dawn-cmake/src/tint/transform/builtin_polyfill.cc

// 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 <algorithm>
#include <tuple>
#include <unordered_map>
#include <utility>

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

using namespace tint::number_suffixes;  // NOLINT

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

namespace tint::transform {

/// BinaryOpSignature is tuple of a binary op, LHS type and RHS type
using BinaryOpSignature = std::tuple<ast::BinaryOp, const sem::Type*, const sem::Type*>;

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

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

        auto V = [&](AFloat value) -> const ast::Expression* {
            const ast::Expression* expr = b.Expr(value);
            if (width == 1) {
                return expr;
            }
            return b.Construct(T(ty), expr);
        };

        utils::Vector<const ast::Statement*, 4> body;
        switch (polyfill.acosh) {
            case Level::kFull:
                // return log(x + sqrt(x*x - 1));
                body.Push(b.Return(
                    b.Call("log", b.Add("x", b.Call("sqrt", b.Sub(b.Mul("x", "x"), 1_a))))));
                break;
            case Level::kRangeCheck: {
                // return select(acosh(x), 0, x < 1);
                body.Push(b.Return(
                    b.Call("select", b.Call("acosh", "x"), V(0.0_a), b.LessThan("x", V(1.0_a)))));
                break;
            }
            default:
                TINT_ICE(Transform, b.Diagnostics())
                    << "unhandled polyfill level: " << static_cast<int>(polyfill.acosh);
                return {};
        }

        b.Func(name, utils::Vector{b.Param("x", T(ty))}, T(ty), body);

        return name;
    }

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

        // return log(x + sqrt(x*x + 1));
        b.Func(name, utils::Vector{b.Param("x", T(ty))}, T(ty),
               utils::Vector{
                   b.Return(b.Call("log", b.Add("x", b.Call("sqrt", b.Add(b.Mul("x", "x"), 1_a))))),
               });

        return name;
    }

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

        auto V = [&](AFloat value) -> const ast::Expression* {
            const ast::Expression* expr = b.Expr(value);
            if (width == 1) {
                return expr;
            }
            return b.Construct(T(ty), expr);
        };

        utils::Vector<const ast::Statement*, 1> body;
        switch (polyfill.atanh) {
            case Level::kFull:
                // return log((1+x) / (1-x)) * 0.5
                body.Push(
                    b.Return(b.Mul(b.Call("log", b.Div(b.Add(1_a, "x"), b.Sub(1_a, "x"))), 0.5_a)));
                break;
            case Level::kRangeCheck:
                // return select(atanh(x), 0, x >= 1);
                body.Push(b.Return(b.Call("select", b.Call("atanh", "x"), V(0.0_a),
                                          b.GreaterThanEqual("x", V(1.0_a)))));
                break;
            default:
                TINT_ICE(Transform, b.Diagnostics())
                    << "unhandled polyfill level: " << static_cast<int>(polyfill.acosh);
                return {};
        }

        b.Func(name, utils::Vector{b.Param("x", T(ty))}, T(ty), body);

        return name;
    }

    /// Builds the polyfill function for the `clamp` builtin when called with integer arguments
    /// (scalar or vector)
    /// @param ty the parameter and return type for the function
    /// @return the polyfill function name
    Symbol clampInteger(const sem::Type* ty) {
        auto name = b.Symbols().New("tint_clamp");

        b.Func(name,
               utils::Vector{
                   b.Param("e", T(ty)),
                   b.Param("low", T(ty)),
                   b.Param("high", T(ty)),
               },
               T(ty),
               utils::Vector{
                   // return min(max(e, low), high);
                   b.Return(b.Call("min", b.Call("max", "e", "low"), "high")),
               });
        return name;
    }

