[Shape Inference] Try to fold the operation before attempting to infer its shape.

If the operation can be folded to a constant, it is trivial to infer the shape after wards. This also enables other cases that may rely on folding for the inference to be successful, e.g. tf.Shape+tf.Conv2DBackpropInput.

PiperOrigin-RevId: 281904440
Change-Id: Id7374b6f20750799b97d2419aa0113d39c30ace3

tensorflow/compiler/mlir/tensorflow/tests/shape_inference.mlir

@@ -34,15 +34,29 @@ module attributes {tf.versions = {bad_consumers = [], min_consumer = 0 : i32, pr
     return %1 : tensor<*xf32>
   }
 
+// Tests the case where an inference opportunity relies on folding.
+
+// CHECK-LABEL: func @simple_folding
+  func @simple_folding(%arg0: tensor<1x1x1x1xi32>, %arg1: tensor<1x1x1x1xf32>) -> tensor<?x?x?x?xf32> {
+// CHECK: %[[CST:.*]] = "tf.Const"{{.*}} {value = dense<1> : tensor<4xi32>} : () -> tensor<4xi32>
+// CHECK: %[[CONV:.*]] = "tf.Conv2DBackpropInput"(%[[CST]]
+// CHECK-SAME: (tensor<4xi32>, tensor<1x1x1x1xf32>, tensor<1x1x1x1xf32>) -> tensor<1x1x1x1xf32>
+// CHECK: %[[CAST:.*]] = "tf.Cast"(%[[CONV]]) {{.*}} : (tensor<1x1x1x1xf32>) -> tensor<?x?x?x?xf32>
+// CHECK: return %[[CAST]] : tensor<?x?x?x?xf32>
+    %0 = "tf.Shape"(%arg0) : (tensor<1x1x1x1xi32>) -> tensor<4xi32>
+    %1 = "tf.Conv2DBackpropInput"(%0, %arg1, %arg1) {
+      padding = "VALID", strides = [1, 1, 1, 1]
+    } : (tensor<4xi32>, tensor<1x1x1x1xf32>, tensor<1x1x1x1xf32>) -> tensor<?x?x?x?xf32>
+    return %1 : tensor<?x?x?x?xf32>
+  }
+
 // Tests the case where an op's shape function returns non-fully-defined shapes.
 
 // CHECK-LABEL: func @op_non_fully_defined_shape_fn
-  func @op_non_fully_defined_shape_fn() -> tensor<?xi32> {
+  func @op_non_fully_defined_shape_fn(%arg0: tensor<0xi32>, %arg1: tensor<0xi32>) -> tensor<?xi32> {
-    %0 = "tf.Const"() {dtype = "tfdtype$DT_INT32", value = dense<[]> : tensor<0xi32>} : () -> tensor<0xi32>
-    %1 = "tf.Const"() {dtype = "tfdtype$DT_INT32", value = dense<[]> : tensor<0xi32>} : () -> tensor<0xi32>
     // CHECK: tf.BroadcastGradientArgs
     // CHECK-SAME: (tensor<0xi32>, tensor<0xi32>) -> (tensor<?xi32>, tensor<?xi32>)
-    %2:2 = "tf.BroadcastGradientArgs"(%0, %1) {T = "tfdtype$DT_INT32", name = "BroadcastGradientArgs"} : (tensor<0xi32>, tensor<0xi32>) -> (tensor<?xi32>, tensor<?xi32>)
+    %2:2 = "tf.BroadcastGradientArgs"(%arg0, %arg1) {T = "tfdtype$DT_INT32", name = "BroadcastGradientArgs"} : (tensor<0xi32>, tensor<0xi32>) -> (tensor<?xi32>, tensor<?xi32>)
     return %2#0 : tensor<?xi32>
   }
 

tensorflow/compiler/mlir/tensorflow/transforms/shape_inference.cc

@@ -32,6 +32,7 @@ limitations under the License.
 #include "mlir/Pass/PassRegistry.h"  // TF:local_config_mlir
 #include "mlir/Support/LLVM.h"  // TF:local_config_mlir
 #include "mlir/Support/LogicalResult.h"  // TF:local_config_mlir
+#include "mlir/Transforms/FoldUtils.h"  // TF:local_config_mlir
 #include "tensorflow/compiler/mlir/tensorflow/ir/tf_executor.h"
 #include "tensorflow/compiler/mlir/tensorflow/ir/tf_ops.h"
 #include "tensorflow/compiler/mlir/tensorflow/transforms/passes.h"
@@ -213,9 +214,13 @@ bool InferShapeForSingleOperation(Operation* op, Dialect* tf_dialect,
 
 LogicalResult InferShapeUntilFixPoint(Region* region, int64_t graph_version,
                                       int64_t max_iteration) {
-  Dialect* tf_dialect = region->getContext()->getRegisteredDialect(
+  MLIRContext* ctx = region->getContext();
-      TensorFlowDialect::getDialectNamespace());
+  Dialect* tf_dialect = ctx->getRegisteredDialect<TensorFlowDialect>();
+
+  // An operation folder that is used to attempt folding before inference.
+  OperationFolder folder(ctx);
   bool changed = true;
+
   // TODO(aminim): we could have a more efficient traversal by guiding the
   // traversal with a worklist and reconsider only the nodes for which an
   // operand type was inferred. This would need to be careful if working on a
@@ -225,15 +230,17 @@ LogicalResult InferShapeUntilFixPoint(Region* region, int64_t graph_version,
     LLVM_DEBUG(llvm::dbgs()
                << "Shape inference, iteration " << iteration << "\n");
     region->walk([&](Operation* op) {
-      if (op->getDialect() == tf_dialect)
+      if (op->getDialect() != tf_dialect) return;
+
+      // Before attempting inference, just try to fold the operation.
+      if (failed(folder.tryToFold(op)))
         changed |= InferShapeForSingleOperation(op, tf_dialect, graph_version);
     });
   }
   if (changed) {
-    region->getParentOp()->emitWarning()
+    return region->getParentOp()->emitWarning()
-        << "Shape inference did not reach stable state after " << max_iteration
+           << "Shape inference did not reach stable state after "
-        << " iterations";
+           << max_iteration << " iterations";
-    return failure();
   }
   return success();
 }