// Copyright 2023 The Dawn & Tint Authors
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#include "src/tint/lang/core/ir/transform/builtin_polyfill.h"

#include <vector>

#include "src/tint/lang/core/ir/builder.h"
#include "src/tint/lang/core/ir/module.h"
#include "src/tint/lang/core/ir/validator.h"
#include "src/tint/lang/core/type/sampled_texture.h"
#include "src/tint/lang/core/type/texture.h"

using namespace tint::core::fluent_types;     // NOLINT
using namespace tint::core::number_suffixes;  // NOLINT

namespace tint::core::ir::transform {

namespace {

/// Constant value used to polyfill the radians() builtin.
static constexpr double kDegToRad = 0.017453292519943295474;

/// Constant value used to polyfill the degrees() builtin.
static constexpr double kRadToDeg = 57.295779513082322865;

/// PIMPL state for the transform.
struct State {
    /// The polyfill config.
    const BuiltinPolyfillConfig& config;

    /// The IR module.
    Module& ir;

    /// The IR builder.
    Builder b{ir};

    /// The type manager.
    core::type::Manager& ty{ir.Types()};

    /// The symbol table.
    SymbolTable& sym{ir.symbols};

    /// Process the module.
    void Process() {
        std::vector<std::function<void()>> worklist;
        worklist.reserve(128);

        // Find the builtin call instructions that may need to be polyfilled.
        for (auto* inst : ir.Instructions()) {
            if (auto* builtin = inst->As<ir::CoreBuiltinCall>()) {
                switch (builtin->Func()) {
                    case core::BuiltinFn::kClamp:
                        if ((config.clamp_int &&
                             builtin->Result()->Type()->IsIntegerScalarOrVector()) ||
                            (config.clamp_float &&
                             builtin->Result()->Type()->IsFloatScalarOrVector())) {
                            worklist.push_back([this, builtin] { Clamp(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kAbs:
                        if (config.abs_signed_int &&
                            builtin->Result()->Type()->IsSignedIntegerScalarOrVector()) {
                            worklist.push_back([this, builtin] { AbsSignedInt(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kCountLeadingZeros:
                        if (config.count_leading_zeros) {
                            worklist.push_back([this, builtin] { CountLeadingZeros(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kCountTrailingZeros:
                        if (config.count_trailing_zeros) {
                            worklist.push_back([this, builtin] { CountTrailingZeros(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kDegrees:
                        if (config.degrees) {
                            worklist.push_back([this, builtin] { Degrees(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kDistance:
                        if (config.distance_scalar_float &&
                            builtin->Args()[0]->Type()->IsFloatScalar()) {
                            worklist.push_back([this, builtin] { DistanceScalarFloat(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kSmoothstep:
                        worklist.push_back([this, builtin] { SmoothStep(builtin); });
                        break;
                    case core::BuiltinFn::kExtractBits:
                        if (config.extract_bits != BuiltinPolyfillLevel::kNone) {
                            worklist.push_back([this, builtin] { ExtractBits(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kFirstLeadingBit:
                        if (config.first_leading_bit) {
                            worklist.push_back([this, builtin] { FirstLeadingBit(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kFirstTrailingBit:
                        if (config.first_trailing_bit) {
                            worklist.push_back([this, builtin] { FirstTrailingBit(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kFwidthFine:
                        if (config.fwidth_fine) {
                            worklist.push_back([this, builtin] { FwidthFine(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kInsertBits:
                        if (config.insert_bits != BuiltinPolyfillLevel::kNone) {
                            worklist.push_back([this, builtin] { InsertBits(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kLength:
                        if (config.length_scalar_float &&
                            builtin->Args()[0]->Type()->IsFloatScalar()) {
                            worklist.push_back([this, builtin] { LengthScalarFloat(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kRadians:
                        if (config.radians) {
                            worklist.push_back([this, builtin] { Radians(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kReflect:
                        if (config.reflect_vec2_f32) {
                            // Polyfill for vec2<f32>. See crbug.com/tint/1798
                            auto* vec_ty = builtin->Result()->Type()->As<core::type::Vector>();
                            if (vec_ty->Width() == 2 && vec_ty->Type()->Is<core::type::F32>()) {
                                worklist.push_back([this, builtin] { Reflect(builtin); });
                            }
                        }
                        break;
                    case core::BuiltinFn::kSaturate: {
                        const bool is_vec_f16 =
                            builtin->Args()[0]->Type()->DeepestElement()->Is<core::type::F16>() &&
                            builtin->Args()[0]->Type()->IsFloatVector();
                        if ((is_vec_f16 && config.saturate_as_min_max) || config.saturate) {
                            worklist.push_back([this, builtin] { Saturate(builtin); });
                        }
                        break;
                    }
                    case core::BuiltinFn::kTextureSampleBias:
                        worklist.push_back([this, builtin] { TextureSampleBiasClamp(builtin); });
                        break;
                    case core::BuiltinFn::kTextureSampleBaseClampToEdge:
                        if (config.texture_sample_base_clamp_to_edge_2d_f32) {
                            auto* tex =
                                builtin->Args()[0]->Type()->As<core::type::SampledTexture>();
                            if (tex && tex->Dim() == core::type::TextureDimension::k2d &&
                                tex->Type()->Is<core::type::F32>()) {
                                worklist.push_back([this, builtin] {
                                    TextureSampleBaseClampToEdge_2d_f32(builtin);
                                });
                            }
                        }
                        break;
                    case core::BuiltinFn::kDot4U8Packed: {
                        if (config.dot_4x8_packed) {
                            worklist.push_back([this, builtin] { Dot4U8Packed(builtin); });
                        }
                        break;
                    }
                    case core::BuiltinFn::kDot4I8Packed: {
                        if (config.dot_4x8_packed) {
                            worklist.push_back([this, builtin] { Dot4I8Packed(builtin); });
                        }
                        break;
                    }
                    case core::BuiltinFn::kPack4XI8: {
                        if (config.pack_unpack_4x8) {
                            worklist.push_back([this, builtin] { Pack4xI8(builtin); });
                        }
                        break;
                    }
                    case core::BuiltinFn::kPack4XU8: {
                        if (config.pack_unpack_4x8) {
                            worklist.push_back([this, builtin] { Pack4xU8(builtin); });
                        }
                        break;
                    }
                    case core::BuiltinFn::kPack4XI8Clamp: {
                        if (config.pack_unpack_4x8) {
                            worklist.push_back([this, builtin] { Pack4xI8Clamp(builtin); });
                        }
                        break;
                    }
                    case core::BuiltinFn::kPack4XU8Clamp: {
                        if (config.pack_4xu8_clamp) {
                            worklist.push_back([this, builtin] { Pack4xU8Clamp(builtin); });
                        }
                        break;
                    }
                    case core::BuiltinFn::kUnpack4XI8: {
                        if (config.pack_unpack_4x8) {
                            worklist.push_back([this, builtin] { Unpack4xI8(builtin); });
                        }
                        break;
                    }
                    case core::BuiltinFn::kUnpack4XU8: {
                        if (config.pack_unpack_4x8) {
                            worklist.push_back([this, builtin] { Unpack4xU8(builtin); });
                        }
                        break;
                    }
                    case core::BuiltinFn::kPack4X8Snorm:
                        if (config.pack_unpack_4x8_norm) {
                            worklist.push_back([this, builtin] { Pack4x8Snorm(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kPack4X8Unorm:
                        if (config.pack_unpack_4x8_norm) {
                            worklist.push_back([this, builtin] { Pack4x8Unorm(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kUnpack4X8Snorm:
                        if (config.pack_unpack_4x8_norm) {
                            worklist.push_back([this, builtin] { Unpack4x8Snorm(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kUnpack4X8Unorm:
                        if (config.pack_unpack_4x8_norm) {
                            worklist.push_back([this, builtin] { Unpack4x8Unorm(builtin); });
                        }
                        break;
                    case core::BuiltinFn::kSubgroupBroadcast:
                        if (config.subgroup_broadcast_f16 &&
                            builtin->Result()->Type()->DeepestElement()->Is<core::type::F16>()) {
                            worklist.push_back([this, builtin] { SubgroupBroadcast(builtin); });
                        }
                        break;
                    default:
                        break;
                }
            }
        }

