DXILResourceAccess.cpp

//===- DXILResourceAccess.cpp - Resource access via load/store ------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "DXILResourceAccess.h"
#include "DirectX.h"
#include "llvm/Analysis/DXILResource.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/IntrinsicsDirectX.h"
#include "llvm/InitializePasses.h"

#define DEBUG_TYPE "dxil-resource-access"

using namespace llvm;

static Value *calculateGEPOffset(GetElementPtrInst *GEP, Value *PrevOffset,
                                 dxil::ResourceTypeInfo &RTI) {
  assert(!PrevOffset && "Non-constant GEP chains not handled yet");

  const DataLayout &DL = GEP->getDataLayout();

  uint64_t ScalarSize = 1;
  if (RTI.isTyped()) {
    Type *ContainedType = RTI.getHandleTy()->getTypeParameter(0);
    // We need the size of an element in bytes so that we can calculate the
    // offset in elements given a total offset in bytes.
    Type *ScalarType = ContainedType->getScalarType();
    ScalarSize = DL.getTypeSizeInBits(ScalarType) / 8;
  }

  APInt ConstantOffset(DL.getIndexTypeSizeInBits(GEP->getType()), 0);
  if (GEP->accumulateConstantOffset(DL, ConstantOffset)) {
    APInt Scaled = ConstantOffset.udiv(ScalarSize);
    return ConstantInt::get(Type::getInt32Ty(GEP->getContext()), Scaled);
  }

  auto IndexIt = GEP->idx_begin();
  assert(cast<ConstantInt>(IndexIt)->getZExtValue() == 0 &&
         "GEP is not indexing through pointer");
  ++IndexIt;
  Value *Offset = *IndexIt;
  assert(++IndexIt == GEP->idx_end() && "Too many indices in GEP");
  return Offset;
}

static void createTypedBufferStore(IntrinsicInst *II, StoreInst *SI,
                                   Value *Offset, dxil::ResourceTypeInfo &RTI) {
  IRBuilder<> Builder(SI);
  Type *ContainedType = RTI.getHandleTy()->getTypeParameter(0);
  Type *LoadType = StructType::get(ContainedType, Builder.getInt1Ty());

  Value *V = SI->getValueOperand();
  if (V->getType() == ContainedType) {
    // V is already the right type.
    assert(!Offset && "store of whole element has offset?");
  } else if (V->getType() == ContainedType->getScalarType()) {
    // We're storing a scalar, so we need to load the current value and only
    // replace the relevant part.
    auto *Load = Builder.CreateIntrinsic(
        LoadType, Intrinsic::dx_resource_load_typedbuffer,
        {II->getOperand(0), II->getOperand(1)});
    auto *Struct = Builder.CreateExtractValue(Load, {0});

    // If we have an offset from seeing a GEP earlier, use that. Otherwise, 0.
    if (!Offset)
      Offset = ConstantInt::get(Builder.getInt32Ty(), 0);
    V = Builder.CreateInsertElement(Struct, V, Offset);
  } else {
    llvm_unreachable("Store to typed resource has invalid type");
  }

  auto *Inst = Builder.CreateIntrinsic(
      Builder.getVoidTy(), Intrinsic::dx_resource_store_typedbuffer,
      {II->getOperand(0), II->getOperand(1), V});
  SI->replaceAllUsesWith(Inst);
}

static void createRawStore(IntrinsicInst *II, StoreInst *SI, Value *Offset) {
  IRBuilder<> Builder(SI);

  if (!Offset)
    Offset = ConstantInt::get(Builder.getInt32Ty(), 0);
  Value *V = SI->getValueOperand();
  // TODO: break up larger types
  auto *Inst = Builder.CreateIntrinsic(
      Builder.getVoidTy(), Intrinsic::dx_resource_store_rawbuffer,
      {II->getOperand(0), II->getOperand(1), Offset, V});
  SI->replaceAllUsesWith(Inst);
}

