lib/Support/ScopHelper.cpp

   1 //===- ScopHelper.cpp - Some Helper Functions for Scop.  ------------------===//
   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 // Small functions that help with Scop and LLVM-IR.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "polly/Support/ScopHelper.h"
  15 #include "polly/Options.h"
  16 #include "polly/ScopInfo.h"
  17 #include "polly/Support/SCEVValidator.h"
  18 #include "llvm/Analysis/LoopInfo.h"
  19 #include "llvm/Analysis/RegionInfo.h"
  20 #include "llvm/Analysis/ScalarEvolution.h"
  21 #include "llvm/Analysis/ScalarEvolutionExpander.h"
  22 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
  23 #include "llvm/IR/CFG.h"
  24 #include "llvm/IR/IntrinsicInst.h"
  25 #include "llvm/Support/Debug.h"
  26 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  27
  28 using namespace llvm;
  29 using namespace polly;
  30
  31 #define DEBUG_TYPE "polly-scop-helper"
  32
  33 static cl::opt<bool> PollyAllowErrorBlocks(
  34     "polly-allow-error-blocks",
  35     cl::desc("Allow to speculate on the execution of 'error blocks'."),
  36     cl::Hidden, cl::init(true), cl::ZeroOrMore, cl::cat(PollyCategory));
  37
  38 // Ensures that there is just one predecessor to the entry node from outside the
  39 // region.
  40 // The identity of the region entry node is preserved.
  41 static void simplifyRegionEntry(Region *R, DominatorTree *DT, LoopInfo *LI,
  42                                 RegionInfo *RI) {
  43   BasicBlock *EnteringBB = R->getEnteringBlock();
  44   BasicBlock *Entry = R->getEntry();
  45
  46   // Before (one of):
  47   //
  48   //                       \    /            //
  49   //                      EnteringBB         //
  50   //                        |    \------>    //
  51   //   \   /                |                //
  52   //   Entry <--\         Entry <--\         //
  53   //   /   \    /         /   \    /         //
  54   //        ....               ....          //
  55
  56   // Create single entry edge if the region has multiple entry edges.
  57   if (!EnteringBB) {
  58     SmallVector<BasicBlock *, 4> Preds;
  59     for (BasicBlock *P : predecessors(Entry))
  60       if (!R->contains(P))
  61         Preds.push_back(P);
  62
  63     BasicBlock *NewEntering =
  64         SplitBlockPredecessors(Entry, Preds, ".region_entering", DT, LI);
  65
  66     if (RI) {
  67       // The exit block of predecessing regions must be changed to NewEntering
  68       for (BasicBlock *ExitPred : predecessors(NewEntering)) {
  69         Region *RegionOfPred = RI->getRegionFor(ExitPred);
  70         if (RegionOfPred->getExit() != Entry)
  71           continue;
  72
  73         while (!RegionOfPred->isTopLevelRegion() &&
  74                RegionOfPred->getExit() == Entry) {
  75           RegionOfPred->replaceExit(NewEntering);
  76           RegionOfPred = RegionOfPred->getParent();
  77         }
  78       }
  79
  80       // Make all ancestors use EnteringBB as entry; there might be edges to it
  81       Region *AncestorR = R->getParent();
  82       RI->setRegionFor(NewEntering, AncestorR);
  83       while (!AncestorR->isTopLevelRegion() && AncestorR->getEntry() == Entry) {
  84         AncestorR->replaceEntry(NewEntering);
  85         AncestorR = AncestorR->getParent();
  86       }
  87     }
  88
  89     EnteringBB = NewEntering;
  90   }
  91   assert(R->getEnteringBlock() == EnteringBB);
  92
  93   // After:
  94   //
  95   //    \    /       //
  96   //  EnteringBB     //
  97   //      |          //
  98   //      |          //
  99   //    Entry <--\   //
 100   //    /   \    /   //
 101   //         ....    //
 102 }
 103
 104 // Ensure that the region has a single block that branches to the exit node.
