// Copyright 2022 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/tint/transform/builtin_polyfill.h"

#include <unordered_map>

#include "src/tint/program_builder.h"
#include "src/tint/sem/builtin.h"
#include "src/tint/sem/call.h"
#include "src/tint/utils/map.h"

TINT_INSTANTIATE_TYPEINFO(tint::transform::BuiltinPolyfill);
TINT_INSTANTIATE_TYPEINFO(tint::transform::BuiltinPolyfill::Config);

namespace tint {
namespace transform {

/// The PIMPL state for the BuiltinPolyfill transform
struct BuiltinPolyfill::State {
  /// Constructor
  /// @param c the CloneContext
  /// @param p the builtins to polyfill
  State(CloneContext& c, Builtins p) : ctx(c), polyfill(p) {}

  /// The clone context
  CloneContext& ctx;
  /// The builtins to polyfill
  Builtins polyfill;
  /// The destination program builder
  ProgramBuilder& b = *ctx.dst;
  /// The source clone context
  const sem::Info& sem = ctx.src->Sem();

  /// Builds the polyfill function for the `countLeadingZeros` builtin
  /// @param ty the parameter and return type for the function
  /// @return the polyfill function name
  Symbol countLeadingZeros(const sem::Type* ty) {
    auto name = b.Symbols().New("tint_count_leading_zeros");
    uint32_t width = WidthOf(ty);

    // Returns either u32 or vecN<u32>
    auto U = [&]() -> const ast::Type* {
      if (width == 1) {
        return b.ty.u32();
      }
      return b.ty.vec<ProgramBuilder::u32>(width);
    };
    auto V = [&](uint32_t value) -> const ast::Expression* {
      return ScalarOrVector(width, value);
    };
    b.Func(
        name, {b.Param("v", T(ty))}, T(ty),
        {
            // var x = U(v);
            b.Decl(b.Var("x", nullptr, b.Construct(U(), b.Expr("v")))),
            // let b16 = select(0, 16, x <= 0x0000ffff);
            b.Decl(b.Const("b16", nullptr,
                           b.Call("select", V(0), V(16),
                                  b.LessThanEqual("x", V(0x0000ffff))))),
            // x = x << b16;
            b.Assign("x", b.Shl("x", "b16")),
            // let b8  = select(0, 8,  x <= 0x00ffffff);
            b.Decl(b.Const("b8", nullptr,
                           b.Call("select", V(0), V(8),
                                  b.LessThanEqual("x", V(0x00ffffff))))),
            // x = x << b8;
            b.Assign("x", b.Shl("x", "b8")),
            // let b4  = select(0, 4,  x <= 0x0fffffff);
            b.Decl(b.Const("b4", nullptr,
                           b.Call("select", V(0), V(4),
                                  b.LessThanEqual("x", V(0x0fffffff))))),
            // x = x << b4;
            b.Assign("x", b.Shl("x", "b4")),
            // let b2  = select(0, 2,  x <= 0x3fffffff);
            b.Decl(b.Const("b2", nullptr,
                           b.Call("select", V(0), V(2),
                                  b.LessThanEqual("x", V(0x3fffffff))))),
            // x = x << b2;
            b.Assign("x", b.Shl("x", "b2")),
            // let b1  = select(0, 1,  x <= 0x7fffffff);
            b.Decl(b.Const("b1", nullptr,
                           b.Call("select", V(0), V(1),
                                  b.LessThanEqual("x", V(0x7fffffff))))),
            // let is_zero  = select(0, 1, x == 0);
            b.Decl(b.Const("is_zero", nullptr,
                           b.Call("select", V(0), V(1), b.Equal("x", V(0))))),
            // return R((b16 | b8 | b4 | b2 | b1) + zero);
            b.Return(b.Construct(
                T(ty),
                b.Add(b.Or(b.Or(b.Or(b.Or("b16", "b8"), "b4"), "b2"), "b1"),
                      "is_zero"))),
        });
    return name;
  }

