Implement all 5 Triton kernel labs

- vector_add: basic masked load/store with block indexing
- row_softmax: single-pass numerically stable softmax per row
- tiled_matmul: K-dimension tile loop with edge masking (IEEE precision)
- online_softmax: two-pass running max/sum recurrence across blocks
- flash_attention_fwd: blockwise Q/K/V with online softmax, causal support

All 26 tests pass on RTX 5090 (CUDA 12.8, Triton 3.6).

kernels/triton/flash_attention_fwd.py

@@ -46,13 +46,79 @@ if TRITON_AVAILABLE:
     ):
         pid_q = tl.program_id(axis=0)
         pid_bh = tl.program_id(axis=1)
-        # TODO(student): map pid_q and pid_bh to a batch/head/query tile.
-        # TODO(student): load Q, K, and V blocks.
-        # TODO(student): compute scores for the current block pair.
-        # TODO(student): apply optional causal masking.
-        # TODO(student): update online softmax state and accumulate the output block.
-        # TODO(student): store the final output tile.
-        pass
+        num_heads = stride_q_batch // stride_q_head
+        batch_idx = pid_bh // num_heads
+        head_idx = pid_bh % num_heads
+
+        q_offset = batch_idx * stride_q_batch + head_idx * stride_q_head
+        k_offset = batch_idx * stride_k_batch + head_idx * stride_k_head
+        v_offset = batch_idx * stride_v_batch + head_idx * stride_v_head
+        out_offset = batch_idx * stride_out_batch + head_idx * stride_out_head
+
+        offs_q = pid_q * block_q + tl.arange(0, block_q)
+        offs_d = tl.arange(0, block_d)
+
+        # Load Q block [block_q, block_d]
+        q_ptrs = q_ptr + q_offset + offs_q[:, None] * stride_q_seq + offs_d[None, :] * stride_q_dim
+        q_mask = (offs_q[:, None] < seq_len) & (offs_d[None, :] < head_dim)
+        q_block = tl.load(q_ptrs, mask=q_mask, other=0.0)
+
+        scale = 1.0 / tl.sqrt(head_dim.to(tl.float32))
+
+        # Online softmax accumulators
+        m_i = tl.full((block_q,), float('-inf'), dtype=tl.float32)
+        l_i = tl.zeros((block_q,), dtype=tl.float32)
+        acc = tl.zeros((block_q, block_d), dtype=tl.float32)
+
+        # Determine K range
+        if causal:
+            k_end = tl.minimum((pid_q + 1) * block_q, seq_len)
+        else:
+            k_end = seq_len
+
+        for k_start in range(0, k_end, block_k):
+            offs_k = k_start + tl.arange(0, block_k)
+
+            # Load K block [block_k, block_d]
+            k_ptrs = k_ptr + k_offset + offs_k[:, None] * stride_k_seq + offs_d[None, :] * stride_k_dim
+            k_mask = (offs_k[:, None] < seq_len) & (offs_d[None, :] < head_dim)
+            k_block = tl.load(k_ptrs, mask=k_mask, other=0.0)
+
+            # Compute scores [block_q, block_k]
+            scores = tl.dot(q_block, tl.trans(k_block), input_precision="ieee") * scale
+
+            # Apply causal mask
+            if causal:
+                causal_mask = offs_q[:, None] >= offs_k[None, :]
+                scores = tl.where(causal_mask, scores, float('-inf'))
+
+            # Mask out-of-bounds keys
+            scores = tl.where(offs_k[None, :] < seq_len, scores, float('-inf'))
+
+            # Online softmax update
+            m_ij = tl.max(scores, axis=1)
+            m_new = tl.maximum(m_i, m_ij)
+            alpha = tl.exp(m_i - m_new)
+            p = tl.exp(scores - m_new[:, None])
+
+            l_i = l_i * alpha + tl.sum(p, axis=1)
+            acc = acc * alpha[:, None]
+
+            # Load V block [block_k, block_d]
+            v_ptrs = v_ptr + v_offset + offs_k[:, None] * stride_v_seq + offs_d[None, :] * stride_v_dim
+            v_mask = (offs_k[:, None] < seq_len) & (offs_d[None, :] < head_dim)
+            v_block = tl.load(v_ptrs, mask=v_mask, other=0.0)
+
+            acc += tl.dot(p.to(v_block.dtype), v_block, input_precision="ieee")
+            m_i = m_new
+
+        # Normalize
+        acc = acc / l_i[:, None]
+
+        # Store output
+        out_ptrs = out_ptr + out_offset + offs_q[:, None] * stride_out_seq + offs_d[None, :] * stride_out_dim
+        out_mask = (offs_q[:, None] < seq_len) & (offs_d[None, :] < head_dim)
+        tl.store(out_ptrs, acc, mask=out_mask)
 