    /// 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<u32>(width);
        };
        auto V = [&](uint32_t value) -> const ast::Expression* {
            return ScalarOrVector(width, u32(value));
        };
        b.Func(name,
               utils::Vector{
                   b.Param("v", T(ty)),
               },
               T(ty),
               utils::Vector{
                   // var x = U(v);
                   b.Decl(b.Var("x", b.Construct(U(), b.Expr("v")))),
                   // let b16 = select(0, 16, x <= 0x0000ffff);
                   b.Decl(b.Let(
                       "b16", 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.Let("b8",
                                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.Let("b4",
                                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.Let("b2",
                                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.Let("b1",
                                b.Call("select", V(0), V(1), b.LessThanEqual("x", V(0x7fffffff))))),
                   // let is_zero  = select(0, 1, x == 0);
                   b.Decl(b.Let("is_zero", 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<u32>(width);
        };
        auto V = [&](uint32_t value) -> const ast::Expression* {
            return ScalarOrVector(width, u32(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,
            utils::Vector{
                b.Param("v", T(ty)),
            },
            T(ty),
            utils::Vector{
                // var x = U(v);
                b.Decl(b.Var("x", b.Construct(U(), b.Expr("v")))),
                // let b16 = select(16, 0, bool(x & 0x0000ffff));
                b.Decl(b.Let("b16", 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.Let("b8", 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.Let("b4", 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.Let("b2", 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.Let("b1", b.Call("select", V(1), V(0), B(b.And("x", V(0x00000001)))))),
                // let is_zero  = select(0, 1, x == 0);
                b.Decl(b.Let("is_zero", 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<u32>(width), value);
        };

        utils::Vector<const ast::Statement*, 8> body{
            b.Decl(b.Let("s", b.Call("min", "offset", u32(W)))),
            b.Decl(b.Let("e", b.Call("min", u32(W), b.Add("s", "count")))),
        };

        switch (polyfill.extract_bits) {
            case Level::kFull:
                body.Push(b.Decl(b.Let("shl", b.Sub(u32(W), "e"))));
                body.Push(b.Decl(b.Let("shr", b.Add("shl", "s"))));
                body.Push(
                    b.Return(b.Shr(b.Shl("v", vecN_u32(b.Expr("shl"))), vecN_u32(b.Expr("shr")))));
                break;
            case Level::kClampParameters:
                body.Push(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,
               utils::Vector{
                   b.Param("v", T(ty)),
                   b.Param("offset", b.ty.u32()),
                   b.Param("count", b.ty.u32()),
               },
               T(ty), std::move(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<u32>(width);
        };
        auto V = [&](uint32_t value) -> const ast::Expression* {
            return ScalarOrVector(width, u32(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_i)));
        }

        b.Func(
            name,
            utils::Vector{
                b.Param("v", T(ty)),
            },
            T(ty),
            utils::Vector{
                // var x = v;                          (unsigned)
                // var x = select(U(v), ~U(v), v < 0); (signed)
                b.Decl(b.Var("x", x)),
                // let b16 = select(0, 16, bool(x & 0xffff0000));
                b.Decl(b.Let("b16", 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.Let("b8", 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.Let("b4", 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.Let("b2", 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.Let("b1", b.Call("select", V(0), V(1), B(b.And("x", V(0x00000002)))))),
                // let is_zero  = select(0, 0xffffffff, x == 0);
                b.Decl(b.Let("is_zero", 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<u32>(width);
        };
        auto V = [&](uint32_t value) -> const ast::Expression* {
            return ScalarOrVector(width, u32(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,
            utils::Vector{
                b.Param("v", T(ty)),
            },
            T(ty),
            utils::Vector{
                // var x = U(v);
                b.Decl(b.Var("x", b.Construct(U(), b.Expr("v")))),
                // let b16 = select(16, 0, bool(x & 0x0000ffff));
                b.Decl(b.Let("b16", 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.Let("b8", 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.Let("b4", 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.Let("b2", 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.Let("b1", b.Call("select", V(1), V(0), B(b.And("x", V(0x00000001)))))),
                // let is_zero  = select(0, 0xffffffff, x == 0);
                b.Decl(b.Let("is_zero", 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;
    }

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

        // Currently in WGSL parameters of insertBits must be i32, u32, vecN<i32> or vecN<u32>
        if (!sem::Type::DeepestElementOf(ty)->IsAnyOf<sem::I32, sem::U32>()) {
            TINT_ICE(Transform, b.Diagnostics())
                << "insertBits polyfill only support i32, u32, and vector of i32 or u32, got "
                << b.FriendlyName(ty);
            return {};
        }

