lib/CodeGen/TargetRegisterInfo.cpp

   1 //==- TargetRegisterInfo.cpp - Target Register Information Implementation --==//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements the TargetRegisterInfo interface.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/CodeGen/TargetRegisterInfo.h"
  14 #include "llvm/ADT/ArrayRef.h"
  15 #include "llvm/ADT/BitVector.h"
  16 #include "llvm/ADT/SmallSet.h"
  17 #include "llvm/ADT/STLExtras.h"
  18 #include "llvm/ADT/StringExtras.h"
  19 #include "llvm/CodeGen/MachineFrameInfo.h"
  20 #include "llvm/CodeGen/MachineFunction.h"
  21 #include "llvm/CodeGen/MachineRegisterInfo.h"
  22 #include "llvm/CodeGen/TargetFrameLowering.h"
  23 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  24 #include "llvm/CodeGen/VirtRegMap.h"
  25 #include "llvm/Config/llvm-config.h"
  26 #include "llvm/IR/Attributes.h"
  27 #include "llvm/IR/Function.h"
  28 #include "llvm/MC/MCRegisterInfo.h"
  29 #include "llvm/Support/Compiler.h"
  30 #include "llvm/Support/Debug.h"
  31 #include "llvm/Support/MachineValueType.h"
  32 #include "llvm/Support/MathExtras.h"
  33 #include "llvm/Support/Printable.h"
  34 #include "llvm/Support/raw_ostream.h"
  35 #include <cassert>
  36 #include <utility>
  37
  38 #define DEBUG_TYPE "target-reg-info"
  39
  40 using namespace llvm;
  41
  42 TargetRegisterInfo::TargetRegisterInfo(const TargetRegisterInfoDesc *ID,
  43                              regclass_iterator RCB, regclass_iterator RCE,
  44                              const char *const *SRINames,
  45                              const LaneBitmask *SRILaneMasks,
  46                              LaneBitmask SRICoveringLanes,
  47                              const RegClassInfo *const RCIs,
  48                              unsigned Mode)
  49   : InfoDesc(ID), SubRegIndexNames(SRINames),
  50     SubRegIndexLaneMasks(SRILaneMasks),
  51     RegClassBegin(RCB), RegClassEnd(RCE),
  52     CoveringLanes(SRICoveringLanes),
  53     RCInfos(RCIs), HwMode(Mode) {
  54 }
  55
  56 TargetRegisterInfo::~TargetRegisterInfo() = default;
  57
  58 void TargetRegisterInfo::markSuperRegs(BitVector &RegisterSet, unsigned Reg)
  59     const {
  60   for (MCSuperRegIterator AI(Reg, this, true); AI.isValid(); ++AI)
  61     RegisterSet.set(*AI);
  62 }
  63
  64 bool TargetRegisterInfo::checkAllSuperRegsMarked(const BitVector &RegisterSet,
  65     ArrayRef<MCPhysReg> Exceptions) const {
  66   // Check that all super registers of reserved regs are reserved as well.
  67   BitVector Checked(getNumRegs());
  68   for (unsigned Reg : RegisterSet.set_bits()) {
  69     if (Checked[Reg])
  70       continue;
  71     for (MCSuperRegIterator SR(Reg, this); SR.isValid(); ++SR) {
  72       if (!RegisterSet[*SR] && !is_contained(Exceptions, Reg)) {
  73         dbgs() << "Error: Super register " << printReg(*SR, this)
  74                << " of reserved register " << printReg(Reg, this)
  75                << " is not reserved.\n";
  76         return false;
  77       }
  78
  79       // We transitively check superregs. So we can remember this for later
  80       // to avoid compiletime explosion in deep register hierarchies.
