lib/Transforms/Scalar/InferAddressSpaces.cpp

   1 //===- InferAddressSpace.cpp - --------------------------------------------===//
   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 // CUDA C/C++ includes memory space designation as variable type qualifers (such
  10 // as __global__ and __shared__). Knowing the space of a memory access allows
  11 // CUDA compilers to emit faster PTX loads and stores. For example, a load from
  12 // shared memory can be translated to `ld.shared` which is roughly 10% faster
  13 // than a generic `ld` on an NVIDIA Tesla K40c.
  14 //
  15 // Unfortunately, type qualifiers only apply to variable declarations, so CUDA
  16 // compilers must infer the memory space of an address expression from
  17 // type-qualified variables.
  18 //
  19 // LLVM IR uses non-zero (so-called) specific address spaces to represent memory
  20 // spaces (e.g. addrspace(3) means shared memory). The Clang frontend
  21 // places only type-qualified variables in specific address spaces, and then
  22 // conservatively `addrspacecast`s each type-qualified variable to addrspace(0)
  23 // (so-called the generic address space) for other instructions to use.
  24 //
  25 // For example, the Clang translates the following CUDA code
  26 //   __shared__ float a[10];
  27 //   float v = a[i];
  28 // to
  29 //   %0 = addrspacecast [10 x float] addrspace(3)* @a to [10 x float]*
  30 //   %1 = gep [10 x float], [10 x float]* %0, i64 0, i64 %i
  31 //   %v = load float, float* %1 ; emits ld.f32
  32 // @a is in addrspace(3) since it's type-qualified, but its use from %1 is
  33 // redirected to %0 (the generic version of @a).
  34 //
  35 // The optimization implemented in this file propagates specific address spaces
  36 // from type-qualified variable declarations to its users. For example, it
  37 // optimizes the above IR to
  38 //   %1 = gep [10 x float] addrspace(3)* @a, i64 0, i64 %i
  39 //   %v = load float addrspace(3)* %1 ; emits ld.shared.f32
  40 // propagating the addrspace(3) from @a to %1. As the result, the NVPTX
  41 // codegen is able to emit ld.shared.f32 for %v.
  42 //
  43 // Address space inference works in two steps. First, it uses a data-flow
  44 // analysis to infer as many generic pointers as possible to point to only one
  45 // specific address space. In the above example, it can prove that %1 only
  46 // points to addrspace(3). This algorithm was published in
  47 //   CUDA: Compiling and optimizing for a GPU platform
  48 //   Chakrabarti, Grover, Aarts, Kong, Kudlur, Lin, Marathe, Murphy, Wang
  49 //   ICCS 2012
  50 //
  51 // Then, address space inference replaces all refinable generic pointers with
  52 // equivalent specific pointers.
  53 //
  54 // The major challenge of implementing this optimization is handling PHINodes,
  55 // which may create loops in the data flow graph. This brings two complications.
  56 //
  57 // First, the data flow analysis in Step 1 needs to be circular. For example,
  58 //     %generic.input = addrspacecast float addrspace(3)* %input to float*
  59 //   loop:
  60 //     %y = phi [ %generic.input, %y2 ]
  61 //     %y2 = getelementptr %y, 1
  62 //     %v = load %y2
  63 //     br ..., label %loop, ...
  64 // proving %y specific requires proving both %generic.input and %y2 specific,
  65 // but proving %y2 specific circles back to %y. To address this complication,
  66 // the data flow analysis operates on a lattice:
  67 //   uninitialized > specific address spaces > generic.
  68 // All address expressions (our implementation only considers phi, bitcast,
  69 // addrspacecast, and getelementptr) start with the uninitialized address space.
  70 // The monotone transfer function moves the address space of a pointer down a
  71 // lattice path from uninitialized to specific and then to generic. A join
  72 // operation of two different specific address spaces pushes the expression down
  73 // to the generic address space. The analysis completes once it reaches a fixed
  74 // point.
  75 //
  76 // Second, IR rewriting in Step 2 also needs to be circular. For example,
  77 // converting %y to addrspace(3) requires the compiler to know the converted
  78 // %y2, but converting %y2 needs the converted %y. To address this complication,
  79 // we break these cycles using "undef" placeholders. When converting an
  80 // instruction `I` to a new address space, if its operand `Op` is not converted
  81 // yet, we let `I` temporarily use `undef` and fix all the uses of undef later.
  82 // For instance, our algorithm first converts %y to
  83 //   %y' = phi float addrspace(3)* [ %input, undef ]
  84 // Then, it converts %y2 to
  85 //   %y2' = getelementptr %y', 1
  86 // Finally, it fixes the undef in %y' so that
  87 //   %y' = phi float addrspace(3)* [ %input, %y2' ]
  88 //
  89 //===----------------------------------------------------------------------===//
  90
  91 #include "llvm/ADT/ArrayRef.h"
  92 #include "llvm/ADT/DenseMap.h"
  93 #include "llvm/ADT/DenseSet.h"
  94 #include "llvm/ADT/None.h"
  95 #include "llvm/ADT/Optional.h"
  96 #include "llvm/ADT/SetVector.h"
  97 #include "llvm/ADT/SmallVector.h"
  98 #include "llvm/Analysis/TargetTransformInfo.h"
  99 #include "llvm/Transforms/Utils/Local.h"
 100 #include "llvm/IR/BasicBlock.h"
 101 #include "llvm/IR/Constant.h"
 102 #include "llvm/IR/Constants.h"
 103 #include "llvm/IR/Function.h"
 104 #include "llvm/IR/IRBuilder.h"
 105 #include "llvm/IR/InstIterator.h"
 106 #include "llvm/IR/Instruction.h"
 107 #include "llvm/IR/Instructions.h"
 108 #include "llvm/IR/IntrinsicInst.h"
 109 #include "llvm/IR/Intrinsics.h"
 110 #include "llvm/IR/LLVMContext.h"
 111 #include "llvm/IR/Operator.h"
 112 #include "llvm/IR/Type.h"
 113 #include "llvm/IR/Use.h"
 114 #include "llvm/IR/User.h"
 115 #include "llvm/IR/Value.h"
 116 #include "llvm/IR/ValueHandle.h"
 117 #include "llvm/Pass.h"
 118 #include "llvm/Support/Casting.h"
 119 #include "llvm/Support/Compiler.h"
 120 #include "llvm/Support/Debug.h"
 121 #include "llvm/Support/ErrorHandling.h"
 122 #include "llvm/Support/raw_ostream.h"
 123 #include "llvm/Transforms/Scalar.h"
 124 #include "llvm/Transforms/Utils/ValueMapper.h"
 125 #include <cassert>
 126 #include <iterator>
 127 #include <limits>
 128 #include <utility>
 129 #include <vector>
 130
 131 #define DEBUG_TYPE "infer-address-spaces"
 132
 133 using namespace llvm;
 134
 135 static const unsigned UninitializedAddressSpace =
 136     std::numeric_limits<unsigned>::max();
 137
 138 namespace {
 139
 140 using ValueToAddrSpaceMapTy = DenseMap<const Value *, unsigned>;
 141
 142 /// InferAddressSpaces
 143 class InferAddressSpaces : public FunctionPass {
 144   /// Target specific address space which uses of should be replaced if
 145   /// possible.
