Support onnx.If (#2825)

This is probably a decent PR for learning about blocks and regions.

If you're here to learn about that, consider also looking at
lib/Conversion/TorchToSCF/TorchToSCF.cpp

While this doesn't include an e2e test, it is tested downstream in
https://github.com/nod-ai/SHARK-TestSuite/blob/main/e2eshark/onnx/operators/If/model.py

---------

Co-authored-by: Xida Ren <xida.ren.dev@gmail.com>

include/torch-mlir/Conversion/TorchOnnxToTorch/Patterns.h

@@ -97,6 +97,31 @@ struct OpBinder {
     return success();
   }
 
+  ParseResult tensorResultTypes(llvm::SmallVector<mlir::Type> &typeList) {
+    for (auto result : op->getResults()) {
+      auto t = toValidTensorType(result.getType());
+      if (!t)
+        return failure();
+      typeList.push_back(t);
+    }
+    return success();
+  }
+
+  // The importer imports Onnx.GraphProto attributes as regions attached to the
+  // op.
+  ParseResult getRegionAtIndex(mlir::Region *&region, int64_t idx) {
+    if (idx >= op->getNumRegions())
+      return failure();
+
+    region = &op->getRegion(idx);
+
+    if (region == nullptr) {
+      return failure();
+    }
+
+    return success();
+  }
+
   ParseResult tensorResultTypeAtIndex(Torch::ValueTensorType &typeIdx,
                                       int64_t idx) {
     if (idx >= op->getNumResults())

lib/Conversion/TorchOnnxToTorch/DefaultDomainGtoP.cpp

@@ -158,6 +158,60 @@ void mlir::torch::onnx_c::populateDefaultDomainGtoP(
             alignCorners);
         return success();
       });
+  patterns.onOp(
+      "If", 1, [](OpBinder binder, ConversionPatternRewriter &rewriter) {
+        Value conditionTensor;
+        if (binder.tensorOperand(conditionTensor)) {
+          return rewriter.notifyMatchFailure(binder.op,
+                                             "condition bind failure");
+        }
+
+        auto conditionType =
+            conditionTensor.getType().cast<Torch::ValueTensorType>();
+        if (!conditionType || conditionType.getSizes().size() != 1)
+          return rewriter.notifyMatchFailure(
+              binder.op, "condition must have one single element per "
+                         "https://onnx.ai/onnx/operators/onnx__If.html");
+        auto conditionInt = rewriter.create<Torch::AtenItemOp>(
+            binder.getLoc(), rewriter.getType<Torch::IntType>(),
+            conditionTensor);
+        auto conditionBool = rewriter.create<Torch::AtenBoolIntOp>(
+            binder.getLoc(), rewriter.getType<Torch::BoolType>(), conditionInt);
+
+        llvm::SmallVector<mlir::Type> resultTypes;
+        if (binder.tensorResultTypes(resultTypes)) {
+          return rewriter.notifyMatchFailure(binder.op,
+                                             "result type bind failure");
+        }
+
+        Region *thenRegion, *elseRegion;
+        if (binder.getRegionAtIndex(elseRegion, 0) ||
+            binder.getRegionAtIndex(thenRegion, 1)) {
+          return rewriter.notifyMatchFailure(binder.op, "region bind failure");
+        }
+
+        auto primIfOp = rewriter.create<Torch::PrimIfOp>(
+            binder.getLoc(), TypeRange(resultTypes), conditionBool);
+
+        auto inlineIfCase = [&](Region &srcRegion, Region &dstRegion) {
+          rewriter.inlineRegionBefore(srcRegion, dstRegion, dstRegion.begin());
+        };
+        inlineIfCase(*thenRegion, primIfOp.getThenRegion());
+        inlineIfCase(*elseRegion, primIfOp.getElseRegion());
+
+        auto replaceTerminator = [&](Region &region) {
+          PatternRewriter::InsertionGuard guard(rewriter);
+          Operation *terminator = region.front().getTerminator();
+          rewriter.setInsertionPoint(terminator);
+          rewriter.replaceOpWithNewOp<Torch::PrimIfYieldOp>(
+              terminator, terminator->getOperands());
+        };
+        replaceTerminator(primIfOp.getThenRegion());
+        replaceTerminator(primIfOp.getElseRegion());
+
+        rewriter.replaceOp(binder.op, primIfOp.getResults());
+        return success();
+      });
   patterns.onOp("Less", 13,
                 [](OpBinder binder, ConversionPatternRewriter &rewriter) {
                   Torch::ValueTensorType resultType;

