diff --git a/src/dialect/onnx/onnx_ops.cpp b/src/dialect/onnx/onnx_ops.cpp
index f98c5f0..82c37da 100644
--- a/src/dialect/onnx/onnx_ops.cpp
+++ b/src/dialect/onnx/onnx_ops.cpp
@@ -42,6 +42,11 @@ static int64_t ArrayAttrIntVal(Optional<ArrayAttr> a, int i) {
   return (a.getValue().getValue()[i]).cast<IntegerAttr>().getInt();
 }
 
+// Returns the ConstantOp which defines an MLIR Value or null.
+static mlir::ONNXConstantOp getONNXConstantOp(Value value) {
+  return dyn_cast_or_null<mlir::ONNXConstantOp>(value.getDefiningOp());
+}
+
 //===----------------------------------------------------------------------===//
 // Get reduction type
 //===----------------------------------------------------------------------===//
@@ -861,26 +866,48 @@ void ONNXReshapeOp::inferShapes() {
   if (outputRank < 0)
     emitError("Shape tensor must have constant shape");
 
+  // Compute total number of elements.
+  int64_t totalInputSize = 1;
+  for(auto inputDim : inputTensorTy.getShape())
+    totalInputSize *= inputDim;
+
   // Check if second argument of ReshapeOp is a constant.
-  // Get operation that defines the second argument. If this operation is a
-  // `ConstantTensor` operation, the shape of this `Reshape` operation
-  // resides in the `value` attribute of the `ConstantTensor` operation.
-  auto *secondArgDefiningOp = (*getODSOperands(1).begin()).getDefiningOp();
-  auto constantOp =
-      dyn_cast_or_null<mlir::ONNXConstantOp>(secondArgDefiningOp);
+  auto constantOp = getONNXConstantOp(shape());
 
   SmallVector<int64_t, 2> dims(outputRank, -1);
   if (constantOp) {
+    // Cast attribute to ArrayAttr.
     ArrayAttr valueAttribute = constantOp.valueAttr().dyn_cast<ArrayAttr>();
-
     if (!valueAttribute)
       emitError("ArrayAttr expected");
 
-    if (valueAttribute.getValue().size() != outputRank)
+    if (ArrayAttrSize(valueAttribute) != outputRank)
       emitError("Constant value must have same rank as output");
 
-    for (int i=0; i<outputRank; ++i)
-      dims[i] = valueAttribute.getValue()[i].cast<IntegerAttr>().getInt();
+    int64_t numberOfDynamicInputs = 0;
+    int64_t totalKnownDimsSize = 1;
+    int64_t dynamicValueIndex = -1;
+    for (int i=0; i<outputRank; ++i) {
+      // Set output dimension.
+      dims[i] = ArrayAttrIntVal(valueAttribute, i);
+      if (dims[i] == 0)
+        dims[i] = inputTensorTy.getShape()[i];
+
+      if (dims[i] < 0) {
+        numberOfDynamicInputs++;
+        dynamicValueIndex = i;
+      } else {
+        totalKnownDimsSize *= dims[i];
+      }
+    }
+
+    // If the number of dynamic inputs is 1 then deduce the missing value
+    // based on the total input size. The total input size must be greater
+    // than 0 i.e. all constant dimensions.
+    // TODO: Support dynamic input dimensons.
+    if (numberOfDynamicInputs == 1 && totalKnownDimsSize > 0 &&
+        totalInputSize > 0)
+      dims[dynamicValueIndex] = totalInputSize / totalKnownDimsSize;
   }
 
   getResult().setType(
@@ -970,6 +997,8 @@ void ONNXReduceSumOp::inferShapes() {
   getResult().setType(getReductionOutputType(operandTy, axes(), keepdims()));
 }
 
+//===----------------------------------------------------------------------===//
+
 // Conv
 
 // For this operation, we define the attributes once in the original Conv
@@ -995,6 +1024,7 @@ void ONNXConvNoBiasOp::inferShapes() {
   auto xShape = xTy.getShape();
   auto weightTy = W().getType().cast<RankedTensorType>();
   auto weightShape = weightTy.getShape();
+  auto builder = mlir::Builder(this->getContext());
 
   // Lowest supported convolution is a one dimensional convolution.
   if (xShape.size() < 3)
@@ -1006,6 +1036,11 @@ void ONNXConvNoBiasOp::inferShapes() {
 