        for (auto& cb : worklist) {
            cb();
        }
    }

    /// Polyfill a `pack4x8snorm` builtin call
    void Pack4x8Snorm(ir::CoreBuiltinCall* call) {
        auto* arg = call->Args()[0];

        b.InsertBefore(call, [&] {
            auto* vec4f = ty.vec4f();
            auto* vec4u = ty.vec4u();

            auto* neg_one = b.Splat(vec4f, -1_f);
            auto* one = b.Splat(vec4f, 1_f);

            core::ir::Value* v = b.Clamp(arg, neg_one, one)->Result();
            v = b.Multiply(b.Splat(vec4f, 127_f), v)->Result();
            v = b.Add(b.Splat(vec4f, 0.5_f), v)->Result();
            v = b.Call(vec4f, core::BuiltinFn::kFloor, Vector{v})->Result();
            v = b.Convert(ty.vec4i(), v)->Result();
            v = b.Bitcast(vec4u, v)->Result();
            v = b.And(v, b.Splat(vec4u, 0xff_u))->Result();
            v = b.ShiftLeft(v, b.Construct(vec4u, 0_u, 8_u, 16_u, 24_u))->Result();

            auto* x = b.Access(ty.u32(), v, 0_u);
            auto* y = b.Access(ty.u32(), v, 1_u);
            auto* z = b.Access(ty.u32(), v, 2_u);
            auto* w = b.Access(ty.u32(), v, 3_u);

            v = b.Or(x, b.Or(y, b.Or(z, w)))->Result();

            call->Result()->ReplaceAllUsesWith(v);
        });
        call->Destroy();
    }

    /// Polyfill a `pack4x8unorm` builtin call
    void Pack4x8Unorm(ir::CoreBuiltinCall* call) {
        auto* arg = call->Args()[0];

        b.InsertBefore(call, [&] {
            auto* vec4f = ty.vec4f();
            auto* vec4u = ty.vec4u();

            auto* zero = b.Zero(vec4f);
            auto* one = b.Splat(vec4f, 1_f);

            auto* v = b.Clamp(arg, zero, one)->Result();
            v = b.Multiply(b.Splat(vec4f, 255_f), v)->Result();
            v = b.Add(b.Splat(vec4f, 0.5_f), v)->Result();
            v = b.Call(vec4f, core::BuiltinFn::kFloor, Vector{v})->Result();
            v = b.Convert(vec4u, v)->Result();
            v = b.And(v, b.Splat(vec4u, 0xff_u))->Result();
            v = b.ShiftLeft(v, b.Construct(vec4u, 0_u, 8_u, 16_u, 24_u))->Result();

            auto* x = b.Access(ty.u32(), v, 0_u);
            auto* y = b.Access(ty.u32(), v, 1_u);
            auto* z = b.Access(ty.u32(), v, 2_u);
            auto* w = b.Access(ty.u32(), v, 3_u);

            v = b.Or(x, b.Or(y, b.Or(z, w)))->Result();

            call->Result()->ReplaceAllUsesWith(v);
        });
        call->Destroy();
    }

    /// Polyfill a `unpack4x8snorm` builtin call
    void Unpack4x8Snorm(ir::CoreBuiltinCall* call) {
        auto* arg = call->Args()[0];

        b.InsertBefore(call, [&] {
            auto* vec4f = ty.vec4f();
            auto* vec4u = ty.vec4u();
            auto* vec4i = ty.vec4i();

            auto* v = b.Construct(vec4u, arg)->Result();
            // Shift left to put the 8th bit of each number into the sign bit location, we then
            // convert to an i32 and shift back, so the sign bit will be set as needed. The bits
            // outside the bottom 8 are then masked off.
            v = b.ShiftLeft(v, b.Construct(vec4u, 24_u, 16_u, 8_u, 0_u))->Result();
            v = b.Bitcast(vec4i, v)->Result();
            v = b.ShiftRight(v, b.Splat(vec4u, 24_u))->Result();
            v = b.Convert(vec4f, v)->Result();
            v = b.Divide(v, b.Splat(vec4f, 127_f))->Result();
            v = b.Max(v, b.Splat(vec4f, -1_f))->Result();

            call->Result()->ReplaceAllUsesWith(v);
        });
        call->Destroy();
    }

    /// Polyfill a `unpack4x8unorm` builtin call
    void Unpack4x8Unorm(ir::CoreBuiltinCall* call) {
        auto* arg = call->Args()[0];

        b.InsertBefore(call, [&] {
            auto* vec4f = ty.vec4f();
            auto* vec4u = ty.vec4u();

            auto* v = b.Construct(vec4u, arg)->Result();
            v = b.ShiftRight(v, b.Construct(vec4u, 0_u, 8_u, 16_u, 24_u))->Result();
            v = b.And(v, b.Splat(vec4u, 0xff_u))->Result();
            v = b.Convert(vec4f, v)->Result();
            v = b.Divide(v, b.Splat(vec4f, 255_f))->Result();

            call->Result()->ReplaceAllUsesWith(v);
        });
        call->Destroy();
    }

    /// Polyfill a `clamp()` builtin call for integers and floats.
    /// @param call the builtin call instruction
    void Clamp(ir::CoreBuiltinCall* call) {
        auto* e = call->Args()[0];
        auto* low = call->Args()[1];
        auto* high = call->Args()[2];

        b.InsertBefore(call, [&] {
            auto* max = b.Max(e, low);
            b.Min(max, high)->SetResult(call->DetachResult());
        });
        call->Destroy();
    }