  81       Checked.set(*SR);
  82     }
  83   }
  84   return true;
  85 }
  86
  87 namespace llvm {
  88
  89 Printable printReg(Register Reg, const TargetRegisterInfo *TRI,
  90                    unsigned SubIdx, const MachineRegisterInfo *MRI) {
  91   return Printable([Reg, TRI, SubIdx, MRI](raw_ostream &OS) {
  92     if (!Reg)
  93       OS << "$noreg";
  94     else if (Register::isStackSlot(Reg))
  95       OS << "SS#" << Register::stackSlot2Index(Reg);
  96     else if (Register::isVirtualRegister(Reg)) {
  97       StringRef Name = MRI ? MRI->getVRegName(Reg) : "";
  98       if (Name != "") {
  99         OS << '%' << Name;
 100       } else {
 101         OS << '%' << Register::virtReg2Index(Reg);
 102       }
 103     } else if (!TRI)
 104       OS << '$' << "physreg" << Reg;
 105     else if (Reg < TRI->getNumRegs()) {
 106       OS << '$';
 107       printLowerCase(TRI->getName(Reg), OS);
 108     } else
 109       llvm_unreachable("Register kind is unsupported.");
 110
 111     if (SubIdx) {
 112       if (TRI)
 113         OS << ':' << TRI->getSubRegIndexName(SubIdx);
 114       else
 115         OS << ":sub(" << SubIdx << ')';
 116     }
 117   });
 118 }
 119
 120 Printable printRegUnit(unsigned Unit, const TargetRegisterInfo *TRI) {
 121   return Printable([Unit, TRI](raw_ostream &OS) {
 122     // Generic printout when TRI is missing.
 123     if (!TRI) {
 124       OS << "Unit~" << Unit;
 125       return;
 126     }
 127
 128     // Check for invalid register units.
 129     if (Unit >= TRI->getNumRegUnits()) {
 130       OS << "BadUnit~" << Unit;
 131       return;
 132     }
 133
 134     // Normal units have at least one root.
 135     MCRegUnitRootIterator Roots(Unit, TRI);
 136     assert(Roots.isValid() && "Unit has no roots.");
 137     OS << TRI->getName(*Roots);
 138     for (++Roots; Roots.isValid(); ++Roots)
 139       OS << '~' << TRI->getName(*Roots);
 140   });
 141 }
 142
 143 Printable printVRegOrUnit(unsigned Unit, const TargetRegisterInfo *TRI) {
 144   return Printable([Unit, TRI](raw_ostream &OS) {
 145     if (Register::isVirtualRegister(Unit)) {
 146       OS << '%' << Register::virtReg2Index(Unit);
 147     } else {
 148       OS << printRegUnit(Unit, TRI);
 149     }
 150   });
 151 }
 152
 153 Printable printRegClassOrBank(unsigned Reg, const MachineRegisterInfo &RegInfo,
 154                               const TargetRegisterInfo *TRI) {
 155   return Printable([Reg, &RegInfo, TRI](raw_ostream &OS) {
 156     if (RegInfo.getRegClassOrNull(Reg))
 157       OS << StringRef(TRI->getRegClassName(RegInfo.getRegClass(Reg))).lower();
 158     else if (RegInfo.getRegBankOrNull(Reg))
 159       OS << StringRef(RegInfo.getRegBankOrNull(Reg)->getName()).lower();
 160     else {
 161       OS << "_";
 162       assert((RegInfo.def_empty(Reg) || RegInfo.getType(Reg).isValid()) &&
 163              "Generic registers must have a valid type");
 164     }
 165   });
 166 }
 167
 168 } // end namespace llvm
 169
 170 /// getAllocatableClass - Return the maximal subclass of the given register
 171 /// class that is alloctable, or NULL.
 172 const TargetRegisterClass *
 173 TargetRegisterInfo::getAllocatableClass(const TargetRegisterClass *RC) const {
 174   if (!RC || RC->isAllocatable())
 175     return RC;
 176
 177   for (BitMaskClassIterator It(RC->getSubClassMask(), *this); It.isValid();
 178        ++It) {
 179     const TargetRegisterClass *SubRC = getRegClass(It.getID());
 180     if (SubRC->isAllocatable())
 181       return SubRC;
 182   }
 183   return nullptr;
 184 }
 185
 186 /// getMinimalPhysRegClass - Returns the Register Class of a physical
 187 /// register of the given type, picking the most sub register class of
 188 /// the right type that contains this physreg.