   // Group is a required attribute and should have default value of 1.
   int64_t group = ONNXConvNoBiasOp::group().getSExtValue();
+
+  // Check if the attribute actually exists. If it does not then add it.
+  if (!groupAttr())
+    groupAttr(builder.getI64IntegerAttr(group));
+
   // Check that the X.shape[1] == (W.shape[1] * group) == C condition holds.
   if (xShape[1] != -1 && weightShape[1] != -1 &&
       xShape[1] != (weightShape[1] * group))
diff --git a/test/mlir/onnx/onnx_shape_inference.mlir b/test/mlir/onnx/onnx_shape_inference.mlir
index 14e3a8c..ec2f63d 100644
--- a/test/mlir/onnx/onnx_shape_inference.mlir
+++ b/test/mlir/onnx/onnx_shape_inference.mlir
@@ -282,64 +282,74 @@ func @test_conv_no_bias_11(%arg0 : tensor<1x2x32x64xf32>, %arg1 : tensor<5x2x6x7
 func @test_PadConstantValuePad_1(%arg0 : tensor<16x13xf32>) -> tensor<*xf32> {
   %0 = "onnx.PadConstantValuePad"(%arg0) {constant_value = 0.000000e+00 : f32, mode = "constant", pads = [0, 0, 2, 0]} : (tensor<16x13xf32>) -> tensor<*xf32>
   "std.return"(%0) : (tensor<*xf32>) -> ()
+
+  // CHECK-LABEL: test_PadConstantValuePad_1
+  // CHECK: [[RES:%.+]] = "onnx.PadConstantValuePad"(%arg0) {constant_value = 0.000000e+00 : f32, mode = "constant", pads = [0, 0, 2, 0]} : (tensor<16x13xf32>) -> tensor<18x13xf32>
+  // CHECK: return [[RES]] : tensor<18x13xf32>
 }
-// CHECK-LABEL: test_PadConstantValuePad_1
-// CHECK: [[RES:%.+]] = "onnx.PadConstantValuePad"(%arg0) {constant_value = 0.000000e+00 : f32, mode = "constant", pads = [0, 0, 2, 0]} : (tensor<16x13xf32>) -> tensor<18x13xf32>
-// CHECK: return [[RES]] : tensor<18x13xf32>
 
 /// Test PadConstantPad_1
 func @test_PadConstantPad_1(%arg0 : tensor<16x13xf32>, %arg1 : tensor<*xf32>) -> tensor<*xf32> {
   %0 = "onnx.PadConstantPad"(%arg0, %arg1) {mode = "constant", pads = [0, 3, 2, 1]} : (tensor<16x13xf32>, tensor<*xf32>) -> tensor<*xf32>
   "std.return"(%0) : (tensor<*xf32>) -> ()
+  // CHECK-LABEL: test_PadConstantPad_1
+  // CHECK: [[RES:%.+]] = "onnx.PadConstantPad"(%arg0, %arg1) {mode = "constant", pads = [0, 3, 2, 1]} : (tensor<16x13xf32>, tensor<*xf32>) -> tensor<18x17xf32>
+  // CHECK: return [[RES]] : tensor<18x17xf32>
 }
-// CHECK-LABEL: test_PadConstantPad_1
-// CHECK: [[RES:%.+]] = "onnx.PadConstantPad"(%arg0, %arg1) {mode = "constant", pads = [0, 3, 2, 1]} : (tensor<16x13xf32>, tensor<*xf32>) -> tensor<18x17xf32>
-// CHECK: return [[RES]] : tensor<18x17xf32>
 
 /// Test PadConstantPad_2
 func @test_PadConstantPad_2(%arg0 : tensor<16x?xf32>, %arg1 : tensor<*xf32>) -> tensor<*xf32> {
   %0 = "onnx.PadConstantPad"(%arg0, %arg1) {mode = "constant", pads = [0, 3, 2, 1]} : (tensor<16x?xf32>, tensor<*xf32>) -> tensor<*xf32>
   "std.return"(%0) : (tensor<*xf32>) -> ()
+
+  // CHECK-LABEL: test_PadConstantPad_2
+  // CHECK: [[RES:%.+]] = "onnx.PadConstantPad"(%arg0, %arg1) {mode = "constant", pads = [0, 3, 2, 1]} : (tensor<16x?xf32>, tensor<*xf32>) -> tensor<18x?xf32>
+  // CHECK: return [[RES]] : tensor<18x?xf32>
 }
-// CHECK-LABEL: test_PadConstantPad_2
-// CHECK: [[RES:%.+]] = "onnx.PadConstantPad"(%arg0, %arg1) {mode = "constant", pads = [0, 3, 2, 1]} : (tensor<16x?xf32>, tensor<*xf32>) -> tensor<18x?xf32>
-// CHECK: return [[RES]] : tensor<18x?xf32>
+
+//===----------------------------------------------------------------------===//
+/// Test for constant op.
+//===----------------------------------------------------------------------===//
 
