Re-applying G42 bias triton fix on 0.4.3 (#41)

* Using rocm_flash_attention that supports bias computed from alibi slopes; Using attn_fwd triton kernel from ROCm/triton main_perf that does not cause triton compolier to hang

* Uninitialized variable fix

vllm/attention/backends/rocm_flash_attn.py

@@ -165,6 +165,62 @@ def decode_metadata(self) -> Optional["ROCmFlashAttentionMetadata"]:
         )
         return self._cached_decode_metadata
 
+def _make_alibi_bias(
+    alibi_slopes: torch.Tensor,
+    dtype: torch.dtype,
+    seq_lens: List[int],
+) -> List[torch.Tensor]:
+    attn_biases = []
+    for seq_len in seq_lens:
+        bias = torch.arange(seq_len, dtype=dtype)
+        # NOTE(zhuohan): HF uses
+        #     `bias = bias[None, :].repeat(seq_len, 1)`
+        # here. We find that both biases give the same results, but
+        # the bias below more accurately follows the original ALiBi
+        # paper.
+        bias = bias[None, :] - bias[:, None]
+
+        num_heads = alibi_slopes.shape[0]
+        bias = bias[None, :].repeat((num_heads, 1, 1)).to(alibi_slopes.device)
+        bias.mul_(alibi_slopes[:, None, None])
+        inf_mask = torch.empty(
+            (1, seq_len, seq_len),
+            dtype=bias.dtype).fill_(-torch.inf).triu_(diagonal=1).to(alibi_slopes.device)
+        attn_biases.append((bias + inf_mask).to(dtype))
+
+    return attn_biases
+
+
+def _make_alibi_bias_v2(
+    alibi_slopes: torch.Tensor,
+    dtype: torch.dtype,
+    seq_lens: List[int],
+    make_attn_mask: bool = True
+) -> List[torch.Tensor]:
+    attn_biases = []
+    for seq_len in seq_lens:
+        bias = torch.arange(seq_len, dtype=dtype)
+        # NOTE(zhuohan): HF uses
+        #     `bias = bias[None, :].repeat(seq_len, 1)`
+        # here. We find that both biases give the same results, but
+        # the bias below more accurately follows the original ALiBi
+        # paper.
+        bias = bias[None, :] - bias[:, None]
+
+        num_heads = alibi_slopes.shape[0]
+        bias = bias[None, :].repeat((num_heads, 1, 1)).to(alibi_slopes.device)
+        bias.mul_(alibi_slopes[:, None, None])
+        if make_attn_mask:
+            inf_mask = torch.empty(
+                (1, seq_len, seq_len),
+                dtype=bias.dtype).fill_(-torch.inf).triu_(diagonal=1).to(alibi_slopes.device)
+            attn_biases.append((bias + inf_mask).to(dtype))
+        else:
+            attn_biases.append(bias.to(dtype))
+
+    return attn_biases
+
+
 
 class ROCmFlashAttentionImpl(AttentionImpl):
     """
@@ -324,7 +380,12 @@ def forward(
                 # triton attention
                 # When block_tables are not filled, it means q and k are the
                 # prompt, and they have the same length.
+                att_masks = None
                 if self.use_triton_flash_attn:
+                    if self.alibi_slopes is not None:
+                        att_masks = _make_alibi_bias_v2(
+                            self.alibi_slopes, query.dtype,
+                            attn_metadata.seq_lens, make_attn_mask=False)  # type: ignore
                     out, _ = self.attn_func(
                         query,
                         key,
@@ -336,8 +397,13 @@ def forward(
                         prefill_meta.max_prefill_seq_len,
                         True,
                         self.scale,
+                        att_masks[0][None] if att_masks is not None else None,
                     )
                 elif self.use_naive_attn:
+                    if self.alibi_slopes is not None:
+                        att_masks = _make_alibi_bias_v2(
+                            self.alibi_slopes, query.dtype,
+                            attn_metadata.seq_lens, make_attn_mask=True)  # type: ignore
                     if self.num_kv_heads != self.num_heads:
                         # Interleave for MQA workaround.
                         key = self.repeat_kv(key, self.num_queries_per_kv)
@@ -348,6 +414,7 @@ def forward(
                         value,
                         prefill_meta.seq_lens,
                         self.scale,
+                        att_masks
                     )
                 else:
                     out = self.attn_func(
@@ -408,16 +475,18 @@ def _naive_attention(
     value: torch.Tensor,
     seq_lens: List[int],
     scale: float,
+    attn_masks: Optional[List[torch.Tensor]],
 ) -> torch.Tensor:
     output = torch.empty_like(query)
     start = 0
-    for _, seq_len in enumerate(seq_lens):
+    for i, seq_len in enumerate(seq_lens):
         end = start + seq_len
         out = _naive_masked_attention(
             query[start:end],
             key[start:end],
             value[start:end],
             scale,
+            attn_masks[i],
         )
         # TODO(woosuk): Unnecessary copy. Optimize.
         output[start:end].copy_(out)
@@ -431,16 +500,18 @@ def _naive_masked_attention(
     key: torch.Tensor,
     value: torch.Tensor,
     scale: float,
+    attn_mask: Optional[torch.Tensor],
 ) -> torch.Tensor:
     seq_len, head_size, head_dim = query.shape
-    attn_mask = torch.triu(torch.ones(seq_len,
-                                      seq_len,
-                                      dtype=query.dtype,
-                                      device=query.device),
-                           diagonal=1)
-    attn_mask = attn_mask * torch.finfo(query.dtype).min
+    if attn_mask is None:
+        attn_mask = torch.triu(torch.ones(seq_len,
+                                        seq_len,
+                                        dtype=query.dtype,
+                                        device=query.device),
+                            diagonal=1)
+        attn_mask = attn_mask * torch.finfo(query.dtype).min
     attn_weights = scale * torch.einsum("qhd,khd->hqk", query, key).float()
     attn_weights = attn_weights + attn_mask.float()
     attn_weights = torch.softmax(attn_weights, dim=-1).to(value.dtype)
     out = torch.einsum("hqk,khd->qhd", attn_weights, value)
-    return out
+    return out