditional branch from OrigBB to NewBB. 787 // Note the new unconditional branch is not being recorded. 788 // There doesn't seem to be meaningful DebugInfo available; this doesn't 789 // correspond to anything in the source. 790 BuildMI(OrigBB, DebugLoc(), TII->get(Mips::BimmX16)).addMBB(NewBB); 791 ++NumSplit; 792 793 // Update the CFG. All succs of OrigBB are now succs of NewBB. 794 NewBB->transferSuccessors(OrigBB); 795 796 // OrigBB branches to NewBB. 797 OrigBB->addSuccessor(NewBB); 798 799 // Update internal data structures to account for the newly inserted MBB. 800 // This is almost the same as updateForInsertedWaterBlock, except that 801 // the Water goes after OrigBB, not NewBB. 802 MF->RenumberBlocks(NewBB); 803 804 // Insert an entry into BBInfo to align it properly with the (newly 805 // renumbered) block numbers. 806 BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo()); 807 808 // Next, update WaterList. Specifically, we need to add OrigMBB as having 809 // available water after it (but not if it's already there, which happens 810 // when splitting before a conditional branch that is followed by an 811 // unconditional branch - in that case we want to insert NewBB). 812 water_iterator IP = 813 std::lower_bound(WaterList.begin(), WaterList.end(), OrigBB, 814 CompareMBBNumbers); 815 MachineBasicBlock* WaterBB = *IP; 816 if (WaterBB == OrigBB) 817 WaterList.insert(llvm::next(IP), NewBB); 818 else 819 WaterList.insert(IP, OrigBB); 820 NewWaterList.insert(OrigBB); 821 822 // Figure out how large the OrigBB is. As the first half of the original 823 // block, it cannot contain a tablejump. The size includes 824 // the new jump we added. (It should be possible to do this without 825 // recounting everything, but it's very confusing, and this is rarely 826 // executed.) 827 computeBlockSize(OrigBB); 828 829 // Figure out how large the NewMBB is. As the second half of the original 830 // block, it may contain a tablejump. 831 computeBlockSize(NewBB); 832 833 // All BBOffsets following these blocks must be modified. 834 adjustBBOffsetsAfter(OrigBB); 835 836 return NewBB; 837} 838 839 840 841/// isOffsetInRange - Checks whether UserOffset (the location of a constant pool 842/// reference) is within MaxDisp of TrialOffset (a proposed location of a 843/// constant pool entry). 844/// UserOffset is computed by getUserOffset above to include PC adjustments. If 845/// the mod 4 alignment of UserOffset is not known, the uncertainty must be 846/// subtracted from MaxDisp instead. CPUser::getMaxDisp() does that. 847bool MipsConstantIslands::isOffsetInRange(unsigned UserOffset, 848 unsigned TrialOffset, unsigned MaxDisp, 849 bool NegativeOK) { 850 if (UserOffset <= TrialOffset) { 851 // User before the Trial. 852 if (TrialOffset - UserOffset <= MaxDisp) 853 return true; 854 } else if (NegativeOK) { 855 if (UserOffset - TrialOffset <= MaxDisp) 856 return true; 857 } 858 return false; 859} 860 861/// isWaterInRange - Returns true if a CPE placed after the specified 862/// Water (a basic block) will be in range for the specific MI. 863/// 864/// Compute how much the function will grow by inserting a CPE after Water. 865bool MipsConstantIslands::isWaterInRange(unsigned UserOffset, 866 MachineBasicBlock* Water, CPUser &U, 867 unsigned &Growth) { 868 unsigned CPELogAlign = getCPELogAlign(U.CPEMI); 869 unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset(CPELogAlign); 870 unsigned NextBlockOffset, NextBlockAlignment; 871 MachineFunction::const_iterator NextBlock = Water; 872 if (++NextBlock == MF->end()) { 873 NextBlockOffset = BBInfo[Water->getNumber()].postOffset(); 874 NextBlockAlignment = 0; 875 } else { 876 NextBlockOffset = BBInfo[NextBlock->getNumber()].Offset; 877 NextBlockAlignment = NextBlock->getAlignment(); 878 } 879 unsigned Size = U.CPEMI->getOperand(2).getImm(); 880 unsigned CPEEnd = CPEOffset + Size; 881 882 // The CPE may be able to hide in the alignment padding before the next 883 // block. It may also cause more padding to be required if it is more aligned 884 // that the next block. 