 146   unsigned FlatAddrSpace;
 147
 148 public:
 149   static char ID;
 150
 151   InferAddressSpaces() : FunctionPass(ID) {}
 152
 153   void getAnalysisUsage(AnalysisUsage &AU) const override {
 154     AU.setPreservesCFG();
 155     AU.addRequired<TargetTransformInfoWrapperPass>();
 156   }
 157
 158   bool runOnFunction(Function &F) override;
 159
 160 private:
 161   // Returns the new address space of V if updated; otherwise, returns None.
 162   Optional<unsigned>
 163   updateAddressSpace(const Value &V,
 164                      const ValueToAddrSpaceMapTy &InferredAddrSpace) const;
 165
 166   // Tries to infer the specific address space of each address expression in
 167   // Postorder.
 168   void inferAddressSpaces(ArrayRef<WeakTrackingVH> Postorder,
 169                           ValueToAddrSpaceMapTy *InferredAddrSpace) const;
 170
 171   bool isSafeToCastConstAddrSpace(Constant *C, unsigned NewAS) const;
 172
 173   // Changes the flat address expressions in function F to point to specific
 174   // address spaces if InferredAddrSpace says so. Postorder is the postorder of
 175   // all flat expressions in the use-def graph of function F.
 176   bool rewriteWithNewAddressSpaces(
 177       const TargetTransformInfo &TTI, ArrayRef<WeakTrackingVH> Postorder,
 178       const ValueToAddrSpaceMapTy &InferredAddrSpace, Function *F) const;
 179
 180   void appendsFlatAddressExpressionToPostorderStack(
 181     Value *V, std::vector<std::pair<Value *, bool>> &PostorderStack,
 182     DenseSet<Value *> &Visited) const;
 183
 184   bool rewriteIntrinsicOperands(IntrinsicInst *II,
 185                                 Value *OldV, Value *NewV) const;
 186   void collectRewritableIntrinsicOperands(
 187     IntrinsicInst *II,
 188     std::vector<std::pair<Value *, bool>> &PostorderStack,
 189     DenseSet<Value *> &Visited) const;
 190
 191   std::vector<WeakTrackingVH> collectFlatAddressExpressions(Function &F) const;
 192
 193   Value *cloneValueWithNewAddressSpace(
 194     Value *V, unsigned NewAddrSpace,
 195     const ValueToValueMapTy &ValueWithNewAddrSpace,
 196     SmallVectorImpl<const Use *> *UndefUsesToFix) const;
 197   unsigned joinAddressSpaces(unsigned AS1, unsigned AS2) const;
 198 };
 199
 200 } // end anonymous namespace
 201
 202 char InferAddressSpaces::ID = 0;
 203
 204 namespace llvm {
 205
 206 void initializeInferAddressSpacesPass(PassRegistry &);
 207
 208 } // end namespace llvm
 209
 210 INITIALIZE_PASS(InferAddressSpaces, DEBUG_TYPE, "Infer address spaces",
 211                 false, false)
 212
 213 // Returns true if V is an address expression.
 214 // TODO: Currently, we consider only phi, bitcast, addrspacecast, and
 215 // getelementptr operators.
 216 static bool isAddressExpression(const Value &V) {
 217   if (!isa<Operator>(V))
 218     return false;
 219
 220   switch (cast<Operator>(V).getOpcode()) {
 221   case Instruction::PHI:
 222   case Instruction::BitCast:
 223   case Instruction::AddrSpaceCast:
 224   case Instruction::GetElementPtr:
 225   case Instruction::Select:
 226     return true;
 227   default:
 228     return false;
 229   }
 230 }
 231
 232 // Returns the pointer operands of V.
 233 //
 234 // Precondition: V is an address expression.
 235 static SmallVector<Value *, 2> getPointerOperands(const Value &V) {
 236   const Operator &Op = cast<Operator>(V);
 237   switch (Op.getOpcode()) {
 238   case Instruction::PHI: {
 239     auto IncomingValues = cast<PHINode>(Op).incoming_values();
 240     return SmallVector<Value *, 2>(IncomingValues.begin(),
 241                                    IncomingValues.end());
 242   }
 243   case Instruction::BitCast:
 244   case Instruction::AddrSpaceCast:
 245   case Instruction::GetElementPtr:
 246     return {Op.getOperand(0)};
 247   case Instruction::Select:
 248     return {Op.getOperand(1), Op.getOperand(2)};
 249   default:
 250     llvm_unreachable("Unexpected instruction type.");
 251   }
 252 }
 253
 254 // TODO: Move logic to TTI?