  /// Builds the polyfill function for the `countTrailingZeros` builtin
  /// @param ty the parameter and return type for the function
  /// @return the polyfill function name
  Symbol countTrailingZeros(const sem::Type* ty) {
    auto name = b.Symbols().New("tint_count_trailing_zeros");
    uint32_t width = WidthOf(ty);

    // Returns either u32 or vecN<u32>
    auto U = [&]() -> const ast::Type* {
      if (width == 1) {
        return b.ty.u32();
      }
      return b.ty.vec<ProgramBuilder::u32>(width);
    };
    auto V = [&](uint32_t value) -> const ast::Expression* {
      return ScalarOrVector(width, value);
    };
    auto B = [&](const ast::Expression* value) -> const ast::Expression* {
      if (width == 1) {
        return b.Construct<bool>(value);
      }
      return b.Construct(b.ty.vec<bool>(width), value);
    };
    b.Func(
        name, {b.Param("v", T(ty))}, T(ty),
        {
            // var x = U(v);
            b.Decl(b.Var("x", nullptr, b.Construct(U(), b.Expr("v")))),
            // let b16 = select(16, 0, bool(x & 0x0000ffff));
            b.Decl(b.Const(
                "b16", nullptr,
                b.Call("select", V(16), V(0), B(b.And("x", V(0x0000ffff)))))),
            // x = x >> b16;
            b.Assign("x", b.Shr("x", "b16")),
            // let b8  = select(8,  0, bool(x & 0x000000ff));
            b.Decl(b.Const(
                "b8", nullptr,
                b.Call("select", V(8), V(0), B(b.And("x", V(0x000000ff)))))),
            // x = x >> b8;
            b.Assign("x", b.Shr("x", "b8")),
            // let b4  = select(4,  0, bool(x & 0x0000000f));
            b.Decl(b.Const(
                "b4", nullptr,
                b.Call("select", V(4), V(0), B(b.And("x", V(0x0000000f)))))),
            // x = x >> b4;
            b.Assign("x", b.Shr("x", "b4")),
            // let b2  = select(2,  0, bool(x & 0x00000003));
            b.Decl(b.Const(
                "b2", nullptr,
                b.Call("select", V(2), V(0), B(b.And("x", V(0x00000003)))))),
            // x = x >> b2;
            b.Assign("x", b.Shr("x", "b2")),
            // let b1  = select(1,  0, bool(x & 0x00000001));
            b.Decl(b.Const(
                "b1", nullptr,
                b.Call("select", V(1), V(0), B(b.And("x", V(0x00000001)))))),
            // let is_zero  = select(0, 1, x == 0);
            b.Decl(b.Const("is_zero", nullptr,
                           b.Call("select", V(0), V(1), b.Equal("x", V(0))))),
            // return R((b16 | b8 | b4 | b2 | b1) + zero);
            b.Return(b.Construct(
                T(ty),
                b.Add(b.Or(b.Or(b.Or(b.Or("b16", "b8"), "b4"), "b2"), "b1"),
                      "is_zero"))),
        });
    return name;
  }

  /// Builds the polyfill function for the `extractBits` builtin
  /// @param ty the parameter and return type for the function
  /// @return the polyfill function name
  Symbol extractBits(const sem::Type* ty) {
    auto name = b.Symbols().New("tint_extract_bits");
    uint32_t width = WidthOf(ty);

    constexpr uint32_t W = 32u;  // 32-bit

    auto vecN_u32 =
        [&](const ast::Expression* value) -> const ast::Expression* {
      if (width == 1) {
        return value;
      }
      return b.Construct(b.ty.vec<ProgramBuilder::u32>(width), value);
    };

    ast::StatementList body = {
        b.Decl(b.Const("s", nullptr, b.Call("min", "offset", W))),
        b.Decl(b.Const("e", nullptr, b.Call("min", W, b.Add("s", "count")))),
    };

