Add useXLA flag to TFFunction.execute.

Author: bgogul

Sources/TensorFlow/Core/LazyTensorTFFunctionBuilder.swift

@@ -269,7 +269,7 @@ class TFFunction {
         checkOk(status)
     }
 
-    func execute(_ inputs: [TFETensorHandle]) -> [TFETensorHandle] {
+    func execute(_ inputs: [TFETensorHandle], useXLA: Bool = false) -> [TFETensorHandle] {
         let status: CTFStatus = TF_NewStatus()
         defer { TF_DeleteStatus(status) }
 
@@ -286,6 +286,11 @@ class TFFunction {
             checkOk(status)
         }
 
+        if useXLA {
+            debugLog("Enabling XLA compilation")
+            TFE_OpSetAttrBool(eagerOp, "_XlaCompile", 1)
+        }
+
         for input in inputs {
             TFE_OpAddInput(eagerOp, input._cTensorHandle, status)
             checkOk(status)