Add lowering that will evaluate all intrinsic const expressions

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/ConstEvaluationLowering.kt

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2010-2019 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.common.lower
+
+import org.jetbrains.kotlin.backend.common.CommonBackendContext
+import org.jetbrains.kotlin.backend.common.FileLoweringPass
+import org.jetbrains.kotlin.backend.common.phaser.makeIrModulePhase
+import org.jetbrains.kotlin.ir.declarations.IrFile
+import org.jetbrains.kotlin.ir.interpreter.IrInterpreter
+import org.jetbrains.kotlin.ir.interpreter.checker.EvaluationMode
+import org.jetbrains.kotlin.ir.interpreter.checker.IrConstTransformer
+
+val constEvaluationPhase = makeIrModulePhase(
+    ::ConstEvaluationLowering,
+    name = "ConstEvaluationLowering",
+    description = "Evaluate functions that are marked as `Foldable`"
+)
+
+class ConstEvaluationLowering(val context: CommonBackendContext) : FileLoweringPass {
+    val interpreter = IrInterpreter(context.irBuiltIns)
+
+    override fun lower(irFile: IrFile) {
+        irFile.transformChildren(IrConstTransformer(interpreter, irFile, mode = EvaluationMode.ONLY_INTRINSIC_CONST), null)
+    }
+}
+