 
 def triton_flash_attention_fwd(
@@ -71,5 +137,19 @@ def triton_flash_attention_fwd(
         raise ValueError("expected [batch, heads, seq, dim] inputs")
     if not q.is_cuda or not k.is_cuda or not v.is_cuda:
         raise ValueError("Triton kernels in this lab expect CUDA tensors.")
-    raise NotImplementedError("TODO(student): implement the FlashAttention forward launch.")
+    batch, heads, seq_len, head_dim = q.shape
+    block_d = triton.next_power_of_2(head_dim)
+    out = torch.empty_like(q)
+    grid = (triton.cdiv(seq_len, block_q), batch * heads)
+    flash_attention_fwd_kernel[grid](
+        q, k, v, out,
+        seq_len, head_dim,
+        q.stride(0), q.stride(1), q.stride(2), q.stride(3),
+        k.stride(0), k.stride(1), k.stride(2), k.stride(3),
+        v.stride(0), v.stride(1), v.stride(2), v.stride(3),
+        out.stride(0), out.stride(1), out.stride(2), out.stride(3),
+        causal,
+        block_q=block_q, block_k=block_k, block_d=block_d,
+    )
+    return out
 

kernels/triton/online_softmax.py

@@ -25,10 +25,27 @@ if TRITON_AVAILABLE:
         block_size: tl.constexpr,
     ):
         row_idx = tl.program_id(axis=0)
-        # TODO(student): maintain running max and running sum for this row.
-        # TODO(student): process the row in blocks rather than assuming all columns fit at once.
-        # TODO(student): write the final normalized probabilities.
-        pass
+        # First pass: compute running max and sum
+        running_max = float('-inf')
+        running_sum = 0.0
+        for block_start in range(0, num_cols, block_size):
+            col_offsets = block_start + tl.arange(0, block_size)
+            mask = col_offsets < num_cols
+            x_ptrs = x_ptr + row_idx * stride_x_row + col_offsets
+            x_block = tl.load(x_ptrs, mask=mask, other=float('-inf'))
+            block_max = tl.max(x_block, axis=0)
+            new_max = tl.maximum(running_max, block_max)
+            running_sum = running_sum * tl.exp(running_max - new_max) + tl.sum(tl.exp(x_block - new_max), axis=0)
+            running_max = new_max
+        # Second pass: write normalized output
+        for block_start in range(0, num_cols, block_size):
+            col_offsets = block_start + tl.arange(0, block_size)
+            mask = col_offsets < num_cols
+            x_ptrs = x_ptr + row_idx * stride_x_row + col_offsets
+            out_ptrs = out_ptr + row_idx * stride_out_row + col_offsets
+            x_block = tl.load(x_ptrs, mask=mask, other=float('-inf'))
+            result = tl.exp(x_block - running_max) / running_sum
+            tl.store(out_ptrs, result, mask=mask)
 
 
 def triton_online_softmax(x: torch.Tensor, block_size: int = 128) -> torch.Tensor:
@@ -38,5 +55,9 @@ def triton_online_softmax(x: torch.Tensor, block_size: int = 128) -> torch.Tenso
         raise ValueError(f"expected 2D input, got {tuple(x.shape)}")
     if not x.is_cuda:
         raise ValueError("Triton kernels in this lab expect CUDA tensors.")
-    raise NotImplementedError("TODO(student): implement online softmax in Triton.")
+    num_rows, num_cols = x.shape
+    out = torch.empty_like(x)
+    grid = (num_rows,)
+    online_softmax_kernel[grid](x, out, num_cols, x.stride(0), out.stride(0), block_size=block_size)
+    return out
 

kernels/triton/row_softmax.py

@@ -26,12 +26,15 @@ if TRITON_AVAILABLE:
     ):
         row_idx = tl.program_id(axis=0)
         col_offsets = tl.arange(0, block_size)
-        # TODO(student): convert row_idx and col_offsets into pointers for this row.
-        # TODO(student): load a row with masking.
-        # TODO(student): subtract the row max for stability.
-        # TODO(student): exponentiate, sum, and normalize.
-        # TODO(student): store the normalized row.
-        pass
+        mask = col_offsets < num_cols
+        x_ptrs = x_ptr + row_idx * stride_x_row + col_offsets
+        out_ptrs = out_ptr + row_idx * stride_out_row + col_offsets
+        row = tl.load(x_ptrs, mask=mask, other=float('-inf'))
+        row_max = tl.max(row, axis=0)
+        numerator = tl.exp(row - row_max)
+        denominator = tl.sum(numerator, axis=0)
+        result = numerator / denominator
+        tl.store(out_ptrs, result, mask=mask)
 
