1 //===-- NVPTXFavorNonGenericAddrSpace.cpp - ---------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // When a load/store accesses the generic address space, checks whether the
11 // address is casted from a non-generic address space. If so, remove this
12 // addrspacecast because accessing non-generic address spaces is typically
13 // faster. Besides seeking addrspacecasts, this optimization also traces into
14 // the base pointer of a GEP.
16 // For instance, the code below loads a float from an array allocated in
19 // %0 = addrspacecast [10 x float] addrspace(3)* @a to [10 x float]*
20 // %1 = gep [10 x float]* %0, i64 0, i64 %i
21 // %2 = load float* %1 ; emits ld.f32
23 // First, function hoistAddrSpaceCastFromGEP reorders the addrspacecast
24 // and the GEP to expose more optimization opportunities to function
25 // optimizeMemoryInst. The intermediate code looks like:
27 // %0 = gep [10 x float] addrspace(3)* @a, i64 0, i64 %i
28 // %1 = addrspacecast float addrspace(3)* %0 to float*
29 // %2 = load float* %1 ; still emits ld.f32, but will be optimized shortly
31 // Then, function optimizeMemoryInstruction detects a load from addrspacecast'ed
32 // generic pointers, and folds the load and the addrspacecast into a load from
33 // the original address space. The final code looks like:
35 // %0 = gep [10 x float] addrspace(3)* @a, i64 0, i64 %i
36 // %2 = load float addrspace(3)* %0 ; emits ld.shared.f32
38 // This pass may remove an addrspacecast in a different BB. Therefore, we
39 // implement it as a FunctionPass.
41 //===----------------------------------------------------------------------===//
44 #include "llvm/IR/Function.h"
45 #include "llvm/IR/Instructions.h"
46 #include "llvm/IR/Operator.h"
47 #include "llvm/Support/CommandLine.h"
51 // An option to disable this optimization. Enable it by default.
52 static cl::opt<bool> DisableFavorNonGeneric(
53 "disable-nvptx-favor-non-generic",
55 cl::desc("Do not convert generic address space usage "
56 "to non-generic address space usage"),
60 /// \brief NVPTXFavorNonGenericAddrSpaces
61 class NVPTXFavorNonGenericAddrSpaces : public FunctionPass {
64 NVPTXFavorNonGenericAddrSpaces() : FunctionPass(ID) {}
66 bool runOnFunction(Function &F) override;
68 /// Optimizes load/store instructions. Idx is the index of the pointer operand
69 /// (0 for load, and 1 for store). Returns true if it changes anything.
70 bool optimizeMemoryInstruction(Instruction *I, unsigned Idx);
71 /// Transforms "gep (addrspacecast X), indices" into "addrspacecast (gep X,
72 /// indices)". This reordering exposes to optimizeMemoryInstruction more
73 /// optimization opportunities on loads and stores. Returns true if it changes
75 bool hoistAddrSpaceCastFromGEP(GEPOperator *GEP);
79 char NVPTXFavorNonGenericAddrSpaces::ID = 0;
82 void initializeNVPTXFavorNonGenericAddrSpacesPass(PassRegistry &);
84 INITIALIZE_PASS(NVPTXFavorNonGenericAddrSpaces, "nvptx-favor-non-generic",
85 "Remove unnecessary non-generic-to-generic addrspacecasts",
88 // Decides whether removing Cast is valid and beneficial. Cast can be an
89 // instruction or a constant expression.
90 static bool IsEliminableAddrSpaceCast(Operator *Cast) {
91 // Returns false if not even an addrspacecast.
92 if (Cast->getOpcode() != Instruction::AddrSpaceCast)
95 Value *Src = Cast->getOperand(0);
96 PointerType *SrcTy = cast<PointerType>(Src->getType());
97 PointerType *DestTy = cast<PointerType>(Cast->getType());
98 // TODO: For now, we only handle the case where the addrspacecast only changes
99 // the address space but not the type. If the type also changes, we could
100 // still get rid of the addrspacecast by adding an extra bitcast, but we
101 // rarely see such scenarios.
102 if (SrcTy->getElementType() != DestTy->getElementType())
105 // Checks whether the addrspacecast is from a non-generic address space to the
106 // generic address space.
107 return (SrcTy->getAddressSpace() != AddressSpace::ADDRESS_SPACE_GENERIC &&
108 DestTy->getAddressSpace() == AddressSpace::ADDRESS_SPACE_GENERIC);
111 bool NVPTXFavorNonGenericAddrSpaces::hoistAddrSpaceCastFromGEP(
113 Operator *Cast = dyn_cast<Operator>(GEP->getPointerOperand());
117 if (!IsEliminableAddrSpaceCast(Cast))
120 SmallVector<Value *, 8> Indices(GEP->idx_begin(), GEP->idx_end());
121 if (Instruction *GEPI = dyn_cast<Instruction>(GEP)) {
122 // %1 = gep (addrspacecast X), indices
124 // %0 = gep X, indices
125 // %1 = addrspacecast %0
126 GetElementPtrInst *NewGEPI = GetElementPtrInst::Create(Cast->getOperand(0),
130 NewGEPI->setIsInBounds(GEP->isInBounds());
131 GEP->replaceAllUsesWith(
132 new AddrSpaceCastInst(NewGEPI, GEP->getType(), "", GEPI));
134 // GEP is a constant expression.
135 Constant *NewGEPCE = ConstantExpr::getGetElementPtr(
136 cast<Constant>(Cast->getOperand(0)),
139 GEP->replaceAllUsesWith(
140 ConstantExpr::getAddrSpaceCast(NewGEPCE, GEP->getType()));
146 bool NVPTXFavorNonGenericAddrSpaces::optimizeMemoryInstruction(Instruction *MI,
148 // If the pointer operand is a GEP, hoist the addrspacecast if any from the
149 // GEP to expose more optimization opportunites.
150 if (GEPOperator *GEP = dyn_cast<GEPOperator>(MI->getOperand(Idx))) {
151 hoistAddrSpaceCastFromGEP(GEP);
154 // load/store (addrspacecast X) => load/store X if shortcutting the
155 // addrspacecast is valid and can improve performance.
158 // %1 = addrspacecast float addrspace(3)* %0 to float*
159 // %2 = load float* %1
161 // %2 = load float addrspace(3)* %0
163 // Note: the addrspacecast can also be a constant expression.
164 if (Operator *Cast = dyn_cast<Operator>(MI->getOperand(Idx))) {
165 if (IsEliminableAddrSpaceCast(Cast)) {
166 MI->setOperand(Idx, Cast->getOperand(0));
174 bool NVPTXFavorNonGenericAddrSpaces::runOnFunction(Function &F) {
175 if (DisableFavorNonGeneric)
178 bool Changed = false;
179 for (Function::iterator B = F.begin(), BE = F.end(); B != BE; ++B) {
180 for (BasicBlock::iterator I = B->begin(), IE = B->end(); I != IE; ++I) {
181 if (isa<LoadInst>(I)) {
183 Changed |= optimizeMemoryInstruction(I, 0);
184 } else if (isa<StoreInst>(I)) {
186 Changed |= optimizeMemoryInstruction(I, 1);
193 FunctionPass *llvm::createNVPTXFavorNonGenericAddrSpacesPass() {
194 return new NVPTXFavorNonGenericAddrSpaces();