885 if (CPEEnd > NextBlockOffset) { 886 Growth = CPEEnd - NextBlockOffset; 887 // Compute the padding that would go at the end of the CPE to align the next 888 // block. 889 Growth += OffsetToAlignment(CPEEnd, 1u << NextBlockAlignment); 890 891 // If the CPE is to be inserted before the instruction, that will raise 892 // the offset of the instruction. Also account for unknown alignment padding 893 // in blocks between CPE and the user. 894 if (CPEOffset < UserOffset) 895 UserOffset += Growth + UnknownPadding(MF->getAlignment(), CPELogAlign); 896 } else 897 // CPE fits in existing padding. 898 Growth = 0; 899 900 return isOffsetInRange(UserOffset, CPEOffset, U); 901} 902 903/// isCPEntryInRange - Returns true if the distance between specific MI and 904/// specific ConstPool entry instruction can fit in MI's displacement field. 905bool MipsConstantIslands::isCPEntryInRange 906 (MachineInstr *MI, unsigned UserOffset, 907 MachineInstr *CPEMI, unsigned MaxDisp, 908 bool NegOk, bool DoDump) { 909 unsigned CPEOffset = getOffsetOf(CPEMI); 910 911 if (DoDump) { 912 DEBUG({ 913 unsigned Block = MI->getParent()->getNumber(); 914 const BasicBlockInfo &BBI = BBInfo[Block]; 915 dbgs() << "User of CPE#" << CPEMI->getOperand(0).getImm() 916 << " max delta=" << MaxDisp 917 << format(" insn address=%#x", UserOffset) 918 << " in BB#" << Block << ": " 919 << format("%#x-%x\t", BBI.Offset, BBI.postOffset()) << *MI 920 << format("CPE address=%#x offset=%+d: ", CPEOffset, 921 int(CPEOffset-UserOffset)); 922 }); 923 } 924 925 return isOffsetInRange(UserOffset, CPEOffset, MaxDisp, NegOk); 926} 927 928#ifndef NDEBUG 929/// BBIsJumpedOver - Return true of the specified basic block's only predecessor 930/// unconditionally branches to its only successor. 931static bool BBIsJumpedOver(MachineBasicBlock *MBB) { 932 if (MBB->pred_size() != 1 || MBB->succ_size() != 1) 933 return false; 934 MachineBasicBlock *Succ = *MBB->succ_begin(); 935 MachineBasicBlock *Pred = *MBB->pred_begin(); 936 MachineInstr *PredMI = &Pred->back(); 937 if (PredMI->getOpcode() == Mips::BimmX16) 938 return PredMI->getOperand(0).getMBB() == Succ; 939 return false; 940} 941#endif 942 943void MipsConstantIslands::adjustBBOffsetsAfter(MachineBasicBlock *BB) { 944 unsigned BBNum = BB->getNumber(); 945 for(unsigned i = BBNum + 1, e = MF->getNumBlockIDs(); i < e; ++i) { 946 // Get the offset and known bits at the end of the layout predecessor. 947 // Include the alignment of the current block. 948 unsigned Offset = BBInfo[i - 1].postOffset(); 949 BBInfo[i].Offset = Offset; 950 } 951} 952 953/// decrementCPEReferenceCount - find the constant pool entry with index CPI 954/// and instruction CPEMI, and decrement its refcount. If the refcount 955/// becomes 0 remove the entry and instruction. Returns true if we removed 956/// the entry, false if we didn't. 957 958bool MipsConstantIslands::decrementCPEReferenceCount(unsigned CPI, 959 MachineInstr *CPEMI) { 960 // Find the old entry. Eliminate it if it is no longer used. 961 CPEntry *CPE = findConstPoolEntry(CPI, CPEMI); 962 assert(CPE && "Unexpected!"); 963 if (--CPE->RefCount == 0) { 964 removeDeadCPEMI(CPEMI); 965 CPE->CPEMI = NULL; 966 --NumCPEs; 967 return true; 968 } 969 return false; 970} 971 972/// LookForCPEntryInRange - see if the currently referenced CPE is in range; 973/// if not, see if an in-range clone of the CPE is in range, and if so, 974/// change the data structures so the user references the clone. Returns: 975/// 0 = no existing entry found 976/// 1 = entry found, and there were no code insertions or deletions 977/// 2 = entry found, and there were code insertions or deletions 978int MipsConstantIslands::findInRangeCPEntry(CPUser& U, unsigned UserOffset) 979{ 980 MachineInstr *UserMI = U.MI; 981 MachineInstr *CPEMI = U.CPEMI; 982 983 // Check to see if the CPE is already in-range. 