vLLM/tests/v1/sample/test_diffusion_gemma_reads.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
"""Per-request DiffusionGemma state behind structured reads: seed canvases,
pinned positions, read-only slots and the per-slot step cap."""

import numpy as np
import pytest
import torch

from vllm.model_executor.models.diffusion_gemma import (
    DiffusionGemmaRequestStates,
    _compiled_sample_step,
    _concat_logprob_stashes,
)
from vllm.platforms import current_platform
from vllm.v1.outputs import LogprobsTensors

pytestmark = pytest.mark.skipif(
    not current_platform.is_cuda(), reason="the sampler state lives on the GPU"
)

CL = 8
VOCAB = 64
MAX_REQS = 4
MAX_STEPS = 48


def _states() -> DiffusionGemmaRequestStates:
    return DiffusionGemmaRequestStates(
        max_num_reqs=MAX_REQS,
        canvas_length=CL,
        vocab_size=VOCAB,
        max_denoising_steps=MAX_STEPS,
        device=torch.device("cuda"),
        hidden_size=4,
        stability_threshold=2,
    )


def _slots(*idx: int) -> tuple[np.ndarray, torch.Tensor]:
    slots = np.array(idx, dtype=np.int64)
    return slots, torch.tensor(slots, device="cuda")


def test_seed_canvas_replaces_only_seeded_slots():
    states = _states()
    for slot in range(3):
        states.add_request(slot)
    seed = list(range(CL))
    states.set_seed_canvas(1, seed)
    slots, slots_gpu = _slots(0, 1, 2)
    states.init_canvas(slots_gpu)
    before = states.canvas[slots_gpu].clone()

    states.apply_seed_canvases(slots, slots_gpu)

    after = states.canvas[slots_gpu]
    assert after[1].tolist() == seed
    assert torch.equal(after[0], before[0])
    assert torch.equal(after[2], before[2])


def test_apply_seed_canvases_leaves_unseeded_batches_alone():
    states = _states()
    states.add_request(0)
    slots, slots_gpu = _slots(0)
    states.init_canvas(slots_gpu)
    before = states.canvas[0].clone()

    states.apply_seed_canvases(slots, slots_gpu)

    assert torch.equal(states.canvas[0], before)


def test_add_request_clears_seed_and_read_only():
    states = _states()
    states.add_request(0)
    states.set_seed_canvas(0, [1] * CL)
    states.set_read_only(0)
    assert states.seeded_slots == {0}
    assert states.read_only_slots == {0}

    states.add_request(0)

    assert not states.seeded_slots
    assert not states.read_only_slots
    assert not bool(states.has_seed[0])
    assert not bool(states.read_only[0])


def test_canvas_width_resets_with_the_slot():
    states = _states()
    states.add_request(0)
    states.canvas_width_np[0] = 4
    states.set_seed_canvas(0, [7, 7, 7, 7])
    assert states.seed_canvas[0, :4].tolist() == [7, 7, 7, 7]

    states.add_request(0)

    assert states.canvas_width_np[0] == CL


def test_remove_request_forgets_the_slot():
    states = _states()
    states.add_request(0)
    states.set_seed_canvas(0, [1] * CL)
    states.set_read_only(0)

    states.remove_request(0)

    assert not states.seeded_slots
    assert not states.read_only_slots


def _denoise_once(
    states: DiffusionGemmaRequestStates,
    slots: list[int],
    compute_sc: bool = True,
    width: int = CL,
    embed_weight: torch.Tensor | None = None,
    embed_dtype: torch.dtype = torch.float32,
) -> tuple[torch.Tensor, torch.Tensor]:
    """One compiled denoise step over ``slots`` with flat logits, so nothing
    converges by stability or confidence and only the step cap can end it.
    ``width`` below CL runs the step on [:, :width] views, as the sampler
    does for a narrow tile."""
    n = len(slots)
    device = states.device
    decode_slots = torch.tensor(slots, dtype=torch.int64, device=device)
    decode_idx = torch.arange(n, dtype=torch.int64, device=device)
    sampled = torch.zeros(n, CL, dtype=torch.int32, device=device)[:, :width]
    num_sampled = torch.zeros(n, dtype=torch.int32, device=device)
    _compiled_sample_step(
        torch.zeros(n * width, VOCAB, device=device),
        decode_slots,
        decode_idx,
        decode_slots,
        torch.full((n,), width, dtype=torch.int64, device=device),
        states.canvas[:, :width],
        states.argmax_canvas[:, :width],
        states.step,
        states.is_encoder_phase,
        states.confident,
        states.self_conditioning_embeds[:, :width],
        (
            torch.zeros(VOCAB, 4, dtype=embed_dtype, device=device)
            if embed_weight is None
            else embed_weight
        ),
        torch.tensor(1.0, dtype=embed_dtype, device=device),
        states.accepted_canvas_history[:, :, :width],
        states.accepted_canvas_history_len,
        states.max_steps,
        states.pin_mask[:, :width],
        states.seed_canvas[:, :width],
        states.read_only,
        sampled,
        num_sampled,
        torch.zeros(MAX_REQS, CL, dtype=torch.int64, device=device),
        max_denoising_steps=float(MAX_STEPS),
        t_min=0.5,
        t_max=1.0,
        confidence_threshold=0.1,
        vocab_size=VOCAB,
        CL=width,
        ST=states.stability_threshold,
        entropy_bound=0.1,
        sc_vocab_start=0,
        sc_vocab_end=VOCAB,
        tp_size=1,
        tp_group_name="",
        compute_sc=compute_sc,
    )
    return sampled, num_sampled


def test_pinned_positions_hold_their_seed_through_a_step():
    states = _states()
    states.add_request(0)
    states.is_encoder_phase[0] = False
    seed = list(range(10, 10 + CL))
    states.set_seed_canvas(0, seed)
    states.canvas[0] = torch.tensor(seed, device="cuda")
    states.set_pins(0, [0, 1, 2, 3])