 255 bool InferAddressSpaces::rewriteIntrinsicOperands(IntrinsicInst *II,
 256                                                   Value *OldV,
 257                                                   Value *NewV) const {
 258   Module *M = II->getParent()->getParent()->getParent();
 259
 260   switch (II->getIntrinsicID()) {
 261   case Intrinsic::amdgcn_atomic_inc:
 262   case Intrinsic::amdgcn_atomic_dec:
 263   case Intrinsic::amdgcn_ds_fadd:
 264   case Intrinsic::amdgcn_ds_fmin:
 265   case Intrinsic::amdgcn_ds_fmax: {
 266     const ConstantInt *IsVolatile = dyn_cast<ConstantInt>(II->getArgOperand(4));
 267     if (!IsVolatile || !IsVolatile->isZero())
 268       return false;
 269
 270     LLVM_FALLTHROUGH;
 271   }
 272   case Intrinsic::objectsize: {
 273     Type *DestTy = II->getType();
 274     Type *SrcTy = NewV->getType();
 275     Function *NewDecl =
 276         Intrinsic::getDeclaration(M, II->getIntrinsicID(), {DestTy, SrcTy});
 277     II->setArgOperand(0, NewV);
 278     II->setCalledFunction(NewDecl);
 279     return true;
 280   }
 281   default:
 282     return false;
 283   }
 284 }
 285
 286 // TODO: Move logic to TTI?
 287 void InferAddressSpaces::collectRewritableIntrinsicOperands(
 288     IntrinsicInst *II, std::vector<std::pair<Value *, bool>> &PostorderStack,
 289     DenseSet<Value *> &Visited) const {
 290   switch (II->getIntrinsicID()) {
 291   case Intrinsic::objectsize:
 292   case Intrinsic::amdgcn_atomic_inc:
 293   case Intrinsic::amdgcn_atomic_dec:
 294   case Intrinsic::amdgcn_ds_fadd:
 295   case Intrinsic::amdgcn_ds_fmin:
 296   case Intrinsic::amdgcn_ds_fmax:
 297     appendsFlatAddressExpressionToPostorderStack(II->getArgOperand(0),
 298                                                  PostorderStack, Visited);
 299     break;
 300   default:
 301     break;
 302   }
 303 }
 304
 305 // Returns all flat address expressions in function F. The elements are
 306 // If V is an unvisited flat address expression, appends V to PostorderStack
 307 // and marks it as visited.
 308 void InferAddressSpaces::appendsFlatAddressExpressionToPostorderStack(
 309     Value *V, std::vector<std::pair<Value *, bool>> &PostorderStack,
 310     DenseSet<Value *> &Visited) const {
 311   assert(V->getType()->isPointerTy());
 312
 313   // Generic addressing expressions may be hidden in nested constant
 314   // expressions.
 315   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
 316     // TODO: Look in non-address parts, like icmp operands.
 317     if (isAddressExpression(*CE) && Visited.insert(CE).second)
 318       PostorderStack.push_back(std::make_pair(CE, false));
 319
 320     return;
 321   }
 322
 323   if (isAddressExpression(*V) &&
 324       V->getType()->getPointerAddressSpace() == FlatAddrSpace) {
 325     if (Visited.insert(V).second) {
 326       PostorderStack.push_back(std::make_pair(V, false));
 327
 328       Operator *Op = cast<Operator>(V);
 329       for (unsigned I = 0, E = Op->getNumOperands(); I != E; ++I) {
 330         if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Op->getOperand(I))) {
 331           if (isAddressExpression(*CE) && Visited.insert(CE).second)
 332             PostorderStack.emplace_back(CE, false);
 333         }
 334       }
 335     }
 336   }
 337 }
 338
 339 // Returns all flat address expressions in function F. The elements are ordered
 340 // ordered in postorder.
 341 std::vector<WeakTrackingVH>
 342 InferAddressSpaces::collectFlatAddressExpressions(Function &F) const {
 343   // This function implements a non-recursive postorder traversal of a partial
 344   // use-def graph of function F.
 345   std::vector<std::pair<Value *, bool>> PostorderStack;
 346   // The set of visited expressions.
 347   DenseSet<Value *> Visited;
 348
 349   auto PushPtrOperand = [&](Value *Ptr) {
 350     appendsFlatAddressExpressionToPostorderStack(Ptr, PostorderStack,
 351                                                  Visited);
 352   };
 353
 354   // Look at operations that may be interesting accelerate by moving to a known
 355   // address space. We aim at generating after loads and stores, but pure
 356   // addressing calculations may also be faster.
 357   for (Instruction &I : instructions(F)) {
 358     if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
 359       if (!GEP->getType()->isVectorTy())
 360         PushPtrOperand(GEP->getPointerOperand());
 361     } else if (auto *LI = dyn_cast<LoadInst>(&I))
 362       PushPtrOperand(LI->getPointerOperand());
 363     else if (auto *SI = dyn_cast<StoreInst>(&I))
 364       PushPtrOperand(SI->getPointerOperand());
 365     else if (auto *RMW = dyn_cast<AtomicRMWInst>(&I))
 366       PushPtrOperand(RMW->getPointerOperand());
 367     else if (auto *CmpX = dyn_cast<AtomicCmpXchgInst>(&I))
 368       PushPtrOperand(CmpX->getPointerOperand());
 369     else if (auto *MI = dyn_cast<MemIntrinsic>(&I)) {
 370       // For memset/memcpy/memmove, any pointer operand can be replaced.
 371       PushPtrOperand(MI->getRawDest());
 372
 373       // Handle 2nd operand for memcpy/memmove.
 374       if (auto *MTI = dyn_cast<MemTransferInst>(MI))
 375         PushPtrOperand(MTI->getRawSource());
 376     } else if (auto *II = dyn_cast<IntrinsicInst>(&I))
 377       collectRewritableIntrinsicOperands(II, PostorderStack, Visited);
 378     else if (ICmpInst *Cmp = dyn_cast<ICmpInst>(&I)) {
 379       // FIXME: Handle vectors of pointers
 380       if (Cmp->getOperand(0)->getType()->isPointerTy()) {
 381         PushPtrOperand(Cmp->getOperand(0));
 382         PushPtrOperand(Cmp->getOperand(1));
 383       }
 384     } else if (auto *ASC = dyn_cast<AddrSpaceCastInst>(&I)) {
 385       if (!ASC->getType()->isVectorTy())
 386         PushPtrOperand(ASC->getPointerOperand());
 387     }
 388   }
 389
 390   std::vector<WeakTrackingVH> Postorder; // The resultant postorder.
