lib/Target/AMDGPU/AMDGPUAliasAnalysis.cpp

   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
  44 ImmutablePass *llvm::createAMDGPUAAWrapperPass() {
  45   return new AMDGPUAAWrapperPass();
  46 }
  47
  48 ImmutablePass *llvm::createAMDGPUExternalAAWrapperPass() {
  49   return new AMDGPUExternalAAWrapper();
  50 }
  51
  52 void AMDGPUAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
  53   AU.setPreservesAll();
  54 }
  55
  56 // These arrays are indexed by address space value enum elements 0 ... to 6
  57 static const AliasResult ASAliasRules[7][7] = {
  58   /*                    Flat       Global    Region    Group     Constant  Private   Constant 32-bit */
  59   /* Flat     */        {MayAlias, MayAlias, MayAlias, MayAlias, MayAlias, MayAlias, MayAlias},
  60   /* Global   */        {MayAlias, MayAlias, NoAlias , NoAlias , MayAlias, NoAlias , MayAlias},
  61   /* Region   */        {MayAlias, NoAlias , NoAlias , NoAlias,  MayAlias, NoAlias , MayAlias},
  62   /* Group    */        {MayAlias, NoAlias , NoAlias , MayAlias, NoAlias , NoAlias , NoAlias},
  63   /* Constant */        {MayAlias, MayAlias, MayAlias, NoAlias , NoAlias,  NoAlias , MayAlias},
  64   /* Private  */        {MayAlias, NoAlias , NoAlias , NoAlias , NoAlias , MayAlias, NoAlias},
  65   /* Constant 32-bit */ {MayAlias, MayAlias, MayAlias, NoAlias , MayAlias, NoAlias , NoAlias}
  66 };
  67
  68 static AliasResult getAliasResult(unsigned AS1, unsigned AS2) {
  69   static_assert(AMDGPUAS::MAX_AMDGPU_ADDRESS <= 6, "Addr space out of range");
  70
  71   if (AS1 > AMDGPUAS::MAX_AMDGPU_ADDRESS || AS2 > AMDGPUAS::MAX_AMDGPU_ADDRESS)
  72     return MayAlias;
  73
  74   return ASAliasRules[AS1][AS2];
  75 }
  76
  77 AliasResult AMDGPUAAResult::alias(const MemoryLocation &LocA,
  78                                   const MemoryLocation &LocB) {
  79   unsigned asA = LocA.Ptr->getType()->getPointerAddressSpace();
  80   unsigned asB = LocB.Ptr->getType()->getPointerAddressSpace();
  81
  82   AliasResult Result = getAliasResult(asA, asB);
  83   if (Result == NoAlias)
  84     return Result;
  85
  86   // Forward the query to the next alias analysis.
  87   return AAResultBase::alias(LocA, LocB);
  88 }
  89
  90 bool AMDGPUAAResult::pointsToConstantMemory(const MemoryLocation &Loc,
  91                                             bool OrLocal) {
  92   const Value *Base = GetUnderlyingObject(Loc.Ptr, DL);
  93   unsigned AS = Base->getType()->getPointerAddressSpace();
  94   if (AS == AMDGPUAS::CONSTANT_ADDRESS ||
  95       AS == AMDGPUAS::CONSTANT_ADDRESS_32BIT) {
  96     return true;
  97   }
  98
  99   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
 100     if (GV->isConstant())
 101       return true;
 102   } else if (const Argument *Arg = dyn_cast<Argument>(Base)) {
 103     const Function *F = Arg->getParent();
 104
 105     // Only assume constant memory for arguments on kernels.
 106     switch (F->getCallingConv()) {
 107     default:
 108       return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
 109     case CallingConv::AMDGPU_LS:
 110     case CallingConv::AMDGPU_HS:
 111     case CallingConv::AMDGPU_ES:
 112     case CallingConv::AMDGPU_GS:
 113     case CallingConv::AMDGPU_VS:
 114     case CallingConv::AMDGPU_PS:
 115     case CallingConv::AMDGPU_CS:
 116     case CallingConv::AMDGPU_KERNEL:
 117     case CallingConv::SPIR_KERNEL:
 118       break;
 119     }
 120
 121     unsigned ArgNo = Arg->getArgNo();
 122     /* On an argument, ReadOnly attribute indicates that the function does
 123        not write through this pointer argument, even though it may write
 124        to the memory that the pointer points to.
 125        On an argument, ReadNone attribute indicates that the function does
 126        not dereference that pointer argument, even though it may read or write
 127        the memory that the pointer points to if accessed through other pointers.
 128      */
 129     if (F->hasParamAttribute(ArgNo, Attribute::NoAlias) &&
 130         (F->hasParamAttribute(ArgNo, Attribute::ReadNone) ||
 131          F->hasParamAttribute(ArgNo, Attribute::ReadOnly))) {
 132       return true;
 133     }
 134   }
 135   return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
 136 }