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 char AMDGPUExternalAAWrapper::ID = 0;
38 
39 INITIALIZE_PASS(AMDGPUAAWrapperPass, "amdgpu-aa",
40                 "AMDGPU Address space based Alias Analysis", false, true)
41 
42 INITIALIZE_PASS(AMDGPUExternalAAWrapper, "amdgpu-aa-wrapper",
43                 "AMDGPU Address space based Alias Analysis Wrapper", false, true)
44 
45 ImmutablePass *llvm::createAMDGPUAAWrapperPass() {
46   return new AMDGPUAAWrapperPass();
47 }
48 
49 ImmutablePass *llvm::createAMDGPUExternalAAWrapperPass() {
50   return new AMDGPUExternalAAWrapper();
51 }
52 
53 void AMDGPUAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
54   AU.setPreservesAll();
55 }
56 
57 // These arrays are indexed by address space value enum elements 0 ... to 6
58 static const AliasResult ASAliasRules[7][7] = {
59   /*                    Flat       Global    Region    Group     Constant  Private   Constant 32-bit */
60   /* Flat     */        {MayAlias, MayAlias, MayAlias, MayAlias, MayAlias, MayAlias, MayAlias},
61   /* Global   */        {MayAlias, MayAlias, NoAlias , NoAlias , MayAlias, NoAlias , MayAlias},
62   /* Region   */        {MayAlias, NoAlias , NoAlias , NoAlias,  MayAlias, NoAlias , MayAlias},
63   /* Group    */        {MayAlias, NoAlias , NoAlias , MayAlias, NoAlias , NoAlias , NoAlias},
64   /* Constant */        {MayAlias, MayAlias, MayAlias, NoAlias , NoAlias,  NoAlias , MayAlias},
65   /* Private  */        {MayAlias, NoAlias , NoAlias , NoAlias , NoAlias , MayAlias, NoAlias},
66   /* Constant 32-bit */ {MayAlias, MayAlias, MayAlias, NoAlias , MayAlias, NoAlias , NoAlias}
67 };
68 
69 static AliasResult getAliasResult(unsigned AS1, unsigned AS2) {
70   static_assert(AMDGPUAS::MAX_AMDGPU_ADDRESS <= 6, "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 
78 AliasResult AMDGPUAAResult::alias(const MemoryLocation &LocA,
79                                   const MemoryLocation &LocB) {
80   unsigned asA = LocA.Ptr->getType()->getPointerAddressSpace();
81   unsigned asB = LocB.Ptr->getType()->getPointerAddressSpace();
82 
83   AliasResult Result = getAliasResult(asA, asB);
84   if (Result == NoAlias)
85     return Result;
86 
87   // Forward the query to the next alias analysis.
88   return AAResultBase::alias(LocA, LocB);
89 }
90 
91 bool AMDGPUAAResult::pointsToConstantMemory(const MemoryLocation &Loc,
92                                             bool OrLocal) {
93   const Value *Base = GetUnderlyingObject(Loc.Ptr, DL);
94   unsigned AS = Base->getType()->getPointerAddressSpace();
95   if (AS == AMDGPUAS::CONSTANT_ADDRESS ||
96       AS == AMDGPUAS::CONSTANT_ADDRESS_32BIT) {
97     return true;
98   }
99 
100   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
101     if (GV->isConstant())
102       return true;
103   } else if (const Argument *Arg = dyn_cast<Argument>(Base)) {
104     const Function *F = Arg->getParent();
105 
106     // Only assume constant memory for arguments on kernels.
107     switch (F->getCallingConv()) {
108     default:
109       return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
110     case CallingConv::AMDGPU_LS:
111     case CallingConv::AMDGPU_HS:
112     case CallingConv::AMDGPU_ES:
113     case CallingConv::AMDGPU_GS:
114     case CallingConv::AMDGPU_VS:
115     case CallingConv::AMDGPU_PS:
116     case CallingConv::AMDGPU_CS:
117     case CallingConv::AMDGPU_KERNEL:
118     case CallingConv::SPIR_KERNEL:
119       break;
120     }
121 
122     unsigned ArgNo = Arg->getArgNo();
123     /* On an argument, ReadOnly attribute indicates that the function does
124        not write through this pointer argument, even though it may write
125        to the memory that the pointer points to.
126        On an argument, ReadNone attribute indicates that the function does
127        not dereference that pointer argument, even though it may read or write
128        the memory that the pointer points to if accessed through other pointers.
129      */
130     if (F->hasParamAttribute(ArgNo, Attribute::NoAlias) &&
131         (F->hasParamAttribute(ArgNo, Attribute::ReadNone) ||
132          F->hasParamAttribute(ArgNo, Attribute::ReadOnly))) {
133       return true;
134     }
135   }
136   return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
137 }
138