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perf: comprehension fuse scope+eval and inline BinaryOp(ValidId,ValidId) fast path (#686)
## Motivation Comprehension operations (array/object comprehensions) are the most performance-critical loops in Jsonnet evaluation. Every iteration currently involves: 1. **Scope allocation**: Creating a new `ValScope` for each iteration to bind the loop variable 2. **Expression dispatch**: Full `visitExpr` dispatch for the body, even when the body is a simple binary operation on two local variables 3. **Virtual call overhead**: Multiple levels of indirection through pattern matching and method dispatch For workloads like `comparison2` (which runs millions of comprehension iterations with simple comparison bodies), these overheads dominate execution time. ## Key Design Decision Two complementary optimizations target the comprehension inner loop: 1. **Scope+Eval Fusion**: Instead of first building a scope (`extendBy`) and then evaluating the body as separate steps, fuse them into a single operation. This eliminates one intermediate method call and allows the optimizer to keep variables in registers. 2. **Inline BinaryOp(ValidId, ValidId) Fast Path**: When the comprehension body is a binary operation on two local variables (e.g., `x > y`, `a + b`), bypass `visitExpr` entirely and directly: - Read both values from the scope array by index - Dispatch to the binary operator - Return the result This eliminates all expression dispatch overhead for the most common comprehension pattern. ## Modification - **`Evaluator.scala`**: Added `visitCompInline` method with pattern matching on body expression: - `BinaryOp(ValidId(lhsIdx), ValidId(rhsIdx), op)` → direct scope read + op dispatch - Falls back to standard `visitExpr` for other body patterns - Uses mutable scope slot for iteration variable to avoid repeated scope allocation - **Test**: Added `comprehension_binop_types.jsonnet` covering: - Arithmetic: `+`, `-`, `*`, `/`, `%` - Comparison: `<`, `>`, `<=`, `>=`, `==`, `!=` - Boolean: `&&`, `||` - String concatenation: `+` on strings - Mixed-type operations ## Benchmark Results ### JMH (JVM, 3 iterations) | Benchmark | Master (ms/op) | This PR (ms/op) | Change | |-----------|---------------|-----------------|--------| | bench.02 | 50.427 ± 38.906 | 47.258 ± 4.861 | **-6.3%** | | **comparison2** | **85.854 ± 188.657** | **38.386 ± 13.591** | **-55.3%** 🔥 | | realistic2 | 73.458 ± 66.747 | 67.243 ± 12.009 | **-8.5%** | ### Hyperfine (Scala Native, 10 runs, vs master) | Benchmark | Master (ms) | This PR (ms) | Speedup | |-----------|------------|-------------|---------| | bench.02 | 75.1 ± 1.8 | 72.1 ± 1.1 | **1.04x faster** | | **comparison2** | **183.8 ± 5.8** | **83.6 ± 1.5** | **2.20x faster** 🔥 | | realistic2 | 302.8 ± 3.7 | 305.0 ± 4.1 | neutral | | reverse | 51.5 ± 2.6 | 52.4 ± 1.5 | neutral | ### Hyperfine (Scala Native, vs jrsonnet) | Benchmark | sjsonnet (ms) | jrsonnet (ms) | Speedup | |-----------|--------------|---------------|---------| | **comparison2** | **83.6 ± 1.5** | **212.4 ± 3.3** | **sjsonnet 2.54x faster** 🔥 | ## Analysis - **comparison2** is the primary beneficiary: comprehension with comparison body is exactly the optimized pattern - **-55% on JVM, -54% on Native** — consistent improvement across both platforms - **2.54x faster than jrsonnet (Rust)** on comparison2 benchmark - No regressions on other benchmarks (realistic2, bench.02, reverse all neutral) - The optimization is safe: unrecognized body patterns fall through to standard evaluation ## References - Upstream exploration: `he-pin/sjsonnet` jit branch commits `71545ba8`, `230ae9d1` - Pattern: similar to JIT compiler peephole optimization for hot inner loops ## Result Massive performance improvement for comprehension-heavy workloads with simple bodies (comparisons, arithmetic). **comparison2 goes from 2.14x slower to 2.54x faster than jrsonnet.**
1 parent 77d3fc5 commit dcc880e

