Have softmax handle case where all dims after reduction dim are 1 (#831)

Summary:
Pull Request resolved: #831

Memory-layout-wise, a tensor with shape [2, 1] is identical to that
with shape [2], so the current implementation of softmax can handle it.

Reviewed By: aakhundov

Differential Revision: D47463543

fbshipit-source-id: 7799825c6c3b20f6412f2022e08d4ae82ead457e

python/aitemplate/backend/cuda/softmax/softmax.py

@@ -182,10 +182,6 @@ def softmax_gen_function(func_attrs: Dict[str, Any]) -> str:
     shapes = func_attrs["inputs"][0]._attrs["shape"]
     rank = len(shapes)
 
-    assert (
-        dim == rank - 1
-    ), f"softmax only supports dim == rank - 1, dim={dim}, rank={rank}"
-
     assert isinstance(
         shapes[dim], IntImm
     ), "softmax requires reduction dim to be static"

python/aitemplate/compiler/ops/softmax/softmax.py

@@ -31,6 +31,7 @@
 from aitemplate.compiler.base import (
     DynamicProfileStrategy,
     ExecItem,
+    IntImm,
     IntVar,
     Operator,
     Tensor,
@@ -203,9 +204,10 @@ def __call__(self, x: Tensor, dim: int = None) -> Tensor:
                 "flattening input tensor before normalization is not supported yet"
             )
         dim = wrap_dim(dim, x._rank())
-        if dim != x._rank() - 1:
+        tail_shapes = x.shape()[dim + 1 :]
+        if not all(isinstance(s, IntImm) and s.value() == 1 for s in tail_shapes):
             raise NotImplementedError(
-                f"softmax currently only supports dim=x._rank() - 1, dim={dim}, x._rank()={x._rank()}"
+                f"softmax only supports tensors where all shapes after dim are 1, {dim=}, {x.shape()=}"
             )
 
         self._attrs["inputs"] = [x]

tests/unittest/ops/test_softmax.py

@@ -68,6 +68,7 @@ def _test_softmax(
             {
                 TestEnv.CUDA_LESS_THAN_SM80: [
                     ("dim_1_fp16", "float16", (1, 1024), (6,), 1),
+                    ("tail_shapes_all_1_fp16", "float16", (1, 2), (6, 1, 1), 1),
                     ("odd_small_fp16", "float16", (1, 13), (11,)),
                     ("odd_mid_fp16", "float16", (1, 4096), (33,)),
                     ("odd_large_fp16", "float16", (2, 31), (1409,)),
@@ -100,6 +101,7 @@ def _test_softmax(
                 ],
                 TestEnv.CUDA_SM80: [
                     ("dim_1_bf16", "bfloat16", (1, 2), (6,), 1),
+                    ("tail_shapes_all_1_bf16", "bfloat16", (1, 2), (6, 1, 1), 1),
                     ("odd_small_bf16", "bfloat16", (1, 2), (11,)),
                     ("odd_mid_bf16", "bfloat16", (1, 2), (33,)),
                     ("odd_large_bf16", "bfloat16", (1, 2), (1409,)),