projects/pt1/e2e_testing/xfail_sets.py

@@ -2562,16 +2562,12 @@ ONNX_XFAIL_SET = {
     "_ConvolutionDeprecated2DCudnnModule_basic",
     "_ConvolutionDeprecated2DDeterministicModule_basic",
     "_SoftmaxModule_basic",
+    # Failure - onnx_import
     # Failure - onnx_lowering: onnx.AveragePool
     "AdaptiveAvgPool1dGeneralDynamicNoBatches_basic",
-    # Failure - onnx_lowering: onnx.If
+    # these diagonal modules are currently failing due to dynamic shape.
-    "DiagonalModule_basic",
+    # We are currently testing aten.diagonal using DiagonalWithStaticShapeModule instead.
-    "DiagonalModule_nonsquare",
+    # when the issue is fixed, please remove DiagonalWithStaticShapeModule as well as the xfails here.
-    "DiagonalModule_transposed",
-    "DiagonalModule_with_dims",
-    "DiagonalModule_with_dims_and_offset",
-    "DiagonalModule_with_negative_dims",
-    "DiagonalModule_with_offset",
     "TileBigDimsSizeModule_basic",
     "TileSmallDimsSizeModule_basic",
     # Failure - onnx_lowering: onnx.MaxPool

projects/pt1/python/torch_mlir_e2e_test/test_suite/diagonal.py

@@ -39,6 +39,37 @@ def DiagonalModule_nonsquare(module, tu: TestUtils):
 # ==============================================================================
 
 
+class DiagonalWithStaticShapeModule(torch.nn.Module):
+    """
+    Diagonal with static shape. The other diagonal modules are failing in onnx
+    because DecomoposeAtenEyeMOp requires constants n, m, which are only constant
+    when the shape is static.
+
+    Please remove this module and associated test once the issue is fixed.
+    """
+
+    def __init__(self):
+        super().__init__()
+
+    @export
+    @annotate_args(
+        [
+            None,
+            ([5, 9], torch.float32, True),
+        ]
+    )
+    def forward(self, a):
+        return torch.ops.aten.diagonal(a)
+
+
+@register_test_case(module_factory=lambda: DiagonalWithStaticShapeModule())
+def DiagonalWithStaticShapeModule_basic(module, tu: TestUtils):
+    module.forward(tu.rand(5, 9))
+
+
+# ==============================================================================
+
+
 class DiagonalTransposedModule(torch.nn.Module):
     def __init__(self):
         super().__init__()

python/torch_mlir/extras/onnx_importer.py

@@ -347,8 +347,14 @@ class NodeImporter:
                 continue
             elif handler is False:
                 # Active error.
+                # try matching attribute type ID to name for a more descriptive error message
+                try:
+                    attr_type_name = onnx.AttributeProto.AttributeType.Name(attr_type)
+                except ValueError:
+                    attr_type_name = "UNKNOWN"
                 raise OnnxImportError(
-                    f"ONNX importer does not support generic node attribute type {attr_type}. "
+                    f"ONNX importer does not support generic node attribute type {attr_type_name} "
+                    f"with ID {attr_type}. "
                     f"This likely means that this is a special node which requires specific "
                     f"handling in the importer: {onnx_attr}"
                 )

test/Conversion/TorchOnnxToTorch/ops/if.mlir

@@ -0,0 +1,20 @@
+// RUN: torch-mlir-opt <%s --split-input-file -convert-torch-onnx-to-torch | FileCheck %s
+
+// CHECK-LABEL: func.func @test_ifop_basic
+// CHECK: %[[IF:.*]] = torch.prim.If %{{.*}} -> (!torch.vtensor<[1],f32>)
+// CHECK-DAG: %[[SUB:.*]] = torch.aten.sub.Tensor %arg1, %arg2, %{{.*}} : !torch.vtensor<[1],f32>, !torch.vtensor<[1],f32>, !torch.int -> !torch.vtensor<[1],f32>
+// CHECK-DAG: torch.prim.If.yield %[[SUB]] : !torch.vtensor<[1],f32>
+// CHECK-DAG: } else {
+// CHECK-DAG: %[[ADD:.*]] = torch.aten.add.Tensor %arg1, %arg2, %{{.*}} : !torch.vtensor<[1],f32>, !torch.vtensor<[1],f32>, !torch.int -> !torch.vtensor<[1],f32>
+// CHECK-DAG: torch.prim.If.yield %[[ADD]] : !torch.vtensor<[1],f32>
+func.func @test_ifop_basic(%arg0: !torch.vtensor<[1],i1>, %arg1: !torch.vtensor<[1],f32>, %arg2: !torch.vtensor<[1],f32>) -> !torch.vtensor<[1],f32> attributes {torch.onnx_meta.ir_version = 9 : si64, torch.onnx_meta.opset_version = 20 : si64, torch.onnx_meta.producer_name = "conditional_example", torch.onnx_meta.producer_version = ""} {
+  %none = torch.constant.none
+  %0 = torch.operator "onnx.If"(%arg0) : (!torch.vtensor<[1],i1>) -> !torch.vtensor<[1],f32> {
+    %1 = torch.operator "onnx.Add"(%arg1, %arg2) : (!torch.vtensor<[1],f32>, !torch.vtensor<[1],f32>) -> !torch.vtensor<[1],f32>
+    torch.operator_terminator %1 : !torch.vtensor<[1],f32>
+  }, {
+    %1 = torch.operator "onnx.Sub"(%arg1, %arg2) : (!torch.vtensor<[1],f32>, !torch.vtensor<[1],f32>) -> !torch.vtensor<[1],f32>
+    torch.operator_terminator %1 : !torch.vtensor<[1],f32>
+  }
+  return %0 : !torch.vtensor<[1],f32>
+}