feat(optimizer): support logical filter expression simplify rule

src/frontend/planner_test/tests/testdata/output/temporal_filter.yaml

@@ -384,15 +384,15 @@
       │     ├─StreamProject { exprs: [t1.ts, AddWithTimeZone(t1.ts, '01:00:00':Interval, 'UTC':Varchar) as $expr1, t1._row_id] }
       │     │ └─StreamFilter { predicate: Not((t1.ts > '2023-12-18 00:00:00+00:00':Timestamptz)) }
       │     │   └─StreamShare { id: 2 }
-      │     │     └─StreamFilter { predicate: (Not((t1.ts > '2023-12-18 00:00:00+00:00':Timestamptz)) OR (t1.ts > '2023-12-18 00:00:00+00:00':Timestamptz)) }
+      │     │     └─StreamFilter { predicate: IsNotNull(t1.ts) }
       │     │       └─StreamTableScan { table: t1, columns: [t1.ts, t1._row_id], pk: [t1._row_id], dist: UpstreamHashShard(t1._row_id) }
       │     └─StreamExchange { dist: Broadcast }
       │       └─StreamNow { output: [now] }
       └─StreamExchange { dist: HashShard(t1._row_id, 1:Int32) }
         └─StreamProject { exprs: [t1.ts, t1._row_id, 1:Int32] }
           └─StreamFilter { predicate: (t1.ts > '2023-12-18 00:00:00+00:00':Timestamptz) }
             └─StreamShare { id: 2 }
-              └─StreamFilter { predicate: (Not((t1.ts > '2023-12-18 00:00:00+00:00':Timestamptz)) OR (t1.ts > '2023-12-18 00:00:00+00:00':Timestamptz)) }
+              └─StreamFilter { predicate: IsNotNull(t1.ts) }
                 └─StreamTableScan { table: t1, columns: [t1.ts, t1._row_id], pk: [t1._row_id], dist: UpstreamHashShard(t1._row_id) }
 - name: Temporal filter with or is null
   sql: |
@@ -406,17 +406,15 @@
       │   └─StreamDynamicFilter { predicate: ($expr1 > now), output_watermarks: [$expr1], output: [t1.ts, $expr1, t1._row_id], cleaned_by_watermark: true }
       │     ├─StreamProject { exprs: [t1.ts, AddWithTimeZone(t1.ts, '01:00:00':Interval, 'UTC':Varchar) as $expr1, t1._row_id] }
       │     │ └─StreamFilter { predicate: Not(IsNull(t1.ts)) }
-      │     │   └─StreamShare { id: 2 }
-      │     │     └─StreamFilter { predicate: (Not(IsNull(t1.ts)) OR IsNull(t1.ts)) }
-      │     │       └─StreamTableScan { table: t1, columns: [t1.ts, t1._row_id], pk: [t1._row_id], dist: UpstreamHashShard(t1._row_id) }
+      │     │   └─StreamShare { id: 1 }
+      │     │     └─StreamTableScan { table: t1, columns: [t1.ts, t1._row_id], pk: [t1._row_id], dist: UpstreamHashShard(t1._row_id) }
       │     └─StreamExchange { dist: Broadcast }
       │       └─StreamNow { output: [now] }
       └─StreamExchange { dist: HashShard(t1._row_id, 1:Int32) }
         └─StreamProject { exprs: [t1.ts, t1._row_id, 1:Int32] }
           └─StreamFilter { predicate: IsNull(t1.ts) }
-            └─StreamShare { id: 2 }
-              └─StreamFilter { predicate: (Not(IsNull(t1.ts)) OR IsNull(t1.ts)) }
-                └─StreamTableScan { table: t1, columns: [t1.ts, t1._row_id], pk: [t1._row_id], dist: UpstreamHashShard(t1._row_id) }
+            └─StreamShare { id: 1 }
+              └─StreamTableScan { table: t1, columns: [t1.ts, t1._row_id], pk: [t1._row_id], dist: UpstreamHashShard(t1._row_id) }
 - name: Temporal filter with or predicate
   sql: |
     create table t1 (ts timestamp with time zone);
@@ -458,7 +456,7 @@
       │     │     │   └─StreamDynamicFilter { predicate: (t.t > $expr1), output_watermarks: [t.t], output: [t.t, t.a, t._row_id], cleaned_by_watermark: true }
       │     │     │     ├─StreamFilter { predicate: (Not((t.a > 1:Int32)) OR (t.a > 1:Int32)) AND Not(IsNull(t.t)) AND Not((t.a < 1:Int32)) }
       │     │     │     │ └─StreamShare { id: 2 }
