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Improve constant folding for associative operations #23215

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480bb57
first pass
hadrian-reppas Jun 27, 2026
81032a9
clean up code
hadrian-reppas Jun 27, 2026
d8a3be5
check type
hadrian-reppas Jun 27, 2026
7c4e8e9
check types
hadrian-reppas Jun 27, 2026
9408aed
fix typo
hadrian-reppas Jun 28, 2026
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116 changes: 115 additions & 1 deletion datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,12 +39,12 @@ use datafusion_common::{
metadata::FieldMetadata,
tree_node::{Transformed, TransformedResult, TreeNode, TreeNodeRewriter},
};
use datafusion_expr::expr::HigherOrderFunction;
use datafusion_expr::{
BinaryExpr, Case, ColumnarValue, Expr, ExprSchemable, Like, Operator, Volatility,
and, binary::BinaryTypeCoercer, lit, or, preimage::PreimageResult,
};
use datafusion_expr::{Cast, TryCast, simplify::ExprSimplifyResult};
use datafusion_expr::{binary_expr, expr::HigherOrderFunction};
use datafusion_expr::{expr::ScalarFunction, interval_arithmetic::NullableInterval};
use datafusion_expr::{
expr::{InList, InSubquery},
Expand Down Expand Up @@ -1095,6 +1095,11 @@ impl TreeNodeRewriter for Simplifier<'_> {
Transformed::yes(*right)
}

// (A + 1) + 2 -> A + (1 + 2)
expr if is_associative_with_adjacent_literals(&expr, self.info) => {
Transformed::yes(reassociate_literals(expr, self.info))
}

//
// Rules for Multiply
//
Expand Down Expand Up @@ -2355,6 +2360,60 @@ fn simplify_right_is_one_case(
}
}

fn reassociate_literals(expr: Expr, info: &SimplifyContext) -> Expr {
fn flatten(
op: Operator,
datatype: &DataType,
info: &SimplifyContext,
expr: Expr,
out: &mut Vec<Expr>,
) {
match &expr {
Expr::BinaryExpr(binary)
if binary.op == op
&& matches!(info.get_data_type(&expr), Ok(dt) if &dt == datatype) =>
{
let Expr::BinaryExpr(binary) = expr else {
unreachable!()
};
flatten(op, datatype, info, *binary.left, out);
flatten(op, datatype, info, *binary.right, out);
}
_ => out.push(expr),
}
}

let (op, datatype) = match (&expr, info.get_data_type(&expr)) {
(Expr::BinaryExpr(expr), Ok(datatype)) => (expr.op, datatype),
_ => return expr,
};
let mut exprs = Vec::new();
flatten(op, &datatype, info, expr, &mut exprs);
let mut exprs = exprs.into_iter();

let mut out = exprs.next().unwrap();
let mut lit = None;
for expr in exprs {
if is_lit(&expr) {
if let Some(left) = lit {
lit = Some(binary_expr(left, op, expr));
} else {
lit = Some(expr);
}
} else {
if let Some(lit) = lit.take() {
out = binary_expr(out, op, lit);
}
out = binary_expr(out, op, expr);
}
}
if let Some(lit) = lit.take() {
binary_expr(out, op, lit)
} else {
out
}
}

#[cfg(test)]
mod tests {
use super::*;
Expand Down Expand Up @@ -3368,6 +3427,60 @@ mod tests {
assert_eq!(simplify(expr_eq), lit(true));
}

#[test]
fn test_simplify_nested_literals_associative() {
assert_change(
col("c3") + lit(1i64) + lit(2i64) + lit(3i64) + col("c3_non_null"),
col("c3") + lit(6i64) + col("c3_non_null"),
);
assert_change(
(col("c3") + lit(1i64)) + (lit(2i64) + col("c3_non_null")),
col("c3") + lit(3i64) + col("c3_non_null"),
);
assert_change(lit(1i64) + lit(2i64) + col("c3"), lit(3i64) + col("c3"));
assert_change(col("c4") + lit(1u32) + lit(2u32), col("c4") + lit(3u32));
assert_change(
col("c3") + lit(1i64) + col("c3_non_null") + lit(2i64) + lit(3i64),
col("c3") + lit(1i64) + col("c3_non_null") + lit(5i64),
);
assert_change(
col("c3") * col("c3") + lit(2i64) + (lit(3i64) + lit(4i64) * col("c3")),
col("c3") * col("c3") + lit(5i64) + lit(4i64) * col("c3"),
);
assert_change(col("c3") * lit(2i64) * lit(3i64), col("c3") * lit(6i64));
assert_change(
(col("c3") * lit(2i64)) * (lit(3i64) * col("c3_non_null")),
col("c3") * lit(6i64) * col("c3_non_null"),
);

let cat = |left, right| binary_expr(left, Operator::StringConcat, right);
assert_change(
cat(cat(cat(col("c1"), lit("a")), lit("b")), col("c1")),
cat(cat(col("c1"), lit("ab")), col("c1")),
);

assert_change(col("c3") & lit(12i64) & lit(10i64), col("c3") & lit(8i64));
assert_change(
(col("c4") & lit(12u32)) & (lit(10u32) & col("c4_non_null")),
col("c4") & lit(8u32) & col("c4_non_null"),
);

assert_change(col("c3") | lit(1i64) | lit(2i64), col("c3") | lit(3i64));
assert_change(col("c4") ^ lit(1u32) ^ lit(3u32), col("c4") ^ lit(2u32));

assert_no_change(col("c3") + lit(1i64));
assert_no_change(lit(1i64) + col("c3"));
assert_no_change(col("c6") + lit(1.0) + lit(2.0));
assert_no_change(col("c6") * lit(3.0) * lit(4.0));
assert_no_change(col("c4") + lit(5u32) + lit(6u8));
assert_no_change(lit(7i64) + col("c3") + lit(8i64));

assert_change(
col("c4") + lit(1u32) + lit(2i64) + lit(3i64),
col("c4") + lit(1u32) + lit(5i64),
);
}