 391   while (!PostorderStack.empty()) {
 392     Value *TopVal = PostorderStack.back().first;
 393     // If the operands of the expression on the top are already explored,
 394     // adds that expression to the resultant postorder.
 395     if (PostorderStack.back().second) {
 396       if (TopVal->getType()->getPointerAddressSpace() == FlatAddrSpace)
 397         Postorder.push_back(TopVal);
 398       PostorderStack.pop_back();
 399       continue;
 400     }
 401     // Otherwise, adds its operands to the stack and explores them.
 402     PostorderStack.back().second = true;
 403     for (Value *PtrOperand : getPointerOperands(*TopVal)) {
 404       appendsFlatAddressExpressionToPostorderStack(PtrOperand, PostorderStack,
 405                                                    Visited);
 406     }
 407   }
 408   return Postorder;
 409 }
 410
 411 // A helper function for cloneInstructionWithNewAddressSpace. Returns the clone
 412 // of OperandUse.get() in the new address space. If the clone is not ready yet,
 413 // returns an undef in the new address space as a placeholder.
 414 static Value *operandWithNewAddressSpaceOrCreateUndef(
 415     const Use &OperandUse, unsigned NewAddrSpace,
 416     const ValueToValueMapTy &ValueWithNewAddrSpace,
 417     SmallVectorImpl<const Use *> *UndefUsesToFix) {
 418   Value *Operand = OperandUse.get();
 419
 420   Type *NewPtrTy =
 421       Operand->getType()->getPointerElementType()->getPointerTo(NewAddrSpace);
 422
 423   if (Constant *C = dyn_cast<Constant>(Operand))
 424     return ConstantExpr::getAddrSpaceCast(C, NewPtrTy);
 425
 426   if (Value *NewOperand = ValueWithNewAddrSpace.lookup(Operand))
 427     return NewOperand;
 428
 429   UndefUsesToFix->push_back(&OperandUse);
 430   return UndefValue::get(NewPtrTy);
 431 }
 432
 433 // Returns a clone of `I` with its operands converted to those specified in
 434 // ValueWithNewAddrSpace. Due to potential cycles in the data flow graph, an
 435 // operand whose address space needs to be modified might not exist in
 436 // ValueWithNewAddrSpace. In that case, uses undef as a placeholder operand and
 437 // adds that operand use to UndefUsesToFix so that caller can fix them later.
 438 //
 439 // Note that we do not necessarily clone `I`, e.g., if it is an addrspacecast
 440 // from a pointer whose type already matches. Therefore, this function returns a
 441 // Value* instead of an Instruction*.
 442 static Value *cloneInstructionWithNewAddressSpace(
 443     Instruction *I, unsigned NewAddrSpace,
 444     const ValueToValueMapTy &ValueWithNewAddrSpace,
 445     SmallVectorImpl<const Use *> *UndefUsesToFix) {
 446   Type *NewPtrType =
 447       I->getType()->getPointerElementType()->getPointerTo(NewAddrSpace);
 448
 449   if (I->getOpcode() == Instruction::AddrSpaceCast) {
 450     Value *Src = I->getOperand(0);
 451     // Because `I` is flat, the source address space must be specific.
 452     // Therefore, the inferred address space must be the source space, according
 453     // to our algorithm.
 454     assert(Src->getType()->getPointerAddressSpace() == NewAddrSpace);
 455     if (Src->getType() != NewPtrType)
 456       return new BitCastInst(Src, NewPtrType);
 457     return Src;
 458   }
 459
 460   // Computes the converted pointer operands.
 461   SmallVector<Value *, 4> NewPointerOperands;
 462   for (const Use &OperandUse : I->operands()) {
 463     if (!OperandUse.get()->getType()->isPointerTy())
 464       NewPointerOperands.push_back(nullptr);
 465     else
 466       NewPointerOperands.push_back(operandWithNewAddressSpaceOrCreateUndef(
 467                                      OperandUse, NewAddrSpace, ValueWithNewAddrSpace, UndefUsesToFix));
 468   }
 469
 470   switch (I->getOpcode()) {
 471   case Instruction::BitCast:
 472     return new BitCastInst(NewPointerOperands[0], NewPtrType);
 473   case Instruction::PHI: {
 474     assert(I->getType()->isPointerTy());
 475     PHINode *PHI = cast<PHINode>(I);
 476     PHINode *NewPHI = PHINode::Create(NewPtrType, PHI->getNumIncomingValues());
 477     for (unsigned Index = 0; Index < PHI->getNumIncomingValues(); ++Index) {
 478       unsigned OperandNo = PHINode::getOperandNumForIncomingValue(Index);
 479       NewPHI->addIncoming(NewPointerOperands[OperandNo],
 480                           PHI->getIncomingBlock(Index));
 481     }
 482     return NewPHI;
 483   }
 484   case Instruction::GetElementPtr: {
 485     GetElementPtrInst *GEP = cast<GetElementPtrInst>(I);
 486     GetElementPtrInst *NewGEP = GetElementPtrInst::Create(
 487         GEP->getSourceElementType(), NewPointerOperands[0],
 488         SmallVector<Value *, 4>(GEP->idx_begin(), GEP->idx_end()));
 489     NewGEP->setIsInBounds(GEP->isInBounds());
 490     return NewGEP;
 491   }
 492   case Instruction::Select:
 493     assert(I->getType()->isPointerTy());
 494     return SelectInst::Create(I->getOperand(0), NewPointerOperands[1],
 495                               NewPointerOperands[2], "", nullptr, I);
 496   default:
 497     llvm_unreachable("Unexpected opcode");
 498   }
 499 }
 500
 501 // Similar to cloneInstructionWithNewAddressSpace, returns a clone of the
 502 // constant expression `CE` with its operands replaced as specified in
 503 // ValueWithNewAddrSpace.
