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
createAMDGPUAAWrapperPass()32 ImmutablePass *llvm::createAMDGPUAAWrapperPass() {
33 return new AMDGPUAAWrapperPass();
34 }
35
createAMDGPUExternalAAWrapperPass()36 ImmutablePass *llvm::createAMDGPUExternalAAWrapperPass() {
37 return new AMDGPUExternalAAWrapper();
38 }
39
getAnalysisUsage(AnalysisUsage & AU) const40 void AMDGPUAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
41 AU.setPreservesAll();
42 }
43
getAliasResult(unsigned AS1,unsigned AS2)44 static AliasResult getAliasResult(unsigned AS1, unsigned AS2) {
45 static_assert(AMDGPUAS::MAX_AMDGPU_ADDRESS <= 7, "Addr space out of range");
46
47 if (AS1 > AMDGPUAS::MAX_AMDGPU_ADDRESS || AS2 > AMDGPUAS::MAX_AMDGPU_ADDRESS)
48 return AliasResult::MayAlias;
49
50 #define ASMay AliasResult::MayAlias
51 #define ASNo AliasResult::NoAlias
52 // This array is indexed by address space value enum elements 0 ... to 7
53 static const AliasResult ASAliasRules[8][8] = {
54 /* Flat Global Region Group Constant Private Const32 Buf Fat Ptr */
55 /* Flat */ {ASMay, ASMay, ASNo, ASMay, ASMay, ASMay, ASMay, ASMay},
56 /* Global */ {ASMay, ASMay, ASNo, ASNo, ASMay, ASNo, ASMay, ASMay},
57 /* Region */ {ASNo, ASNo, ASMay, ASNo, ASNo, ASNo, ASNo, ASNo},
58 /* Group */ {ASMay, ASNo, ASNo, ASMay, ASNo, ASNo, ASNo, ASNo},
59 /* Constant */ {ASMay, ASMay, ASNo, ASNo, ASNo, ASNo, ASMay, ASMay},
60 /* Private */ {ASMay, ASNo, ASNo, ASNo, ASNo, ASMay, ASNo, ASNo},
61 /* Constant 32-bit */ {ASMay, ASMay, ASNo, ASNo, ASMay, ASNo, ASNo, ASMay},
62 /* Buffer Fat Ptr */ {ASMay, ASMay, ASNo, ASNo, ASMay, ASNo, ASMay, ASMay}
63 };
64 #undef ASMay
65 #undef ASNo
66
67 return ASAliasRules[AS1][AS2];
68 }
69
alias(const MemoryLocation & LocA,const MemoryLocation & LocB,AAQueryInfo & AAQI)70 AliasResult AMDGPUAAResult::alias(const MemoryLocation &LocA,
71 const MemoryLocation &LocB,
72 AAQueryInfo &AAQI) {
73 unsigned asA = LocA.Ptr->getType()->getPointerAddressSpace();
74 unsigned asB = LocB.Ptr->getType()->getPointerAddressSpace();
75
76 AliasResult Result = getAliasResult(asA, asB);
77 if (Result == AliasResult::NoAlias)
78 return Result;
79
80 // In general, FLAT (generic) pointers could be aliased to LOCAL or PRIVATE
81 // pointers. However, as LOCAL or PRIVATE pointers point to local objects, in
82 // certain cases, it's still viable to check whether a FLAT pointer won't
83 // alias to a LOCAL or PRIVATE pointer.
84 MemoryLocation A = LocA;
85 MemoryLocation B = LocB;
86 // Canonicalize the location order to simplify the following alias check.
87 if (asA != AMDGPUAS::FLAT_ADDRESS) {
88 std::swap(asA, asB);
89 std::swap(A, B);
90 }
91 if (asA == AMDGPUAS::FLAT_ADDRESS &&
92 (asB == AMDGPUAS::LOCAL_ADDRESS || asB == AMDGPUAS::PRIVATE_ADDRESS)) {
93 const auto *ObjA =
94 getUnderlyingObject(A.Ptr->stripPointerCastsForAliasAnalysis());
95 if (const LoadInst *LI = dyn_cast<LoadInst>(ObjA)) {
96 // If a generic pointer is loaded from the constant address space, it
97 // could only be a GLOBAL or CONSTANT one as that address space is soley
98 // prepared on the host side, where only GLOBAL or CONSTANT variables are
99 // visible. Note that this even holds for regular functions.
100 if (LI->getPointerAddressSpace() == AMDGPUAS::CONSTANT_ADDRESS)
101 return AliasResult::NoAlias;
102 } else if (const Argument *Arg = dyn_cast<Argument>(ObjA)) {
103 const Function *F = Arg->getParent();
104 switch (F->getCallingConv()) {
105 case CallingConv::AMDGPU_KERNEL:
106 // In the kernel function, kernel arguments won't alias to (local)
107 // variables in shared or private address space.
108 return AliasResult::NoAlias;
109 default:
110 // TODO: In the regular function, if that local variable in the
111 // location B is not captured, that argument pointer won't alias to it
112 // as well.
113 break;
114 }
115 }
116 }
117
118 // Forward the query to the next alias analysis.
119 return AAResultBase::alias(LocA, LocB, AAQI);
120 }
121
pointsToConstantMemory(const MemoryLocation & Loc,AAQueryInfo & AAQI,bool OrLocal)122 bool AMDGPUAAResult::pointsToConstantMemory(const MemoryLocation &Loc,
123 AAQueryInfo &AAQI, bool OrLocal) {
124 unsigned AS = Loc.Ptr->getType()->getPointerAddressSpace();
125 if (AS == AMDGPUAS::CONSTANT_ADDRESS ||
126 AS == AMDGPUAS::CONSTANT_ADDRESS_32BIT)
127 return true;
128
129 const Value *Base = getUnderlyingObject(Loc.Ptr);
130 AS = Base->getType()->getPointerAddressSpace();
131 if (AS == AMDGPUAS::CONSTANT_ADDRESS ||
132 AS == AMDGPUAS::CONSTANT_ADDRESS_32BIT)
133 return true;
134
135 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
136 if (GV->isConstant())
137 return true;
138 } else if (const Argument *Arg = dyn_cast<Argument>(Base)) {
139 const Function *F = Arg->getParent();
140
141 // Only assume constant memory for arguments on kernels.
142 switch (F->getCallingConv()) {
143 default:
144 return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal);
145 case CallingConv::AMDGPU_LS:
146 case CallingConv::AMDGPU_HS:
147 case CallingConv::AMDGPU_ES:
148 case CallingConv::AMDGPU_GS:
149 case CallingConv::AMDGPU_VS:
150 case CallingConv::AMDGPU_PS:
151 case CallingConv::AMDGPU_CS:
152 case CallingConv::AMDGPU_KERNEL:
153 case CallingConv::SPIR_KERNEL:
154 break;
155 }
156
157 unsigned ArgNo = Arg->getArgNo();
158 /* On an argument, ReadOnly attribute indicates that the function does
159 not write through this pointer argument, even though it may write
160 to the memory that the pointer points to.
161 On an argument, ReadNone attribute indicates that the function does
162 not dereference that pointer argument, even though it may read or write
163 the memory that the pointer points to if accessed through other pointers.
164 */
165 if (F->hasParamAttribute(ArgNo, Attribute::NoAlias) &&
166 (F->hasParamAttribute(ArgNo, Attribute::ReadNone) ||
167 F->hasParamAttribute(ArgNo, Attribute::ReadOnly))) {
168 return true;
169 }
170 }
171 return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal);
172 }
173