lib/Target/X86/SSEDomainFix.cpp

   1 //===- SSEDomainFix.cpp - Use proper int/float domain for SSE ---*- C++ -*-===//
   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 // This file contains the SSEDomainFix pass.
  11 //
  12 // Some SSE instructions like mov, and, or, xor are available in different
  13 // variants for different operand types. These variant instructions are
  14 // equivalent, but on Nehalem and newer cpus there is extra latency
  15 // transferring data between integer and floating point domains.
  16 //
  17 // This pass changes the variant instructions to minimize domain crossings.
  18 //
  19 //===----------------------------------------------------------------------===//
  20
  21 #define DEBUG_TYPE "sse-domain-fix"
  22 #include "X86InstrInfo.h"
  23 #include "llvm/CodeGen/MachineFunctionPass.h"
  24 #include "llvm/CodeGen/MachineRegisterInfo.h"
  25 #include "llvm/ADT/DepthFirstIterator.h"
  26 #include "llvm/Support/Allocator.h"
  27 #include "llvm/Support/Debug.h"
  28 #include "llvm/Support/raw_ostream.h"
  29 using namespace llvm;
  30
  31 /// A DomainValue is a bit like LiveIntervals' ValNo, but it also keeps track
  32 /// of execution domains.
  33 ///
  34 /// An open DomainValue represents a set of instructions that can still switch
  35 /// execution domain. Multiple registers may refer to the same open
  36 /// DomainValue - they will eventually be collapsed to the same execution
  37 /// domain.
  38 ///
  39 /// A collapsed DomainValue represents a single register that has been forced
  40 /// into one of more execution domains. There is a separate collapsed
  41 /// DomainValue for each register, but it may contain multiple execution
  42 /// domains. A register value is initially created in a single execution
  43 /// domain, but if we were forced to pay the penalty of a domain crossing, we
  44 /// keep track of the fact the the register is now available in multiple
  45 /// domains.
  46 namespace {
  47 struct DomainValue {
  48   // Basic reference counting.
  49   unsigned Refs;
  50
  51   // Bitmask of available domains. For an open DomainValue, it is the still
  52   // possible domains for collapsing. For a collapsed DomainValue it is the
  53   // domains where the register is available for free.
  54   unsigned AvailableDomains;
  55
  56   // Position of the last defining instruction.
  57   unsigned Dist;
  58
  59   // Twiddleable instructions using or defining these registers.
  60   SmallVector<MachineInstr*, 8> Instrs;
  61
  62   // A collapsed DomainValue has no instructions to twiddle - it simply keeps
  63   // track of the domains where the registers are already available.
  64   bool isCollapsed() const { return Instrs.empty(); }
  65
  66   // Is domain available?
  67   bool hasDomain(unsigned domain) const {
  68     return AvailableDomains & (1u << domain);
  69   }
  70
  71   // Mark domain as available.
  72   void addDomain(unsigned domain) {
  73     AvailableDomains |= 1u << domain;
  74   }
  75
  76   // Restrict to a single domain available.
  77   void setSingleDomain(unsigned domain) {
  78     AvailableDomains = 1u << domain;
  79   }
  80
  81   // Return bitmask of domains that are available and in mask.
  82   unsigned getCommonDomains(unsigned mask) const {
  83     return AvailableDomains & mask;
  84   }
  85
  86   // First domain available.
  87   unsigned getFirstDomain() const {
  88     return CountTrailingZeros_32(AvailableDomains);
  89   }
  90
  91   DomainValue() { clear(); }
  92
  93   void clear() {
  94     Refs = AvailableDomains = Dist = 0;
  95     Instrs.clear();
  96   }
  97 };
  98 }
  99
 100 static const unsigned NumRegs = 16;
 101
 102 namespace {
 103 class SSEDomainFixPass : public MachineFunctionPass {
 104   static char ID;
 105   SpecificBumpPtrAllocator<DomainValue> Allocator;
 106   SmallVector<DomainValue*,16> Avail;
 107
 108   MachineFunction *MF;
 109   const X86InstrInfo *TII;
 110   const TargetRegisterInfo *TRI;
 111   MachineBasicBlock *MBB;
 112   DomainValue **LiveRegs;
 113   typedef DenseMap<MachineBasicBlock*,DomainValue**> LiveOutMap;
 114   LiveOutMap LiveOuts;
 115   unsigned Distance;
 116
 117 public:
 118   SSEDomainFixPass() : MachineFunctionPass(ID) {}
 119
 120   virtual void getAnalysisUsage(AnalysisUsage &AU) const {
 121     AU.setPreservesAll();
 122     MachineFunctionPass::getAnalysisUsage(AU);
 123   }
 124
 125   virtual bool runOnMachineFunction(MachineFunction &MF);
 126
 127   virtual const char *getPassName() const {
 128     return "SSE execution domain fixup";
 129   }
 130
 131 private:
 132   // Register mapping.
