/*
 * Copyright 2021 Google LLC
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "src/sksl/SkSLAnalysis.h"
#include "src/sksl/SkSLConstantFolder.h"
#include "src/sksl/SkSLContext.h"
#include "src/sksl/SkSLProgramSettings.h"
#include "src/sksl/dsl/priv/DSLWriter.h"
#include "src/sksl/ir/SkSLChildCall.h"
#include "src/sksl/ir/SkSLConstructorCompound.h"
#include "src/sksl/ir/SkSLExternalFunctionCall.h"
#include "src/sksl/ir/SkSLExternalFunctionReference.h"
#include "src/sksl/ir/SkSLFunctionCall.h"
#include "src/sksl/ir/SkSLFunctionReference.h"
#include "src/sksl/ir/SkSLLiteral.h"
#include "src/sksl/ir/SkSLMethodReference.h"
#include "src/sksl/ir/SkSLTypeReference.h"

#include "include/private/SkFloatingPoint.h"
#include "include/sksl/DSLCore.h"
#include "src/core/SkMatrixInvert.h"

#include <array>

namespace SkSL {

using IntrinsicArguments = std::array<const Expression*, 3>;

static bool has_compile_time_constant_arguments(const ExpressionArray& arguments) {
    for (const std::unique_ptr<Expression>& arg : arguments) {
        const Expression* expr = ConstantFolder::GetConstantValueForVariable(*arg);
        if (!expr->isCompileTimeConstant()) {
            return false;
        }
    }
    return true;
}

template <typename T>
static void type_check_expression(const Expression& expr);

template <>
void type_check_expression<float>(const Expression& expr) {
    SkASSERT(expr.type().componentType().isFloat());
}

template <>
void type_check_expression<SKSL_INT>(const Expression& expr) {
    SkASSERT(expr.type().componentType().isInteger());
}

template <>
void type_check_expression<bool>(const Expression& expr) {
    SkASSERT(expr.type().componentType().isBoolean());
}

static std::unique_ptr<Expression> assemble_compound(const Context& context,
                                                     Position pos,
                                                     const Type& returnType,
                                                     double value[]) {
    int numSlots = returnType.slotCount();
    ExpressionArray array;
    array.reserve_back(numSlots);
    for (int index = 0; index < numSlots; ++index) {
        array.push_back(Literal::Make(pos, value[index], &returnType.componentType()));
    }
    return ConstructorCompound::Make(context, pos, returnType, std::move(array));
}

using CoalesceFn = double (*)(double, double, double);
using FinalizeFn = double (*)(double);

static std::unique_ptr<Expression> coalesce_n_way_vector(const Expression* arg0,
                                                         const Expression* arg1,
                                                         double startingState,
                                                         const Type& returnType,
                                                         CoalesceFn coalesce,
                                                         FinalizeFn finalize) {
    // Takes up to two vector or scalar arguments and coalesces them in sequence:
    //     scalar = startingState;
    //     scalar = coalesce(scalar, arg0.x, arg1.x);
    //     scalar = coalesce(scalar, arg0.y, arg1.y);
    //     scalar = coalesce(scalar, arg0.z, arg1.z);
    //     scalar = coalesce(scalar, arg0.w, arg1.w);
    //     scalar = finalize(scalar);
    //
    // If an argument is null, zero is passed to the coalesce function. If the arguments are a mix
    // of scalars and vectors, the scalars is interpreted as a vector containing the same value for
    // every component.

    Position pos = arg0->fPosition;

    const Type& vecType =          arg0->type().isVector()  ? arg0->type() :
                          (arg1 && arg1->type().isVector()) ? arg1->type() :
                                                              arg0->type();
    SkASSERT(         arg0->type().componentType().matches(vecType.componentType()));
    SkASSERT(!arg1 || arg1->type().componentType().matches(vecType.componentType()));

    double value = startingState;
    int arg0Index = 0;
    int arg1Index = 0;
    for (int index = 0; index < vecType.columns(); ++index) {
        std::optional<double> arg0Value = arg0->getConstantValue(arg0Index);
        arg0Index += arg0->type().isVector() ? 1 : 0;
        SkASSERT(arg0Value.has_value());

        std::optional<double> arg1Value = 0.0;
        if (arg1) {
            arg1Value = arg1->getConstantValue(arg1Index);
            arg1Index += arg1->type().isVector() ? 1 : 0;
            SkASSERT(arg1Value.has_value());
        }

        value = coalesce(value, *arg0Value, *arg1Value);