-      │     │     │     │   └─StreamFilter { predicate: (Not((t.a > 1:Int32)) OR (t.a > 1:Int32)) AND (((Not(IsNull(t.t)) AND Not((t.a < 1:Int32))) OR IsNull(t.t)) OR (t.a < 1:Int32)) }
+      │     │     │     │   └─StreamFilter { predicate: IsNotNull(t.a) AND (((Not(IsNull(t.t)) AND Not((t.a < 1:Int32))) OR IsNull(t.t)) OR (t.a < 1:Int32)) }
       │     │     │     │     └─StreamTableScan { table: t, columns: [t.t, t.a, t._row_id], pk: [t._row_id], dist: UpstreamHashShard(t._row_id) }
       │     │     │     └─StreamExchange { dist: Broadcast }
       │     │     │       └─StreamProject { exprs: [SubtractWithTimeZone(now, '01:00:00':Interval, 'UTC':Varchar) as $expr1], output_watermarks: [$expr1] }
@@ -467,7 +465,7 @@
       │     │       └─StreamProject { exprs: [t.t, t.a, t._row_id, 1:Int32] }
       │     │         └─StreamFilter { predicate: (Not((t.a > 1:Int32)) OR (t.a > 1:Int32)) AND (IsNull(t.t) OR (t.a < 1:Int32)) }
       │     │           └─StreamShare { id: 2 }
-      │     │             └─StreamFilter { predicate: (Not((t.a > 1:Int32)) OR (t.a > 1:Int32)) AND (((Not(IsNull(t.t)) AND Not((t.a < 1:Int32))) OR IsNull(t.t)) OR (t.a < 1:Int32)) }
+      │     │             └─StreamFilter { predicate: IsNotNull(t.a) AND (((Not(IsNull(t.t)) AND Not((t.a < 1:Int32))) OR IsNull(t.t)) OR (t.a < 1:Int32)) }
       │     │               └─StreamTableScan { table: t, columns: [t.t, t.a, t._row_id], pk: [t._row_id], dist: UpstreamHashShard(t._row_id) }
       │     └─StreamExchange { dist: Broadcast }
       │       └─StreamProject { exprs: [SubtractWithTimeZone(now, '01:00:00':Interval, 'UTC':Varchar) as $expr2], output_watermarks: [$expr2] }
@@ -482,7 +480,7 @@
                 │   └─StreamDynamicFilter { predicate: (t.t > $expr1), output_watermarks: [t.t], output: [t.t, t.a, t._row_id], cleaned_by_watermark: true }
                 │     ├─StreamFilter { predicate: (Not((t.a > 1:Int32)) OR (t.a > 1:Int32)) AND Not(IsNull(t.t)) AND Not((t.a < 1:Int32)) }
                 │     │ └─StreamShare { id: 2 }
-                │     │   └─StreamFilter { predicate: (Not((t.a > 1:Int32)) OR (t.a > 1:Int32)) AND (((Not(IsNull(t.t)) AND Not((t.a < 1:Int32))) OR IsNull(t.t)) OR (t.a < 1:Int32)) }
+                │     │   └─StreamFilter { predicate: IsNotNull(t.a) AND (((Not(IsNull(t.t)) AND Not((t.a < 1:Int32))) OR IsNull(t.t)) OR (t.a < 1:Int32)) }
                 │     │     └─StreamTableScan { table: t, columns: [t.t, t.a, t._row_id], pk: [t._row_id], dist: UpstreamHashShard(t._row_id) }
                 │     └─StreamExchange { dist: Broadcast }
                 │       └─StreamProject { exprs: [SubtractWithTimeZone(now, '01:00:00':Interval, 'UTC':Varchar) as $expr1], output_watermarks: [$expr1] }
@@ -491,5 +489,5 @@
                   └─StreamProject { exprs: [t.t, t.a, t._row_id, 1:Int32] }
                     └─StreamFilter { predicate: (Not((t.a > 1:Int32)) OR (t.a > 1:Int32)) AND (IsNull(t.t) OR (t.a < 1:Int32)) }
                       └─StreamShare { id: 2 }
-                        └─StreamFilter { predicate: (Not((t.a > 1:Int32)) OR (t.a > 1:Int32)) AND (((Not(IsNull(t.t)) AND Not((t.a < 1:Int32))) OR IsNull(t.t)) OR (t.a < 1:Int32)) }
+                        └─StreamFilter { predicate: IsNotNull(t.a) AND (((Not(IsNull(t.t)) AND Not((t.a < 1:Int32))) OR IsNull(t.t)) OR (t.a < 1:Int32)) }
                           └─StreamTableScan { table: t, columns: [t.t, t.a, t._row_id], pk: [t._row_id], dist: UpstreamHashShard(t._row_id) }

