lower_tile_op.cc

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

/*!
 * \file lower_tile_op.cc
 * \brief Lower the tile op for further codegen.
 */

#include <tvm/tir/builtin.h>
#include <tvm/tir/stmt_functor.h>
#include <tvm/tir/transform.h>
#include <tvm/tir/utils.h>

#include "../layout/layout.h"
#include "../layout/utils.h"
#include "../op/op.h"

#include "arith/ir_mutator_with_analyzer.h"
#include "loop_partition.h"

namespace tvm {
namespace tl {

using namespace tir;

static Buffer makeBufferWithLayout(const Buffer &buffer, const Layout &layout) {
  const auto *ptr_type =
      TVM_TYPE_AS(buffer->data->type_annotation, PointerTypeNode);
  Type new_type;
  // convert fragments to normal local buffer
  if (ptr_type->storage_scope == "local.fragment") {
    new_type = PointerType(ptr_type->element_type, "local");
  } else {
    new_type = buffer->data->type_annotation;
  }
  Var new_var;
  if (ptr_type->storage_scope == "global") {
    new_var = buffer->data;
  } else {
    new_var = Var(buffer->data->name_hint, new_type);
  }
  return Buffer(new_var, buffer->dtype, layout->OutputShape(), {},
                buffer->elem_offset, buffer->name, buffer->data_alignment,
                buffer->offset_factor, buffer->buffer_type);
}

class LowerTileOpPass : arith::IRMutatorWithAnalyzer {
public:
  static PrimFunc Substitute(PrimFunc f) {
    arith::Analyzer analyzer;
    LowerTileOpPass substituter(&analyzer);
    // Trace the buffer map for tvm_access_ptr
    substituter.buffer_map_.insert(f->buffer_map.begin(), f->buffer_map.end());
    for (const auto &[_, buffer] : f->buffer_map) {
      substituter.buffer_data_to_buffer_.Set(buffer->data, buffer);
    }
    auto target = f->GetAttr<Target>(tvm::attr::kTarget);
    ICHECK(target.defined()) << "LowerTileOpPass: Require the target attribute";
    substituter.target_ = target.value();
    PrimFuncNode *fptr = f.CopyOnWrite();
    fptr->body = substituter.VisitStmt(f->body);
    return f;
  }

private:
  using arith::IRMutatorWithAnalyzer::IRMutatorWithAnalyzer;

  Stmt VisitStmt_(const BlockNode *op) final {
    // Record the mapping from buffer data var to buffer for later lookup
    for (auto buffer : op->alloc_buffers) {
      buffer_map_.insert({buffer->data, buffer});
    }
    for (auto match_buffer : op->match_buffers) {
      buffer_map_.insert({match_buffer->buffer->data, match_buffer->buffer});
    }
    for (auto buffer : op->alloc_buffers) {
      buffer_data_to_buffer_.Set(buffer->data, buffer);
    }
    Map<Var, Layout> vmap;
    if (op->annotations.count(attr::kLayoutMap)) {
      auto layout_map = op->annotations.at(attr::kLayoutMap)
                            .as<Map<Buffer, Layout>>()
                            .value();
      for (auto [buffer, layout] : layout_map) {
        buffer_remap_.Set(buffer, makeBufferWithLayout(buffer, layout));
        layout_map_.Set(buffer, layout);
      }
    }
    auto block = Downcast<Block>(arith::IRMutatorWithAnalyzer::VisitStmt_(op));
    auto block_ptr = block.CopyOnWrite();
    for (size_t i = 0; i < block->alloc_buffers.size(); i++) {
      auto buffer = block->alloc_buffers[i];
      if (buffer_remap_.count(buffer)) {
        block_ptr->alloc_buffers.Set(i, buffer_remap_[buffer]);
      }
    }
    for (const auto &buffer : workspaces_)
      block_ptr->alloc_buffers.push_back(buffer);
    workspaces_.clear();
    block_ptr->annotations.erase(attr::kLayoutMap);
    return block;
  }

  int CheckAndGetBufferRowSize(Buffer buffer) {
    CHECK(buffer->shape.size() >= 2)
        << "The dimension of Buffer \"" << buffer->name << "\" with shape "
        << buffer->shape << " should be at least 2";

    auto dim = buffer->shape.size();
    auto buffer_row_size = buffer->shape[dim - 1].as<IntImmNode>()->value;
    return buffer_row_size;
  }