        // If coalescing the intrinsic yields a non-finite value, do not optimize.
        if (!std::isfinite(value)) {
            return nullptr;
        }
    }

    if (finalize) {
        value = finalize(value);
    }

    return Literal::Make(pos, value, &returnType);
}

template <typename T>
static std::unique_ptr<Expression> coalesce_vector(const IntrinsicArguments& arguments,
                                                   double startingState,
                                                   const Type& returnType,
                                                   CoalesceFn coalesce,
                                                   FinalizeFn finalize) {
    SkASSERT(arguments[0]);
    SkASSERT(!arguments[1]);
    type_check_expression<T>(*arguments[0]);

    return coalesce_n_way_vector(arguments[0], /*arg1=*/nullptr,
                                 startingState, returnType, coalesce, finalize);
}

template <typename T>
static std::unique_ptr<Expression> coalesce_pairwise_vectors(const IntrinsicArguments& arguments,
                                                             double startingState,
                                                             const Type& returnType,
                                                             CoalesceFn coalesce,
                                                             FinalizeFn finalize) {
    SkASSERT(arguments[0]);
    SkASSERT(arguments[1]);
    SkASSERT(!arguments[2]);
    type_check_expression<T>(*arguments[0]);
    type_check_expression<T>(*arguments[1]);

    return coalesce_n_way_vector(arguments[0], arguments[1],
                                 startingState, returnType, coalesce, finalize);
}

using CompareFn = bool (*)(double, double);

static std::unique_ptr<Expression> optimize_comparison(const Context& context,
                                                       const IntrinsicArguments& arguments,
                                                       CompareFn compare) {
    const Expression* left = arguments[0];
    const Expression* right = arguments[1];
    SkASSERT(left);
    SkASSERT(right);
    SkASSERT(!arguments[2]);

    const Type& type = left->type();
    SkASSERT(type.isVector());
    SkASSERT(type.componentType().isScalar());
    SkASSERT(type.matches(right->type()));

    double array[4];

    for (int index = 0; index < type.columns(); ++index) {
        std::optional<double> leftValue = left->getConstantValue(index);
        std::optional<double> rightValue = right->getConstantValue(index);
        SkASSERT(leftValue.has_value());
        SkASSERT(rightValue.has_value());
        array[index] = compare(*leftValue, *rightValue) ? 1.0 : 0.0;
    }

    const Type& bvecType = context.fTypes.fBool->toCompound(context, type.columns(), /*rows=*/1);
    return assemble_compound(context, left->fPosition, bvecType, array);
}

using EvaluateFn = double (*)(double, double, double);

static std::unique_ptr<Expression> evaluate_n_way_intrinsic(const Context& context,
                                                            const Expression* arg0,
                                                            const Expression* arg1,
                                                            const Expression* arg2,
                                                            const Type& returnType,
                                                            EvaluateFn eval) {
    // Takes up to three arguments and evaluates all of them, left-to-right, in tandem.
    // Equivalent to constructing a new compound value containing the results from:
    //     eval(arg0.x, arg1.x, arg2.x),
    //     eval(arg0.y, arg1.y, arg2.y),
    //     eval(arg0.z, arg1.z, arg2.z),
    //     eval(arg0.w, arg1.w, arg2.w)
    //
    // If an argument is null, zero is passed to the evaluation function. If the arguments are a mix
    // of scalars and compounds, scalars are interpreted as a compound containing the same value for
    // every component.

    int slots = returnType.slotCount();
    double array[16];

    int arg0Index = 0;
    int arg1Index = 0;
    int arg2Index = 0;
    for (int index = 0; index < slots; ++index) {
        std::optional<double> arg0Value = arg0->getConstantValue(arg0Index);
        arg0Index += arg0->type().isScalar() ? 0 : 1;
        SkASSERT(arg0Value.has_value());

        std::optional<double> arg1Value = 0.0;
        if (arg1) {
            arg1Value = arg1->getConstantValue(arg1Index);
            arg1Index += arg1->type().isScalar() ? 0 : 1;
            SkASSERT(arg1Value.has_value());
        }

        std::optional<double> arg2Value = 0.0;
        if (arg2) {
            arg2Value = arg2->getConstantValue(arg2Index);
            arg2Index += arg2->type().isScalar() ? 0 : 1;
            SkASSERT(arg2Value.has_value());
        }

        array[index] = eval(*arg0Value, *arg1Value, *arg2Value);

        // If evaluation of the intrinsic yields a non-finite value, do not optimize.
        if (!std::isfinite(array[index])) {
            return nullptr;
        }
    }

    return assemble_compound(context, arg0->fPosition, returnType, array);
}

template <typename T>
static std::unique_ptr<Expression> evaluate_intrinsic(const Context& context,
                                                      const IntrinsicArguments& arguments,
                                                      const Type& returnType,
                                                      EvaluateFn eval) {
    SkASSERT(arguments[0]);
    SkASSERT(!arguments[1]);
    type_check_expression<T>(*arguments[0]);

    return evaluate_n_way_intrinsic(context, arguments[0], /*arg1=*/nullptr, /*arg2=*/nullptr,
                                    returnType, eval);
}

static std::unique_ptr<Expression> evaluate_intrinsic_numeric(const Context& context,
                                                              const IntrinsicArguments& arguments,
                                                              const Type& returnType,
                                                              EvaluateFn eval) {
    SkASSERT(arguments[0]);
    SkASSERT(!arguments[1]);
    const Type& type = arguments[0]->type().componentType();

    if (type.isFloat()) {
        return evaluate_intrinsic<float>(context, arguments, returnType, eval);
    }
    if (type.isInteger()) {
        return evaluate_intrinsic<SKSL_INT>(context, arguments, returnType, eval);
    }

