src/sksl/ir/SkSLPrefixExpression.cpp

/*
 * Copyright 2020 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/ir/SkSLPrefixExpression.h"

#include "include/core/SkTypes.h"
#include "src/sksl/SkSLAnalysis.h"
#include "src/sksl/SkSLConstantFolder.h"
#include "src/sksl/SkSLContext.h"
#include "src/sksl/SkSLDefines.h"
#include "src/sksl/SkSLErrorReporter.h"
#include "src/sksl/SkSLOperator.h"
#include "src/sksl/SkSLProgramSettings.h"
#include "src/sksl/ir/SkSLBinaryExpression.h"
#include "src/sksl/ir/SkSLConstructorArray.h"
#include "src/sksl/ir/SkSLConstructorCompound.h"
#include "src/sksl/ir/SkSLConstructorDiagonalMatrix.h"
#include "src/sksl/ir/SkSLLiteral.h"
#include "src/sksl/ir/SkSLType.h"
#include "src/sksl/ir/SkSLVariableReference.h"

#include <cstddef>
#include <optional>

namespace SkSL {

static ExpressionArray negate_operands(const Context& context,
                                       Position pos,
                                       const ExpressionArray& operands);

static double negate_value(double value) {
    return -value;
}

static double bitwise_not_value(double value) {
    return ~static_cast<SKSL_INT>(value);
}

static std::unique_ptr<Expression> apply_to_elements(const Context& context,
                                                     Position pos,
                                                     const Expression& expr,
                                                     double (*fn)(double)) {
    const Type& elementType = expr.type().componentType();

    double values[16];
    size_t numSlots = expr.type().slotCount();
    if (numSlots > std::size(values)) {
        // The expression has more slots than we expected.
        return nullptr;
    }

    for (size_t index = 0; index < numSlots; ++index) {
        if (std::optional<double> slotValue = expr.getConstantValue(index)) {
            values[index] = fn(*slotValue);
            if (elementType.checkForOutOfRangeLiteral(context, values[index], pos)) {
                // We can't simplify the expression if the new value is out-of-range for the type.
                return nullptr;
            }
        } else {
            // There's a non-constant element; we can't simplify this expression.
            return nullptr;
        }
    }
    return ConstructorCompound::MakeFromConstants(context, pos, expr.type(), values);
}

static std::unique_ptr<Expression> simplify_negation(const Context& context,
                                                     Position pos,
                                                     const Expression& originalExpr) {
    const Expression* value = ConstantFolder::GetConstantValueForVariable(originalExpr);
    switch (value->kind()) {
        case Expression::Kind::kLiteral:
        case Expression::Kind::kConstructorSplat:
        case Expression::Kind::kConstructorCompound: {
            // Convert `-vecN(literal, ...)` into `vecN(-literal, ...)`.
            if (std::unique_ptr<Expression> expr = apply_to_elements(context, pos, *value,
                                                                     negate_value)) {
                return expr;
            }
            break;
        }
        case Expression::Kind::kPrefix: {
            // Convert `-(-expression)` into `expression`.
            const PrefixExpression& prefix = value->as<PrefixExpression>();
            if (prefix.getOperator().kind() == Operator::Kind::MINUS) {
                return prefix.operand()->clone(pos);
            }
            break;
        }
        case Expression::Kind::kConstructorArray:
            // Convert `-array[N](literal, ...)` into `array[N](-literal, ...)`.
            if (Analysis::IsCompileTimeConstant(*value)) {
                const ConstructorArray& ctor = value->as<ConstructorArray>();
                return ConstructorArray::Make(context, pos, ctor.type(),
                                              negate_operands(context, pos, ctor.arguments()));
            }
            break;

        case Expression::Kind::kConstructorDiagonalMatrix:
            // Convert `-matrix(literal)` into `matrix(-literal)`.
            if (Analysis::IsCompileTimeConstant(*value)) {
                const ConstructorDiagonalMatrix& ctor = value->as<ConstructorDiagonalMatrix>();
                if (std::unique_ptr<Expression> simplified = simplify_negation(context,
                                                                               pos,
                                                                               *ctor.argument())) {
                    return ConstructorDiagonalMatrix::Make(context, pos, ctor.type(),
                                                           std::move(simplified));
                }
            }
            break;