 189 const TargetRegisterClass *
 190 TargetRegisterInfo::getMinimalPhysRegClass(unsigned reg, MVT VT) const {
 191   assert(Register::isPhysicalRegister(reg) &&
 192          "reg must be a physical register");
 193
 194   // Pick the most sub register class of the right type that contains
 195   // this physreg.
 196   const TargetRegisterClass* BestRC = nullptr;
 197   for (const TargetRegisterClass* RC : regclasses()) {
 198     if ((VT == MVT::Other || isTypeLegalForClass(*RC, VT)) &&
 199         RC->contains(reg) && (!BestRC || BestRC->hasSubClass(RC)))
 200       BestRC = RC;
 201   }
 202
 203   assert(BestRC && "Couldn't find the register class");
 204   return BestRC;
 205 }
 206
 207 /// getAllocatableSetForRC - Toggle the bits that represent allocatable
 208 /// registers for the specific register class.
 209 static void getAllocatableSetForRC(const MachineFunction &MF,
 210                                    const TargetRegisterClass *RC, BitVector &R){
 211   assert(RC->isAllocatable() && "invalid for nonallocatable sets");
 212   ArrayRef<MCPhysReg> Order = RC->getRawAllocationOrder(MF);
 213   for (unsigned i = 0; i != Order.size(); ++i)
 214     R.set(Order[i]);
 215 }
 216
 217 BitVector TargetRegisterInfo::getAllocatableSet(const MachineFunction &MF,
 218                                           const TargetRegisterClass *RC) const {
 219   BitVector Allocatable(getNumRegs());
 220   if (RC) {
 221     // A register class with no allocatable subclass returns an empty set.
 222     const TargetRegisterClass *SubClass = getAllocatableClass(RC);
 223     if (SubClass)
 224       getAllocatableSetForRC(MF, SubClass, Allocatable);
 225   } else {
 226     for (const TargetRegisterClass *C : regclasses())
 227       if (C->isAllocatable())
 228         getAllocatableSetForRC(MF, C, Allocatable);
 229   }
 230
 231   // Mask out the reserved registers
 232   BitVector Reserved = getReservedRegs(MF);
 233   Allocatable &= Reserved.flip();
 234
 235   return Allocatable;
 236 }
 237
 238 static inline
 239 const TargetRegisterClass *firstCommonClass(const uint32_t *A,
 240                                             const uint32_t *B,
 241                                             const TargetRegisterInfo *TRI) {
 242   for (unsigned I = 0, E = TRI->getNumRegClasses(); I < E; I += 32)
 243     if (unsigned Common = *A++ & *B++)
 244       return TRI->getRegClass(I + countTrailingZeros(Common));
 245   return nullptr;
 246 }
 247
 248 const TargetRegisterClass *
 249 TargetRegisterInfo::getCommonSubClass(const TargetRegisterClass *A,
 250                                       const TargetRegisterClass *B) const {
 251   // First take care of the trivial cases.
 252   if (A == B)
 253     return A;
 254   if (!A || !B)
 255     return nullptr;
 256
 257   // Register classes are ordered topologically, so the largest common
 258   // sub-class it the common sub-class with the smallest ID.
 259   return firstCommonClass(A->getSubClassMask(), B->getSubClassMask(), this);
 260 }
 261
 262 const TargetRegisterClass *
 263 TargetRegisterInfo::getMatchingSuperRegClass(const TargetRegisterClass *A,
 264                                              const TargetRegisterClass *B,
 265                                              unsigned Idx) const {
 266   assert(A && B && "Missing register class");
 267   assert(Idx && "Bad sub-register index");
 268
 269   // Find Idx in the list of super-register indices.
