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