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

        auto V = [&](auto value) -> const ast::Expression* {
            const ast::Expression* expr = b.Expr(value);
            if (!ty->is_unsigned_scalar_or_vector()) {
                expr = b.Construct<i32>(expr);
            }
            if (ty->Is<sem::Vector>()) {
                expr = b.Construct(T(ty), expr);
            }
            return expr;
        };
        auto U = [&](auto value) -> const ast::Expression* {
            if (width == 1) {
                return b.Expr(value);
            }
            return b.vec(b.ty.u32(), width, value);
        };

        // Polyfill algorithm:
        //      s = min(offset, 32u);
        //      e = min(32u, (s + count));
        //      mask = (((1u << s) - 1u) ^ ((1u << e) - 1u));
        //      return (((n << s) & mask) | (v & ~(mask)));
        // Note that the algorithm above use the left-shifting in C++ manner, but in WGSL, HLSL, MSL
        // the rhs are modulo to bit-width of lhs (that is 32u in this case), and in GLSL the result
        // is undefined if rhs is greater than or equal to bit-width of lhs. The results of `x << y`
        // in C++ and HLSL are different when `y >= 32u`, and the `s` and `e` defined above can be
        // 32u, which are cases we must handle specially. Replace all `(x << y)` to
        // `select(Tx(), x << y, y < 32u)`, in which `Tx` is the type of x, where y can be greater
        // than or equal to 32u.
        // WGSL polyfill function:
        //      fn tint_insert_bits(v : T, n : T, offset : u32, count : u32) -> T {
        //          let e = offset + count;
        //          let mask = (
        //                        (select(0u, 1u << offset, offset < 32u) - 1u) ^
        //                        (select(0u, 1u << e, e < 32u) - 1u)
        //                     );
        //          return ((select(T(), n << offset, offset < 32u) & mask) | (v & ~(mask)));
        //      }

        utils::Vector<const ast::Statement*, 8> body;

        switch (polyfill.insert_bits) {
            case Level::kFull:
                // let e = offset + count;
                body.Push(b.Decl(b.Let("e", b.Add("offset", "count"))));

                // let mask = (
                //              (select(0u, 1u << offset, offset < 32u) - 1u) ^
                //              (select(0u, 1u << e, e < 32u) - 1u)
                //            );
                body.Push(b.Decl(b.Let(
                    "mask",
                    b.Xor(  //
                        b.Sub(
                            b.Call("select", 0_u, b.Shl(1_u, "offset"), b.LessThan("offset", 32_u)),
                            1_u),
                        b.Sub(b.Call("select", 0_u, b.Shl(1_u, "e"), b.LessThan("e", 32_u)),
                              1_u)  //
                        ))));

                // return ((select(T(), n << offset, offset < 32u) & mask) | (v & ~(mask)));
                body.Push(
                    b.Return(b.Or(b.And(b.Call("select", b.Construct(T(ty)),
                                               b.Shl("n", U("offset")), b.LessThan("offset", 32_u)),
                                        V("mask")),
                                  b.And("v", V(b.Complement("mask"))))));

                break;
            case Level::kClampParameters:
                body.Push(b.Decl(b.Let("s", b.Call("min", "offset", u32(W)))));
                body.Push(b.Decl(b.Let("e", b.Call("min", u32(W), b.Add("s", "count")))));
                body.Push(b.Return(b.Call("insertBits", "v", "n", "s", b.Sub("e", "s"))));
                break;
            default:
                TINT_ICE(Transform, b.Diagnostics())
                    << "unhandled polyfill level: " << static_cast<int>(polyfill.insert_bits);
                return {};
        }

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

        return name;
    }

    /// Builds the polyfill function for a divide or modulo operator with integer scalar or vector
    /// operands.
    /// @param sig the signature of the binary operator
    /// @return the polyfill function name
    Symbol int_div_mod(const BinaryOpSignature& sig) {
        const auto op = std::get<0>(sig);
        const auto* lhs_ty = std::get<1>(sig);
        const auto* rhs_ty = std::get<2>(sig);
        const bool is_div = op == ast::BinaryOp::kDivide;

        uint32_t lhs_width = 1;
        uint32_t rhs_width = 1;
        const auto* lhs_el_ty = sem::Type::ElementOf(lhs_ty, &lhs_width);
        const auto* rhs_el_ty = sem::Type::ElementOf(rhs_ty, &rhs_width);

