src/transform/array_length_from_uniform.cc

// Copyright 2021 The Tint Authors.
//
// Licensed 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.

#include "src/transform/array_length_from_uniform.h"

#include <memory>
#include <string>
#include <utility>

#include "src/program_builder.h"
#include "src/sem/call.h"
#include "src/sem/variable.h"
#include "src/transform/simplify_pointers.h"

TINT_INSTANTIATE_TYPEINFO(tint::transform::ArrayLengthFromUniform);
TINT_INSTANTIATE_TYPEINFO(tint::transform::ArrayLengthFromUniform::Config);
TINT_INSTANTIATE_TYPEINFO(tint::transform::ArrayLengthFromUniform::Result);

namespace tint {
namespace transform {

ArrayLengthFromUniform::ArrayLengthFromUniform() = default;
ArrayLengthFromUniform::~ArrayLengthFromUniform() = default;

/// Iterate over all arrayLength() intrinsics that operate on
/// storage buffer variables.
/// @param ctx the CloneContext.
/// @param functor of type void(const ast::CallExpression*, const
/// sem::VariableUser, const sem::GlobalVariable*). It takes in an
/// ast::CallExpression of the arrayLength call expression node, a
/// sem::VariableUser of the used storage buffer variable, and the
/// sem::GlobalVariable for the storage buffer.
template <typename F>
static void IterateArrayLengthOnStorageVar(CloneContext& ctx, F&& functor) {
  auto& sem = ctx.src->Sem();

  // Find all calls to the arrayLength() intrinsic.
  for (auto* node : ctx.src->ASTNodes().Objects()) {
    auto* call_expr = node->As<ast::CallExpression>();
    if (!call_expr) {
      continue;
    }

    auto* call = sem.Get(call_expr);
    auto* intrinsic = call->Target()->As<sem::Intrinsic>();
    if (!intrinsic || intrinsic->Type() != sem::IntrinsicType::kArrayLength) {
      continue;
    }

    // Get the storage buffer that contains the runtime array.
    // We assume that the argument to `arrayLength` has the form
    // `&resource.array`, which requires that `SimplifyPointers` have been run
    // before this transform.
    auto* param = call_expr->args[0]->As<ast::UnaryOpExpression>();
    if (!param || param->op != ast::UnaryOp::kAddressOf) {
      TINT_ICE(Transform, ctx.dst->Diagnostics())
          << "expected form of arrayLength argument to be "
             "&resource.array";
      break;
    }
    auto* accessor = param->expr->As<ast::MemberAccessorExpression>();
    if (!accessor) {
      TINT_ICE(Transform, ctx.dst->Diagnostics())
          << "expected form of arrayLength argument to be "
             "&resource.array";
      break;
    }
    auto* storage_buffer_expr = accessor->structure;
    auto* storage_buffer_sem =
        sem.Get(storage_buffer_expr)->As<sem::VariableUser>();
    if (!storage_buffer_sem) {
      TINT_ICE(Transform, ctx.dst->Diagnostics())
          << "expected form of arrayLength argument to be "
             "&resource.array";
      break;
    }

    // Get the index to use for the buffer size array.
    auto* var = tint::As<sem::GlobalVariable>(storage_buffer_sem->Variable());
    if (!var) {
      TINT_ICE(Transform, ctx.dst->Diagnostics())
          << "storage buffer is not a global variable";
      break;
    }
    functor(call_expr, storage_buffer_sem, var);
  }
}

void ArrayLengthFromUniform::Run(CloneContext& ctx,
                                 const DataMap& inputs,
                                 DataMap& outputs) {
  if (!Requires<SimplifyPointers>(ctx)) {
    return;
  }

  auto* cfg = inputs.Get<Config>();
  if (cfg == nullptr) {
    ctx.dst->Diagnostics().add_error(
        diag::System::Transform,
        "missing transform data for " + std::string(TypeInfo().name));
    return;
  }

  const char* kBufferSizeMemberName = "buffer_size";

  // Determine the size of the buffer size array.
  uint32_t max_buffer_size_index = 0;

