leanprover / leanprover/lean4

Slow elaboration of `List Nat` literals

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bug P-medium
Dominant language
Lean
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1d 17h
Merged PRs (30d)
175

Description

Description

Long lists of natural number literals can take a long time to elaborate.

Context

Reported by @dwrensha on the Lean Zulip.

Steps to Reproduce

Given the following:

set_option trace.profiler true in
def dualEquationIds : List Nat :=
  [  1,   2,   3,   5,   4,   6,   7,  23,  28,  25,  31,  34,  24,  29,  30,  26,  32,  36,  27,  35,
    33,  37,   8,  13,  10,  16,  19,   9,  14,  15,  11,  17,  21,  12,  20,  18,  22,  39,  38,  40,
    41,  45,  43,  44,  42,  46, 255, 270, 260, 280, 290, 257, 273, 276, 263, 283, 298, 266, 294, 286,
   302, 256, 271, 272, 261, 281, 292, 262, 291, 282, 293, 258, 274, 278, 264, 284, 300, 268, 295, 288,
   305, 259, 277, 275, 279, 267, 287, 296, 304, 265, 299, 285, 301, 269, 303, 297, 289, 306, 203, 218,
   208, 228, 238, 205, 221, 224, 211, 231, 246, 214, 242, 234, 250, 204, 219, 220, 209, 229, 240, 210,
   239, 230, 241, 206, 222, 226, 212, 232, 248, 216, 243, 236, 253, 207, 225, 223, 227, 215, 235, 244,
   252, 213, 247, 233, 249, 217, 251, 245, 237, 254, 151, 166, 156, 176, 186, 153, 169, 172, 159, 179,
   194, 162, 190, 182, 198, 152, 167, 168, 157, 177, 188, 158, 187, 178, 189, 154, 170, 174, 160, 180,
   196, 164, 191, 184, 201, 155, 173, 171, 175, 163, 183, 192, 200, 161, 195, 181, 197, 165, 199, 193,
   185, 202,  99, 114, 104, 124, 134, 101, 117, 120, 107, 127, 142, 110, 138, 130, 146, 100, 115, 116,
   105, 125, 136, 106, 135, 126, 137, 102, 118, 122, 108, 128, 144, 112, 139, 132, 149, 103, 121, 119,
   123, 111, 131, 140, 148, 109, 143, 129, 145, 113, 147, 141, 133, 150,  47,  62,  52,  72,  82,  49,
    65,  68,  55,  75,  90,  58,  86,  78,  94,  48,  63,  64,  53,  73,  84,  54,  83,  74,  85,  50,
    66,  70,  56,  76,  92,  60,  87,  80,  97,  51,  69,  67,  71,  59,  79,  88,  96,  57,  91,  77,
    93,  61,  95,  89,  81,  98, 359, 364, 361, 367, 370, 360, 365, 366, 362, 368, 372, 363, 371, 369,
   373, 388, 378, 399, 385, 375, 395, 391, 381, 403, 407, 387, 377, 398, 384, 374, 394, 390, 380, 402,
   406, 389, 379, 400, 401, 386, 376, 396, 397, 392, 382, 404, 409, 393, 383, 408, 405, 410, 307, 312,
   309, 315, 318, 308, 313, 314, 310, 316, 320, 311, 319, 317, 321, 336, 326, 347, 333, 323, 343, 339,
   329, 351, 355, 335, 325, 346, 332, 322, 342, 338, 328, 350, 354, 337, 327, 348, 349, 334, 324, 344,
   345, 340, 330, 352, 357, 341, 331, 356, 353, 358,3050,3102,3065,3139,3176,3055,3112,3122,3075,3149,
  3210,3085,3193,3159,3227,3052,3105,3108,3068,3142,3184,3071,3180,3145,3188,3058,3115,3130,3078,3152,
  3218,3093,3197,3167,3242,3061,3126,3118,3134,3089,3163,3201,3237,3081,3214,3155,3222,3097,3232,3205,
  3171,3247,3051,3103,3104,3066,3140,3178,3067,3177,3141,3179,3056,3113,3124,3076,3150,3212,3087,3194,
  3161,3230,3057,3123,3114,3125,3086,3160,3195,3229,3077,3211,3151,3213,3088,3228,3196,3162,3231,3053,
  3106,3110,3069,3143,3186,3073,3181,3147,3191,3059,3116,3132,3079,3153,3220,3095,3198,3169,3245,3063,
  3127,3120,3137,3090,3164,3203,3239,3083,3215,3157,3225,3100,3233,3208,3174,3251,3054,3109,3107,3111,
