Add warning if both -Xuse-ir and -Xuse-old-backend are passed

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/jvmArguments.kt

@@ -171,6 +171,16 @@ fun CompilerConfiguration.configureAdvancedJvmOptions(arguments: K2JVMCompilerAr
             } else {
                 arguments.useIR && !arguments.useOldBackend
             }
+
+    if (arguments.useIR && arguments.useOldBackend) {
+        messageCollector.report(
+            STRONG_WARNING,
+            "Both -Xuse-ir and -Xuse-old-backend are passed. This is an inconsistent configuration. " +
+                    "The compiler will use the ${if (useIR) "JVM IR" else "old JVM"} backend"
+        )
+    }
+    messageCollector.report(LOGGING, "Using ${if (useIR) "JVM IR" else "old JVM"} backend")
+
     put(JVMConfigurationKeys.IR, useIR)
 
     val abiStability = JvmAbiStability.fromStringOrNull(arguments.abiStability)

compiler/testData/cli/jvm/bothJvmIrAndOldBackend.args

@@ -0,0 +1,5 @@
+$TESTDATA_DIR$/simple.kt
+-d
+$TEMP_DIR$
+-Xuse-ir
+-Xuse-old-backend

compiler/testData/cli/jvm/bothJvmIrAndOldBackend.out

@@ -0,0 +1,2 @@
+warning: both -Xuse-ir and -Xuse-old-backend are passed. This is an inconsistent configuration. The compiler will use the old JVM backend
+OK

compiler/testData/integration/ant/jvm/verbose/build.log.expected

@@ -4,6 +4,7 @@ Buildfile: [TestData]/build.xml
 build:
   [kotlinc] Compiling [[TestData]/hello.kt] => [[Temp]/hello.jar]
   [kotlinc] logging: using Kotlin home directory [KotlinProjectHome]/dist/kotlinc
+  [kotlinc] logging: using old JVM backend
   [kotlinc] logging: configuring the compilation environment
   [kotlinc] logging: configure scripting: Added template org.jetbrains.kotlin.mainKts.MainKtsScript from [[CompilerLib]/kotlin-main-kts.jar, [CompilerLib]/kotlin-reflect.jar, [CompilerLib]/kotlin-script-runtime.jar, [CompilerLib]/kotlin-stdlib.jar]
 

compiler/tests-gen/org/jetbrains/kotlin/cli/CliTestGenerated.java

@@ -101,6 +101,11 @@ public class CliTestGenerated extends AbstractCliTest {
             runTest("compiler/testData/cli/jvm/argumentPassedMultipleTimes.args");
         }
 
+        @TestMetadata("bothJvmIrAndOldBackend.args")
+        public void testBothJvmIrAndOldBackend() throws Exception {
+            runTest("compiler/testData/cli/jvm/bothJvmIrAndOldBackend.args");
+        }
+
         @TestMetadata("classAndFileClassClash.args")
         public void testClassAndFileClassClash() throws Exception {
             runTest("compiler/testData/cli/jvm/classAndFileClassClash.args");