Jax infer support negative prompt (#1337)

* support negative prompts in sd jax pipeline

* pass batched neg_prompt

* only encode when negative prompt is None
Co-authored-by: Juan Acevedo <jfacevedo@google.com>

src/diffusers/pipelines/stable_diffusion/pipeline_flax_stable_diffusion.py

@@ -165,6 +165,7 @@ class FlaxStableDiffusionPipeline(FlaxDiffusionPipeline):
         guidance_scale: float = 7.5,
         latents: Optional[jnp.array] = None,
         debug: bool = False,
+        neg_prompt_ids: jnp.array = None,
     ):
         if height % 8 != 0 or width % 8 != 0:
             raise ValueError(f"`height` and `width` have to be divisible by 8 but are {height} and {width}.")
@@ -177,10 +178,14 @@ class FlaxStableDiffusionPipeline(FlaxDiffusionPipeline):
         batch_size = prompt_ids.shape[0]
 
         max_length = prompt_ids.shape[-1]
-        uncond_input = self.tokenizer(
-            [""] * batch_size, padding="max_length", max_length=max_length, return_tensors="np"
-        )
-        uncond_embeddings = self.text_encoder(uncond_input.input_ids, params=params["text_encoder"])[0]
+
+        if neg_prompt_ids is None:
+            uncond_input = self.tokenizer(
+                [""] * batch_size, padding="max_length", max_length=max_length, return_tensors="np"
+            ).input_ids
+        else:
+            uncond_input = neg_prompt_ids
+        uncond_embeddings = self.text_encoder(uncond_input, params=params["text_encoder"])[0]
         context = jnp.concatenate([uncond_embeddings, text_embeddings])
 
         latents_shape = (batch_size, self.unet.in_channels, height // 8, width // 8)
@@ -251,6 +256,7 @@ class FlaxStableDiffusionPipeline(FlaxDiffusionPipeline):
         return_dict: bool = True,
         jit: bool = False,
         debug: bool = False,
+        neg_prompt_ids: jnp.array = None,
         **kwargs,
     ):
         r"""
@@ -298,11 +304,30 @@ class FlaxStableDiffusionPipeline(FlaxDiffusionPipeline):
         """
         if jit:
             images = _p_generate(
-                self, prompt_ids, params, prng_seed, num_inference_steps, height, width, guidance_scale, latents, debug
+                self,
+                prompt_ids,
+                params,
+                prng_seed,
+                num_inference_steps,
+                height,
+                width,
+                guidance_scale,
+                latents,
+                debug,
+                neg_prompt_ids,
             )
         else:
             images = self._generate(
-                prompt_ids, params, prng_seed, num_inference_steps, height, width, guidance_scale, latents, debug
+                prompt_ids,
+                params,
+                prng_seed,
+                num_inference_steps,
+                height,
+                width,
+                guidance_scale,
+                latents,
+                debug,
+                neg_prompt_ids,
             )
 
         if self.safety_checker is not None:
@@ -333,10 +358,29 @@ class FlaxStableDiffusionPipeline(FlaxDiffusionPipeline):
 # TODO: maybe use a config dict instead of so many static argnums
 @partial(jax.pmap, static_broadcasted_argnums=(0, 4, 5, 6, 7, 9))
 def _p_generate(
-    pipe, prompt_ids, params, prng_seed, num_inference_steps, height, width, guidance_scale, latents, debug
+    pipe,
+    prompt_ids,
+    params,
+    prng_seed,
+    num_inference_steps,
+    height,
+    width,
+    guidance_scale,
+    latents,
+    debug,
+    neg_prompt_ids,
 ):
     return pipe._generate(
-        prompt_ids, params, prng_seed, num_inference_steps, height, width, guidance_scale, latents, debug
+        prompt_ids,
+        params,
+        prng_seed,
+        num_inference_steps,
+        height,
+        width,
+        guidance_scale,
+        latents,
+        debug,
+        neg_prompt_ids,
     )