 105 static void simplifyRegionExit(Region *R, DominatorTree *DT, LoopInfo *LI,
 106                                RegionInfo *RI) {
 107   BasicBlock *ExitBB = R->getExit();
 108   BasicBlock *ExitingBB = R->getExitingBlock();
 109
 110   // Before:
 111   //
 112   //   (Region)   ______/  //
 113   //      \  |   /         //
 114   //       ExitBB          //
 115   //       /    \          //
 116
 117   if (!ExitingBB) {
 118     SmallVector<BasicBlock *, 4> Preds;
 119     for (BasicBlock *P : predecessors(ExitBB))
 120       if (R->contains(P))
 121         Preds.push_back(P);
 122
 123     //  Preds[0] Preds[1]      otherBB //
 124     //         \  |  ________/         //
 125     //          \ | /                  //
 126     //           BB                    //
 127     ExitingBB =
 128         SplitBlockPredecessors(ExitBB, Preds, ".region_exiting", DT, LI);
 129     // Preds[0] Preds[1]      otherBB  //
 130     //        \  /           /         //
 131     // BB.region_exiting    /          //
 132     //                  \  /           //
 133     //                   BB            //
 134
 135     if (RI)
 136       RI->setRegionFor(ExitingBB, R);
 137
 138     // Change the exit of nested regions, but not the region itself,
 139     R->replaceExitRecursive(ExitingBB);
 140     R->replaceExit(ExitBB);
 141   }
 142   assert(ExitingBB == R->getExitingBlock());
 143
 144   // After:
 145   //
 146   //     \   /                //
 147   //    ExitingBB     _____/  //
 148   //          \      /        //
 149   //           ExitBB         //
 150   //           /    \         //
 151 }
 152
 153 void polly::simplifyRegion(Region *R, DominatorTree *DT, LoopInfo *LI,
 154                            RegionInfo *RI) {
 155   assert(R && !R->isTopLevelRegion());
 156   assert(!RI || RI == R->getRegionInfo());
 157   assert((!RI || DT) &&
 158          "RegionInfo requires DominatorTree to be updated as well");
 159
 160   simplifyRegionEntry(R, DT, LI, RI);
 161   simplifyRegionExit(R, DT, LI, RI);
 162   assert(R->isSimple());
 163 }
 164
 165 // Split the block into two successive blocks.
 166 //
 167 // Like llvm::SplitBlock, but also preserves RegionInfo
 168 static BasicBlock *splitBlock(BasicBlock *Old, Instruction *SplitPt,
 169                               DominatorTree *DT, llvm::LoopInfo *LI,
 170                               RegionInfo *RI) {
 171   assert(Old && SplitPt);
 172
 173   // Before:
 174   //
 175   //  \   /  //
 176   //   Old   //
 177   //  /   \  //
 178
 179   BasicBlock *NewBlock = llvm::SplitBlock(Old, SplitPt, DT, LI);
 180
 181   if (RI) {
 182     Region *R = RI->getRegionFor(Old);
 183     RI->setRegionFor(NewBlock, R);
 184   }
 185
 186   // After:
 187   //
 188   //   \   /    //
 189   //    Old     //
 190   //     |      //
 191   //  NewBlock  //
 192   //   /   \    //
 193
 194   return NewBlock;
 195 }
 196
 197 void polly::splitEntryBlockForAlloca(BasicBlock *EntryBlock, Pass *P) {
 198   // Find first non-alloca instruction. Every basic block has a non-alloc
 199   // instruction, as every well formed basic block has a terminator.
 200   BasicBlock::iterator I = EntryBlock->begin();
 201   while (isa<AllocaInst>(I))
 202     ++I;
 203
 204   auto *DTWP = P->getAnalysisIfAvailable<DominatorTreeWrapperPass>();
 205   auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
 206   auto *LIWP = P->getAnalysisIfAvailable<LoopInfoWrapperPass>();
 207   auto *LI = LIWP ? &LIWP->getLoopInfo() : nullptr;
 208   RegionInfoPass *RIP = P->getAnalysisIfAvailable<RegionInfoPass>();
 209   RegionInfo *RI = RIP ? &RIP->getRegionInfo() : nullptr;
 210
 211   // splitBlock updates DT, LI and RI.