 133   int RegIndex(unsigned Reg);
 134
 135   // DomainValue allocation.
 136   DomainValue *Alloc(int domain = -1);
 137   void Recycle(DomainValue*);
 138
 139   // LiveRegs manipulations.
 140   void SetLiveReg(int rx, DomainValue *DV);
 141   void Kill(int rx);
 142   void Force(int rx, unsigned domain);
 143   void Collapse(DomainValue *dv, unsigned domain);
 144   bool Merge(DomainValue *A, DomainValue *B);
 145
 146   void enterBasicBlock();
 147   void visitGenericInstr(MachineInstr*);
 148   void visitSoftInstr(MachineInstr*, unsigned mask);
 149   void visitHardInstr(MachineInstr*, unsigned domain);
 150 };
 151 }
 152
 153 char SSEDomainFixPass::ID = 0;
 154
 155 /// Translate TRI register number to an index into our smaller tables of
 156 /// interesting registers. Return -1 for boring registers.
 157 int SSEDomainFixPass::RegIndex(unsigned reg) {
 158   assert(X86::XMM15 == X86::XMM0+NumRegs-1 && "Unexpected sort");
 159   reg -= X86::XMM0;
 160   return reg < NumRegs ? (int) reg : -1;
 161 }
 162
 163 DomainValue *SSEDomainFixPass::Alloc(int domain) {
 164   DomainValue *dv = Avail.empty() ?
 165                       new(Allocator.Allocate()) DomainValue :
 166                       Avail.pop_back_val();
 167   dv->Dist = Distance;
 168   if (domain >= 0)
 169     dv->addDomain(domain);
 170   return dv;
 171 }
 172
 173 void SSEDomainFixPass::Recycle(DomainValue *dv) {
 174   assert(dv && "Cannot recycle NULL");
 175   dv->clear();
 176   Avail.push_back(dv);
 177 }
 178
 179 /// Set LiveRegs[rx] = dv, updating reference counts.
 180 void SSEDomainFixPass::SetLiveReg(int rx, DomainValue *dv) {
 181   assert(unsigned(rx) < NumRegs && "Invalid index");
 182   if (!LiveRegs) {
 183     LiveRegs = new DomainValue*[NumRegs];
 184     std::fill(LiveRegs, LiveRegs+NumRegs, (DomainValue*)0);
 185   }
 186
 187   if (LiveRegs[rx] == dv)
 188     return;
 189   if (LiveRegs[rx]) {
 190     assert(LiveRegs[rx]->Refs && "Bad refcount");
 191     if (--LiveRegs[rx]->Refs == 0) Recycle(LiveRegs[rx]);
 192   }
 193   LiveRegs[rx] = dv;
 194   if (dv) ++dv->Refs;
 195 }
 196
 197 // Kill register rx, recycle or collapse any DomainValue.
 198 void SSEDomainFixPass::Kill(int rx) {
 199   assert(unsigned(rx) < NumRegs && "Invalid index");
 200   if (!LiveRegs || !LiveRegs[rx]) return;
 201
 202   // Before killing the last reference to an open DomainValue, collapse it to
 203   // the first available domain.
 204   if (LiveRegs[rx]->Refs == 1 && !LiveRegs[rx]->isCollapsed())
 205     Collapse(LiveRegs[rx], LiveRegs[rx]->getFirstDomain());
 206   else
 207     SetLiveReg(rx, 0);
 208 }
 209
 210 /// Force register rx into domain.