  IterateArrayLengthOnStorageVar(
      ctx, [&](const ast::CallExpression*, const sem::VariableUser*,
               const sem::GlobalVariable* var) {
        auto binding = var->BindingPoint();
        auto idx_itr = cfg->bindpoint_to_size_index.find(binding);
        if (idx_itr == cfg->bindpoint_to_size_index.end()) {
          return;
        }
        if (idx_itr->second > max_buffer_size_index) {
          max_buffer_size_index = idx_itr->second;
        }
      });

  // Get (or create, on first call) the uniform buffer that will receive the
  // size of each storage buffer in the module.
  const ast::Variable* buffer_size_ubo = nullptr;
  auto get_ubo = [&]() {
    if (!buffer_size_ubo) {
      // Emit an array<vec4<u32>, N>, where N is 1/4 number of elements.
      // We do this because UBOs require an element stride that is 16-byte
      // aligned.
      auto* buffer_size_struct = ctx.dst->Structure(
          ctx.dst->Sym(),
          {ctx.dst->Member(
              kBufferSizeMemberName,
              ctx.dst->ty.array(ctx.dst->ty.vec4(ctx.dst->ty.u32()),
                                (max_buffer_size_index / 4) + 1))});
      buffer_size_ubo = ctx.dst->Global(
          ctx.dst->Sym(), ctx.dst->ty.Of(buffer_size_struct),
          ast::StorageClass::kUniform,
          ast::DecorationList{
              ctx.dst->create<ast::GroupDecoration>(cfg->ubo_binding.group),
              ctx.dst->create<ast::BindingDecoration>(
                  cfg->ubo_binding.binding)});
    }
    return buffer_size_ubo;
  };

  std::unordered_set<uint32_t> used_size_indices;

  IterateArrayLengthOnStorageVar(
      ctx, [&](const ast::CallExpression* call_expr,
               const sem::VariableUser* storage_buffer_sem,
               const sem::GlobalVariable* var) {
        auto binding = var->BindingPoint();
        auto idx_itr = cfg->bindpoint_to_size_index.find(binding);
        if (idx_itr == cfg->bindpoint_to_size_index.end()) {
          return;
        }

        uint32_t size_index = idx_itr->second;
        used_size_indices.insert(size_index);

        // Load the total storage buffer size from the UBO.
        uint32_t array_index = size_index / 4;
        auto* vec_expr = ctx.dst->IndexAccessor(
            ctx.dst->MemberAccessor(get_ubo()->symbol, kBufferSizeMemberName),
            array_index);
        uint32_t vec_index = size_index % 4;
        auto* total_storage_buffer_size =
            ctx.dst->IndexAccessor(vec_expr, vec_index);

        // Calculate actual array length
        //                total_storage_buffer_size - array_offset
        // array_length = ----------------------------------------
        //                             array_stride
        auto* storage_buffer_type =
            storage_buffer_sem->Type()->UnwrapRef()->As<sem::Struct>();
        auto* array_member_sem = storage_buffer_type->Members().back();
        uint32_t array_offset = array_member_sem->Offset();
        uint32_t array_stride = array_member_sem->Size();
        auto* array_length =
            ctx.dst->Div(ctx.dst->Sub(total_storage_buffer_size, array_offset),
                         array_stride);

        ctx.Replace(call_expr, array_length);
      });

  ctx.Clone();

  outputs.Add<Result>(used_size_indices);
}

ArrayLengthFromUniform::Config::Config(sem::BindingPoint ubo_bp)
    : ubo_binding(ubo_bp) {}
ArrayLengthFromUniform::Config::Config(const Config&) = default;
ArrayLengthFromUniform::Config& ArrayLengthFromUniform::Config::operator=(
    const Config&) = default;
ArrayLengthFromUniform::Config::~Config() = default;

ArrayLengthFromUniform::Result::Result(
    std::unordered_set<uint32_t> used_size_indices_in)
    : used_size_indices(std::move(used_size_indices_in)) {}
ArrayLengthFromUniform::Result::Result(const Result&) = default;
ArrayLengthFromUniform::Result::~Result() = default;

}  // namespace transform
}  // namespace tint