1 //===- AMDGPUAliasAnalysis ------------------------------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 /// \file
10 /// This is the AMGPU address space based alias analysis pass.
11 //===----------------------------------------------------------------------===//
12 
13 #include "AMDGPUAliasAnalysis.h"
14 #include "AMDGPU.h"
15 #include "llvm/ADT/Triple.h"
16 #include "llvm/Analysis/AliasAnalysis.h"
17 #include "llvm/Analysis/MemoryLocation.h"
18 #include "llvm/Analysis/ValueTracking.h"
19 #include "llvm/IR/Argument.h"
20 #include "llvm/IR/Attributes.h"
21 #include "llvm/IR/CallingConv.h"
22 #include "llvm/IR/Function.h"
23 #include "llvm/IR/GlobalVariable.h"
24 #include "llvm/IR/Type.h"
25 #include "llvm/IR/Value.h"
26 #include "llvm/Pass.h"
27 #include "llvm/Support/Casting.h"
28 #include "llvm/Support/ErrorHandling.h"
29 #include <cassert>
30 
31 using namespace llvm;
32 
33 #define DEBUG_TYPE "amdgpu-aa"
34 
35 // Register this pass...
36 char AMDGPUAAWrapperPass::ID = 0;
37 
38 INITIALIZE_PASS(AMDGPUAAWrapperPass, "amdgpu-aa",
39                 "AMDGPU Address space based Alias Analysis", false, true)
40 
41 ImmutablePass *llvm::createAMDGPUAAWrapperPass() {
42   return new AMDGPUAAWrapperPass();
43 }
44 
45 void AMDGPUAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
46   AU.setPreservesAll();
47 }
48 
49 // Must match the table in getAliasResult.
50 AMDGPUAAResult::ASAliasRulesTy::ASAliasRulesTy(Triple::ArchType Arch_)
51   : Arch(Arch_) {
52   // These arrarys are indexed by address space value
53   // enum elements 0 ... to 6
54   static const AliasResult ASAliasRulesGenIsZero[7][7] = {
55   /*                    Flat       Global    Region    Group     Constant  Private   Constant 32-bit */
56   /* Flat     */        {MayAlias, MayAlias, MayAlias, MayAlias, MayAlias, MayAlias, MayAlias},
57   /* Global   */        {MayAlias, MayAlias, NoAlias , NoAlias , MayAlias, NoAlias , MayAlias},
58   /* Region   */        {MayAlias, NoAlias , NoAlias , NoAlias,  MayAlias, NoAlias , MayAlias},
59   /* Group    */        {MayAlias, NoAlias , NoAlias , MayAlias, NoAlias , NoAlias , NoAlias},
60   /* Constant */        {MayAlias, MayAlias, MayAlias, NoAlias , NoAlias,  NoAlias , MayAlias},
61   /* Private  */        {MayAlias, NoAlias , NoAlias , NoAlias , NoAlias , MayAlias, NoAlias},
62   /* Constant 32-bit */ {MayAlias, MayAlias, MayAlias, NoAlias , MayAlias, NoAlias , NoAlias}
63   };
64 
65   static_assert(AMDGPUAS::MAX_AMDGPU_ADDRESS <= 6, "Addr space out of range");
66 
67   ASAliasRules = &ASAliasRulesGenIsZero;
68 }
69 
70 AliasResult AMDGPUAAResult::ASAliasRulesTy::getAliasResult(unsigned AS1,
71     unsigned AS2) const {
72   if (AS1 > AMDGPUAS::MAX_AMDGPU_ADDRESS || AS2 > AMDGPUAS::MAX_AMDGPU_ADDRESS) {
73     if (Arch == Triple::amdgcn)
74       report_fatal_error("Pointer address space out of range");
75     return AS1 == AS2 ? MayAlias : NoAlias;
76   }
77 
78   return (*ASAliasRules)[AS1][AS2];
79 }
80 
81 AliasResult AMDGPUAAResult::alias(const MemoryLocation &LocA,
82                                   const MemoryLocation &LocB) {
83   unsigned asA = LocA.Ptr->getType()->getPointerAddressSpace();
84   unsigned asB = LocB.Ptr->getType()->getPointerAddressSpace();
85 
86   AliasResult Result = ASAliasRules.getAliasResult(asA, asB);
87   if (Result == NoAlias) return Result;
88 
89   // Forward the query to the next alias analysis.
90   return AAResultBase::alias(LocA, LocB);
91 }
92 
93 bool AMDGPUAAResult::pointsToConstantMemory(const MemoryLocation &Loc,
94                                             bool OrLocal) {
95   const Value *Base = GetUnderlyingObject(Loc.Ptr, DL);
96   unsigned AS = Base->getType()->getPointerAddressSpace();
97   if (AS == AMDGPUAS::CONSTANT_ADDRESS ||
98       AS == AMDGPUAS::CONSTANT_ADDRESS_32BIT) {
99     return true;
100   }
101 
102   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
103     if (GV->isConstant())
104       return true;
105   } else if (const Argument *Arg = dyn_cast<Argument>(Base)) {
106     const Function *F = Arg->getParent();
107 
108     // Only assume constant memory for arguments on kernels.
109     switch (F->getCallingConv()) {
110     default:
111       return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
112     case CallingConv::AMDGPU_LS:
113     case CallingConv::AMDGPU_HS:
114     case CallingConv::AMDGPU_ES:
115     case CallingConv::AMDGPU_GS:
116     case CallingConv::AMDGPU_VS:
117     case CallingConv::AMDGPU_PS:
118     case CallingConv::AMDGPU_CS:
119     case CallingConv::AMDGPU_KERNEL:
120     case CallingConv::SPIR_KERNEL:
121       break;
122     }
123 
124     unsigned ArgNo = Arg->getArgNo();
125     /* On an argument, ReadOnly attribute indicates that the function does
126        not write through this pointer argument, even though it may write
127        to the memory that the pointer points to.
128        On an argument, ReadNone attribute indicates that the function does
129        not dereference that pointer argument, even though it may read or write
130        the memory that the pointer points to if accessed through other pointers.
131      */
132     if (F->hasParamAttribute(ArgNo, Attribute::NoAlias) &&
133         (F->hasParamAttribute(ArgNo, Attribute::ReadNone) ||
134          F->hasParamAttribute(ArgNo, Attribute::ReadOnly))) {
135       return true;
136     }
137   }
138   return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
139 }
140