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#include "optimizer/bool_folding_optimizer.h"
#include "binder/expression/literal_expression.h"
#include "binder/expression/scalar_function_expression.h"
#include "common/enums/expression_type.h"
#include "common/types/value/value.h"
#include "planner/operator/logical_empty_result.h"
#include "planner/operator/logical_filter.h"
using namespace lbug::binder;
using namespace lbug::common;
using namespace lbug::planner;
namespace lbug {
namespace optimizer {
// ---------------------------------------------------------------------------
// Helper: detect whether two expressions are logical negations
// ---------------------------------------------------------------------------
/// Returns true if `a` and `b` can never be true simultaneously.
///
/// Recognised forms:
/// - NOT(p) and p
/// - IS_NULL(x) and IS_NOT_NULL(x)
static bool areNegations(const Expression& a, const Expression& b) {
// NOT(p) == b
if (a.expressionType == ExpressionType::NOT && a.getNumChildren() == 1 && *a.getChild(0) == b) {
return true;
}
// NOT(q) == a
if (b.expressionType == ExpressionType::NOT && b.getNumChildren() == 1 && *b.getChild(0) == a) {
return true;
}
// IS_NULL(x) vs IS_NOT_NULL(x)
if (a.expressionType == ExpressionType::IS_NULL &&
b.expressionType == ExpressionType::IS_NOT_NULL) {
return a.getNumChildren() > 0 && b.getNumChildren() > 0 && *a.getChild(0) == *b.getChild(0);
}
if (a.expressionType == ExpressionType::IS_NOT_NULL &&
b.expressionType == ExpressionType::IS_NULL) {
return a.getNumChildren() > 0 && b.getNumChildren() > 0 && *a.getChild(0) == *b.getChild(0);
}
return false;
}
// ---------------------------------------------------------------------------
// Helper: build a boolean literal expression
// ---------------------------------------------------------------------------
static std::shared_ptr<Expression> boolLiteral(bool v) {
return std::make_shared<LiteralExpression>(Value(v),
std::string("_lit_") + (v ? "true" : "false"));
}
// ---------------------------------------------------------------------------
// Core folding (tree-propagating version)
// ---------------------------------------------------------------------------
/// Recursively simplify a boolean expression through constant folding and
/// algebraic simplification (bottom-up tree propagation).
///
/// Returns `nullptr` when the expression is already as simple as it can be.
/// Otherwise returns a simplified expression: a LiteralExpression when the
/// whole expression is always-true or always-false, or a non-literal when
/// a subtree collapsed (e.g. `AND(true, x)` → `x`).
///
/// Because children are folded before the parent is examined, nested
/// simplifications cascade upward:
///
/// AND(OR(IS_NULL(x), IS_NOT_NULL(x)), y > 5)
/// → AND(true, y > 5) [OR tautology folded to true]
/// → y > 5 [AND(true, x) → x]
///
/// OR(AND(IS_NULL(x), IS_NOT_NULL(x)), n.k = 1)
/// → OR(false, n.k = 1) [AND contradiction folded to false]
/// → n.k = 1 [OR(false, x) → x]
static std::shared_ptr<Expression> foldBool(const std::shared_ptr<Expression>& expr) {
// --- NOT -----------------------------------------------------------
if (expr->expressionType == ExpressionType::NOT) {
// NOT(NOT(x)) → x — structural, no folding needed.
auto child = expr->getChild(0);
if (child->expressionType == ExpressionType::NOT && child->getNumChildren() == 1) {
return child->getChild(0);
}
// Fold the inner expression and invert if it becomes a constant.
auto folded = foldBool(child);
auto effective = folded ? folded : child;
if (effective->expressionType == ExpressionType::LITERAL) {
auto& lit = effective->constCast<LiteralExpression>();
return boolLiteral(lit.isNull() || !lit.getValue().getValue<bool>());
}
return folded ? effective : nullptr;
}
// --- AND -----------------------------------------------------------
if (expr->expressionType == ExpressionType::AND) {
auto parts = expr->splitOnAND();
expression_vector kept;
bool anyChanged = false;
// 1) Fold each child; short-circuit on false; drop true.
for (auto& part : parts) {
auto folded = foldBool(part);
auto effective = folded ? folded : part;
if (folded) {
anyChanged = true;
}
if (effective->expressionType == ExpressionType::LITERAL) {
auto& lit = effective->constCast<LiteralExpression>();
if (lit.isNull() || !lit.getValue().getValue<bool>()) {
return boolLiteral(false); // false ∧ … ≡ false
}
// true conjunct is a no-op – drop it.
