From 4c3e62acff0cc1aeae2b4c2b60b5ae7b651e7d55 Mon Sep 17 00:00:00 2001
From: Xujin Chris Liu <36082433+Aceticia@users.noreply.github.com>
Date: Fri, 29 Nov 2024 15:23:29 -0500
Subject: [PATCH 1/2] Custom pos alibi flash attn fix (#300)

* handle custom pos for alibi in flash attn

* test for custom pos alibi+flash attn
---
 tests/test_x_transformers.py | 10 +++++++---
 x_transformers/attend.py     |  2 +-
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/tests/test_x_transformers.py b/tests/test_x_transformers.py
index cd1be33d..18c03b48 100644
--- a/tests/test_x_transformers.py
+++ b/tests/test_x_transformers.py
@@ -388,7 +388,8 @@ def test_neo_mlp():
     out = mlp(x)
     assert out.shape == (3, 7)
 
-def test_custom_alibi():
+@pytest.mark.parametrize('flash', (True, False))
+def test_custom_alibi(flash: bool):
 
     model = TransformerWrapper(
         num_tokens = 20_000,
@@ -397,7 +398,8 @@ def test_custom_alibi():
             dim = 512,
             depth = 2,
             heads = 8,
-            alibi_pos_bias = True
+            alibi_pos_bias = True,
+            attn_flash = flash
         )
     )
 
@@ -407,7 +409,8 @@ def test_custom_alibi():
 
     logits = model(x, pos = pos)
 
-def test_custom_alibi_across_heads():
+@pytest.mark.parametrize('flash', (True, False))
+def test_custom_alibi_across_heads(flash: bool):
 
     model = Decoder(
         dim = 512,
@@ -417,6 +420,7 @@ def test_custom_alibi_across_heads():
         rel_pos_kwargs = dict(
             slopes = [1, 1]
         ),
+        attn_flash = flash
     )
 
     x = torch.randn(2, 4, 512)
diff --git a/x_transformers/attend.py b/x_transformers/attend.py
index d354f915..c2bad988 100644
--- a/x_transformers/attend.py
+++ b/x_transformers/attend.py
@@ -370,7 +370,7 @@ def flash_attn(
         # convert from bool to float
 
         if exists(attn_bias):
-            attn_bias = rearrange(attn_bias, 'h i j -> 1 h i j').expand(batch, heads, -1, -1)
+            attn_bias = attn_bias.expand(batch, heads, -1, -1)
 
             # if mask given, the mask would already contain the causal mask from above logic
             # otherwise, if no mask given but still causal, mask out alibi positional bias to a large negative number

From 8c993f0dd850d4b15a737c271c55db54b1db2e6b Mon Sep 17 00:00:00 2001
From: Phil Wang <lucidrains@gmail.com>
Date: Fri, 29 Nov 2024 12:23:59 -0800
Subject: [PATCH 2/2] 1.42.20

---
 setup.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/setup.py b/setup.py
index 37a3f636..49086114 100644
--- a/setup.py
+++ b/setup.py
@@ -3,7 +3,7 @@
 setup(
   name = 'x-transformers',
   packages = find_packages(exclude=['examples']),
-  version = '1.42.19',
+  version = '1.42.20',
   license='MIT',
   description = 'X-Transformers - Pytorch',
   author = 'Phil Wang',