984 if (isCPEntryInRange(UserMI, UserOffset, CPEMI, U.getMaxDisp(), U.NegOk, 985 true)) { 986 DEBUG(dbgs() << "In range\n"); 987 return 1; 988 } 989 990 // No. Look for previously created clones of the CPE that are in range. 991 unsigned CPI = CPEMI->getOperand(1).getIndex(); 992 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 993 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 994 // We already tried this one 995 if (CPEs[i].CPEMI == CPEMI) 996 continue; 997 // Removing CPEs can leave empty entries, skip 998 if (CPEs[i].CPEMI == NULL) 999 continue; 1000 if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, U.getMaxDisp(), 1001 U.NegOk)) { 1002 DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" 1003 << CPEs[i].CPI << "\n"); 1004 // Point the CPUser node to the replacement 1005 U.CPEMI = CPEs[i].CPEMI; 1006 // Change the CPI in the instruction operand to refer to the clone. 1007 for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j) 1008 if (UserMI->getOperand(j).isCPI()) { 1009 UserMI->getOperand(j).setIndex(CPEs[i].CPI); 1010 break; 1011 } 1012 // Adjust the refcount of the clone... 1013 CPEs[i].RefCount++; 1014 // ...and the original. If we didn't remove the old entry, none of the 1015 // addresses changed, so we don't need another pass. 1016 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1; 1017 } 1018 } 1019 return 0; 1020} 1021 1022/// LookForCPEntryInRange - see if the currently referenced CPE is in range; 1023/// This version checks if the longer form of the instruction can be used to 1024/// to satisfy things. 1025/// if not, see if an in-range clone of the CPE is in range, and if so, 1026/// change the data structures so the user references the clone. Returns: 1027/// 0 = no existing entry found 1028/// 1 = entry found, and there were no code insertions or deletions 1029/// 2 = entry found, and there were code insertions or deletions 1030int MipsConstantIslands::findLongFormInRangeCPEntry 1031 (CPUser& U, unsigned UserOffset) 1032{ 1033 MachineInstr *UserMI = U.MI; 1034 MachineInstr *CPEMI = U.CPEMI; 1035 1036 // Check to see if the CPE is already in-range. 1037 if (isCPEntryInRange(UserMI, UserOffset, CPEMI, 1038 U.getLongFormMaxDisp(), U.NegOk, 1039 true)) { 1040 DEBUG(dbgs() << "In range\n"); 1041 UserMI->setDesc(TII->get(U.getLongFormOpcode())); 1042 return 2; // instruction is longer length now 1043 } 1044 1045 // No. Look for previously created clones of the CPE that are in range. 1046 unsigned CPI = CPEMI->getOperand(1).getIndex(); 1047 std::vector<CPEntry> &CPEs = CPEntries[CPI]; 1048 for (unsigned i = 0, e = CPEs.size(); i != e; ++i) { 1049 // We already tried this one 1050 if (CPEs[i].CPEMI == CPEMI) 1051 continue; 1052 // Removing CPEs can leave empty entries, skip 1053 if (CPEs[i].CPEMI == NULL) 1054 continue; 1055 if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, 1056 U.getLongFormMaxDisp(), U.NegOk)) { 1057 DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#" 1058 << CPEs[i].CPI << "\n"); 1059 // Point the CPUser node to the replacement 1060 U.CPEMI = CPEs[i].CPEMI; 1061 // Change the CPI in the instruction operand to refer to the clone. 1062 for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j) 1063 if (UserMI->getOperand(j).isCPI()) { 1064 UserMI->getOperand(j).setIndex(CPEs[i].CPI); 1065 break; 1066 } 1067 // Adjust the refcount of the clone... 1068 CPEs[i].RefCount++; 1069 // ...and the original. If we didn't remove the old entry, none of the 1070 // addresses changed, so we don't need another pass. 1071 return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1; 1072 } 1073 } 1074 return 0; 1075} 1076 1077/// getUnconditionalBrDisp - Returns the maximum displacement that can fit in 1078/// the specific unconditional branch instruction. 1079static inline unsigned getUnconditionalBrDisp(int Opc) { 1080 switch (Opc) { 1081 case Mips::BimmX16: 1082 return ((1<<16)-1)*2; 1083 default: 1084 break; 1085 } 1086 return ((1<<16)-1)*2; 1087} 1088 1089/// findAvailableWater - Look for an existing entry in the WaterList in which 1090/// we can place the CPE referenced from U so it's within range of U's MI. 1091/// Returns true if found, false if not. If it returns true, WaterIter 1092/// is set to the WaterList entry. 