    # Flat logits accept nothing, so every free position is renoised.
    _denoise_once(states, [0], embed_weight=torch.ones(VOCAB, 4, device="cuda"))

    assert states.canvas[0, :4].tolist() == seed[:4]
    # The soft embed is zero at pinned positions and non-zero elsewhere.
    sc = states.self_conditioning_embeds[0]
    assert not sc[:4].any()
    assert sc[4:].any()


def test_add_request_clears_pins():
    states = _states()
    states.add_request(0)
    states.set_seed_canvas(0, [1] * CL)
    states.set_pins(0, [2, 3])
    assert states.pin_mask[0].tolist() == [False, False, True, True] + [False] * 4

    states.add_request(0)

    assert not states.pin_mask[0].any()


def test_single_step_tile_skips_self_conditioning():
    states = _states()
    states.add_request(0)
    states.is_encoder_phase[0] = False
    states.self_conditioning_embeds[0] = 1.0

    _denoise_once(states, [0], compute_sc=False)

    assert not states.self_conditioning_embeds[0].any()


@pytest.mark.parametrize("stance", ["default", "force_eager"])
def test_self_conditioning_stores_a_bf16_model_in_the_fp32_buffer(stance):
    # The model's embeddings are bf16 while the buffer is fp32. Compiled code
    # casts on the store, but eager does not, and the step runs eager once
    # torch.compile hits its recompile limit.
    states = _states()
    states.add_request(0)
    states.is_encoder_phase[0] = False

    with torch.compiler.set_stance(stance):
        _denoise_once(
            states,
            [0],
            embed_weight=torch.ones(VOCAB, 4, dtype=torch.bfloat16, device="cuda"),
            embed_dtype=torch.bfloat16,
        )

    assert states.self_conditioning_embeds.dtype == torch.float32
    # uniform probs @ an all-ones embedding
    assert torch.allclose(
        states.self_conditioning_embeds[0], torch.ones(CL, 4, device="cuda")
    )


def test_narrow_tile_leaves_the_rest_of_the_canvas_alone():
    states = _states()
    states.add_request(0)
    states.is_encoder_phase[0] = False
    states.canvas[0] = 5
    states.argmax_canvas[0] = 5

    _denoise_once(states, [0], width=4)

    # Columns past the width are untouched; the step counted.
    assert states.canvas[0, 4:].tolist() == [5] * (CL - 4)
    assert states.argmax_canvas[0, 4:].tolist() == [5] * (CL - 4)
    assert states.step[0] == 1


def test_step_cap_is_per_slot():
    states = _states()
    for slot in (0, 1):
        states.add_request(slot)
        states.is_encoder_phase[slot] = False
    states.max_steps[0] = 1

    _denoise_once(states, [0, 1])

    # Slot 0 hit its cap and moves to commit. Slot 1 keeps denoising.
    assert states.is_encoder_phase[:2].tolist() == [True, False]
    assert states.step[:2].tolist() == [1, 1]


def _stash(rows: int, width: int, first_id: int) -> LogprobsTensors:
    ids = torch.arange(first_id, first_id + rows * width).reshape(rows, width)
    return LogprobsTensors(
        logprob_token_ids=ids,
        logprobs=-ids.float(),
        selected_token_ranks=torch.zeros(rows, dtype=torch.int64),
    )


def test_stashes_of_different_widths_join():
    # A read that asked for 10 label ids and a generation that asked for 2
    # logprobs converged in different steps, so their stashes differ in width.
    wide, narrow = _stash(2, 11, 100), _stash(3, 3, 0)

    out = _concat_logprob_stashes([narrow, wide], [0, 3])

    assert out.logprob_token_ids.shape == (5, 11)
    assert out.logprobs.shape == (5, 11)
    assert out.cu_num_generated_tokens == [0, 3]
    # The narrow rows keep their values and pad with id 0 at -inf.
    assert torch.equal(out.logprob_token_ids[:3, :3], narrow.logprob_token_ids)
    assert not out.logprob_token_ids[:3, 3:].any()
    assert torch.isneginf(out.logprobs[:3, 3:]).all()
    assert torch.equal(out.logprobs[3:], wide.logprobs)


@pytest.mark.parametrize("width", [4, CL])
@pytest.mark.parametrize("steps", [1, 2])
def test_read_emits_at_convergence_while_generation_waits_for_commit(width, steps):
    states = _states()
    for slot in (2, 0):
        states.add_request(slot)
        states.is_encoder_phase[slot] = False
        states.max_steps[slot] = steps
    states.set_read_only(2)

    for step in range(steps):
        sampled, counts = _denoise_once(states, [2, 0], width=width)
        assert counts.tolist() == ([width, 0] if step == steps - 1 else [0, 0])

    assert torch.equal(sampled[0], states.argmax_canvas[2, :width].int())
    assert not states.is_encoder_phase[2]
    assert states.is_encoder_phase[0]
    assert not states.self_conditioning_embeds[2].any()

    sampled, counts = _denoise_once(states, [0], width=width)
    assert counts.tolist() == [width]
    assert torch.equal(sampled[0], states.argmax_canvas[0, :width].int())