    SkDEBUGFAILF("unsupported type %s", type.description().c_str());
    return nullptr;
}

static std::unique_ptr<Expression> evaluate_pairwise_intrinsic(const Context& context,
                                                               const IntrinsicArguments& arguments,
                                                               const Type& returnType,
                                                               EvaluateFn eval) {
    SkASSERT(arguments[0]);
    SkASSERT(arguments[1]);
    SkASSERT(!arguments[2]);
    const Type& type = arguments[0]->type().componentType();

    if (type.isFloat()) {
        type_check_expression<float>(*arguments[0]);
        type_check_expression<float>(*arguments[1]);
    } else if (type.isInteger()) {
        type_check_expression<SKSL_INT>(*arguments[0]);
        type_check_expression<SKSL_INT>(*arguments[1]);
    } else {
        SkDEBUGFAILF("unsupported type %s", type.description().c_str());
        return nullptr;
    }

    return evaluate_n_way_intrinsic(context, arguments[0], arguments[1], /*arg2=*/nullptr,
                                    returnType, eval);
}

static std::unique_ptr<Expression> evaluate_3_way_intrinsic(const Context& context,
                                                            const IntrinsicArguments& arguments,
                                                            const Type& returnType,
                                                            EvaluateFn eval) {
    SkASSERT(arguments[0]);
    SkASSERT(arguments[1]);
    SkASSERT(arguments[2]);
    const Type& type = arguments[0]->type().componentType();

    if (type.isFloat()) {
        type_check_expression<float>(*arguments[0]);
        type_check_expression<float>(*arguments[1]);
        type_check_expression<float>(*arguments[2]);
    } else if (type.isInteger()) {
        type_check_expression<SKSL_INT>(*arguments[0]);
        type_check_expression<SKSL_INT>(*arguments[1]);
        type_check_expression<SKSL_INT>(*arguments[2]);
    } else {
        SkDEBUGFAILF("unsupported type %s", type.description().c_str());
        return nullptr;
    }

    return evaluate_n_way_intrinsic(context, arguments[0], arguments[1], arguments[2],
                                    returnType, eval);
}

template <typename T1, typename T2>
static double pun_value(double val) {
    // Interpret `val` as a value of type T1.
    static_assert(sizeof(T1) == sizeof(T2));
    T1 inputValue = (T1)val;
    // Reinterpret those bits as a value of type T2.
    T2 outputValue;
    memcpy(&outputValue, &inputValue, sizeof(T2));
    // Return the value-of-type-T2 as a double. (Non-finite values will prohibit optimization.)
    return (double)outputValue;
}

// Helper functions for optimizing all of our intrinsics.
namespace Intrinsics {
namespace {

double coalesce_length(double a, double b, double)     { return a + (b * b); }
double finalize_length(double a)                       { return std::sqrt(a); }

double coalesce_distance(double a, double b, double c) { b -= c; return a + (b * b); }
double finalize_distance(double a)                     { return std::sqrt(a); }

double coalesce_dot(double a, double b, double c)      { return a + (b * c); }
double coalesce_any(double a, double b, double)        { return a || b; }
double coalesce_all(double a, double b, double)        { return a && b; }

bool compare_lessThan(double a, double b)              { return a < b; }
bool compare_lessThanEqual(double a, double b)         { return a <= b; }
bool compare_greaterThan(double a, double b)           { return a > b; }
bool compare_greaterThanEqual(double a, double b)      { return a >= b; }
bool compare_equal(double a, double b)                 { return a == b; }
bool compare_notEqual(double a, double b)              { return a != b; }

double evaluate_radians(double a, double, double)      { return a * 0.0174532925; }
double evaluate_degrees(double a, double, double)      { return a * 57.2957795; }
double evaluate_sin(double a, double, double)          { return std::sin(a); }
double evaluate_cos(double a, double, double)          { return std::cos(a); }
double evaluate_tan(double a, double, double)          { return std::tan(a); }
double evaluate_asin(double a, double, double)         { return std::asin(a); }
double evaluate_acos(double a, double, double)         { return std::acos(a); }
double evaluate_atan(double a, double, double)         { return std::atan(a); }
double evaluate_atan2(double a, double b, double)      { return std::atan2(a, b); }
double evaluate_asinh(double a, double, double)        { return std::asinh(a); }
double evaluate_acosh(double a, double, double)        { return std::acosh(a); }
double evaluate_atanh(double a, double, double)        { return std::atanh(a); }

double evaluate_pow(double a, double b, double)        { return std::pow(a, b); }
double evaluate_exp(double a, double, double)          { return std::exp(a); }
double evaluate_log(double a, double, double)          { return std::log(a); }
double evaluate_exp2(double a, double, double)         { return std::exp2(a); }
double evaluate_log2(double a, double, double)         { return std::log2(a); }
double evaluate_sqrt(double a, double, double)         { return std::sqrt(a); }
double evaluate_inversesqrt(double a, double, double) {
    return sk_ieee_double_divide(1.0, std::sqrt(a));
}

