1 //===- AMDGPUAliasAnalysis ------------------------------------------------===// 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 /// \file 9 /// This is the AMGPU address space based alias analysis pass. 10 //===----------------------------------------------------------------------===// 11 12 #include "AMDGPUAliasAnalysis.h" 13 #include "AMDGPU.h" 14 #include "llvm/Analysis/ValueTracking.h" 15 #include "llvm/IR/Instructions.h" 16 17 using namespace llvm; 18 19 #define DEBUG_TYPE "amdgpu-aa" 20 21 AnalysisKey AMDGPUAA::Key; 22 23 // Register this pass... 24 char AMDGPUAAWrapperPass::ID = 0; 25 char AMDGPUExternalAAWrapper::ID = 0; 26 27 INITIALIZE_PASS(AMDGPUAAWrapperPass, "amdgpu-aa", 28 "AMDGPU Address space based Alias Analysis", false, true) 29 30 INITIALIZE_PASS(AMDGPUExternalAAWrapper, "amdgpu-aa-wrapper", 31 "AMDGPU Address space based Alias Analysis Wrapper", false, true) 32 33 ImmutablePass *llvm::createAMDGPUAAWrapperPass() { 34 return new AMDGPUAAWrapperPass(); 35 } 36 37 ImmutablePass *llvm::createAMDGPUExternalAAWrapperPass() { 38 return new AMDGPUExternalAAWrapper(); 39 } 40 41 AMDGPUAAWrapperPass::AMDGPUAAWrapperPass() : ImmutablePass(ID) { 42 initializeAMDGPUAAWrapperPassPass(*PassRegistry::getPassRegistry()); 43 } 44 45 void AMDGPUAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { 46 AU.setPreservesAll(); 47 } 48 49 static AliasResult getAliasResult(unsigned AS1, unsigned AS2) { 50 static_assert(AMDGPUAS::MAX_AMDGPU_ADDRESS <= 7, "Addr space out of range"); 51 52 if (AS1 > AMDGPUAS::MAX_AMDGPU_ADDRESS || AS2 > AMDGPUAS::MAX_AMDGPU_ADDRESS) 53 return AliasResult::MayAlias; 54 55 #define ASMay AliasResult::MayAlias 56 #define ASNo AliasResult::NoAlias 57 // This array is indexed by address space value enum elements 0 ... to 7 58 static const AliasResult ASAliasRules[8][8] = { 59 /* Flat Global Region Group Constant Private Const32 Buf Fat Ptr */ 60 /* Flat */ {ASMay, ASMay, ASNo, ASMay, ASMay, ASMay, ASMay, ASMay}, 61 /* Global */ {ASMay, ASMay, ASNo, ASNo, ASMay, ASNo, ASMay, ASMay}, 62 /* Region */ {ASNo, ASNo, ASMay, ASNo, ASNo, ASNo, ASNo, ASNo}, 63 /* Group */ {ASMay, ASNo, ASNo, ASMay, ASNo, ASNo, ASNo, ASNo}, 64 /* Constant */ {ASMay, ASMay, ASNo, ASNo, ASNo, ASNo, ASMay, ASMay}, 65 /* Private */ {ASMay, ASNo, ASNo, ASNo, ASNo, ASMay, ASNo, ASNo}, 66 /* Constant 32-bit */ {ASMay, ASMay, ASNo, ASNo, ASMay, ASNo, ASNo, ASMay}, 67 /* Buffer Fat Ptr */ {ASMay, ASMay, ASNo, ASNo, ASMay, ASNo, ASMay, ASMay} 68 }; 69 #undef ASMay 70 #undef ASNo 71 72 return ASAliasRules[AS1][AS2]; 73 } 74 75 AliasResult AMDGPUAAResult::alias(const MemoryLocation &LocA, 76 const MemoryLocation &LocB, 77 AAQueryInfo &AAQI) { 78 unsigned asA = LocA.Ptr->getType()->getPointerAddressSpace(); 79 unsigned asB = LocB.Ptr->getType()->getPointerAddressSpace(); 80 81 AliasResult Result = getAliasResult(asA, asB); 82 if (Result == AliasResult::NoAlias) 83 return Result; 84 85 // In general, FLAT (generic) pointers could be aliased to LOCAL or PRIVATE 86 // pointers. However, as LOCAL or PRIVATE pointers point to local objects, in 87 // certain cases, it's still viable to check whether a FLAT pointer won't 88 // alias to a LOCAL or PRIVATE pointer. 89 MemoryLocation A = LocA; 90 MemoryLocation B = LocB; 91 // Canonicalize the location order to simplify the following alias check. 