diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/Mappings.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/Mappings.kt
index 0823832b910..eae0583d05f 100644
--- a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/Mappings.kt
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/Mappings.kt
@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.backend.common
 
 import org.jetbrains.kotlin.ir.declarations.*
+import java.util.concurrent.ConcurrentHashMap
 import kotlin.reflect.KMutableProperty0
 import kotlin.reflect.KProperty
 
@@ -47,7 +48,7 @@ open class DefaultMapping : Mapping {
     override val reflectedNameAccessor: Mapping.Delegate<IrClass, IrSimpleFunction> = newMapping()
 
     protected open fun <K : IrDeclaration, V> newMapping() = object : Mapping.Delegate<K, V>() {
-        private val map: MutableMap<K, V> = mutableMapOf()
+        private val map: MutableMap<K, V> = ConcurrentHashMap()
 
         override operator fun get(key: K): V? {
             return map[key]
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt
index 420c40dd8e1..a6fc57809b4 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt
@@ -39,6 +39,7 @@ import org.jetbrains.kotlin.psi2ir.PsiErrorBuilder
 import org.jetbrains.kotlin.psi2ir.PsiSourceManager
 import org.jetbrains.kotlin.resolve.jvm.JvmClassName
 import org.jetbrains.org.objectweb.asm.Type
+import java.util.concurrent.ConcurrentHashMap
 
 class JvmBackendContext(
     val state: GenerationState,
@@ -55,7 +56,7 @@ class JvmBackendContext(
     val classNameOverride: MutableMap<IrClass, JvmClassName>
         get() = generatorExtensions.classNameOverride
 
-    override val extractedLocalClasses: MutableSet<IrClass> = hashSetOf()
+    override val extractedLocalClasses: MutableSet<IrClass> = ConcurrentHashMap.newKeySet()
 
     override val irFactory: IrFactory = IrFactoryImpl
 
@@ -78,7 +79,7 @@ class JvmBackendContext(
 
     val irIntrinsics by lazy { IrIntrinsicMethods(irBuiltIns, ir.symbols) }
 
-    private val localClassType = mutableMapOf<IrAttributeContainer, Type>()
+    private val localClassType = ConcurrentHashMap<IrAttributeContainer, Type>()
 
     internal fun getLocalClassType(container: IrAttributeContainer): Type? =
         localClassType[container.attributeOwnerId]
@@ -87,18 +88,18 @@ class JvmBackendContext(
         localClassType[container.attributeOwnerId] = value
     }
 
-    internal val isEnclosedInConstructor = mutableSetOf<IrAttributeContainer>()
+    internal val isEnclosedInConstructor = ConcurrentHashMap.newKeySet<IrAttributeContainer>()
 
     internal val classCodegens = mutableMapOf<IrClass, ClassCodegen>()
 
-    val localDelegatedProperties = mutableMapOf<IrAttributeContainer, List<IrLocalDelegatedPropertySymbol>>()
+    val localDelegatedProperties = ConcurrentHashMap<IrAttributeContainer, List<IrLocalDelegatedPropertySymbol>>()
 
     internal val multifileFacadesToAdd = mutableMapOf<JvmClassName, MutableList<IrClass>>()
     val multifileFacadeForPart = mutableMapOf<IrClass, JvmClassName>()
     internal val multifileFacadeClassForPart = mutableMapOf<IrClass, IrClass>()
     internal val multifileFacadeMemberToPartMember = mutableMapOf<IrSimpleFunction, IrSimpleFunction>()
 
-    internal val hiddenConstructors = mutableMapOf<IrConstructor, IrConstructor>()
+    internal val hiddenConstructors = ConcurrentHashMap<IrConstructor, IrConstructor>()
 
     internal val collectionStubComputer = CollectionStubComputer(this)
 
@@ -112,19 +113,19 @@ class JvmBackendContext(
         overridesWithoutStubs.getOrElse(function) { function.overriddenSymbols }
 
     internal val bridgeLoweringCache = BridgeLowering.BridgeLoweringCache(this)
-    internal val functionsWithSpecialBridges: MutableSet<IrFunction> = HashSet()
+    internal val functionsWithSpecialBridges: MutableSet<IrFunction> = ConcurrentHashMap.newKeySet()
 
-    override var inVerbosePhase: Boolean = false
+    override var inVerbosePhase: Boolean = false // TODO: needs parallelizing
 
     override val configuration get() = state.configuration
 
     override val internalPackageFqn = FqName("kotlin.jvm")
 
-    val suspendLambdaToOriginalFunctionMap = mutableMapOf<IrFunctionReference, IrFunction>()
-    val suspendFunctionOriginalToView = mutableMapOf<IrFunction, IrFunction>()
+    val suspendLambdaToOriginalFunctionMap = ConcurrentHashMap<IrFunctionReference, IrFunction>()
+    val suspendFunctionOriginalToView = ConcurrentHashMap<IrFunction, IrFunction>()
     val fakeContinuation: IrExpression = createFakeContinuation(this)
 