double evaluate_abs(double a, double, double)          { return std::abs(a); }
double evaluate_sign(double a, double, double)         { return (a > 0) - (a < 0); }
double evaluate_floor(double a, double, double)        { return std::floor(a); }
double evaluate_ceil(double a, double, double)         { return std::ceil(a); }
double evaluate_fract(double a, double, double)        { return a - std::floor(a); }
double evaluate_min(double a, double b, double)        { return (a < b) ? a : b; }
double evaluate_max(double a, double b, double)        { return (a > b) ? a : b; }
double evaluate_clamp(double x, double l, double h)    { return (x < l) ? l : (x > h) ? h : x; }
double evaluate_saturate(double a, double, double)     { return (a < 0) ? 0 : (a > 1) ? 1 : a; }
double evaluate_mix(double x, double y, double a)      { return x * (1 - a) + y * a; }
double evaluate_step(double e, double x, double)       { return (x < e) ? 0 : 1; }
double evaluate_mod(double a, double b, double) {
    return a - b * std::floor(sk_ieee_double_divide(a, b));
}
double evaluate_smoothstep(double edge0, double edge1, double x) {
    double t = sk_ieee_double_divide(x - edge0, edge1 - edge0);
    t = (t < 0) ? 0 : (t > 1) ? 1 : t;
    return t * t * (3.0 - 2.0 * t);
}

double evaluate_matrixCompMult(double x, double y, double) { return x * y; }

double evaluate_not(double a, double, double)          { return !a; }
double evaluate_sinh(double a, double, double)         { return std::sinh(a); }
double evaluate_cosh(double a, double, double)         { return std::cosh(a); }
double evaluate_tanh(double a, double, double)         { return std::tanh(a); }
double evaluate_trunc(double a, double, double)        { return std::trunc(a); }
double evaluate_round(double a, double, double) {
    // The semantics of std::remainder guarantee a rounded-to-even result here, regardless of the
    // current float-rounding mode.
    return a - std::remainder(a, 1.0);
}
double evaluate_floatBitsToInt(double a, double, double)  { return pun_value<float, int32_t> (a); }
double evaluate_floatBitsToUint(double a, double, double) { return pun_value<float, uint32_t>(a); }
double evaluate_intBitsToFloat(double a, double, double)  { return pun_value<int32_t,  float>(a); }
double evaluate_uintBitsToFloat(double a, double, double) { return pun_value<uint32_t, float>(a); }

}  // namespace
}  // namespace Intrinsics

static void extract_matrix(const Expression* expr, float mat[16]) {
    size_t numSlots = expr->type().slotCount();
    for (size_t index = 0; index < numSlots; ++index) {
        mat[index] = *expr->getConstantValue(index);
    }
}

static std::unique_ptr<Expression> optimize_intrinsic_call(const Context& context,
                                                           Position pos,
                                                           IntrinsicKind intrinsic,
                                                           const ExpressionArray& argArray,
                                                           const Type& returnType) {
    // Replace constant variables with their literal values.
    IntrinsicArguments arguments = {};
    SkASSERT(argArray.size() <= arguments.size());
    for (int index = 0; index < argArray.count(); ++index) {
        arguments[index] = ConstantFolder::GetConstantValueForVariable(*argArray[index]);
    }

    auto Get = [&](int idx, int col) -> float {
        return *arguments[idx]->getConstantValue(col);
    };

    using namespace SkSL::dsl;
    switch (intrinsic) {
        // 8.1 : Angle and Trigonometry Functions
        case k_radians_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_radians);
        case k_degrees_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_degrees);
        case k_sin_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_sin);
        case k_cos_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_cos);
        case k_tan_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_tan);
        case k_sinh_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_sinh);
        case k_cosh_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_cosh);
        case k_tanh_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_tanh);
        case k_asin_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_asin);
        case k_acos_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_acos);
        case k_atan_IntrinsicKind:
            if (argArray.size() == 1) {
                return evaluate_intrinsic<float>(context, arguments, returnType,
                                                 Intrinsics::evaluate_atan);
            } else {
                return evaluate_pairwise_intrinsic(context, arguments, returnType,
                                                   Intrinsics::evaluate_atan2);
            }
        case k_asinh_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_asinh);