    /// Polyfill a `abs()` builtin call for signed integers.
    /// @param call the builtin call instruction
    void AbsSignedInt(ir::CoreBuiltinCall* call) {
        auto* e = call->Args()[0];
        b.InsertBefore(call, [&] { b.Max(e, b.Negation(e))->SetResult(call->DetachResult()); });
        call->Destroy();
    }

    /// Polyfill a `countLeadingZeros()` builtin call.
    /// @param call the builtin call instruction
    void CountLeadingZeros(ir::CoreBuiltinCall* call) {
        auto* input = call->Args()[0];
        auto* result_ty = input->Type();
        auto* uint_ty = ty.MatchWidth(ty.u32(), result_ty);

        // Make an u32 constant with the same component count as result_ty.
        auto V = [&](uint32_t u) { return b.MatchWidth(u32(u), result_ty); };

        b.InsertBefore(call, [&] {
            // %x = %input;
            // if (%x is signed) {
            //   %x = bitcast<u32>(%x)
            // }
            // %b16 = select(0, 16, %x <= 0x0000ffff);
            // %x <<= %b16;
            // %b8  = select(0, 8, %x <= 0x00ffffff);
            // %x <<= %b8;
            // %b4  = select(0, 4, %x <= 0x0fffffff);
            // %x <<= %b4;
            // %b2  = select(0, 2, %x <= 0x3fffffff);
            // %x <<= %b2;
            // %b1  = select(0, 1, %x <= 0x7fffffff);
            // %b0  = select(0, 1, %x == 0);
            // %result = (%b16 | %b8 | %b4 | %b2 | %b1) + %b0;

            auto* x = input;
            if (result_ty->IsSignedIntegerScalarOrVector()) {
                x = b.Bitcast(uint_ty, x)->Result();
            }
            auto* b16 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(16),
                               b.LessThanEqual(x, V(0x0000ffff)));
            x = b.ShiftLeft(x, b16)->Result();
            auto* b8 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(8),
                              b.LessThanEqual(x, V(0x00ffffff)));
            x = b.ShiftLeft(x, b8)->Result();
            auto* b4 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(4),
                              b.LessThanEqual(x, V(0x0fffffff)));
            x = b.ShiftLeft(x, b4)->Result();
            auto* b2 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(2),
                              b.LessThanEqual(x, V(0x3fffffff)));
            x = b.ShiftLeft(x, b2)->Result();
            auto* b1 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(1),
                              b.LessThanEqual(x, V(0x7fffffff)));
            auto* b0 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(1), b.Equal(x, V(0)));
            Instruction* result = b.Add(b.Or(b16, b.Or(b8, b.Or(b4, b.Or(b2, b.Or(b1, b0))))), b0);
            if (result_ty->IsSignedIntegerScalarOrVector()) {
                result = b.Bitcast(result_ty, result);
            }
            result->SetResult(call->DetachResult());
        });
        call->Destroy();
    }

    /// Polyfill a `countTrailingZeros()` builtin call.
    /// @param call the builtin call instruction
    void CountTrailingZeros(ir::CoreBuiltinCall* call) {
        auto* input = call->Args()[0];
        auto* result_ty = input->Type();
        auto* uint_ty = ty.MatchWidth(ty.u32(), result_ty);

        // Make an u32 constant with the same component count as result_ty.
        auto V = [&](uint32_t u) { return b.MatchWidth(u32(u), result_ty); };

        b.InsertBefore(call, [&] {
            // %x = %input;
            // if (%x is signed) {
            //   %x = bitcast<u32>(%x)
            // }
            // %b16 = select(0, 16, (%x & 0x0000ffff) == 0);
            // %x >>= %b16;
            // %b8  = select(0, 8,  (%x & 0x000000ff) == 0);
            // %x >>= %b8;
            // %b4  = select(0, 4,  (%x & 0x0000000f) == 0);
            // %x >>= %b4;
            // %b2  = select(0, 2,  (%x & 0x00000003) == 0);
            // %x >>= %b2;
            // %b1  = select(0, 1,  (%x & 0x00000001) == 0);
            // %b0  = select(0, 1,  (%x & 0x00000001) == 0);
            // %result = (%b16 | %b8 | %b4 | %b2 | %b1) + %b0;

            auto* x = input;
            if (result_ty->IsSignedIntegerScalarOrVector()) {
                x = b.Bitcast(uint_ty, x)->Result();
            }
            auto* b16 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(16),
                               b.Equal(b.And(x, V(0x0000ffff)), V(0)));
            x = b.ShiftRight(x, b16)->Result();
            auto* b8 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(8),
                              b.Equal(b.And(x, V(0x000000ff)), V(0)));
            x = b.ShiftRight(x, b8)->Result();
            auto* b4 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(4),
                              b.Equal(b.And(x, V(0x0000000f)), V(0)));
            x = b.ShiftRight(x, b4)->Result();
            auto* b2 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(2),
                              b.Equal(b.And(x, V(0x00000003)), V(0)));
            x = b.ShiftRight(x, b2)->Result();
            auto* b1 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(1),
                              b.Equal(b.And(x, V(0x00000001)), V(0)));
            auto* b0 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(1), b.Equal(x, V(0)));
            Instruction* result = b.Add(b.Or(b16, b.Or(b8, b.Or(b4, b.Or(b2, b1)))), b0);
            if (result_ty->IsSignedIntegerScalarOrVector()) {
                result = b.Bitcast(result_ty, result);
            }
            result->SetResult(call->DetachResult());
        });
        call->Destroy();
    }

    /// Polyfill an `degrees()` builtin call.
    /// @param call the builtin call instruction
    void Degrees(ir::CoreBuiltinCall* call) {
        auto* arg = call->Args()[0];
        auto* type = arg->Type()->DeepestElement();
        ir::Value* value = nullptr;
        if (type->Is<core::type::F16>()) {
            value = b.Constant(f16(kRadToDeg));
        } else if (type->Is<core::type::F32>()) {
            value = b.Constant(f32(kRadToDeg));
        }
        b.InsertBefore(call, [&] {
            auto* mul = b.Multiply(arg, value);
            mul->SetResult(call->DetachResult());
        });
        call->Destroy();
    }

    /// Polyfill a `distance()` builtin call for scalar f32 and f16.
    /// @param call the builtin call instruction
    void DistanceScalarFloat(ir::CoreBuiltinCall* call) {
        // distance(x, y) -> abs(x - y)
        b.InsertBefore(call, [&] {
            auto* sub = b.Subtract(call->Args()[0], call->Args()[1]);
            b.CallWithResult(call->DetachResult(), core::BuiltinFn::kAbs, sub);
        });
        call->Destroy();
    }