    switch (polyfill.extract_bits) {
      case Level::kFull:
        body.emplace_back(b.Decl(b.Const("shl", nullptr, b.Sub(W, "e"))));
        body.emplace_back(b.Decl(b.Const("shr", nullptr, b.Add("shl", "s"))));
        body.emplace_back(b.Return(b.Shr(b.Shl("v", vecN_u32(b.Expr("shl"))),
                                         vecN_u32(b.Expr("shr")))));
        break;
      case Level::kClampParameters:
        body.emplace_back(
            b.Return(b.Call("extractBits", "v", "s", b.Sub("e", "s"))));
        break;
      default:
        TINT_ICE(Transform, b.Diagnostics())
            << "unhandled polyfill level: "
            << static_cast<int>(polyfill.extract_bits);
        return {};
    }

    b.Func(name,
           {
               b.Param("v", T(ty)),
               b.Param("offset", b.ty.u32()),
               b.Param("count", b.ty.u32()),
           },
           T(ty), body);

    return name;
  }

  /// Builds the polyfill function for the `firstLeadingBit` builtin
  /// @param ty the parameter and return type for the function
  /// @return the polyfill function name
  Symbol firstLeadingBit(const sem::Type* ty) {
    auto name = b.Symbols().New("tint_first_leading_bit");
    uint32_t width = WidthOf(ty);

    // Returns either u32 or vecN<u32>
    auto U = [&]() -> const ast::Type* {
      if (width == 1) {
        return b.ty.u32();
      }
      return b.ty.vec<ProgramBuilder::u32>(width);
    };
    auto V = [&](uint32_t value) -> const ast::Expression* {
      return ScalarOrVector(width, value);
    };
    auto B = [&](const ast::Expression* value) -> const ast::Expression* {
      if (width == 1) {
        return b.Construct<bool>(value);
      }
      return b.Construct(b.ty.vec<bool>(width), value);
    };

    const ast::Expression* x = nullptr;
    if (ty->is_unsigned_scalar_or_vector()) {
      x = b.Expr("v");
    } else {
      // If ty is signed, then the value is inverted if the sign is negative
      x = b.Call("select",                             //
                 b.Construct(U(), "v"),                //
                 b.Construct(U(), b.Complement("v")),  //
                 b.LessThan("v", ScalarOrVector(width, 0)));
    }

    b.Func(name, {b.Param("v", T(ty))}, T(ty),
           {
               // var x = v;                          (unsigned)
               // var x = select(U(v), ~U(v), v < 0); (signed)
               b.Decl(b.Var("x", nullptr, x)),
               // let b16 = select(0, 16, bool(x & 0xffff0000));
               b.Decl(b.Const("b16", nullptr,
                              b.Call("select", V(0), V(16),
                                     B(b.And("x", V(0xffff0000)))))),
               // x = x >> b16;
               b.Assign("x", b.Shr("x", "b16")),
               // let b8  = select(0, 8,  bool(x & 0x0000ff00));
               b.Decl(b.Const(
                   "b8", nullptr,
                   b.Call("select", V(0), V(8), B(b.And("x", V(0x0000ff00)))))),
               // x = x >> b8;
               b.Assign("x", b.Shr("x", "b8")),
               // let b4  = select(0, 4,  bool(x & 0x000000f0));
               b.Decl(b.Const(
                   "b4", nullptr,
                   b.Call("select", V(0), V(4), B(b.And("x", V(0x000000f0)))))),
               // x = x >> b4;
               b.Assign("x", b.Shr("x", "b4")),
               // let b2  = select(0, 2,  bool(x & 0x0000000c));
               b.Decl(b.Const(
                   "b2", nullptr,
                   b.Call("select", V(0), V(2), B(b.And("x", V(0x0000000c)))))),
               // x = x >> b2;
               b.Assign("x", b.Shr("x", "b2")),
               // let b1  = select(0, 1,  bool(x & 0x00000002));
               b.Decl(b.Const(
                   "b1", nullptr,
                   b.Call("select", V(0), V(1), B(b.And("x", V(0x00000002)))))),
               // let is_zero  = select(0, 0xffffffff, x == 0);
               b.Decl(b.Const("is_zero", nullptr,
                              b.Call("select", V(0), V(0xffffffff),
                                     b.Equal("x", V(0))))),
               // return R(b16 | b8 | b4 | b2 | b1 | zero);
               b.Return(b.Construct(
                   T(ty),
                   b.Or(b.Or(b.Or(b.Or(b.Or("b16", "b8"), "b4"), "b2"), "b1"),
                        "is_zero"))),
           });
    return name;
  }