1093/// To ensure that this pass 1094/// terminates, the CPE location for a particular CPUser is only allowed to 1095/// move to a lower address, so search backward from the end of the list and 1096/// prefer the first water that is in range. 1097bool MipsConstantIslands::findAvailableWater(CPUser &U, unsigned UserOffset, 1098 water_iterator &WaterIter) { 1099 if (WaterList.empty()) 1100 return false; 1101 1102 unsigned BestGrowth = ~0u; 1103 for (water_iterator IP = prior(WaterList.end()), B = WaterList.begin();; 1104 --IP) { 1105 MachineBasicBlock* WaterBB = *IP; 1106 // Check if water is in range and is either at a lower address than the 1107 // current "high water mark" or a new water block that was created since 1108 // the previous iteration by inserting an unconditional branch. In the 1109 // latter case, we want to allow resetting the high water mark back to 1110 // this new water since we haven't seen it before. Inserting branches 1111 // should be relatively uncommon and when it does happen, we want to be 1112 // sure to take advantage of it for all the CPEs near that block, so that 1113 // we don't insert more branches than necessary. 1114 unsigned Growth; 1115 if (isWaterInRange(UserOffset, WaterBB, U, Growth) && 1116 (WaterBB->getNumber() < U.HighWaterMark->getNumber() || 1117 NewWaterList.count(WaterBB)) && Growth < BestGrowth) { 1118 // This is the least amount of required padding seen so far. 1119 BestGrowth = Growth; 1120 WaterIter = IP; 1121 DEBUG(dbgs() << "Found water after BB#" << WaterBB->getNumber() 1122 << " Growth=" << Growth << '\n'); 1123 1124 // Keep looking unless it is perfect. 1125 if (BestGrowth == 0) 1126 return true; 1127 } 1128 if (IP == B) 1129 break; 1130 } 1131 return BestGrowth != ~0u; 1132} 1133 1134/// createNewWater - No existing WaterList entry will work for 1135/// CPUsers[CPUserIndex], so create a place to put the CPE. The end of the 1136/// block is used if in range, and the conditional branch munged so control 1137/// flow is correct. Otherwise the block is split to create a hole with an 1138/// unconditional branch around it. In either case NewMBB is set to a 1139/// block following which the new island can be inserted (the WaterList 1140/// is not adjusted). 1141void MipsConstantIslands::createNewWater(unsigned CPUserIndex, 1142 unsigned UserOffset, 1143 MachineBasicBlock *&NewMBB) { 1144 CPUser &U = CPUsers[CPUserIndex]; 1145 MachineInstr *UserMI = U.MI; 1146 MachineInstr *CPEMI = U.CPEMI; 1147 unsigned CPELogAlign = getCPELogAlign(CPEMI); 1148 MachineBasicBlock *UserMBB = UserMI->getParent(); 1149 const BasicBlockInfo &UserBBI = BBInfo[UserMBB->getNumber()]; 1150 1151 // If the block does not end in an unconditional branch already, and if the 1152 // end of the block is within range, make new water there. 1153 if (BBHasFallthrough(UserMBB)) { 1154 // Size of branch to insert. 1155 unsigned Delta = 2; 1156 // Compute the offset where the CPE will begin. 1157 unsigned CPEOffset = UserBBI.postOffset(CPELogAlign) + Delta; 1158 1159 if (isOffsetInRange(UserOffset, CPEOffset, U)) { 1160 DEBUG(dbgs() << "Split at end of BB#" << UserMBB->getNumber() 1161 << format(", expected CPE offset %#x\n", CPEOffset)); 1162 NewMBB = llvm::next(MachineFunction::iterator(UserMBB)); 1163 // Add an unconditional branch from UserMBB to fallthrough block. Record 1164 // it for branch lengthening; this new branch will not get out of range, 1165 // but if the preceding conditional branch is out of range, the targets 1166 // will be exchanged, and the altered branch may be out of range, so the 1167 // machinery has to know about it. 1168 int UncondBr = Mips::BimmX16; 1169 BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB); 1170 unsigned MaxDisp = getUnconditionalBrDisp(UncondBr); 1171 ImmBranches.push_back(ImmBranch(&UserMBB->back(), 1172 MaxDisp, false, UncondBr)); 1173 BBInfo[UserMBB->getNumber()].Size += Delta; 1174 adjustBBOffsetsAfter(UserMBB); 1175 return; 1176 } 1177 } 1178 1179 // What a big block. Find a place within the block to split it. 1180 1181 // Try to split the block so it's fully aligned. Compute the latest split 1182 // point where we can add a 4-byte branch instruction, and then align to 1183 // LogAlign which is the largest possible alignment in the function. 