  PrimExpr HandleAccessPtrAndOffset(PrimExpr access_ptr,
                                    Optional<PrimExpr> offset = NullOpt,
                                    DataType dtype = DataType::Int(32)) {
    // The 2th arg of T.tvm_access_ptr call is offset, we set it to 0 and
    // accumulate it to smem_offset
    CHECK(access_ptr->IsInstance<CallNode>())
        << "Invalid access ptr for permuted layout: " << access_ptr;
    auto access_ptr_call = Downcast<Call>(access_ptr);
    if (access_ptr_call->op.same_as(builtin::tvm_access_ptr())) {
      LOG(FATAL) << "Transformation for tvm_access_ptr is not implemented yet";
    } else if (access_ptr_call->op.same_as(builtin::address_of())) {
      BufferLoad load = Downcast<BufferLoad>(access_ptr_call->args[0]);
      Array<PrimExpr> indices = load->indices;
      Array<PrimExpr> shape = load->buffer->shape;

      CHECK_EQ(indices.size(), shape.size())
          << "Indices size and shape size must match for general N-dimensional "
             "buffer "
          << "but got indices size: " << indices.size()
          << " and shape size: " << shape.size();

      PrimExpr elem_offset = 0;
      PrimExpr stride = 1;

      for (int i = static_cast<int>(shape.size()) - 1; i >= 0; --i) {
        elem_offset += indices[i] * stride;
        stride *= shape[i];
      }

      PrimExpr smem_offset =
          elem_offset + (offset.defined() ? offset.value() : 0);

      auto new_buffer = buffer_remap_[load->buffer];

      auto buffer_map_iter =
          buffer_map_.find(Downcast<Var>(load->buffer->data));
      CHECK(buffer_map_iter != buffer_map_.end())
          << "The buffer corresponding to data Var " << access_ptr_call->args[0]
          << " is not found";

      int buffer_row_size = CheckAndGetBufferRowSize(buffer_map_iter->second);
      (void)buffer_row_size;

      // Convert offset to target-dimension, reindex it and convert it back
      Array<PrimExpr> multi_dim_indices;
      PrimExpr remaining_offset = smem_offset;

      for (int i = static_cast<int>(shape.size()) - 1; i >= 0; --i) {
        multi_dim_indices.insert(multi_dim_indices.begin(),
                                 floormod(remaining_offset, shape[i]));
        remaining_offset = floordiv(remaining_offset, shape[i]);
      }

      auto forward_indices =
          layout_map_[load->buffer]->Forward(multi_dim_indices);
      PrimExpr new_offset = 0;
      PrimExpr stride_offset = 1;
      for (int i = static_cast<int>(shape.size()) - 1; i >= 0; --i) {
        new_offset += forward_indices[i] * stride_offset;
        stride_offset *= shape[i];
      }
      new_offset = analyzer_->Simplify(new_offset);

      Array<PrimExpr> new_indices;
      for (int i = static_cast<int>(shape.size()) - 1; i >= 0; --i) {
        new_indices.insert(new_indices.begin(), floormod(new_offset, shape[i]));
        new_offset = floordiv(new_offset, shape[i]);
      }

      auto new_access_ptr = access_ptr_call.CopyOnWrite();
      new_access_ptr->args.Set(0, BufferLoad(new_buffer, new_indices));
    } else {
      LOG(FATAL) << "Invalid access op for permuted layout: " << access_ptr;
    }

    return access_ptr_call;
  }

  PrimExpr VisitExpr_(const tir::CallNode *op) final {
    Array<RelayExpr> ptx_instructions = {builtin::ptx_ldmatrix(),
                                         builtin::mma_store()};

    if (std::find(ptx_instructions.begin(), ptx_instructions.end(), op->op) ==
        ptx_instructions.end()) {
      auto call = Downcast<Call>(IRMutatorWithAnalyzer::VisitExpr_(op));
      return call;
    } else {
      is_ptx_ = true;
    }
    // Rewrite from/to shared or shared.dyn to/from local
    auto call = Downcast<Call>(IRMutatorWithAnalyzer::VisitExpr_(op));
    if (call->op.same_as(builtin::ptx_ldmatrix())) {
      // form: T.ptx_ldmatrix(..., smem_ptr, smem_offset)
      // smem_ptr: T.tvm_access_ptr(ptype, data, offset, extent, rw_mask)
      // or T.address_of(buffer, offset)
      auto access_ptr = call->args[5];
      PrimExpr smem_offset = call->args[6];
      Call address_of_call = Downcast<Call>(access_ptr);
      if (!address_of_call->op.same_as(builtin::address_of())) {
        LOG(FATAL) << "Invalid access ptr for permuted layout: " << access_ptr;
      }
      BufferLoad load = Downcast<BufferLoad>(address_of_call->args[0]);

      if (buffer_remap_.count(load->buffer)) {
        auto new_access_ptr =
            HandleAccessPtrAndOffset(access_ptr, smem_offset, call->dtype);
        auto new_call = call.CopyOnWrite();
        new_call->args.Set(5, new_access_ptr);
        new_call->args.Set(6, IntImm(smem_offset->dtype, 0));
      }
    } else if (call->op.same_as(builtin::mma_store())) {
      // because we will directly store result to Buffer instead of calling
      // mma_store now
      auto access_ptr = call->args[2];
      auto new_access_ptr =
          HandleAccessPtrAndOffset(access_ptr, NullOpt, call->dtype);
      auto new_call = call.CopyOnWrite();
      new_call->args.Set(2, new_access_ptr);
    } else {
      LOG(FATAL) << "Invalid call node: " << call;
    }
    is_ptx_ = false;
    return call;
  }

