[Wasm] Better preserve IR types after inlining

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmLoweringPhases.kt

@@ -98,7 +98,7 @@ private val wrapInlineDeclarationsWithReifiedTypeParametersPhase = makeWasmModul
 
 private val functionInliningPhase = makeCustomWasmModulePhase(
     { context, module ->
-        FunctionInlining(context).inline(module)
+        FunctionInlining(context, null, true).inline(module)
         module.patchDeclarationParents()
     },
     name = "FunctionInliningPhase",

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/lower/WasmTypeOperatorLowering.kt

@@ -177,6 +177,12 @@ class WasmBaseTypeOperatorTransformer(val context: WasmBackendContext) : IrEleme
             }
         }
 
+        // A bit of a hack. Inliner tends to insert null casts from nothing to any. It's hard to express in wasm, so we simply replace
+        // them with single const null.
+        if (toType == builtIns.anyNType && fromType == builtIns.nothingNType && value is IrConst<*> && value.kind == IrConstKind.Null) {
+            return builder.irNull(builtIns.nothingNType)
+        }
+
         // Handled by autoboxing transformer
         if (toType.isInlined() && !fromType.isInlined()) {
             return builder.irCall(