[bug] Precedence of operations in VAE should be slicing -> tiling (#9342)

* bugfix: precedence of operations should be slicing -> tiling

* fix typo

* fix another typo

* deprecate current implementation of tiled_encode and use new impl

* Update src/diffusers/models/autoencoders/autoencoder_kl.py
Co-authored-by: YiYi Xu <yixu310@gmail.com>

* Update src/diffusers/models/autoencoders/autoencoder_kl.py

---------
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
Co-authored-by: YiYi Xu <yixu310@gmail.com>

src/diffusers/models/autoencoders/autoencoder_kl.py

@@ -18,6 +18,7 @@ import torch.nn as nn
 
 from ...configuration_utils import ConfigMixin, register_to_config
 from ...loaders.single_file_model import FromOriginalModelMixin
+from ...utils import deprecate
 from ...utils.accelerate_utils import apply_forward_hook
 from ..attention_processor import (
     ADDED_KV_ATTENTION_PROCESSORS,
@@ -245,6 +246,18 @@ class AutoencoderKL(ModelMixin, ConfigMixin, FromOriginalModelMixin):
 
         self.set_attn_processor(processor)
 
+    def _encode(self, x: torch.Tensor) -> torch.Tensor:
+        batch_size, num_channels, height, width = x.shape
+
+        if self.use_tiling and (width > self.tile_sample_min_size or height > self.tile_sample_min_size):
+            return self._tiled_encode(x)
+
+        enc = self.encoder(x)
+        if self.quant_conv is not None:
+            enc = self.quant_conv(enc)
+
+        return enc
+
     @apply_forward_hook
     def encode(
         self, x: torch.Tensor, return_dict: bool = True
@@ -261,21 +274,13 @@ class AutoencoderKL(ModelMixin, ConfigMixin, FromOriginalModelMixin):
                 The latent representations of the encoded images. If `return_dict` is True, a
                 [`~models.autoencoder_kl.AutoencoderKLOutput`] is returned, otherwise a plain `tuple` is returned.
         """
-        if self.use_tiling and (x.shape[-1] > self.tile_sample_min_size or x.shape[-2] > self.tile_sample_min_size):
-            return self.tiled_encode(x, return_dict=return_dict)
-
         if self.use_slicing and x.shape[0] > 1:
-            encoded_slices = [self.encoder(x_slice) for x_slice in x.split(1)]
+            encoded_slices = [self._encode(x_slice) for x_slice in x.split(1)]
             h = torch.cat(encoded_slices)
         else:
-            h = self.encoder(x)
-
-        if self.quant_conv is not None:
-            moments = self.quant_conv(h)
-        else:
-            moments = h
+            h = self._encode(x)
 
-        posterior = DiagonalGaussianDistribution(moments)
+        posterior = DiagonalGaussianDistribution(h)
 
         if not return_dict:
             return (posterior,)
@@ -337,6 +342,54 @@ class AutoencoderKL(ModelMixin, ConfigMixin, FromOriginalModelMixin):
             b[:, :, :, x] = a[:, :, :, -blend_extent + x] * (1 - x / blend_extent) + b[:, :, :, x] * (x / blend_extent)
         return b
 
+    def _tiled_encode(self, x: torch.Tensor) -> torch.Tensor:
+        r"""Encode a batch of images using a tiled encoder.
+
+        When this option is enabled, the VAE will split the input tensor into tiles to compute encoding in several
+        steps. This is useful to keep memory use constant regardless of image size. The end result of tiled encoding is
+        different from non-tiled encoding because each tile uses a different encoder. To avoid tiling artifacts, the
+        tiles overlap and are blended together to form a smooth output. You may still see tile-sized changes in the
+        output, but they should be much less noticeable.
+
+        Args:
+            x (`torch.Tensor`): Input batch of images.
+
+        Returns:
+            `torch.Tensor`:
+                The latent representation of the encoded videos.
+        """
+
+        overlap_size = int(self.tile_sample_min_size * (1 - self.tile_overlap_factor))
+        blend_extent = int(self.tile_latent_min_size * self.tile_overlap_factor)
+        row_limit = self.tile_latent_min_size - blend_extent
+
+        # Split the image into 512x512 tiles and encode them separately.
+        rows = []
+        for i in range(0, x.shape[2], overlap_size):
+            row = []
+            for j in range(0, x.shape[3], overlap_size):
+                tile = x[:, :, i : i + self.tile_sample_min_size, j : j + self.tile_sample_min_size]
+                tile = self.encoder(tile)
+                if self.config.use_quant_conv:
+                    tile = self.quant_conv(tile)
+                row.append(tile)
+            rows.append(row)
+        result_rows = []
+        for i, row in enumerate(rows):
+            result_row = []
+            for j, tile in enumerate(row):
+                # blend the above tile and the left tile
+                # to the current tile and add the current tile to the result row
+                if i > 0:
+                    tile = self.blend_v(rows[i - 1][j], tile, blend_extent)
+                if j > 0:
+                    tile = self.blend_h(row[j - 1], tile, blend_extent)
+                result_row.append(tile[:, :, :row_limit, :row_limit])
+            result_rows.append(torch.cat(result_row, dim=3))
+
+        enc = torch.cat(result_rows, dim=2)
+        return enc
+
     def tiled_encode(self, x: torch.Tensor, return_dict: bool = True) -> AutoencoderKLOutput:
         r"""Encode a batch of images using a tiled encoder.
 
@@ -356,6 +409,13 @@ class AutoencoderKL(ModelMixin, ConfigMixin, FromOriginalModelMixin):
                 If return_dict is True, a [`~models.autoencoder_kl.AutoencoderKLOutput`] is returned, otherwise a plain
                 `tuple` is returned.
         """
+        deprecation_message = (
+            "The tiled_encode implementation supporting the `return_dict` parameter is deprecated. In the future, the "
+            "implementation of this method will be replaced with that of `_tiled_encode` and you will no longer be able "
+            "to pass `return_dict`. You will also have to create a `DiagonalGaussianDistribution()` from the returned value."
+        )
+        deprecate("tiled_encode", "1.0.0", deprecation_message, standard_warn=False)
+
         overlap_size = int(self.tile_sample_min_size * (1 - self.tile_overlap_factor))
         blend_extent = int(self.tile_latent_min_size * self.tile_overlap_factor)
         row_limit = self.tile_latent_min_size - blend_extent