 504 static Value *cloneConstantExprWithNewAddressSpace(
 505   ConstantExpr *CE, unsigned NewAddrSpace,
 506   const ValueToValueMapTy &ValueWithNewAddrSpace) {
 507   Type *TargetType =
 508     CE->getType()->getPointerElementType()->getPointerTo(NewAddrSpace);
 509
 510   if (CE->getOpcode() == Instruction::AddrSpaceCast) {
 511     // Because CE is flat, the source address space must be specific.
 512     // Therefore, the inferred address space must be the source space according
 513     // to our algorithm.
 514     assert(CE->getOperand(0)->getType()->getPointerAddressSpace() ==
 515            NewAddrSpace);
 516     return ConstantExpr::getBitCast(CE->getOperand(0), TargetType);
 517   }
 518
 519   if (CE->getOpcode() == Instruction::BitCast) {
 520     if (Value *NewOperand = ValueWithNewAddrSpace.lookup(CE->getOperand(0)))
 521       return ConstantExpr::getBitCast(cast<Constant>(NewOperand), TargetType);
 522     return ConstantExpr::getAddrSpaceCast(CE, TargetType);
 523   }
 524
 525   if (CE->getOpcode() == Instruction::Select) {
 526     Constant *Src0 = CE->getOperand(1);
 527     Constant *Src1 = CE->getOperand(2);
 528     if (Src0->getType()->getPointerAddressSpace() ==
 529         Src1->getType()->getPointerAddressSpace()) {
 530
 531       return ConstantExpr::getSelect(
 532           CE->getOperand(0), ConstantExpr::getAddrSpaceCast(Src0, TargetType),
 533           ConstantExpr::getAddrSpaceCast(Src1, TargetType));
 534     }
 535   }
 536
 537   // Computes the operands of the new constant expression.
 538   bool IsNew = false;
 539   SmallVector<Constant *, 4> NewOperands;
 540   for (unsigned Index = 0; Index < CE->getNumOperands(); ++Index) {
 541     Constant *Operand = CE->getOperand(Index);
 542     // If the address space of `Operand` needs to be modified, the new operand
 543     // with the new address space should already be in ValueWithNewAddrSpace
 544     // because (1) the constant expressions we consider (i.e. addrspacecast,
 545     // bitcast, and getelementptr) do not incur cycles in the data flow graph
 546     // and (2) this function is called on constant expressions in postorder.
 547     if (Value *NewOperand = ValueWithNewAddrSpace.lookup(Operand)) {
 548       IsNew = true;
 549       NewOperands.push_back(cast<Constant>(NewOperand));
 550     } else {
 551       // Otherwise, reuses the old operand.
 552       NewOperands.push_back(Operand);
 553     }
 554   }
 555
 556   // If !IsNew, we will replace the Value with itself. However, replaced values
 557   // are assumed to wrapped in a addrspace cast later so drop it now.
 558   if (!IsNew)
 559     return nullptr;
 560
 561   if (CE->getOpcode() == Instruction::GetElementPtr) {
 562     // Needs to specify the source type while constructing a getelementptr
 563     // constant expression.
 564     return CE->getWithOperands(
 565       NewOperands, TargetType, /*OnlyIfReduced=*/false,
 566       NewOperands[0]->getType()->getPointerElementType());
 567   }
 568
 569   return CE->getWithOperands(NewOperands, TargetType);
 570 }
 571
 572 // Returns a clone of the value `V`, with its operands replaced as specified in
 573 // ValueWithNewAddrSpace. This function is called on every flat address
 574 // expression whose address space needs to be modified, in postorder.
 575 //
 576 // See cloneInstructionWithNewAddressSpace for the meaning of UndefUsesToFix.
 577 Value *InferAddressSpaces::cloneValueWithNewAddressSpace(
 578   Value *V, unsigned NewAddrSpace,
 579   const ValueToValueMapTy &ValueWithNewAddrSpace,
 580   SmallVectorImpl<const Use *> *UndefUsesToFix) const {
 581   // All values in Postorder are flat address expressions.
 582   assert(isAddressExpression(*V) &&
 583          V->getType()->getPointerAddressSpace() == FlatAddrSpace);
 584
 585   if (Instruction *I = dyn_cast<Instruction>(V)) {
 586     Value *NewV = cloneInstructionWithNewAddressSpace(
 587       I, NewAddrSpace, ValueWithNewAddrSpace, UndefUsesToFix);
 588     if (Instruction *NewI = dyn_cast<Instruction>(NewV)) {
 589       if (NewI->getParent() == nullptr) {
 590         NewI->insertBefore(I);
 591         NewI->takeName(I);
 592       }
 593     }
 594     return NewV;
 595   }
 596
 597   return cloneConstantExprWithNewAddressSpace(
 598     cast<ConstantExpr>(V), NewAddrSpace, ValueWithNewAddrSpace);
 599 }
 600
 601 // Defines the join operation on the address space lattice (see the file header
 602 // comments).
 603 unsigned InferAddressSpaces::joinAddressSpaces(unsigned AS1,
 604                                                unsigned AS2) const {
 605   if (AS1 == FlatAddrSpace || AS2 == FlatAddrSpace)
 606     return FlatAddrSpace;
 607
 608   if (AS1 == UninitializedAddressSpace)
 609     return AS2;
 610   if (AS2 == UninitializedAddressSpace)
 611     return AS1;
 612
 613   // The join of two different specific address spaces is flat.
 614   return (AS1 == AS2) ? AS1 : FlatAddrSpace;
 615 }
 616
 617 bool InferAddressSpaces::runOnFunction(Function &F) {
 618   if (skipFunction(F))
 619     return false;
 620
 621   const TargetTransformInfo &TTI =
 622       getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
 623   FlatAddrSpace = TTI.getFlatAddressSpace();
 624   if (FlatAddrSpace == UninitializedAddressSpace)
 625     return false;
 626
 627   // Collects all flat address expressions in postorder.
 628   std::vector<WeakTrackingVH> Postorder = collectFlatAddressExpressions(F);
 629
 630   // Runs a data-flow analysis to refine the address spaces of every expression
 631   // in Postorder.
