DCE-driven mode

:js:js.tests:jsIrTest works same as before
:js:js.tests:jsPirTest runs tests in DCE-driven mode

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JSCompilerArguments.kt

@@ -125,6 +125,9 @@ class K2JSCompilerArguments : CommonCompilerArguments() {
     @Argument(value = "-Xir-dce", description = "Perform experimental dead code elimination")
     var irDce: Boolean by FreezableVar(false)
 
+    @Argument(value = "-Xir-dce-driven", description = "Perform a more experimental faster dead code elimination")
+    var irDceDriven: Boolean by FreezableVar(false)
+
     @Argument(value = "-Xir-only", description = "Disables pre-IR backend")
     var irOnly: Boolean by FreezableVar(false)
 

compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/K2JsIrCompiler.kt

@@ -228,13 +228,14 @@ class K2JsIrCompiler : CLICompiler<K2JSCompilerArguments>() {
                     friendDependencies = friendDependencies,
                     mainArguments = mainCallArguments,
                     generateFullJs = !arguments.irDce,
-                    generateDceJs = arguments.irDce
+                    generateDceJs = arguments.irDce,
+                    dceDriven = arguments.irDceDriven
                 )
             } catch (e: JsIrCompilationError) {
                 return COMPILATION_ERROR
             }
 
-            val jsCode = if (arguments.irDce) compiledModule.dceJsCode!! else compiledModule.jsCode!!
+            val jsCode = if (arguments.irDce && !arguments.irDceDriven) compiledModule.dceJsCode!! else compiledModule.jsCode!!
             outputFile.writeText(jsCode)
             if (arguments.generateDts) {
                 val dtsFile = outputFile.withReplacedExtensionOrNull(outputFile.extension, "d.ts")!!