[K/N] Add -Xllvm-variant` compiler option

We need a handle that allows user to pick `dev` variant instead of
`user` one just in case.
Additionally, I added a possibility to provide a path to an arbitrary
LLVM distribution because it is useful for development purposes.

kotlin-native/backend.native/cli.bc/src/org/jetbrains/kotlin/cli/bc/K2Native.kt

@@ -353,6 +353,20 @@ class K2Native : CLICompiler<K2NativeCompilerArguments>() {
                 })
 
                 arguments.externalDependencies?.let { put(EXTERNAL_DEPENDENCIES, it) }
+                putIfNotNull(LLVM_VARIANT, when (val variant = arguments.llvmVariant) {
+                    "user" -> LlvmVariant.User
+                    "dev" -> LlvmVariant.Dev
+                    null -> null
+                    else -> {
+                        val file = File(variant)
+                        if (!file.exists) {
+                            configuration.report(ERROR, "`-Xllvm-variant` should be `user`, `dev` or an absolute path. Got: $variant")
+                            null
+                        } else {
+                            LlvmVariant.Custom(file)
+                        }
+                    }
+                })
             }
         }
     }

kotlin-native/backend.native/cli.bc/src/org/jetbrains/kotlin/cli/bc/K2NativeCompilerArguments.kt

@@ -337,6 +337,13 @@ class K2NativeCompilerArguments : CommonCompilerArguments() {
     )
     var workerExceptionHandling: String? = null
 
+    @Argument(
+            value = "-Xllvm-variant",
+            valueDescription = "{dev|user}",
+            description = "Choose LLVM distribution which will be used during compilation."
+    )
+    var llvmVariant: String? = null
+
     override fun configureAnalysisFlags(collector: MessageCollector, languageVersion: LanguageVersion): MutableMap<AnalysisFlag<*>, Any> =
             super.configureAnalysisFlags(collector, languageVersion).also {
                 val useExperimental = it[AnalysisFlags.useExperimental] as List<*>

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanConfig.kt

@@ -29,12 +29,21 @@ import org.jetbrains.kotlin.utils.addToStdlib.cast
 
 class KonanConfig(val project: Project, val configuration: CompilerConfiguration) {
 
-    internal val distribution = Distribution(
-            configuration.get(KonanConfigKeys.KONAN_HOME) ?: KonanHomeProvider.determineKonanHome(),
-            false,
-            configuration.get(KonanConfigKeys.RUNTIME_FILE),
-            configuration.get(KonanConfigKeys.OVERRIDE_KONAN_PROPERTIES)
-    )
+    internal val distribution = run {
+        val overridenProperties = mutableMapOf<String, String>().apply {
+            configuration.get(KonanConfigKeys.OVERRIDE_KONAN_PROPERTIES)?.let(this::putAll)
+            configuration.get(KonanConfigKeys.LLVM_VARIANT)?.getKonanPropertiesEntry()?.let { (key, value) ->
+                put(key, value)
+            }
+        }
+
+        Distribution(
+                configuration.get(KonanConfigKeys.KONAN_HOME) ?: KonanHomeProvider.determineKonanHome(),
+                false,
+                configuration.get(KonanConfigKeys.RUNTIME_FILE),
+                overridenProperties
+        )
+    }
 
     private val platformManager = PlatformManager(distribution)
     internal val targetManager = platformManager.targetManager(configuration.get(KonanConfigKeys.TARGET))

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanConfigurationKeys.kt

@@ -167,6 +167,7 @@ class KonanConfigKeys {
         val WORKER_EXCEPTION_HANDLING: CompilerConfigurationKey<WorkerExceptionHandling> = CompilerConfigurationKey.create("unhandled exception processing in Worker.executeAfter")
         val EXTERNAL_DEPENDENCIES: CompilerConfigurationKey<String?> =
                 CompilerConfigurationKey.create("use external dependencies to enhance IR linker error messages")
+        val LLVM_VARIANT: CompilerConfigurationKey<LlvmVariant?> = CompilerConfigurationKey.create("llvm variant")
     }
 }
 

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/LlvmVariant.kt

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.backend.konan
+
+import org.jetbrains.kotlin.konan.file.File
+import org.jetbrains.kotlin.konan.target.HostManager
+
+sealed class LlvmVariant {
+    object User : LlvmVariant() {
+        override fun getKonanPropertiesEntry(): Pair<String, String> =
+                konanPropertiesKey to "\$llvm.${HostManager.hostName}.user"
+    }
+
+    object Dev : LlvmVariant() {
+        override fun getKonanPropertiesEntry(): Pair<String, String> =
+                konanPropertiesKey to "\$llvm.${HostManager.hostName}.user"
+
+    }
+
+    class Custom(val path: File) : LlvmVariant() {
+        override fun getKonanPropertiesEntry(): Pair<String, String> =
+                konanPropertiesKey to path.canonicalPath
+
+    }
+
+    abstract fun getKonanPropertiesEntry(): Pair<String, String>
+
+    companion object {
+        private val konanPropertiesKey: String by lazy {
+            "llvmHome.${HostManager.hostName}"
+        }
+    }
+}