src/transform/first_index_offset.cc

// Copyright 2020 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/first_index_offset.h"

#include <cassert>
#include <utility>

#include "src/ast/array_accessor_expression.h"
#include "src/ast/assignment_statement.h"
#include "src/ast/binary_expression.h"
#include "src/ast/bitcast_expression.h"
#include "src/ast/break_statement.h"
#include "src/ast/builtin_decoration.h"
#include "src/ast/call_statement.h"
#include "src/ast/case_statement.h"
#include "src/ast/constructor_expression.h"
#include "src/ast/else_statement.h"
#include "src/ast/expression.h"
#include "src/ast/fallthrough_statement.h"
#include "src/ast/identifier_expression.h"
#include "src/ast/if_statement.h"
#include "src/ast/loop_statement.h"
#include "src/ast/member_accessor_expression.h"
#include "src/ast/return_statement.h"
#include "src/ast/scalar_constructor_expression.h"
#include "src/ast/struct.h"
#include "src/ast/struct_block_decoration.h"
#include "src/ast/struct_decoration.h"
#include "src/ast/struct_member.h"
#include "src/ast/struct_member_offset_decoration.h"
#include "src/ast/switch_statement.h"
#include "src/ast/type_constructor_expression.h"
#include "src/ast/unary_op_expression.h"
#include "src/ast/variable.h"
#include "src/ast/variable_decl_statement.h"
#include "src/ast/variable_decoration.h"
#include "src/clone_context.h"
#include "src/program.h"
#include "src/program_builder.h"
#include "src/semantic/function.h"
#include "src/type/struct_type.h"
#include "src/type/u32_type.h"
#include "src/type_determiner.h"

namespace tint {
namespace transform {
namespace {

constexpr char kStructName[] = "TintFirstIndexOffsetData";
constexpr char kBufferName[] = "tint_first_index_data";
constexpr char kFirstVertexName[] = "tint_first_vertex_index";
constexpr char kFirstInstanceName[] = "tint_first_instance_index";
constexpr char kIndexOffsetPrefix[] = "tint_first_index_offset_";

ast::Variable* clone_variable_with_new_name(CloneContext* ctx,
                                            ast::Variable* in,
                                            std::string new_name) {
  // Clone arguments outside of create() call to have deterministic ordering
  auto source = ctx->Clone(in->source());
  auto symbol = ctx->dst->Symbols().Register(new_name);
  auto* type = ctx->Clone(in->type());
  auto* constructor = ctx->Clone(in->constructor());
  auto decorations = ctx->Clone(in->decorations());
  return ctx->dst->create<ast::Variable>(
      source, symbol, in->declared_storage_class(), type, in->is_const(),
      constructor, decorations);
}

}  // namespace

FirstIndexOffset::FirstIndexOffset(uint32_t binding, uint32_t group)
    : binding_(binding), group_(group) {}

FirstIndexOffset::~FirstIndexOffset() = default;

Transform::Output FirstIndexOffset::Run(const Program* in) {
  // First do a quick check to see if the transform has already been applied.
  for (ast::Variable* var : in->AST().GlobalVariables()) {
    if (auto* dec_var = var->As<ast::Variable>()) {
      if (dec_var->symbol() == in->Symbols().Get(kBufferName)) {
        Output out;
        out.diagnostics.add_error(
            "First index offset transform has already been applied.");
        return out;
      }
    }
  }

  Symbol vertex_index_sym;
  Symbol instance_index_sym;

  // Lazilly construct the UniformBuffer on first call to
  // maybe_create_buffer_var()
  ast::Variable* buffer_var = nullptr;
  auto maybe_create_buffer_var = [&](ProgramBuilder* dst) {
    if (buffer_var == nullptr) {
      buffer_var = AddUniformBuffer(dst);
    }
  };

  // Clone the AST, renaming the kVertexIndex and kInstanceIndex builtins, and
  // add a CreateFirstIndexOffset() statement to each function that uses one of
  // these builtins.