 212   splitBlock(EntryBlock, &*I, DT, LI, RI);
 213 }
 214
 215 /// The SCEVExpander will __not__ generate any code for an existing SDiv/SRem
 216 /// instruction but just use it, if it is referenced as a SCEVUnknown. We want
 217 /// however to generate new code if the instruction is in the analyzed region
 218 /// and we generate code outside/in front of that region. Hence, we generate the
 219 /// code for the SDiv/SRem operands in front of the analyzed region and then
 220 /// create a new SDiv/SRem operation there too.
 221 struct ScopExpander : SCEVVisitor<ScopExpander, const SCEV *> {
 222   friend struct SCEVVisitor<ScopExpander, const SCEV *>;
 223
 224   explicit ScopExpander(const Region &R, ScalarEvolution &SE,
 225                         const DataLayout &DL, const char *Name, ValueMapT *VMap,
 226                         BasicBlock *RTCBB)
 227       : Expander(SCEVExpander(SE, DL, Name)), SE(SE), Name(Name), R(R),
 228         VMap(VMap), RTCBB(RTCBB) {}
 229
 230   Value *expandCodeFor(const SCEV *E, Type *Ty, Instruction *I) {
 231     // If we generate code in the region we will immediately fall back to the
 232     // SCEVExpander, otherwise we will stop at all unknowns in the SCEV and if
 233     // needed replace them by copies computed in the entering block.
 234     if (!R.contains(I))
 235       E = visit(E);
 236     return Expander.expandCodeFor(E, Ty, I);
 237   }
 238
 239 private:
 240   SCEVExpander Expander;
 241   ScalarEvolution &SE;
 242   const char *Name;
 243   const Region &R;
 244   ValueMapT *VMap;
 245   BasicBlock *RTCBB;
 246
 247   const SCEV *visitGenericInst(const SCEVUnknown *E, Instruction *Inst,
 248                                Instruction *IP) {
 249     if (!Inst || !R.contains(Inst))
 250       return E;
 251
 252     assert(!Inst->mayThrow() && !Inst->mayReadOrWriteMemory() &&
 253            !isa<PHINode>(Inst));
 254
 255     auto *InstClone = Inst->clone();
 256     for (auto &Op : Inst->operands()) {
 257       assert(SE.isSCEVable(Op->getType()));
 258       auto *OpSCEV = SE.getSCEV(Op);
 259       auto *OpClone = expandCodeFor(OpSCEV, Op->getType(), IP);
 260       InstClone->replaceUsesOfWith(Op, OpClone);
 261     }
 262
 263     InstClone->setName(Name + Inst->getName());
 264     InstClone->insertBefore(IP);
 265     return SE.getSCEV(InstClone);
 266   }
 267
 268   const SCEV *visitUnknown(const SCEVUnknown *E) {
 269
 270     // If a value mapping was given try if the underlying value is remapped.
 271     Value *NewVal = VMap ? VMap->lookup(E->getValue()) : nullptr;
 272     if (NewVal) {
 273       auto *NewE = SE.getSCEV(NewVal);
 274
 275       // While the mapped value might be different the SCEV representation might
 276       // not be. To this end we will check before we go into recursion here.