static void createStoreIntrinsic(IntrinsicInst *II, StoreInst *SI,
                                 Value *Offset, dxil::ResourceTypeInfo &RTI) {
  switch (RTI.getResourceKind()) {
  case dxil::ResourceKind::TypedBuffer:
    return createTypedBufferStore(II, SI, Offset, RTI);
  case dxil::ResourceKind::RawBuffer:
  case dxil::ResourceKind::StructuredBuffer:
    return createRawStore(II, SI, Offset);
  case dxil::ResourceKind::Texture1D:
  case dxil::ResourceKind::Texture2D:
  case dxil::ResourceKind::Texture2DMS:
  case dxil::ResourceKind::Texture3D:
  case dxil::ResourceKind::TextureCube:
  case dxil::ResourceKind::Texture1DArray:
  case dxil::ResourceKind::Texture2DArray:
  case dxil::ResourceKind::Texture2DMSArray:
  case dxil::ResourceKind::TextureCubeArray:
  case dxil::ResourceKind::FeedbackTexture2D:
  case dxil::ResourceKind::FeedbackTexture2DArray:
    reportFatalUsageError("DXIL Load not implemented yet");
    return;
  case dxil::ResourceKind::CBuffer:
  case dxil::ResourceKind::Sampler:
  case dxil::ResourceKind::TBuffer:
  case dxil::ResourceKind::RTAccelerationStructure:
  case dxil::ResourceKind::Invalid:
  case dxil::ResourceKind::NumEntries:
    llvm_unreachable("Invalid resource kind for store");
  }
  llvm_unreachable("Unhandled case in switch");
}

static void createTypedBufferLoad(IntrinsicInst *II, LoadInst *LI,
                                  Value *Offset, dxil::ResourceTypeInfo &RTI) {
  IRBuilder<> Builder(LI);
  Type *ContainedType = RTI.getHandleTy()->getTypeParameter(0);
  Type *LoadType = StructType::get(ContainedType, Builder.getInt1Ty());

  Value *V =
      Builder.CreateIntrinsic(LoadType, Intrinsic::dx_resource_load_typedbuffer,
                              {II->getOperand(0), II->getOperand(1)});
  V = Builder.CreateExtractValue(V, {0});

  if (Offset)
    V = Builder.CreateExtractElement(V, Offset);

  // If we loaded a <1 x ...> instead of a scalar (presumably to feed a
  // shufflevector), then make sure we're maintaining the resulting type.
  if (auto *VT = dyn_cast<FixedVectorType>(LI->getType()))
    if (VT->getNumElements() == 1 && !isa<FixedVectorType>(V->getType()))
      V = Builder.CreateInsertElement(PoisonValue::get(VT), V,
                                      Builder.getInt32(0));

  LI->replaceAllUsesWith(V);
}

static void createRawLoad(IntrinsicInst *II, LoadInst *LI, Value *Offset) {
  IRBuilder<> Builder(LI);
  // TODO: break up larger types
  Type *LoadType = StructType::get(LI->getType(), Builder.getInt1Ty());
  if (!Offset)
    Offset = ConstantInt::get(Builder.getInt32Ty(), 0);
  Value *V =
      Builder.CreateIntrinsic(LoadType, Intrinsic::dx_resource_load_rawbuffer,
                              {II->getOperand(0), II->getOperand(1), Offset});
  V = Builder.CreateExtractValue(V, {0});

  LI->replaceAllUsesWith(V);
}

static void createLoadIntrinsic(IntrinsicInst *II, LoadInst *LI, Value *Offset,
                                dxil::ResourceTypeInfo &RTI) {
  switch (RTI.getResourceKind()) {
  case dxil::ResourceKind::TypedBuffer:
    return createTypedBufferLoad(II, LI, Offset, RTI);
  case dxil::ResourceKind::RawBuffer:
  case dxil::ResourceKind::StructuredBuffer:
    return createRawLoad(II, LI, Offset);
  case dxil::ResourceKind::Texture1D:
  case dxil::ResourceKind::Texture2D:
  case dxil::ResourceKind::Texture2DMS:
  case dxil::ResourceKind::Texture3D:
  case dxil::ResourceKind::TextureCube:
  case dxil::ResourceKind::Texture1DArray:
  case dxil::ResourceKind::Texture2DArray:
  case dxil::ResourceKind::Texture2DMSArray:
  case dxil::ResourceKind::TextureCubeArray:
  case dxil::ResourceKind::FeedbackTexture2D:
  case dxil::ResourceKind::FeedbackTexture2DArray:
  case dxil::ResourceKind::CBuffer:
  case dxil::ResourceKind::TBuffer:
    // TODO: handle these
    return;
  case dxil::ResourceKind::Sampler:
  case dxil::ResourceKind::RTAccelerationStructure:
  case dxil::ResourceKind::Invalid:
  case dxil::ResourceKind::NumEntries:
    llvm_unreachable("Invalid resource kind for load");
  }
  llvm_unreachable("Unhandled case in switch");
}

static void replaceAccess(IntrinsicInst *II, dxil::ResourceTypeInfo &RTI) {
  // Process users keeping track of indexing accumulated from GEPs.
  struct AccessAndOffset {
    User *Access;
    Value *Offset;
  };
  SmallVector<AccessAndOffset> Worklist;
  for (User *U : II->users())
    Worklist.push_back({U, nullptr});

