[IR] Initialize IrFunction.returnType eagerly, when possible

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/FunctionGenerator.kt

@@ -296,7 +296,7 @@ internal class FunctionGenerator(declarationGenerator: DeclarationGenerator) : D
                     visibility = visibility,
                     isInline = isInline,
                     isExpect = isExpect,
-                    returnType = null,
+                    returnType = constructorDescriptor.returnType.toIrType(),
                     symbol = it,
                     isPrimary = isPrimary,
                     isExternal = isEffectivelyExternal(),
@@ -310,7 +310,6 @@ internal class FunctionGenerator(declarationGenerator: DeclarationGenerator) : D
             if (context.configuration.generateBodies) {
                 irConstructor.body = createBodyGenerator(irConstructor.symbol).generateBody(irConstructor)
             }
-            irConstructor.returnType = constructorDescriptor.returnType.toIrType()
         }
     }
 

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/StandaloneDeclarationGenerator.kt

@@ -180,7 +180,7 @@ internal class StandaloneDeclarationGenerator(private val context: GeneratorCont
                 visibility = visibility,
                 isInline = isInline,
                 isExpect = isExpect,
-                returnType = null,
+                returnType = descriptor.returnType.toIrType(),
                 symbol = symbol,
                 isPrimary = isPrimary,
                 isExternal = isEffectivelyExternal(),
@@ -192,7 +192,6 @@ internal class StandaloneDeclarationGenerator(private val context: GeneratorCont
             val ctorTypeParameters = descriptor.typeParameters.filter { it.containingDeclaration === descriptor }
             generateScopedTypeParameterDeclarations(irConstructor, ctorTypeParameters)
             generateValueParameterDeclarations(irConstructor, descriptor, defaultArgumentFactory)
-            irConstructor.returnType = descriptor.returnType.toIrType()
         }
 
         return irConstructor

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

@@ -94,7 +94,7 @@ internal interface DescriptorToIrTranslationMixin {
                         visibility,
                         isInline,
                         isExpect,
-                        null,
+                        constructorDescriptor.returnType.toIrType(),
                         it,
                         isPrimary,
                         isEffectivelyExternal(),
@@ -109,7 +109,6 @@ internal interface DescriptorToIrTranslationMixin {
                 it.parent = irConstructor
             }
         }
-        irConstructor.returnType = constructorDescriptor.returnType.toIrType()
         irConstructor.generateAnnotations()
         return irConstructor
     }