 277       if (E != NewE)
 278         return visit(NewE);
 279     }
 280
 281     Instruction *Inst = dyn_cast<Instruction>(E->getValue());
 282     Instruction *IP;
 283     if (Inst && !R.contains(Inst))
 284       IP = Inst;
 285     else if (Inst && RTCBB->getParent() == Inst->getFunction())
 286       IP = RTCBB->getTerminator();
 287     else
 288       IP = RTCBB->getParent()->getEntryBlock().getTerminator();
 289
 290     if (!Inst || (Inst->getOpcode() != Instruction::SRem &&
 291                   Inst->getOpcode() != Instruction::SDiv))
 292       return visitGenericInst(E, Inst, IP);
 293
 294     const SCEV *LHSScev = SE.getSCEV(Inst->getOperand(0));
 295     const SCEV *RHSScev = SE.getSCEV(Inst->getOperand(1));
 296
 297     if (!SE.isKnownNonZero(RHSScev))
 298       RHSScev = SE.getUMaxExpr(RHSScev, SE.getConstant(E->getType(), 1));
 299
 300     Value *LHS = expandCodeFor(LHSScev, E->getType(), IP);
 301     Value *RHS = expandCodeFor(RHSScev, E->getType(), IP);
 302
 303     Inst = BinaryOperator::Create((Instruction::BinaryOps)Inst->getOpcode(),
 304                                   LHS, RHS, Inst->getName() + Name, IP);
 305     return SE.getSCEV(Inst);
 306   }
 307
 308   /// The following functions will just traverse the SCEV and rebuild it with
 309   /// the new operands returned by the traversal.
 310   ///
 311   ///{
 312   const SCEV *visitConstant(const SCEVConstant *E) { return E; }
 313   const SCEV *visitTruncateExpr(const SCEVTruncateExpr *E) {
 314     return SE.getTruncateExpr(visit(E->getOperand()), E->getType());
 315   }
 316   const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *E) {
 317     return SE.getZeroExtendExpr(visit(E->getOperand()), E->getType());
 318   }
 319   const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *E) {
 320     return SE.getSignExtendExpr(visit(E->getOperand()), E->getType());
 321   }
 322   const SCEV *visitUDivExpr(const SCEVUDivExpr *E) {
 323     auto *RHSScev = visit(E->getRHS());
 324     if (!SE.isKnownNonZero(RHSScev))
 325       RHSScev = SE.getUMaxExpr(RHSScev, SE.getConstant(E->getType(), 1));
 326     return SE.getUDivExpr(visit(E->getLHS()), RHSScev);
 327   }
 328   const SCEV *visitAddExpr(const SCEVAddExpr *E) {
 329     SmallVector<const SCEV *, 4> NewOps;
 330     for (const SCEV *Op : E->operands())
 331       NewOps.push_back(visit(Op));
 332     return SE.getAddExpr(NewOps);
 333   }
 334   const SCEV *visitMulExpr(const SCEVMulExpr *E) {
 335     SmallVector<const SCEV *, 4> NewOps;
 336     for (const SCEV *Op : E->operands())
 337       NewOps.push_back(visit(Op));
 338     return SE.getMulExpr(NewOps);
 339   }
 340   const SCEV *visitUMaxExpr(const SCEVUMaxExpr *E) {
 341     SmallVector<const SCEV *, 4> NewOps;
 342     for (const SCEV *Op : E->operands())
 343       NewOps.push_back(visit(Op));
 344     return SE.getUMaxExpr(NewOps);
 345   }
 346   const SCEV *visitSMaxExpr(const SCEVSMaxExpr *E) {
 347     SmallVector<const SCEV *, 4> NewOps;
 348     for (const SCEV *Op : E->operands())
 349       NewOps.push_back(visit(Op));
 350     return SE.getSMaxExpr(NewOps);
 351   }
 352   const SCEV *visitAddRecExpr(const SCEVAddRecExpr *E) {
 353     SmallVector<const SCEV *, 4> NewOps;
 354     for (const SCEV *Op : E->operands())
 355       NewOps.push_back(visit(Op));
 356     return SE.getAddRecExpr(NewOps, E->getLoop(), E->getNoWrapFlags());
 357   }
 358   ///}
 359 };
 360
 361 Value *polly::expandCodeFor(Scop &S, ScalarEvolution &SE, const DataLayout &DL,
 362                             const char *Name, const SCEV *E, Type *Ty,
 363                             Instruction *IP, ValueMapT *VMap,
 364                             BasicBlock *RTCBB) {
 365   ScopExpander Expander(S.getRegion(), SE, DL, Name, VMap, RTCBB);
 366   return Expander.expandCodeFor(E, Ty, IP);
 367 }
 368
 369 bool polly::isErrorBlock(BasicBlock &BB, const Region &R, LoopInfo &LI,
 370                          const DominatorTree &DT) {
 371   if (!PollyAllowErrorBlocks)
 372     return false;
 373
 374   if (isa<UnreachableInst>(BB.getTerminator()))
 375     return true;
 376
 377   if (LI.isLoopHeader(&BB))
 378     return false;
 379
 380   // Basic blocks that are always executed are not considered error blocks,
 381   // as their execution can not be a rare event.