        case k_acosh_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_acosh);
        case k_atanh_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_atanh);
        // 8.2 : Exponential Functions
        case k_pow_IntrinsicKind:
            return evaluate_pairwise_intrinsic(context, arguments, returnType,
                                               Intrinsics::evaluate_pow);
        case k_exp_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_exp);
        case k_log_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_log);
        case k_exp2_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_exp2);
        case k_log2_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_log2);
        case k_sqrt_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_sqrt);
        case k_inversesqrt_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_inversesqrt);
        // 8.3 : Common Functions
        case k_abs_IntrinsicKind:
            return evaluate_intrinsic_numeric(context, arguments, returnType,
                                              Intrinsics::evaluate_abs);
        case k_sign_IntrinsicKind:
            return evaluate_intrinsic_numeric(context, arguments, returnType,
                                              Intrinsics::evaluate_sign);
        case k_floor_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_floor);
        case k_ceil_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_ceil);
        case k_fract_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_fract);
        case k_mod_IntrinsicKind:
            return evaluate_pairwise_intrinsic(context, arguments, returnType,
                                               Intrinsics::evaluate_mod);
        case k_min_IntrinsicKind:
            return evaluate_pairwise_intrinsic(context, arguments, returnType,
                                               Intrinsics::evaluate_min);
        case k_max_IntrinsicKind:
            return evaluate_pairwise_intrinsic(context, arguments, returnType,
                                               Intrinsics::evaluate_max);
        case k_clamp_IntrinsicKind:
            return evaluate_3_way_intrinsic(context, arguments, returnType,
                                            Intrinsics::evaluate_clamp);
        case k_saturate_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_saturate);
        case k_mix_IntrinsicKind:
            if (arguments[2]->type().componentType().isBoolean()) {
                const SkSL::Type& numericType = arguments[0]->type().componentType();

                if (numericType.isFloat()) {
                    type_check_expression<float>(*arguments[0]);
                    type_check_expression<float>(*arguments[1]);
                } else if (numericType.isInteger()) {
                    type_check_expression<SKSL_INT>(*arguments[0]);
                    type_check_expression<SKSL_INT>(*arguments[1]);
                } else if (numericType.isBoolean()) {
                    type_check_expression<bool>(*arguments[0]);
                    type_check_expression<bool>(*arguments[1]);
                } else {
                    SkDEBUGFAILF("unsupported type %s", numericType.description().c_str());
                    return nullptr;
                }
                return evaluate_n_way_intrinsic(context, arguments[0], arguments[1], arguments[2],
                                                returnType, Intrinsics::evaluate_mix);
            } else {
                return evaluate_3_way_intrinsic(context, arguments, returnType,
                                                Intrinsics::evaluate_mix);
            }
        case k_step_IntrinsicKind:
            return evaluate_pairwise_intrinsic(context, arguments, returnType,
                                               Intrinsics::evaluate_step);
        case k_smoothstep_IntrinsicKind:
            return evaluate_3_way_intrinsic(context, arguments, returnType,
                                            Intrinsics::evaluate_smoothstep);
        case k_trunc_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_trunc);
        case k_round_IntrinsicKind:      // GLSL `round` documents its rounding mode as unspecified
        case k_roundEven_IntrinsicKind:  // and is allowed to behave identically to `roundEven`.
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_round);
        case k_floatBitsToInt_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_floatBitsToInt);
        case k_floatBitsToUint_IntrinsicKind:
            return evaluate_intrinsic<float>(context, arguments, returnType,
                                             Intrinsics::evaluate_floatBitsToUint);
        case k_intBitsToFloat_IntrinsicKind:
            return evaluate_intrinsic<SKSL_INT>(context, arguments, returnType,
                                                Intrinsics::evaluate_intBitsToFloat);
        case k_uintBitsToFloat_IntrinsicKind:
            return evaluate_intrinsic<SKSL_INT>(context, arguments, returnType,
                                                Intrinsics::evaluate_uintBitsToFloat);
        // 8.4 : Floating-Point Pack and Unpack Functions
        case k_packUnorm2x16_IntrinsicKind: {
            auto Pack = [&](int n) -> unsigned int {
                float x = Get(0, n);
                return (int)std::round(Intrinsics::evaluate_clamp(x, 0.0, 1.0) * 65535.0);
            };
            return UInt(((Pack(0) << 0)  & 0x0000FFFF) |
                        ((Pack(1) << 16) & 0xFFFF0000)).release();
        }
        case k_unpackUnorm2x16_IntrinsicKind: {
            SKSL_INT x = *arguments[0]->getConstantValue(0);
            return Float2(double((x >> 0)  & 0x0000FFFF) / 65535.0,
                          double((x >> 16) & 0x0000FFFF) / 65535.0).release();
        }
        // 8.5 : Geometric Functions
        case k_length_IntrinsicKind:
            return coalesce_vector<float>(arguments, /*startingState=*/0, returnType,
                                          Intrinsics::coalesce_length,
                                          Intrinsics::finalize_length);
        case k_distance_IntrinsicKind:
            return coalesce_pairwise_vectors<float>(arguments, /*startingState=*/0, returnType,
                                                    Intrinsics::coalesce_distance,
                                                    Intrinsics::finalize_distance);
        case k_dot_IntrinsicKind:
            return coalesce_pairwise_vectors<float>(arguments, /*startingState=*/0, returnType,
                                                    Intrinsics::coalesce_dot,
                                                    /*finalize=*/nullptr);
        case k_cross_IntrinsicKind: {
            auto X = [&](int n) -> float { return Get(0, n); };
            auto Y = [&](int n) -> float { return Get(1, n); };
            SkASSERT(arguments[0]->type().columns() == 3);  // the vec2 form is not a real intrinsic