        default:
            break;
    }
    return nullptr;
}

static ExpressionArray negate_operands(const Context& context,
                                       Position pos,
                                       const ExpressionArray& array) {
    ExpressionArray replacement;
    replacement.reserve_exact(array.size());
    for (const std::unique_ptr<Expression>& expr : array) {
        // The logic below is very similar to `negate_operand`, but with different ownership rules.
        if (std::unique_ptr<Expression> simplified = simplify_negation(context, pos, *expr)) {
            replacement.push_back(std::move(simplified));
        } else {
            replacement.push_back(std::make_unique<PrefixExpression>(pos, Operator::Kind::MINUS,
                                                                     expr->clone()));
        }
    }
    return replacement;
}

static std::unique_ptr<Expression> negate_operand(const Context& context,
                                                  Position pos,
                                                  std::unique_ptr<Expression> value) {
    // Attempt to simplify this negation (e.g. eliminate double negation, literal values)
    if (std::unique_ptr<Expression> simplified = simplify_negation(context, pos, *value)) {
        return simplified;
    }

    // No simplified form; convert expression to Prefix(MINUS, expression).
    return std::make_unique<PrefixExpression>(pos, Operator::Kind::MINUS, std::move(value));
}

static std::unique_ptr<Expression> logical_not_operand(const Context& context,
                                                       Position pos,
                                                       std::unique_ptr<Expression> operand) {
    const Expression* value = ConstantFolder::GetConstantValueForVariable(*operand);
    switch (value->kind()) {
        case Expression::Kind::kLiteral: {
            // Convert !boolLiteral(true) to boolLiteral(false).
            SkASSERT(value->type().isBoolean());
            const Literal& b = value->as<Literal>();
            return Literal::MakeBool(pos, !b.boolValue(), &operand->type());
        }
        case Expression::Kind::kPrefix: {
            // Convert `!(!expression)` into `expression`.
            PrefixExpression& prefix = operand->as<PrefixExpression>();
            if (prefix.getOperator().kind() == Operator::Kind::LOGICALNOT) {
                prefix.operand()->fPosition = pos;
                return std::move(prefix.operand());
            }
            break;
        }
        case Expression::Kind::kBinary: {
            BinaryExpression& binary = operand->as<BinaryExpression>();
            std::optional<Operator> replacement;
            switch (binary.getOperator().kind()) {
                case OperatorKind::EQEQ: replacement = OperatorKind::NEQ;  break;
                case OperatorKind::NEQ:  replacement = OperatorKind::EQEQ; break;
                case OperatorKind::LT:   replacement = OperatorKind::GTEQ; break;
                case OperatorKind::LTEQ: replacement = OperatorKind::GT;   break;
                case OperatorKind::GT:   replacement = OperatorKind::LTEQ; break;
                case OperatorKind::GTEQ: replacement = OperatorKind::LT;   break;
                default:                                                   break;
            }
            if (replacement.has_value()) {
                return BinaryExpression::Make(context, pos, std::move(binary.left()),
                                              *replacement, std::move(binary.right()),
                                              &binary.type());
            }
            break;
        }
        default:
            break;
    }

    // No simplified form; convert expression to Prefix(LOGICALNOT, expression).
    return std::make_unique<PrefixExpression>(pos, Operator::Kind::LOGICALNOT, std::move(operand));
}

static std::unique_ptr<Expression> bitwise_not_operand(const Context& context,
                                                       Position pos,
                                                       std::unique_ptr<Expression> operand) {
    SkASSERT(operand->type().componentType().isInteger());

    const Expression* value = ConstantFolder::GetConstantValueForVariable(*operand);

    switch (value->kind()) {
        case Expression::Kind::kLiteral:
        case Expression::Kind::kConstructorSplat:
        case Expression::Kind::kConstructorCompound: {
            // Convert ~vecN(1, 2, ...) to vecN(~1, ~2, ...).
            if (std::unique_ptr<Expression> expr = apply_to_elements(context, pos, *value,
                                                                     bitwise_not_value)) {
                return expr;
            }
            break;
        }
        case Expression::Kind::kPrefix: {
            // Convert `~(~expression)` into `expression`.
            PrefixExpression& prefix = operand->as<PrefixExpression>();
            if (prefix.getOperator().kind() == Operator::Kind::BITWISENOT) {
                prefix.operand()->fPosition = pos;
                return std::move(prefix.operand());
            }
            break;
        }
        default:
            break;
    }

