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 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
  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
  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
  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 }