mx: delete triton_f4_to_bf16 kernel

Summary:

This is dead code from early days, test is broken, deleting.

Test Plan:

```bash
pytest test/prototype/mx_formats/ -s -x
```

Reviewers:

Subscribers:

Tasks:

Tags:
ghstack-source-id: 3460e23
ghstack-comment-id: 3210590444
Pull-Request: #2830

Author: vkuzo

test/prototype/mx_formats/test_kernels.py

@@ -35,7 +35,6 @@
     get_bits,
     pack_uint4,
     pack_uint6,
-    triton_f4_to_bf16,
     triton_f6_e2m3_to_bf16,
     triton_f6_e3m2_to_bf16,
     triton_to_mxfp8_dim1,
@@ -327,17 +326,6 @@ def test_fp4_pack_unpack():
     assert torch.all(orig_vals_dq == orig_vals)
 
 
-# TODO(future PR): fix or delete this test
-@pytest.mark.skipif(not torch.cuda.is_available(), reason="CUDA not available")
-@pytest.mark.skipif(not has_triton(), reason="unsupported without triton")
-@pytest.mark.skipif(is_sm_at_least_89(), reason="broken on CUDA capability 8.9+")
-def test_fp4_triton_unscaled_cast():
-    packed_vals = torch.arange(0, 255, dtype=torch.uint8, device="cuda")
-    f32_ref = f4_unpacked_to_f32(unpack_uint4(packed_vals))
-    f32_triton = triton_f4_to_bf16(packed_vals).to(torch.float)
-    assert torch.all(torch.eq(f32_ref, f32_triton))
-
-
 # TODO(future PR): fix or delete this test
 @pytest.mark.skipif(not torch.cuda.is_available(), reason="CUDA not available")
 @pytest.mark.skipif(not has_triton(), reason="unsupported without triton")

torchao/prototype/mx_formats/kernels.py

@@ -196,55 +196,6 @@ def _fp4_packed_to_bf16(
         output = output.to(tl.bfloat16)
         return output
 
-    @triton.jit
-    def triton_f4_to_bf16_kernel(
-        x_ptr,
-        output_ptr,
-        n_elements_in,
-        sign_mask_f4: tl.constexpr,
-        mantissa_mask_f4: tl.constexpr,
-        mbits_f4_e2m1: tl.constexpr,
-        ebits_f4_e2m1: tl.constexpr,
-        f4_e2m1_exp_bias: tl.constexpr,
-        mbits_f32: tl.constexpr,
-        ebits_f32: tl.constexpr,
-        f32_exp_bias: tl.constexpr,
-        zero_bits_f32: tl.constexpr,
-        zero_point_five_bits_f32: tl.constexpr,
-        BLOCK_SIZE_IN: tl.constexpr,
-    ):
-        pid = tl.program_id(axis=0)
-        n_elements_out = n_elements_in * 2
-        BLOCK_SIZE_OUT: tl.constexpr = BLOCK_SIZE_IN * 2
-
-        block_start_in = pid * BLOCK_SIZE_IN
-        offsets_in = block_start_in + tl.arange(0, BLOCK_SIZE_IN)
-
-        mask_in = offsets_in < n_elements_in
-
-        # packed uint8
-        x_packed = tl.load(x_ptr + offsets_in, mask=mask_in)
-        output = _fp4_packed_to_bf16(
-            x_packed,
-            sign_mask_f4,
-            mantissa_mask_f4,
-            mbits_f4_e2m1,
-            ebits_f4_e2m1,
-            f4_e2m1_exp_bias,
-            mbits_f32,
-            ebits_f32,
-            f32_exp_bias,
-            zero_bits_f32,
-            zero_point_five_bits_f32,
-        )
-
-        # set up output offsets
-        block_start_out = pid * BLOCK_SIZE_OUT
-        offsets_out = block_start_out + tl.arange(0, BLOCK_SIZE_OUT)
-        mask_out = offsets_out < n_elements_out
-
-        tl.store(output_ptr + offsets_out, output, mask=mask_out)
-
     @triton.autotune(
         configs=[
             triton.Config({"BLOCK_SIZE_IN": 128}),
@@ -624,24 +575,6 @@ def triton_pack_uint6_kernel(
 
 else:
 
-    def triton_f4_to_bf16_kernel(
-        x_ptr,
-        output_ptr,
-        n_elements_in,
-        sign_mask_f4,
-        mantissa_mask_f4,
-        mbits_f4_e2m1,
-        ebits_f4_e2m1,
-        f4_e2m1_exp_bias,
-        mbits_f32,
-        ebits_f32,
-        f32_exp_bias,
-        zero_bits_f32,
-        zero_point_five_bits_f32,
-        BLOCK_SIZE_IN,
-    ):
-        raise AssertionError("unsupported without triton")
-
     def triton_f4_to_scaled_bf16_kernel(
         x_ptr,
         s_ptr,
@@ -705,41 +638,6 @@ def triton_pack_uint6_kernel(
         raise AssertionError("unsupported without triton")
 
 
-def triton_f4_to_bf16(x: torch.Tensor):
-    """
-    Input: a tensor of packed fp4 values
-    Output: a tensor of bfloat16 values
-
-    Note: this function is only used in testing, so we can test
-      the numerical correctness of the cast without the scaling.
-    """
-    new_shape = (*x.shape[:-1], x.shape[-1] * 2)
-    output = torch.empty(*new_shape, device=x.device, dtype=torch.bfloat16)
-    assert x.is_contiguous()
-    assert x.is_cuda and output.is_cuda
-    n_elements_in = x.numel()
-    grid = lambda meta: (  # noqa: E731
-        triton.cdiv(n_elements_in, meta["BLOCK_SIZE_IN"]),
-    )  # noqa: E731,E501
-    triton_f4_to_bf16_kernel[grid](
-        x,
-        output,
-        n_elements_in,
-        sign_mask_f4=SIGN_MASK_F4,
-        mantissa_mask_f4=MANTISSA_MASK_F4,
-        mbits_f4_e2m1=MBITS_F4_E2M1,
-        ebits_f4_e2m1=EBITS_F4_E2M1,
-        f4_e2m1_exp_bias=F4_E2M1_EXP_BIAS,
-        mbits_f32=MBITS_F32,
-        ebits_f32=EBITS_F32,
-        f32_exp_bias=F32_EXP_BIAS,
-        zero_bits_f32=ZERO_BITS_F32,
-        zero_point_five_bits_f32=ZERO_POINT_FIVE_BITS_F32,
-        BLOCK_SIZE_IN=512,
-    )
-    return output
-
-
 def triton_f4_to_scaled_bf16(
     x: torch.Tensor,
     s_e8m0: torch.Tensor,