        const uint32_t width = std::max(lhs_width, rhs_width);

        const char* lhs = "lhs";
        const char* rhs = "rhs";

        utils::Vector<const ast::Statement*, 4> body;

        if (lhs_width < width) {
            // lhs is scalar, rhs is vector. Convert lhs to vector.
            body.Push(b.Decl(b.Let("l", b.vec(T(lhs_el_ty), width, b.Expr(lhs)))));
            lhs = "l";
        }
        if (rhs_width < width) {
            // lhs is vector, rhs is scalar. Convert rhs to vector.
            body.Push(b.Decl(b.Let("r", b.vec(T(rhs_el_ty), width, b.Expr(rhs)))));
            rhs = "r";
        }

        auto name = b.Symbols().New(is_div ? "tint_div" : "tint_mod");
        auto* use_one = b.Equal(rhs, ScalarOrVector(width, 0_a));
        if (lhs_ty->is_signed_scalar_or_vector()) {
            const auto bits = lhs_el_ty->Size() * 8;
            auto min_int = AInt(AInt::kLowestValue >> (AInt::kNumBits - bits));
            const ast::Expression* lhs_is_min = b.Equal(lhs, ScalarOrVector(width, min_int));
            const ast::Expression* rhs_is_minus_one = b.Equal(rhs, ScalarOrVector(width, -1_a));
            // use_one = use_one | ((lhs == MIN_INT) & (rhs == -1))
            use_one = b.Or(use_one, b.And(lhs_is_min, rhs_is_minus_one));
        }
        auto* select = b.Call("select", rhs, ScalarOrVector(width, 1_a), use_one);

        body.Push(b.Return(is_div ? b.Div(lhs, select) : b.Mod(lhs, select)));
        b.Func(name,
               utils::Vector{
                   b.Param("lhs", T(lhs_ty)),
                   b.Param("rhs", T(rhs_ty)),
               },
               width == 1 ? T(lhs_ty) : b.ty.vec(T(lhs_el_ty), width),  // return type
               std::move(body));

        return name;
    }

    /// Builds the polyfill function for the `saturate` builtin
    /// @param ty the parameter and return type for the function
    /// @return the polyfill function name
    Symbol saturate(const sem::Type* ty) {
        auto name = b.Symbols().New("tint_saturate");
        auto body = utils::Vector{
            b.Return(b.Call("clamp", "v", b.Construct(T(ty), 0_a), b.Construct(T(ty), 1_a))),
        };
        b.Func(name,
               utils::Vector{
                   b.Param("v", T(ty)),
               },
               T(ty), body);

        return name;
    }

    /// Builds the polyfill function for the `textureSampleBaseClampToEdge` builtin, when the
    /// texture type is texture_2d<f32>.
    /// @return the polyfill function name
    Symbol textureSampleBaseClampToEdge_2d_f32() {
        auto name = b.Symbols().New("tint_textureSampleBaseClampToEdge");
        auto body = utils::Vector{
            b.Decl(b.Let("dims",
                         b.Construct(b.ty.vec2<f32>(), b.Call("textureDimensions", "t", 0_a)))),
            b.Decl(b.Let("half_texel", b.Div(b.vec2<f32>(0.5_a), "dims"))),
            b.Decl(
                b.Let("clamped", b.Call("clamp", "coord", "half_texel", b.Sub(1_a, "half_texel")))),
            b.Return(b.Call("textureSampleLevel", "t", "s", "clamped", 0_a)),
        };
        b.Func(name,
               utils::Vector{
                   b.Param("t", b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32())),
                   b.Param("s", b.ty.sampler(ast::SamplerKind::kSampler)),
                   b.Param("coord", b.ty.vec2<f32>()),
               },
               b.ty.vec4<f32>(), body);
        return name;
    }

    /// Builds the polyfill function for the `quantizeToF16` builtin, by replacing the vector form
    /// with scalar calls.
    /// @param vec the vector type
    /// @return the polyfill function name
    Symbol quantizeToF16(const sem::Vector* vec) {
        auto name = b.Symbols().New("tint_quantizeToF16");
        utils::Vector<const ast::Expression*, 4> args;
        for (uint32_t i = 0; i < vec->Width(); i++) {
            args.Push(b.Call("quantizeToF16", b.IndexAccessor("v", u32(i))));
        }
        b.Func(name,
               utils::Vector{
                   b.Param("v", T(vec)),
               },
               T(vec),
               utils::Vector{
                   b.Return(b.Construct(T(vec), std::move(args))),
               });
        return name;
    }

  private:
    /// 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();