    /// Polyfill an `smoothStep()` builtin call.
    /// @param call the builtin call instruction
    void SmoothStep(ir::CoreBuiltinCall* call) {
        auto* edge0_arg = call->Args()[0];
        auto* edge1_arg = call->Args()[1];
        auto* x_arg = call->Args()[2];
        auto* type = x_arg->Type();
        ir::Constant* zero = nullptr;
        ir::Constant* one = nullptr;
        ir::Constant* two = nullptr;
        ir::Constant* three = nullptr;
        if (type->DeepestElement()->Is<core::type::F32>()) {
            zero = b.MatchWidth(0_f, type);
            one = b.MatchWidth(1_f, type);
            two = b.MatchWidth(2_f, type);
            three = b.MatchWidth(3_f, type);
        } else if (type->DeepestElement()->Is<core::type::F16>()) {
            zero = b.MatchWidth(0_h, type);
            one = b.MatchWidth(1_h, type);
            two = b.MatchWidth(2_h, type);
            three = b.MatchWidth(3_h, type);
        }

        b.InsertBefore(call, [&] {
            auto* dividend = b.Subtract(x_arg, edge0_arg);
            auto* divisor = b.Subtract(edge1_arg, edge0_arg);
            auto* quotient = b.Divide(dividend, divisor);
            auto* t_clamped = b.Clamp(quotient, zero, one);

            // Smoothstep is a well defined function.
            // result = t * t * (3.0 - 2.0 * t);
            auto* smooth_result = b.Multiply(
                t_clamped, b.Multiply(t_clamped, b.Subtract(three, b.Multiply(two, t_clamped))));
            smooth_result->SetResult(call->DetachResult());
        });
        call->Destroy();
    }

    /// Polyfill an `extractBits()` builtin call.
    /// @param call the builtin call instruction
    void ExtractBits(ir::CoreBuiltinCall* call) {
        auto* offset = call->Args()[1];
        auto* count = call->Args()[2];
        switch (config.extract_bits) {
            case BuiltinPolyfillLevel::kClampOrRangeCheck: {
                b.InsertBefore(call, [&] {
                    // Replace:
                    //    extractBits(e, offset, count)
                    // With:
                    //    let o = min(offset, 32);
                    //    let c = min(count, w - o);
                    //    extractBits(e, o, c);
                    auto* o = b.Min(offset, 32_u);
                    auto* c = b.Min(count, b.Subtract(32_u, o));
                    call->SetOperand(ir::CoreBuiltinCall::kArgsOperandOffset + 1, o->Result());
                    call->SetOperand(ir::CoreBuiltinCall::kArgsOperandOffset + 2, c->Result());
                });
            } break;
            case BuiltinPolyfillLevel::kFull: {
                // Replace:
                //    result = extractBits(e, offset, count)
                // With:
                //   let s = min(offset, 32u);
                //   let clamped_count = min(count, 32u);
                //   let t = min(32u, (s + clamped_count));
                //   let shl = (32u - t);
                //   let shr = (shl + s);
                //   let shl_result = select(i32(), (e << shl), (shl < 32u));
                //   result = select(((shl_result >> 31u) >> 1u), (shl_result >> shr), (shr < 32u));
                // }
                auto* e = call->Args()[0];
                auto* result_ty = e->Type();
                auto* uint_ty = ty.MatchWidth(ty.u32(), result_ty);
                auto V = [&](uint32_t u) { return b.MatchWidth(u32(u), result_ty); };
                b.InsertBefore(call, [&] {
                    auto* s = b.Min(offset, 32_u);
                    auto* clamped_count = b.Min(count, 32_u);
                    auto* t = b.Min(32_u, b.Add(s, clamped_count));
                    auto* shl = b.Subtract(32_u, t);
                    auto* shr = b.Add(shl, s);
                    auto* f1 = b.Zero(result_ty);
                    auto* t1 = b.ShiftLeft(e, b.Construct(uint_ty, shl));
                    auto* shl_result =
                        b.Call(result_ty, core::BuiltinFn::kSelect, f1, t1, b.LessThan(shl, 32_u));
                    auto* f2 = b.ShiftRight(b.ShiftRight(shl_result, V(31)), V(1));
                    auto* t2 = b.ShiftRight(shl_result, b.Construct(uint_ty, shr));
                    b.CallWithResult(call->DetachResult(), core::BuiltinFn::kSelect, f2, t2,
                                     b.LessThan(shr, 32_u));
                });
                call->Destroy();
            } break;
            default:
                TINT_IR_UNIMPLEMENTED(ir) << "extractBits polyfill level";
        }
    }

    /// Polyfill a `firstLeadingBit()` builtin call.
    /// @param call the builtin call instruction
    void FirstLeadingBit(ir::CoreBuiltinCall* call) {
        auto* input = call->Args()[0];
        auto* result_ty = input->Type();
        auto* uint_ty = ty.MatchWidth(ty.u32(), result_ty);

        // Make an u32 constant with the same component count as result_ty.
        auto V = [&](uint32_t u) { return b.MatchWidth(u32(u), result_ty); };

        b.InsertBefore(call, [&] {
            // %x = %input;
            // if (%x is signed) {
            //   %x = select(u32(%x), ~u32(%x), x > 0x80000000);
            // }
            // %b16 = select(16, 0, (%x & 0xffff0000) == 0);
            // %x >>= %b16;
            // %b8  = select(8, 0,  (%x & 0x0000ff00) == 0);
            // %x >>= %b8;
            // %b4  = select(4, 0,  (%x & 0x000000f0) == 0);
            // %x >>= %b4;
            // %b2  = select(2, 0,  (%x & 0x0000000c) == 0);
            // %x >>= %b2;
            // %b1  = select(1, 0,  (%x & 0x00000002) == 0);
            // %result = %b16 | %b8 | %b4 | %b2 | %b1;
            // %result = select(%result, 0xffffffff, %x == 0);

            auto* x = input;
            if (result_ty->IsSignedIntegerScalarOrVector()) {
                x = b.Bitcast(uint_ty, x)->Result();
                auto* inverted = b.Complement(x);
                x = b.Call(uint_ty, core::BuiltinFn::kSelect, inverted, x,
                           b.LessThan(x, V(0x80000000)))
                        ->Result();
            }
            auto* b16 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(16), V(0),
                               b.Equal(b.And(x, V(0xffff0000)), V(0)));
            x = b.ShiftRight(x, b16)->Result();
            auto* b8 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(8), V(0),
                              b.Equal(b.And(x, V(0x0000ff00)), V(0)));
            x = b.ShiftRight(x, b8)->Result();
            auto* b4 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(4), V(0),
                              b.Equal(b.And(x, V(0x000000f0)), V(0)));
            x = b.ShiftRight(x, b4)->Result();
            auto* b2 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(2), V(0),
                              b.Equal(b.And(x, V(0x0000000c)), V(0)));
            x = b.ShiftRight(x, b2)->Result();
            auto* b1 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(1), V(0),
                              b.Equal(b.And(x, V(0x00000002)), V(0)));
            Instruction* result = b.Or(b16, b.Or(b8, b.Or(b4, b.Or(b2, b1))));
            result =
                b.Call(uint_ty, core::BuiltinFn::kSelect, result, V(0xffffffff), b.Equal(x, V(0)));
            if (result_ty->IsSignedIntegerScalarOrVector()) {
                result = b.Bitcast(result_ty, result);
            }
            result->SetResult(call->DetachResult());
        });
        call->Destroy();
    }

