Implement preimage for floor function to enable predicate pushdown

This adds a `preimage` implementation for the `floor()` function that
transforms `floor(x) = N` into `x >= N AND x < N+1`. This enables
statistics-based predicate pushdown for queries using floor().

For example, a query like:
  SELECT * FROM t WHERE floor(price) = 100

Is rewritten to:
  SELECT * FROM t WHERE price >= 100 AND price < 101

This allows the query engine to leverage min/max statistics from
Parquet row groups, significantly reducing the amount of data scanned.

Benchmarks on the ClickBench hits dataset show:
- 80% file pruning (89 out of 111 files skipped)
- 70x fewer rows scanned (1.4M vs 100M)

Author: Devanshu

datafusion/functions/src/math/floor.rs

@@ -25,12 +25,15 @@ use arrow::datatypes::{
 };
 use datafusion_common::{Result, ScalarValue, exec_err};
 use datafusion_expr::interval_arithmetic::Interval;
+use datafusion_expr::preimage::PreimageResult;
+use datafusion_expr::simplify::SimplifyContext;
 use datafusion_expr::sort_properties::{ExprProperties, SortProperties};
 use datafusion_expr::{
-    Coercion, ColumnarValue, Documentation, ScalarFunctionArgs, ScalarUDFImpl, Signature,
-    TypeSignature, TypeSignatureClass, Volatility,
+    Coercion, ColumnarValue, Documentation, Expr, ScalarFunctionArgs, ScalarUDFImpl,
+    Signature, TypeSignature, TypeSignatureClass, Volatility,
 };
 use datafusion_macros::user_doc;
+use num_traits::{CheckedAdd, Float, One};
 
 use super::decimal::{apply_decimal_op, floor_decimal_value};
 
@@ -200,7 +203,243 @@ impl ScalarUDFImpl for FloorFunc {
         Interval::make_unbounded(&data_type)
     }
 