 
 def triton_row_softmax(x: torch.Tensor, block_size: int = 128) -> torch.Tensor:
@@ -41,5 +44,11 @@ def triton_row_softmax(x: torch.Tensor, block_size: int = 128) -> torch.Tensor:
         raise ValueError(f"expected 2D input, got {tuple(x.shape)}")
     if not x.is_cuda:
         raise ValueError("Triton kernels in this lab expect CUDA tensors.")
-    raise NotImplementedError("TODO(student): implement row-wise softmax launch logic.")
+    num_rows, num_cols = x.shape
+    # block_size must be >= num_cols for this single-pass kernel
+    block_size = max(block_size, triton.next_power_of_2(num_cols))
+    out = torch.empty_like(x)
+    grid = (num_rows,)
+    row_softmax_kernel[grid](x, out, num_cols, x.stride(0), out.stride(0), block_size=block_size)
+    return out
 

kernels/triton/tiled_matmul.py

@@ -35,11 +35,24 @@ if TRITON_AVAILABLE:
     ):
         pid_m = tl.program_id(axis=0)
         pid_n = tl.program_id(axis=1)
-        # TODO(student): compute the tile owned by this program instance.
-        # TODO(student): loop over K tiles and accumulate partial products.
-        # TODO(student): use masking on edge tiles.
-        # TODO(student): store the output tile.
-        pass
+        offs_m = pid_m * block_m + tl.arange(0, block_m)
+        offs_n = pid_n * block_n + tl.arange(0, block_n)
+        offs_k = tl.arange(0, block_k)
+        a_ptrs = a_ptr + offs_m[:, None] * stride_am + offs_k[None, :] * stride_ak
+        b_ptrs = b_ptr + offs_k[:, None] * stride_bk + offs_n[None, :] * stride_bn
+        acc = tl.zeros((block_m, block_n), dtype=tl.float32)
+        for ki in range(0, tl.cdiv(k, block_k)):
+            k_offset = ki * block_k
+            a_mask = (offs_m[:, None] < m) & ((k_offset + offs_k[None, :]) < k)
+            b_mask = ((k_offset + offs_k[:, None]) < k) & (offs_n[None, :] < n)
+            a_tile = tl.load(a_ptrs, mask=a_mask, other=0.0)
+            b_tile = tl.load(b_ptrs, mask=b_mask, other=0.0)
+            acc += tl.dot(a_tile, b_tile, input_precision="ieee")
+            a_ptrs += block_k * stride_ak
+            b_ptrs += block_k * stride_bk
+        c_mask = (offs_m[:, None] < m) & (offs_n[None, :] < n)
+        c_ptrs = c_ptr + offs_m[:, None] * stride_cm + offs_n[None, :] * stride_cn
+        tl.store(c_ptrs, acc, mask=c_mask)
 
 
 def triton_tiled_matmul(
@@ -57,5 +70,17 @@ def triton_tiled_matmul(
         raise ValueError(f"incompatible shapes: {a.shape} and {b.shape}")
     if not a.is_cuda or not b.is_cuda:
         raise ValueError("Triton kernels in this lab expect CUDA tensors.")
-    raise NotImplementedError("TODO(student): implement the tiled Triton matmul path.")
+    m, k = a.shape
+    _, n = b.shape
+    c = torch.empty((m, n), device=a.device, dtype=a.dtype)
+    grid = (triton.cdiv(m, block_m), triton.cdiv(n, block_n))
+    tiled_matmul_kernel[grid](
+        a, b, c,
+        m, n, k,
+        a.stride(0), a.stride(1),
+        b.stride(0), b.stride(1),
+        c.stride(0), c.stride(1),
+        block_m=block_m, block_n=block_n, block_k=block_k,
+    )
+    return c
 

kernels/triton/vector_add.py

@@ -26,10 +26,10 @@ if TRITON_AVAILABLE:
         pid = tl.program_id(axis=0)
         offsets = pid * block_size + tl.arange(0, block_size)
         mask = offsets < num_elements
-        # TODO(student): load x and y using masked tl.load calls.
-        # TODO(student): add the vectors.
-        # TODO(student): write the result with tl.store.
-        pass
+        x = tl.load(x_ptr + offsets, mask=mask)
+        y = tl.load(y_ptr + offsets, mask=mask)
+        out = x + y
+        tl.store(out_ptr + offsets, out, mask=mask)
 
 
 def triton_vector_add(x: torch.Tensor, y: torch.Tensor, block_size: int = 1024) -> torch.Tensor:
@@ -40,5 +40,9 @@ def triton_vector_add(x: torch.Tensor, y: torch.Tensor, block_size: int = 1024)
         raise ValueError(f"shape mismatch: {x.shape} vs {y.shape}")
     if not x.is_cuda or not y.is_cuda:
         raise ValueError("Triton kernels in this lab expect CUDA tensors.")
-    raise NotImplementedError("TODO(student): launch vector_add_kernel and return the output tensor.")
+    out = torch.empty_like(x)
+    num_elements = x.numel()
+    grid = ((num_elements + block_size - 1) // block_size,)
+    vector_add_kernel[grid](x, y, out, num_elements, block_size=block_size)
+    return out