            double vec[3] = {X(1) * Y(2) - Y(1) * X(2),
                             X(2) * Y(0) - Y(2) * X(0),
                             X(0) * Y(1) - Y(0) * X(1)};
            return assemble_compound(context, arguments[0]->fPosition, returnType, vec);
        }
        case k_normalize_IntrinsicKind: {
            auto Vec  = [&] { return DSLExpression{arguments[0]->clone()}; };
            return (Vec() / Length(Vec())).release();
        }
        case k_faceforward_IntrinsicKind: {
            auto N    = [&] { return DSLExpression{arguments[0]->clone()}; };
            auto I    = [&] { return DSLExpression{arguments[1]->clone()}; };
            auto NRef = [&] { return DSLExpression{arguments[2]->clone()}; };
            return (N() * Select(Dot(NRef(), I()) < 0, 1, -1)).release();
        }
        case k_reflect_IntrinsicKind: {
            auto I    = [&] { return DSLExpression{arguments[0]->clone()}; };
            auto N    = [&] { return DSLExpression{arguments[1]->clone()}; };
            return (I() - 2.0 * Dot(N(), I()) * N()).release();
        }
        case k_refract_IntrinsicKind: {
            // Refract uses its arguments out-of-order in such a way that we end up trying to create
            // an invalid Position range, so we rewrite the arguments' positions to avoid that here.
            auto clone = [&](const Expression* expr) {
                return DSLExpression(expr->clone(pos));
            };
            auto I    = [&] { return clone(arguments[0]); };
            auto N    = [&] { return clone(arguments[1]); };
            auto Eta  = [&] { return clone(arguments[2]); };

            std::unique_ptr<Expression> k =
                    (1 - Pow(Eta(), 2) * (1 - Pow(Dot(N(), I()), 2))).release();
            if (!k->is<Literal>()) {
                return nullptr;
            }
            double kValue = k->as<Literal>().value();
            return ((kValue < 0) ?
                       (0 * I()) :
                       (Eta() * I() - (Eta() * Dot(N(), I()) + std::sqrt(kValue)) * N())).release();
        }

        // 8.6 : Matrix Functions
        case k_matrixCompMult_IntrinsicKind:
            return evaluate_pairwise_intrinsic(context, arguments, returnType,
                                               Intrinsics::evaluate_matrixCompMult);
        case k_transpose_IntrinsicKind: {
            double mat[16];
            int index = 0;
            for (int c = 0; c < returnType.columns(); ++c) {
                for (int r = 0; r < returnType.rows(); ++r) {
                    mat[index++] = Get(0, (returnType.columns() * r) + c);
                }
            }
            return assemble_compound(context, arguments[0]->fPosition, returnType, mat);
        }
        case k_outerProduct_IntrinsicKind: {
            double mat[16];
            int index = 0;
            for (int c = 0; c < returnType.columns(); ++c) {
                for (int r = 0; r < returnType.rows(); ++r) {
                    mat[index++] = Get(0, r) * Get(1, c);
                }
            }
            return assemble_compound(context, arguments[0]->fPosition, returnType, mat);
        }
        case k_determinant_IntrinsicKind: {
            float mat[16];
            extract_matrix(arguments[0], mat);
            float determinant;
            switch (arguments[0]->type().slotCount()) {
                case 4:
                    determinant = SkInvert2x2Matrix(mat, /*outMatrix=*/nullptr);
                    break;
                case 9:
                    determinant = SkInvert3x3Matrix(mat, /*outMatrix=*/nullptr);
                    break;
                case 16:
                    determinant = SkInvert4x4Matrix(mat, /*outMatrix=*/nullptr);
                    break;
                default:
                    SkDEBUGFAILF("unsupported type %s", arguments[0]->type().description().c_str());
                    return nullptr;
            }
            return Literal::MakeFloat(arguments[0]->fPosition, determinant, &returnType);
        }
        case k_inverse_IntrinsicKind: {
            float mat[16] = {};
            extract_matrix(arguments[0], mat);
            switch (arguments[0]->type().slotCount()) {
                case 4:
                    if (SkInvert2x2Matrix(mat, mat) == 0.0f) {
                        return nullptr;
                    }
                    break;
                case 9:
                    if (SkInvert3x3Matrix(mat, mat) == 0.0f) {
                        return nullptr;
                    }
                    break;
                case 16:
                    if (SkInvert4x4Matrix(mat, mat) == 0.0f) {
                        return nullptr;
                    }
                    break;
                default:
                    SkDEBUGFAILF("unsupported type %s", arguments[0]->type().description().c_str());
                    return nullptr;
            }

            double dmat[16];
            std::copy(mat, mat + SK_ARRAY_COUNT(mat), dmat);
            return assemble_compound(context, arguments[0]->fPosition, returnType, dmat);
        }
        // 8.7 : Vector Relational Functions
        case k_lessThan_IntrinsicKind:
            return optimize_comparison(context, arguments, Intrinsics::compare_lessThan);

        case k_lessThanEqual_IntrinsicKind:
            return optimize_comparison(context, arguments, Intrinsics::compare_lessThanEqual);

        case k_greaterThan_IntrinsicKind:
            return optimize_comparison(context, arguments, Intrinsics::compare_greaterThan);