1184 unsigned LogAlign = MF->getAlignment(); 1185 assert(LogAlign >= CPELogAlign && "Over-aligned constant pool entry"); 1186 unsigned KnownBits = UserBBI.internalKnownBits(); 1187 unsigned UPad = UnknownPadding(LogAlign, KnownBits); 1188 unsigned BaseInsertOffset = UserOffset + U.getMaxDisp() - UPad; 1189 DEBUG(dbgs() << format("Split in middle of big block before %#x", 1190 BaseInsertOffset)); 1191 1192 // The 4 in the following is for the unconditional branch we'll be inserting 1193 // Alignment of the island is handled 1194 // inside isOffsetInRange. 1195 BaseInsertOffset -= 4; 1196 1197 DEBUG(dbgs() << format(", adjusted to %#x", BaseInsertOffset) 1198 << " la=" << LogAlign 1199 << " kb=" << KnownBits 1200 << " up=" << UPad << '\n'); 1201 1202 // This could point off the end of the block if we've already got constant 1203 // pool entries following this block; only the last one is in the water list. 1204 // Back past any possible branches (allow for a conditional and a maximally 1205 // long unconditional). 1206 if (BaseInsertOffset + 8 >= UserBBI.postOffset()) { 1207 BaseInsertOffset = UserBBI.postOffset() - UPad - 8; 1208 DEBUG(dbgs() << format("Move inside block: %#x\n", BaseInsertOffset)); 1209 } 1210 unsigned EndInsertOffset = BaseInsertOffset + 4 + UPad + 1211 CPEMI->getOperand(2).getImm(); 1212 MachineBasicBlock::iterator MI = UserMI; 1213 ++MI; 1214 unsigned CPUIndex = CPUserIndex+1; 1215 unsigned NumCPUsers = CPUsers.size(); 1216 //MachineInstr *LastIT = 0; 1217 for (unsigned Offset = UserOffset+TII->GetInstSizeInBytes(UserMI); 1218 Offset < BaseInsertOffset; 1219 Offset += TII->GetInstSizeInBytes(MI), 1220 MI = llvm::next(MI)) { 1221 assert(MI != UserMBB->end() && "Fell off end of block"); 1222 if (CPUIndex < NumCPUsers && CPUsers[CPUIndex].MI == MI) { 1223 CPUser &U = CPUsers[CPUIndex]; 1224 if (!isOffsetInRange(Offset, EndInsertOffset, U)) { 1225 // Shift intertion point by one unit of alignment so it is within reach. 1226 BaseInsertOffset -= 1u << LogAlign; 1227 EndInsertOffset -= 1u << LogAlign; 1228 } 1229 // This is overly conservative, as we don't account for CPEMIs being 1230 // reused within the block, but it doesn't matter much. Also assume CPEs 1231 // are added in order with alignment padding. We may eventually be able 1232 // to pack the aligned CPEs better. 1233 EndInsertOffset += U.CPEMI->getOperand(2).getImm(); 1234 CPUIndex++; 1235 } 1236 } 1237 1238 --MI; 1239 NewMBB = splitBlockBeforeInstr(MI); 1240} 1241 1242/// handleConstantPoolUser - Analyze the specified user, checking to see if it 1243/// is out-of-range. If so, pick up the constant pool value and move it some 1244/// place in-range. Return true if we changed any addresses (thus must run 1245/// another pass of branch lengthening), false otherwise. 1246bool MipsConstantIslands::handleConstantPoolUser(unsigned CPUserIndex) { 1247 CPUser &U = CPUsers[CPUserIndex]; 1248 MachineInstr *UserMI = U.MI; 1249 MachineInstr *CPEMI = U.CPEMI; 1250 unsigned CPI = CPEMI->getOperand(1).getIndex(); 1251 unsigned Size = CPEMI->getOperand(2).getImm(); 1252 // Compute this only once, it's expensive. 1253 unsigned UserOffset = getUserOffset(U); 1254 1255 // See if the current entry is within range, or there is a clone of it 1256 // in range. 