Add simplified se_block kernel (#989)

Summary:
Pull Request resolved: #989

We add a helion kernel to compute 2 * x * sigmoid(x @ w)

Differential Revision: D84968671

Author: mengluy0125

examples/se_block.py

@@ -0,0 +1,215 @@
+"""
+Helion SE Block Example
+============================
+This example demonstrates a Helion kernel implementation of SE Block.
+"""
+
+# %%
+from __future__ import annotations
+
+import torch
+from torch import Tensor
+
+import helion
+from helion._testing import run_example
+import helion.language as hl
+
+
+# %%
+@helion.kernel(
+    # static_shapes=True gives a performance boost for matmuls
+    static_shapes=True,
+)
+def se_block_fwd(x: Tensor, w: Tensor) -> tuple[Tensor, Tensor]:
+    """
+    Performs 2 * x * sigmoid(x @ w)
+    Args:
+        x: 2D tensor of shape [m, n].
+        w: 2D tensor of shape [n, n].
+    Returns:
+        out: Resulting matrix of shape [m, n].
+        s: sigmoid(x @ w) of shape [m, n].
+    """
+    m, n = x.size()
+    
+    out = torch.empty([m, n], dtype=x.dtype, device=x.device)
+    s = torch.empty([m, n], dtype=x.dtype, device=x.device)
+    
+    for tile_m in hl.tile(m):
+        for tile_n in hl.tile(n):
+            s[tile_m, tile_n] = torch.sigmoid(x[tile_m, :] @ w[:, tile_n])
+            acc = 2.0 * x[tile_m, tile_n] * s[tile_m, tile_n]
+            out[tile_m, tile_n] = acc
+    
+    return out, s
+
+
+# %%
+@helion.kernel(static_shapes=True)
+def se_block_bwd_dx(
+    grad_out: Tensor, x: Tensor, w: Tensor, s: Tensor
+) -> Tensor:
+    """
+    Compute gradient for x.
+    grad_x = 2 * grad_out * s + (2 * grad_out * x * s * (1 - s)) @ w.T
+    
+    Args:
+        grad_out: Gradient w.r.t output [m, n]
+        x: Input tensor [m, n]
+        w: Weight matrix [n, n]
+        s: sigmoid(x @ w) from forward pass [m, n]
+    
+    Returns:
+        grad_x: Gradient w.r.t x [m, n]
+    """
+    m, n = x.size()
+    
+    grad_x = torch.empty([m, n], dtype=torch.float32, device=x.device)
+
+    for tile_m, tile_n in hl.tile([m, n]):
+        # 2 * grad_out * s
+        acc = hl.zeros([tile_m, tile_n], dtype=torch.float32)
+        acc += 2.0 * grad_out[tile_m, tile_n] * s[tile_m, tile_n]
+
+        for tile_k in hl.tile(n):
+            # 2 * grad_out * x * s * (1-s) for tile_k
+            grad_to_w = (
+                2.0 * grad_out[tile_m, tile_k].to(torch.float32)
+                * x[tile_m, tile_k].to(torch.float32)
+                * s[tile_m, tile_k].to(torch.float32)
+                * (1.0 - s[tile_m, tile_k].to(torch.float32))
+            )
+            # grad_to_w @ w.T[tile_k, tile_n] = grad_to_w @ w[tile_n, tile_k].T
+            acc += grad_to_w @ w[tile_n, tile_k].to(torch.float32).T
+        
+        grad_x[tile_m, tile_n] = acc.to(x.dtype)
+    
+    return grad_x
+
+
+# %%
+@helion.kernel(static_shapes=True)
+def se_block_bwd_dw(
+    grad_out: Tensor, x: Tensor, s: Tensor
+) -> Tensor:
+    """
+    Compute gradient for w.
+    grad_w = x.T @ (2 * grad_out * x * s * (1 - s))
+    
+    Args:
+        grad_out: Gradient w.r.t output [m, n]
+        x: Input tensor [m, n]
+        s: sigmoid(x @ w) from forward pass [m, n]
+    
+    Returns:
+        grad_w: Gradient w.r.t w [n, n]
+    """
+    m, n = x.size()
+    
+    grad_w = torch.zeros([n, n], dtype=torch.float32, device=x.device)
+
+    for tile_n1, tile_n2 in hl.tile([n, n]):
+        acc_w = hl.zeros([tile_n1, tile_n2], dtype=torch.float32)
+        for tile_m in hl.tile(m):
+            # 2 * grad_out * x * s * (1-s)
+            grad_to_w = (
+                2.0 * grad_out[tile_m, tile_n2].to(torch.float32)
+                * x[tile_m, tile_n2].to(torch.float32)
+                * s[tile_m, tile_n2].to(torch.float32)
+                * (1.0 - s[tile_m, tile_n2].to(torch.float32))
+            )
+            # x[tile_m, tile_n1].T @ grad_to_w[tile_m, tile_n2]
+            acc_w += x[tile_m, tile_n1].to(torch.float32).T @ grad_to_w
+        
+        grad_w[tile_n1, tile_n2] = acc_w.to(x.dtype)
+    
+    return grad_w
+
+
+# %%
+# Reference Implementation
+# --------------------
+def se_block_pytorch(
+    x: torch.Tensor, w: torch.Tensor
+) -> torch.Tensor:
+    """
+    PyTorch reference implementation se_block.
+
+    Args:
+        x, w: Input tensors
+
+    Returns:
+        tensor of 2 * x * sigmoid(x @ w)
+    """
+    return 2 * x * torch.sigmoid(x @ w)
+
+
+# %%
+# Autograd Function
+# ------------------
+class SEBlockFunction(torch.autograd.Function):
+    @staticmethod
+    def forward(  # type: ignore[override]
+        ctx: object,
+        x: torch.Tensor,
+        w: torch.Tensor,
+    ) -> torch.Tensor:
+        """Forward pass for se block."""
+        out, s = se_block_fwd(x, w)
+        ctx.save_for_backward(x, w, s)  # type: ignore[attr-defined]
+        return out
+
+    @staticmethod
+    def backward(  # type: ignore[override]
+        ctx: object,
+        grad_out: torch.Tensor,
+    ) -> tuple[torch.Tensor, torch.Tensor]:
+        """Backward pass for se block."""
+        x, w, s = ctx.saved_tensors  # type: ignore[attr-defined]
+        
+        grad_x = se_block_bwd_dx(grad_out, x, w, s)
+        grad_w = se_block_bwd_dw(grad_out, x, s)
+        
+        return grad_x, grad_w
+
+
+def se_block(
+    x: torch.Tensor, w: torch.Tensor
+) -> torch.Tensor:
+    """
+    SE Block with autograd support.
+    
+    Args:
+        x: Input tensor [m, n]
+        w: Weight matrix [n, n]
+    
+    Returns:
+        Output tensor [m, n]
+    """
+    return SEBlockFunction.apply(x, w)  # type: ignore[no-any-return]
+
+
+def check(m: int, n: int) -> None:
+    """
+    Checks the correctness against PyTorch.
+    Args:
+        m (int): Number of rows in matrix x.
+        n (int): Number of columns in matrix x.
+    """
+    x = torch.randn([m, n], device="cuda", dtype=torch.float16, requires_grad=True)
+    w = torch.randn([n, n], device="cuda", dtype=torch.float16, requires_grad=True)
+    for bwd in [True, False]:
+        run_example(se_block, se_block_pytorch, (x, w), bwd=bwd)
+
+
+# %%
+def main() -> None:
+    """
+    Main function to run correctness checks.
+    """
+    check(1024, 1024)
+
+
+# %%
+if __name__ == "__main__":
+    main()