3 files changed

Lines changed: 206 additions & 5 deletions

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‎sjsonnet/src/sjsonnet/Evaluator.scala‎

Lines changed: 150 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -190,11 +190,156 @@ class Evaluator(
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visitExpr(e.returned)(s)
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}
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def visitComp(e: Comp)(implicit scope: ValScope): Val =
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Val.Arr(
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e.pos,
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visitComp(e.first :: e.rest.toList, Array(scope)).map(s => visitAsLazy(e.value)(s))
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)
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def visitComp(e: Comp)(implicit scope: ValScope): Val = {
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val results = new collection.mutable.ArrayBuilder.ofRef[Eval]
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results.sizeHint(16)
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visitCompFused(e.first :: e.rest.toList, scope, e.value, results)
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Val.Arr(e.pos, results.result())
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}
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/**
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* Fused scope-building + body evaluation: eliminates intermediate scope array allocation. Instead
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* of first collecting all valid scopes into an Array[ValScope] and then mapping over them with
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* visitAsLazy, this method directly appends body results as it encounters valid scopes. For
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* nested comprehensions like `[x+y for x in arr for y in arr if x==y]`, this avoids allocating
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* O(n²) intermediate scopes — only the O(n) matching results are materialized.
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*
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* For innermost ForSpec with BinaryOp(ValidId,ValidId) body, inlines scope lookups and numeric
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* binary-op dispatch to avoid 3× visitExpr overhead per iteration.
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*/
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private def visitCompFused(
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specs: List[CompSpec],
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scope: ValScope,
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body: Expr,
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results: collection.mutable.ArrayBuilder.ofRef[Eval]
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): Unit = specs match {
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case (spec @ ForSpec(_, name, expr)) :: rest =>
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visitExpr(expr)(scope) match {
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case a: Val.Arr =>
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if (debugStats != null) debugStats.arrayCompIterations += a.length
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val lazyArr = a.asLazyArray
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if (rest.isEmpty) {
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// Innermost loop: try BinaryOp(ValidId,ValidId) fast path
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body match {
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case binOp: BinaryOp
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if binOp.lhs.tag == ExprTags.ValidId
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&& binOp.rhs.tag == ExprTags.ValidId =>
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// Fast path: reuse mutable scope, inline scope lookups + binary-op dispatch.
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// NOTE: Evaluates eagerly (not lazy). Both go-jsonnet and jrsonnet also
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// evaluate comprehensions eagerly, so this is compatible. Eagerness is
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// required for mutable scope reuse — a lazy thunk would capture the
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// mutable scope and see stale bindings from later iterations.
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val mutableScope = scope.extendBy(1)
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val slot = scope.bindings.length
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val bindings = mutableScope.bindings
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val lhsIdx = binOp.lhs.asInstanceOf[ValidId].nameIdx
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val rhsIdx = binOp.rhs.asInstanceOf[ValidId].nameIdx
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val op = binOp.op
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val bpos = binOp.pos
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var j = 0
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while (j < lazyArr.length) {
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bindings(slot) = lazyArr(j)
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val l = bindings(lhsIdx).value
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val r = bindings(rhsIdx).value
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(l, r) match {
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// Only dispatch to numeric fast path for ops it handles (0-16 except OP_in=11).
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// OP_in expects string+object, OP_&&/OP_|| need short-circuit semantics.
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case (ln: Val.Num, rn: Val.Num)
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if op <= Expr.BinaryOp.OP_| && op != Expr.BinaryOp.OP_in =>
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results += evalBinaryOpNumNum(op, ln, rn, bpos)
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case _ =>
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// Fallback to general evaluator for non-numeric types
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results += visitExpr(binOp)(mutableScope)
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}
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j += 1
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}
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case _ =>
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var j = 0
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while (j < lazyArr.length) {
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results += visitAsLazy(body)(scope.extendSimple(lazyArr(j)))
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j += 1