 632   ValueToAddrSpaceMapTy InferredAddrSpace;
 633   inferAddressSpaces(Postorder, &InferredAddrSpace);
 634
 635   // Changes the address spaces of the flat address expressions who are inferred
 636   // to point to a specific address space.
 637   return rewriteWithNewAddressSpaces(TTI, Postorder, InferredAddrSpace, &F);
 638 }
 639
 640 // Constants need to be tracked through RAUW to handle cases with nested
 641 // constant expressions, so wrap values in WeakTrackingVH.
 642 void InferAddressSpaces::inferAddressSpaces(
 643     ArrayRef<WeakTrackingVH> Postorder,
 644     ValueToAddrSpaceMapTy *InferredAddrSpace) const {
 645   SetVector<Value *> Worklist(Postorder.begin(), Postorder.end());
 646   // Initially, all expressions are in the uninitialized address space.
 647   for (Value *V : Postorder)
 648     (*InferredAddrSpace)[V] = UninitializedAddressSpace;
 649
 650   while (!Worklist.empty()) {
 651     Value *V = Worklist.pop_back_val();
 652
 653     // Tries to update the address space of the stack top according to the
 654     // address spaces of its operands.
 655     LLVM_DEBUG(dbgs() << "Updating the address space of\n  " << *V << '\n');
 656     Optional<unsigned> NewAS = updateAddressSpace(*V, *InferredAddrSpace);
 657     if (!NewAS.hasValue())
 658       continue;
 659     // If any updates are made, grabs its users to the worklist because
 660     // their address spaces can also be possibly updated.
 661     LLVM_DEBUG(dbgs() << "  to " << NewAS.getValue() << '\n');
 662     (*InferredAddrSpace)[V] = NewAS.getValue();
 663
 664     for (Value *User : V->users()) {
 665       // Skip if User is already in the worklist.
 666       if (Worklist.count(User))
 667         continue;
 668
 669       auto Pos = InferredAddrSpace->find(User);
 670       // Our algorithm only updates the address spaces of flat address
 671       // expressions, which are those in InferredAddrSpace.
 672       if (Pos == InferredAddrSpace->end())
 673         continue;
 674
 675       // Function updateAddressSpace moves the address space down a lattice
 676       // path. Therefore, nothing to do if User is already inferred as flat (the
 677       // bottom element in the lattice).
 678       if (Pos->second == FlatAddrSpace)
 679         continue;
 680
 681       Worklist.insert(User);
 682     }
 683   }
 684 }
 685
 686 Optional<unsigned> InferAddressSpaces::updateAddressSpace(
 687     const Value &V, const ValueToAddrSpaceMapTy &InferredAddrSpace) const {
 688   assert(InferredAddrSpace.count(&V));
 689
 690   // The new inferred address space equals the join of the address spaces
 691   // of all its pointer operands.
 692   unsigned NewAS = UninitializedAddressSpace;
 693
 694   const Operator &Op = cast<Operator>(V);
 695   if (Op.getOpcode() == Instruction::Select) {
 696     Value *Src0 = Op.getOperand(1);
 697     Value *Src1 = Op.getOperand(2);
 698
 699     auto I = InferredAddrSpace.find(Src0);
 700     unsigned Src0AS = (I != InferredAddrSpace.end()) ?
 701       I->second : Src0->getType()->getPointerAddressSpace();
 702
 703     auto J = InferredAddrSpace.find(Src1);
 704     unsigned Src1AS = (J != InferredAddrSpace.end()) ?
 705       J->second : Src1->getType()->getPointerAddressSpace();
 706
 707     auto *C0 = dyn_cast<Constant>(Src0);
 708     auto *C1 = dyn_cast<Constant>(Src1);
 709
 710     // If one of the inputs is a constant, we may be able to do a constant
 711     // addrspacecast of it. Defer inferring the address space until the input
 712     // address space is known.
 713     if ((C1 && Src0AS == UninitializedAddressSpace) ||
 714         (C0 && Src1AS == UninitializedAddressSpace))
 715       return None;
 716
 717     if (C0 && isSafeToCastConstAddrSpace(C0, Src1AS))
 718       NewAS = Src1AS;
 719     else if (C1 && isSafeToCastConstAddrSpace(C1, Src0AS))
 720       NewAS = Src0AS;
 721     else
 722       NewAS = joinAddressSpaces(Src0AS, Src1AS);
 723   } else {
 724     for (Value *PtrOperand : getPointerOperands(V)) {
 725       auto I = InferredAddrSpace.find(PtrOperand);
 726       unsigned OperandAS = I != InferredAddrSpace.end() ?
 727         I->second : PtrOperand->getType()->getPointerAddressSpace();
 728
 729       // join(flat, *) = flat. So we can break if NewAS is already flat.
 730       NewAS = joinAddressSpaces(NewAS, OperandAS);
 731       if (NewAS == FlatAddrSpace)
 732         break;
 733     }
 734   }
 735
 736   unsigned OldAS = InferredAddrSpace.lookup(&V);
 737   assert(OldAS != FlatAddrSpace);
 738   if (OldAS == NewAS)
 739     return None;
 740   return NewAS;
 741 }
 742
 743 /// \p returns true if \p U is the pointer operand of a memory instruction with
 744 /// a single pointer operand that can have its address space changed by simply
 745 /// mutating the use to a new value. If the memory instruction is volatile,
 746 /// return true only if the target allows the memory instruction to be volatile
 747 /// in the new address space.