-    val staticDefaultStubs = mutableMapOf<IrSimpleFunctionSymbol, IrSimpleFunction>()
+    val staticDefaultStubs = ConcurrentHashMap<IrSimpleFunctionSymbol, IrSimpleFunction>()
 
     val inlineClassReplacements = MemoizedInlineClassReplacements(state.functionsWithInlineClassReturnTypesMangled, irFactory, this)
 
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmCachedDeclarations.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmCachedDeclarations.kt
index 5b6c9931e6f..8058b1f6813 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmCachedDeclarations.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmCachedDeclarations.kt
@@ -30,19 +30,20 @@ import org.jetbrains.kotlin.load.java.JavaDescriptorVisibilities
 import org.jetbrains.kotlin.load.java.JvmAbi
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.deprecation.DeprecationResolver
+import java.util.concurrent.ConcurrentHashMap
 
 class JvmCachedDeclarations(
     private val context: JvmBackendContext,
     private val languageVersionSettings: LanguageVersionSettings
 ) {
-    private val singletonFieldDeclarations = HashMap<IrSymbolOwner, IrField>()
-    private val interfaceCompanionFieldDeclarations = HashMap<IrSymbolOwner, IrField>()
-    private val staticBackingFields = HashMap<IrProperty, IrField>()
+    private val singletonFieldDeclarations = ConcurrentHashMap<IrSymbolOwner, IrField>()
+    private val interfaceCompanionFieldDeclarations = ConcurrentHashMap<IrSymbolOwner, IrField>()
+    private val staticBackingFields = ConcurrentHashMap<IrProperty, IrField>()
 
-    private val defaultImplsMethods = HashMap<IrSimpleFunction, IrSimpleFunction>()
-    private val defaultImplsClasses = HashMap<IrClass, IrClass>()
-    private val defaultImplsRedirections = HashMap<IrSimpleFunction, IrSimpleFunction>()
-    private val defaultImplsOriginalMethods = HashMap<IrSimpleFunction, IrSimpleFunction>()
+    private val defaultImplsMethods = ConcurrentHashMap<IrSimpleFunction, IrSimpleFunction>()
+    private val defaultImplsClasses = ConcurrentHashMap<IrClass, IrClass>()
+    private val defaultImplsRedirections = ConcurrentHashMap<IrSimpleFunction, IrSimpleFunction>()
+    private val defaultImplsOriginalMethods = ConcurrentHashMap<IrSimpleFunction, IrSimpleFunction>()
 
     fun getFieldForEnumEntry(enumEntry: IrEnumEntry): IrField =
         singletonFieldDeclarations.getOrPut(enumEntry) {
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/MethodSignatureMapper.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/MethodSignatureMapper.kt
index 09fb473e718..bc16a88365f 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/MethodSignatureMapper.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/MethodSignatureMapper.kt
@@ -124,7 +124,7 @@ class MethodSignatureMapper(private val context: JvmBackendContext) {
 
     private fun IrSimpleFunction.isInvisibleInMultifilePart(): Boolean =
         name.asString() != "<clinit>" &&
-                (parent as? IrClass)?.attributeOwnerId in context.multifileFacadeForPart &&
+                (parent as? IrClass)?.attributeOwnerId in context.multifileFacadeForPart.keys &&
                 (DescriptorVisibilities.isPrivate(suspendFunctionOriginal().visibility) ||
                         originalForDefaultAdapter?.isInvisibleInMultifilePart() == true)
 
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/BridgeLowering.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/BridgeLowering.kt
index ccbb511e39d..07f17809ae1 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/BridgeLowering.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/BridgeLowering.kt
@@ -37,6 +37,7 @@ import org.jetbrains.kotlin.util.OperatorNameConventions
 import org.jetbrains.kotlin.utils.addToStdlib.safeAs
 import org.jetbrains.org.objectweb.asm.Type
 import org.jetbrains.org.objectweb.asm.commons.Method
+import java.util.concurrent.ConcurrentHashMap
 
