lib/Target/AMDGPU/AMDGPUAliasAnalysis.cpp

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