    // No simplified form; convert expression to Prefix(BITWISENOT, expression).
    return std::make_unique<PrefixExpression>(pos, Operator::Kind::BITWISENOT, std::move(operand));
}

std::unique_ptr<Expression> PrefixExpression::Convert(const Context& context,
                                                      Position pos,
                                                      Operator op,
                                                      std::unique_ptr<Expression> base) {
    const Type& baseType = base->type();
    switch (op.kind()) {
        case Operator::Kind::PLUS:
            if (baseType.isArray() || !baseType.componentType().isNumber()) {
                context.fErrors->error(pos,
                                       "'+' cannot operate on '" + baseType.displayName() + "'");
                return nullptr;
            }
            break;

        case Operator::Kind::MINUS:
            if (baseType.isArray() || !baseType.componentType().isNumber()) {
                context.fErrors->error(pos,
                                       "'-' cannot operate on '" + baseType.displayName() + "'");
                return nullptr;
            }
            break;

        case Operator::Kind::PLUSPLUS:
        case Operator::Kind::MINUSMINUS:
            if (baseType.isArray() || !baseType.componentType().isNumber()) {
                context.fErrors->error(pos,
                                       "'" + std::string(op.tightOperatorName()) +
                                       "' cannot operate on '" + baseType.displayName() + "'");
                return nullptr;
            }
            if (!Analysis::UpdateVariableRefKind(base.get(), VariableReference::RefKind::kReadWrite,
                                                 context.fErrors)) {
                return nullptr;
            }
            break;

        case Operator::Kind::LOGICALNOT:
            if (!baseType.isBoolean()) {
                context.fErrors->error(pos,
                                       "'" + std::string(op.tightOperatorName()) +
                                       "' cannot operate on '" + baseType.displayName() + "'");
                return nullptr;
            }
            break;

        case Operator::Kind::BITWISENOT:
            if (context.fConfig->strictES2Mode()) {
                // GLSL ES 1.00, Section 5.1
                context.fErrors->error(
                        pos,
                        "operator '" + std::string(op.tightOperatorName()) + "' is not allowed");
                return nullptr;
            }
            if (baseType.isArray() || !baseType.componentType().isInteger()) {
                context.fErrors->error(pos,
                                       "'" + std::string(op.tightOperatorName()) +
                                       "' cannot operate on '" + baseType.displayName() + "'");
                return nullptr;
            }
            break;

        default:
            SK_ABORT("unsupported prefix operator");
    }

    std::unique_ptr<Expression> result = PrefixExpression::Make(context, pos, op, std::move(base));
    SkASSERT(result->fPosition == pos);
    return result;
}

std::unique_ptr<Expression> PrefixExpression::Make(const Context& context,
                                                   Position pos,
                                                   Operator op,
                                                   std::unique_ptr<Expression> base) {
    const Type& baseType = base->type();
    switch (op.kind()) {
        case Operator::Kind::PLUS:
            SkASSERT(!baseType.isArray());
            SkASSERT(baseType.componentType().isNumber());
            base->fPosition = pos;
            return base;

        case Operator::Kind::MINUS:
            SkASSERT(!baseType.isArray());
            SkASSERT(baseType.componentType().isNumber());
            return negate_operand(context, pos, std::move(base));

        case Operator::Kind::LOGICALNOT:
            SkASSERT(baseType.isBoolean());
            return logical_not_operand(context, pos, std::move(base));

        case Operator::Kind::PLUSPLUS:
        case Operator::Kind::MINUSMINUS:
            SkASSERT(!baseType.isArray());
            SkASSERT(baseType.componentType().isNumber());
            SkASSERT(Analysis::IsAssignable(*base));
            break;

        case Operator::Kind::BITWISENOT:
            SkASSERT(!context.fConfig->strictES2Mode());
            SkASSERT(!baseType.isArray());
            SkASSERT(baseType.componentType().isInteger());
            if (baseType.isLiteral()) {
                // The expression `~123` is no longer a literal; coerce to the actual type.
                base = baseType.scalarTypeForLiteral().coerceExpression(std::move(base), context);
                SkASSERT(base);
            }
            return bitwise_not_operand(context, pos, std::move(base));

        default:
            SkDEBUGFAILF("unsupported prefix operator: %s", op.operatorName());
    }

    return std::make_unique<PrefixExpression>(pos, op, std::move(base));
}

std::string PrefixExpression::description(OperatorPrecedence parentPrecedence) const {
    bool needsParens = (OperatorPrecedence::kPrefix >= parentPrecedence);
    return std::string(needsParens ? "(" : "") +
           std::string(this->getOperator().tightOperatorName()) +
           this->operand()->description(OperatorPrecedence::kPrefix) +
           std::string(needsParens ? ")" : "");
}

}  // namespace SkSL