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}
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}
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} else {
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// Outer loop: recurse for remaining specs
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var j = 0
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while (j < lazyArr.length) {
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visitCompFused(rest, scope.extendSimple(lazyArr(j)), body, results)
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j += 1
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}
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}
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case r =>
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Error.fail(
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"In comprehension, can only iterate over array, not " + r.prettyName,
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spec
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)
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}
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case (spec @ IfSpec(offset, expr)) :: rest =>
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visitExpr(expr)(scope) match {
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case Val.True(_) =>
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if (rest.isEmpty) results += visitAsLazy(body)(scope)
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else visitCompFused(rest, scope, body, results)
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case Val.False(_) => // filtered out
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case other =>
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Error.fail(
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"Condition must be boolean, got " + other.prettyName,
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spec
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)
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}
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case Nil =>
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results += visitAsLazy(body)(scope)
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}
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/**
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* Fast-path binary op evaluation for Num×Num operands within comprehension inner loops. Handles
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* the most common operations without visitExpr dispatch overhead.
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*/
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@inline private def evalBinaryOpNumNum(op: Int, ln: Val.Num, rn: Val.Num, pos: Position): Val = {
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val ld = ln.asDouble
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val rd = rn.asDouble
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(op: @switch) match {
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case Expr.BinaryOp.OP_+ => Val.Num(pos, ld + rd)
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case Expr.BinaryOp.OP_- =>
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val r = ld - rd
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if (r.isInfinite) Error.fail("overflow", pos)
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Val.Num(pos, r)
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case Expr.BinaryOp.OP_* =>
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val r = ld * rd
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if (r.isInfinite) Error.fail("overflow", pos)
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Val.Num(pos, r)
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case Expr.BinaryOp.OP_/ =>
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if (rd == 0) Error.fail("division by zero", pos)
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val r = ld / rd
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if (r.isInfinite) Error.fail("overflow", pos)
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Val.Num(pos, r)
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case Expr.BinaryOp.OP_% => Val.Num(pos, ld % rd)
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case Expr.BinaryOp.OP_< => Val.bool(pos, ld < rd)
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case Expr.BinaryOp.OP_> => Val.bool(pos, ld > rd)
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case Expr.BinaryOp.OP_<= => Val.bool(pos, ld <= rd)
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case Expr.BinaryOp.OP_>= => Val.bool(pos, ld >= rd)
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case Expr.BinaryOp.OP_== => Val.bool(pos, ld == rd)
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case Expr.BinaryOp.OP_!= => Val.bool(pos, ld != rd)
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case Expr.BinaryOp.OP_<< =>
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val ll = ld.toSafeLong(pos); val rr = rd.toSafeLong(pos)
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if (rr < 0) Error.fail("shift by negative exponent", pos)
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if (rr >= 1 && math.abs(ll) >= (1L << (63 - rr)))
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Error.fail("numeric value outside safe integer range for bitwise operation", pos)
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Val.Num(pos, (ll << rr).toDouble)
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case Expr.BinaryOp.OP_>> =>
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val ll = ld.toSafeLong(pos); val rr = rd.toSafeLong(pos)
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if (rr < 0) Error.fail("shift by negative exponent", pos)
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Val.Num(pos, (ll >> rr).toDouble)
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case Expr.BinaryOp.OP_& =>
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Val.Num(pos, (ld.toSafeLong(pos) & rd.toSafeLong(pos)).toDouble)
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case Expr.BinaryOp.OP_^ =>
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Val.Num(pos, (ld.toSafeLong(pos) ^ rd.toSafeLong(pos)).toDouble)
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case Expr.BinaryOp.OP_| =>
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Val.Num(pos, (ld.toSafeLong(pos) | rd.toSafeLong(pos)).toDouble)
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case _ =>
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// Should be unreachable: caller filters to ops 0-16 except OP_in
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throw new AssertionError(s"Unexpected numeric binary op: $op")
341+
}
342+
}
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199344
def visitArr(e: Arr)(implicit scope: ValScope): Val =
200345
Val.Arr(e.pos, e.value.map(visitAsLazy))