    /// Polyfill a `firstTrailingBit()` builtin call.
    /// @param call the builtin call instruction
    void FirstTrailingBit(ir::CoreBuiltinCall* call) {
        auto* input = call->Args()[0];
        auto* result_ty = input->Type();
        auto* uint_ty = ty.MatchWidth(ty.u32(), result_ty);

        // Make an u32 constant with the same component count as result_ty.
        auto V = [&](uint32_t u) { return b.MatchWidth(u32(u), result_ty); };

        b.InsertBefore(call, [&] {
            // %x = %input;
            // if (%x is signed) {
            //   %x = bitcast<u32>(%x)
            // }
            // %b16 = select(0, 16, (%x & 0x0000ffff) == 0);
            // %x >>= %b16;
            // %b8  = select(0, 8,  (%x & 0x000000ff) == 0);
            // %x >>= %b8;
            // %b4  = select(0, 4,  (%x & 0x0000000f) == 0);
            // %x >>= %b4;
            // %b2  = select(0, 2,  (%x & 0x00000003) == 0);
            // %x >>= %b2;
            // %b1  = select(0, 1,  (%x & 0x00000001) == 0);
            // %result = %b16 | %b8 | %b4 | %b2 | %b1;
            // %result = select(%result, 0xffffffff, %x == 0);

            auto* x = input;
            if (result_ty->IsSignedIntegerScalarOrVector()) {
                x = b.Bitcast(uint_ty, x)->Result();
            }
            auto* b16 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(16),
                               b.Equal(b.And(x, V(0x0000ffff)), V(0)));
            x = b.ShiftRight(x, b16)->Result();
            auto* b8 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(8),
                              b.Equal(b.And(x, V(0x000000ff)), V(0)));
            x = b.ShiftRight(x, b8)->Result();
            auto* b4 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(4),
                              b.Equal(b.And(x, V(0x0000000f)), V(0)));
            x = b.ShiftRight(x, b4)->Result();
            auto* b2 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(2),
                              b.Equal(b.And(x, V(0x00000003)), V(0)));
            x = b.ShiftRight(x, b2)->Result();
            auto* b1 = b.Call(uint_ty, core::BuiltinFn::kSelect, V(0), V(1),
                              b.Equal(b.And(x, V(0x00000001)), V(0)));
            Instruction* result = b.Or(b16, b.Or(b8, b.Or(b4, b.Or(b2, b1))));
            result =
                b.Call(uint_ty, core::BuiltinFn::kSelect, result, V(0xffffffff), b.Equal(x, V(0)));
            if (result_ty->IsSignedIntegerScalarOrVector()) {
                result = b.Bitcast(result_ty, result);
            }
            result->SetResult(call->DetachResult());
        });
        call->Destroy();
    }

    /// Polyfill a `fwidthFine()` builtin call.
    /// @param call the builtin call instruction
    void FwidthFine(ir::CoreBuiltinCall* call) {
        auto* value = call->Args()[0];
        auto* type = value->Type();
        b.InsertBefore(call, [&] {
            auto* dpdx = b.Call(type, core::BuiltinFn::kDpdxFine, value);
            auto* dpdy = b.Call(type, core::BuiltinFn::kDpdyFine, value);
            auto* abs_dpdx = b.Call(type, core::BuiltinFn::kAbs, dpdx);
            auto* abs_dpdy = b.Call(type, core::BuiltinFn::kAbs, dpdy);
            auto* result = b.Add(abs_dpdx, abs_dpdy);
            call->Result()->ReplaceAllUsesWith(result->Result());
        });
        call->Destroy();
    }

    /// Polyfill an `insertBits()` builtin call.
    /// @param call the builtin call instruction
    void InsertBits(ir::CoreBuiltinCall* call) {
        auto* offset = call->Args()[2];
        auto* count = call->Args()[3];

        switch (config.insert_bits) {
            case BuiltinPolyfillLevel::kClampOrRangeCheck: {
                b.InsertBefore(call, [&] {
                    // Replace:
                    //    insertBits(e, newbits, offset, count)
                    // With:
                    //    let o = min(offset, 32);
                    //    let c = min(count, w - o);
                    //    insertBits(e, newbits, o, c);
                    auto* o = b.Min(offset, 32_u);
                    auto* c = b.Min(count, b.Subtract(32_u, o));
                    call->SetOperand(ir::CoreBuiltinCall::kArgsOperandOffset + 2, o->Result());
                    call->SetOperand(ir::CoreBuiltinCall::kArgsOperandOffset + 3, c->Result());
                });
            } break;
            case BuiltinPolyfillLevel::kFull: {
                // Replace:
                //    result = insertBits(e, newbits, offset, count)
                // With:
                //   let oc = (offset + count);
                //   let mask = ((select(0u, (1u << offset), (offset < 32u)) - 1u)
                //              ^ (select(0u, (1u << oc), (oc < 32u)) - 1u));
                //   result = ((select(i32(), (newbits << offset), (offset < 32u)) & i32(mask))
                //              | (e & i32(~(mask))));
                auto* e = call->Args()[0];
                auto* newbits = call->Args()[1];
                auto* result_ty = e->Type();
                auto* uint_ty = ty.MatchWidth(ty.u32(), result_ty);
                const bool result_is_signed = result_ty->DeepestElement()->Is<type::I32>();

                auto mask_as_result_type = [&](Instruction* mask) {
                    if (result_is_signed) {
                        mask = b.Convert<i32>(mask);
                    }
                    if (auto* vec = result_ty->As<type::Vector>()) {
                        mask = b.Construct(vec, mask);
                    }
                    return mask;
                };

                b.InsertBefore(call, [&] {
                    auto* clamped_count = b.Min(count, 32_u);
                    auto* clamped_offset = b.Min(offset, 32_u);
                    auto* oc = b.Add(clamped_offset, clamped_count);

                    auto* t1 = b.ShiftLeft(1_u, offset);
                    auto* s1 = b.Call<u32>(core::BuiltinFn::kSelect, b.Zero<u32>(), t1,
                                           b.LessThan(offset, 32_u));
                    auto* t2 = b.ShiftLeft(1_u, oc);
                    auto* s2 = b.Call<u32>(core::BuiltinFn::kSelect, b.Zero<u32>(), t2,
                                           b.LessThan(oc, 32_u));
                    auto* mask_lhs = b.Subtract(s1, 1_u);
                    auto* mask_rhs = b.Subtract(s2, 1_u);
                    auto* mask = b.Xor(mask_lhs, mask_rhs);
                    auto* f3 = b.Zero(result_ty);
                    auto* t3 = b.ShiftLeft(newbits, b.Construct(uint_ty, offset));
                    auto* s3 = b.Call(result_ty, core::BuiltinFn::kSelect, f3, t3,
                                      b.LessThan(offset, 32_u));
                    auto* result_lhs = b.And(s3, mask_as_result_type(mask));
                    auto* result_rhs = b.And(e, mask_as_result_type(b.Complement(mask)));
                    auto* result = b.Or(result_lhs, result_rhs);
                    result->SetResult(call->DetachResult());
                });
                call->Destroy();
            } break;
            default:
                TINT_IR_UNIMPLEMENTED(ir) << "insertBits polyfill level";
        }
    }