 211 void SSEDomainFixPass::Force(int rx, unsigned domain) {
 212   assert(unsigned(rx) < NumRegs && "Invalid index");
 213   DomainValue *dv;
 214   if (LiveRegs && (dv = LiveRegs[rx])) {
 215     if (dv->isCollapsed())
 216       dv->addDomain(domain);
 217     else if (dv->hasDomain(domain))
 218       Collapse(dv, domain);
 219     else {
 220       // This is an incompatible open DomainValue. Collapse it to whatever and force
 221       // the new value into domain. This costs a domain crossing.
 222       Collapse(dv, dv->getFirstDomain());
 223       assert(LiveRegs[rx] && "Not live after collapse?");
 224       LiveRegs[rx]->addDomain(domain);
 225     }
 226   } else {
 227     // Set up basic collapsed DomainValue.
 228     SetLiveReg(rx, Alloc(domain));
 229   }
 230 }
 231
 232 /// Collapse open DomainValue into given domain. If there are multiple
 233 /// registers using dv, they each get a unique collapsed DomainValue.
 234 void SSEDomainFixPass::Collapse(DomainValue *dv, unsigned domain) {
 235   assert(dv->hasDomain(domain) && "Cannot collapse");
 236
 237   // Collapse all the instructions.
 238   while (!dv->Instrs.empty())
 239     TII->SetSSEDomain(dv->Instrs.pop_back_val(), domain);
 240   dv->setSingleDomain(domain);
 241
 242   // If there are multiple users, give them new, unique DomainValues.
 243   if (LiveRegs && dv->Refs > 1)
 244     for (unsigned rx = 0; rx != NumRegs; ++rx)
 245       if (LiveRegs[rx] == dv)
 246         SetLiveReg(rx, Alloc(domain));
 247 }
 248
 249 /// Merge - All instructions and registers in B are moved to A, and B is
 250 /// released.
 251 bool SSEDomainFixPass::Merge(DomainValue *A, DomainValue *B) {
 252   assert(!A->isCollapsed() && "Cannot merge into collapsed");
 253   assert(!B->isCollapsed() && "Cannot merge from collapsed");
 254   if (A == B)
 255     return true;
 256   // Restrict to the domains that A and B have in common.
 257   unsigned common = A->getCommonDomains(B->AvailableDomains);
 258   if (!common)
 259     return false;
 260   A->AvailableDomains = common;
 261   A->Dist = std::max(A->Dist, B->Dist);
 262   A->Instrs.append(B->Instrs.begin(), B->Instrs.end());
 263   for (unsigned rx = 0; rx != NumRegs; ++rx)
 264     if (LiveRegs[rx] == B)
 265       SetLiveReg(rx, A);
 266   return true;
 267 }
 268
 269 void SSEDomainFixPass::enterBasicBlock() {
 270   // Try to coalesce live-out registers from predecessors.
 271   for (MachineBasicBlock::livein_iterator i = MBB->livein_begin(),
 272          e = MBB->livein_end(); i != e; ++i) {
 273     int rx = RegIndex(*i);
 274     if (rx < 0) continue;
 275     for (MachineBasicBlock::const_pred_iterator pi = MBB->pred_begin(),
 276            pe = MBB->pred_end(); pi != pe; ++pi) {
 277       LiveOutMap::const_iterator fi = LiveOuts.find(*pi);
 278       if (fi == LiveOuts.end()) continue;
 279       DomainValue *pdv = fi->second[rx];
 280       if (!pdv) continue;
 281       if (!LiveRegs || !LiveRegs[rx]) {
 282         SetLiveReg(rx, pdv);
 283         continue;
 284       }
 285
 286       // We have a live DomainValue from more than one predecessor.
 287       if (LiveRegs[rx]->isCollapsed()) {
 288         // We are already collapsed, but predecessor is not. Force him.
 289         unsigned domain = LiveRegs[rx]->getFirstDomain();
 290         if (!pdv->isCollapsed() && pdv->hasDomain(domain))
 291           Collapse(pdv, domain);
 292         continue;
 293       }
 294
 295       // Currently open, merge in predecessor.
 296       if (!pdv->isCollapsed())
 297         Merge(LiveRegs[rx], pdv);
 298       else
 299         Force(rx, pdv->getFirstDomain());
 300     }
 301   }
 302 }
 303
 304 // A hard instruction only works in one domain. All input registers will be
 305 // forced into that domain.
 306 void SSEDomainFixPass::visitHardInstr(MachineInstr *mi, unsigned domain) {
 307   // Collapse all uses.
