v0.12.0 regression: evaluation time exponential in derived features referenced from untaken if branches

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@devin-ai-integration がすでに取り組んでいます。

2026年11月4日 から。

  • #1933 @devin-ai-integration による — オープン

評価

難易度
4/5
見積もり時間
3〜5日
初心者へのやさしさ
25/100
issue の種類
バグ
明瞭さ
明確に書かれている
活発さ
停滞
技術スタック
go
領域
performance

調査の方向性

Start by reviewing the v0.12.0 changelog entries about order-dependence marks and cycle detection, then trace evaluation of if operands declared as in expr in ControlFunctions. Reproduce with the supplied gen.py model and compare the expression-valued and plain-default feature timings. Done means untaken branches avoid exponential evaluation while preserving the reported results; linked pull request #1933 is already open.

索引モデルが issue の本文から書いたものです。

説明

bug

Summary

In v0.12.0, evaluating a feature valued by an expression takes time exponential in the number of other expression-valued features referenced from untaken if branches. v0.11.0 evaluates the same model in constant time. The results are the same in both versions; only the time differs. No diagnostic is emitted, so a larger model just appears to hang.

Reproduction

gen.py writes N features a1..aN. Each ai picks another feature by an integer selector pi (default 0, so every branch is untaken):

import sys
n, target = int(sys.argv[1]), sys.argv[2]   # target: "a" (expression-valued features) or "c" (plain defaults)
print(f"package R {{ private import ScalarValues::*; part def T {{")
for i in range(1, n + 1):
    e = "false"
    for j in range(n, 0, -1):
        e = f"(if p{i} == {j} ? {target}{j} else {e})"
    print(f"  attribute p{i} : Integer default 0; attribute c{i} : Boolean default true;")
    print(f"  attribute a{i} : Boolean = {e};")
print("} part t : T; }")

python3 gen.py 9 a > r.sysml
sysml r.sysml -e '$::R::t.a1'

Timings (linux-amd64 release binaries, same machine)

N branches reference a_j — v0.11.0 branches reference a_j — v0.12.0 branches reference c_j — v0.12.0
7 ~0.05 s 0.17 s 0.05 s
8 0.05 s 0.31 s 0.05 s
9 0.06 s 2.71 s 0.05 s
10 0.07 s 29.94 s 0.05 s

All runs print = false. Loading and validating r.sysml alone takes about 0.02 s, so the time is spent in evaluation.

Control experiments (N = 9, v0.12.0)

  • Only if, all branches untaken (the generator above): 2.8 s. This rules out or/and as the cause.
  • The same chain prefixed with p1 == 0 or …, or with p1 != 0 and …: about 3 s each.
  • The same shape, but the branches reference plain default features c_j, so there are no references between expression-valued features: 0.05 s.
  • A direct self-reference only (a = true or a): 0.06 s.

So the slowdown needs untaken branches that reference other expression-valued features which, syntactically, form cycles. The cycles are never taken at run time.

Expected

ControlFunctions declares the branch operands of if, and, or and implies as in expr. Its doc describes these operands as "expressions whose evaluation is determined by another operand". An untaken branch should therefore not need to be evaluated. In any case, the cost should not grow exponentially with the size of the model, as it did not in v0.11.0.

Notes

The 0.12.0 changelog has two entries that may be related, though we have not confirmed either:

  • expression-valued features now carry order-dependence marks "through features so valued in turn";
  • "a cycle among such features is refused by the interpreter at the start".

We found this in a model with about 9 mutually referencing derived features. One evaluation went from 0.45 s in v0.11.0 to more than 90 s in v0.12.0, after which we stopped it. We have since rewritten that model with ref features, which v0.12.0 evaluates fast, so this is not blocking us. We are reporting it as a regression.

主要言語
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12時間 38分
マージ済み PR（30日）
903

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