diff --git a/compiler/testData/integration/ant/jvm/additionalArguments/build.xml b/compiler/testData/integration/ant/jvm/additionalArguments/build.xml
index e751a767a76..01bcce8c2c4 100644
--- a/compiler/testData/integration/ant/jvm/additionalArguments/build.xml
+++ b/compiler/testData/integration/ant/jvm/additionalArguments/build.xml
@@ -11,6 +11,7 @@
         <javac srcdir="${test.data}" destdir="${temp}" includeantruntime="false">
             <withKotlin>
                 <compilerarg value="-version"/>
+                <compilerarg line="-Xuse-fir-lt=false"/>
             </withKotlin>
         </javac>
     </target>
diff --git a/compiler/testData/integration/ant/jvm/doNotFailOnError/build.log.expected b/compiler/testData/integration/ant/jvm/doNotFailOnError/build.log.expected
index bf3f570ca21..2d5c9b71d03 100644
--- a/compiler/testData/integration/ant/jvm/doNotFailOnError/build.log.expected
+++ b/compiler/testData/integration/ant/jvm/doNotFailOnError/build.log.expected
@@ -13,6 +13,12 @@ build:
     [javac] [TestData]/incorrectKotlinCode.kt:4:1: error: expecting ')'
     [javac]
     [javac] ^
+    [javac] [TestData]/incorrectKotlinCode.kt:4:1: error: a type annotation is required on a value parameter
+    [javac]
+    [javac] ^
+    [javac] [TestData]/incorrectKotlinCode.kt:3:1: error: function 'main' must have a body
+    [javac] fun main(
+    [javac] ^
   [kotlinc] Compiling [[TestData]] => [[Temp]]
   [kotlinc] [TestData]/incorrectKotlinCode.kt:4:1: error: parameter name expected
   [kotlinc]
@@ -23,6 +29,12 @@ build:
   [kotlinc] [TestData]/incorrectKotlinCode.kt:4:1: error: expecting ')'
   [kotlinc]
   [kotlinc] ^
+  [kotlinc] [TestData]/incorrectKotlinCode.kt:4:1: error: a type annotation is required on a value parameter
+  [kotlinc]
+  [kotlinc] ^
+  [kotlinc] [TestData]/incorrectKotlinCode.kt:3:1: error: function 'main' must have a body
+  [kotlinc] fun main(
+  [kotlinc] ^
 
 BUILD SUCCESSFUL
 Total time: [time]
diff --git a/compiler/testData/integration/ant/jvm/doNotFailOnError/build.xml b/compiler/testData/integration/ant/jvm/doNotFailOnError/build.xml
index 8faf3e5e599..5fad10cf13d 100644
--- a/compiler/testData/integration/ant/jvm/doNotFailOnError/build.xml
+++ b/compiler/testData/integration/ant/jvm/doNotFailOnError/build.xml
@@ -3,9 +3,13 @@
 
     <target name="build">
         <javac srcdir="${test.data}" destdir="${temp}" includeantruntime="false" failonerror="false">
-            <withKotlin/>
+            <withKotlin>
+                <compilerarg line="-Xuse-fir-lt=false"/>
+            </withKotlin>
         </javac>
 
-        <kotlinc src="${test.data}" output="${temp}" failonerror="false"/>
+        <kotlinc src="${test.data}" output="${temp}" failonerror="false">
+            <compilerarg line="-Xuse-fir-lt=false"/>
+        </kotlinc>
     </target>
 </project>
diff --git a/compiler/testData/integration/ant/jvm/failOnErrorByDefault/build.xml b/compiler/testData/integration/ant/jvm/failOnErrorByDefault/build.xml
index dbdd88c71d3..f94b7e2603b 100644
--- a/compiler/testData/integration/ant/jvm/failOnErrorByDefault/build.xml
+++ b/compiler/testData/integration/ant/jvm/failOnErrorByDefault/build.xml
@@ -2,6 +2,8 @@
     <taskdef resource="org/jetbrains/kotlin/ant/antlib.xml" classpath="${kotlin.lib}/kotlin-ant.jar"/>
 