        case k_greaterThanEqual_IntrinsicKind:
            return optimize_comparison(context, arguments, Intrinsics::compare_greaterThanEqual);

        case k_equal_IntrinsicKind:
            return optimize_comparison(context, arguments, Intrinsics::compare_equal);

        case k_notEqual_IntrinsicKind:
            return optimize_comparison(context, arguments, Intrinsics::compare_notEqual);

        case k_any_IntrinsicKind:
            return coalesce_vector<bool>(arguments, /*startingState=*/false, returnType,
                                         Intrinsics::coalesce_any,
                                         /*finalize=*/nullptr);
        case k_all_IntrinsicKind:
            return coalesce_vector<bool>(arguments, /*startingState=*/true, returnType,
                                         Intrinsics::coalesce_all,
                                         /*finalize=*/nullptr);
        case k_not_IntrinsicKind:
            return evaluate_intrinsic<bool>(context, arguments, returnType,
                                            Intrinsics::evaluate_not);
        default:
            return nullptr;
    }
}

bool FunctionCall::hasProperty(Property property) const {
    if (property == Property::kSideEffects &&
        (this->function().modifiers().fFlags & Modifiers::kHasSideEffects_Flag)) {
        return true;
    }
    for (const auto& arg : this->arguments()) {
        if (arg->hasProperty(property)) {
            return true;
        }
    }
    return false;
}

std::unique_ptr<Expression> FunctionCall::clone(Position pos) const {
    return std::make_unique<FunctionCall>(pos, &this->type(), &this->function(),
                                          this->arguments().clone());
}

std::string FunctionCall::description() const {
    std::string result = std::string(this->function().name()) + "(";
    std::string separator;
    for (const std::unique_ptr<Expression>& arg : this->arguments()) {
        result += separator;
        result += arg->description();
        separator = ", ";
    }
    result += ")";
    return result;
}

/**
 * Determines the cost of coercing the arguments of a function to the required types. Cost has no
 * particular meaning other than "lower costs are preferred". Returns CoercionCost::Impossible() if
 * the call is not valid.
 */
CoercionCost FunctionCall::CallCost(const Context& context, const FunctionDeclaration& function,
        const ExpressionArray& arguments){
    if (context.fConfig->strictES2Mode() &&
        (function.modifiers().fFlags & Modifiers::kES3_Flag)) {
        return CoercionCost::Impossible();
    }
    if (function.parameters().size() != arguments.size()) {
        return CoercionCost::Impossible();
    }
    FunctionDeclaration::ParamTypes types;
    const Type* ignored;
    if (!function.determineFinalTypes(arguments, &types, &ignored)) {
        return CoercionCost::Impossible();
    }
    CoercionCost total = CoercionCost::Free();
    for (size_t i = 0; i < arguments.size(); i++) {
        total = total + arguments[i]->coercionCost(*types[i]);
    }
    return total;
}

const FunctionDeclaration* FunctionCall::FindBestFunctionForCall(
        const Context& context,
        const std::vector<const FunctionDeclaration*>& functions,
        const ExpressionArray& arguments) {
    if (functions.size() == 1) {
        return functions.front();
    }
    CoercionCost bestCost = CoercionCost::Impossible();
    const FunctionDeclaration* best = nullptr;
    for (const auto& f : functions) {
        CoercionCost cost = CallCost(context, *f, arguments);
        if (cost < bestCost) {
            bestCost = cost;
            best = f;
        }
    }
    return best;
}

std::unique_ptr<Expression> FunctionCall::Convert(const Context& context,
                                                  Position pos,
                                                  std::unique_ptr<Expression> functionValue,
                                                  ExpressionArray arguments) {
    switch (functionValue->kind()) {
        case Expression::Kind::kTypeReference:
            return Constructor::Convert(context,
                                        pos,
                                        functionValue->as<TypeReference>().value(),
                                        std::move(arguments));
        case Expression::Kind::kExternalFunctionReference: {
            const ExternalFunction& f = functionValue->as<ExternalFunctionReference>().function();
            int count = f.callParameterCount();
            if (count != (int) arguments.size()) {
                context.fErrors->error(pos,
                        "external function expected " + std::to_string(count) +
                        " arguments, but found " + std::to_string(arguments.size()));
                return nullptr;
            }
            static constexpr int PARAMETER_MAX = 16;
            SkASSERT(count < PARAMETER_MAX);
            const Type* types[PARAMETER_MAX];
            f.getCallParameterTypes(types);
            for (int i = 0; i < count; ++i) {
                arguments[i] = types[i]->coerceExpression(std::move(arguments[i]), context);
                if (!arguments[i]) {
                    return nullptr;
                }
            }
            return std::make_unique<ExternalFunctionCall>(pos, &f, std::move(arguments));
        }
        case Expression::Kind::kFunctionReference: {
            const FunctionReference& ref = functionValue->as<FunctionReference>();
            const std::vector<const FunctionDeclaration*>& functions = ref.functions();
            const FunctionDeclaration* best = FindBestFunctionForCall(context, functions,
                    arguments);
            if (best) {
                return FunctionCall::Convert(context, pos, *best, std::move(arguments));
            }
            std::string msg = "no match for " + std::string(functions[0]->name()) + "(";
            std::string separator;
            for (size_t i = 0; i < arguments.size(); i++) {
                msg += separator;
                separator = ", ";
                msg += arguments[i]->type().displayName();
            }
            msg += ")";
            context.fErrors->error(pos, msg);
            return nullptr;
        }
        case Expression::Kind::kMethodReference: {
            MethodReference& ref = functionValue->as<MethodReference>();
            arguments.push_back(std::move(ref.self()));