 748 static bool isSimplePointerUseValidToReplace(const TargetTransformInfo &TTI,
 749                                              Use &U, unsigned AddrSpace) {
 750   User *Inst = U.getUser();
 751   unsigned OpNo = U.getOperandNo();
 752   bool VolatileIsAllowed = false;
 753   if (auto *I = dyn_cast<Instruction>(Inst))
 754     VolatileIsAllowed = TTI.hasVolatileVariant(I, AddrSpace);
 755
 756   if (auto *LI = dyn_cast<LoadInst>(Inst))
 757     return OpNo == LoadInst::getPointerOperandIndex() &&
 758            (VolatileIsAllowed || !LI->isVolatile());
 759
 760   if (auto *SI = dyn_cast<StoreInst>(Inst))
 761     return OpNo == StoreInst::getPointerOperandIndex() &&
 762            (VolatileIsAllowed || !SI->isVolatile());
 763
 764   if (auto *RMW = dyn_cast<AtomicRMWInst>(Inst))
 765     return OpNo == AtomicRMWInst::getPointerOperandIndex() &&
 766            (VolatileIsAllowed || !RMW->isVolatile());
 767
 768   if (auto *CmpX = dyn_cast<AtomicCmpXchgInst>(Inst))
 769     return OpNo == AtomicCmpXchgInst::getPointerOperandIndex() &&
 770            (VolatileIsAllowed || !CmpX->isVolatile());
 771
 772   return false;
 773 }
 774
 775 /// Update memory intrinsic uses that require more complex processing than
 776 /// simple memory instructions. Thse require re-mangling and may have multiple
 777 /// pointer operands.
 778 static bool handleMemIntrinsicPtrUse(MemIntrinsic *MI, Value *OldV,
 779                                      Value *NewV) {
 780   IRBuilder<> B(MI);
 781   MDNode *TBAA = MI->getMetadata(LLVMContext::MD_tbaa);
 782   MDNode *ScopeMD = MI->getMetadata(LLVMContext::MD_alias_scope);
 783   MDNode *NoAliasMD = MI->getMetadata(LLVMContext::MD_noalias);
 784
 785   if (auto *MSI = dyn_cast<MemSetInst>(MI)) {
 786     B.CreateMemSet(NewV, MSI->getValue(),
 787                    MSI->getLength(), MSI->getDestAlignment(),
 788                    false, // isVolatile
 789                    TBAA, ScopeMD, NoAliasMD);
 790   } else if (auto *MTI = dyn_cast<MemTransferInst>(MI)) {
 791     Value *Src = MTI->getRawSource();
 792     Value *Dest = MTI->getRawDest();
 793
 794     // Be careful in case this is a self-to-self copy.
 795     if (Src == OldV)
 796       Src = NewV;
 797
 798     if (Dest == OldV)
 799       Dest = NewV;
 800
 801     if (isa<MemCpyInst>(MTI)) {
 802       MDNode *TBAAStruct = MTI->getMetadata(LLVMContext::MD_tbaa_struct);
 803       B.CreateMemCpy(Dest, MTI->getDestAlignment(),
 804                      Src, MTI->getSourceAlignment(),
 805                      MTI->getLength(),
 806                      false, // isVolatile
 807                      TBAA, TBAAStruct, ScopeMD, NoAliasMD);
 808     } else {
 809       assert(isa<MemMoveInst>(MTI));
 810       B.CreateMemMove(Dest, MTI->getDestAlignment(),
 811                       Src, MTI->getSourceAlignment(),
 812                       MTI->getLength(),
 813                       false, // isVolatile
 814                       TBAA, ScopeMD, NoAliasMD);
 815     }
 816   } else
 817     llvm_unreachable("unhandled MemIntrinsic");
 818
 819   MI->eraseFromParent();
 820   return true;
 821 }
 822
 823 // \p returns true if it is OK to change the address space of constant \p C with
 824 // a ConstantExpr addrspacecast.
 825 bool InferAddressSpaces::isSafeToCastConstAddrSpace(Constant *C, unsigned NewAS) const {
 826   assert(NewAS != UninitializedAddressSpace);
 827
 828   unsigned SrcAS = C->getType()->getPointerAddressSpace();
 829   if (SrcAS == NewAS || isa<UndefValue>(C))
 830     return true;
 831
 832   // Prevent illegal casts between different non-flat address spaces.
 833   if (SrcAS != FlatAddrSpace && NewAS != FlatAddrSpace)
 834     return false;
 835
 836   if (isa<ConstantPointerNull>(C))
 837     return true;
 838
 839   if (auto *Op = dyn_cast<Operator>(C)) {
 840     // If we already have a constant addrspacecast, it should be safe to cast it
 841     // off.
 842     if (Op->getOpcode() == Instruction::AddrSpaceCast)
 843       return isSafeToCastConstAddrSpace(cast<Constant>(Op->getOperand(0)), NewAS);
 844
 845     if (Op->getOpcode() == Instruction::IntToPtr &&
 846         Op->getType()->getPointerAddressSpace() == FlatAddrSpace)
 847       return true;
 848   }
 849
 850   return false;
 851 }
 852
 853 static Value::use_iterator skipToNextUser(Value::use_iterator I,
 854                                           Value::use_iterator End) {
 855   User *CurUser = I->getUser();
 856   ++I;
 857
 858   while (I != End && I->getUser() == CurUser)
 859     ++I;
 860
 861   return I;
 862 }
 863
 864 bool InferAddressSpaces::rewriteWithNewAddressSpaces(
 865     const TargetTransformInfo &TTI, ArrayRef<WeakTrackingVH> Postorder,
 866     const ValueToAddrSpaceMapTy &InferredAddrSpace, Function *F) const {
 867   // For each address expression to be modified, creates a clone of it with its
 868   // pointer operands converted to the new address space. Since the pointer
 869   // operands are converted, the clone is naturally in the new address space by
 870   // construction.
 871   ValueToValueMapTy ValueWithNewAddrSpace;
 872   SmallVector<const Use *, 32> UndefUsesToFix;
 873   for (Value* V : Postorder) {
 874     unsigned NewAddrSpace = InferredAddrSpace.lookup(V);
 875     if (V->getType()->getPointerAddressSpace() != NewAddrSpace) {
 876       ValueWithNewAddrSpace[V] = cloneValueWithNewAddressSpace(
 877         V, NewAddrSpace, ValueWithNewAddrSpace, &UndefUsesToFix);
 878     }
 879   }
 880
 881   if (ValueWithNewAddrSpace.empty())
 882     return false;
 883
 884   // Fixes all the undef uses generated by cloneInstructionWithNewAddressSpace.