     <target name="build">
-        <kotlinc src="${test.data}" output="${temp}"/>
+        <kotlinc src="${test.data}" output="${temp}">
+            <compilerarg line="-Xuse-fir-lt=false"/>
+        </kotlinc>
     </target>
 </project>
diff --git a/compiler/testData/integration/ant/jvm/fork/build.xml b/compiler/testData/integration/ant/jvm/fork/build.xml
index 5dffa59b1db..9cfb23cf1df 100644
--- a/compiler/testData/integration/ant/jvm/fork/build.xml
+++ b/compiler/testData/integration/ant/jvm/fork/build.xml
@@ -20,6 +20,7 @@
             <jvmarg value="-Xmx128m"/>
             <jvmarg value="-javaagent:${temp}/premain.jar"/>
             <compilerarg value="-nowarn"/>
+            <compilerarg line="-Xuse-fir-lt=false"/>
         </kotlinc>
     </target>
 </project>
diff --git a/compiler/testData/integration/ant/jvm/forkOnError/build.log.expected b/compiler/testData/integration/ant/jvm/forkOnError/build.log.expected
index 2d6555d5737..7e792863f17 100644
--- a/compiler/testData/integration/ant/jvm/forkOnError/build.log.expected
+++ b/compiler/testData/integration/ant/jvm/forkOnError/build.log.expected
@@ -9,6 +9,15 @@ build:
   [kotlinc] Compiling [[TestData]] => [[Temp]/fork.jar]
   [kotlinc] -Xms64m
   [kotlinc] -Xmx128m
+  [kotlinc] warning: ATTENTION!
+  [kotlinc] This build uses unsafe internal compiler arguments:
+  [kotlinc]
+  [kotlinc] -XXLanguage:+EnableDfaWarningsInK2
+  [kotlinc]
+  [kotlinc] This mode is not recommended for production use,
+  [kotlinc] as no stability/compatibility guarantees are given on
+  [kotlinc] compiler or generated code. Use it at your own risk!
+  [kotlinc]
   [kotlinc] error: warnings found and -Werror specified
   [kotlinc] [TestData]/test.kt:4:15: warning: this cast can never succeed
   [kotlinc]     println(0 as String)
diff --git a/compiler/testData/integration/ant/jvm/forkOnError/build.xml b/compiler/testData/integration/ant/jvm/forkOnError/build.xml
index e62ad865146..9629f0dd9e2 100644
--- a/compiler/testData/integration/ant/jvm/forkOnError/build.xml
+++ b/compiler/testData/integration/ant/jvm/forkOnError/build.xml
@@ -20,6 +20,8 @@
             <jvmarg value="-Xmx128m"/>
             <jvmarg value="-javaagent:${temp}/premain.jar"/>
             <compilerarg value="-Werror"/>
+            <compilerarg line="-Xuse-fir-lt=false"/>
+            <compilerarg line="-XXLanguage:+EnableDfaWarningsInK2"/>
         </kotlinc>
     </target>
 </project>
diff --git a/compiler/testData/integration/ant/jvm/jvmClasspath/build.log.expected b/compiler/testData/integration/ant/jvm/jvmClasspath/build.log.expected
index cf8480a38b4..95e9fb48357 100644
--- a/compiler/testData/integration/ant/jvm/jvmClasspath/build.log.expected
+++ b/compiler/testData/integration/ant/jvm/jvmClasspath/build.log.expected
@@ -3,9 +3,6 @@ Buildfile: [TestData]/build.xml
 
 build:
   [kotlinc] Compiling [[TestData]/hello.kt] => [[Temp]/hello.jar]
-  [kotlinc] [TestData]/hello.kt:15:9: warning: variable 'result' is never used
-  [kotlinc]     val result = "$a$c$e$f$j"
-  [kotlinc]         ^
      [java] OK
 
 BUILD SUCCESSFUL
diff --git a/compiler/testData/integration/ant/jvm/mainInFiles/build.xml b/compiler/testData/integration/ant/jvm/mainInFiles/build.xml
index 7200da3b10b..520772e682b 100644
--- a/compiler/testData/integration/ant/jvm/mainInFiles/build.xml
+++ b/compiler/testData/integration/ant/jvm/mainInFiles/build.xml
@@ -4,6 +4,7 @@
     <target name="build">
         <kotlinc output="${temp}/hello.jar">
             <src path="${test.data}"/>
+            <compilerarg line="-Xuse-fir-lt=false"/>
         </kotlinc>
 