    /// Polyfill a `length()` builtin call for scalar f32 and f16.
    /// @param call the builtin call instruction
    void LengthScalarFloat(ir::CoreBuiltinCall* call) {
        // length(x) -> abs(x)
        b.InsertBefore(call, [&] {
            b.CallWithResult(call->DetachResult(), core::BuiltinFn::kAbs, call->Args()[0]);
        });
        call->Destroy();
    }

    /// Polyfill an `radians()` builtin call.
    /// @param call the builtin call instruction
    void Radians(ir::CoreBuiltinCall* call) {
        auto* arg = call->Args()[0];
        auto* type = arg->Type()->DeepestElement();
        ir::Value* value = nullptr;
        if (type->Is<core::type::F16>()) {
            value = b.Constant(f16(kDegToRad));
        } else if (type->Is<core::type::F32>()) {
            value = b.Constant(f32(kDegToRad));
        }
        b.InsertBefore(call, [&] {
            auto* mul = b.Multiply(arg, value);
            mul->SetResult(call->DetachResult());
        });
        call->Destroy();
    }

    /// Polyfill a `reflect()` builtin call.
    /// @param call the builtin call instruction
    void Reflect(ir::CoreBuiltinCall* call) {
        auto* e1 = call->Args()[0];
        auto* e2 = call->Args()[1];
        auto* vec_ty = e1->Type()->As<core::type::Vector>();
        // Only polyfills vec2<f32> (crbug.com/tint/1798)
        TINT_IR_ASSERT(ir, vec_ty && vec_ty->Width() == 2 && vec_ty->Type()->Is<core::type::F32>());

        b.InsertBefore(call, [&] {
            // The generated HLSL must effectively be emitted as:
            //      e1 + (-2 * dot(e1,e2) * e2)
            // Rather than the mathemetically equivalent:
            //      e1 - 2 * dot(e2,e2) * e2
            //
            // When FXC compiles HLSL reflect, or the second case above,
            // it emits a `dp4` instruction for `2 * dot(e1,e2)`, which is
            // miscompiled by certain Intel drivers. The workaround (first
            // case above) results in FXC emitting a `dp2` for the dot,
            // followed by a `mul 2`, which works around the bug.
            auto* dot = b.Call(ty.f32(), core::BuiltinFn::kDot, e1, e2);
            auto* factor = b.Multiply(-2.0_f, dot);
            auto* vfactor = b.Construct(vec_ty, factor);
            auto* mul = b.Multiply(vfactor, e2);
            b.AddWithResult(call->DetachResult(), e1, mul);
        });
        call->Destroy();
    }

    /// Polyfill a `saturate()` builtin call.
    /// @param call the builtin call instruction
    void Saturate(ir::CoreBuiltinCall* call) {
        // Replace `saturate(x)` with `clamp(x, 0., 1.)`.
        auto* type = call->Result()->Type();
        const bool is_vec_f16 =
            type->DeepestElement()->Is<core::type::F16>() && type->IsFloatVector();
        ir::Constant* zero = nullptr;
        ir::Constant* one = nullptr;
        if (type->DeepestElement()->Is<core::type::F32>()) {
            zero = b.MatchWidth(0_f, type);
            one = b.MatchWidth(1_f, type);
        } else if (type->DeepestElement()->Is<core::type::F16>()) {
            zero = b.MatchWidth(0_h, type);
            one = b.MatchWidth(1_h, type);
        }

        // Intel Mesa incorrectly performs saturate on vec f16 loads from uniforms.
        // Note: to avoid compiler pattern matching, we do the min then the max which is
        // functionally different than doing the max then the min for high/low swapped (this doesn't
        // matter in the case with saturate). See crbug.com/448873316
        if (config.saturate_as_min_max && is_vec_f16) {
            b.InsertBefore(call, [&] {
                auto* clamped_via_min_max = b.Max(b.Min(call->Args()[0], one), zero);
                clamped_via_min_max->SetResult(call->DetachResult());
            });
        } else {
            auto* clamp = b.Clamp(call->Args()[0], zero, one);
            clamp->SetResult(call->DetachResult());
            clamp->InsertBefore(call);
        }

        call->Destroy();
    }

    /// Polyfill a `textureSampleBaseClampToEdge()` builtin call for 2D F32 textures.
    /// @param call the builtin call instruction
    void TextureSampleBaseClampToEdge_2d_f32(ir::CoreBuiltinCall* call) {
        // Replace `textureSampleBaseClampToEdge(%texture, %sample, %coords)` with:
        //   %dims       = vec2f(textureDimensions(%texture));
        //   %half_texel = vec2f(0.5) / dims;
        //   %clamped    = clamp(%coord, %half_texel, 1.0 - %half_texel);
        //   %result     = textureSampleLevel(%texture, %sampler, %clamped, 0);
        auto* texture = call->Args()[0];
        auto* sampler = call->Args()[1];
        auto* coords = call->Args()[2];
        b.InsertBefore(call, [&] {
            auto* dims = b.Call<vec2u>(core::BuiltinFn::kTextureDimensions, texture);
            auto* fdims = b.Convert<vec2f>(dims);
            auto* half_texel = b.Divide(b.Splat<vec2f>(0.5_f), fdims);
            auto* one_minus_half_texel = b.Subtract(b.Splat<vec2f>(1_f), half_texel);
            auto* clamped = b.Clamp(coords, half_texel, one_minus_half_texel);
            b.CallWithResult(call->DetachResult(), core::BuiltinFn::kTextureSampleLevel, texture,
                             sampler, clamped, 0_f);
        });
        call->Destroy();
    }

    /// Polyfill clamping for the (f32) bias parameter of TextureSampleBias
    /// @param call the builtin call instruction
    void TextureSampleBiasClamp(ir::CoreBuiltinCall* call) {
        b.InsertBefore(call, [&] {
            auto* texture_type = call->Args()[0]->Type()->As<core::type::Texture>();
            bool is_array_texture = type::IsTextureArray(texture_type->Dim());
            const uint32_t kBiasParameterIndex = is_array_texture ? 4 : 3;
            auto* bias_parameter = call->Args()[kBiasParameterIndex];
            // TODO(crbug.com/371033198): Consider applying clamp here if 'bias_parameter' is a
            // constant. This might not be the most prudent idea for two reasons: 1. the platform
            // compilers will perform this optimization 2. it will bifurcate the testing paths.
            call->SetArg(kBiasParameterIndex, b.Clamp(bias_parameter, -16.00_f, 15.99_f)->Result());
        });
    }