 270   for (SuperRegClassIterator RCI(B, this); RCI.isValid(); ++RCI)
 271     if (RCI.getSubReg() == Idx)
 272       // The bit mask contains all register classes that are projected into B
 273       // by Idx. Find a class that is also a sub-class of A.
 274       return firstCommonClass(RCI.getMask(), A->getSubClassMask(), this);
 275   return nullptr;
 276 }
 277
 278 const TargetRegisterClass *TargetRegisterInfo::
 279 getCommonSuperRegClass(const TargetRegisterClass *RCA, unsigned SubA,
 280                        const TargetRegisterClass *RCB, unsigned SubB,
 281                        unsigned &PreA, unsigned &PreB) const {
 282   assert(RCA && SubA && RCB && SubB && "Invalid arguments");
 283
 284   // Search all pairs of sub-register indices that project into RCA and RCB
 285   // respectively. This is quadratic, but usually the sets are very small. On
 286   // most targets like X86, there will only be a single sub-register index
 287   // (e.g., sub_16bit projecting into GR16).
 288   //
 289   // The worst case is a register class like DPR on ARM.
 290   // We have indices dsub_0..dsub_7 projecting into that class.
 291   //
 292   // It is very common that one register class is a sub-register of the other.
 293   // Arrange for RCA to be the larger register so the answer will be found in
 294   // the first iteration. This makes the search linear for the most common
 295   // case.
 296   const TargetRegisterClass *BestRC = nullptr;
 297   unsigned *BestPreA = &PreA;
 298   unsigned *BestPreB = &PreB;
 299   if (getRegSizeInBits(*RCA) < getRegSizeInBits(*RCB)) {
 300     std::swap(RCA, RCB);
 301     std::swap(SubA, SubB);
 302     std::swap(BestPreA, BestPreB);
 303   }
 304
 305   // Also terminate the search one we have found a register class as small as
 306   // RCA.
 307   unsigned MinSize = getRegSizeInBits(*RCA);
 308
 309   for (SuperRegClassIterator IA(RCA, this, true); IA.isValid(); ++IA) {
 310     unsigned FinalA = composeSubRegIndices(IA.getSubReg(), SubA);
 311     for (SuperRegClassIterator IB(RCB, this, true); IB.isValid(); ++IB) {
 312       // Check if a common super-register class exists for this index pair.
 313       const TargetRegisterClass *RC =
 314         firstCommonClass(IA.getMask(), IB.getMask(), this);
 315       if (!RC || getRegSizeInBits(*RC) < MinSize)
 316         continue;
 317
 318       // The indexes must compose identically: PreA+SubA == PreB+SubB.
 319       unsigned FinalB = composeSubRegIndices(IB.getSubReg(), SubB);
 320       if (FinalA != FinalB)
 321         continue;
 322
 323       // Is RC a better candidate than BestRC?
 324       if (BestRC && getRegSizeInBits(*RC) >= getRegSizeInBits(*BestRC))
 325         continue;
 326
 327       // Yes, RC is the smallest super-register seen so far.
 328       BestRC = RC;
 329       *BestPreA = IA.getSubReg();
 330       *BestPreB = IB.getSubReg();
 331
 332       // Bail early if we reached MinSize. We won't find a better candidate.
 333       if (getRegSizeInBits(*BestRC) == MinSize)
 334         return BestRC;
 335     }
 336   }
 337   return BestRC;
 338 }
 339
 340 /// Check if the registers defined by the pair (RegisterClass, SubReg)
 341 /// share the same register file.
 342 static bool shareSameRegisterFile(const TargetRegisterInfo &TRI,
 343                                   const TargetRegisterClass *DefRC,
 344                                   unsigned DefSubReg,
 345                                   const TargetRegisterClass *SrcRC,
 346                                   unsigned SrcSubReg) {
 347   // Same register class.