  /// Builds the polyfill function for the `firstTrailingBit` builtin
  /// @param ty the parameter and return type for the function
  /// @return the polyfill function name
  Symbol firstTrailingBit(const sem::Type* ty) {
    auto name = b.Symbols().New("tint_first_trailing_bit");
    uint32_t width = WidthOf(ty);

    // Returns either u32 or vecN<u32>
    auto U = [&]() -> const ast::Type* {
      if (width == 1) {
        return b.ty.u32();
      }
      return b.ty.vec<ProgramBuilder::u32>(width);
    };
    auto V = [&](uint32_t value) -> const ast::Expression* {
      return ScalarOrVector(width, value);
    };
    auto B = [&](const ast::Expression* value) -> const ast::Expression* {
      if (width == 1) {
        return b.Construct<bool>(value);
      }
      return b.Construct(b.ty.vec<bool>(width), value);
    };
    b.Func(name, {b.Param("v", T(ty))}, T(ty),
           {
               // var x = U(v);
               b.Decl(b.Var("x", nullptr, b.Construct(U(), b.Expr("v")))),
               // let b16 = select(16, 0, bool(x & 0x0000ffff));
               b.Decl(b.Const("b16", nullptr,
                              b.Call("select", V(16), V(0),
                                     B(b.And("x", V(0x0000ffff)))))),
               // x = x >> b16;
               b.Assign("x", b.Shr("x", "b16")),
               // let b8  = select(8,  0, bool(x & 0x000000ff));
               b.Decl(b.Const(
                   "b8", nullptr,
                   b.Call("select", V(8), V(0), B(b.And("x", V(0x000000ff)))))),
               // x = x >> b8;
               b.Assign("x", b.Shr("x", "b8")),
               // let b4  = select(4,  0, bool(x & 0x0000000f));
               b.Decl(b.Const(
                   "b4", nullptr,
                   b.Call("select", V(4), V(0), B(b.And("x", V(0x0000000f)))))),
               // x = x >> b4;
               b.Assign("x", b.Shr("x", "b4")),
               // let b2  = select(2,  0, bool(x & 0x00000003));
               b.Decl(b.Const(
                   "b2", nullptr,
                   b.Call("select", V(2), V(0), B(b.And("x", V(0x00000003)))))),
               // x = x >> b2;
               b.Assign("x", b.Shr("x", "b2")),
               // let b1  = select(1,  0, bool(x & 0x00000001));
               b.Decl(b.Const(
                   "b1", nullptr,
                   b.Call("select", V(1), V(0), B(b.And("x", V(0x00000001)))))),
               // let is_zero  = select(0, 0xffffffff, x == 0);
               b.Decl(b.Const("is_zero", nullptr,
                              b.Call("select", V(0), V(0xffffffff),
                                     b.Equal("x", V(0))))),
               // return R(b16 | b8 | b4 | b2 | b1 | is_zero);
               b.Return(b.Construct(
                   T(ty),
                   b.Or(b.Or(b.Or(b.Or(b.Or("b16", "b8"), "b4"), "b2"), "b1"),
                        "is_zero"))),
           });
    return name;
  }

 private:
  const ast::Type* T(const sem::Type* ty) const {
    return CreateASTTypeFor(ctx, ty);
  }
  uint32_t WidthOf(const sem::Type* ty) const {
    if (auto* v = ty->As<sem::Vector>()) {
      return v->Width();
    }
    return 1;
  }
  template <typename T>
  const ast::Expression* ScalarOrVector(uint32_t width, T value) const {
    if (width == 1) {
      return b.Expr(value);
    }
    return b.Construct(b.ty.vec<T>(width), value);
  }
};