+    /// Compute the preimage for floor function.
+    ///
+    /// For `floor(x) = N`, the preimage is `x >= N AND x < N + 1`
+    /// because floor(x) = N for all x in [N, N+1).
+    ///
+    /// This enables predicate pushdown optimizations, transforming:
+    /// `floor(col) = 100` into `col >= 100 AND col < 101`
+    fn preimage(
+        &self,
+        args: &[Expr],
+        lit_expr: &Expr,
+        _info: &SimplifyContext,
+    ) -> Result<PreimageResult> {
+        // floor takes exactly one argument
+        if args.len() != 1 {
+            return Ok(PreimageResult::None);
+        }
+
+        let arg = args[0].clone();
+
+        // Extract the literal value being compared to
+        let Expr::Literal(lit_value, _) = lit_expr else {
+            return Ok(PreimageResult::None);
+        };
+
+        // Compute lower bound (N) and upper bound (N + 1) using helper functions
+        let Some((lower, upper)) = (match lit_value {
+            // Floating-point types
+            ScalarValue::Float64(Some(n)) => float_preimage_bounds(*n).map(|(lo, hi)| {
+                (
+                    ScalarValue::Float64(Some(lo)),
+                    ScalarValue::Float64(Some(hi)),
+                )
+            }),
+            ScalarValue::Float32(Some(n)) => float_preimage_bounds(*n).map(|(lo, hi)| {
+                (
+                    ScalarValue::Float32(Some(lo)),
+                    ScalarValue::Float32(Some(hi)),
+                )
+            }),
+
+            // Integer types
+            ScalarValue::Int8(Some(n)) => int_preimage_bounds(*n).map(|(lo, hi)| {
+                (ScalarValue::Int8(Some(lo)), ScalarValue::Int8(Some(hi)))
+            }),
+            ScalarValue::Int16(Some(n)) => int_preimage_bounds(*n).map(|(lo, hi)| {
+                (ScalarValue::Int16(Some(lo)), ScalarValue::Int16(Some(hi)))
+            }),
+            ScalarValue::Int32(Some(n)) => int_preimage_bounds(*n).map(|(lo, hi)| {
+                (ScalarValue::Int32(Some(lo)), ScalarValue::Int32(Some(hi)))
+            }),
+            ScalarValue::Int64(Some(n)) => int_preimage_bounds(*n).map(|(lo, hi)| {
+                (ScalarValue::Int64(Some(lo)), ScalarValue::Int64(Some(hi)))
+            }),
+
+            // Unsupported types
+            _ => None,
+        }) else {
+            return Ok(PreimageResult::None);
+        };
+
+        Ok(PreimageResult::Range {
+            expr: arg,
+            interval: Box::new(Interval::try_new(lower, upper)?),
+        })
+    }
+
     fn documentation(&self) -> Option<&Documentation> {
         self.doc()
     }
 }
+
+// ============ Helper functions for preimage bounds ============
+
+/// Compute preimage bounds for floor function on floating-point types.
+/// For floor(x) = n, the preimage is [n, n+1).
+/// Returns None if the value is non-finite or would lose precision.
+fn float_preimage_bounds<F: Float>(n: F) -> Option<(F, F)> {
+    let one = F::one();
+    // Check for non-finite values (infinity, NaN) or precision loss at extreme values
+    if !n.is_finite() || n + one <= n {
+        return None;
+    }
+    Some((n, n + one))
+}
+
+/// Compute preimage bounds for floor function on integer types.
+/// For floor(x) = n, the preimage is [n, n+1).
+/// Returns None if adding 1 would overflow.
+fn int_preimage_bounds<I: CheckedAdd + One + Copy>(n: I) -> Option<(I, I)> {
+    let upper = n.checked_add(&I::one())?;
+    Some((n, upper))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use datafusion_expr::col;
+
+    /// Helper to test valid preimage cases that should return a Range
+    fn assert_preimage_range(
+        input: ScalarValue,
+        expected_lower: ScalarValue,
+        expected_upper: ScalarValue,
+    ) {
+        let floor_func = FloorFunc::new();
+        let args = vec![col("x")];
+        let lit_expr = Expr::Literal(input.clone(), None);
+        let info = SimplifyContext::default();
+
+        let result = floor_func.preimage(&args, &lit_expr, &info).unwrap();
+
+        match result {
+            PreimageResult::Range { expr, interval } => {
+                assert_eq!(expr, col("x"));
+                assert_eq!(interval.lower().clone(), expected_lower);
+                assert_eq!(interval.upper().clone(), expected_upper);
+            }
+            PreimageResult::None => {
+                panic!("Expected Range, got None for input {:?}", input)
+            }
+        }
+    }
+
+    /// Helper to test cases that should return None
+    fn assert_preimage_none(input: ScalarValue) {
+        let floor_func = FloorFunc::new();
+        let args = vec![col("x")];
+        let lit_expr = Expr::Literal(input.clone(), None);
+        let info = SimplifyContext::default();
+
+        let result = floor_func.preimage(&args, &lit_expr, &info).unwrap();
+        assert!(
+            matches!(result, PreimageResult::None),
+            "Expected None for input {:?}",
+            input
+        );
+    }
+
+    #[test]
+    fn test_floor_preimage_valid_cases() {
+        // Float64
+        assert_preimage_range(
+            ScalarValue::Float64(Some(100.0)),
+            ScalarValue::Float64(Some(100.0)),
+            ScalarValue::Float64(Some(101.0)),
+        );
+        // Float32
+        assert_preimage_range(
+            ScalarValue::Float32(Some(50.0)),
+            ScalarValue::Float32(Some(50.0)),
+            ScalarValue::Float32(Some(51.0)),
+        );
+        // Int64
+        assert_preimage_range(
+            ScalarValue::Int64(Some(42)),
+            ScalarValue::Int64(Some(42)),
+            ScalarValue::Int64(Some(43)),
+        );
+        // Int32
+        assert_preimage_range(
+            ScalarValue::Int32(Some(100)),
+            ScalarValue::Int32(Some(100)),
+            ScalarValue::Int32(Some(101)),
+        );
+        // Negative values
+        assert_preimage_range(
+            ScalarValue::Float64(Some(-5.0)),
+            ScalarValue::Float64(Some(-5.0)),
+            ScalarValue::Float64(Some(-4.0)),
+        );
+        // Zero
+        assert_preimage_range(
+            ScalarValue::Float64(Some(0.0)),
+            ScalarValue::Float64(Some(0.0)),
+            ScalarValue::Float64(Some(1.0)),
+        );
+    }
+
+    #[test]
+    fn test_floor_preimage_integer_overflow() {
+        // All integer types at MAX value should return None
+        assert_preimage_none(ScalarValue::Int64(Some(i64::MAX)));
+        assert_preimage_none(ScalarValue::Int32(Some(i32::MAX)));
+        assert_preimage_none(ScalarValue::Int16(Some(i16::MAX)));
+        assert_preimage_none(ScalarValue::Int8(Some(i8::MAX)));
+    }
+
+    #[test]
+    fn test_floor_preimage_float_edge_cases() {
+        // Float64 edge cases
+        assert_preimage_none(ScalarValue::Float64(Some(f64::INFINITY)));
+        assert_preimage_none(ScalarValue::Float64(Some(f64::NEG_INFINITY)));
+        assert_preimage_none(ScalarValue::Float64(Some(f64::NAN)));
+        assert_preimage_none(ScalarValue::Float64(Some(f64::MAX))); // precision loss
+
+        // Float32 edge cases
+        assert_preimage_none(ScalarValue::Float32(Some(f32::INFINITY)));
+        assert_preimage_none(ScalarValue::Float32(Some(f32::NEG_INFINITY)));
+        assert_preimage_none(ScalarValue::Float32(Some(f32::NAN)));
+        assert_preimage_none(ScalarValue::Float32(Some(f32::MAX))); // precision loss
+    }
+
+    #[test]
+    fn test_floor_preimage_null_values() {
+        assert_preimage_none(ScalarValue::Float64(None));
+        assert_preimage_none(ScalarValue::Float32(None));
+        assert_preimage_none(ScalarValue::Int64(None));
+    }
+
+    #[test]
+    fn test_floor_preimage_invalid_inputs() {
+        let floor_func = FloorFunc::new();
+        let info = SimplifyContext::default();
+
+        // Non-literal comparison value
+        let result = floor_func.preimage(&[col("x")], &col("y"), &info).unwrap();
+        assert!(
+            matches!(result, PreimageResult::None),
+            "Expected None for non-literal"
+        );
+
+        // Wrong argument count (too many)
+        let lit = Expr::Literal(ScalarValue::Float64(Some(100.0)), None);
+        let result = floor_func
+            .preimage(&[col("x"), col("y")], &lit, &info)
+            .unwrap();
+        assert!(
+            matches!(result, PreimageResult::None),
+            "Expected None for wrong arg count"
+        );
+
+        // Wrong argument count (zero)
+        let result = floor_func.preimage(&[], &lit, &info).unwrap();
+        assert!(
+            matches!(result, PreimageResult::None),
+            "Expected None for zero args"
+        );
+    }
+}