    /// @returns the AST type for the given sem type
    const ast::Type* T(const sem::Type* ty) const { return CreateASTTypeFor(ctx, ty); }

    /// @returns 1 if `ty` is not a vector, otherwise the vector width
    uint32_t WidthOf(const sem::Type* ty) const {
        if (auto* v = ty->As<sem::Vector>()) {
            return v->Width();
        }
        return 1;
    }

    /// @returns a scalar or vector with the given width, with each element with
    /// the given value.
    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;

Transform::ApplyResult BuiltinPolyfill::Apply(const Program* src,
                                              const DataMap& data,
                                              DataMap&) const {
    auto* cfg = data.Get<Config>();
    if (!cfg) {
        return SkipTransform;
    }

    auto& polyfill = cfg->builtins;

    utils::Hashmap<const sem::Builtin*, Symbol, 8> builtin_polyfills;
    utils::Hashmap<BinaryOpSignature, Symbol, 8> binary_op_polyfills;

    ProgramBuilder b;
    CloneContext ctx{&b, src, /* auto_clone_symbols */ true};
    State s{ctx, polyfill};

    bool made_changes = false;
    for (auto* node : src->ASTNodes().Objects()) {
        auto* expr = src->Sem().Get<sem::Expression>(node);
        if (!expr || expr->Stage() == sem::EvaluationStage::kConstant) {
            continue;  // Don't polyfill @const expressions
        }

        if (auto* call = expr->As<sem::Call>()) {
            auto* builtin = call->Target()->As<sem::Builtin>();
            if (!builtin) {
                continue;
            }
            Symbol fn;
            switch (builtin->Type()) {
                case sem::BuiltinType::kAcosh:
                    if (polyfill.acosh != Level::kNone) {
                        fn = builtin_polyfills.GetOrCreate(
                            builtin, [&] { return s.acosh(builtin->ReturnType()); });
                    }
                    break;
                case sem::BuiltinType::kAsinh:
                    if (polyfill.asinh) {
                        fn = builtin_polyfills.GetOrCreate(
                            builtin, [&] { return s.asinh(builtin->ReturnType()); });
                    }
                    break;
                case sem::BuiltinType::kAtanh:
                    if (polyfill.atanh != Level::kNone) {
                        fn = builtin_polyfills.GetOrCreate(
                            builtin, [&] { return s.atanh(builtin->ReturnType()); });
                    }
                    break;
                case sem::BuiltinType::kClamp:
                    if (polyfill.clamp_int) {
                        auto& sig = builtin->Signature();
                        if (sig.parameters[0]->Type()->is_integer_scalar_or_vector()) {
                            fn = builtin_polyfills.GetOrCreate(
                                builtin, [&] { return s.clampInteger(builtin->ReturnType()); });
                        }
                    }
                    break;
                case sem::BuiltinType::kCountLeadingZeros:
                    if (polyfill.count_leading_zeros) {
                        fn = builtin_polyfills.GetOrCreate(
                            builtin, [&] { return s.countLeadingZeros(builtin->ReturnType()); });
                    }
                    break;
                case sem::BuiltinType::kCountTrailingZeros:
                    if (polyfill.count_trailing_zeros) {
                        fn = builtin_polyfills.GetOrCreate(
                            builtin, [&] { return s.countTrailingZeros(builtin->ReturnType()); });
                    }
                    break;
                case sem::BuiltinType::kExtractBits:
                    if (polyfill.extract_bits != Level::kNone) {
                        fn = builtin_polyfills.GetOrCreate(
                            builtin, [&] { return s.extractBits(builtin->ReturnType()); });
                    }
                    break;
                case sem::BuiltinType::kFirstLeadingBit:
                    if (polyfill.first_leading_bit) {
                        fn = builtin_polyfills.GetOrCreate(
                            builtin, [&] { return s.firstLeadingBit(builtin->ReturnType()); });
                    }
                    break;
                case sem::BuiltinType::kFirstTrailingBit:
                    if (polyfill.first_trailing_bit) {
                        fn = builtin_polyfills.GetOrCreate(
                            builtin, [&] { return s.firstTrailingBit(builtin->ReturnType()); });
                    }
                    break;
                case sem::BuiltinType::kInsertBits:
                    if (polyfill.insert_bits != Level::kNone) {
                        fn = builtin_polyfills.GetOrCreate(
                            builtin, [&] { return s.insertBits(builtin->ReturnType()); });
                    }
                    break;
                case sem::BuiltinType::kSaturate:
                    if (polyfill.saturate) {
                        fn = builtin_polyfills.GetOrCreate(
                            builtin, [&] { return s.saturate(builtin->ReturnType()); });
                    }
                    break;
                case sem::BuiltinType::kTextureSampleBaseClampToEdge:
                    if (polyfill.texture_sample_base_clamp_to_edge_2d_f32) {
                        auto& sig = builtin->Signature();
                        auto* tex = sig.Parameter(sem::ParameterUsage::kTexture);
                        if (auto* stex = tex->Type()->As<sem::SampledTexture>()) {
                            if (stex->type()->Is<sem::F32>()) {
                                fn = builtin_polyfills.GetOrCreate(builtin, [&] {
                                    return s.textureSampleBaseClampToEdge_2d_f32();
                                });
                            }
                        }
                    }
                    break;
                case sem::BuiltinType::kQuantizeToF16:
                    if (polyfill.quantize_to_vec_f16) {
                        if (auto* vec = builtin->ReturnType()->As<sem::Vector>()) {
                            fn = builtin_polyfills.GetOrCreate(
                                builtin, [&] { return s.quantizeToF16(vec); });
                        }
                    }
                    break;