 /// Test ConstantOp shape inference for 1-D dense tensor.
 func @test_constant_dense_1d_value() -> tensor<*xf32> {
   %0 = "onnx.Constant"() {value = dense<[0.0, 1.0, 2.0]> : tensor<3xf32>} : () -> tensor<*xf32>
   "std.return"(%0) : (tensor<*xf32>) -> ()
+
+  // CHECK-LABEL: test_constant_dense_1d_value
+  // CHECK: [[RES:%.+]] = "onnx.Constant"() {value = dense<[0.000000e+00, 1.000000e+00, 2.000000e+00]> : tensor<3xf32>} : () -> tensor<3xf32>
+  // CHECK: return [[RES]] : tensor<3xf32>
 }
-// CHECK-LABEL: test_constant_dense_1d_value
-// CHECK: [[RES:%.+]] = "onnx.Constant"() {value = dense<[0.000000e+00, 1.000000e+00, 2.000000e+00]> : tensor<3xf32>} : () -> tensor<3xf32>
-// CHECK: return [[RES]] : tensor<3xf32>
 
 /// Test ConstantOp shape inference for 2-D dense tensor.
 func @test_constant_dense_2d_value() -> tensor<*xf32> {
   %0 = "onnx.Constant"() {value = dense<[[0.0, 0.0], [1.0, 1.1], [2.0, 2.1]]> : tensor<3x2xf32>} : () -> tensor<*xf32>
   "std.return"(%0) : (tensor<*xf32>) -> ()
+
+  // CHECK-LABEL: test_constant_dense_2d_value
+  // CHECK: [[RES:%.+]] = "onnx.Constant"() {value = dense<{{\[}}[0.000000e+00, 0.000000e+00], [1.000000e+00, 1.100000e+00], [2.000000e+00, 2.100000e+00{{\]}}]> : tensor<3x2xf32>} : () -> tensor<3x2xf32>
+  // CHECK: return [[RES]] : tensor<3x2xf32>
 }
-// CHECK-LABEL: test_constant_dense_2d_value
-// CHECK: [[RES:%.+]] = "onnx.Constant"() {value = dense<{{\[}}[0.000000e+00, 0.000000e+00], [1.000000e+00, 1.100000e+00], [2.000000e+00, 2.100000e+00{{\]}}]> : tensor<3x2xf32>} : () -> tensor<3x2xf32>
-// CHECK: return [[RES]] : tensor<3x2xf32>
 
 /// Test ConstantOp shape inference for 1-D sparse tensor.
 func @test_constant_sparse_1d_value() -> tensor<*xf32> {
   %0 = "onnx.Constant"() {sparse_value = sparse<[[0]], [1.0]> : tensor<3xf32>} : () -> tensor<*xf32>
   "std.return"(%0) : (tensor<*xf32>) -> ()
+
+  // CHECK-LABEL: test_constant_sparse_1d_value
+  // CHECK: [[RES:%.+]] = "onnx.Constant"() {sparse_value = sparse<0, 1.000000e+00> : tensor<3xf32>} : () -> tensor<3xf32>
+  // CHECK: return [[RES]] : tensor<3xf32>
 }
-// CHECK-LABEL: test_constant_sparse_1d_value
-// CHECK: [[RES:%.+]] = "onnx.Constant"() {sparse_value = sparse<0, 1.000000e+00> : tensor<3xf32>} : () -> tensor<3xf32>
-// CHECK: return [[RES]] : tensor<3xf32>
 