            const std::vector<const FunctionDeclaration*>& functions = ref.functions();
            const FunctionDeclaration* best = FindBestFunctionForCall(context, functions,
                    arguments);
            if (best) {
                return FunctionCall::Convert(context, pos, *best, std::move(arguments));
            }
            std::string msg = "no match for " + arguments.back()->type().displayName() +
                              "::" + std::string(functions[0]->name().substr(1)) + "(";
            std::string separator;
            for (size_t i = 0; i < arguments.size() - 1; i++) {
                msg += separator;
                separator = ", ";
                msg += arguments[i]->type().displayName();
            }
            msg += ")";
            context.fErrors->error(pos, msg);
            return nullptr;
        }
        case Expression::Kind::kPoison:
            functionValue->fPosition = pos;
            return functionValue;
        default:
            context.fErrors->error(pos, "not a function");
            return nullptr;
    }
}

std::unique_ptr<Expression> FunctionCall::Convert(const Context& context,
                                                  Position pos,
                                                  const FunctionDeclaration& function,
                                                  ExpressionArray arguments) {
    // Reject ES3 function calls in strict ES2 mode.
    if (context.fConfig->strictES2Mode() && (function.modifiers().fFlags & Modifiers::kES3_Flag)) {
        context.fErrors->error(pos, "call to '" + function.description() + "' is not supported");
        return nullptr;
    }

    // Reject function calls with the wrong number of arguments.
    if (function.parameters().size() != arguments.size()) {
        std::string msg = "call to '" + std::string(function.name()) + "' expected " +
                          std::to_string(function.parameters().size()) + " argument";
        if (function.parameters().size() != 1) {
            msg += "s";
        }
        msg += ", but found " + std::to_string(arguments.count());
        context.fErrors->error(pos, msg);
        return nullptr;
    }

    // Resolve generic types.
    FunctionDeclaration::ParamTypes types;
    const Type* returnType;
    if (!function.determineFinalTypes(arguments, &types, &returnType)) {
        std::string msg = "no match for " + std::string(function.name()) + "(";
        std::string separator ;
        for (const std::unique_ptr<Expression>& arg : arguments) {
            msg += separator;
            msg += arg->type().displayName();
            separator = ", ";
        }
        msg += ")";
        context.fErrors->error(pos, msg);
        return nullptr;
    }

    for (size_t i = 0; i < arguments.size(); i++) {
        // Coerce each argument to the proper type.
        arguments[i] = types[i]->coerceExpression(std::move(arguments[i]), context);
        if (!arguments[i]) {
            return nullptr;
        }
        // Update the refKind on out-parameters, and ensure that they are actually assignable.
        const Modifiers& paramModifiers = function.parameters()[i]->modifiers();
        if (paramModifiers.fFlags & Modifiers::kOut_Flag) {
            const VariableRefKind refKind = paramModifiers.fFlags & Modifiers::kIn_Flag
                                                    ? VariableReference::RefKind::kReadWrite
                                                    : VariableReference::RefKind::kPointer;
            if (!Analysis::UpdateVariableRefKind(arguments[i].get(), refKind, context.fErrors)) {
                return nullptr;
            }
        }
    }

    if (function.intrinsicKind() == k_eval_IntrinsicKind) {
        // This is a method call on an effect child. Translate it into a ChildCall, which simplifies
        // handling in the generators and analysis code.
        const Variable& child = *arguments.back()->as<VariableReference>().variable();
        arguments.pop_back();
        return ChildCall::Make(context, pos, returnType, child, std::move(arguments));
    }

    return Make(context, pos, returnType, function, std::move(arguments));
}

std::unique_ptr<Expression> FunctionCall::Make(const Context& context,
                                               Position pos,
                                               const Type* returnType,
                                               const FunctionDeclaration& function,
                                               ExpressionArray arguments) {
    SkASSERT(function.parameters().size() == arguments.size());

    // We might be able to optimize built-in intrinsics.
    if (function.isIntrinsic() && has_compile_time_constant_arguments(arguments)) {
        // The function is an intrinsic and all inputs are compile-time constants. Optimize it.
        if (std::unique_ptr<Expression> expr = optimize_intrinsic_call(context,
                                                                       pos,
                                                                       function.intrinsicKind(),
                                                                       arguments,
                                                                       *returnType)) {
            expr->fPosition = pos;
            return expr;
        }
    }

    return std::make_unique<FunctionCall>(pos, returnType, &function, std::move(arguments));
}

}  // namespace SkSL