src/frontend/src/optimizer/logical_optimization.rs

@@ -416,6 +416,14 @@ static COMMON_SUB_EXPR_EXTRACT: LazyLock<OptimizationStage> = LazyLock::new(|| {
     )
 });
 
+static LOGICAL_FILTER_EXPRESSION_SIMPLIFY: LazyLock<OptimizationStage> = LazyLock::new(|| {
+    OptimizationStage::new(
+        "Logical Filter Expression Simplify",
+        vec![LogicalFilterExpressionSimplifyRule::create()],
+        ApplyOrder::TopDown,
+    )
+});
+
 impl LogicalOptimizer {
     pub fn predicate_pushdown(
         plan: PlanRef,
@@ -624,6 +632,8 @@ impl LogicalOptimizer {
 
         plan = plan.optimize_by_rules(&COMMON_SUB_EXPR_EXTRACT);
 
+        plan = plan.optimize_by_rules(&LOGICAL_FILTER_EXPRESSION_SIMPLIFY);
+
         #[cfg(debug_assertions)]
         InputRefValidator.validate(plan.clone());
 
@@ -720,6 +730,8 @@ impl LogicalOptimizer {
 
         plan = plan.optimize_by_rules(&DAG_TO_TREE);
 
+        plan = plan.optimize_by_rules(&LOGICAL_FILTER_EXPRESSION_SIMPLIFY);
+
         #[cfg(debug_assertions)]
         InputRefValidator.validate(plan.clone());
 

src/frontend/src/optimizer/plan_expr_visitor/mod.rs

@@ -14,7 +14,7 @@
 
 mod expr_counter;
 mod input_ref_counter;
-mod strong;
+pub mod strong;
 
 pub(crate) use expr_counter::CseExprCounter;
 pub(crate) use input_ref_counter::InputRefCounter;

src/frontend/src/optimizer/plan_expr_visitor/strong.rs

@@ -44,8 +44,9 @@ impl Strong {
         Self { null_columns }
     }
 
-    /// Returns whether the analyzed expression will definitely return null if
+    /// Returns whether the analyzed expression will *definitely* return null if
     /// all of a given set of input columns are null.
+    /// Note: we could not assume any null-related property for the input expression if `is_null` returns false
     pub fn is_null(expr: &ExprImpl, null_columns: FixedBitSet) -> bool {
         let strong = Strong::new(null_columns);
         strong.is_null_visit(expr)

src/frontend/src/optimizer/plan_node/expr_rewritable.rs

@@ -18,7 +18,7 @@ use super::*;
 use crate::expr::ExprRewriter;
 
 /// Rewrites expressions in a `PlanRef`. Due to `Share` operator,
-/// the `ExprRewriter` needs to be idempotent i.e. applying it more than once
+/// the `ExprRewriter` needs to be idempotent i.e., applying it more than once
 /// to the same `ExprImpl` will be a noop on subsequent applications.
 /// `rewrite_exprs` should only return a plan with the given node modified.
 /// To rewrite recursively, call `rewrite_exprs_recursive` on [`RewriteExprsRecursive`].