         <java classname="pkg.AKt" fork="true">
diff --git a/compiler/testData/integration/ant/jvm/moduleNameWithKotlin/build.xml b/compiler/testData/integration/ant/jvm/moduleNameWithKotlin/build.xml
index 529fc1b4c2f..d9fe002a5df 100644
--- a/compiler/testData/integration/ant/jvm/moduleNameWithKotlin/build.xml
+++ b/compiler/testData/integration/ant/jvm/moduleNameWithKotlin/build.xml
@@ -4,7 +4,9 @@
     <target name="build">
         <mkdir dir="${temp}/classes"/>
         <javac srcdir="${test.data}" destdir="${temp}/classes" includeantruntime="false">
-            <withKotlin/>
+            <withKotlin>
+                <compilerarg line="-Xuse-fir-lt=false"/>
+            </withKotlin>
         </javac>
         <jar destfile="${temp}/hello.jar">
             <fileset dir="${temp}/classes"/>
diff --git a/compiler/testData/integration/ant/jvm/overloadResolutionOnCollectionLiteral/build.log.expected b/compiler/testData/integration/ant/jvm/overloadResolutionOnCollectionLiteral/build.log.expected
index b36190b633b..1dcfa7d93de 100644
--- a/compiler/testData/integration/ant/jvm/overloadResolutionOnCollectionLiteral/build.log.expected
+++ b/compiler/testData/integration/ant/jvm/overloadResolutionOnCollectionLiteral/build.log.expected
@@ -5,20 +5,13 @@ build:
     [mkdir] Created dir: [Temp]/classes
     [javac] Compiling 2 source files to [Temp]/classes
     [javac] Compiling [[TestData]] => [[Temp]/classes]
-    [javac] [TestData]/literals.kt:6:9: error: overload resolution ambiguity:
-    [javac] public fun intArrayOf(vararg elements: Int): IntArray defined in kotlin in file myArrayOf.kt
-    [javac] public fun intArrayOf(vararg elements: Int): IntArray defined in kotlin in file myArrayOf.kt
-    [javac] @AnnInt([1, 2])
-    [javac]         ^
-    [javac] [TestData]/literals.kt:9:9: error: overload resolution ambiguity:
-    [javac] public fun intArrayOf(vararg elements: Int): IntArray defined in kotlin in file myArrayOf.kt
-    [javac] public fun intArrayOf(vararg elements: Int): IntArray defined in kotlin in file myArrayOf.kt
+    [javac] [TestData]/literals.kt:9:9: error: overload resolution ambiguity between candidates: [fun intArrayOf(vararg elements: IntArray): IntArray, fun intArrayOf(vararg elements: IntArray): IntArray]
     [javac] @AnnInt(intArrayOf(1, 2))
     [javac]         ^
-    [javac] [TestData]/myArrayOf.kt:3:1: error: conflicting overloads: public fun intArrayOf(vararg elements: Int): IntArray defined in kotlin in file myArrayOf.kt, public fun intArrayOf(vararg elements: Int): IntArray defined in kotlin in file myArrayOf.kt
+    [javac] [TestData]/myArrayOf.kt:3:1: error: conflicting overloads: [fun intArrayOf(vararg elements: IntArray): IntArray]
     [javac] public fun intArrayOf(vararg elements: Int): IntArray = TODO()
     [javac] ^
-    [javac] [TestData]/myArrayOf.kt:4:1: error: conflicting overloads: public fun intArrayOf(vararg elements: Int): IntArray defined in kotlin in file myArrayOf.kt, public fun intArrayOf(vararg elements: Int): IntArray defined in kotlin in file myArrayOf.kt
+    [javac] [TestData]/myArrayOf.kt:4:1: error: conflicting overloads: [fun intArrayOf(vararg elements: IntArray): IntArray]
     [javac] public fun intArrayOf(vararg elements: Int): IntArray = TODO()
     [javac] ^
 
diff --git a/compiler/testData/integration/ant/jvm/overloadResolutionOnCollectionLiteral/build.xml b/compiler/testData/integration/ant/jvm/overloadResolutionOnCollectionLiteral/build.xml
index dfc95db6187..8edccf6f1f7 100644
--- a/compiler/testData/integration/ant/jvm/overloadResolutionOnCollectionLiteral/build.xml
+++ b/compiler/testData/integration/ant/jvm/overloadResolutionOnCollectionLiteral/build.xml
@@ -9,6 +9,7 @@
             </classpath>
             <withKotlin>
                 <compilerarg value="-Xallow-kotlin-package"/>
+                <compilerarg line="-Xuse-fir-lt=false"/>
             </withKotlin>
         </javac>
         <jar destfile="${temp}/literals.jar">
diff --git a/compiler/testData/integration/ant/jvm/twoStdlibForCollectionLiterals/build.log.expected b/compiler/testData/integration/ant/jvm/twoStdlibForCollectionLiterals/build.log.expected
index 86ebaf82fbc..fe13f0a5b7b 100644
--- a/compiler/testData/integration/ant/jvm/twoStdlibForCollectionLiterals/build.log.expected
+++ b/compiler/testData/integration/ant/jvm/twoStdlibForCollectionLiterals/build.log.expected
@@ -5,9 +5,6 @@ build:
     [mkdir] Created dir: [Temp]/classes
     [javac] Compiling 2 source files to [Temp]/classes
     [javac] Compiling [[TestData]] => [[Temp]/classes]
-    [javac] [TestData]/myArrayOf.kt:3:30: warning: parameter 'elements' is never used
-    [javac] public fun intArrayOf(vararg elements: Int): IntArray = TODO()
-    [javac]                              ^
     [javac] Running javac...
       [jar] Building jar: [Temp]/literals.jar
 
