Make use of contracts of time measurement functions

compiler/fir/raw-fir/psi2fir/tests/org/jetbrains/kotlin/fir/builder/RawFirBuilderTotalKotlinTestCase.kt

@@ -56,13 +56,13 @@ class RawFirBuilderTotalKotlinTestCase : AbstractRawFirBuilderTestCase() {
             if (file.extension != "kt") continue
             try {
                 val ktFile = createKtFile(file.toRelativeString(root))
-                var firFile: FirFile? = null
+                val firFile: FirFile
                 time += measureNanoTime {
                     firFile = ktFile.toFirFile(stubMode)
                 }
-                totalLength += StringBuilder().also { FirRenderer(it).visitFile(firFile!!) }.length
+                totalLength += StringBuilder().also { FirRenderer(it).visitFile(firFile) }.length
                 counter++
-                firFile?.accept(object : FirVisitorVoid() {
+                firFile.accept(object : FirVisitorVoid() {
                     override fun visitElement(element: FirElement) {
                         element.acceptChildren(this)
                     }

compiler/tests-common/tests/org/jetbrains/kotlin/fir/FirResolveBench.kt

@@ -99,15 +99,15 @@ class FirResolveBench(val withProgress: Boolean) {
     ): List<FirFile> {
         return ktFiles.map { file ->
             val before = vmStateSnapshot()
-            var firFile: FirFile? = null
+            val firFile: FirFile
             val time = measureNanoTime {
                 firFile = builder.buildFirFile(file)
-                (builder.baseSession.firProvider as FirProviderImpl).recordFile(firFile!!)
+                (builder.baseSession.firProvider as FirProviderImpl).recordFile(firFile)
             }
             val after = vmStateSnapshot()
             val diff = after - before
             recordTime(builder::class, diff, time)
-            firFile!!
+            firFile
         }.also {
             totalTime = timePerTransformer.values.sumByLong { it.time }
         }
@@ -119,15 +119,15 @@ class FirResolveBench(val withProgress: Boolean) {
     ): List<FirFile> {
         return files.map { file ->
             val before = vmStateSnapshot()
-            var firFile: FirFile? = null
+            val firFile: FirFile
             val time = measureNanoTime {
                 firFile = builder.buildFirFile(file)
-                (builder.session.firProvider as FirProviderImpl).recordFile(firFile!!)
+                (builder.session.firProvider as FirProviderImpl).recordFile(firFile)
             }
             val after = vmStateSnapshot()
             val diff = after - before
             recordTime(builder::class, diff, time)
-            firFile!!
+            firFile
         }.also {
             totalTime = timePerTransformer.values.sumByLong { it.time }
         }

compiler/util-io/src/org/jetbrains/kotlin/util/Util.kt

@@ -10,12 +10,12 @@ import org.jetbrains.kotlin.konan.file.*
 import java.lang.StringBuilder
 
 fun <T> printMillisec(message: String, body: () -> T): T {
-    var result: T? = null
-    val msec = measureTimeMillis{
+    val result: T
+    val msec = measureTimeMillis {
         result = body()
     }
     println("$message: $msec msec")
-    return result!!
+    return result
 }
 
 fun profile(message: String, body: () -> Unit) = profileIf(

jps-plugin/src/org/jetbrains/kotlin/jps/build/KotlinBuilder.kt

@@ -128,7 +128,7 @@ class KotlinBuilder : ModuleLevelBuilder(BuilderCategory.SOURCE_PROCESSOR) {
     }
 
     private fun initializeKotlinContext(context: CompileContext): KotlinCompileContext {
-        lateinit var kotlinContext: KotlinCompileContext
+        val kotlinContext: KotlinCompileContext
 
         val time = measureTimeMillis {
             kotlinContext = KotlinCompileContext(context)