 308   for (unsigned i = mi->getDesc().getNumDefs(),
 309                 e = mi->getDesc().getNumOperands(); i != e; ++i) {
 310     MachineOperand &mo = mi->getOperand(i);
 311     if (!mo.isReg()) continue;
 312     int rx = RegIndex(mo.getReg());
 313     if (rx < 0) continue;
 314     Force(rx, domain);
 315   }
 316
 317   // Kill all defs and force them.
 318   for (unsigned i = 0, e = mi->getDesc().getNumDefs(); i != e; ++i) {
 319     MachineOperand &mo = mi->getOperand(i);
 320     if (!mo.isReg()) continue;
 321     int rx = RegIndex(mo.getReg());
 322     if (rx < 0) continue;
 323     Kill(rx);
 324     Force(rx, domain);
 325   }
 326 }
 327
 328 // A soft instruction can be changed to work in other domains given by mask.
 329 void SSEDomainFixPass::visitSoftInstr(MachineInstr *mi, unsigned mask) {
 330   // Bitmask of available domains for this instruction after taking collapsed
 331   // operands into account.
 332   unsigned available = mask;
 333
 334   // Scan the explicit use operands for incoming domains.
 335   SmallVector<int, 4> used;
 336   if (LiveRegs)
 337     for (unsigned i = mi->getDesc().getNumDefs(),
 338                   e = mi->getDesc().getNumOperands(); i != e; ++i) {
 339       MachineOperand &mo = mi->getOperand(i);
 340       if (!mo.isReg()) continue;
 341       int rx = RegIndex(mo.getReg());
 342       if (rx < 0) continue;
 343       if (DomainValue *dv = LiveRegs[rx]) {
 344         // Bitmask of domains that dv and available have in common.
 345         unsigned common = dv->getCommonDomains(available);
 346         // Is it possible to use this collapsed register for free?
 347         if (dv->isCollapsed()) {
 348           // Restrict available domains to the ones in common with the operand.
 349           // If there are no common domains, we must pay the cross-domain
 350           // penalty for this operand.
 351           if (common) available = common;
 352         } else if (common)
 353           // Open DomainValue is compatible, save it for merging.
 354           used.push_back(rx);
 355         else
 356           // Open DomainValue is not compatible with instruction. It is useless
 357           // now.
 358           Kill(rx);
 359       }
 360     }
 361
 362   // If the collapsed operands force a single domain, propagate the collapse.
 363   if (isPowerOf2_32(available)) {
 364     unsigned domain = CountTrailingZeros_32(available);
 365     TII->SetSSEDomain(mi, domain);
 366     visitHardInstr(mi, domain);
 367     return;
 368   }
 369
 370   // Kill off any remaining uses that don't match available, and build a list of
 371   // incoming DomainValues that we want to merge.
 372   SmallVector<DomainValue*,4> doms;
 373   for (SmallVector<int, 4>::iterator i=used.begin(), e=used.end(); i!=e; ++i) {
 374     int rx = *i;
 375     DomainValue *dv = LiveRegs[rx];
 376     // This useless DomainValue could have been missed above.
 377     if (!dv->getCommonDomains(available)) {
 378       Kill(*i);
 379       continue;
 380     }
 381     // sorted, uniqued insert.
 382     bool inserted = false;
 383     for (SmallVector<DomainValue*,4>::iterator i = doms.begin(), e = doms.end();
 384            i != e && !inserted; ++i) {
 385       if (dv == *i)
 386         inserted = true;
 387       else if (dv->Dist < (*i)->Dist) {
 388         inserted = true;
 389         doms.insert(i, dv);
 390       }
 391     }
 392     if (!inserted)
 393       doms.push_back(dv);
 394   }
 395
 396   // doms are now sorted in order of appearance. Try to merge them all, giving
 397   // priority to the latest ones.
 398   DomainValue *dv = 0;
 399   while (!doms.empty()) {
 400     if (!dv) {
 401       dv = doms.pop_back_val();
 402       continue;
 403     }
 404
 405     DomainValue *latest = doms.pop_back_val();
 406     if (Merge(dv, latest)) continue;
 407
 408     // If latest didn't merge, it is useless now. Kill all registers using it.
