DXILCBufferAccess.cpp

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//===- DXILCBufferAccess.cpp - Translate CBuffer Loads --------------------===//
//
// 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 "DirectX.h"
#include "llvm/Analysis/DXILResource.h"
#include "llvm/Frontend/HLSL/CBuffer.h"
#include "llvm/Frontend/HLSL/HLSLResource.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/IntrinsicsDirectX.h"
#include "llvm/IR/ReplaceConstant.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
 
#define DEBUG_TYPE "dxil-cbuffer-access"
using namespace llvm;
 
static void replaceUsersOfGlobal(GlobalVariable *Global,
                                 GlobalVariable *HandleGV, size_t Offset) {
  for (Use &U : make_early_inc_range(Global->uses())) {
    auto UseInst = dyn_cast<Instruction>(U.getUser());
    // TODO: Constants? Metadata?
    assert(UseInst && "Non-instruction use of cbuffer");
 
    IRBuilder<> Builder(UseInst);
    LoadInst *Handle = Builder.CreateLoad(HandleGV->getValueType(), HandleGV,
                                          HandleGV->getName());
    Value *Ptr = Builder.CreateIntrinsic(
        Global->getType(), Intrinsic::dx_resource_getpointer,
        ArrayRef<Value *>{Handle,
                          ConstantInt::get(Builder.getInt32Ty(), Offset)});
    U.set(Ptr);
  }
 
  Global->eraseFromParent();
}
 
static bool replaceCBufferAccesses(Module &M) {
  std::optional<hlsl::CBufferMetadata> CBufMD = hlsl::CBufferMetadata::get(
      M, [](Type *Ty) { return isa<llvm::dxil::PaddingExtType>(Ty); });
  if (!CBufMD)
    return false;
 
  SmallVector<Constant *> CBufferGlobals;
  SmallPtrSet<GlobalVariable *, 8> CBufferHandles;
  for (const hlsl::CBufferMapping &Mapping : *CBufMD) {
    CBufferHandles.insert(Mapping.Handle);
    for (const hlsl::CBufferMember &Member : Mapping.Members)
      CBufferGlobals.push_back(Member.GV);
  }
  convertUsersOfConstantsToInstructions(CBufferGlobals);
 
  for (const hlsl::CBufferMapping &Mapping : *CBufMD)
    for (const hlsl::CBufferMember &Member : Mapping.Members)
      replaceUsersOfGlobal(Member.GV, Mapping.Handle, Member.Offset);
 
  // Remove cbuffer handle globals from @llvm.compiler.used list.
  llvm::removeFromUsedLists(M, [&](Constant *C) -> bool {
    auto *GV = dyn_cast<GlobalVariable>(C);
    return GV && CBufferHandles.contains(GV);
  });
  for (GlobalVariable *HandleGV : CBufferHandles)
    HandleGV->removeDeadConstantUsers();
 
  CBufMD->eraseFromModule();
  return true;
}
 
PreservedAnalyses DXILCBufferAccessPass::run(Module &M,
                                             ModuleAnalysisManager &AM) {
  PreservedAnalyses PA;
  bool Changed = replaceCBufferAccesses(M);
 
  if (!Changed)
    return PreservedAnalyses::all();
  return PA;
}
 
namespace {
class DXILCBufferAccessLegacy : public ModulePass {
public:
  bool runOnModule(Module &M) override { return replaceCBufferAccesses(M); }
  StringRef getPassName() const override { return "DXIL CBuffer Access"; }
  DXILCBufferAccessLegacy() : ModulePass(ID) {}
 
  static char ID; // Pass identification.
};
char DXILCBufferAccessLegacy::ID = 0;
} // end anonymous namespace
 
INITIALIZE_PASS(DXILCBufferAccessLegacy, DEBUG_TYPE, "DXIL CBuffer Access",
                false, false)
 
ModulePass *llvm::createDXILCBufferAccessLegacyPass() {
  return new DXILCBufferAccessLegacy();
}