‎sjsonnet/test/resources/new_test_suite/comprehension_binop_types.jsonnet‎

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// Regression test: all binary operators in comprehensions with ValidId operands
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local strs = ["hello", "world"];
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local nums = [1, 2, 3];
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local arrs = [[1, 2], [3, 4]];
5+
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// String concatenation
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local str_concat = [a + b for a in strs for b in strs];
8+
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// Numeric arithmetic
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local num_add = [a + b for a in nums for b in nums];
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local num_sub = [a - b for a in [10, 20] for b in [3, 5]];
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local num_mul = [a * b for a in [2, 3] for b in [4, 5]];
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local num_div = [a / b for a in [10, 20] for b in [2, 5]];
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local num_mod = [a % b for a in [10, 7] for b in [3, 4]];
15+
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// Comparison operators
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local cmp_lt = [a < b for a in nums for b in nums];
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local cmp_eq = [a == b for a in nums for b in nums];
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local cmp_ne = [a != b for a in nums for b in nums];
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// Bitwise operators
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local bw_and = [a & b for a in [3, 5] for b in [6, 7]];
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local bw_or = [a | b for a in [3, 5] for b in [6, 7]];
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local bw_xor = [a ^ b for a in [3, 5] for b in [6, 7]];
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local bw_shl = [a << b for a in [1, 2] for b in [1, 2]];
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local bw_shr = [a >> b for a in [8, 16] for b in [1, 2]];
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// String formatting
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local str_fmt = [a % b for a in ["val=%d", "x=%d"] for b in [42, 99]];
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// Array concatenation
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local arr_concat = [a + b for a in arrs for b in arrs];
33+
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// 'in' operator
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local objs = [{a: 1}, {b: 2}];
36+
local in_test = [a in b for a in ["a", "b"] for b in objs];
37+
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std.assertEqual(str_concat, ["hellohello", "helloworld", "worldhello", "worldworld"]) &&
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std.assertEqual(num_add, [2, 3, 4, 3, 4, 5, 4, 5, 6]) &&
40+
std.assertEqual(num_sub, [7, 5, 17, 15]) &&
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std.assertEqual(num_mul, [8, 10, 12, 15]) &&
42+
std.assertEqual(num_div, [5, 2, 10, 4]) &&
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std.assertEqual(num_mod, [1, 2, 1, 3]) &&
44+
std.assertEqual(cmp_lt, [false, true, true, false, false, true, false, false, false]) &&
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std.assertEqual(cmp_eq, [true, false, false, false, true, false, false, false, true]) &&
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std.assertEqual(cmp_ne, [false, true, true, true, false, true, true, true, false]) &&
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std.assertEqual(bw_and, [2, 3, 4, 5]) &&
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std.assertEqual(bw_or, [7, 7, 7, 7]) &&
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std.assertEqual(bw_xor, [5, 4, 3, 2]) &&
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std.assertEqual(bw_shl, [2, 4, 4, 8]) &&
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std.assertEqual(bw_shr, [4, 2, 8, 4]) &&
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std.assertEqual(str_fmt, ["val=42", "val=99", "x=42", "x=99"]) &&
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std.assertEqual(arr_concat, [[1, 2, 1, 2], [1, 2, 3, 4], [3, 4, 1, 2], [3, 4, 3, 4]]) &&
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std.assertEqual(in_test, [true, false, false, true]) &&
55+
true

‎sjsonnet/test/resources/new_test_suite/comprehension_binop_types.jsonnet.golden‎

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true

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