  PrimExpr VisitExpr_(const BufferLoadNode *op) final {
    auto load = Downcast<BufferLoad>(IRMutatorWithAnalyzer::VisitExpr_(op));
    if (is_ptx_) {
      return load;
    }

    if (buffer_remap_.count(load->buffer)) {
      auto new_indices = layout_map_[load->buffer]->Forward(load->indices);
      auto new_buffer = buffer_remap_[load->buffer];
      return BufferLoad(new_buffer, new_indices);
    }
    return load;
  }

  Stmt VisitStmt_(const BufferStoreNode *op) final {
    auto store = Downcast<BufferStore>(IRMutatorWithAnalyzer::VisitStmt_(op));
    if (buffer_remap_.count(store->buffer)) {
      auto new_indices = layout_map_[store->buffer]->Forward(store->indices);
      auto new_buffer = buffer_remap_[store->buffer];
      return BufferStore(new_buffer, store->value, new_indices);
    }
    return store;
  }

  PrimExpr VisitExpr_(const VarNode *op) final {
    auto var = Downcast<Var>(IRMutatorWithAnalyzer::VisitExpr_(op));
    if (buffer_data_to_buffer_.count(var)) {
      auto buffer = buffer_data_to_buffer_[var];
      if (buffer_remap_.count(buffer))
        return buffer_remap_[buffer]->data;
    }
    return var;
  }

  Stmt VisitStmt_(const EvaluateNode *op) final {
    const CallNode *call = op->value.as<CallNode>();
    // Do not analysis the call node to the global function.
    if (call && call->op.as<GlobalVarNode>())
      return Downcast<Evaluate>(IRMutatorWithAnalyzer::VisitStmt_(op));

    auto tile_op = ParseOperator(GetRef<Stmt>(op), buffer_data_to_buffer_);
    if (tile_op == nullptr)
      return IRMutatorWithAnalyzer::VisitStmt_(op);
    AddWorkspaceCallback callback = [this](int num_elem, DataType dtype) {
      auto workspace =
          decl_buffer({PrimExpr(num_elem)}, dtype, "workspace", "shared.dyn");
      workspaces_.push_back(workspace);
      return workspace.access_ptr(2); // write
    };

    auto lowered =
        tile_op->Lower(LowerArgs{target_, thread_block_size_, thread_var_,
                                 callback, layout_map_, buffer_remap_},
                       analyzer_);
    return IRMutatorWithAnalyzer::VisitStmt(lowered);
  }

  Stmt VisitStmt_(const AttrStmtNode *op) final {
    if (op->attr_key == tir::attr::thread_extent) {
      IterVar iv = Downcast<IterVar>(op->node);
      ICHECK_NE(iv->thread_tag.length(), 0U);
      if (iv->thread_tag == "threadIdx.x") {
        thread_var_ = iv->var;
        ICHECK(iv->dom->extent.as<IntImmNode>());
        thread_block_size_ = iv->dom->extent.as<IntImmNode>()->value;
      }
    }
    return arith::IRMutatorWithAnalyzer::VisitStmt_(op);
  }

  Target target_;
  Map<Var, Buffer> buffer_data_to_buffer_;
  Map<Buffer, Layout> layout_map_;
  Map<Buffer, Buffer> buffer_remap_;
  Var thread_var_;
  size_t thread_block_size_ = 0;
  Array<Buffer> workspaces_;
  // For ptx Node, we need to remap the buffer and indices
  // By access CallNode instead of BufferLoad Node.
  bool is_ptx_{false};
  // Mapping from data Var of a Buffer to Buffer, for lookup
  std::unordered_map<Var, Buffer, ObjectPtrHash, ObjectPtrEqual> buffer_map_;
};

namespace transform {

using namespace tir::transform;

tvm::transform::Pass LowerTileOp() {
  auto pass_func = [=](PrimFunc f, IRModule m, PassContext ctx) {
    return LowerTileOpPass::Substitute(std::move(f));
  };
  return CreatePrimFuncPass(pass_func, 0, "tl.LowerTileOp", {});
}

TVM_REGISTER_GLOBAL("tl.transform.LowerTileOp").set_body_typed(LowerTileOp);
} // namespace transform

} // namespace tl
} // namespace tvm