 /// Test ConstantOp shape inference for 2-D sparse tensor.
 func @test_constant_sparse_2d_value() -> tensor<*xf32> {
   %0 = "onnx.Constant"() {sparse_value = sparse<[[0, 1]], [2.0]> : tensor<3x2xf32>} : () -> tensor<*xf32>
   "std.return"(%0) : (tensor<*xf32>) -> ()
+
+  // CHECK-LABEL: test_constant_sparse_2d_value
+  // CHECK: [[RES:%.+]] = "onnx.Constant"() {sparse_value = sparse<{{\[}}[0, 1{{\]}}], 2.000000e+00> : tensor<3x2xf32>} : () -> tensor<3x2xf32>
+  // CHECK: return [[RES]] : tensor<3x2xf32>
 }
-// CHECK-LABEL: test_constant_sparse_2d_value
-// CHECK: [[RES:%.+]] = "onnx.Constant"() {sparse_value = sparse<{{\[}}[0, 1{{\]}}], 2.000000e+00> : tensor<3x2xf32>} : () -> tensor<3x2xf32>
-// CHECK: return [[RES]] : tensor<3x2xf32>
 
 /// Test the default behavior of Average Pool with no padding (pad are set but shoud be ignored)
 func @test_default_averagepool(%arg0 : tensor<5x5x32x32xf32>) -> tensor<*xf32> {
@@ -411,3 +421,45 @@ func @test_default_averagepool_strides_nonunifpad_ceil(%arg0 : tensor<5x5x30x32x
   // CHECK: return [[RES]] : tensor<5x5x16x16xf32>
 }
 
+//===----------------------------------------------------------------------===//
+/// Test the reshape op inference when constants are present.
+//===----------------------------------------------------------------------===//
+
+func @test_reshape_dynamic(%arg0 : tensor<5x5x1x32xf32>, %arg1 : tensor<4xi32>) -> tensor<*xf32> {
+  %0 = "onnx.Reshape"(%arg0, %arg1) : (tensor<5x5x1x32xf32>, tensor<4xi32>) -> tensor<*xf32>
+  "std.return"(%0) : (tensor<*xf32>) -> ()
+
+  // CHECK-LABEL: test_reshape_dynamic
+  // CHECK: [[RES:%.+]] = "onnx.Reshape"(%arg0, %arg1) : (tensor<5x5x1x32xf32>, tensor<4xi32>) -> tensor<?x?x?x?xf32>
+  // CHECK: return [[RES]] : tensor<?x?x?x?xf32>
+}
+
+func @test_reshape_1(%arg0 : tensor<5x5x1x32xf32>) -> tensor<*xf32> {
+  %0 = "onnx.Constant"() {sparse_value = [], value = [5, 5, 16, 2] } : () -> tensor<4xi32>
+  %1 = "onnx.Reshape"(%arg0, %0) : (tensor<5x5x1x32xf32>, tensor<4xi32>) -> tensor<*xf32>
+  "std.return"(%1) : (tensor<*xf32>) -> ()
+
+  // CHECK-LABEL: test_reshape_1
+  // CHECK: [[RES:%.+]] = "onnx.Reshape"(%arg0, %0) : (tensor<5x5x1x32xf32>, tensor<4xi32>) -> tensor<5x5x16x2xf32>
+  // CHECK: return [[RES]] : tensor<5x5x16x2xf32>
+}
+
+func @test_reshape_2(%arg0 : tensor<5x5x1x32xf32>) -> tensor<*xf32> {
+  %0 = "onnx.Constant"() {sparse_value = [], value = [-1, 16, 2] } : () -> tensor<3xi32>
+  %1 = "onnx.Reshape"(%arg0, %0) : (tensor<5x5x1x32xf32>, tensor<3xi32>) -> tensor<*xf32>
+  "std.return"(%1) : (tensor<*xf32>) -> ()
+
+  // CHECK-LABEL: test_reshape_2
+  // CHECK: [[RES:%.+]] = "onnx.Reshape"(%arg0, %0) : (tensor<5x5x1x32xf32>, tensor<3xi32>) -> tensor<25x16x2xf32>
+  // CHECK: return [[RES]] : tensor<25x16x2xf32>
+}
+
+func @test_reshape_3(%arg0 : tensor<5x5x1x32xf32>) -> tensor<*xf32> {
+  %0 = "onnx.Constant"() {sparse_value = [], value = [-1, 0, 2] } : () -> tensor<3xi32>
+  %1 = "onnx.Reshape"(%arg0, %0) : (tensor<5x5x1x32xf32>, tensor<3xi32>) -> tensor<*xf32>
+  "std.return"(%1) : (tensor<*xf32>) -> ()
+
+  // CHECK-LABEL: test_reshape_3
+  // CHECK: [[RES:%.+]] = "onnx.Reshape"(%arg0, %0) : (tensor<5x5x1x32xf32>, tensor<3xi32>) -> tensor<80x5x2xf32>
+  // CHECK: return [[RES]] : tensor<80x5x2xf32>
+}