[inductor] Don't import torchvision

Fixes #93019

Since PyTorch regularly breaks binary compatibility, `torchvision` must be
compiled with the exact same version of PyTorch. If not, then importing it may
cause mysterious failures at runtime due to binary incompatibility.

This fixes the issue by delaying the `make_fallback` call for
`torchvision.roi_align` until the operator appears in a graph being lowered, by
which point the user must have imported torchvision themself.

ghstack-source-id: 052c5d9f87803b4cf31b8fd88f32bdd4f1886122
Pull Request resolved: #93027

test/inductor/test_torchinductor.py

@@ -48,7 +48,7 @@
     from torch._inductor.codegen.cpp import cexpr, CppOverrides, CppVecOverrides
     from torch._inductor.codegen.triton import texpr
     from torch._inductor.compile_fx import compile_fx, complex_memory_overlap
-    from torch._inductor.ir import IndexingDiv, ModularIndexing
+    from torch._inductor.ir import ModularIndexing
     from torch._inductor.overrides import (
         linear_permute_fusion,
         linear_transpose,

torch/_inductor/graph.py

@@ -26,6 +26,7 @@
 )
 from .ir import Constant, FixedLayout, InputBuffer, Pointwise, Reduction, TensorBox
 from .lowering import (
+    FALLBACK_ALLOW_LIST,
     layout_constraints,
     lowerings,
     make_fallback,
@@ -291,7 +292,10 @@ def call_function(self, target, args, kwargs):
                 return super().call_function(target, args, kwargs)
 
             if target not in lowerings:
-                if config.implicit_fallbacks:
+                base_name = target.name().split(".")[0]
+                if base_name in FALLBACK_ALLOW_LIST:
+                    make_fallback(target)
+                elif config.implicit_fallbacks:
                     error = (
                         MissingOperatorWithDecomp
                         if get_decompositions([target])

torch/_inductor/lowering.py

@@ -37,7 +37,7 @@
     TensorBox,
     View,
 )
-from .utils import ceildiv, has_torchvision_roi_align, sympy_product
+from .utils import ceildiv, sympy_product
 from .virtualized import ops, V
 
 log = logging.getLogger(__name__)
@@ -1165,10 +1165,6 @@ def require_contiguous(_, *args, **kwargs):
     return args, kwargs
 
 
-if has_torchvision_roi_align():
-    make_fallback(torch.ops.torchvision.roi_align)
-
-
 def constrain_to_fx_strides(fx_node, *args, **kwargs):
     def apply_constraint(arg, fx_arg):
         if isinstance(arg, ir.IRNode):
@@ -1183,6 +1179,9 @@ def apply_constraint(arg, fx_arg):
 
 # TODO(jansel): we should implement decomps or lowerings for these
 # https://github.com/pytorch/torchdynamo/issues/327
+FALLBACK_ALLOW_LIST = {
+    "torchvision::roi_align",
+}
 make_fallback(aten._adaptive_avg_pool2d_backward, require_dense)
 make_fallback(aten.convolution_backward, constrain_to_fx_strides)
 make_fallback(aten._cudnn_rnn, require_dense)