| //===-- NVPTXFavorNonGenericAddrSpace.cpp - ---------------------*- C++ -*-===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // When a load/store accesses the generic address space, checks whether the |
| // address is casted from a non-generic address space. If so, remove this |
| // addrspacecast because accessing non-generic address spaces is typically |
| // faster. Besides seeking addrspacecasts, this optimization also traces into |
| // the base pointer of a GEP. |
| // |
| // For instance, the code below loads a float from an array allocated in |
| // addrspace(3). |
| // |
| // %0 = addrspacecast [10 x float] addrspace(3)* @a to [10 x float]* |
| // %1 = gep [10 x float]* %0, i64 0, i64 %i |
| // %2 = load float* %1 ; emits ld.f32 |
| // |
| // First, function hoistAddrSpaceCastFromGEP reorders the addrspacecast |
| // and the GEP to expose more optimization opportunities to function |
| // optimizeMemoryInst. The intermediate code looks like: |
| // |
| // %0 = gep [10 x float] addrspace(3)* @a, i64 0, i64 %i |
| // %1 = addrspacecast float addrspace(3)* %0 to float* |
| // %2 = load float* %1 ; still emits ld.f32, but will be optimized shortly |
| // |
| // Then, function optimizeMemoryInstruction detects a load from addrspacecast'ed |
| // generic pointers, and folds the load and the addrspacecast into a load from |
| // the original address space. The final code looks like: |
| // |
| // %0 = gep [10 x float] addrspace(3)* @a, i64 0, i64 %i |
| // %2 = load float addrspace(3)* %0 ; emits ld.shared.f32 |
| // |
| // This pass may remove an addrspacecast in a different BB. Therefore, we |
| // implement it as a FunctionPass. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "NVPTX.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/Operator.h" |
| #include "llvm/Support/CommandLine.h" |
| |
| using namespace llvm; |
| |
| // An option to disable this optimization. Enable it by default. |
| static cl::opt<bool> DisableFavorNonGeneric( |
| "disable-nvptx-favor-non-generic", |
| cl::init(false), |
| cl::desc("Do not convert generic address space usage " |
| "to non-generic address space usage"), |
| cl::Hidden); |
| |
| namespace { |
| /// \brief NVPTXFavorNonGenericAddrSpaces |
| class NVPTXFavorNonGenericAddrSpaces : public FunctionPass { |
| public: |
| static char ID; |
| NVPTXFavorNonGenericAddrSpaces() : FunctionPass(ID) {} |
| |
| bool runOnFunction(Function &F) override; |
| |
| /// Optimizes load/store instructions. Idx is the index of the pointer operand |
| /// (0 for load, and 1 for store). Returns true if it changes anything. |
| bool optimizeMemoryInstruction(Instruction *I, unsigned Idx); |
| /// Transforms "gep (addrspacecast X), indices" into "addrspacecast (gep X, |
| /// indices)". This reordering exposes to optimizeMemoryInstruction more |
| /// optimization opportunities on loads and stores. Returns true if it changes |
| /// the program. |
| bool hoistAddrSpaceCastFromGEP(GEPOperator *GEP); |
| }; |
| } |
| |
| char NVPTXFavorNonGenericAddrSpaces::ID = 0; |
| |
| namespace llvm { |
| void initializeNVPTXFavorNonGenericAddrSpacesPass(PassRegistry &); |
| } |
| INITIALIZE_PASS(NVPTXFavorNonGenericAddrSpaces, "nvptx-favor-non-generic", |
| "Remove unnecessary non-generic-to-generic addrspacecasts", |
| false, false) |
| |
| // Decides whether removing Cast is valid and beneficial. Cast can be an |
| // instruction or a constant expression. |
| static bool IsEliminableAddrSpaceCast(Operator *Cast) { |
| // Returns false if not even an addrspacecast. |