1257 int result = findInRangeCPEntry(U, UserOffset); 1258 if (result==1) return false; 1259 else if (result==2) return true; 1260 1261 1262 // Look for water where we can place this CPE. 1263 MachineBasicBlock *NewIsland = MF->CreateMachineBasicBlock(); 1264 MachineBasicBlock *NewMBB; 1265 water_iterator IP; 1266 if (findAvailableWater(U, UserOffset, IP)) { 1267 DEBUG(dbgs() << "Found water in range\n"); 1268 MachineBasicBlock *WaterBB = *IP; 1269 1270 // If the original WaterList entry was "new water" on this iteration, 1271 // propagate that to the new island. This is just keeping NewWaterList 1272 // updated to match the WaterList, which will be updated below. 1273 if (NewWaterList.erase(WaterBB)) 1274 NewWaterList.insert(NewIsland); 1275 1276 // The new CPE goes before the following block (NewMBB). 1277 NewMBB = llvm::next(MachineFunction::iterator(WaterBB)); 1278 1279 } else { 1280 // No water found. 1281 // we first see if a longer form of the instrucion could have reached 1282 // the constant. in that case we won't bother to split 1283#ifdef IN_PROGRESS 1284 result = findLongFormInRangeCPEntry(U, UserOffset); 1285#endif 1286 DEBUG(dbgs() << "No water found\n"); 1287 createNewWater(CPUserIndex, UserOffset, NewMBB); 1288 1289 // splitBlockBeforeInstr adds to WaterList, which is important when it is 1290 // called while handling branches so that the water will be seen on the 1291 // next iteration for constant pools, but in this context, we don't want 1292 // it. Check for this so it will be removed from the WaterList. 1293 // Also remove any entry from NewWaterList. 1294 MachineBasicBlock *WaterBB = prior(MachineFunction::iterator(NewMBB)); 1295 IP = std::find(WaterList.begin(), WaterList.end(), WaterBB); 1296 if (IP != WaterList.end()) 1297 NewWaterList.erase(WaterBB); 1298 1299 // We are adding new water. Update NewWaterList. 1300 NewWaterList.insert(NewIsland); 1301 } 1302 1303 // Remove the original WaterList entry; we want subsequent insertions in 1304 // this vicinity to go after the one we're about to insert. This 1305 // considerably reduces the number of times we have to move the same CPE 1306 // more than once and is also important to ensure the algorithm terminates. 1307 if (IP != WaterList.end()) 1308 WaterList.erase(IP); 1309 1310 // Okay, we know we can put an island before NewMBB now, do it! 1311 MF->insert(NewMBB, NewIsland); 1312 1313 // Update internal data structures to account for the newly inserted MBB. 1314 updateForInsertedWaterBlock(NewIsland); 1315 1316 // Decrement the old entry, and remove it if refcount becomes 0. 1317 decrementCPEReferenceCount(CPI, CPEMI); 1318 1319 // Now that we have an island to add the CPE to, clone the original CPE and 1320 // add it to the island. 1321 U.HighWaterMark = NewIsland; 1322 U.CPEMI = BuildMI(NewIsland, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY)) 1323 .addImm(ID).addConstantPoolIndex(CPI).addImm(Size); 1324 CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1)); 1325 ++NumCPEs; 1326 1327 // Mark the basic block as aligned as required by the const-pool entry. 1328 NewIsland->setAlignment(getCPELogAlign(U.CPEMI)); 1329 1330 // Increase the size of the island block to account for the new entry. 1331 BBInfo[NewIsland->getNumber()].Size += Size; 1332 adjustBBOffsetsAfter(llvm::prior(MachineFunction::iterator(NewIsland))); 1333 1334 // No existing clone of this CPE is within range. 1335 // We will be generating a new clone. Get a UID for it. 1336 unsigned ID = createPICLabelUId(); 1337 1338 // Finally, change the CPI in the instruction operand to be ID. 1339 for (unsigned i = 0, e = UserMI->getNumOperands(); i != e; ++i) 1340 if (UserMI->getOperand(i).isCPI()) { 1341 UserMI->getOperand(i).setIndex(ID); 1342 break; 1343 } 1344 1345 DEBUG(dbgs() << " Moved CPE to #" << ID << " CPI=" << CPI 1346 << format(" offset=%#x\n", BBInfo[NewIsland->getNumber()].Offset)); 1347 1348 return true; 1349} 1350 1351/// removeDeadCPEMI - Remove a dead constant pool entry instruction. Update 1352/// sizes and offsets of impacted basic blocks. 1353void MipsConstantIslands::removeDeadCPEMI(MachineInstr *CPEMI) { 1354 MachineBasicBlock *CPEBB = CPEMI->getParent(); 1355 unsigned Size = CPEMI->getOperand(2).getImm(); 1356 CPEMI->eraseFromParent(); 1357 BBInfo[CPEBB->getNumber()].Size -= Size; 1358 // All succeeding offsets have the current size value added in, fix this. 1359 if (CPEBB->empty()) { 1360 BBInfo[CPEBB->getNumber()].Size = 0; 1361 1362 // This block no longer needs to be aligned. 