 885   for (const Use *UndefUse : UndefUsesToFix) {
 886     User *V = UndefUse->getUser();
 887     User *NewV = cast<User>(ValueWithNewAddrSpace.lookup(V));
 888     unsigned OperandNo = UndefUse->getOperandNo();
 889     assert(isa<UndefValue>(NewV->getOperand(OperandNo)));
 890     NewV->setOperand(OperandNo, ValueWithNewAddrSpace.lookup(UndefUse->get()));
 891   }
 892
 893   SmallVector<Instruction *, 16> DeadInstructions;
 894
 895   // Replaces the uses of the old address expressions with the new ones.
 896   for (const WeakTrackingVH &WVH : Postorder) {
 897     assert(WVH && "value was unexpectedly deleted");
 898     Value *V = WVH;
 899     Value *NewV = ValueWithNewAddrSpace.lookup(V);
 900     if (NewV == nullptr)
 901       continue;
 902
 903     LLVM_DEBUG(dbgs() << "Replacing the uses of " << *V << "\n  with\n  "
 904                       << *NewV << '\n');
 905
 906     if (Constant *C = dyn_cast<Constant>(V)) {
 907       Constant *Replace = ConstantExpr::getAddrSpaceCast(cast<Constant>(NewV),
 908                                                          C->getType());
 909       if (C != Replace) {
 910         LLVM_DEBUG(dbgs() << "Inserting replacement const cast: " << Replace
 911                           << ": " << *Replace << '\n');
 912         C->replaceAllUsesWith(Replace);
 913         V = Replace;
 914       }
 915     }
 916
 917     Value::use_iterator I, E, Next;
 918     for (I = V->use_begin(), E = V->use_end(); I != E; ) {
 919       Use &U = *I;
 920
 921       // Some users may see the same pointer operand in multiple operands. Skip
 922       // to the next instruction.
 923       I = skipToNextUser(I, E);
 924
 925       if (isSimplePointerUseValidToReplace(
 926               TTI, U, V->getType()->getPointerAddressSpace())) {
 927         // If V is used as the pointer operand of a compatible memory operation,
 928         // sets the pointer operand to NewV. This replacement does not change
 929         // the element type, so the resultant load/store is still valid.
 930         U.set(NewV);
 931         continue;
 932       }
 933
 934       User *CurUser = U.getUser();
 935       // Handle more complex cases like intrinsic that need to be remangled.
 936       if (auto *MI = dyn_cast<MemIntrinsic>(CurUser)) {
 937         if (!MI->isVolatile() && handleMemIntrinsicPtrUse(MI, V, NewV))
 938           continue;
 939       }
 940
 941       if (auto *II = dyn_cast<IntrinsicInst>(CurUser)) {
 942         if (rewriteIntrinsicOperands(II, V, NewV))
 943           continue;
 944       }
 945
 946       if (isa<Instruction>(CurUser)) {
 947         if (ICmpInst *Cmp = dyn_cast<ICmpInst>(CurUser)) {
 948           // If we can infer that both pointers are in the same addrspace,
 949           // transform e.g.
 950           //   %cmp = icmp eq float* %p, %q
 951           // into
 952           //   %cmp = icmp eq float addrspace(3)* %new_p, %new_q
 953
 954           unsigned NewAS = NewV->getType()->getPointerAddressSpace();
 955           int SrcIdx = U.getOperandNo();
 956           int OtherIdx = (SrcIdx == 0) ? 1 : 0;
 957           Value *OtherSrc = Cmp->getOperand(OtherIdx);
 958
 959           if (Value *OtherNewV = ValueWithNewAddrSpace.lookup(OtherSrc)) {
 960             if (OtherNewV->getType()->getPointerAddressSpace() == NewAS) {
 961               Cmp->setOperand(OtherIdx, OtherNewV);
 962               Cmp->setOperand(SrcIdx, NewV);
 963               continue;
 964             }
 965           }
 966
 967           // Even if the type mismatches, we can cast the constant.
 968           if (auto *KOtherSrc = dyn_cast<Constant>(OtherSrc)) {
 969             if (isSafeToCastConstAddrSpace(KOtherSrc, NewAS)) {
 970               Cmp->setOperand(SrcIdx, NewV);
 971               Cmp->setOperand(OtherIdx,
 972                 ConstantExpr::getAddrSpaceCast(KOtherSrc, NewV->getType()));
 973               continue;
 974             }
 975           }
 976         }
 977
 978         if (AddrSpaceCastInst *ASC = dyn_cast<AddrSpaceCastInst>(CurUser)) {
 979           unsigned NewAS = NewV->getType()->getPointerAddressSpace();
 980           if (ASC->getDestAddressSpace() == NewAS) {
 981             if (ASC->getType()->getPointerElementType() !=
 982                 NewV->getType()->getPointerElementType()) {
 983               NewV = CastInst::Create(Instruction::BitCast, NewV,
 984                                       ASC->getType(), "", ASC);
 985             }
 986             ASC->replaceAllUsesWith(NewV);
 987             DeadInstructions.push_back(ASC);
 988             continue;
 989           }
 990         }
 991
 992         // Otherwise, replaces the use with flat(NewV).
 993         if (Instruction *I = dyn_cast<Instruction>(V)) {
 994           BasicBlock::iterator InsertPos = std::next(I->getIterator());
 995           while (isa<PHINode>(InsertPos))
 996             ++InsertPos;
 997           U.set(new AddrSpaceCastInst(NewV, V->getType(), "", &*InsertPos));
 998         } else {
 999           U.set(ConstantExpr::getAddrSpaceCast(cast<Constant>(NewV),
1000                                                V->getType()));
1001         }
1002       }
1003     }
1004
1005     if (V->use_empty()) {
1006       if (Instruction *I = dyn_cast<Instruction>(V))
1007         DeadInstructions.push_back(I);
1008     }
1009   }
1010
1011   for (Instruction *I : DeadInstructions)
1012     RecursivelyDeleteTriviallyDeadInstructions(I);
1013
1014   return true;
1015 }
1016
1017 FunctionPass *llvm::createInferAddressSpacesPass() {
1018   return new InferAddressSpaces();
1019 }