  3072,3146,3182,3190,3070,3185,3144,3187,3074,3189,3183,3148,3192,3062,3119,3128,3136,3082,3156,3216,
  3224,3091,3202,3165,3240,3099,3206,3235,3173,3250,3060,3131,3117,3133,3094,3168,3199,3244,3080,3219,
  3154,3221,3096,3243,3200,3170,3246,3064,3135,3129,3121,3138,3098,3172,3234,3207,3249,3092,3238,3166,
  3204,3241,3084,3223,3217,3158,3226,3101,3248,3236,3209,3175,3252,2847,2899,2862,2936,2973,2852,2909,
  2919,2872,2946,3007,2882,2990,2956,3024,2849,2902,2905,2865,2939,2981,2868,2977,2942,2985,2855,2912,
  2927,2875,2949,3015,2890,2994,2964,3039,2858,2923,2915,2931,2886,2960,2998,3034,2878,3011,2952,3019,
  2894,3029,3002,2968,3044,2848,2900,2901,2863,2937,2975,2864,2974,2938,2976,2853,2910,2921,2873,2947,
  3009,2884,2991,2958,3027,2854,2920,2911,2922,2883,2957,2992,3026,2874,3008,2948,3010,2885,3025,2993,
  2959,3028,2850,2903,2907,2866,2940,2983,2870,2978,2944,2988,2856,2913,2929,2876,2950,3017,2892,2995,
  2966,3042,2860,2924,2917,2934,2887,2961,3000,3036,2880,3012,2954,3022,2897,3030,3005,2971,3048,2851,
  2906,2904,2908,2869,2943,2979,2987,2867,2982,2941,2984,2871,2986,2980,2945,2989,2859,2916,2925,2933,
  2879,2953,3013,3021,2888,2999,2962,3037,2896,3003,3032,2970,3047,2857,2928,2914,2930,2891,2965,2996,
  3041,2877,3016,2951,3018,2893,3040,2997,2967,3043,2861,2932,2926,2918,2935,2895,2969,3031,3004,3046,
  2889,3035,2963,3001,3038,2881,3020,3014,2955,3023,2898,3045,3033,3006,2972,3049,2644,2696,2659,2733,
  2770,2649,2706,2716,2669,2743,2804,2679,2787,2753,2821,2646,2699,2702,2662,2736,2778,2665,2774,2739,
  2782,2652,2709,2724,2672,2746,2812,2687,2791,2761,2836,2655,2720,2712,2728,2683,2757,2795,2831,2675,
  2808,2749,2816,2691,2826,2799,2765,2841,2645,2697,2698,2660,2734,2772,2661,2771,2735,2773,2650,2707,
  2718,2670,2744,2806,2681,2788,2755,2824,2651,2717,2708,2719,2680,2754,2789,2823,2671,2805,2745,2807,
  2682,2822,2790,2756,2825,2647,2700,2704,2663,2737,2780,2667,2775,2741,2785,2653,2710,2726,2673,2747,
  2814,2689,2792,2763,2839,2657,2721,2714,2731,2684,2758,2797,2833,2677,2809,2751,2819,2694,2827,2802,
  2768,2845,2648,2703,2701,2705,2666,2740,2776,2784,2664,2779,2738,2781,2668,2783,2777,2742,2786,2656]

Expected behavior: Elaborates quickly

Actual behavior: Takes 1.4s to elaborate

Versions

4.13.0-rc3 macOS m2

Additional Information

Doubling the length of the list takes 4.6s, and quadrupling it takes 19.4s, suggesting there is some superlinear algorithm in elaboration (the amount of time in seconds taken to elaborate a list of length n is roughly modeled by (0.0012 * n) ^ 2).

Related issue: #5502

Impact

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Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the List Nat literal example from the issue with set_option trace.profiler true on Lean 4.13.0-rc3, then compare the reported timings for the original, doubled, and quadrupled lists. Use related issue #5502 as context; done means long List Nat literals elaborate quickly without the reported superlinear scaling.

Written by the indexing model from the issue text.

Assessment

Domain
compilers, performance
Issue type
Bug
Difficulty
5/5
Estimated time
Over a week
Activity status
Active
Clarity
Mostly clear
Newbie friendliness
45/100

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