 348   if (DefRC == SrcRC)
 349     return true;
 350
 351   // Both operands are sub registers. Check if they share a register class.
 352   unsigned SrcIdx, DefIdx;
 353   if (SrcSubReg && DefSubReg) {
 354     return TRI.getCommonSuperRegClass(SrcRC, SrcSubReg, DefRC, DefSubReg,
 355                                       SrcIdx, DefIdx) != nullptr;
 356   }
 357
 358   // At most one of the register is a sub register, make it Src to avoid
 359   // duplicating the test.
 360   if (!SrcSubReg) {
 361     std::swap(DefSubReg, SrcSubReg);
 362     std::swap(DefRC, SrcRC);
 363   }
 364
 365   // One of the register is a sub register, check if we can get a superclass.
 366   if (SrcSubReg)
 367     return TRI.getMatchingSuperRegClass(SrcRC, DefRC, SrcSubReg) != nullptr;
 368
 369   // Plain copy.
 370   return TRI.getCommonSubClass(DefRC, SrcRC) != nullptr;
 371 }
 372
 373 bool TargetRegisterInfo::shouldRewriteCopySrc(const TargetRegisterClass *DefRC,
 374                                               unsigned DefSubReg,
 375                                               const TargetRegisterClass *SrcRC,
 376                                               unsigned SrcSubReg) const {
 377   // If this source does not incur a cross register bank copy, use it.
 378   return shareSameRegisterFile(*this, DefRC, DefSubReg, SrcRC, SrcSubReg);
 379 }
 380
 381 // Compute target-independent register allocator hints to help eliminate copies.
 382 bool
 383 TargetRegisterInfo::getRegAllocationHints(unsigned VirtReg,
 384                                           ArrayRef<MCPhysReg> Order,
 385                                           SmallVectorImpl<MCPhysReg> &Hints,
 386                                           const MachineFunction &MF,
 387                                           const VirtRegMap *VRM,
 388                                           const LiveRegMatrix *Matrix) const {
 389   const MachineRegisterInfo &MRI = MF.getRegInfo();
 390   const std::pair<unsigned, SmallVector<unsigned, 4>> &Hints_MRI =
 391     MRI.getRegAllocationHints(VirtReg);
 392
 393   SmallSet<unsigned, 32> HintedRegs;
 394   // First hint may be a target hint.
 395   bool Skip = (Hints_MRI.first != 0);
 396   for (auto Reg : Hints_MRI.second) {
 397     if (Skip) {
 398       Skip = false;
 399       continue;
 400     }
 401
 402     // Target-independent hints are either a physical or a virtual register.
 403     unsigned Phys = Reg;
 404     if (VRM && Register::isVirtualRegister(Phys))
 405       Phys = VRM->getPhys(Phys);
 406
 407     // Don't add the same reg twice (Hints_MRI may contain multiple virtual
 408     // registers allocated to the same physreg).
 409     if (!HintedRegs.insert(Phys).second)
 410       continue;
 411     // Check that Phys is a valid hint in VirtReg's register class.
 412     if (!Register::isPhysicalRegister(Phys))
 413       continue;
 414     if (MRI.isReserved(Phys))
 415       continue;
 416     // Check that Phys is in the allocation order. We shouldn't heed hints
 417     // from VirtReg's register class if they aren't in the allocation order. The
 418     // target probably has a reason for removing the register.
 419     if (!is_contained(Order, Phys))
 420       continue;
 421
 422     // All clear, tell the register allocator to prefer this register.
