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/ADT/Triple.h"
15 #include "llvm/Analysis/AliasAnalysis.h"
16 #include "llvm/Analysis/MemoryLocation.h"
17 #include "llvm/Analysis/ValueTracking.h"
18 #include "llvm/IR/Argument.h"
19 #include "llvm/IR/Attributes.h"
20 #include "llvm/IR/CallingConv.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/IR/GlobalVariable.h"
23 #include "llvm/IR/Type.h"
24 #include "llvm/IR/Value.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Support/Casting.h"
27 #include "llvm/Support/ErrorHandling.h"
28 #include <cassert>
29
30 using namespace llvm;
31
32 #define DEBUG_TYPE "amdgpu-aa"
33
34 // Register this pass...
35 char AMDGPUAAWrapperPass::ID = 0;
36 char AMDGPUExternalAAWrapper::ID = 0;
37
38 INITIALIZE_PASS(AMDGPUAAWrapperPass, "amdgpu-aa",
39 "AMDGPU Address space based Alias Analysis", false, true)
40
41 INITIALIZE_PASS(AMDGPUExternalAAWrapper, "amdgpu-aa-wrapper",
42 "AMDGPU Address space based Alias Analysis Wrapper", false, true)
43
createAMDGPUAAWrapperPass()44 ImmutablePass *llvm::createAMDGPUAAWrapperPass() {
45 return new AMDGPUAAWrapperPass();
46 }
47
createAMDGPUExternalAAWrapperPass()48 ImmutablePass *llvm::createAMDGPUExternalAAWrapperPass() {
49 return new AMDGPUExternalAAWrapper();
50 }
51
getAnalysisUsage(AnalysisUsage & AU) const52 void AMDGPUAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
53 AU.setPreservesAll();
54 }
55
56 // These arrays are indexed by address space value enum elements 0 ... to 7
57 static const AliasResult ASAliasRules[8][8] = {
58 /* Flat Global Region Group Constant Private Constant 32-bit Buffer Fat Ptr */
59 /* Flat */ {MayAlias, MayAlias, NoAlias, MayAlias, MayAlias, MayAlias, MayAlias, MayAlias},
60 /* Global */ {MayAlias, MayAlias, NoAlias , NoAlias , MayAlias, NoAlias , MayAlias, MayAlias},
61 /* Region */ {NoAlias, NoAlias , MayAlias, NoAlias , NoAlias, NoAlias , NoAlias, NoAlias},
62 /* Group */ {MayAlias, NoAlias , NoAlias , MayAlias, NoAlias , NoAlias , NoAlias , NoAlias},
63 /* Constant */ {MayAlias, MayAlias, NoAlias, NoAlias , NoAlias , NoAlias , MayAlias, MayAlias},
64 /* Private */ {MayAlias, NoAlias , NoAlias , NoAlias , NoAlias , MayAlias, NoAlias , NoAlias},
65 /* Constant 32-bit */ {MayAlias, MayAlias, NoAlias, NoAlias , MayAlias, NoAlias , NoAlias , MayAlias},
66 /* Buffer Fat Ptr */ {MayAlias, MayAlias, NoAlias , NoAlias , MayAlias, NoAlias , MayAlias, MayAlias}
67 };
68
getAliasResult(unsigned AS1,unsigned AS2)69 static AliasResult getAliasResult(unsigned AS1, unsigned AS2) {
70 static_assert(AMDGPUAS::MAX_AMDGPU_ADDRESS <= 7, "Addr space out of range");
71
72 if (AS1 > AMDGPUAS::MAX_AMDGPU_ADDRESS || AS2 > AMDGPUAS::MAX_AMDGPU_ADDRESS)
73 return MayAlias;
74
75 return ASAliasRules[AS1][AS2];
76 }
77
alias(const MemoryLocation & LocA,const MemoryLocation & LocB,AAQueryInfo & AAQI)78 AliasResult AMDGPUAAResult::alias(const MemoryLocation &LocA,
79 const MemoryLocation &LocB,
80 AAQueryInfo &AAQI) {
81 unsigned asA = LocA.Ptr->getType()->getPointerAddressSpace();
82 unsigned asB = LocB.Ptr->getType()->getPointerAddressSpace();
83
84 AliasResult Result = getAliasResult(asA, asB);
85 if (Result == NoAlias)
86 return Result;
87
88 // Forward the query to the next alias analysis.
89 return AAResultBase::alias(LocA, LocB, AAQI);
90 }
91
pointsToConstantMemory(const MemoryLocation & Loc,AAQueryInfo & AAQI,bool OrLocal)92 bool AMDGPUAAResult::pointsToConstantMemory(const MemoryLocation &Loc,
93 AAQueryInfo &AAQI, bool OrLocal) {
94 const Value *Base = GetUnderlyingObject(Loc.Ptr, DL);
95 unsigned AS = Base->getType()->getPointerAddressSpace();
96 if (AS == AMDGPUAS::CONSTANT_ADDRESS ||
97 AS == AMDGPUAS::CONSTANT_ADDRESS_32BIT) {
98 return true;
99 }
100
101 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
102 if (GV->isConstant())
103 return true;
104 } else if (const Argument *Arg = dyn_cast<Argument>(Base)) {
105 const Function *F = Arg->getParent();
106
107 // Only assume constant memory for arguments on kernels.
108 switch (F->getCallingConv()) {
109 default:
110 return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal);
111 case CallingConv::AMDGPU_LS:
112 case CallingConv::AMDGPU_HS:
113 case CallingConv::AMDGPU_ES:
114 case CallingConv::AMDGPU_GS:
115 case CallingConv::AMDGPU_VS:
116 case CallingConv::AMDGPU_PS:
117 case CallingConv::AMDGPU_CS:
118 case CallingConv::AMDGPU_KERNEL:
119 case CallingConv::SPIR_KERNEL:
120 break;
121 }
122
123 unsigned ArgNo = Arg->getArgNo();
124 /* On an argument, ReadOnly attribute indicates that the function does
125 not write through this pointer argument, even though it may write
126 to the memory that the pointer points to.
127 On an argument, ReadNone attribute indicates that the function does
128 not dereference that pointer argument, even though it may read or write
129 the memory that the pointer points to if accessed through other pointers.
130 */
131 if (F->hasParamAttribute(ArgNo, Attribute::NoAlias) &&
132 (F->hasParamAttribute(ArgNo, Attribute::ReadNone) ||
133 F->hasParamAttribute(ArgNo, Attribute::ReadOnly))) {
134 return true;
135 }
136 }
137 return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal);
138 }
139