 382   bool DominatesAllPredecessors = true;
 383   for (auto Pred : predecessors(R.getExit()))
 384     if (R.contains(Pred) && !DT.dominates(&BB, Pred))
 385       DominatesAllPredecessors = false;
 386
 387   if (DominatesAllPredecessors)
 388     return false;
 389
 390   // FIXME: This is a simple heuristic to determine if the load is executed
 391   //        in a conditional. However, we actually would need the control
 392   //        condition, i.e., the post dominance frontier. Alternatively we
 393   //        could walk up the dominance tree until we find a block that is
 394   //        not post dominated by the load and check if it is a conditional
 395   //        or a loop header.
 396   auto *DTNode = DT.getNode(&BB);
 397   auto *IDomBB = DTNode->getIDom()->getBlock();
 398   if (LI.isLoopHeader(IDomBB))
 399     return false;
 400
 401   for (Instruction &Inst : BB)
 402     if (CallInst *CI = dyn_cast<CallInst>(&Inst)) {
 403       if (isIgnoredIntrinsic(CI))
 404         return false;
 405
 406       if (!CI->doesNotAccessMemory())
 407         return true;
 408       if (CI->doesNotReturn())
 409         return true;
 410     }
 411
 412   return false;
 413 }
 414
 415 Value *polly::getConditionFromTerminator(TerminatorInst *TI) {
 416   if (BranchInst *BR = dyn_cast<BranchInst>(TI)) {
 417     if (BR->isUnconditional())
 418       return ConstantInt::getTrue(Type::getInt1Ty(TI->getContext()));
 419
 420     return BR->getCondition();
 421   }
 422
 423   if (SwitchInst *SI = dyn_cast<SwitchInst>(TI))
 424     return SI->getCondition();
 425
 426   return nullptr;
 427 }
 428
 429 bool polly::isHoistableLoad(LoadInst *LInst, Region &R, LoopInfo &LI,
 430                             ScalarEvolution &SE, const DominatorTree &DT) {
 431   Loop *L = LI.getLoopFor(LInst->getParent());
 432   auto *Ptr = LInst->getPointerOperand();
 433   const SCEV *PtrSCEV = SE.getSCEVAtScope(Ptr, L);
 434   while (L && R.contains(L)) {
 435     if (!SE.isLoopInvariant(PtrSCEV, L))
 436       return false;
 437     L = L->getParentLoop();
 438   }
 439
 440   for (auto *User : Ptr->users()) {
 441     auto *UserI = dyn_cast<Instruction>(User);
 442     if (!UserI || !R.contains(UserI))
 443       continue;
 444     if (!UserI->mayWriteToMemory())
 445       continue;
 446
 447     auto &BB = *UserI->getParent();
 448     if (DT.dominates(&BB, LInst->getParent()))
 449       return false;
 450
 451     bool DominatesAllPredecessors = true;
 452     for (auto Pred : predecessors(R.getExit()))
 453       if (R.contains(Pred) && !DT.dominates(&BB, Pred))
 454         DominatesAllPredecessors = false;
 455
 456     if (!DominatesAllPredecessors)
 457       continue;
 458
 459     return false;
 460   }
 461
 462   return true;
 463 }
 464
 465 bool polly::isIgnoredIntrinsic(const Value *V) {
 466   if (auto *IT = dyn_cast<IntrinsicInst>(V)) {
 467     switch (IT->getIntrinsicID()) {
 468     // Lifetime markers are supported/ignored.