 /*
  * Generate bridge methods to fix virtual dispatch after type erasure and to adapt Kotlin collections to
@@ -595,7 +596,7 @@ internal class BridgeLowering(val context: JvmBackendContext) : FileLoweringPass
         // It might benefit performance, but can lead to confusing behavior if some declarations are changed along the way.
         // For example, adding an override for a declaration whose signature is already cached can result in incorrect signature
         // if its return type is a primitive type, and the new override's return type is an object type.
-        private val signatureCache = hashMapOf<IrFunctionSymbol, Method>()
+        private val signatureCache = ConcurrentHashMap<IrFunctionSymbol, Method>()
 
         fun computeJvmMethod(function: IrFunction): Method =
             signatureCache.getOrPut(function.symbol) { context.methodSignatureMapper.mapAsmMethod(function) }
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/CollectionStubMethodLowering.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/CollectionStubMethodLowering.kt
index 2dbd3e9f69e..c80dd401a2d 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/CollectionStubMethodLowering.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/CollectionStubMethodLowering.kt
@@ -29,6 +29,7 @@ import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.types.AbstractTypeChecker
 import org.jetbrains.kotlin.types.AbstractTypeCheckerContext
 import org.jetbrains.kotlin.utils.addToStdlib.cast
+import java.util.concurrent.ConcurrentHashMap
 
 internal val collectionStubMethodLowering = makeIrFilePhase(
     ::CollectionStubMethodLowering,
@@ -469,7 +470,7 @@ internal class CollectionStubComputer(val context: JvmBackendContext) {
         }
     }
 
-    private val stubsCache = mutableMapOf<IrClass, List<StubsForCollectionClass>>()
+    private val stubsCache = ConcurrentHashMap<IrClass, List<StubsForCollectionClass>>()
 
     fun stubsForCollectionClasses(irClass: IrClass): List<StubsForCollectionClass> =
         stubsCache.getOrPut(irClass) {
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmInnerClassesSupport.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmInnerClassesSupport.kt
index 75467772513..9a45c70db44 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmInnerClassesSupport.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmInnerClassesSupport.kt
@@ -23,11 +23,12 @@ import org.jetbrains.kotlin.ir.util.dump
 import org.jetbrains.kotlin.ir.util.parentAsClass
 import org.jetbrains.kotlin.load.java.JavaDescriptorVisibilities
 import org.jetbrains.kotlin.name.Name
+import java.util.concurrent.ConcurrentHashMap
 
 class JvmInnerClassesSupport(private val irFactory: IrFactory) : InnerClassesSupport {
-    private val outerThisDeclarations = HashMap<IrClass, IrField>()
-    private val innerClassConstructors = HashMap<IrConstructor, IrConstructor>()
-    private val originalInnerClassPrimaryConstructorByClass = HashMap<IrClass, IrConstructor>()
+    private val outerThisDeclarations = ConcurrentHashMap<IrClass, IrField>()
+    private val innerClassConstructors = ConcurrentHashMap<IrConstructor, IrConstructor>()
+    private val originalInnerClassPrimaryConstructorByClass = ConcurrentHashMap<IrClass, IrConstructor>()
 
     override fun getOuterThisField(innerClass: IrClass): IrField =
         outerThisDeclarations.getOrPut(innerClass) {
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/SyntheticAccessorLowering.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/SyntheticAccessorLowering.kt
index bccad36e16c..7077b5aa87e 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/SyntheticAccessorLowering.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/SyntheticAccessorLowering.kt
@@ -217,7 +217,7 @@ internal class SyntheticAccessorLowering(val context: JvmBackendContext) : IrEle
 
     private val IrConstructor.isOrShouldBeHidden: Boolean
         get() {
-            if (this in context.hiddenConstructors)
+            if (this in context.hiddenConstructors.keys)
                 return true
 
             if (origin == IrDeclarationOrigin.FUNCTION_FOR_DEFAULT_PARAMETER ||
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/inlineclasses/MemoizedInlineClassReplacements.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/inlineclasses/MemoizedInlineClassReplacements.kt
index 5f85b89f619..1fe8815e2bf 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/inlineclasses/MemoizedInlineClassReplacements.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/inlineclasses/MemoizedInlineClassReplacements.kt
@@ -35,6 +35,7 @@ import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.InlineClassDescriptorResolver
 import org.jetbrains.kotlin.storage.LockBasedStorageManager
 import org.jetbrains.kotlin.utils.addToStdlib.safeAs
+import java.util.concurrent.ConcurrentHashMap
 
 /**
  * Keeps track of replacement functions and inline class box/unbox functions.
@@ -45,9 +46,9 @@ class MemoizedInlineClassReplacements(
     private val context: JvmBackendContext
 ) {
     private val storageManager = LockBasedStorageManager("inline-class-replacements")
-    private val propertyMap = mutableMapOf<IrPropertySymbol, IrProperty>()
+    private val propertyMap = ConcurrentHashMap<IrPropertySymbol, IrProperty>()
 
-    internal val originalFunctionForStaticReplacement: MutableMap<IrFunction, IrFunction> = HashMap()
+    internal val originalFunctionForStaticReplacement: MutableMap<IrFunction, IrFunction> = ConcurrentHashMap()
 
     /**
      * Get a replacement for a function or a constructor.