BuiltinPolyfill::BuiltinPolyfill() = default;

BuiltinPolyfill::~BuiltinPolyfill() = default;

bool BuiltinPolyfill::ShouldRun(const Program* program,
                                const DataMap& data) const {
  if (auto* cfg = data.Get<Config>()) {
    auto builtins = cfg->builtins;
    auto& sem = program->Sem();
    for (auto* node : program->ASTNodes().Objects()) {
      if (auto* call = sem.Get<sem::Call>(node)) {
        if (auto* builtin = call->Target()->As<sem::Builtin>()) {
          switch (builtin->Type()) {
            case sem::BuiltinType::kCountLeadingZeros:
              if (builtins.count_leading_zeros) {
                return true;
              }
              break;
            case sem::BuiltinType::kCountTrailingZeros:
              if (builtins.count_trailing_zeros) {
                return true;
              }
              break;
            case sem::BuiltinType::kExtractBits:
              if (builtins.extract_bits != Level::kNone) {
                return true;
              }
              break;
            case sem::BuiltinType::kFirstLeadingBit:
              if (builtins.first_leading_bit) {
                return true;
              }
              break;
            case sem::BuiltinType::kFirstTrailingBit:
              if (builtins.first_trailing_bit) {
                return true;
              }
              break;
            default:
              break;
          }
        }
      }
    }
  }
  return false;
}

void BuiltinPolyfill::Run(CloneContext& ctx,
                          const DataMap& data,
                          DataMap&) const {
  auto* cfg = data.Get<Config>();
  if (!cfg) {
    ctx.Clone();
    return;
  }

  std::unordered_map<const sem::Builtin*, Symbol> polyfills;

  ctx.ReplaceAll(
      [&](const ast::CallExpression* expr) -> const ast::CallExpression* {
        auto builtins = cfg->builtins;
        State s{ctx, builtins};
        if (auto* call = s.sem.Get<sem::Call>(expr)) {
          if (auto* builtin = call->Target()->As<sem::Builtin>()) {
            Symbol polyfill;
            switch (builtin->Type()) {
              case sem::BuiltinType::kCountLeadingZeros:
                if (builtins.count_leading_zeros) {
                  polyfill = utils::GetOrCreate(polyfills, builtin, [&] {
                    return s.countLeadingZeros(builtin->ReturnType());
                  });
                }
                break;
              case sem::BuiltinType::kCountTrailingZeros:
                if (builtins.count_trailing_zeros) {
                  polyfill = utils::GetOrCreate(polyfills, builtin, [&] {
                    return s.countTrailingZeros(builtin->ReturnType());
                  });
                }
                break;
              case sem::BuiltinType::kExtractBits:
                if (builtins.extract_bits != Level::kNone) {
                  polyfill = utils::GetOrCreate(polyfills, builtin, [&] {
                    return s.extractBits(builtin->ReturnType());
                  });
                }
                break;
              case sem::BuiltinType::kFirstLeadingBit:
                if (builtins.first_leading_bit) {
                  polyfill = utils::GetOrCreate(polyfills, builtin, [&] {
                    return s.firstLeadingBit(builtin->ReturnType());
                  });
                }
                break;
              case sem::BuiltinType::kFirstTrailingBit:
                if (builtins.first_trailing_bit) {
                  polyfill = utils::GetOrCreate(polyfills, builtin, [&] {
                    return s.firstTrailingBit(builtin->ReturnType());
                  });
                }
                break;
              default:
                break;
            }
            if (polyfill.IsValid()) {
              return s.b.Call(polyfill, ctx.Clone(call->Declaration()->args));
            }
          }
        }
        return nullptr;
      });

  ctx.Clone();
}

BuiltinPolyfill::Config::Config(const Builtins& b) : builtins(b) {}
BuiltinPolyfill::Config::Config(const Config&) = default;
BuiltinPolyfill::Config::~Config() = default;

}  // namespace transform
}  // namespace tint