1363 CPEBB->setAlignment(0); 1364 } else 1365 // Entries are sorted by descending alignment, so realign from the front. 1366 CPEBB->setAlignment(getCPELogAlign(CPEBB->begin())); 1367 1368 adjustBBOffsetsAfter(CPEBB); 1369 // An island has only one predecessor BB and one successor BB. Check if 1370 // this BB's predecessor jumps directly to this BB's successor. This 1371 // shouldn't happen currently. 1372 assert(!BBIsJumpedOver(CPEBB) && "How did this happen?"); 1373 // FIXME: remove the empty blocks after all the work is done? 1374} 1375 1376/// removeUnusedCPEntries - Remove constant pool entries whose refcounts 1377/// are zero. 1378bool MipsConstantIslands::removeUnusedCPEntries() { 1379 unsigned MadeChange = false; 1380 for (unsigned i = 0, e = CPEntries.size(); i != e; ++i) { 1381 std::vector<CPEntry> &CPEs = CPEntries[i]; 1382 for (unsigned j = 0, ee = CPEs.size(); j != ee; ++j) { 1383 if (CPEs[j].RefCount == 0 && CPEs[j].CPEMI) { 1384 removeDeadCPEMI(CPEs[j].CPEMI); 1385 CPEs[j].CPEMI = NULL; 1386 MadeChange = true; 1387 } 1388 } 1389 } 1390 return MadeChange; 1391} 1392 1393/// isBBInRange - Returns true if the distance between specific MI and 1394/// specific BB can fit in MI's displacement field. 1395bool MipsConstantIslands::isBBInRange 1396 (MachineInstr *MI,MachineBasicBlock *DestBB, unsigned MaxDisp) { 1397 1398unsigned PCAdj = 4; 1399 1400 unsigned BrOffset = getOffsetOf(MI) + PCAdj; 1401 unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset; 1402 1403 DEBUG(dbgs() << "Branch of destination BB#" << DestBB->getNumber() 1404 << " from BB#" << MI->getParent()->getNumber() 1405 << " max delta=" << MaxDisp 1406 << " from " << getOffsetOf(MI) << " to " << DestOffset 1407 << " offset " << int(DestOffset-BrOffset) << "\t" << *MI); 1408 1409 if (BrOffset <= DestOffset) { 1410 // Branch before the Dest. 1411 if (DestOffset-BrOffset <= MaxDisp) 1412 return true; 1413 } else { 1414 if (BrOffset-DestOffset <= MaxDisp) 1415 return true; 1416 } 1417 return false; 1418} 1419 1420/// fixupImmediateBr - Fix up an immediate branch whose destination is too far 1421/// away to fit in its displacement field. 1422bool MipsConstantIslands::fixupImmediateBr(ImmBranch &Br) { 1423 MachineInstr *MI = Br.MI; 1424 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB(); 1425 1426 // Check to see if the DestBB is already in-range. 1427 if (isBBInRange(MI, DestBB, Br.MaxDisp)) 1428 return false; 1429 1430 if (!Br.isCond) 1431 return fixupUnconditionalBr(Br); 1432 return fixupConditionalBr(Br); 1433} 1434 1435/// fixupUnconditionalBr - Fix up an unconditional branch whose destination is 1436/// too far away to fit in its displacement field. If the LR register has been 1437/// spilled in the epilogue, then we can use BL to implement a far jump. 1438/// Otherwise, add an intermediate branch instruction to a branch. 1439bool 1440MipsConstantIslands::fixupUnconditionalBr(ImmBranch &Br) { 1441 MachineInstr *MI = Br.MI; 1442 MachineBasicBlock *MBB = MI->getParent(); 1443 // Use BL to implement far jump. 1444 Br.MaxDisp = ((1 << 16)-1) * 2; 1445 MI->setDesc(TII->get(Mips::BimmX16)); 1446 BBInfo[MBB->getNumber()].Size += 2; 1447 adjustBBOffsetsAfter(MBB); 1448 HasFarJump = true; 1449 ++NumUBrFixed; 1450 1451 DEBUG(dbgs() << " Changed B to long jump " << *MI); 1452 1453 return true; 1454} 1455 1456/// fixupConditionalBr - Fix up a conditional branch whose destination is too 1457/// far away to fit in its displacement field. It is converted to an inverse 1458/// conditional branch + an unconditional branch to the destination. 