continue;
}
kept.push_back(effective);
}
// 2) Check pair-wise contradictions among kept children.
for (auto i = 0u; i < kept.size(); ++i) {
for (auto j = i + 1; j < kept.size(); ++j) {
if (areNegations(*kept[i], *kept[j])) {
return boolLiteral(false); // p ∧ ¬p ≡ false
}
}
}
// 3) All conjuncts were true.
if (kept.empty()) {
return boolLiteral(true);
}
// 4) Single remaining child — e.g. AND(true, x) → x.
if (kept.size() == 1) {
return kept[0];
}
// 5) Multiple children remain; we currently do not rebuild the
// AND tree. If any child was simplified it is a missed
// opportunity, but the predicate is still correct as-is.
return anyChanged ? kept[0] : nullptr;
}
// --- OR ------------------------------------------------------------
if (expr->expressionType == ExpressionType::OR) {
// 1) Fold all children in one pass.
std::vector<std::shared_ptr<Expression>> folded;
bool anyChanged = false;
for (auto i = 0u; i < expr->getNumChildren(); ++i) {
auto f = foldBool(expr->getChild(i));
auto eff = f ? f : expr->getChild(i);
if (f) {
anyChanged = true;
}
folded.push_back(eff);
}
// 2) Walk children; short-circuit on true, drop false, detect
// tautology pairs.
expression_vector kept;
for (auto i = 0u; i < folded.size(); ++i) {
auto& eff = folded[i];
if (eff->expressionType == ExpressionType::LITERAL) {
auto& lit = eff->constCast<LiteralExpression>();
if (!lit.isNull() && lit.getValue().getValue<bool>()) {
return boolLiteral(true); // true ∨ … ≡ true
}
// false disjunct is a no-op.
continue;
}
// Check for tautology: p ∨ ¬p ≡ true.
for (auto j = i + 1; j < folded.size(); ++j) {
if (areNegations(*eff, *folded[j])) {
return boolLiteral(true);
}
}
kept.push_back(eff);
}
// 3) All disjuncts were false.
if (kept.empty()) {
return boolLiteral(false);
}
// 4) Single remaining child — e.g. OR(false, x) → x.
if (kept.size() == 1) {
return kept[0];
}
return anyChanged ? kept[0] : nullptr;
}
return nullptr;
}
// ---------------------------------------------------------------------------
// BoolFoldingOptimizer
// ---------------------------------------------------------------------------
void BoolFoldingOptimizer::rewrite(LogicalPlan* plan) {
visitOperator(plan->getLastOperator());
}
std::shared_ptr<LogicalOperator> BoolFoldingOptimizer::visitOperator(
const std::shared_ptr<LogicalOperator>& op) {
// bottom-up traversal
for (auto i = 0u; i < op->getNumChildren(); ++i) {
op->setChild(i, visitOperator(op->getChild(i)));
}
auto result = visitOperatorReplaceSwitch(op);
result->computeFlatSchema();
return result;
}
std::shared_ptr<LogicalOperator> BoolFoldingOptimizer::visitFilterReplace(
std::shared_ptr<LogicalOperator> op) {
auto& filter = op->constCast<LogicalFilter>();
auto predicate = filter.getPredicate();
// Already a literal – handled by the existing filter-push-down logic too,
// but folding may produce new literals from composite expressions.
if (predicate->expressionType == ExpressionType::LITERAL) {
auto& lit = predicate->constCast<LiteralExpression>();
if (lit.isNull() || !lit.getValue().getValue<bool>()) {
return std::make_shared<LogicalEmptyResult>(*op->getSchema());
}
return op->getChild(0); // true literal → drop filter
}
auto folded = foldBool(predicate);
if (!folded) {
return op; // no simplification
}
if (folded->expressionType == ExpressionType::LITERAL) {
auto& lit = folded->constCast<LiteralExpression>();
if (lit.isNull() || !lit.getValue().getValue<bool>()) {
return std::make_shared<LogicalEmptyResult>(*op->getSchema());
}
// Folded to true – the filter is redundant.
return op->getChild(0);
}
// Non-literal simplification – replace the filter predicate.
auto newFilter = std::make_shared<LogicalFilter>(std::move(folded), op->getChild(0));
newFilter->computeFlatSchema();
return newFilter;
}
} // namespace optimizer
} // namespace lbug