 469     case llvm::Intrinsic::lifetime_start:
 470     case llvm::Intrinsic::lifetime_end:
 471     // Invariant markers are supported/ignored.
 472     case llvm::Intrinsic::invariant_start:
 473     case llvm::Intrinsic::invariant_end:
 474     // Some misc annotations are supported/ignored.
 475     case llvm::Intrinsic::var_annotation:
 476     case llvm::Intrinsic::ptr_annotation:
 477     case llvm::Intrinsic::annotation:
 478     case llvm::Intrinsic::donothing:
 479     case llvm::Intrinsic::assume:
 480     case llvm::Intrinsic::expect:
 481     // Some debug info intrisics are supported/ignored.
 482     case llvm::Intrinsic::dbg_value:
 483     case llvm::Intrinsic::dbg_declare:
 484       return true;
 485     default:
 486       break;
 487     }
 488   }
 489   return false;
 490 }
 491
 492 bool polly::canSynthesize(const Value *V, const Scop &S, ScalarEvolution *SE,
 493                           Loop *Scope) {
 494   if (!V || !SE->isSCEVable(V->getType()))
 495     return false;
 496
 497   if (const SCEV *Scev = SE->getSCEVAtScope(const_cast<Value *>(V), Scope))
 498     if (!isa<SCEVCouldNotCompute>(Scev))
 499       if (!hasScalarDepsInsideRegion(Scev, &S.getRegion(), Scope, false))
 500         return true;
 501
 502   return false;
 503 }
 504
 505 llvm::BasicBlock *polly::getUseBlock(llvm::Use &U) {
 506   Instruction *UI = dyn_cast<Instruction>(U.getUser());
 507   if (!UI)
 508     return nullptr;
 509
 510   if (PHINode *PHI = dyn_cast<PHINode>(UI))
 511     return PHI->getIncomingBlock(U);
 512
 513   return UI->getParent();
 514 }
 515
 516 std::tuple<std::vector<const SCEV *>, std::vector<int>>
 517 polly::getIndexExpressionsFromGEP(GetElementPtrInst *GEP, ScalarEvolution &SE) {
 518   std::vector<const SCEV *> Subscripts;
 519   std::vector<int> Sizes;
 520
 521   Type *Ty = GEP->getPointerOperandType();
 522
 523   bool DroppedFirstDim = false;
 524
 525   for (unsigned i = 1; i < GEP->getNumOperands(); i++) {
 526
 527     const SCEV *Expr = SE.getSCEV(GEP->getOperand(i));
 528
 529     if (i == 1) {
 530       if (auto *PtrTy = dyn_cast<PointerType>(Ty)) {
 531         Ty = PtrTy->getElementType();
 532       } else if (auto *ArrayTy = dyn_cast<ArrayType>(Ty)) {
 533         Ty = ArrayTy->getElementType();
 534       } else {
 535         Subscripts.clear();
 536         Sizes.clear();
 537         break;
 538       }
 539       if (auto *Const = dyn_cast<SCEVConstant>(Expr))
 540         if (Const->getValue()->isZero()) {
 541           DroppedFirstDim = true;
 542           continue;
 543         }
 544       Subscripts.push_back(Expr);
 545       continue;
 546     }
 547
 548     auto *ArrayTy = dyn_cast<ArrayType>(Ty);
 549     if (!ArrayTy) {
 550       Subscripts.clear();
 551       Sizes.clear();
 552       break;
 553     }
 554
 555     Subscripts.push_back(Expr);
 556     if (!(DroppedFirstDim && i == 2))
 557       Sizes.push_back(ArrayTy->getNumElements());
 558
 559     Ty = ArrayTy->getElementType();
 560   }
 561
 562   return std::make_tuple(Subscripts, Sizes);
 563 }