src/frontend/src/optimizer/rule/logical_filter_expression_simplify_rule.rs

@@ -0,0 +1,258 @@
+// Copyright 2024 RisingWave Labs
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use fixedbitset::FixedBitSet;
+use risingwave_common::types::ScalarImpl;
+use risingwave_connector::source::DataType;
+
+use crate::expr::{Expr, ExprImpl, ExprRewriter, ExprType, FunctionCall};
+use crate::optimizer::plan_expr_visitor::strong::Strong;
+use crate::optimizer::plan_node::{ExprRewritable, LogicalFilter, LogicalShare, PlanTreeNodeUnary};
+use crate::optimizer::rule::{BoxedRule, Rule};
+use crate::optimizer::PlanRef;
+
+/// Specially for the predicate under `LogicalFilter -> LogicalShare -> LogicalFilter`
+pub struct LogicalFilterExpressionSimplifyRule {}
+impl Rule for LogicalFilterExpressionSimplifyRule {
+    /// The pattern we aim to optimize, e.g.,
+    /// 1. (NOT (e)) OR (e) => True
+    /// 2. (NOT (e)) AND (e) => False
+    /// NOTE: `e` should only contain at most a single column
+    /// otherwise we will not conduct the optimization
+    fn apply(&self, plan: PlanRef) -> Option<PlanRef> {
+        let filter: &LogicalFilter = plan.as_logical_filter()?;
+        let mut rewriter = ExpressionSimplifyRewriter {};
+        let logical_share_plan = filter.input();
+        let share: &LogicalShare = logical_share_plan.as_logical_share()?;
+        let input = share.input().rewrite_exprs(&mut rewriter);
+        share.replace_input(input);
+        Some(LogicalFilter::create(
+            share.clone().into(),
+            filter.predicate().clone(),
+        ))
+    }
+}
+
+impl LogicalFilterExpressionSimplifyRule {
+    pub fn create() -> BoxedRule {
+        Box::new(LogicalFilterExpressionSimplifyRule {})
+    }
+}
+
+/// `True` => the return value of the input `func_type` will *definitely* not be null
+/// `False` => vice versa
+fn is_not_null(func_type: ExprType) -> bool {
+    func_type == ExprType::IsNull
+        || func_type == ExprType::IsNotNull
+        || func_type == ExprType::IsTrue
+        || func_type == ExprType::IsFalse
+        || func_type == ExprType::IsNotTrue
+        || func_type == ExprType::IsNotFalse
+}
+
+/// Simply extract every possible `InputRef` out from the input `expr`
+fn extract_column(expr: ExprImpl, columns: &mut Vec<ExprImpl>) {
+    match expr.clone() {
+        ExprImpl::FunctionCall(func_call) => {
+            // the functions that *never* return null will be ignored
+            if is_not_null(func_call.func_type()) {
+                return;
+            }
+            for sub_expr in func_call.inputs() {
+                extract_column(sub_expr.clone(), columns);
+            }
+        }
+        ExprImpl::InputRef(_) => {
+            if !columns.contains(&expr) {
+                // only add the column if not exists
+                columns.push(expr);
+            }
+        }
+        _ => (),
+    }
+}
+
+/// If ever `Not (e)` and `(e)` appear together
+/// First return value indicates if the optimizable pattern exist
+/// Second return value indicates if the term `e` should be converted to either `IsNotNull` or `IsNull`
+/// If so, it will contain the actual wrapper `ExprImpl` for that; otherwise it will be `None`
+fn check_optimizable_pattern(e1: ExprImpl, e2: ExprImpl) -> (bool, Option<ExprImpl>) {
+    /// Try wrapping inner *column* with `IsNotNull`
+    fn try_wrap_inner_expression(expr: ExprImpl) -> Option<ExprImpl> {
+        let mut columns = vec![];
+
+        extract_column(expr, &mut columns);
+
+        assert!(columns.len() <= 1, "should only contain a single column");
+
+        if columns.is_empty() {
+            return None;
+        }
+
+        // From `c1` to `IsNotNull(c1)`
+        let Ok(expr) = FunctionCall::new(ExprType::IsNotNull, vec![columns[0].clone()]) else {
+            return None;
+        };
+
+        Some(expr.into())
+    }
+
+    // Due to constant folding, we only need to consider `FunctionCall` here (presumably)
+    let ExprImpl::FunctionCall(e1_func) = e1.clone() else {
+        return (false, None);
+    };
+    let ExprImpl::FunctionCall(e2_func) = e2.clone() else {
+        return (false, None);
+    };
+
+    // No chance to optimize
+    if e1_func.func_type() != ExprType::Not && e2_func.func_type() != ExprType::Not {
+        return (false, None);
+    }
+
+    if e1_func.func_type() != ExprType::Not {
+        // (e1) [op] (Not (e2))
+        if e2_func.inputs().len() != 1 {
+            // `not` should only have a single operand, which is `e2` in this case