diff --git a/compiler/testData/integration/ant/jvm/twoStdlibForCollectionLiterals/build.xml b/compiler/testData/integration/ant/jvm/twoStdlibForCollectionLiterals/build.xml
index dfc95db6187..8edccf6f1f7 100644
--- a/compiler/testData/integration/ant/jvm/twoStdlibForCollectionLiterals/build.xml
+++ b/compiler/testData/integration/ant/jvm/twoStdlibForCollectionLiterals/build.xml
@@ -9,6 +9,7 @@
             </classpath>
             <withKotlin>
                 <compilerarg value="-Xallow-kotlin-package"/>
+                <compilerarg line="-Xuse-fir-lt=false"/>
             </withKotlin>
         </javac>
         <jar destfile="${temp}/literals.jar">
diff --git a/compiler/testData/integration/ant/jvm/withKotlinNoJavaSources/build.xml b/compiler/testData/integration/ant/jvm/withKotlinNoJavaSources/build.xml
index 3b3c222aab9..0132508f8cd 100644
--- a/compiler/testData/integration/ant/jvm/withKotlinNoJavaSources/build.xml
+++ b/compiler/testData/integration/ant/jvm/withKotlinNoJavaSources/build.xml
@@ -4,7 +4,9 @@
     <target name="build">
         <mkdir dir="${temp}/classes"/>
         <javac srcdir="${test.data}" destdir="${temp}/classes" includeantruntime="false">
-            <withKotlin/>
+            <withKotlin>
+                <compilerarg line="-Xuse-fir-lt=false"/>
+            </withKotlin>
         </javac>
         <jar destfile="${temp}/hello.jar">
             <fileset dir="${temp}/classes"/>
diff --git a/compiler/testData/integration/ant/jvm/wrongCallForCollectionLiteral/build.log.expected b/compiler/testData/integration/ant/jvm/wrongCallForCollectionLiteral/build.log.expected
index 805d02a9e6a..eef03e6b829 100644
--- a/compiler/testData/integration/ant/jvm/wrongCallForCollectionLiteral/build.log.expected
+++ b/compiler/testData/integration/ant/jvm/wrongCallForCollectionLiteral/build.log.expected
@@ -8,7 +8,7 @@ build:
     [javac] [TestData]/literals.kt:6:9: error: type mismatch: inferred type is FloatArray but IntArray was expected
     [javac] @AnnInt([1, 2])
     [javac]         ^
-    [javac] [TestData]/literals.kt:9:9: error: type mismatch: inferred type is FloatArray but IntArray was expected
+    [javac] [TestData]/literals.kt:9:9: error: argument type mismatch: actual type is kotlin/FloatArray but kotlin/IntArray was expected
     [javac] @AnnInt(intArrayOf(1, 2))
     [javac]         ^
 
diff --git a/compiler/testData/integration/ant/jvm/wrongCallForCollectionLiteral/build.xml b/compiler/testData/integration/ant/jvm/wrongCallForCollectionLiteral/build.xml
index dfc95db6187..8edccf6f1f7 100644
--- a/compiler/testData/integration/ant/jvm/wrongCallForCollectionLiteral/build.xml
+++ b/compiler/testData/integration/ant/jvm/wrongCallForCollectionLiteral/build.xml
@@ -9,6 +9,7 @@
             </classpath>
             <withKotlin>
                 <compilerarg value="-Xallow-kotlin-package"/>
+                <compilerarg line="-Xuse-fir-lt=false"/>
             </withKotlin>
         </javac>
         <jar destfile="${temp}/literals.jar">