 409     for (SmallVector<int,4>::iterator i=used.begin(), e=used.end(); i != e; ++i)
 410       if (LiveRegs[*i] == latest)
 411         Kill(*i);
 412   }
 413
 414   // dv is the DomainValue we are going to use for this instruction.
 415   if (!dv)
 416     dv = Alloc();
 417   dv->Dist = Distance;
 418   dv->AvailableDomains = available;
 419   dv->Instrs.push_back(mi);
 420
 421   // Finally set all defs and non-collapsed uses to dv.
 422   for (unsigned i = 0, e = mi->getDesc().getNumOperands(); i != e; ++i) {
 423     MachineOperand &mo = mi->getOperand(i);
 424     if (!mo.isReg()) continue;
 425     int rx = RegIndex(mo.getReg());
 426     if (rx < 0) continue;
 427     if (!LiveRegs || !LiveRegs[rx] || (mo.isDef() && LiveRegs[rx]!=dv)) {
 428       Kill(rx);
 429       SetLiveReg(rx, dv);
 430     }
 431   }
 432 }
 433
 434 void SSEDomainFixPass::visitGenericInstr(MachineInstr *mi) {
 435   // Process explicit defs, kill any XMM registers redefined.
 436   for (unsigned i = 0, e = mi->getDesc().getNumDefs(); i != e; ++i) {
 437     MachineOperand &mo = mi->getOperand(i);
 438     if (!mo.isReg()) continue;
 439     int rx = RegIndex(mo.getReg());
 440     if (rx < 0) continue;
 441     Kill(rx);
 442   }
 443 }
 444
 445 bool SSEDomainFixPass::runOnMachineFunction(MachineFunction &mf) {
 446   MF = &mf;
 447   TII = static_cast<const X86InstrInfo*>(MF->getTarget().getInstrInfo());
 448   TRI = MF->getTarget().getRegisterInfo();
 449   MBB = 0;
 450   LiveRegs = 0;
 451   Distance = 0;
 452   assert(NumRegs == X86::VR128RegClass.getNumRegs() && "Bad regclass");
 453
 454   // If no XMM registers are used in the function, we can skip it completely.
 455   bool anyregs = false;
 456   for (TargetRegisterClass::const_iterator I = X86::VR128RegClass.begin(),
 457          E = X86::VR128RegClass.end(); I != E; ++I)
 458     if (MF->getRegInfo().isPhysRegUsed(*I)) {
 459       anyregs = true;
 460       break;
 461     }
 462   if (!anyregs) return false;
 463
 464   MachineBasicBlock *Entry = MF->begin();
 465   SmallPtrSet<MachineBasicBlock*, 16> Visited;
 466   for (df_ext_iterator<MachineBasicBlock*, SmallPtrSet<MachineBasicBlock*, 16> >
 467          DFI = df_ext_begin(Entry, Visited), DFE = df_ext_end(Entry, Visited);
 468          DFI != DFE; ++DFI) {
 469     MBB = *DFI;
 470     enterBasicBlock();
 471     for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
 472         ++I) {
 473       MachineInstr *mi = I;
 474       if (mi->isDebugValue()) continue;
 475       ++Distance;
 476       std::pair<uint16_t, uint16_t> domp = TII->GetSSEDomain(mi);
 477       if (domp.first)
 478         if (domp.second)
 479           visitSoftInstr(mi, domp.second);
 480         else
 481           visitHardInstr(mi, domp.first);
 482       else if (LiveRegs)
 483         visitGenericInstr(mi);
 484     }
 485
 486     // Save live registers at end of MBB - used by enterBasicBlock().
 487     if (LiveRegs)
 488       LiveOuts.insert(std::make_pair(MBB, LiveRegs));
 489     LiveRegs = 0;
 490   }
 491
 492   // Clear the LiveOuts vectors. Should we also collapse any remaining
 493   // DomainValues?
 494   for (LiveOutMap::const_iterator i = LiveOuts.begin(), e = LiveOuts.end();
 495          i != e; ++i)
 496     delete[] i->second;
 497   LiveOuts.clear();
 498   Avail.clear();
 499   Allocator.DestroyAll();
 500
 501   return false;
 502 }
 503
 504 FunctionPass *llvm::createSSEDomainFixPass() {
 505   return new SSEDomainFixPass();
 506 }