1459bool 1460MipsConstantIslands::fixupConditionalBr(ImmBranch &Br) { 1461 MachineInstr *MI = Br.MI; 1462 MachineBasicBlock *DestBB = MI->getOperand(0).getMBB(); 1463 1464 // Add an unconditional branch to the destination and invert the branch 1465 // condition to jump over it: 1466 // blt L1 1467 // => 1468 // bge L2 1469 // b L1 1470 // L2: 1471 unsigned CCReg = 0; // FIXME 1472 unsigned CC=0; //FIXME 1473 1474 // If the branch is at the end of its MBB and that has a fall-through block, 1475 // direct the updated conditional branch to the fall-through block. Otherwise, 1476 // split the MBB before the next instruction. 1477 MachineBasicBlock *MBB = MI->getParent(); 1478 MachineInstr *BMI = &MBB->back(); 1479 bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB); 1480 1481 ++NumCBrFixed; 1482 if (BMI != MI) { 1483 if (llvm::next(MachineBasicBlock::iterator(MI)) == prior(MBB->end()) && 1484 BMI->getOpcode() == Br.UncondBr) { 1485 // Last MI in the BB is an unconditional branch. Can we simply invert the 1486 // condition and swap destinations: 1487 // beq L1 1488 // b L2 1489 // => 1490 // bne L2 1491 // b L1 1492 MachineBasicBlock *NewDest = BMI->getOperand(0).getMBB(); 1493 if (isBBInRange(MI, NewDest, Br.MaxDisp)) { 1494 DEBUG(dbgs() << " Invert Bcc condition and swap its destination with " 1495 << *BMI); 1496 BMI->getOperand(0).setMBB(DestBB); 1497 MI->getOperand(0).setMBB(NewDest); 1498 return true; 1499 } 1500 } 1501 } 1502 1503 if (NeedSplit) { 1504 splitBlockBeforeInstr(MI); 1505 // No need for the branch to the next block. We're adding an unconditional 1506 // branch to the destination. 1507 int delta = TII->GetInstSizeInBytes(&MBB->back()); 1508 BBInfo[MBB->getNumber()].Size -= delta; 1509 MBB->back().eraseFromParent(); 1510 // BBInfo[SplitBB].Offset is wrong temporarily, fixed below 1511 } 1512 MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB)); 1513 1514 DEBUG(dbgs() << " Insert B to BB#" << DestBB->getNumber() 1515 << " also invert condition and change dest. to BB#" 1516 << NextBB->getNumber() << "\n"); 1517 1518 // Insert a new conditional branch and a new unconditional branch. 1519 // Also update the ImmBranch as well as adding a new entry for the new branch. 1520 BuildMI(MBB, DebugLoc(), TII->get(MI->getOpcode())) 1521 .addMBB(NextBB).addImm(CC).addReg(CCReg); 1522 Br.MI = &MBB->back(); 1523 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back()); 1524 BuildMI(MBB, DebugLoc(), TII->get(Br.UncondBr)).addMBB(DestBB); 1525 BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back()); 1526 unsigned MaxDisp = getUnconditionalBrDisp(Br.UncondBr); 1527 ImmBranches.push_back(ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr)); 1528 1529 // Remove the old conditional branch. It may or may not still be in MBB. 1530 BBInfo[MI->getParent()->getNumber()].Size -= TII->GetInstSizeInBytes(MI); 1531 MI->eraseFromParent(); 1532 adjustBBOffsetsAfter(MBB); 1533 return true; 1534} 1535 1536 1537void MipsConstantIslands::prescanForConstants() { 1538 unsigned J = 0; 1539 (void)J; 1540 PrescannedForConstants = true; 1541 for (MachineFunction::iterator B = 1542 MF->begin(), E = MF->end(); B != E; ++B) { 1543 for (MachineBasicBlock::instr_iterator I = 1544 B->instr_begin(), EB = B->instr_end(); I != EB; ++I) { 1545 switch(I->getDesc().getOpcode()) { 1546 case Mips::LwConstant32: { 1547 DEBUG(dbgs() << "constant island constant " << *I << "\n"); 1548 J = I->getNumOperands(); 1549 DEBUG(dbgs() << "num operands " << J << "\n"); 1550 MachineOperand& Literal = I->getOperand(1); 1551 if (Literal.isImm()) { 1552 int64_t V = Literal.getImm(); 1553 DEBUG(dbgs() << "literal " << V << "\n"); 1554 Type *Int32Ty = 1555 Type::getInt32Ty(MF->getFunction()->getContext()); 1556 const Constant *C = ConstantInt::get(Int32Ty, V); 1557 unsigned index = MCP->getConstantPoolIndex(C, 4); 1558 I->getOperand(2).ChangeToImmediate(index); 1559 DEBUG(dbgs() << "constant island constant " << *I << "\n"); 1560 I->setDesc(TII->get(Mips::LwRxPcTcp16)); 1561 I->RemoveOperand(1); 1562 I->RemoveOperand(1); 1563 I->addOperand(MachineOperand::CreateCPI(index, 0)); 1564 I->addOperand(MachineOperand::CreateImm(4)); 1565 } 1566 break; 1567 } 1568 default: 1569 break; 1570 } 1571 } 1572 } 1573} 1574 1575