 423     Hints.push_back(Phys);
 424   }
 425   return false;
 426 }
 427
 428 bool TargetRegisterInfo::isCalleeSavedPhysReg(
 429     unsigned PhysReg, const MachineFunction &MF) const {
 430   if (PhysReg == 0)
 431     return false;
 432   const uint32_t *callerPreservedRegs =
 433       getCallPreservedMask(MF, MF.getFunction().getCallingConv());
 434   if (callerPreservedRegs) {
 435     assert(Register::isPhysicalRegister(PhysReg) &&
 436            "Expected physical register");
 437     return (callerPreservedRegs[PhysReg / 32] >> PhysReg % 32) & 1;
 438   }
 439   return false;
 440 }
 441
 442 bool TargetRegisterInfo::canRealignStack(const MachineFunction &MF) const {
 443   return !MF.getFunction().hasFnAttribute("no-realign-stack");
 444 }
 445
 446 bool TargetRegisterInfo::needsStackRealignment(
 447     const MachineFunction &MF) const {
 448   const MachineFrameInfo &MFI = MF.getFrameInfo();
 449   const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
 450   const Function &F = MF.getFunction();
 451   unsigned StackAlign = TFI->getStackAlignment();
 452   bool requiresRealignment = ((MFI.getMaxAlignment() > StackAlign) ||
 453                               F.hasFnAttribute(Attribute::StackAlignment));
 454   if (F.hasFnAttribute("stackrealign") || requiresRealignment) {
 455     if (canRealignStack(MF))
 456       return true;
 457     LLVM_DEBUG(dbgs() << "Can't realign function's stack: " << F.getName()
 458                       << "\n");
 459   }
 460   return false;
 461 }
 462
 463 bool TargetRegisterInfo::regmaskSubsetEqual(const uint32_t *mask0,
 464                                             const uint32_t *mask1) const {
 465   unsigned N = (getNumRegs()+31) / 32;
 466   for (unsigned I = 0; I < N; ++I)
 467     if ((mask0[I] & mask1[I]) != mask0[I])
 468       return false;
 469   return true;
 470 }
 471
 472 unsigned TargetRegisterInfo::getRegSizeInBits(unsigned Reg,
 473                                          const MachineRegisterInfo &MRI) const {
 474   const TargetRegisterClass *RC{};
 475   if (Register::isPhysicalRegister(Reg)) {
 476     // The size is not directly available for physical registers.
 477     // Instead, we need to access a register class that contains Reg and
 478     // get the size of that register class.
 479     RC = getMinimalPhysRegClass(Reg);
 480   } else {
 481     LLT Ty = MRI.getType(Reg);
 482     unsigned RegSize = Ty.isValid() ? Ty.getSizeInBits() : 0;
 483     // If Reg is not a generic register, query the register class to
 484     // get its size.
 485     if (RegSize)
 486       return RegSize;
 487     // Since Reg is not a generic register, it must have a register class.
 488     RC = MRI.getRegClass(Reg);
 489   }
 490   assert(RC && "Unable to deduce the register class");
 491   return getRegSizeInBits(*RC);
 492 }
 493
 494 unsigned
 495 TargetRegisterInfo::lookThruCopyLike(unsigned SrcReg,
 496                                      const MachineRegisterInfo *MRI) const {
 497   while (true) {
 498     const MachineInstr *MI = MRI->getVRegDef(SrcReg);
 499     if (!MI->isCopyLike())
 500       return SrcReg;
 501
 502     unsigned CopySrcReg;
 503     if (MI->isCopy())
 504       CopySrcReg = MI->getOperand(1).getReg();
 505     else {
 506       assert(MI->isSubregToReg() && "Bad opcode for lookThruCopyLike");
 507       CopySrcReg = MI->getOperand(2).getReg();
 508     }
 509
 510     if (!Register::isVirtualRegister(CopySrcReg))
 511       return CopySrcReg;
 512
 513     SrcReg = CopySrcReg;
 514   }
 515 }
 516
 517 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 518 LLVM_DUMP_METHOD
 519 void TargetRegisterInfo::dumpReg(unsigned Reg, unsigned SubRegIndex,
 520                                  const TargetRegisterInfo *TRI) {
 521   dbgs() << printReg(Reg, TRI, SubRegIndex) << "\n";
 522 }
 523 #endif