+            return (false, None);
+        }
+        (
+            e1 == e2_func.inputs()[0].clone(),
+            try_wrap_inner_expression(e1),
+        )
+    } else {
+        // (Not (e1)) [op] (e2)
+        if e1_func.inputs().len() != 1 {
+            return (false, None);
+        }
+        (
+            e2 == e1_func.inputs()[0].clone(),
+            try_wrap_inner_expression(e2),
+        )
+    }
+}
+
+/// 1. True or (...) | (...) or True => True
+/// 2. False and (...) | (...) and False => False
+/// NOTE: the `True` and `False` here not only represent a single `ExprImpl::Literal`
+/// but represent every `ExprImpl` that can be *evaluated* to `ScalarImpl::Bool`
+/// during optimization phase as well
+fn check_special_pattern(e1: ExprImpl, e2: ExprImpl, op: ExprType) -> Option<bool> {
+    fn check_special_pattern_inner(e: ExprImpl, op: ExprType) -> Option<bool> {
+        let Some(Ok(Some(scalar))) = e.try_fold_const() else {
+            return None;
+        };
+        match op {
+            ExprType::Or => {
+                if scalar == ScalarImpl::Bool(true) {
+                    Some(true)
+                } else {
+                    None
+                }
+            }
+            ExprType::And => {
+                if scalar == ScalarImpl::Bool(false) {
+                    Some(false)
+                } else {
+                    None
+                }
+            }
+            _ => None,
+        }
+    }
+
+    if e1.is_const() {
+        if let Some(res) = check_special_pattern_inner(e1, op) {
+            return Some(res);
+        }
+    }
+
+    if e2.is_literal() {
+        if let Some(res) = check_special_pattern_inner(e2, op) {
+            return Some(res);
+        }
+    }
+
+    None
+}
+
+struct ExpressionSimplifyRewriter {}
+impl ExprRewriter for ExpressionSimplifyRewriter {
+    fn rewrite_expr(&mut self, expr: ExprImpl) -> ExprImpl {
+        // Check if the input expression is *definitely* null
+        let mut columns = vec![];
+        extract_column(expr.clone(), &mut columns);
+
+        // NOTE: we do NOT optimize cases that involve multiple columns
+        // for detailed reference: <https://github.com/risingwavelabs/risingwave/pull/15275#issuecomment-1975783856>
+        if columns.len() > 1 {
+            return expr;
+        }
+
+        // Eliminate the case where the current expression
+        // will definitely return null by using `Strong::is_null`
+        if !columns.is_empty() {
+            let ExprImpl::InputRef(input_ref) = columns[0].clone() else {
+                return expr;
+            };
+            let index = input_ref.index();
+            let fixedbitset = FixedBitSet::with_capacity(index);
+            if Strong::is_null(&expr, fixedbitset) {
+                return ExprImpl::literal_bool(false);
+            }
+        }
+
+        let ExprImpl::FunctionCall(func_call) = expr.clone() else {
+            return expr;
+        };
+        if func_call.func_type() != ExprType::Or && func_call.func_type() != ExprType::And {
+            return expr;
+        }
+        assert_eq!(func_call.return_type(), DataType::Boolean);
+        // Sanity check, the inputs should only contain two branches
+        if func_call.inputs().len() != 2 {
+            return expr;
+        }
+
+        let inputs = func_call.inputs();
+        let e1 = inputs[0].clone();
+        let e2 = inputs[1].clone();
+
+        // Eliminate special pattern
+        if let Some(res) = check_special_pattern(e1.clone(), e2.clone(), func_call.func_type()) {
+            return ExprImpl::literal_bool(res);
+        }
+
+        let (optimizable_flag, column) = check_optimizable_pattern(e1, e2);
+        if optimizable_flag {
+            match func_call.func_type() {
+                ExprType::Or => {
+                    if let Some(column) = column {
+                        // IsNotNull(col)
+                        column
+                    } else {
+                        ExprImpl::literal_bool(true)
+                    }
+                }
+                // `AND` will always be false, no matter the underlying columns are null or not
+                // i.e., for `(Not (e)) AND (e)`, since this is filter simplification,
+                // whether `e` is null or not does NOT matter
+                ExprType::And => ExprImpl::literal_bool(false),
+                _ => expr,
+            }
+        } else {
+            expr
+        }
+    }
+}