CBuffer.cpp

//===- CBuffer.cpp - HLSL constant buffer handling ------------------------===//
//
// 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 "llvm/Frontend/HLSL/CBuffer.h"
#include "llvm/Frontend/HLSL/HLSLResource.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"

using namespace llvm;
using namespace llvm::hlsl;

static size_t getMemberOffset(GlobalVariable *Handle, size_t Index) {
  auto *HandleTy = cast<TargetExtType>(Handle->getValueType());
  assert(HandleTy->getName().ends_with(".CBuffer") && "Not a cbuffer type");
  assert(HandleTy->getNumTypeParameters() == 1 && "Expected layout type");

  auto *LayoutTy = cast<TargetExtType>(HandleTy->getTypeParameter(0));
  assert(LayoutTy->getName().ends_with(".Layout") && "Not a layout type");

  // Skip the "size" parameter.
  size_t ParamIndex = Index + 1;
  assert(LayoutTy->getNumIntParameters() > ParamIndex &&
         "Not enough parameters");

  return LayoutTy->getIntParameter(ParamIndex);
}

std::optional<CBufferMetadata> CBufferMetadata::get(Module &M) {
  NamedMDNode *CBufMD = M.getNamedMetadata("hlsl.cbs");
  if (!CBufMD)
    return std::nullopt;

  std::optional<CBufferMetadata> Result({CBufMD});

  for (const MDNode *MD : CBufMD->operands()) {
    assert(MD->getNumOperands() && "Invalid cbuffer metadata");

    auto *Handle = cast<GlobalVariable>(
        cast<ValueAsMetadata>(MD->getOperand(0))->getValue());
    CBufferMapping &Mapping = Result->Mappings.emplace_back(Handle);

    for (int I = 1, E = MD->getNumOperands(); I < E; ++I) {
      Metadata *OpMD = MD->getOperand(I);
      // Some members may be null if they've been optimized out.
      if (!OpMD)
        continue;
      auto *V = cast<GlobalVariable>(cast<ValueAsMetadata>(OpMD)->getValue());
      Mapping.Members.emplace_back(V, getMemberOffset(Handle, I - 1));
    }
  }

  return Result;
}

void CBufferMetadata::eraseFromModule() {
  // Remove the cbs named metadata
  MD->eraseFromParent();
}

APInt hlsl::translateCBufArrayOffset(const DataLayout &DL, APInt Offset,
                                     ArrayType *Ty) {
  int64_t TypeSize = DL.getTypeSizeInBits(Ty->getElementType()) / 8;
  int64_t RoundUp = alignTo(TypeSize, Align(CBufferRowSizeInBytes));
  return Offset.udiv(TypeSize) * RoundUp;
}