    /// Polyfill a `dot4I8Packed()` builtin call
    /// @param call the builtin call instruction
    void Dot4I8Packed(ir::CoreBuiltinCall* call) {
        // Replace `dot4I8Packed(%x,%y)` with:
        //   %unpacked_x = unpack4xI8(%x);
        //   %unpacked_y = unpack4xI8(%y);
        //   %result = dot(%unpacked_x, %unpacked_y);
        auto* x = call->Args()[0];
        auto* y = call->Args()[1];
        auto* unpacked_x = Unpack4xI8OnValue(call, x);
        auto* unpacked_y = Unpack4xI8OnValue(call, y);
        b.InsertBefore(call, [&] {
            b.CallWithResult(call->DetachResult(), core::BuiltinFn::kDot, unpacked_x, unpacked_y);
        });
        call->Destroy();
    }

    /// Polyfill a `dot4U8Packed()` builtin call
    /// @param call the builtin call instruction
    void Dot4U8Packed(ir::CoreBuiltinCall* call) {
        // Replace `dot4U8Packed(%x,%y)` with:
        //   %unpacked_x = unpack4xU8(%x);
        //   %unpacked_y = unpack4xU8(%y);
        //   %result = dot(%unpacked_x, %unpacked_y);
        auto* x = call->Args()[0];
        auto* y = call->Args()[1];
        auto* unpacked_x = Unpack4xU8OnValue(call, x);
        auto* unpacked_y = Unpack4xU8OnValue(call, y);
        b.InsertBefore(call, [&] {
            b.CallWithResult(call->DetachResult(), core::BuiltinFn::kDot, unpacked_x, unpacked_y);
        });
        call->Destroy();
    }

    /// Polyfill a `pack4xI8()` builtin call
    /// @param call the builtin call instruction
    void Pack4xI8(ir::CoreBuiltinCall* call) {
        // Replace `pack4xI8(%x)` with:
        //   %n      = vec4u(0, 8, 16, 24);
        //   %x_u32  = bitcast<vec4u>(%x)
        //   %x_u8   = (%x_u32 & vec4u(0xff)) << n;
        //   %result = dot(%x_u8, vec4u(1));
        auto* x = call->Args()[0];
        b.InsertBefore(call, [&] {
            auto* vec4u = ty.vec4u();

            auto* n = b.Construct(vec4u, b.Constant(u32(0)), b.Constant(u32(8)),
                                  b.Constant(u32(16)), b.Constant(u32(24)));
            auto* x_u32 = b.Bitcast(vec4u, x);
            auto* x_u8 = b.ShiftLeft(b.And(x_u32, b.Construct(vec4u, b.Constant(u32(0xff)))), n);
            b.CallWithResult(call->DetachResult(), core::BuiltinFn::kDot, x_u8,
                             b.Construct(vec4u, (b.Constant(u32(1)))));
        });
        call->Destroy();
    }

    /// Polyfill a `pack4xU8()` builtin call
    /// @param call the builtin call instruction
    void Pack4xU8(ir::CoreBuiltinCall* call) {
        // Replace `pack4xU8(%x)` with:
        //   %n      = vec4u(0, 8, 16, 24);
        //   %x_i8   = (%x & vec4u(0xff)) << %n;
        //   %result = dot(%x_i8, vec4u(1));
        auto* x = call->Args()[0];
        b.InsertBefore(call, [&] {
            auto* vec4u = ty.vec4u();

            auto* n = b.Construct(vec4u, b.Constant(u32(0)), b.Constant(u32(8)),
                                  b.Constant(u32(16)), b.Constant(u32(24)));
            auto* x_u8 = b.ShiftLeft(b.And(x, b.Construct(vec4u, b.Constant(u32(0xff)))), n);
            b.CallWithResult(call->DetachResult(), core::BuiltinFn::kDot, x_u8,
                             b.Construct(vec4u, (b.Constant(u32(1)))));
        });
        call->Destroy();
    }

    /// Polyfill a `pack4xI8Clamp()` builtin call
    /// @param call the builtin call instruction
    void Pack4xI8Clamp(ir::CoreBuiltinCall* call) {
        // Replace `pack4xI8Clamp(%x)` with:
        //   %n           = vec4u(0, 8, 16, 24);
        //   %min_i8_vec4 = vec4i(-128);
        //   %max_i8_vec4 = vec4i(127);
        //   %x_clamp     = clamp(%x, %min_i8_vec4, %max_i8_vec4);
        //   %x_u32       = bitcast<vec4u>(%x_clamp);
        //   %x_u8        = (%x_u32 & vec4u(0xff)) << n;
        //   %result      = dot(%x_u8, vec4u(1));
        auto* x = call->Args()[0];
        b.InsertBefore(call, [&] {
            auto* vec4i = ty.vec4i();
            auto* vec4u = ty.vec4u();

            auto* n = b.Construct(vec4u, b.Constant(u32(0)), b.Constant(u32(8)),
                                  b.Constant(u32(16)), b.Constant(u32(24)));
            auto* min_i8_vec4 = b.Construct(vec4i, b.Constant(i32(-128)));
            auto* max_i8_vec4 = b.Construct(vec4i, b.Constant(i32(127)));
            auto* x_clamp = b.Clamp(x, min_i8_vec4, max_i8_vec4);
            auto* x_u32 = b.Bitcast(vec4u, x_clamp);
            auto* x_u8 = b.ShiftLeft(b.And(x_u32, b.Construct(vec4u, b.Constant(u32(0xff)))), n);
            b.CallWithResult(call->DetachResult(), core::BuiltinFn::kDot, x_u8,
                             b.Construct(vec4u, (b.Constant(u32(1)))));
        });
        call->Destroy();
    }

    /// Polyfill a `pack4xU8Clamp()` builtin call
    /// @param call the builtin call instruction
    void Pack4xU8Clamp(ir::CoreBuiltinCall* call) {
        // Replace `pack4xU8Clamp(%x)` with:
        //   %n       = vec4u(0, 8, 16, 24);
        //   %min_u8_vec4 = vec4u(0);
        //   %max_u8_vec4 = vec4u(255);
        //   %x_clamp = clamp(%x, vec4u(0), vec4u(255));
        //   %x_u8    = %x_clamp << n;
        //   %result  = dot(%x_u8, vec4u(1));
        auto* x = call->Args()[0];
        b.InsertBefore(call, [&] {
            auto* vec4u = ty.vec4u();

            auto* n = b.Construct(vec4u, b.Constant(u32(0)), b.Constant(u32(8)),
                                  b.Constant(u32(16)), b.Constant(u32(24)));
            auto* min_u8_vec4 = b.Construct(vec4u, b.Constant(u32(0)));
            auto* max_u8_vec4 = b.Construct(vec4u, b.Constant(u32(255)));
            auto* x_clamp = b.Clamp(x, min_u8_vec4, max_u8_vec4);
            auto* x_u8 = b.ShiftLeft(x_clamp, n);
            b.CallWithResult(call->DetachResult(), core::BuiltinFn::kDot, x_u8,
                             b.Construct(vec4u, (b.Constant(u32(1)))));
        });
        call->Destroy();
    }