| if (Cast->getOpcode() != Instruction::AddrSpaceCast) |
| return false; |
| |
| Value *Src = Cast->getOperand(0); |
| PointerType *SrcTy = cast<PointerType>(Src->getType()); |
| PointerType *DestTy = cast<PointerType>(Cast->getType()); |
| // TODO: For now, we only handle the case where the addrspacecast only changes |
| // the address space but not the type. If the type also changes, we could |
| // still get rid of the addrspacecast by adding an extra bitcast, but we |
| // rarely see such scenarios. |
| if (SrcTy->getElementType() != DestTy->getElementType()) |
| return false; |
| |
| // Checks whether the addrspacecast is from a non-generic address space to the |
| // generic address space. |
| return (SrcTy->getAddressSpace() != AddressSpace::ADDRESS_SPACE_GENERIC && |
| DestTy->getAddressSpace() == AddressSpace::ADDRESS_SPACE_GENERIC); |
| } |
| |
| bool NVPTXFavorNonGenericAddrSpaces::hoistAddrSpaceCastFromGEP( |
| GEPOperator *GEP) { |
| Operator *Cast = dyn_cast<Operator>(GEP->getPointerOperand()); |
| if (!Cast) |
| return false; |
| |
| if (!IsEliminableAddrSpaceCast(Cast)) |
| return false; |
| |
| SmallVector<Value *, 8> Indices(GEP->idx_begin(), GEP->idx_end()); |
| if (Instruction *GEPI = dyn_cast<Instruction>(GEP)) { |
| // %1 = gep (addrspacecast X), indices |
| // => |
| // %0 = gep X, indices |
| // %1 = addrspacecast %0 |
| GetElementPtrInst *NewGEPI = GetElementPtrInst::Create(Cast->getOperand(0), |
| Indices, |
| GEP->getName(), |
| GEPI); |
| NewGEPI->setIsInBounds(GEP->isInBounds()); |
| GEP->replaceAllUsesWith( |
| new AddrSpaceCastInst(NewGEPI, GEP->getType(), "", GEPI)); |
| } else { |
| // GEP is a constant expression. |
| Constant *NewGEPCE = ConstantExpr::getGetElementPtr( |
| cast<Constant>(Cast->getOperand(0)), |
| Indices, |
| GEP->isInBounds()); |
| GEP->replaceAllUsesWith( |
| ConstantExpr::getAddrSpaceCast(NewGEPCE, GEP->getType())); |
| } |
| |
| return true; |
| } |
| |
| bool NVPTXFavorNonGenericAddrSpaces::optimizeMemoryInstruction(Instruction *MI, |
| unsigned Idx) { |
| // If the pointer operand is a GEP, hoist the addrspacecast if any from the |
| // GEP to expose more optimization opportunites. |
| if (GEPOperator *GEP = dyn_cast<GEPOperator>(MI->getOperand(Idx))) { |
| hoistAddrSpaceCastFromGEP(GEP); |
| } |
| |
| // load/store (addrspacecast X) => load/store X if shortcutting the |
| // addrspacecast is valid and can improve performance. |
| // |
| // e.g., |
| // %1 = addrspacecast float addrspace(3)* %0 to float* |
| // %2 = load float* %1 |
| // -> |
| // %2 = load float addrspace(3)* %0 |
| // |
| // Note: the addrspacecast can also be a constant expression. |
| if (Operator *Cast = dyn_cast<Operator>(MI->getOperand(Idx))) { |
| if (IsEliminableAddrSpaceCast(Cast)) { |
| MI->setOperand(Idx, Cast->getOperand(0)); |
| return true; |
| } |
| } |
| |
| return false; |
| } |
| |
| bool NVPTXFavorNonGenericAddrSpaces::runOnFunction(Function &F) { |
| if (DisableFavorNonGeneric) |
| return false; |
| |
| bool Changed = false; |
| for (Function::iterator B = F.begin(), BE = F.end(); B != BE; ++B) { |
| for (BasicBlock::iterator I = B->begin(), IE = B->end(); I != IE; ++I) { |
| if (isa<LoadInst>(I)) { |
| // V = load P |
| Changed |= optimizeMemoryInstruction(I, 0); |
| } else if (isa<StoreInst>(I)) { |
| // store V, P |
| Changed |= optimizeMemoryInstruction(I, 1); |
| } |
| } |
| } |
| return Changed; |
| } |
| |
| FunctionPass *llvm::createNVPTXFavorNonGenericAddrSpacesPass() { |
| return new NVPTXFavorNonGenericAddrSpaces(); |
| } |