92 if (asA != AMDGPUAS::FLAT_ADDRESS) { 93 std::swap(asA, asB); 94 std::swap(A, B); 95 } 96 if (asA == AMDGPUAS::FLAT_ADDRESS && 97 (asB == AMDGPUAS::LOCAL_ADDRESS || asB == AMDGPUAS::PRIVATE_ADDRESS)) { 98 const auto *ObjA = 99 getUnderlyingObject(A.Ptr->stripPointerCastsForAliasAnalysis()); 100 if (const LoadInst *LI = dyn_cast<LoadInst>(ObjA)) { 101 // If a generic pointer is loaded from the constant address space, it 102 // could only be a GLOBAL or CONSTANT one as that address space is solely 103 // prepared on the host side, where only GLOBAL or CONSTANT variables are 104 // visible. Note that this even holds for regular functions. 105 if (LI->getPointerAddressSpace() == AMDGPUAS::CONSTANT_ADDRESS) 106 return AliasResult::NoAlias; 107 } else if (const Argument *Arg = dyn_cast<Argument>(ObjA)) { 108 const Function *F = Arg->getParent(); 109 switch (F->getCallingConv()) { 110 case CallingConv::AMDGPU_KERNEL: 111 // In the kernel function, kernel arguments won't alias to (local) 112 // variables in shared or private address space. 113 return AliasResult::NoAlias; 114 default: 115 // TODO: In the regular function, if that local variable in the 116 // location B is not captured, that argument pointer won't alias to it 117 // as well. 118 break; 119 } 120 } 121 } 122 123 // Forward the query to the next alias analysis. 124 return AAResultBase::alias(LocA, LocB, AAQI); 125 } 126 127 bool AMDGPUAAResult::pointsToConstantMemory(const MemoryLocation &Loc, 128 AAQueryInfo &AAQI, bool OrLocal) { 129 unsigned AS = Loc.Ptr->getType()->getPointerAddressSpace(); 130 if (AS == AMDGPUAS::CONSTANT_ADDRESS || 131 AS == AMDGPUAS::CONSTANT_ADDRESS_32BIT) 132 return true; 133 134 const Value *Base = getUnderlyingObject(Loc.Ptr); 135 AS = Base->getType()->getPointerAddressSpace(); 136 if (AS == AMDGPUAS::CONSTANT_ADDRESS || 137 AS == AMDGPUAS::CONSTANT_ADDRESS_32BIT) 138 return true; 139 140 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) { 141 if (GV->isConstant()) 142 return true; 143 } else if (const Argument *Arg = dyn_cast<Argument>(Base)) { 144 const Function *F = Arg->getParent(); 145 146 // Only assume constant memory for arguments on kernels. 147 switch (F->getCallingConv()) { 148 default: 149 return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal); 150 case CallingConv::AMDGPU_LS: 151 case CallingConv::AMDGPU_HS: 152 case CallingConv::AMDGPU_ES: 153 case CallingConv::AMDGPU_GS: 154 case CallingConv::AMDGPU_VS: 155 case CallingConv::AMDGPU_PS: 156 case CallingConv::AMDGPU_CS: 157 case CallingConv::AMDGPU_KERNEL: 158 case CallingConv::SPIR_KERNEL: 159 break; 160 } 161 162 unsigned ArgNo = Arg->getArgNo(); 163 /* On an argument, ReadOnly attribute indicates that the function does 164 not write through this pointer argument, even though it may write 165 to the memory that the pointer points to. 166 On an argument, ReadNone attribute indicates that the function does 167 not dereference that pointer argument, even though it may read or write 168 the memory that the pointer points to if accessed through other pointers. 169 */ 170 if (F->hasParamAttribute(ArgNo, Attribute::NoAlias) && 171 (F->hasParamAttribute(ArgNo, Attribute::ReadNone) || 172 F->hasParamAttribute(ArgNo, Attribute::ReadOnly))) { 173 return true; 174 } 175 } 176 return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal); 177 } 178