#[test]
fn test_simplify_regex() {
// malformed regex
Expand Down Expand Up @@ -3685,6 +3798,7 @@ mod tests {
Field::new("c3_non_null", DataType::Int64, false),
Field::new("c4_non_null", DataType::UInt32, false),
Field::new("c5", DataType::FixedSizeBinary(3), true),
Field::new("c6", DataType::Float64, true),
]
.into(),
HashMap::new(),
Expand Down
79 changes: 77 additions & 2 deletions datafusion/optimizer/src/simplify_expressions/utils.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,12 +17,16 @@

//! Utility functions for expression simplification

use arrow::datatypes::i256;
use datafusion_common::{Result, ScalarValue, internal_err};
use arrow::datatypes::{DataType, i256};
use datafusion_common::{
Result, ScalarValue, internal_err,
tree_node::{TreeNode, TreeNodeRecursion, TreeNodeVisitor},
};
use datafusion_expr::{
Case, Expr, Like, Operator,
expr::{Between, BinaryExpr, InList},
expr_fn::{and, bitwise_and, bitwise_or, or},
simplify::SimplifyContext,
};

pub static POWS_OF_TEN: [i128; 38] = [
Expand Down Expand Up @@ -290,6 +294,77 @@ pub fn is_lit(expr: &Expr) -> bool {
matches!(expr, Expr::Literal(_, _))
}

pub fn is_associative(op: Operator, datatype: &DataType) -> bool {
match op {
Operator::Plus | Operator::Multiply => datatype.is_integer(),
Operator::StringConcat
| Operator::BitwiseAnd
| Operator::BitwiseOr
| Operator::BitwiseXor => true,
_ => false,
}
}

pub fn is_associative_with_adjacent_literals(
expr: &Expr,
info: &SimplifyContext,
) -> bool {
struct AdjacentLiteralVisitor<'a> {
last_expr_was_literal: bool,
op: Operator,
datatype: DataType,
info: &'a SimplifyContext,
}

impl<'a, 'n> TreeNodeVisitor<'n> for AdjacentLiteralVisitor<'a> {
type Node = Expr;

fn f_down(&mut self, node: &'n Self::Node) -> Result<TreeNodeRecursion> {

@nathanb9 nathanb9 Jun 27, 2026

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last_expr_was_literal is not reset when visiting a nonliteral. For (lit(1) + col("c1")) + lit(2), the rewrite appears to rebuild the same expression but still results in Transformed::yes

Instead you could make has_adjacent_literals inspect the flattened operand sequence for the same operator, and reset adjacency whenever a nonliteral operand appears.

@hadrian-reppas hadrian-reppas Jun 27, 2026

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I kept the AdjacentLiteralVisitor and changed it so that it updates last_expr_was_literal correctly. is_associative_with_adjacent_literals needs to take the expression by reference because we call it from the big match statement in the Simplifier. I'm not sure I can construct the flattened operand sequence with just a reference to the expression. I suppose I could construct a Vec<&Expr>, but I'm not sure how much better that would be. Unless I could somehow write one function that does &Expr -> Vec<&Expr> and Expr -> Vec<Expr>.

match self.info.get_data_type(node) {
Ok(datatype) if datatype == self.datatype => {}
_ => {
self.last_expr_was_literal = false;
return Ok(TreeNodeRecursion::Jump);
}
}

match node {
Expr::BinaryExpr(expr) if expr.op == self.op => {
Ok(TreeNodeRecursion::Continue)
}
Expr::Literal(_, _) => {
if self.last_expr_was_literal {
Ok(TreeNodeRecursion::Stop)
} else {
self.last_expr_was_literal = true;
Ok(TreeNodeRecursion::Continue)
}
}
_ => {
self.last_expr_was_literal = false;
Ok(TreeNodeRecursion::Jump)
}
}
}
}

let (op, datatype) = match (expr, info.get_data_type(expr)) {
(Expr::BinaryExpr(expr), Ok(datatype)) => (expr.op, datatype),
_ => return false,
};
if !is_associative(op, &datatype) {
return false;
}

let mut visitor = AdjacentLiteralVisitor {
last_expr_was_literal: false,
op,
datatype,
info,
};
expr.visit(&mut visitor).unwrap() == TreeNodeRecursion::Stop
}

/// Checks if `eq_expr` is `A = L1` and `ne_expr` is `A != L2` where L1 != L2.
/// This pattern can be simplified to just `A = L1` since if A equals L1
/// and L1 is different from L2, then A is automatically not equal to L2.
Expand Down