//===----------------------- AMDGPUFrameLowering.cpp ----------------------===//
//
// 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
//
//==-----------------------------------------------------------------------===//
//
// Interface to describe a layout of a stack frame on a AMDGPU target machine.
//
//===----------------------------------------------------------------------===//

#include "AMDGPUFrameLowering.h"
#include "GCNSubtarget.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/Target/TargetMachine.h"

using namespace llvm;
AMDGPUFrameLowering::AMDGPUFrameLowering(StackDirection D, Align StackAl,
                                         int LAO, Align TransAl)
    : TargetFrameLowering(D, StackAl, LAO, TransAl) {}

AMDGPUFrameLowering::~AMDGPUFrameLowering() = default;

unsigned AMDGPUFrameLowering::getStackWidth(const MachineFunction &MF) const {
  // XXX: Hardcoding to 1 for now.
  //
  // I think the StackWidth should be stored as metadata associated with the
  // MachineFunction.  This metadata can either be added by a frontend, or
  // calculated by a R600 specific LLVM IR pass.
  //
  // The StackWidth determines how stack objects are laid out in memory.
  // For a vector stack variable, like: int4 stack[2], the data will be stored
  // in the following ways depending on the StackWidth.
  //
  // StackWidth = 1:
  //
  // T0.X = stack[0].x
  // T1.X = stack[0].y
  // T2.X = stack[0].z
  // T3.X = stack[0].w
  // T4.X = stack[1].x
  // T5.X = stack[1].y
  // T6.X = stack[1].z
  // T7.X = stack[1].w
  //
  // StackWidth = 2:
  //
  // T0.X = stack[0].x
  // T0.Y = stack[0].y
  // T1.X = stack[0].z
  // T1.Y = stack[0].w
  // T2.X = stack[1].x
  // T2.Y = stack[1].y
  // T3.X = stack[1].z
  // T3.Y = stack[1].w
  //
  // StackWidth = 4:
  // T0.X = stack[0].x
  // T0.Y = stack[0].y
  // T0.Z = stack[0].z
  // T0.W = stack[0].w
  // T1.X = stack[1].x
  // T1.Y = stack[1].y
  // T1.Z = stack[1].z
  // T1.W = stack[1].w
  return 1;
}

DIExpression *AMDGPUFrameLowering::lowerFIArgToFPArg(const MachineFunction &MF,
                                                     const DIExpression *Expr,
                                                     uint64_t ArgIndex,
                                                     StackOffset Offset) const {
  const DataLayout &DL = MF.getDataLayout();
  LLVMContext &Context = MF.getFunction().getParent()->getContext();
  const auto &ST = MF.getSubtarget<GCNSubtarget>();
  DIExprBuilder Builder(*Expr);
  for (auto &&I = Builder.begin(); I != Builder.end(); ++I) {
    if (auto *Arg = std::get_if<DIOp::Arg>(&*I)) {
      if (Arg->getIndex() != ArgIndex)
        continue;

      Type *ResultType = Arg->getResultType();
      // Weird case: we expect a pointer but on optimized builds it may not be
      // the case.
      if (!ResultType->isPointerTy())
        return Expr->getPoisoned();

      unsigned PointerSizeInBits =
          DL.getPointerSizeInBits(ResultType->getPointerAddressSpace());
      auto *IntTy = IntegerType::get(Context, PointerSizeInBits);
      ConstantData *WavefrontSizeLog2 = static_cast<ConstantData *>(
          ConstantInt::get(IntTy, ST.getWavefrontSizeLog2(), false));
      ConstantData *C = ConstantInt::get(IntTy, Offset.getFixed(), true);
      SmallVector<DIOp::Variant> FL = {DIOp::Reinterpret(IntTy)};
      if (!ST.hasFlatScratchEnabled())
        FL.append({DIOp::Constant(WavefrontSizeLog2), DIOp::LShr()});
      FL.append(
          {DIOp::Constant(C), DIOp::Add(), DIOp::Reinterpret(ResultType)});
      I = Builder.insert(++I, FL);
    }
  }
  return Builder.intoExpression();
}