  ProgramBuilder out;
  CloneContext(&out, in)
      .ReplaceAll([&](CloneContext* ctx, ast::Variable* var) -> ast::Variable* {
        for (ast::VariableDecoration* dec : var->decorations()) {
          if (auto* blt_dec = dec->As<ast::BuiltinDecoration>()) {
            ast::Builtin blt_type = blt_dec->value();
            if (blt_type == ast::Builtin::kVertexIndex) {
              vertex_index_sym = var->symbol();
              has_vertex_index_ = true;
              return clone_variable_with_new_name(
                  ctx, var,
                  kIndexOffsetPrefix + in->Symbols().NameFor(var->symbol()));
            } else if (blt_type == ast::Builtin::kInstanceIndex) {
              instance_index_sym = var->symbol();
              has_instance_index_ = true;
              return clone_variable_with_new_name(
                  ctx, var,
                  kIndexOffsetPrefix + in->Symbols().NameFor(var->symbol()));
            }
          }
        }
        return nullptr;  // Just clone var
      })
      .ReplaceAll(  // Note: This happens in the same pass as the rename above
                    // which determines the original builtin variable names,
                    // but this should be fine, as variables are cloned first.
          [&](CloneContext* ctx, ast::Function* func) -> ast::Function* {
            maybe_create_buffer_var(ctx->dst);
            if (buffer_var == nullptr) {
              return nullptr;  // no transform need, just clone func
            }
            auto* func_sem = in->Sem().Get(func);
            ast::StatementList statements;
            for (const auto& data :
                 func_sem->LocalReferencedBuiltinVariables()) {
              if (data.second->value() == ast::Builtin::kVertexIndex) {
                statements.emplace_back(CreateFirstIndexOffset(
                    in->Symbols().NameFor(vertex_index_sym), kFirstVertexName,
                    buffer_var, ctx->dst));
              } else if (data.second->value() == ast::Builtin::kInstanceIndex) {
                statements.emplace_back(CreateFirstIndexOffset(
                    in->Symbols().NameFor(instance_index_sym),
                    kFirstInstanceName, buffer_var, ctx->dst));
              }
            }
            return CloneWithStatementsAtStart(ctx, func, statements);
          })
      .Clone();

  return Output(Program(std::move(out)));
}

bool FirstIndexOffset::HasVertexIndex() {
  return has_vertex_index_;
}

bool FirstIndexOffset::HasInstanceIndex() {
  return has_instance_index_;
}

uint32_t FirstIndexOffset::GetFirstVertexOffset() {
  assert(has_vertex_index_);
  return vertex_index_offset_;
}

uint32_t FirstIndexOffset::GetFirstInstanceOffset() {
  assert(has_instance_index_);
  return instance_index_offset_;
}

ast::Variable* FirstIndexOffset::AddUniformBuffer(ProgramBuilder* dst) {
  auto* u32_type = dst->create<type::U32>();
  ast::StructMemberList members;
  uint32_t offset = 0;
  if (has_vertex_index_) {
    ast::StructMemberDecorationList member_dec;
    member_dec.push_back(
        dst->create<ast::StructMemberOffsetDecoration>(Source{}, offset));
    members.push_back(dst->create<ast::StructMember>(
        Source{}, dst->Symbols().Register(kFirstVertexName), u32_type,
        std::move(member_dec)));
    vertex_index_offset_ = offset;
    offset += 4;
  }

  if (has_instance_index_) {
    ast::StructMemberDecorationList member_dec;
    member_dec.push_back(
        dst->create<ast::StructMemberOffsetDecoration>(Source{}, offset));
    members.push_back(dst->create<ast::StructMember>(
        Source{}, dst->Symbols().Register(kFirstInstanceName), u32_type,
        std::move(member_dec)));
    instance_index_offset_ = offset;
    offset += 4;
  }

  ast::StructDecorationList decos;
  decos.push_back(dst->create<ast::StructBlockDecoration>(Source{}));

  auto* struct_type = dst->create<type::Struct>(
      dst->Symbols().Register(kStructName),
      dst->create<ast::Struct>(Source{}, std::move(members), std::move(decos)));

  auto* idx_var = dst->create<ast::Variable>(
      Source{},                              // source
      dst->Symbols().Register(kBufferName),  // symbol
      ast::StorageClass::kUniform,           // storage_class
      struct_type,                           // type
      false,                                 // is_const
      nullptr,                               // constructor
      ast::VariableDecorationList{
          dst->create<ast::BindingDecoration>(Source{}, binding_),
          dst->create<ast::GroupDecoration>(Source{}, group_),
      });

  dst->AST().AddGlobalVariable(idx_var);

  dst->AST().AddConstructedType(struct_type);

  return idx_var;
}

ast::VariableDeclStatement* FirstIndexOffset::CreateFirstIndexOffset(
    const std::string& original_name,
    const std::string& field_name,
    ast::Variable* buffer_var,
    ProgramBuilder* dst) {
  auto* buffer =
      dst->create<ast::IdentifierExpression>(Source{}, buffer_var->symbol());

  auto lhs_name = kIndexOffsetPrefix + original_name;
  auto* constructor = dst->create<ast::BinaryExpression>(
      Source{}, ast::BinaryOp::kAdd,
      dst->create<ast::IdentifierExpression>(Source{},
                                             dst->Symbols().Register(lhs_name)),
      dst->create<ast::MemberAccessorExpression>(
          Source{}, buffer,
          dst->create<ast::IdentifierExpression>(
              Source{}, dst->Symbols().Register(field_name))));
  auto* var = dst->create<ast::Variable>(
      Source{},                                // source
      dst->Symbols().Register(original_name),  // symbol
      ast::StorageClass::kNone,                // storage_class
      dst->create<type::U32>(),                // type
      true,                                    // is_const
      constructor,                             // constructor
      ast::VariableDecorationList{});          // decorations
  return dst->create<ast::VariableDeclStatement>(Source{}, var);
}

}  // namespace transform
}  // namespace tint