    /// Emit code for `unpack4xI8` on u32 value `x`, before the given call.
    /// @param call the instruction that should follow the emitted code
    /// @param x the u32 value to be unpacked
    ir::Instruction* Unpack4xI8OnValue(ir::CoreBuiltinCall* call, ir::Value* x) {
        // Replace `unpack4xI8(%x)` with:
        //   %n       = vec4u(24, 16, 8, 0);
        //   %x_splat = vec4u(%x); // splat the scalar to a vector
        //   %x_vec4i = bitcast<vec4i>(%x_splat << n);
        //   %result  = %x_vec4i >> vec4u(24);
        ir::Instruction* result = nullptr;
        b.InsertBefore(call, [&] {
            auto* vec4i = ty.vec4i();
            auto* vec4u = ty.vec4u();

            auto* n = b.Construct(vec4u, b.Constant(u32(24)), b.Constant(u32(16)),
                                  b.Constant(u32(8)), b.Constant(u32(0)));
            auto* x_splat = b.Construct(vec4u, x);
            auto* x_vec4i = b.Bitcast(vec4i, b.ShiftLeft(x_splat, n));
            result = b.ShiftRight(x_vec4i, b.Construct(vec4u, b.Constant(u32(24))));
        });
        return result;
    }

    /// Polyfill a `unpack4xI8()` builtin call
    /// @param call the builtin call instruction
    void Unpack4xI8(ir::CoreBuiltinCall* call) {
        auto* result = Unpack4xI8OnValue(call, call->Args()[0]);
        result->SetResult(call->DetachResult());
        call->Destroy();
    }

    /// Emit code for `unpack4xU8` on u32 value `x`, before the given call.
    /// @param call the instruction that should follow the emitted code
    /// @param x the u32 value to be unpacked
    Instruction* Unpack4xU8OnValue(ir::CoreBuiltinCall* call, ir::Value* x) {
        // Replace `unpack4xU8(%x)` with:
        //   %n       = vec4u(0, 8, 16, 24);
        //   %x_splat = vec4u(%x); // splat the scalar to a vector
        //   %x_vec4u = %x_splat >> n;
        //   %result  = %x_vec4u & vec4u(0xff);
        ir::Instruction* result = nullptr;
        b.InsertBefore(call, [&] {
            auto* vec4u = ty.vec4u();

            auto* n = b.Construct(vec4u, b.Constant(u32(0)), b.Constant(u32(8)),
                                  b.Constant(u32(16)), b.Constant(u32(24)));
            auto* x_splat = b.Construct(vec4u, x);
            auto* x_vec4u = b.ShiftRight(x_splat, n);
            result = b.And(x_vec4u, b.Construct(vec4u, b.Constant(u32(0xff))));
        });
        return result;
    }

    /// Polyfill a `unpack4xU8()` builtin call
    /// @param call the builtin call instruction
    void Unpack4xU8(ir::CoreBuiltinCall* call) {
        auto* result = Unpack4xU8OnValue(call, call->Args()[0]);
        result->SetResult(call->DetachResult());
        call->Destroy();
    }

    /// Polyfill a `subgroupBroadcast(f16)` builtin call.
    /// @param call the builtin call instruction
    void SubgroupBroadcast(ir::CoreBuiltinCall* call) {
        // This polyfill is implemented by bitcasting f16 values to u32, performing the broadcast on
        // the uint type, and then bitcasting back. Uses vec<f16> specific bit casting.
        //
        // f16       -> broadcast as u32 after packing with a zero, then unpack
        // vec2<f16> -> broadcast as u32
        // vec3<f16> -> broadcast as one vec2<u32>
        // vec4<f16> -> broadcast as one vec2<u32>

        auto* value = call->Args()[0];
        auto* type = value->Type();

        auto* lane_id = call->Args()[1];

        b.InsertBefore(call, [&] {
            ir::Value* result = nullptr;

            if (auto* vec_ty = type->As<core::type::Vector>()) {
                // Handle vector types.
                switch (vec_ty->Width()) {
                    case 2: {  // vec2<f16>
                        auto* u32_val = b.Bitcast(ty.u32(), value);
                        auto* broadcasted_u32 =
                            b.Call(ty.u32(), core::BuiltinFn::kSubgroupBroadcast, u32_val, lane_id);
                        result = b.Bitcast(vec_ty, broadcasted_u32)->Result();
                        break;
                    }
                    case 3: {  // vec3<f16>
                        auto* v4f16_val = b.Construct(ty.vec4h(), value, b.Zero(ty.f16()));
                        auto* v2u32_val = b.Bitcast(ty.vec2u(), v4f16_val);
                        auto* broadcasted_v2u32 = b.Call(
                            ty.vec2u(), core::BuiltinFn::kSubgroupBroadcast, v2u32_val, lane_id);
                        auto* broadcasted_v4f16 = b.Bitcast(ty.vec4h(), broadcasted_v2u32);
                        result = b.Swizzle(vec_ty, broadcasted_v4f16, {0u, 1u, 2u})->Result();
                        break;
                    }
                    case 4: {  // vec4<f16>
                        auto* v2u32_val = b.Bitcast(ty.vec2u(), value);
                        auto* broadcasted_v2u32 = b.Call(
                            ty.vec2u(), core::BuiltinFn::kSubgroupBroadcast, v2u32_val, lane_id);
                        result = b.Bitcast(vec_ty, broadcasted_v2u32)->Result();
                        break;
                    }
                    default:
                        TINT_IR_UNREACHABLE(ir)
                            << "unhandled f16 vector width in subgroupBroadcast polyfill";
                }
            } else {  // Scalar f16
                // Construct a vec2<f16>(0, value), then bitcast to u32.
                auto* vec_val = b.Construct(ty.vec2h(), value, b.Zero(ty.f16()));
                auto* u32_val = b.Bitcast(ty.u32(), vec_val);
                auto* broadcasted_u32 =
                    b.Call(ty.u32(), core::BuiltinFn::kSubgroupBroadcast, u32_val, lane_id);
                auto* broadcasted_vec = b.Bitcast(ty.vec2h(), broadcasted_u32);
                result = b.Access(ty.f16(), broadcasted_vec, 0_u)->Result();
            }

            call->Result()->ReplaceAllUsesWith(result);
        });
        call->Destroy();
    }
};

}  // namespace

Result<SuccessType> BuiltinPolyfill(Module& ir, const BuiltinPolyfillConfig& config) {
    core::ir::AssertValid(ir, kBuiltinPolyfillCapabilities, "before core.BuiltinPolyfill");

    State{config, ir}.Process();

    return Success;
}

}  // namespace tint::core::ir::transform