  SmallVector<Instruction *> DeadInsts;
  while (!Worklist.empty()) {
    AccessAndOffset Current = Worklist.back();
    Worklist.pop_back();

    if (auto *GEP = dyn_cast<GetElementPtrInst>(Current.Access)) {
      IRBuilder<> Builder(GEP);

      Value *Offset = calculateGEPOffset(GEP, Current.Offset, RTI);
      for (User *U : GEP->users())
        Worklist.push_back({U, Offset});
      DeadInsts.push_back(GEP);

    } else if (auto *SI = dyn_cast<StoreInst>(Current.Access)) {
      assert(SI->getValueOperand() != II && "Pointer escaped!");
      createStoreIntrinsic(II, SI, Current.Offset, RTI);
      DeadInsts.push_back(SI);

    } else if (auto *LI = dyn_cast<LoadInst>(Current.Access)) {
      createLoadIntrinsic(II, LI, Current.Offset, RTI);
      DeadInsts.push_back(LI);

    } else
      llvm_unreachable("Unhandled instruction - pointer escaped?");
  }

  // Traverse the now-dead instructions in RPO and remove them.
  for (Instruction *Dead : llvm::reverse(DeadInsts))
    Dead->eraseFromParent();
  II->eraseFromParent();
}

static bool transformResourcePointers(Function &F, DXILResourceTypeMap &DRTM) {
  bool Changed = false;
  SmallVector<std::pair<IntrinsicInst *, dxil::ResourceTypeInfo>> Resources;
  for (BasicBlock &BB : F)
    for (Instruction &I : BB)
      if (auto *II = dyn_cast<IntrinsicInst>(&I))
        if (II->getIntrinsicID() == Intrinsic::dx_resource_getpointer) {
          auto *HandleTy = cast<TargetExtType>(II->getArgOperand(0)->getType());
          Resources.emplace_back(II, DRTM[HandleTy]);
        }

  for (auto &[II, RI] : Resources)
    replaceAccess(II, RI);

  return Changed;
}

PreservedAnalyses DXILResourceAccess::run(Function &F,
                                          FunctionAnalysisManager &FAM) {
  auto &MAMProxy = FAM.getResult<ModuleAnalysisManagerFunctionProxy>(F);
  DXILResourceTypeMap *DRTM =
      MAMProxy.getCachedResult<DXILResourceTypeAnalysis>(*F.getParent());
  assert(DRTM && "DXILResourceTypeAnalysis must be available");

  bool MadeChanges = transformResourcePointers(F, *DRTM);
  if (!MadeChanges)
    return PreservedAnalyses::all();

  PreservedAnalyses PA;
  PA.preserve<DXILResourceTypeAnalysis>();
  PA.preserve<DominatorTreeAnalysis>();
  return PA;
}

namespace {
class DXILResourceAccessLegacy : public FunctionPass {
public:
  bool runOnFunction(Function &F) override {
    DXILResourceTypeMap &DRTM =
        getAnalysis<DXILResourceTypeWrapperPass>().getResourceTypeMap();

    return transformResourcePointers(F, DRTM);
  }
  StringRef getPassName() const override { return "DXIL Resource Access"; }
  DXILResourceAccessLegacy() : FunctionPass(ID) {}

  static char ID; // Pass identification.
  void getAnalysisUsage(llvm::AnalysisUsage &AU) const override {
    AU.addRequired<DXILResourceTypeWrapperPass>();
    AU.addPreserved<DominatorTreeWrapperPass>();
  }
};
char DXILResourceAccessLegacy::ID = 0;
} // end anonymous namespace

INITIALIZE_PASS_BEGIN(DXILResourceAccessLegacy, DEBUG_TYPE,
                      "DXIL Resource Access", false, false)
INITIALIZE_PASS_DEPENDENCY(DXILResourceTypeWrapperPass)
INITIALIZE_PASS_END(DXILResourceAccessLegacy, DEBUG_TYPE,
                    "DXIL Resource Access", false, false)

FunctionPass *llvm::createDXILResourceAccessLegacyPass() {
  return new DXILResourceAccessLegacy();
}