                default:
                    break;
            }

            if (fn.IsValid()) {
                auto* replacement = b.Call(fn, ctx.Clone(call->Declaration()->args));
                ctx.Replace(call->Declaration(), replacement);
                made_changes = true;
            }
        } else if (auto* bin_op = node->As<ast::BinaryExpression>()) {
            switch (bin_op->op) {
                case ast::BinaryOp::kShiftLeft:
                case ast::BinaryOp::kShiftRight: {
                    if (polyfill.bitshift_modulo) {
                        auto* lhs_ty = src->TypeOf(bin_op->lhs)->UnwrapRef();
                        auto* rhs_ty = src->TypeOf(bin_op->rhs)->UnwrapRef();
                        auto* lhs_el_ty = sem::Type::DeepestElementOf(lhs_ty);
                        const ast::Expression* mask = b.Expr(AInt(lhs_el_ty->Size() * 8 - 1));
                        if (rhs_ty->Is<sem::Vector>()) {
                            mask = b.Construct(CreateASTTypeFor(ctx, rhs_ty), mask);
                        }
                        auto* mod = b.And(ctx.Clone(bin_op->rhs), mask);
                        ctx.Replace(bin_op->rhs, mod);
                        made_changes = true;
                    }
                    break;
                }
                case ast::BinaryOp::kDivide:
                case ast::BinaryOp::kModulo: {
                    if (polyfill.int_div_mod) {
                        auto* lhs_ty = src->TypeOf(bin_op->lhs)->UnwrapRef();
                        if (lhs_ty->is_integer_scalar_or_vector()) {
                            auto* rhs_ty = src->TypeOf(bin_op->rhs)->UnwrapRef();
                            BinaryOpSignature sig{bin_op->op, lhs_ty, rhs_ty};
                            auto fn = binary_op_polyfills.GetOrCreate(
                                sig, [&] { return s.int_div_mod(sig); });
                            auto* lhs = ctx.Clone(bin_op->lhs);
                            auto* rhs = ctx.Clone(bin_op->rhs);
                            ctx.Replace(bin_op, b.Call(fn, lhs, rhs));
                            made_changes = true;
                        }
                    }
                    break;
                }
                default:
                    break;
            }
        }
    }

    if (!made_changes) {
        return SkipTransform;
    }

    ctx.Clone();
    return Program(std::move(b));
}

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

}  // namespace tint::transform